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JG14_Josf
06-03-2004, 03:06 PM
The following is an attempt to make sense of the world where fighter planes exist.

The title of the topic is a formula as it appears in the book BOYD The Fighter Pilot who changes the art of war by Robert Coram.

That formula is not written the same as it appears in Fighter Combat by Robert Shaw.

The subtle difference are curious, I think, based upon my resent inspection of the properties of inertia, mass, and relative density.

A plane with a higher mass, higher inertia, and higher relative density compared to a plane with lower mass, lower inertia, and lower realative density will react differently to the medium which resists the planes movement i.e. the atmosphere.

Moving the heavier plane requires more energy and releasing that energy once it is gained is formulated by the equation: Ps=[T-D/W]V.

My question concerns math.

Is this a true mathematical statment:
[T-D/W]= T/W - D/W

Take a P-47 and a Bf109K and consider a few things concerning this plane matchup. First, for the purposes of this discussion, let's imagine that these two planes have the same level max speed. If it would help then consider that these planes are not production models that instead they are custom. They both have the same level max speed at 8k meters. Now imagine that the P-47 is twice the weight of the Bf109K. Bear with me here, if you are at all interested in this stuff, my point concerns something specific so it is important to avoid getting caught up in exact plane performance numbers.

The P-47 and Bf109 are flying side by side at the same max level speed.
What happens when both planes are pitched up from that level flight condition?
What happens when both planes are pitched down from that level flight condition?

Mass and or inertia is going to resist any changes in pitch more so with the heavier P-47 than with the Bf109.

Gravity is a constant force applied to these two planes as they fly level, however these two planes are not going to be able to deal with the force of gravity in the same way due to their differences in mass, among other things.

The P-47 has enough thrust and lift to maintain an equal velocity in level flight but in order for the P-47 to gain anymore altitude from this position of equalibrium it will require more thrust and or more lift than the Bf109 because the P-47 has more mass and therefore is more susceptible to the force of the earths gravity. The higher mass of the P-47 requires more energy to move it against the force of gravity.
Since the P-47 and Bf109 are already at max thrust in max level flight then as these two planes pitch up the 109 will require less lift to change direction and less lift to resist the force of gravity to lift it higher, or accelerate against the force of gravity.
Due to relative mass the Bf109 is going to have better climb performance.

In order to see clearly what happens when both planes pitch down it is now important, at least to me, to consider the medium which resists movement or air and the effects of relative density.

Both planes accelerate at the same speed due to the force of gravity in a vacuum. Air hinders this rate of acceleration. This resistance is termed drag, and it is described as a force. Drag force is equal to thrust when both planes are flying level at max speed.

Here comes the important point and the reason for the mathematical question concerning the Specific excess power equation.

As an objects mass increases it becomes relatively more able to pass through a medium of resistance. Mass renders drag less effective. Drag force is more capable of resisting the movement of a lower mass object.

To make this point more clear consider what happens to top level speed for a plane that gains weight.

Chapter 5 Excess Power Characteristics (http://flighttest.navair.navy.mil/unrestricted/FTM108/)

Page 5.14
5.3.5.2 INCREASED GROSS WEIGHT
"The effect of increasing gross weight is similar to that of increasing the normal acceleration, with the difference that both the numerator and denominator are affectd rather than the numberator alone (Figure 5.8):"

and Page 5.15

"The balance of thrust and drag is the same, resulting in identical minimum and maximum level flight speeds."

If it is true that increases in weight do not lower max level flight speeds then it seems clear to me that this is due to a change in relative density.

The air is rendered comparitaively or relatively less dense as the mass of the object passing through the air is increased.

Thrust does not change on the plane as it increases weight. More lift is required to stay level when weight is added and therefore more induced drag is generated. Why does the plane still fly at the same speed when adding weight? It seem clear to me that the total force of drag is the same because the plane does not accelerate. Thrust remains constant, induced drag increases, weight increases, and velocity remains the same. I think that the higher mass plane is more capable of penetrating the atmosphere. The increase in the planes density renders the air relatively less dense.

Chapter 8 DEscent Performance (http://flighttest.navair.navy.mil/unrestricted/FTM108/)

Page 8.7 WEIGHT EFFECT ON DESCENT PERFORMANCE

"At the higher airspeed for the higher gross weight, the increase in drag is offset by the increased weight component along the flight path.":

In level flight the P-47 and the Bf109 both have enough thrust to counter the force of drag (they are both at the same max speed) they both have the same balance between weight and lift (level flight). However the P-47 has a higher mass. The increased mass required more energy to get the vehicle moving and more energy to get to that same altitude. Therefore the P-47 has more energy despite being at the same speed and same altitude. If it is reasonable to conclude that the P-47 will perform relatively poorly as both planes change direction from level flight to a climb because the mass is both more difficult to move and more difficult to lift then what can be said about any change from level flight into a dive?

Conventional thinking has been previously expresses that the P-47 will not accelerate any faster and possibly accelerate slower than the lighter Bf-109 in a dive due to the difficulties associated with moving objects of higher mass. To further complicate the matter it has also been stated that since gravity accelerates all objects at the same rate regardless of weight in a vacuum that both the P-47 and the Bf109 will dive at the same rate, much like what occurs in previous versions of the game. One more complication concerning dive performance has been described as a simple equation where the greater mass vehicle will accelerate slower up to max level speed (in a dive) and above the level max speed the situation reverses where the higher mass vehicle accelerates faster than the lower mass one, in a dive.

Before moving on to the situation where the higher mass vehicle accelerates slower than the lower mass vehicle at speeds below max level speed it may help to look at what happens when two imaginary planes are flying at the same max level speed where one plane has an obviously higher mass.

Back again to the Bf109 and the P-47 flying level at full power where for whatever imaginary configuration these planes are maxed out at the same speed.

Both planes pitch over in a dive.

Gravity is a constant force generated by the earth and this force accelerates both planes at the same rate but only in a vacuum. Since an atmosphere is present and since this form of resistance does limit the acceleration of these vehicles as they are being accelerated by gravity then it is neccesary to measure that form of resistance in an effort to find just how effective that resistance is when acting upon our vehicles.
One such method of measuring the resistance to movement presented by the atmosphere is to quantify density. The higher the density of the atmosphere the greater will be the drag force acting against movement. The lower the density of the atmosphere the lower will be the drag force acting against movement.

Before moving any further it occurs to me to return to the observation of a plane's max level speed and the associated effect of changes in mass. Imagine that the P-47 is filled with mercury, it has a much more powerfull engine to move this increased mass and it has larger, more effective wings to lift this increased mass against the force of gravity. The P-47 is still flying at the same max level speed as the Bf109. Both planes are flying side by side, both planes still have a balance between thrust and drag, lift and gravity. Now imagine that the P-47 dumps the mercury. It is reasonable to conclude that as the mercury is dumped the P-47 will climb if the pilot does not push the stick forward. For the purposes of this discussion it is required that the pilot push the stick forward in an effort to maintain level flight. The reason why this piloting is required is for us to realize what forces are in place that cause any change in max level flight velocity.

Before moving on it is important to indentify what happens in this situation.

It is important to identify why the P-47 is not able to gain any more level flight speed as the P-47 reduces mass.

Picture the P-47 crusing alone in a race with the Bf109. Both pilots are trying to win the race to the finish line. The P-47 happens to be burdened with a cargo of mercury and he thinks it would help to dump the cargo. He does so thinking that he will then be able to speed ahead and win the race.

Who wins the race?

Because I find reason to write and because this subject interests me I am going to move ahead without confirmation of the results of the above race between an imaginary Bf109 and a special high mass P-47. I am going to move on with the assumption that the P-47 will not win the race as it dumps mercury and decreases mass.

I want to bring this line of thinking back to the Specific Excess Power formula.

T/W - D/W suggests to me that weight can be factored relative to drag so as to account for relative density.

That is it for now.

OOOPs I forgot a note of relevance.

On Warclouds I found myself flying alone. My normal wingmen were all busy with real life things. A P-38 zoomed by from about 10 degrees angle off my nose or 1 oclock high. Since then I checked the replay to see how this guy managed to avoid detection and I found that his P-38 was hidden behind the forward up right canopy bars. I went into a dive after being bounced by the P-38. My thinking was that the P-38s will break apart in the game at lower speeds than my 109G6AS. I can therefore gain relative energy. Sure enough the separation grows and I start pulling up into a climb. My thinking was that the game allows the AS to gain in relative energy over the P-38 in a sustained climb.

The text buffer says:

"Timid 109s diving and climbing"

or something to that effect

"<S>" etc.

I've stood under a P-38. It is a large plane. There was one at the Chino air museum along with a Rolls engined Bf109. There is another Bf109 at the Planes of Fame museum in Flagstaff Arizona. I saw that one too.
I can stand next to the 109s and see the instrument panel. I am 6 feet tall.
The 109 is a small plane.

Each of us have our own opinions as to what should or should not be done in Air Combat. I try to fly to my planes strengths. I also try to simulate what has been written in history books. Sometimes I succeed. Somtimes I have to take flak for it.

JG14_Josf
06-03-2004, 03:06 PM
The following is an attempt to make sense of the world where fighter planes exist.

The title of the topic is a formula as it appears in the book BOYD The Fighter Pilot who changes the art of war by Robert Coram.

That formula is not written the same as it appears in Fighter Combat by Robert Shaw.

The subtle difference are curious, I think, based upon my resent inspection of the properties of inertia, mass, and relative density.

A plane with a higher mass, higher inertia, and higher relative density compared to a plane with lower mass, lower inertia, and lower realative density will react differently to the medium which resists the planes movement i.e. the atmosphere.

Moving the heavier plane requires more energy and releasing that energy once it is gained is formulated by the equation: Ps=[T-D/W]V.

My question concerns math.

Is this a true mathematical statment:
[T-D/W]= T/W - D/W

Take a P-47 and a Bf109K and consider a few things concerning this plane matchup. First, for the purposes of this discussion, let's imagine that these two planes have the same level max speed. If it would help then consider that these planes are not production models that instead they are custom. They both have the same level max speed at 8k meters. Now imagine that the P-47 is twice the weight of the Bf109K. Bear with me here, if you are at all interested in this stuff, my point concerns something specific so it is important to avoid getting caught up in exact plane performance numbers.

The P-47 and Bf109 are flying side by side at the same max level speed.
What happens when both planes are pitched up from that level flight condition?
What happens when both planes are pitched down from that level flight condition?

Mass and or inertia is going to resist any changes in pitch more so with the heavier P-47 than with the Bf109.

Gravity is a constant force applied to these two planes as they fly level, however these two planes are not going to be able to deal with the force of gravity in the same way due to their differences in mass, among other things.

The P-47 has enough thrust and lift to maintain an equal velocity in level flight but in order for the P-47 to gain anymore altitude from this position of equalibrium it will require more thrust and or more lift than the Bf109 because the P-47 has more mass and therefore is more susceptible to the force of the earths gravity. The higher mass of the P-47 requires more energy to move it against the force of gravity.
Since the P-47 and Bf109 are already at max thrust in max level flight then as these two planes pitch up the 109 will require less lift to change direction and less lift to resist the force of gravity to lift it higher, or accelerate against the force of gravity.
Due to relative mass the Bf109 is going to have better climb performance.

In order to see clearly what happens when both planes pitch down it is now important, at least to me, to consider the medium which resists movement or air and the effects of relative density.

Both planes accelerate at the same speed due to the force of gravity in a vacuum. Air hinders this rate of acceleration. This resistance is termed drag, and it is described as a force. Drag force is equal to thrust when both planes are flying level at max speed.

Here comes the important point and the reason for the mathematical question concerning the Specific excess power equation.

As an objects mass increases it becomes relatively more able to pass through a medium of resistance. Mass renders drag less effective. Drag force is more capable of resisting the movement of a lower mass object.

To make this point more clear consider what happens to top level speed for a plane that gains weight.

Chapter 5 Excess Power Characteristics (http://flighttest.navair.navy.mil/unrestricted/FTM108/)

Page 5.14
5.3.5.2 INCREASED GROSS WEIGHT
"The effect of increasing gross weight is similar to that of increasing the normal acceleration, with the difference that both the numerator and denominator are affectd rather than the numberator alone (Figure 5.8):"

and Page 5.15

"The balance of thrust and drag is the same, resulting in identical minimum and maximum level flight speeds."

If it is true that increases in weight do not lower max level flight speeds then it seems clear to me that this is due to a change in relative density.

The air is rendered comparitaively or relatively less dense as the mass of the object passing through the air is increased.

Thrust does not change on the plane as it increases weight. More lift is required to stay level when weight is added and therefore more induced drag is generated. Why does the plane still fly at the same speed when adding weight? It seem clear to me that the total force of drag is the same because the plane does not accelerate. Thrust remains constant, induced drag increases, weight increases, and velocity remains the same. I think that the higher mass plane is more capable of penetrating the atmosphere. The increase in the planes density renders the air relatively less dense.

Chapter 8 DEscent Performance (http://flighttest.navair.navy.mil/unrestricted/FTM108/)

Page 8.7 WEIGHT EFFECT ON DESCENT PERFORMANCE

"At the higher airspeed for the higher gross weight, the increase in drag is offset by the increased weight component along the flight path.":

In level flight the P-47 and the Bf109 both have enough thrust to counter the force of drag (they are both at the same max speed) they both have the same balance between weight and lift (level flight). However the P-47 has a higher mass. The increased mass required more energy to get the vehicle moving and more energy to get to that same altitude. Therefore the P-47 has more energy despite being at the same speed and same altitude. If it is reasonable to conclude that the P-47 will perform relatively poorly as both planes change direction from level flight to a climb because the mass is both more difficult to move and more difficult to lift then what can be said about any change from level flight into a dive?

Conventional thinking has been previously expresses that the P-47 will not accelerate any faster and possibly accelerate slower than the lighter Bf-109 in a dive due to the difficulties associated with moving objects of higher mass. To further complicate the matter it has also been stated that since gravity accelerates all objects at the same rate regardless of weight in a vacuum that both the P-47 and the Bf109 will dive at the same rate, much like what occurs in previous versions of the game. One more complication concerning dive performance has been described as a simple equation where the greater mass vehicle will accelerate slower up to max level speed (in a dive) and above the level max speed the situation reverses where the higher mass vehicle accelerates faster than the lower mass one, in a dive.

Before moving on to the situation where the higher mass vehicle accelerates slower than the lower mass vehicle at speeds below max level speed it may help to look at what happens when two imaginary planes are flying at the same max level speed where one plane has an obviously higher mass.

Back again to the Bf109 and the P-47 flying level at full power where for whatever imaginary configuration these planes are maxed out at the same speed.

Both planes pitch over in a dive.

Gravity is a constant force generated by the earth and this force accelerates both planes at the same rate but only in a vacuum. Since an atmosphere is present and since this form of resistance does limit the acceleration of these vehicles as they are being accelerated by gravity then it is neccesary to measure that form of resistance in an effort to find just how effective that resistance is when acting upon our vehicles.
One such method of measuring the resistance to movement presented by the atmosphere is to quantify density. The higher the density of the atmosphere the greater will be the drag force acting against movement. The lower the density of the atmosphere the lower will be the drag force acting against movement.

Before moving any further it occurs to me to return to the observation of a plane's max level speed and the associated effect of changes in mass. Imagine that the P-47 is filled with mercury, it has a much more powerfull engine to move this increased mass and it has larger, more effective wings to lift this increased mass against the force of gravity. The P-47 is still flying at the same max level speed as the Bf109. Both planes are flying side by side, both planes still have a balance between thrust and drag, lift and gravity. Now imagine that the P-47 dumps the mercury. It is reasonable to conclude that as the mercury is dumped the P-47 will climb if the pilot does not push the stick forward. For the purposes of this discussion it is required that the pilot push the stick forward in an effort to maintain level flight. The reason why this piloting is required is for us to realize what forces are in place that cause any change in max level flight velocity.

Before moving on it is important to indentify what happens in this situation.

It is important to identify why the P-47 is not able to gain any more level flight speed as the P-47 reduces mass.

Picture the P-47 crusing alone in a race with the Bf109. Both pilots are trying to win the race to the finish line. The P-47 happens to be burdened with a cargo of mercury and he thinks it would help to dump the cargo. He does so thinking that he will then be able to speed ahead and win the race.

Who wins the race?

Because I find reason to write and because this subject interests me I am going to move ahead without confirmation of the results of the above race between an imaginary Bf109 and a special high mass P-47. I am going to move on with the assumption that the P-47 will not win the race as it dumps mercury and decreases mass.

I want to bring this line of thinking back to the Specific Excess Power formula.

T/W - D/W suggests to me that weight can be factored relative to drag so as to account for relative density.

That is it for now.

OOOPs I forgot a note of relevance.

On Warclouds I found myself flying alone. My normal wingmen were all busy with real life things. A P-38 zoomed by from about 10 degrees angle off my nose or 1 oclock high. Since then I checked the replay to see how this guy managed to avoid detection and I found that his P-38 was hidden behind the forward up right canopy bars. I went into a dive after being bounced by the P-38. My thinking was that the P-38s will break apart in the game at lower speeds than my 109G6AS. I can therefore gain relative energy. Sure enough the separation grows and I start pulling up into a climb. My thinking was that the game allows the AS to gain in relative energy over the P-38 in a sustained climb.

The text buffer says:

"Timid 109s diving and climbing"

or something to that effect

"&lt;S&gt;" etc.

I've stood under a P-38. It is a large plane. There was one at the Chino air museum along with a Rolls engined Bf109. There is another Bf109 at the Planes of Fame museum in Flagstaff Arizona. I saw that one too.
I can stand next to the 109s and see the instrument panel. I am 6 feet tall.
The 109 is a small plane.

Each of us have our own opinions as to what should or should not be done in Air Combat. I try to fly to my planes strengths. I also try to simulate what has been written in history books. Sometimes I succeed. Somtimes I have to take flak for it.

Zayets
06-03-2004, 03:14 PM
Here's my theory: start engine , full throttle,aim,fire,go home. Not neccesary in this order.Instinct.That's all,I lost my chance to be a real pilot , now is time to have some fun in the game. Personally I'm much more concerned about my RAM & CPU speed than any other numbers we think they are using in the game.
But I do have fun http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

Zayets out

k5054
06-03-2004, 03:20 PM
You are making heavy weather of this. The priciples are all laid down in the literature. I suggest 'Flight mechanics of high performance aircraft' by Vinh.

Isn't planes of fame in Mesa?

k5054
06-03-2004, 03:21 PM
Oops, it's Champlin that's in mesa, sorry.

JG14_Josf
06-03-2004, 03:41 PM
k5054,

It has been years since I visited the POF museum and the exact location escapes my memory.

Is it possible to get a comment on the effect of changes in weight on Vmax?

I don't want to deminish the valuable advice to read specific literature. My reading currently is being applied to another form of education. This subject tends to be of a lesser interest for me at this time.

I've also been pointed toward these books:

Aerodynamics, Aeronautics and Flight Mechanics
Barnes W. McCormick

and

Introduction to Flight
John D Anderson

They are on my list, just further down.

Economy is a drag.

Art-J
06-03-2004, 03:52 PM
JG14_Josf, I respect Your devotion to aerodynamic questions (the lenght of Your posts is the best proof for that http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif ), but You remind me these old professors in universities, who can talk about their scientific passions for hours, but 90% of students are, politely speaking, "not-very-interested" in the topic, thinking: "When is this old ***** going to stop and let us go?". This is not Your first post about drag/thrust issues and not the last I'm sure, but I'm afraid You won't get much attention on this board. Just like guys said, You take it too seriously, ESPECIALLY when we consider this game engine limitations and how many things are not modelled correctly / at all. Try just to have fun!

P.S. - sorry if I offend You by this post, I just don't think You will find many partners for such extended and detailed physics discussion here.

Salute!

Chuck_Older
06-03-2004, 03:54 PM
"Boyd" is a great book. But I read your mathematical question and then I have an Engineering school flashback and I want to go get drunk, hide, and clean my guns.

*****************************
The hillsides ring with, "Free the People",
Or can I hear the echoes from the days of '39?
~ Clash

JG14_Josf
06-03-2004, 04:09 PM
Art-J,

Thanks for the note. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Perhaps I don't add enough smiley faces. I am having lots of fun, in the game, and on this forum. Sometimes it is difficult to separate the wheat from the chaff. Sometimes the insults and negative communication become rather heavy. But for the most part this game and these forums are worth the effort in participation.

I am seriously having fun.

If you would like confirmation on that I can ask my fellow squad mates to chime in. We have been having a blast in the Warclouds server.

JG14_Scott has just replied to a recent note I sent him. That note could have been taken as mean spirited criticism, if it were to be taken only on its content. We have, instead, managed to communicate with enough civility and good manners to keep the subject matter in an objective context. Much like your very welcome post.

Thanks again.

Here is what I call fun (High speed pass, deflection shot, on target):

http://mysite.verizon.net/res0l0yx/On%20the%20noggin.jpg

[This message was edited by JG14_Josf on Thu June 03 2004 at 03:52 PM.]

Enkar
06-03-2004, 04:09 PM
If you just want the equation for Vmax, here it is:

Vmax= {[(Tamax/W)(W/S) + (W/S)[(Tamax/W)^2 - (4Cd,oK)]]/[roeinfCd,o]}^1/2

So:
1) Vmax increases as Tamax/W increases
2) Vmax increases as W/S increases
3) Vmax decreases as Cd,o and/or K increases

Aircraft Performance and Design
John D. Anderson, Jr.
page 231

Anderson is good. You should read this book.

DuxCorvan
06-03-2004, 04:16 PM
"Yes, I've bought FB just today...! âÂ¿Eh? âÂ¿Playing? No... âÂ¿why?"

http://www.planethalflife.com/features/articles/delayeditorial/nerd.jpg

- Dux Corvan -
Ten thousand years of Cantabrian skinning.

Cajun76
06-03-2004, 05:26 PM
I've never been good at "figuring" with numbers, but I am a mechanic, and I have a logical mind, except about women. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

Did you know that:

Charles Lindberg calculated and factored in the speed increase to The Spirit of St. Louis as his fuel load decreased? He wasn't interested in climbing, just getting there faster.

Empty bombers not only climb faster, but they fly faster too.

An airplane loaded to the max with normal engines will behave much like a normally loaded plane with underpowered engines in level flight.

I actually did a comparison of a P-47 and a 109 at low level max speeds before. I don't remember the exact numbers or models, but they were contemporaries. The 109 was only a bit faster than the P-47, even though the P-47 had more power. It had something like 1.3 times the power of the 109, yet weighed 2.5 times more or thereabouts. I was demonstrating to a 109 Superfan that the 109 had more drag than the P-47. One of a pair, actually. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

Interesting stuff, but most everything I've read or seen or heard says a 109 or 190 will outdive a P-47 initially, then the P-47 will rapidly overtake them. Some point out the dive test between the P-47 and 190, and that it took (I don't remember the figure, so I won't post a random guess) a fair bit of altitude for the P-47 to catch and pass the 190 with significantly more speed. One thing to remember, 5000ft.? is not very much when talking about diving a P-47. Full power dives were forbidden under a certain limit, because it would build up so much speed and lawn dart.

Anyway, I hope you find what your looking for. Try not to get lost in too many formulas, because they don't always tell the whole story. Good luck. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

Art-J
06-03-2004, 05:41 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:
Art-J,

Thanks for the note. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Perhaps I don't add enough smiley faces. I am having lots of fun, in the game, and on this forum. Sometimes it is difficult to separate the wheat from the chaff. Sometimes the insults and negative communication become rather heavy. But for the most part this game and these forums are worth the effort in participation.

I am seriously having fun.

If you would like confirmation on that I can ask my fellow squad mates to chime in. We have been having a blast in the Warclouds server.

JG14_Scott has just replied to a recent note I sent him. That note could have been taken as mean spirited criticism, if it were to be taken only on its content. We have, instead, managed to communicate with enough civility and good manners to keep the subject matter in an objective context. Much like your very welcome post.

Thanks again.

<HR></BLOCKQUOTE>

If You're having fun, that's ok for me. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Maybe when my LAN administrator will allow me to connect through firewall again, we'll meet on Warclouds server. http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

Salute!

ZG77_Lignite
06-03-2004, 10:44 PM
Just to put it out there, at one point (far) in the past these kinds of discussions were quite common, with extremely important and usefull information (much of which was even correct) given. There were many great guys that would spend hours explaining complex things to dimwits such as myself. Personally I'd like to see those days come again. Regardless, I sure like to see the 'smart guys' discussing this stuff, I find it quite interesting when I have the time to read it.

Unfortunately my brain stores information at a rate equal to an old AppleIIe with 1kb of ram, divided by time since input, therefore at any one time I usually can't remember what I had for breakfast, let alone aerodynamic properties of Bf109's. But its fun. Please continue.

BBB_Hyperion
06-03-2004, 11:32 PM
Maybe another view on the problem might bring up new details.

Dive Limits for P38L
http://home.att.net/%7Eww2aviation/RedLine.html
500 mph = 804,67 km/h

Dive Limits for 109 F4 with G Tailfin
http://109lair.hobbyvista.com/techref/structures/tails/109.05e43_report/05e43-p6.htm
Regards,
Hyperion

Tully__
06-04-2004, 07:13 AM
http://members.optusnet.com.au/tully_78th/aeroformula.jpg

Assuming that to be the case, [T-D/W]= T/W - D/W
is correct. If not, [T-D/W]=T-[D/W].

From my (limited) knowledge of aerodynamics, I'd say that it should be Ps=((T-D)/W)*V

Check your sources to make sure.

=================================================

http://members.optusnet.com.au/tully_78th/sig.jpg

IL2 Forums Moderator
Tully's X-45 profile (SST drivers) (http://members.optusnet.com.au/tully_78th/fb.zip)

Salut
Tully

Biloxi72
06-04-2004, 07:49 AM
S!
Ok i will admit this stuff Josef posts is way out of my league, but i am trying to pick up on it. So if i understood this right, if i took my p38L at level speed as a 109k, I should be able to outdive it and gain more speed in the dive due to my larger plane and (i think) more powerful engines. Yet the 109k should be able to outclimb me in the zoom because there it is lighter and will not burn off its speed/energy faster then my 38L?
If this is the case should i not bet able to out dive and extend from a 109 series on my tail in AEP? http://ubbxforums.ubi.com/images/smiley/blink.gif It does not seem to be the case or am i wrong on this whole matter. PLEASE ENLIGHTEN ME hehe.

Ok i just reread Josefs article and now i am a bit confused. Grated it took me more enrgy to get to alt., but using the premise i have more potential energy should i still not gain more speed in dives and have an initial advantage in the early stages of a climb due to this energy?
Thanks http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

"It was a marveleous aircraft! It was the best aircraft I flew in the war by far. I never flew the P-51, its been one of my life regrets, but I flew just about everything else there was. I liked the P-38s rate of climb, its speed, the way it handled, and its firepower directly out the nose. The P-38 would turn with almost anything, in fact it would out turn the P-47, out climb it, and out maneuver it. The P-38 was one of the great aircraft of WWII."...Charles MacDonald, P-38 Ace

[This message was edited by RufShod on Fri June 04 2004 at 07:05 AM.]

JG14_Josf
06-04-2004, 08:27 AM
Tully,

Thanks.

The book "BOYD" has the brackets that indicate T/W - D/W. Ps = [T-D over W] times V

Robert Shaw has the formula written the more conventional way.

What occured to me is that in the Boyd book version of the formula; Weight is factored into Thrust (weight resists movement) and weight is factored into Drag (mass renders drag relatively less effective) and then the product of Drag divided by weight (Less drag) is subtracted from the product of Thrust divided by weight (resistance to acceleration).

The way the formula is written in Fighter Combat by Robert Shaw may not be interpreted in that way.

My math is poor but I think that the subtle difference is not so subtle. Thrust is subtracted by Drag and that product is divided by weight in the conventional formula.

The differences in the way the formula is written may be a simple error made by the writer of the publisher of the book "BOYD".

However the formula is closer to the source and this has bothered me for some time.

Look Here (http://www.simhq.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=98;t=005442)

The conventional formula does not make much sense to me. For example: anytime Thrust is equal to Drag what happens in the formula?

0/W times V?

0 times anything is still 0.

No Specific excess power?

The more dense P-47 is next to the less dense Bf109 and the both have T-D = 0.

However they both don't have the same factors for T/W - D/W.

They both have different power to weight ratios, and the both have different factors of relative density as they fly along side by side at max level speed.

The conventional expression of the formula may in fact be the only reasonable way to use these measurments of reality. I am trying to figure it out and could use some help.

It is no big deal. Just big enough to hold my interest.

Tully__
06-04-2004, 08:40 AM
Specific excess power determines ability to accelerate or climb. When Ps=0 in level flight, speed is constant. When Ps is positive, the plane will accelerate or climb (depending on trim/control position) and when Ps is negative, the plane will slow or descend.

Thrust is dependant on throttle setting, so Ps can be zero at any speed at or below the plane's max if the throttle is set right.

Drag is dependant on angle of attack, aircraft size, aicraft shape and speed and can consequently also varies considerably depending on pilot input. For level flight, angle of attack for a given speed (& hence drag) varies with aircraft load (fuel & weapons) so drag will be higher at full fuel load or weapons for a given speed than it will for low fuel / no weapons.

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JG14_Josf
06-04-2004, 08:48 AM
RufShod,

I do not know how any of these planes should compare to each other, except where information has been documented by people who do know how these planes did compare to each other and that information can be evidence supporting knowledge.

My example of the P-38 and the Bf109 was nothing more than what I wrote. One plane is big (I saw that first hand) and one plane is small. They are not the same.

One very important factor in determining how these planes stack up when trying to use Math is Drag.

Drag can be calculated with exacting measurements of size, shape, and what I now realize as relative density. The objects are passing through a relative medium of resistance. The relationship of density is such that the lower the relative density the greater is the resistance to movement.

However, shape, is also a factor. Imagine a barn door that measures 10 meters by 10 meters and one inch thick. Make this a solid iron barn door. This barn door is relatively more dense than the air. It will pass through the air quickly. It will pass through the air much quicker when it travels one way as opposed to another. Make the same barn door out of styrofoam.

I'm trying to make sense of these things too, it is also way out of my league.

Tully__
06-04-2004, 08:59 AM
Josf, it's bedtime here (1:05am in Australia), but I'll endeavour to clear it up a bit more tomorrow.

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JG14_Josf
06-04-2004, 09:15 AM
Tully wrote:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>For level flight, angle of attack for a given speed (& hence drag) varies with aircraft load (fuel & weapons) so drag will be higher at full fuel load or weapons for a given speed than it will for low fuel / no weapons.
<HR></BLOCKQUOTE>

That statment appears to say that adding weight will lower max level flight speed.

Is this correct?

More Drag means less speed, or more drag means a need for more thrust to maintain the same speed.

Does adding weight lower max level flight speed?

Udidtoo
06-04-2004, 09:31 AM
The difference between me and Newton. by Udidtoo.

If an apple conked me on the noodle.

When I woke up I'd just make strudel.

..............................
I always have just enough fuel to arrive at the scene of my crash.

k5054
06-04-2004, 09:31 AM
Adding weight does indeed lower max level flight speed, or all aircraft would carry lead ballast and weigh 10,000tons. For an aircraft such as a WW2 fighter, an additional 10% weight might reduce top speed by 1% and climb by 10%+, and increase dive acceleration after max speed by up to 10%.

Biloxi72
06-04-2004, 09:34 AM
S!
ok Josf thanks for the answer!

"It was a marveleous aircraft! It was the best aircraft I flew in the war by far. I never flew the P-51, its been one of my life regrets, but I flew just about everything else there was. I liked the P-38s rate of climb, its speed, the way it handled, and its firepower directly out the nose. The P-38 would turn with almost anything, in fact it would out turn the P-47, out climb it, and out maneuver it. The P-38 was one of the great aircraft of WWII."...Charles MacDonald, P-38 Ace

horseback
06-04-2004, 09:44 AM
Normally, I try to avoid discussions like this, because I have to take a lot of notes & meditate upon them for a while (picture a hairy fat, balding white guy in the lotus position...). But it seems to me that it's impossible to express the whole problem at once mathematically without fatally obscuring the facts.

Fact 1: Real life is a dynamic environment. Conditions change constantly, in varying directions,every time you test something. You can get consistant results but the closer you get to the edge of performance, the more random factors can hose up your results. Business Administration majors should immediately log off now, and consider this concept. Take a couple of days to digest it before returning to this thread. It is huge, and apparently beyond your powers to consider in tandem with any other concept. (that last part is in case my boss ever reads this thread).

Facts 2 & 3: Nothing happens in a vacuum (there is no perfect vacuum, even in space; there's always a little cr@p floating around, and it always finds its way into your eyes, mouth or nose), and only God can generate a random number. Any human creation is infected with human faults, including prejudice.

Fact 4: Comparing aircraft built to different design requirements for different roles is a classic case of apples-to-oranges. The 109 is a classic hotrod point defense design, the most powerful engine available stuffed into the smallest possible airframe, and the Jug was designed for the best possible performance at high altitudes for air superiority (consider that the bulk of the airframe is used to accomodate the turbosupercharger, forcing the fuel tanks into the belly between the wings).

Fact 5: this sim is using the aircraft in their ideal conditions, meaning that German aircraft always have the best possible performance, instead of what they got in RL using ersatz fuel that the Allied blockades forced on them, and the quality defects deserved when using forced labor. You can see through the cellophane canopies of early war Russian fighters, and not suffer the defects of unskilled labor used to build them.

Allied aircraft were only developed up to the standard necessary to win; the urgency behind the development of the P-47N and P-51H, or the deployment of the Spitfire Mk XIV relaxed as their predecessors proved capable of handling the Luftwaffe. They already had excellant quality control, which meant that their aircraft were far more reliable and available than those their enemies flew.

Had Germany had a large, reliable skilled workforce and its own source of high quality oil fields and refineries, the aforementioned aircraft (and probably the P-80) would likely have debuted in large numbers over Europe before D-Day. That they didn't is a reflection of the fact that they weren't needed.

From the standpoint of this sim, that means that Western Allied fighters seem a little weaker in performance compared to their pilots' wartime observations. Between the technical advantages they had gained, and the penalties they had imposed on the Axis' industry and training infrastructures, they didn't need to match the accomplishments of German engineering, because German aircraft rarely met anything like their theoretical capabilities in practice.

cheers

horseback

"Here's your new Mustangs, boys. You can learn to fly'em on the way to the target. Cheers!" -LTCOL Don Blakeslee, 4th FG CO, February 27th, 1944

Biloxi72
06-04-2004, 10:06 AM
S!
Got ya horseback on realistic vs "perfect mode" for planes flying in Fb. I guess i was looking for in game proof that the 109( using that cuz that what shot me down in dive) in terms of speeds in dive for 109 to the p38. Thanks for the more insight, i forgot about a lot of what you said. http://ubbxforums.ubi.com/images/smiley/35.gif

"It was a marveleous aircraft! It was the best aircraft I flew in the war by far. I never flew the P-51, its been one of my life regrets, but I flew just about everything else there was. I liked the P-38s rate of climb, its speed, the way it handled, and its firepower directly out the nose. The P-38 would turn with almost anything, in fact it would out turn the P-47, out climb it, and out maneuver it. The P-38 was one of the great aircraft of WWII."...Charles MacDonald, P-38 Ace

JG14_Josf
06-04-2004, 10:58 AM
RufShod,

This (http://www.lanpartyworld.com/ww2/images/pro_190_survey_b_7.jpg) may help evaluate relative performance of the P-38 vs the Fw. 190 dive performance.

"79. Comparative dives between the two aircaft proved the FW.190 to be better, particularly in the intitial stage. During prolonged dives the P.38F on occasion was catching up slightly with the F.W190, but during actaul combat it is unlikely that the P.38F would have time to catch up before having to break off the attack."

In order to place things in perspective it may help to compare Horseback's post to the documents found on the web page listed above:

Fact 1: Those documents were recorded by Fighter Pilots dealing with Real Life. They used words like 'proved' to describe their findings based upon the best available information they had at the time. They used a captured (random combat example) FW190 in combat test trials to evaluate specific relative performance characteristics between the FW and their own planes.

Facts 2 & 3
Those test trials were inevitably tainted by prejudice however as the following quote suggests the error is, perhaps, minimized.

"Following initial flight trials at the Royal Aircraft Establishment at Farnborough in July 1942, the captured Focke Wulf 190 flew to the Air Fighting Development Unit at Duxford for tactical trials. The resultant report, issued in August 1942 and reproduced below almost in its entirety, is a model of what such an intelligence document should contain. In places the language was complimentary in the extreme. The reader shoud bear in mind that these are not the words of a Focke Wulf salesman trying to boost his firm's product, but those of an enemy forced to give an opponent grudging admiration in time of war."

The above quote is taken from the book Focke Wulf FW190 in Combat by Alfred Price. It describes the same documents that are found on Ring's P.R.O. web page.

Fact 4
Apples fought Oranges so to speak. The real fighter pilots endeavored to identify what makes and apple an apple and what makes an orange an orange. They wanted to use the better parts of the apples when fighting oranges and visa versa.

Fact 5
This sim is using 'unknown' performance data unless such data is reproducable it will remain 'unknown'.

______________________________

k5054,

A plane with a gross weight of 10,000 pounds traveling at a max level speed of 500kph compared to the same plane with more fuel grossing out at 11,000 pounds will have a top speed of 495kph?

Does the increase in mass effectively reduce the force of drag, or in other words; as the plane becomes more dense does the air become relatively less dense?
Does the effective capacity of the air acting to resist the movement of the plane decrease as the plane increases in mass?

k5054
06-04-2004, 11:14 AM
"
Does the increase in mass effectively reduce the force of drag, or in other words; as the plane becomes more dense does the air become relatively less dense?
Does the effective capacity of the air acting to resist the movement of the plane decrease as the plane increases in mass?"

The key here is level flight. To maintain level flight, lift = weight, right? If weight is more, then the lift is more, by the same amount. The wing then has to work a bit harder, and that creates more induced drag. Induced drag is something like 5-10% of the total drag at max speed, depending on many factors, but that's typical for a WW2 fighter. The induced drag varies as the square of the lift. Weight up 10%, induced drag up 21%, 20% of 5% is 1%, so about 1% of speed is lost. For a lightly loaded a/c in thick air at high speed, maybe a little less, for a heavy a/c high and slow, a lot more.
Performance data is largely known or can be calculted from known data. Handling data is not, and must be estimated by sim designers to please people who don't really know either.

JG14_Josf
06-04-2004, 12:23 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>to please people who don't really know either. <HR></BLOCKQUOTE>

I'm not sure what to make of that statemet.

My pleasure is to have a specific question answered concerning relative density or, in other words, the effective ability an object, vehicle, or airplane has when passing through a medium of resistance, fluid, air, or atmosphere; as that object becomes relatively more dense or as that object increases in mass will it be more able to pass through the fluid?

What is the effect of increases in mass and only mass, where size and shape remain the same as that objects movement is held back or resisted by the medium it passes through? Does increases in mass equate to decreases in resistance. As the object increases in density is there a corresponding decrease in the ability of the air to resist movement?

This is simple enough from my viewpoint, as ignorant as I may be: increases in mass renders the resistance to movement less able to resist movement.

Again, perhaps I am simply too stupid to realize what is going on but in my defense the follow quote is made more reasonable when I consider the factor of relative density.

From Fighter Combat by Robert Shaw
page 407

"One further method of increasing fighter acceleration is by the use of gravity: a steep dive will often multiply acceleration many times. Such a dive may follow unloading, which causes the aircraft to fly a ballistic trajectory resulting in gradually steepening dive angles. If altitude is available, however, a sharp pull-down to a steep dive attitude, followed by unloading, produces the most rapid long-term dive acceleration. Discounting the effects of thrust, the acceleration of an aircraft in a dive is a function of its "density," that is, its ratio of weight (actually its mass) to drag. When two fighters are similar in all respects except that one is heavier, the heavier aircraft will accelerate faster in a dive and, assuming structural considerations allow, will have a faster terminal velocity. Likewise, with two fighter of the same weight, the cleaner one (i.e. the one with less drag) will dive better. (This is why a brick falls faster than a feather in air.")

The Brick or P-47 has 2,000 or so horsepower. It may be true that discounting this factor will identify the importance of relative density, however once this factor is added to the equation the 2,000 number representing thrust must be compared to the thrust available on the other plane (feather) in the dive performance comparison.

If relative density allows the heavier plane to accelerate faster in a dive, then does this advantage dissapear when that same plane is traveling in level flight, or climbing, or passing through the same medium of resistance in any manner whatsoever?

JG14_Josf
06-04-2004, 12:44 PM
I may not be seeing the forest or truth of this matter for lack of an ability to see past the trees, or for the lack of an ability to see some very important trees that do in fact contribute in the make up of the forest.

I see no acknowledgment of this important factor or tree i.e. relative density.

Ignore it, if it pleases you. If it is easier for you to view the forest without this tree than that is your choice. What is not reasonable, however, is this assumed possition of superiority based upon that simplification.

'its ratio of weight (actually its mass) to drag.'

When weight (actuall mass) increases what happens to drag?

D/W?

Drag is more than a measurement of the size and shape of an object.

Drag is more than a measurement of the density of the medium resisting movement.

Drag is a total measurement of force.

What is the effect of realtive density upon total Drag force?

gombal40
06-04-2004, 12:50 PM
i like this discussions ( i have to read them a couple of times) but i like it
It is a very great compliment that anybody is trying tp appy existing laws of physics to models of oleg. He must ne pleased ( wanna join oleg?)

Now what i miss in this disscussion is the effect of drag of the different models (as i said its not realley my field so point me to my errors)
Isnt there something to say about clean design,
angle of attack of wings ??

Let my say this again i just barely understand the more serious post in this thread so be gentle with me

DuxCorvan
06-04-2004, 01:09 PM

http://www.royaldeaf.org.uk/clever.gif

k5054
06-04-2004, 03:17 PM
"
If relative density allows the heavier plane to accelerate faster in a dive, then does this advantage dissapear when that same plane is traveling in level flight, or climbing, or passing through the same medium of resistance in any manner whatsoever? "

The advantage does disappear when level, and when climbing it is reversed, that is the heavier aircraft takes more power to climb, or must climb at a slower rate.
Shaw mentions the unloaded dive, this is where the pilot pitches over slowly so as to maintain zero g and thus remove the drag due to lift, the 5-10% I mentioned before.

"Performance data is largely known or can be calculted from known data. Handling data is not, and must be estimated by sim designers to please people who don't really know either."

This was meant to say that the area we are discussing in this thread is all explainable with the normal physics/aerodynamics. If you know just a few facts about an aircraft, you can derive the constants for the various equations and use them to calculate the entire performance envelope. I suspect that this is how the performance model of AEP works, but I don't know for sure.

The handling side of the FM, though, is not so easy, it requires the modeller to produce an estimate of the handling to match the characteristics of the aircraft and also the historical, anecdotal, whatever, data. Sometimes the input data is not sufficient to do this. And NONE of us really know whether the result is 'correct' or not.

So, to get to relative density. This is a superfluous concept to me in the calculation, because it derives from other known figures. It is fine for Shaw to use it in his examples, and it works well when you consider an aircraft with full tanks vs empty ones, the full tanks will cause a faster dive, and a slower max and climb rate (not climb speed, the indicated speed for best climb may well be raised, but the rate will be less). But you can't compare the 'relative density' of differently shaped aircraft without working out the drag, and once you have the drag, the weight, the load factor and the thrust at a given speed you don't need relative density any more, you can calculate (estimate closely, if you like) what is happening to the aircraft.

JG14_Josf
06-04-2004, 11:11 PM
k5054,

If increases in mass renders the medium of resistance less resistive then it is not superfluous.

This property of mass and it's relative ability to pass through a medium of resistance exists. How can it be superfluous if it exists? If calculation identifies this natural fact then nature will be more accurately measured. If it is not calculated than the measure of nature will be simplified.

If increases in mass does render the medium of resistance less resistive in a dive then this natural relationship remains regardless of the direction of movement through the meadium of resistance. The fact that higher mass requires more energy to lift an object is the reason why increases in mass slow down climb rate. The factor of relative density remains, it does not dissapear. It remains an advantage of higher mass over lower mass. It is not enough of an advantage to overcome the larger dissadvantage imposed by the earths gravity.

The same is true for level flight. Higher mass renders the medium through which the vehicle passes less resistive. This remains an advantage, it remains a property of higher mass.
The factor of relative density does not dissapear.
More force is needed to lift the vehicle to maintain level flight against the force of gravity. More lift creates more drag. Mass remains as an advantage against resistance to movement in the medium it moves.

If the extra requirement of lift does include a net addition in total drag force then the plane will be slowed down.

Here is where I see a problem.

How much is added to total drag due to higher requirements of lift and how much more is the plane able to pass through the medium of resistance due to increases in relative density?

The higher mass allows the plane to accelerate faster and reach a higher dive speed because the increase in mass renders the air less capable of slowing it down. The higher mass effectively reduces the total drag force.

The degree of advantage gained in the ability of an object to pass through a medium of resitance as a direct result of an increase in the objects mass may not be easily identified but it is not superfluous. It exists.

If the game does not account for this factor then planes that did, in fact, have dive acceleration advantages will not have them. If those same planes are modeled with the dissadvantages in climb due to increased mass then those planes will recieve a double hit on performance. One that is real and one that is manufactured.

Another possible problem with a game that does not model the property of mass where increases in mass decreases the ability of the atmosphere to resist movement is when an object zooms up.

More from Fighter Combat
by Robert Shaw

"Returning to Equation 3 for a moment, note that aircraft weight has been eliminated and does not enter into ideal-zoom calculations, as shown in Figure A-5. In reality, however, this is not quite the case. Since a zoom takes a finite length of time to complete, the fighter is subject to the effects of weight, thrust, and drag (i.e.,Ps) during the maneuver. The amount of energy gained or lost in the zoom depends on the average value of Ps during this period. To illustrate this concept, assume two fighters are identical in all respects, except one is heavier (maybe it is carrying more internal fuel). If they begin zooms at the same speed and altitude (i.e., same Es), Equation 4 shows that the lighter fighter will have greater Ps, will therefore add more energy during the zoom, and will ultimately zoom higher than the heavy fighter. Ps as well as energy state must, therefore, be taken into account when calculating the zoom capability, or "true energy height," of a fighter.

Clearly mass is effected by the earths gravity more so than mass effects an ability to pass through a medium of resistance. This greater effect of gravity does not elimiate the advantage mass has on relative density, it renders it less of an advantage.

Note this test:

P-47 vs FW190 (http://www.lanpartyworld.com/ww2/images/p47-fw190-2.jpg)

"(c) Diving:
(1) 10,000 feet to 3,000 feet, starting at 250 m.p.h. diving at angle of 65o with constant throttle setting. The FW-190 pulled away rapidy at the beginning but the P-47 passed it at 3,000 feet with a much greater speed and had a decidedly better angle of pull out"

At lower speeds where the FW-190 has a dive acceleration advantage it will have a combat advantage. It will be able to gain relative energy faster than the P-47 at these speeds.

If the game models dive acceleration parity at these speeds then no such combat advantage in energy gain will exist when diving combat is conducted at those speeds.

As dive speed increases the P-47 gains relative energy. At these speeds the P-47 has a combat advantage. When diving combat is conducted at these higher speeds the P-47 will have an ability to gain relative energy.

If the game does not model any differences in acceleration between these planes at these speeds then no such combat advantage will exist in the game for the P-47 over the FW-190 when diving combat is conducted at these dive speeds.

Now imagine that a P-47 is fighting an FW-190 and for the first imaginary example the P-47 is trying to catch the FW-190.

The FW-190 starts to dive and begins pulling away. In reality the P-47 pilot will need to adjust tactics to suit the situation. The real P-47 pilot would most likley smile at this situation. Even if the FW-190 does the smart move and tries to make better his first mistake in diving, even if the FW-190 pilot turns to gain possition while he maintains the speed where his plane has an energy gaining advantage, even if the FW-190 pilot gets smart he already is in throuble becauase that high mass plane with the big motor is above him, and behind him.

In the game the FW-190 pilot smiles.

Now, if the FW-190 pilot compounds his mistake and stays in the dive he is going to increase his problems. The FW-190 pilot is entering the speed zone where the P-47 builds energy at a faster rate. By the time the FW-190 pulls out of the dive in an effort to avoid the inevitable rain of half inch high speed metal jacketed death the P-47 will have a much higher energy state. It will zoom back up to heaven. That much mass moving that fast is not going to slow down soon.

The game that models dive acceleration parity will have both the FW190 and the P-47 going the same speed after a 10,000 to 3,000 foot dive and as Shaw describes the heavier plane will have a lower zoom climb because both planes are at the same energy state.

In reality the P-47 has reached a much higher energy state at the bottom of that dive. It then can sport a zoom advantage.

The FW-190 can hope for an overshoot.

Now reverse the situation.

The FW-190 pilot is going after the P-47.

The P-47 pilot has fewer options starting at the same speed 250mph, same altitude 2,000 feet, just out of range, with the FW on his 6.

In the game the P-47 is in the same situation as the FW was in the first example since they both have the same exact dive acceleration performance.

Now, I have not retested the newest patch. I hope things are different. I will recognize a difference. Will you?

Tully__
06-05-2004, 03:41 AM
My further contribution is still on its way. I'm afraid I'm a little ill and medication is leaving me in no state to work with mathematics I haven't used seriously for over 10 years http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif.

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Cajun76
06-05-2004, 04:12 AM
I see where your going with this Josf, and I heartily agree. Just remember, mass is fine when talking about something sitting on a table, but inertia is mass in motion. An aicraft carrier and a small boat might well reach 30 knots, but shut down the engines, and which do you think will keep moving longer? Mass does not render the medium of resistence less resistive, it minimizes the effect variances the resistence is capable of causing.

In physics, it's of the utmost importance to know in what direction the forces are acting on each other. A man in a capsule in space who has his hatch malfunction is not sucked into space, he is blown out. A puddle jumper and a 747 at the same low altitude are subject to the same atmospheric turbulence, yet the effects will be felt less on the 747 due to its higher inertia resisting the nuances of the atmoshere changes.

I'm not trying disuade you at all, I merely want to make sure that as you reason this out, that you don't put the cart in front of the horse. I reguarly fly the P-47, and I know first hand that in the game I don't have the zoom climb and dive accelaration that the real thing had. However, I don't really know if it is possible to change any of this in the current physics engine Oleg is using. For a sim (I've heard) that was originally concieved to model one plane, it's remarkable how close most everything fits together. I S! your efforts, and I hope someone a bit more knowledge about your specific questions can do a better job than me. In fact, I'm certain someone can. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

k5054
06-05-2004, 08:12 AM
The drag does not change because of a change in weight, except for that portion of the drag which is due to lift, and that increases. A shape with higher relative density does not have lower drag at the same speed and angle of attack.
If we have two aircraft with the same shape, the heavier one will have a higher acceleration in the dive when above normal level max for that altitude, and a higher terminal velocity.

In a dive, there are three forces acting on the aircraft along the direction of travel. Let's say this is a zero g unloaded dive, which gives the best acceleration.
The forces are, engine thrust, Te, drag D and the component of the weight acting along the line, which is W x sin(angle). Each of these must be divided by the mass M to give their contribution to the total acceleration. So you have Wsin(angle)M + Te/M - D/M. Of course W = Mg. The first bit resolves to g x Sin(angle), the second to Te/M and the third to D/M. When Te is greater than D, the result of higher mass is to reduce the acceleration, That's the part of the dive where the a/c has not reached its max speed for the altitude it is passing through. When Te = D, the accel is g x sin(angle) and the mass makes no difference. When the drag is greater than engine thrust then higher mass reduces the size of the drag term and means accel is now faster for higher mass. As speed increases the thrust reduces fast (a prop plane has constant power but reducing thrust with speed) so the term D/M is what makes the difference between any kind of prop plane, as g x sin(angle) is not dependent at all on a/c characteristics. The term D/M is in fact the inverse of the ballistic coefficient I told you about weeks ago.
I posted a list (on ORR somewhere) of the ballistic coeff of all WW2 fighters, in AEP or not.

so, to sum up, below max speed thrust/weight makes a diffference, less as the a/c gets faster.

Above max speed ballistic coeff is the second biggest factor, especially at shallow angles, and the major factor in differences between a/c types.

Both of these only modify the basic acceleration of g x sin(angle) so with steep dives this is the major factor until speeds get very high, then Mach begins to come in and things get nasty anyway.

DuxCorvan
06-05-2004, 08:27 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Tully__:
My further contribution is still on its way. I'm afraid I'm a little ill and medication is leaving me in no state to work with mathematics I haven't used seriously for over 10 years<HR></BLOCKQUOTE>

Mine is better:

The dog ate my homework... http://ubbxforums.ubi.com/images/smiley/16x16_smiley-sad.gif

- Dux Corvan -
Ten thousand years of Cantabrian skinning.

JG14_Josf
06-05-2004, 10:45 AM
I have a hard time ignoring contradictions.

These two statements give me a hard time:

A.
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Mass does not render the medium of resistence less resistive, it minimizes the effect variances the resistence is capable of causing.
<HR></BLOCKQUOTE>
B.
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>A shape with higher relative density does not have lower drag at the same speed and angle of attack.
<HR></BLOCKQUOTE>

To get to the point without too much added confusion will it help to further clarify the term: 'effect variances'?

How can the physical relationship be described where increases in the weight of an object contribute to its ablilty to pass through a medium of resistance while the size and the shape of the object remain constant?

A. Inreases in mass make the object less effected by drag force?

True or false

B. Increases in relative density allow the object to pass through the air with greater ease?

True or false?

C. Increases in weight contained within an object as it passes through a medium of resistance will render the medium of resistance less capable of resisting the movement of the object?

True or False?

If the above are true then:

Does this increased capability to pass through a medium of resistance change if the mass stays the same and the medium of resistance stays the same?

Is it a property of the object to have an increased ability to pass through a medium of resistance as the object increases its weight and as the size and the shape of the object remain the same?

Is the ability to pass through a medium of resistance contained in the object?

Doesn't an object having mass have a measurable ability to move against resistance?

If the object does not change in size, shape or mass then isn't that ability to move against resistance constant?

If you take two rounds of any ammo; such as the 30-06 for example; hollow out the lead in one bullet and replace the space with styrofoam. What can be said about the new light weight bullets ability to pass through the air?

Shoot both bullets straight up using the same gun. This test will require a different charge in the case of each round and a chronograph will be needed to make sure that both bullets leave the barrel at the same speed. The rounds will have to be loaded up lightly to avoid blowing out the styrofoam bullet. The gun barrel may need to be shortened for the same reason.

Which bullet goes higher and why?

If the styrofoam filled bullet goes higher is this due to a greater requirement to force the heavier bullet up against the force of gravity?

If the lead filled bullet goes higher is this due to the higher sectional density or higher mass of this bullet and its greater ability to pass through the air?

Are the forces of thrust against gravity and mass against drag well isolated in this test so as to see only those forces involved without confusing the issue?

JG14_Josf
06-05-2004, 12:40 PM
http://mysite.verizon.net/res0l0yx/Approach.jpg
http://mysite.verizon.net/res0l0yx/Fireball.jpg
http://mysite.verizon.net/res0l0yx/Avoid.jpg

If the bullets can represent the forces involved and if those forces can be compared to Shaws zoom climb example then what can be understood about those forces acting upon the relative ability to zoom between a plane full of fuel and the same plane with less fuel?

What happens if Shaws zoom climb example is considered for those same planes under those same conditions if both planes were zooming up just like the bullets?

Both planes are at the same speed, same trajectory (straight up) and both planes have their engines turned off at the same time.

The bullets and the planes are going straight up, the bullets are the same shape, same size and they have different 'effect variances' The same is true about the relative properties of the planes i.e. same shape, same size, different values for mass.

The bullets and the planes will add no more energy to their trajectories. They will only travel as far as the energy contained within them can moves them against the force of gravity and against the resistance of air molecules.

Which bullet shoots higher, and which plane zooms higher?

Blottogg
06-05-2004, 01:01 PM
Okay, let me take a whack at it. Actually, I'll just regurgitate some stuff that Oryx posted a while ago on the same subject, when he illuminated something that hadn't occurred to me. Starting back with the formula:

Ps=[T-D/W]V

As Tully said, when T = D, Ps = 0, and the aircraft can neither climb nor accelerate without changing the conditions (reducing D, increasing T or reducing V.)

What I had first assumed was that with all other factors being equal, the aircraft with the higher W would accelerate faster in a dive at all velocities. What Oryx pointed out however, was that the contribution to dive acceleration from gravity is independent of W (or more correctly m.) G = 9.8 m/s^2 for everything on Earth. What made the comparison clear for me was when I realized that acceleration could be broken up into two components, one due to engine power, and another due to gravity. Gravitational acceleration is constant, engine thrust is constant (or close enough to make that assumption for this argument.) What affects an aircraft's acceleration in a dive is drag and weight.

As an example, take two P-47's. One has full fuel, the other only 25%. Both have the same T, and similar D (the lighter plane has less induced drag, but for level flight that's a pretty small difference, and much less than the % differences in the two aircraft's weights.) Starting from level flight, at a slow speed (i.e. T&gt;&gt;D for both aircraft), let's put both into vertical power dives. Acceleration due to the engine is directly proportional to Ps, so the lighter plane will accelerate faster at first. This makes sense, since its P/W ratio is better (the same reason Ferrari's out accelerate Yugos.) Gravity's contribution to acceleration is the same for both. Their weights are different, but acceleration due to gravity is the same. Since V is slow at the start, so is D (D proportional to V^2), so the force from gravitational acceleration (i.e. W) is relatively unaffected by D, which is why gravity's contribution to acceleration is the same for both aircraft at slow speeds.

Now let's continue the dive to an airspeed equal to the max level speed of the lighter P-47. Here T = D, so Ps = 0 for both aircraft(we're doing vertical power dives to eliminate lift and induced drag, so the heavier Jug doesn't have a drag penalty.) The only thing accelerating the aircraft at this point is gravity, which is now opposed by a much larger drag. Since this is a power dive, gravity (or more correctly gravitational force, or W) is resisted not by D, but by D - T. Here's where the extra weight starts to pay off in acceleration. Both aircraft's drags are the same at equal velocities, but their weights are different. Total acceleration can be found by summing the forces acting on the aircraft and dividing by their respective masses.

a = (W-(D-T))x m = ((W+T)-D)x m

= (g+T/m) - D/m = g + (T - D)/m

Remember that at low speeds T &gt; D, and at high speeds (above max level flight speed) D &gt; T. What the above equation shows is that for D &gt; T, more mass yields a higher acceleration, by minimizing the affect of both Thrust and Drag, allowing g to have the dominating affect on acceleration. This makes intuitive sense too, since you expect the aircraft with full fuel to have a higher terminal dive speed (discounting compressibility effects in addition to my other assumptions.)

So the lighter Jug will have better initial dive acceleration due to its better P/W ratio. As the effect of drag increases, W becomes the dominant factor affecting further acceleration. Sorry to be so long-winded (again), but I hope this helps.

Blotto

"Speed is life." - Anon
"Sight is life. Speed is merely groovy." - "Junior"

edit for multiple spelling errors

k5054
06-05-2004, 01:01 PM
The heavy one goes higher ,because the drag/mass term is smaller when mass is higher for the same drag. That's the mechanism that is at work here. It's the same as in a dive. The effect of the same amount of air resistance is less when acting on a larger mass. in both cases, climb or dive, the drag is slowing the a/c (or bullet) less when the mass is greater.

JG14_Josf
06-05-2004, 02:07 PM
Thanks for the reasoned, thoughtfull contributions.

I am again presented with contradictions. They may exist only in my mind, however, my hope is to express this contradiction well enought to identify the error.

k5054 wrote:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>The effect of the same amount of air resistance is less when acting on a larger mass. <HR></BLOCKQUOTE>

Blottogg wrote:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>What Oryx pointed out however, was that the contribution to dive acceleration from gravity is independent of W (or more correctly m.) G = 9.8 m/s^2 for everything on Earth. <HR></BLOCKQUOTE>

If the quote from k5054 is correct then the quote from Blottogg is only correct in a vacuum. Once a medium of resistance interferes with the ability of the earth gravity to act upon the objects of different values of mass the larger mass object is effected to a lesser degree by the same amount of air resistance and this is true (although not at a constant rate) regardless of velocity because the object itself contains the required properties that render the air less effective.

Higher mass objects of equal size and shape render the same amount of air resistance less effective in resisting movement. From the moment the bullets leave the gun, from the moment the P-47s start their zoom climb, from the momment two same size and same shape balls are dropped in an atmosphere where one ball weights .0000000000000000000000000000001#
and the other ball weighs 1000000000000000000000000#; the differences in ability for these things to pass through the air exists.

If the above physical relationship is described accurately in Blottogg's formuala then perhaps there is no contradiction. I'm not very good with math.

Cajun76
06-05-2004, 06:46 PM
Your examples of the two bullets and two a/c 'zooming' up is a direct case of inertia at work. Unless you're dealing with energies and speeds a good percentage of the speed of light, or black holes and such, Newton's Laws work quite well for most mundane Earth type stuff, like bullets and aircraft. One of Newton's laws is very relevant here.

An object in motion tends to remain in motion unless acted upon by an outside force.

AFAIK, the air does not become relatively less dense. The ability of a higher mass object in motion to resist the forces of drag (or any other force) is inertia. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

It just occurred to me, we keep talking about air like its not solid parts when it, in fact, is. Example:

Go to your local bowling alley. Select a 6lbs. ball and a 12lbs. ball. Same shape, one is more dense. The pins represent particles of air. I normally bowl in a straight line, using angles, so for this example, that's the way the balls will go down the lane. We're all intelligent people here, and I don't feel I need to walk through the effects of roiling the 12 pounder down the lane slower, or zipping the 6 pounder twice as fast to achieve similar results. What I will point out, is that the mass of the pins stays the same. They are the constant. The ball, the a/c, the bullets are the variable, not the pins changing their relative density.

For the two quotes above, k5054 is using the nomenclature and terms that Josf first used, probably to help avoid confusion for the subject matter. However, the subject matter is partially contained in that statement, and is flawed in a physics related way. It should read more like this:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>A larger mass that is moving has a greater inertia to resist any change in speed or direction from drag (air resistance) <HR></BLOCKQUOTE>

In physics, the effects come after the causes. This is true for many things, but it's critical to understanding how things work. Making the air less resistive would cause a 7 ton Jug to fly faster with less power (not powerloading, just less power) than a lighter a/c with similar power.

For another spin at it, an La-7 and the Jug on the deck come to mind. Both have similar power, about 2000 hp. The La-7 will eat the P-47 alive at this altitude. The Jugs greater mass does not mean it makes the air less resistive, and therefore faster than the La-7. It's turning performance is less, not just for the effects of powerloading and wingloading, but it's inertia also resists changes in direction, just like a 12lbs. bowling ball being deflected only slightly by the head pin. Hope this helps. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

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What if there were no hypothetical questions?

Tully__
06-05-2004, 07:49 PM
Josf, we need some diagrams and trigonometry to make it clear. I'll see if I can dig some up off the internet (or make some).

Edit: Oh, and here's some "light reading" (http://www.av8n.com/how/) that may help a little http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

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[This message was edited by Tully__ on Sat June 05 2004 at 06:59 PM.]

JG14_Josf
06-05-2004, 09:00 PM
Canjun76,

I do not mean nor did I ever say that the air density becomes less dense.

Things are relative to other things. If I stab my finger with a pin I will feel pain. And suppose that pain is constant just for the purposes of this disscusion. Now if I shoot myself in the foot the pain will be enormous compared to the finger. The finger will feel painful but it will feel relativly less painful than the foot.

When the lighter same shape, same size bullet filled with styrofoam and the heavier bullet filled with lead are shot straight up and they leave the gun barrel at the same speed which one goes higher?

Which one goes higher if they are shot in the same way without an atmosphere to restrict thier movement?

.

Cajun76
06-05-2004, 10:32 PM
For the bullets to be fired at the same speed, either more powder would be required for the heavier one, or it would require a longer barrel. This added energy is need to get the one with higher mass going the same speed as the lighter bullet. Atmosphere being equal, and gravity providing first a constant deceleration and then acceleration, the two bullets, for all practical purposes, will both hit the ground at the same time. All this is supposing a reletively low velocity at discharge.

At a much higher velocity, the bullet with more mass, more inertia tends to reamian in motion longer resisting the higher drag effects of higher velocity. Fluid dynamics change drastically as velocity is increased. Drag is the same for both, inertia, independent of the force of gravity, is the deciding factor here.

Mass is only weight when in the presence of a gravitional field. Mass is constant, wieght is not. Inertia is mass in motion. Higher speed in this case is as important, or can give the same result, as higher mass because of inertia.

Speaking of bullets, one of my favorite examples is to have a bullet fired from a level gun and a bullet dropped at the same time and height above the ground. Providing the ground is flat and level, the two bullets will hit the ground at the same time.

http://www.av8n.com/how/htm/motion.html#sec-straight-line-motion

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

JG14_Josf
06-05-2004, 11:14 PM
Cajun76,

My Dad once told me a story that he said was true. He recieved a phone call from a guy who's name was known by my Dad. The guy asked a rediculous question that went something like this:

"Mr. Kelley, I have a real good deal for you that I'm sure you will find impossible to resist."

My Dad knew this guy to be less than honest.

"You must be Joe King."

Cajun76
06-06-2004, 01:57 AM
One of my favorites is:

"Surely you're joking!"

"I'm not joking, and don't call me Shirley."

Perhaps Tully can shed some more light on this, or even correct anything I have wrong. I'm far from perfect, and I'm attempting to explain this the best way I know how. I too am interested in these sorts of things, otherwise I wouldn't post on it. Perhaps if you (Josf) could be more specific about which parts of my post you disagree with....

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

Tully__
06-06-2004, 10:31 AM
I'm working on some diagrams and examples, but it may take a couple of days in my spare time. As I said earlier in this thread, I'm somewhat rusty at working with this sort of mathematics and I'm finding I'm having to work it through from first principles. There's nothing like having to tell someone else how it works to force one to understand it properly http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

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JG14_Josf
06-06-2004, 11:17 AM
Cajun76,

Your post threw me so far off track that I had to sleep on it. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

The first time I read it my original thought was that this must be a joke or rather a trick question type of joke.

I was not at first able to see the error of the gun shooting level statement, instead it looked intuitively wrong. I stuck my neck out so to speak by posting the experience with my Dad.

Now I am certain that such a statement is more than odd, it is very wrong for all but a very limited possible truth.

For any other readers that are interested in where my original post was going i.e. toward explaining why the game contradicts historical examples of relative aircraft performance; this change in my line of thinking is way off target.

I am going to explain how I see this gun shooting level thing; despite the 'off topic' tendency.

It is a very interesting subject to me.

I shoot guns.

First let me quote the statement.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Speaking of bullets, one of my favorite examples is to have a bullet fired from a level gun and a bullet dropped at the same time and height above the ground. Providing the ground is flat and level, the two bullets will hit the ground at the same time. <HR></BLOCKQUOTE>

The above statement may be true if it is set-up perfectly and this may be why I stumbled on the problem so long. Then again I may just be slow.

The above statement is certainly not true if the gun is loaded up to accelerate the bullet to a velocity that will allow it to escape the earths gravity. Even if the bullet is aimed at a lower altitude from the altitude where it is shot but aimed to miss the earth (The earth is not level)then all that is needed to make the satement not true is enough velocity.

One bullet is dropped from 6 inches which is just about my prone shooting altitude. This bullet hits the ground some time after dropping it. The other bullet is being shot by my atomic gun. It makes bullets go real fast. Not just real fast but really really fast. In order to remove some possible error I shoot my gun into the grand canyon. I prone out and aim down into the canyon from 6 inches above the west end. I check my spot on a map and find it's altitude to be higher than the altitude on the other side of the canyon by 200 feet.
I aim very carefully so that my bullet will not hit the other side of the canyon. I aim for clear sky just above the horizon.
My gun is sighted in at 40 miles to be dead on target. I sighted it in at 3,000 miles too; just to check bullet drop. I had to raise the back sight a little to make up for the 1 milimeter drop at 3,000 miles. Remember the bullet goes really really really fast.

I shoot my bullet the same time the other bullet is dropped from 6 inches above the earth. My bullet goes first down into the canyon heading for the other side of the canyon. It misses the other side of the canyon by 4 inches and then it keeps on going and going and going.

The bullet needs to be of such a high mass that it contains a whole lot of inertia once it is accelerated to such a high speed. It will not have any more additional energy once it leaves the gun barrel. (Edit: Since the gun is aimed down just a little bit; the earth will add a little more energy to the bullet as it decends. After the bullet reaches the lowest altitude it will then be moving against the force of gravity and then the earth will be subtracting energy from the bullet)

In an effort to get back on topic I am going to call my bullet: P-47.

The P-47 bullet is so heavy that my gun needs to be bench rested on a very sturdy bench.

I am going to call my gun: Pratt & Whitney Double Wasp.

My gun is also very heavy but it sure does give the bullet named P-47 a whole lot of energy.

In addition to the factor of velocity that makes an object resist the force of gravity to allow that object to lose the race toward earth is the factor of trajectory.

The shortest distance between two points is a straight line. As the bullet is dropped it goes straight toward the source of energy that is acting upon it. Any other path toward that source of energy will take a longer time to travel that path unless another source of energy is aimed to some degree at that source. The only way that the bullet being shot will hit the ground at the same time as the dropped bullet is if the energy applied to shoot the bullet adds an equal amount of energy toward the earth to make up for the greater distance being traveled exacty.

I am cerain that such a thing can be done.

The Earth is not level; an object falling somewhere in China is traveling the opposite direction as will an object falling here in the U.S. and that fact seems to complicate this matter to me.

For the other statment concerning two bullets being shot straight up and at what time these bullets will both hit the ground I am inclined to wait for a difinitive answer as to which bullet goes higher in an atmosphere and which bullet goes higher without an atmosphere when one bullet of the same size and shape is filled with styrofoam; the other filled with lead and both bullets leave the gun barrel at the same speed.

Picture a P-47 and an FW-190 going straight up in a zoom climb with their engines turned off and both planes begin the zoom climb at the same speed.

It is very encouraging to find that my 'Joe King' comment was not recieved badly.

Thanks.

[This message was edited by JG14_Josf on Sun June 06 2004 at 10:52 AM.]

Dammerung
06-06-2004, 02:31 PM
Additionally, I read the book. Any person who has any interest in military flying MUST read it. It's a great bio, but It's a shame such a great man goes unrecognized.

Oh, there are no fighter pilots down in hell...
Oh, there are no fighter pilots down in hell...
The whole damn place is full of queers, navigators, and bombadiers...
Oh, there are no fighter pilots down in hell...

Tully__
06-07-2004, 12:12 AM
Duh!!!! It's taken me three pages to notice the implications of this formula being for specific excess power. Because it's specific excess power, the result is per kilogram of aircraft weight. This formula is not meant to be applied to anything but level flight at constant speed. The result will give a good indication of available sustained climb performance or level flight acceleration due to thrust for the speed at which it's calculated. You can directly compare these factors of aircraft regardless of weight using this formula, but you need to remember that thrust is not the same as power when plugging numbers in. Thrust is a function of power, speed and propellor efficiency for that speed in propellor driven aircraft.

I'll do a little more work and see if I can come up with a simple way to describe how mass affects dive and zoom climb performance.

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Cajun76
06-07-2004, 05:20 AM
http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif The bullet drop was not put there to bake anyone's noodle, it was merely an example of the constant acceleration of gravity, independent of other velocities. In physics examples, certain compromises have to be made between what can easily be expressed with some numbers, and the chaotic real life situations that can exist. It was merely a thought experiment using the known constant of gravitational acceleration on a common item that can have a high velocity.

Our average gun might fire at 800-900 m/s. (fairly typical MG fire, WWII). Fired perfectly level, (no windage, it would invalidate the experiment) http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif say around 5 ft or so, and another bullet dropped at the same time, on a physics example type long level field, our two bullets would each experience an acceleration toward the Earth at approximately 9.8 m/s, squared, regardless of how fast (850 m/s) one of them is traveling. They would hit at the same time.

I've actually used Newton's cannon-on-a-mountaintop in discussions before. Your example is similar to it.

No atmosphere, put a cannon on the top of Mt. Everest. Fire cannonballs at increasing velocities. Each cannonball will fall toward the Earth at a constant rate. As the velocity increases, the cannonballs start to fall farther away. Soon, they start to fall beyond the horizon. The curve of the Earth starts to fall away from the path the cannonball is taking. Fire the cannonball at the right velocity, the Earth falls away (recedes, if you like) from the cannonball at the same speed the cannonball progresses forward. With no atmosphere to give it drag, or slow it down, the cannonball is now in orbit around the Earth, in freefall. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif In fact, I would duck soon.... http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

However, the preceding is merely some thought experiments about the way gravity operates. I'm looking forward to Tully's info. If the changes can be put into future sims, BoB, then that would be awesome.

A couple of things after rereading your post, Josf. A small mass at extreme velocity will have the same inertia as a much bigger mass traveling much slower. Micro meteors in space are a good example of something tiny and fast that can cause a lot of damage.

Good hunting,
Cajun76

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What if there were no hypothetical questions?

JG14_Josf
06-07-2004, 08:25 AM
Cajun76,

Do you have an answer for which object will travel farther going straight up?

A. syrofoam bullet

Both bullets going straight up, both bullets of the same shape and size, both bullets starting at the same altitude and speed.

Do you have an answer for which bullet goes higher with an atmosphere and an answer for which bullet goes higher without an atmosphere?

I am just wondering.

KarayaEine
06-07-2004, 10:41 AM
Interesting to note in rocketry we have something called 'mass optimization' to acheive higher altitudes. You might think a light rocket would fly higher than a heavier one but that's not always the case. In some instances adding mass actually increases altitude.

just my .02 cents....

Johann

Horrido!
"We need more ammo!"
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"Achtung Kommandant, sind Sie FlÃÂ¤che auf Feuer"

Cajun76
06-07-2004, 03:46 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:
Cajun76,

Do you have an answer for which object will travel farther going straight up?

A. syrofoam bullet

Both bullets going straight up, both bullets of the same shape and size, both bullets starting at the same altitude and speed.

Do you have an answer for which bullet goes higher with an atmosphere and an answer for which bullet goes higher without an atmosphere?

I am just wondering.<HR></BLOCKQUOTE>

Well, I did answer, in a more round-about way above. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif If the bullets are being shot at typical velocity, it's important to note the the heavier bullet will need more initial energy imparted to it to reach the same speed as the lighter bullet. That being said, and gravity being constant for both, the heavier lead bullet will have more inertia and would travel higher than the lighter bullet, due to it's inertia resisting drag effects. But nearly the same effect would occur if the same energy for the heavier bullet were applied to another styrofoam bullet. The added speed to it's smaller mass would impart more inertia, and it would go higher than it's energy deficient brother. It would posses more energy that drag would have to bleed from it...

One thing to clarify: The heavier bullet in atmosphere is traveling closer to the same height as it's cousin in a vacuum than the lighter bullet in atmosphere. Not just because it has more inertia, the important part is because the styrofoam bullet is more affected by drag due to it's smaller inertia. The bullet with less inertia is being affected much more by drag than the one with higher inertia.

In a vacuum, firing straight up would be the same as dropping them both from a certain height. Gravity is constant, and there's no drag, so the only thing affecting the two is gravity, which has a constant acceleration. Same speed at discharge, they will both reach the same height, and fall to the ground at the same time. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

When I answered this in the post above, the first part of my answer was an example by me using an extremely low velocity at discharge so that atmospheric drag would have little impact. I should have been clearer about it, my apologies. I hope I've answered your question, correctly. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

Red_Russian13
06-07-2004, 04:01 PM
As Harry Carey would say, "Holy Cow!"

I feel as though I've stumbled onto a forum at MIT! This stuff is great! No idea what most of it means, but by all means gents, carry on! I might learn something.

S!

Red Russian

JG14_Josf
06-07-2004, 05:34 PM
Cajun76,

The question was and remains:

When two bullets of the same size and shape are fired straight up which bullet goes higher up in a vacuum and which bullet goes higher up in an atmosphere?

Note: Both bullets leave the gun barrel at the same speed. One bullet is filled with lead. One bullet is filled with styrofoam.

I think it is safe to assume that your answer states the following:

The lead bullet in an atmosphere goes higher than the styrofoam bullet.

I see no reason at this time to ask why you find it significant to use the word 'typical velocity'.

Instead it occurs to me to look a this in a much more fundamental way instead of adding more complicated things.

Gravity is a force that is generated by the planet. The idea of dropping things to identify the force of gravity is just and only just that i.e. a way to identify or quantify the force of gravity.

Dropping things in a vacuum makes it even easier to identify or quantify the force of gravity.

Before moving on I think it is very important to clear up this possible notion that the force of gravity is only 9.8 odd meters a second. For simplicity let's just say that gravity is 10 meters a second.

Drop an object and it goes 10 meters a second.

In 10 seconds it goes 100 meters.

Now this is not much of a force at all.

A big heavy plane like the P-47 will not get much help from the planet Earth when it tries to dive at 10 meters a second.

But of course it should be pointed out that gravity is not simply 10 meters a second.

There is that extra per second thing attached to it.

10 meters a second/per second.

When an object is dropped on the planet earth in a vacuum it will fall approximately 10 meters in the first second.

The second second that an object will drop on the planet earth in a vacuum will add another 10 meters a second to the first 10 meters a second totalling at the end of the second second a speed of 20 meters a second.

3 seconds dropping = add another 10 meters a second for 30 meters a second.

Where this get's very interesting, to me, is that in the first second the object travels 10 meters. In the second second the object travels 20 meters. In the third second the object travels 30 meters. After 3 seconds the object has traveled 60 meters.

Without a means to slow down the object as it is being pulled by the force of gravity the object continues to add 10 meters a second (acceleration) to every second that it continues to fall.

After 10 seconds how fast is the object falling?

After 10 seconds how much distance did the object travel?

After one minute how fast does the object travel and how much room is needed to get going that fast?

The reason I find this important to point out is to show that the Earth is very big, and allthough it does not generate a force that can pop your eyes out like an aggresive ammusement park ride it does however generate a very powerful force.

Perhaps one of the more Math literate types can calculate how fast an object will be going if it were dropped from one mile high on our planet without an atmosphere.

If gravity was turned up just a little and if 10 meters a second was the acceleration of gravity on the Earth then in 100 seconds the object would be traveling at 1000 meters a second.

1 kilometer/second = 2,236.9 mile/hour (http://www.onlineconversion.com/speed_all.htm)

The P-47 would be at 2,236.9 miles and hour right next to a ballon filled with helium if both of those objects were dropped from enough altitude to allow for 100 seconds of exposure to the accelerating force of Gravity.

Air does get in the way.

Air is another force, just like the force of the planet, it effects objects in the same way to the same degree, because these forces are contained within them.

The Earth generates the force of gravity.

The air generates the force of drag.

What about the objects themselves? What do they contain?

El Turo
06-07-2004, 06:36 PM
Fellas, you're making this entirely more complicated than it needs to be.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>The effect of the same amount of air resistance is less when acting on a larger mass (OF EQUAL SHAPE/SIZE)<HR></BLOCKQUOTE>

All else being equal, the heavier object will accelerate in the dive better because it is able to resist the force (air-resistance/drag) being applied to it.

Let's get real simple here with an analogy..

Your friend rolls his bicycle at you travelling 10mph that you attempt to stop with your bare hands. Then, your friend rolls his CAR at you travelling 10mph that you attempt to stop with your bare hands... the car obviously takes a LOT longer to stop, right? The mass of the heavier object overcomes your ability to decelerate it (you being assumed as a constant value of resistance force/strength).

In this example, YOU are the force of air-resistance on the projectile while the bike/vehicle act as stand-ins for a low vs. high mass/density projectile. The shape is relatively immaterial in this analogous example because the real-world air-resistance would be next to nothing at just 10mph.

If you increase the mass of the object while all else remains the same (shape/size/surface), a force being exerted (drag) upon the object with higher density is going to be less successful in creating deceleration than it will with the less-dense object because the force being exerted will be "pushing" against a heavier mass.. and therefore less able to affect (move) the denser object.

The mass of the object is multiplied by the force of gravity to answer how much force is being applied "downward" in acceleration. The induced/parasitic drag is multiplied by the velocity of the object but it has an inverse relationshp with mass because it is fighting AGAINST it isntead of WITH it to determine how much DEceleration force is being applied.

This is why you will have a higher Terminal Velocity with a denser object, because the mass value is working WITH gravity and AGAINST drag.. so the intersection of the two curves will do so at a higher velocity than with a less dense object.

===============

Now, applying that to IL2FB is a different matter. You cannot effectively do so because the physics model doesn't quite handle this end of the flight model loop very well aparently. Most all aircraft dive at similar rates (indentical?), with the main (only?) differences between them being their rate of acceleration to max level, parasitic drag, and then their subsequent Vmax limits. This is precisely why the P38 and P47 do not enjoy the significant dive advantages they really should.

Let's all say a silent prayer for the FM in Battle of Britain as the next evolution in this lovely world of WWII-era combat flight simulation to include such fidelity!

WWII Online actually does have this functionality in their physics-based flight model but in my humble opinion it is far outweighed by some of the other concessions that botch other regimes of flight. In the end, all flight simulations must make compromises for lack of computing cycles and super-home-computers... so here at IL2 we deal with a little wonkyness with the dive characteristics, spin/stall modelling and associated over-stable aircraft in some situations.

Best,

~Turo

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

[This message was edited by H_Butcher on Mon June 07 2004 at 05:49 PM.]

Cajun76
06-07-2004, 09:04 PM
Nice site for conversions, but I prefer this handy utility. It's free, and you don't need to be connected to use it.

http://www.cybermetrics.com/CyberCalc/CCalc.HTM

A couple of points, because I'm not sure where your going with your last questions. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Everything is attracting everything else. That's gravity. The P-47 is also generating a force toward the earth, although not nearly as strong.

Air does not create drag, an object moving through the air creates friction with air, causing drag. Different shapes, at varying speeds, will cause more or less drag, although the density and composition of the air does play a part, particularly altitude and temperature.

I agree, air does get in the way, but does not supply it's own force. It's been a long while, so I don't remember all the terms, but for every action there is an equal and opposite reaction. Drag is a consequence of moving through the air. It can be minimized, or exaggerated.

H_Butcher, those are some good analogies, and a good way of explaining things. I particularly liked the paragraph "If you increase the mass...." Good stuff. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/Real_35a.gif
What if there were no hypothetical questions?

JG14_Josf
06-07-2004, 10:59 PM
Cajun76,

Which bullet goes higher?

A. The heavy bullet filled with lead.

B. The light bullet filled with styrofoam.

I can procceed with where I am going if you can answer that question for the following conditions.

Both bullets are shot straight up in a vacuum on a planet with gravity just like earths.

Both bullets leave the barrel at the same speed and altitude.

A. The lead bullet goes higher.

B. The styrofoam bullet goes higher.

A or B?

El Turo
06-07-2004, 11:30 PM
Josf,

==================

Edit: Just re-read your question and saw that you qualified it within a vaccuum, identical muzzle velocity and whatnot. (Sorry.. it's late and my brain is fried.. lol) http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

Unfortunately, you don't have the right answer made available in your multiple choices there.. hehe.. (unless you want to get REALLY anal about relativity and gravitational constants)..

It's "C".. all of the above! http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Without the effect of drag (no particulate matter whatsoever), the only force acting upon the projectiles after exiting the gun is gravitational pull. We know that this is a constant and that relatively, if the units in question are about the same mass, then they will come back down at relatively the same instant (barring perhaps some kind of micro-micro millionth of a second gap from the larger-massed projectile having a miniscule amount of greater mutual-gravitational pull).

But, that's in a perfect vacuum. Actually, in that example, you wouldn't even have to have the same sized projectiles or really even the same weight. You could use a wiffle ball and the USS Arizona launched at 800m/s straight up and you'd get the same result more or less.

==================

(Now, my too quick reply thinking of an "atmospheric" ballistic test: )

I don't believe you have enough information to calculate that or speak to such a question in generalities. As the gentleman alluded to earlier (sorry, don't have the name handy) that works with rocketeering.. there are performance curves and calculations involved that sometimes show that a heavier projectile will reach a higher altitude or a lighter projectile will reach a higher altitude depending on a rediculously large list of variables and possible combinations of inputs.

I believe your question is too complicated to be answered without getting needlessly involved in the miniscule facts necessary to calculate such things.

Here's the rub.. we have two bullets of DIFFERENT weight/mass being fired from the same gun... right? If they are acted upon by the same force out of the barrel (same powder charge or other propellant..), then you've got all kinds of performance curves to compare and other related issues to sort out.

It might be a bit easier to speak to this question if we assume that they have the exact same exit velocity, but then we've already introduced non-standardized data into the testing by altering the amount of initial propellant being used out of the starting gate.

Better to stick known quantities and situations that you can standardize all but the variable/solution you are trying to solve for.

Let's say you've got a 50 gallon drum filled with styrofoam and an exact replica filled with lead... and you push them out of the back of a transport plane at altitude.

Q: Which drum accelerates quickest?

A: Because there are no other forces acting upon them (like a propeller generating thrust at speeds under level-max).. probably about the same initially.

Q: Which drum reaches higher terminal velocity and/or accelerates faster in a sustained freefall?

A: The lead filled drum, by a significant margin and with increased acceleration over time that far exceeds the styrofoam drum due to the density and ability to apply more opposing force against drag than the styrofoam drum.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

[This message was edited by H_Butcher on Mon June 07 2004 at 10:48 PM.]

JG14_Josf
06-08-2004, 12:39 AM
H_Butcher,

C. The bullets reach the same altitude.

The lead bullet and the styrofoam bullet are units that are specifically meant to be not the same mass.

Now, please, can you confirm if any difference in altitude is achieved when the same test is done within an atmosphere.

Note: The bullets are shot from whatever combination of guns and loads that allow the bullets to leave the barrels at the same speed and same altitude.

Two bullets shot from the same altitdue at the same velocity going straight up where one bullet is filled with styrofoam and the other bullet is filled with lead, both bullets are the same size and the same shape.

B. Styrofoam bullet goes higher
C. Both bullets reach the same altitude.

El Turo
06-08-2004, 02:10 AM
Here are the problems with "where we're going with this"... when comparing against aircraft (which is our ultimate end-game here, yes?) we're going to also have to account for propulsion/thrust... and completely different drag coefficients, weight, and all that jazz.

Now, regarding our hypothetical projectiles being launched at identical initial velocities...

The force of drag will be identical, as will the pull of gravity which is a constant as well. So, again, the only remaining difference between the two is going to be mass. Initially, the denser of the two projectiles will retain much more velocity for the same reasons as previously stated.. it will be able to "resist" the force being applied by the induced drag better than the less dense projectile. Therefore, under these set of circumstances, the denser projectile should reach a higher net altitude by my logic.

The missing link here is that there MUST exist a substantially larger amount of energy expended in the propulsion of the denser projectile to achieve an identical muzzle velocity.. and so here lies the problem of inequality.

If you're going to be searching for which projectile reaches a greater altitude with all else being equal, you must then begin with an equal beginning energy-state. As we know.. an object with identical velocity but with greater mass has a larger energy state.. so the process must begin not with initial velocity, but with the joules of energy being applied to the propulsion for each projectile.

With an equal initial force being applied, the less dense projectile will leave our "gun" with a higher muzzle velocity for having less inertia and resistance to forces applied. The denser projectile will have more resistance to the propulsion "force" being exerted and thusly have a slower muzzle velocity.

So, here we begin to see the trade off of thrust:weight ratio and "energy retention".

Analogy time: This is kind of like asking if a Hurricane airfoil is better or worse than a me109's airfoil for efficiency. It all really depends on what end of the flight-envelope you're talking about. The Hurricane's wing is going to do much better at low speeds than the 109's but the 109's wing is going to do much better at high speeds. So, you run into problems quantifying a general statement of which wing is more efficient unless you're willing to get very specific and narrow about the set of circumstances in which you are testing and drawing your conclusions from.

(God, I hope that made sense at 1am.. lol)

This quickly becomes a question of ballistics and all that is germain to such a discussion... which is much more than just our simplistic dense vs. less dense situation.

Each projectile will have varying degrees of performance on a curve that will change with weight, energy applied, maximum velocity and drag coefficients applied.

I'm not sure that you can really answer this question without going into a rediculous level of specificity and calculation. Even then, your answer is only going to be applicable for a very narrowly defined set of events.

Perhaps someone has a more difinitive opinion or understanding of things.. but I think that's the stumbling block we're really up against in attempting to answer your question "in atmosphere".

If it were easy, it sure would have made fighter-aircraft design a lot more of a sure thing for the WWII-era engineers.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

[This message was edited by H_Butcher on Tue June 08 2004 at 01:24 AM.]

Cajun76
06-08-2004, 03:19 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:
Cajun76,

Which bullet goes higher?

A. The heavy bullet filled with lead.

B. The light bullet filled with styrofoam.

I can procceed with where I am going if you can answer that question for the following conditions.

Both bullets are shot straight up in a vacuum on a planet with gravity just like earths.

Both bullets leave the barrel at the same speed and altitude.

A. The lead bullet goes higher.

B. The styrofoam bullet goes higher.

A or B?<HR></BLOCKQUOTE>

The answer is C, just as H_Butcher said.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:
Now, please, can you confirm if any difference in altitude is achieved when the same test is done within an atmosphere.

Note: The bullets are shot from whatever combination of guns and loads that allow the bullets to leave the barrels at the same speed and same altitude.

Two bullets shot from the same altitdue at the same velocity going straight up where one bullet is filled with styrofoam and the other bullet is filled with lead, both bullets are the same size and the same shape.<HR></BLOCKQUOTE>

In simplistic terms, http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif the equal drag on both objects means the one with less inertia, the styrofoam-filled bullet, will be bled of it's velocity/energy/inertia sooner than the lead bullet. The lead bullet therefore reaches a higher altitude because of greater inertia.

I don't normally post the same info or answer when I agree with what's already written. As far as I can tell, H_Butcher probably has a better grasp of these physics than I do. As far as "where you're going with this", the Fw-190 and P-47 are different a/c, with different drag coefs, and shape. A simple power off zoom climb between them is difficult to do, and won't really answer any questions. At the initial start of a zoom climb from level max speed, the two a/c rely on both inertia and their individual power to weight ratio, becoming more dependent on the latter the longer the zoom climb is maintained until inertia is used up and the climb is in the hands of the higher p/w aircraft. This doesn't seem modeled in the game, as any illusion of inertia is quickly gobbled up when a climb is started in the heavy Jug. Only speed is there after a dive, and is quickly spent when flying level or climbing. Here's hoping it can be done better in the next sim. I truly hope so. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/p47nh.jpg
What if there were no hypothetical questions?

k5054
06-08-2004, 04:03 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Now, applying that to IL2FB is a different matter. You cannot effectively do so because the physics model doesn't quite handle this end of the flight model loop very well aparently. Most all aircraft dive at similar rates (indentical?), with the main (only?) differences between them being their rate of acceleration to max level, parasitic drag, and then their subsequent Vmax limits. This is precisely why the P38 and P47 do not enjoy the significant dive advantages they really should.<HR></BLOCKQUOTE>

Many suspect this, but nobody can prove it. Few people know what to really expect. If two fighters start a vertical dive, co-speed side-by-side, how much difference from the 1g acceleration speed do you expect to see? If I told you that the faster one had 0.9g and the slower 0.8g, how much speed difference would you expect to develop, given that 30 seconds is as much time as they are going to have before pullout? One is accelerating at 9m/s/s, the other at 8m/s/s. One metre per second difference for 30 seconds, that's a 30 m/s difference in the whole dive (no the g figures aren't exactly like that all the time, this is an approximation). That's 77mph speed difference and it took 30 seconds to build up. As I've said before, this is like standing at a bus stop as the bus pulls away as fast as it can go.
it's my suspicion that AEP models this fairly well, and when it gets difficult in the high speed high mach area, it makes your wings fall off anyway.

El Turo
06-08-2004, 09:27 AM
How much distance do you travel at a speed of roughly 50-70mph in 20-30 seconds?

Let's use 60mph because it's easy on my brain.

60 miles per hour

= 1 mile per minute
= 0.5 mile per 30 seconds
~ 2600feet per 30 seconds
~ 800m per 30 seconds

That's not a significant difference to you?

(Even if you were to cut that value in half?)

http://ubbxforums.ubi.com/images/smiley/35.gif http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

You just don't see it in IL2:FB for whatever reason. It's one of the very few things I actually like about the WWIIOL FM over this one.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

k5054
06-08-2004, 10:22 AM
Describes the mood or content of the topic posted 08-06-04 08:27 Tue June 08 2004 08:27 AM
How much distance do you travel at a speed of roughly 50-70mph in 20-30 seconds?

Let's use 60mph because it's easy on my brain.

60 miles per hour

= 1 mile per minute
= 0.5 mile per 30 seconds
~ 2600feet per 30 seconds
~ 800m per 30 seconds

That's not a significant difference to you?

(Even if you were to cut that value in half?)

Indeed you have to cut it in half, to get a rough idea. In a ORR thread a guy called Hyperion has posted a spreadsheet of vertical dives in the top 6 1944/5 planes, and it shows pretty much the same difference covering P-51, 47, D-9, Ki, K-4 and La-7. He's using devicelink to get exact figures. All six fighters are covered by 400m in altitude after 30 seconds, having dived from 10km(IIRC). That corresponds with the mathematical estimate, but is it really the kind of distance you expect when one a/c is supposed to be able to completely out-dive another? If it is, then the FB model is not far out from reality too. Put in perspective, the enemy P-47 was 400m in front of you when he dived, you followed without loss of time and after 30 secs, when he has to start his pullout, he is only 800m in front, but you can start the pullout when he starts, you don't have to go down the extra 800m, you can cut the corner. What advantage has he gained at this point? Not much, and that's how it pans out in the game.
The secret may be in how he keeps his 70mph speed advantage through the pullout and into the zoom.
Is there a strategy for optimized pullout? The true secret of zoom advantage, the essence of energy fighting, may be to be faster than the other guy throughout the maneuvre, and thus begin the zoom hotter, not to have a better zoom, where in theory if you have .9g in a vertical dive you will have -1.1g in a vertical zoom, or .8/-1.2 for the slow guy.

El Turo
06-08-2004, 11:09 AM
To answer your question directly, YES. I believe that the heavier aircraft should see a bigger difference in dive acceleration beyond level-max than is evidenced in IL2FB.

I do not believe this is modelled correctly in IL2FB at all.

As counterpoint, you can go into WWIIOL and do a dive test with a Hawk81 (P40) or Bell-14a (P39) against something like a 109E4 or even the 109F4 and see a SIGNIFICANT difference in dive acceleration. Even if you're not a subscriber, you can go grab the full version of the game and test it in the offline practice arena if you want to see it first hand.

This is one of the few warts that IL2 has.. but I'm more than willing to put up with it because of the vast superiority in fidelity elsewhere. It's a trade off... because no combat flight sim has a big enough CPU-cycle budget to do EVERYTHING 100% realistic.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

k5054
06-08-2004, 12:46 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
Describes the mood or content of the topic posted 08-06-04 10:09 Tue June 08 2004 10:09 AM
To answer your question directly, YES. I believe that the heavier aircraft should see a bigger difference in dive acceleration beyond level-max than is evidenced in IL2FB.

I do not believe this is modelled correctly in IL2FB at all <HR></BLOCKQUOTE>

I was inclined to agree until I tried to calculate what was happening and test what happens in the game. Now I'm confused. I don't see the big differences which are implied by pilot stories and I realise that the pilot stories, and contemporary air tests, usually do not have the start conditions, so they are not much practical use. I also wonder if the pilots who didn't get away are able to tell their stories.
I believe that good aircraft of similar timescale don't differ by all that much. Maybe 0.1g or a little more. And that amounts to 400m after 30 seconds. Do we need to be thinking of a shallower dive with a longer duration? ( The difference in acceleration seems to be a function of speed, not angle of dive).

El Turo
06-08-2004, 12:59 PM
If you have broadband, just for kicks.. I'd recommend visiting the WWII Online download page for the full-version and give the planes a bit of a test-flight in the offline mode.

The P40 dives like a ROCK and separates from the 109E4 and 109F4 very, very quickly. The 109F4 will catch up in the extended-chase due to higher max-level but the P40 gets a very large headstart, especially when cutting prop-pitch down to "economy" (lowest) setting to reduce prop-drag.

There are some serious concerns about lateral/yaw stability in their flight model, but the surrounding physics-based system of computing "flight" for the aircraft is very spot on otherwise. The lateral/yaw instability is an example of a "concession" made by the WWIIOL Flight Model in exchange for fidelity in other areas. They model an airfoil and other parts of the airplane and it just "flies" through their virtual atmosphere like a "real" plane would. However, due to limitations on CPU-cycle budget, the physics loop has been coded to use a composite value for fuselage drag/lift which REALLY puts a hurting on lateral/yaw stability due to lack of proper weathervaning or "tailfeathers". For me personally, it's annoying enough that I've more or less stopped flying over there as a result of the goofy results that such instability creates.. but to each his own.

Like I said previously.. there are ALWAYS compromises made in combat flight simulation (this isn't x-plane).. which you have to deal with and accept in exchange for OTHER goodies. In IL2-FB, the dive/zoom portion of the flightmodel is a little bit simplified.. which isn't the end of the world by any means, but it is what it is.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-08-2004, 02:31 PM
H_Butcher,

I have been trying to use as little logic as possible and move along with what is actually known.

There does seem to be a consensus, however, as to which bullet will travel higher.

In an atmosphere the heavier bullet travels higher.

The reason the heavier bullet travels higher is due to something contained in the bullet.

I am not trying to confuse the issue by making the bullet travel at a certain speed.

I am trying to identify the principle factors determining what makes one object go faster than another object in an atmosphere.

I think I have succeeded.

I think that what these thought experiments illuminate is the existance of a property contained within the object that allows it to move through a medium of resistance and that if this property is increased so will the ability to pass through a medium of resistance increase.

Furthermore I think these thought experiments show that this property of mass exists in addition to any other properties such as shape, size, propulsion, gravity, or inertia which also effect the ability of the object to pass through a medium of resistance.

Mass alone allows an object to pass through a medium of resistance. Any other factors that contribute to the objects ability to pass through a medium of resistance are added to the property of Mass.

Mass allows an object to pass through a medium of resistance all on its own, always, and forever so to speak. Nothing changes the relationship between Mass and the ability to pass through a resistance, because Mass is contained in the object. Other things can add or subtract to this ability but this ability remains contained within the object.

If the object changes shape then it will change the ability to pass through a resistance, however, as long as the objects mass remains the same it will retain the same ability to pass through a resistance that the property of mass allows.

If the object is accelerated or decelerated by any other force including gravity then the object will change its ability to pass through a medium of resistance, however, if the mass of the object remains the same, then the property of mass will still contribute the same ability to pass through the medium of resistance.

Mass is a measure of the ability to pass through a medium of resistance, and this measurment is constant as long as the Mass remains constant.

If other factors contribute to make an object pass through a medium of resistance they do so in addition to the factor of mass.

This is what I have learned from these disscusions.

I see that this discussion has gone the way of typical subjective opinion.

If that is the case then I differ to choose the opinions of those who were a little closer to the real thing then anyone posting on this board.

"But coming out of a dive, there's not a British or a German fighter than can come close to a Thunderbolt rushing upward in a zoom."
(Robert S. Johnson, Fighter Combat by Robert Shaw)

El Turo
06-08-2004, 04:58 PM
The problem with your test-conditions is that it requires an inequitable amount of force to be applied to each projectile. This is important because we now must ALSO consider the question of thrust:weight ratio which is no longer limiting the investigation into merely a question of density.

Think of it in these terms (analogy time again):

You take a 20lb shot (ball) and a baseball out into your back yard and throw them both up in the air as hard as you can. Which one is going to go higher? The baseball, despite it being considerably less dense and/or massive. This is because the inertia of the shot-put ball lowers the initial velocity as it leaves your hands... whereas you are able to launch the baseball at a MUCH faster initial velocity. In order to launch the shot-put ball at a comparable velocity you would need an INCREDIBLY larger amount of energy.. like a cannon or catapult. Is this then a fair comparison of which is better able to gain the most altitude when you have a man throwing one projectile by hand and a cannon/catapult launching the other?

I think not. While extreme, this illustrates the inequity of your test conditions. It's like racing a 1972 pickup through a mudbog against a 2004 Diablo and declaring the 72 pickup to have the maximum top speed between the two.

It just doesn't work. Sorry. =/

As for the bulk of the rest of your post.. it is most certainly a HUGE issue to change the shape of the projectile. That is why I was very precise to make sure that we were talking about the same size, shape and even the SURFACE of the theoretical projectile to be identical.

Drag/friction will begin to grossly overpower raw mass the faster you go because it is an exponentially increasing force and mass is constant. Otherwise, why would you get an extra 5-10mph just by waxing your aircraft or reducing to just polished metal?

If you create a 2 ton block of steel, and a 2 ton steel arrow-shaped item and drop them out of the back of a transport plane, the arrow shaped projectile is going to dramatically out-perform the block.

I'm still not quite sure what your hypothesis or conclusion IS, to be honest. Heh..

http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

In any given situation, mass OR drag could be effecting our projectile with greater authority. It truly depends on so many other influences and variables that we do not have on hand that it is impossible to make a blanket statement that one is MORE effectual than the other.

As you state, mass is mass. That is a constant. The amount of drag force being applied against the projectile is absolutely tied into the shape and surface of said projectile. How much one is overpowering the other is entirely in the air (no pun intended) depending on the situation we want to examine (such as our inequitable energy state launch issue.)

Hope some of this helped out in some way.. Let me know if you've made any progress/conclusions about whatever it is you're trying to explore/discuss?

Best,

~T.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-08-2004, 05:49 PM
H_Butcher,

Do you assume that I do not know that thrust is a variable in making objects of different mass move to the same velocity? http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

If those same objects were dropped from an altitude or better yet if those same objects are placed on the ground what 'thrust' is contained inside those objects?

What thrust to weight ratio is measurable in the objects as they sit on the ground?

What if those objects were sitting on the ground over a hole that goes down one mile whould they then have thrust?

Take away the support holding those objects over the hole and do they now have thrust?

The objects remain the same mass, they remain acted upon by the same force of gravity, they remain resisted by the same density of air, they remain the same shape, the same size, and they still travel at different speeds. The higher mass object goes faster.

The reason I moved the disscusion from travel toward the earth to a disscusion of travel away from the earth is to point out that an objects mass remains able to pass through the atmosphere regardless of which direction it travels through the atmosphere.

In order to minimized any other factors the need arose to make these objects travel at the same speed going up.
The general consensus is that both objects will go up the same distance if they start out with the same velocity regardless of their mass in a vacuum.
If the atmosphere is added and the charge to propel the objects is adjusted to keep these ojbects traveling 'on their own' at the same speed then the higher mass object goes higher.

The variable of velocity is a constant in all those tests.

The objects on the ground are at the same speed.

The objects dropped from an altitude are at the same speed.

The objects fired from a gun are at the same speed.

Velocity is being factored out of the equation as a constant.

Just like shape and size are factored out of the equation as constants.

Just like the earths force of gravity is a constant and just like the density of the air is a constant.

Mass has a constant ability to pass through a medium of resistance and the more mass the greater the ability to pass through a medium of resistance.

That is what I have learned in this discussion.

It is clear in my mind.

I can look at the P-47 and make sense of why Robert Johnson says what he says about it.

I can see clearly that any attempt to rationalize a game that models a P-47 with the same exact dive acceleration as a Spitfire is just that: i.e. a rationalization.

If the math used to calculate this rationalization does not include the physical property of mass with it's constant ability to pass through a medium of resistance then the rationalization will work for the intended purpose.

El Turo
06-08-2004, 07:30 PM
Agreed on what is said about the P47 historically and what I assume is your similar agreement that IL2FB does not model dive/zoom correctly.

However, there is most certainly a question of inequal thrust being applied in your "firing" test from the ground. You would have to use a much greater amount of energy/propellant to get the denser projectile to the same exit velocity.

This is inequitable and shows a small flaw in your conclusion. Not that it discredits what should be a significantly better dive/zoom for the P47.. only that you should not place all of your argument on "mass" because there are certainly more factors at work. Specifically, when taking into account thrust:weight comparisons.

You conclusion may be correct afterall, but your logical progression is slightly off.

1: I arrived at work 5 minutes early today
2: I wore blue socks today
3: Therefore I will get to work 5 minutes early every day if I wear blue socks

(When in fact it was just because they installed a new traffic control light on my path to work)

See.. I still get to work 5 mintues earlier every day so the end result is the same.. but my logical progression I used to reach that conclusion (however true it may remain under test) was incorrect.

That's all I'm sayin' brutha.

Keep on truckin.

Late,

~T.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

klower
06-08-2004, 09:10 PM
So Josf, what exactly are you trying to say? Are you saying that you think that the dive acceleration of a p-47 is lower than it should be compared to some other aircraft? Or are you saying that the zoom performance of the p-47 is lower? Or both, or something else entirely. Just come right out and say what is bugging you.

JG14_Josf
06-08-2004, 09:59 PM
H_Butcher,

If the two bullets were loaded with the same energy during the shooting straight up test, into the air, then the test would only test the constant force of gravity and the constant resitance of atmosphere.

Is it safe to say that both objects would go up the same distance?

Therefore the analogy would show that a P-47 full of fuel zooming next to a P-47 with 25 percent fuel would need to have less velocity at the start of the zoom to reach the same altitude. (Both planes chop the throttle at the start of the zoom)

I'm not sure what you think my conclusions are if you do not specify what you think are my conclusions.

If you can point out specifically what I have written that is wrong then perhaps we can find where any error exists in my thinking.

I have reason to add more energy in the bullet test because it is meant to describe the ability an object has in utilizing that energy, specifically the energy of velocity.
Both bullets are traveling at the same speed at the start of the zoom climb.

Mass is harder to get moving but when it is moving it is harder to stop. Mass has that property.

Mass does not just appear, it exist somewhere at some time and that existance is relative to any other force or resistance to force.

Plucking an object containing mass out of thin air and viewing that object for any potential movement must include any relevant relationship to the forces acting upon it.

I think that this is becoming clearer in my mind.

The tests help in that regard.

Mass is a physical existance. The realization of that existance is my goal. To see the truth of it.

Your last post is helping to refine the idea.

Thanks for the nudge.

Your post destroys an earlier idea and has returned my thinking toward more questions.

Like the P-47 sitting on the runway on a hot day next to a Spitfire. The P-47 is making bigger dents in the asphalt. It moves toward the earth at a faster rate. The same force of gravity exists and is applied to both planes equally but the Spitfire is decelerating more than the P-47.

They both start out at zero velocity before the sun starts heating up the asphalt. As the asphalt becomes less dense under both planes the P-47 begins to move while the Sptifre remains at 0 velocity.

Again thanks for the post.

It was inspiring. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

JG14_Josf
06-08-2004, 10:41 PM
Klower,

The game models Air combat and it does that with much refinement. However there seems to be something missing. A P-47 should be a very dangerous plane when it is allowed to build up energy. I think energy in altitude and velocity should be more useful in combat for the P-47 due to a higher mass than what is currenty modeled in the game. Of course this is being overly simplistic.

I am inclinded to refrain from pointing out anything more specific than to quote from the people who actually flew these planes in combat and to educate myself in what goes on when things start moving.

Anymore than that is up to you or anyone else who edeavors to evaluate the simulation.

One other note on this subject has to do with the application of tactics. When reading about tactics there are many instances that describe how to apply a dive acceleration and a zoom climb advantage.

If no such advantage, or if less of an advantage is modeled into the game than what really did exist then those tactics will not work in the game to the same degree that they did work in reality.

The game we play called IL2 has improved in this regard. I tend to think that the improvements are simplistic. Instead of actual acceleration and zoom differences the game has only changed max dive speed differences.

I try to limit posting my opinions.

El Turo
06-08-2004, 11:10 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>H_Butcher,

If the two bullets were loaded with the same energy during the shooting straight up test, into the air, then the test would only test the constant force of gravity and the constant resitance of atmosphere.

Is it safe to say that both objects would go up the same distance?<HR></BLOCKQUOTE>

No, they would only go up the same distance in a vaccuum. In atmosphere, you will have drag (air-resistance) to worry about.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Therefore the analogy would show that a P-47 full of fuel zooming next to a P-47 with 25 percent fuel would need to have less velocity at the start of the zoom to reach the same altitude. (Both planes chop the throttle at the start of the zoom)<HR></BLOCKQUOTE>

All else being equal, yes.

If your hypothesis/conclusion was that the denser of two otherwise identical projectiles travelling at the same speed will have a greater total energy state, then you are correct.

Keep in mind, however, that this does not speak to how much energy it TAKES to get that denser projectile to the same velocity, nor how much the greater density/weight may effect the required level of CONTINUED energy to maintain that state.

As the two identical P47's begin to slow down in their zoom climb (with propellors at maximum power output), the less-dense of the two will begin making up distance on the denser unit because there will be less resistance against additional thrust pulling the aircraft farther up.

So, in our hypothetical zoom climb, it really is a bit hard to say exactly which plane will zoom farther with their engines on and applying force upon the two aircraft... which is, you would have to admit, a much more likely scenario.

However, this gets us back into questions of intersecting curves, thrust vs. mass and mass vs. drag.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

Cajun76
06-09-2004, 02:41 AM
Some back to basics reference:

Matter: Anything that occupies space, has mass, and possesses inertia.

Mass: The quantity of matter contained in an object.

Inertia: The resistance to change in state of motion which all matter exhibits.

Now,

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:

If the two bullets were loaded with the same energy during the shooting straight up test, into the air, then the test would only test the constant force of gravity and the constant resitance of atmosphere. <HR></BLOCKQUOTE>

The two bullets that have been in the discussion are the lead and styrofoam bullets. The same energy applied to the heavier bullet would result in a lower velocity. Perhaps you meant that they were imparted with the same amount of velocity. Additionally, the resistence of atmosphere (drag?) is not constant. It varies, in this case, directly with speed, since both objects have the same shape.

The more I read some of these statements, the more convinced I become of their inaccuracy. http://ubbxforums.ubi.com/infopop/emoticons/icon_confused.gif

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:

Like the P-47 sitting on the runway on a hot day next to a Spitfire. The P-47 is making bigger dents in the asphalt. It moves toward the earth at a faster rate. The same force of gravity exists and is applied to both planes equally but the Spitfire is decelerating more than the P-47.

They both start out at zero velocity before the sun starts heating up the asphalt. As the asphalt becomes less dense under both planes the P-47 begins to move while the Sptifre remains at 0 velocity.
<HR></BLOCKQUOTE>

Did you know that a woman's spike-heeled shoe exerts more pressure per cm/2 than an an elephants foot, even though the typical woman weighs far, far less than a six tonne bull male? According to your analysis, the woman is more dense than an elephant on beach sand? If her heels, accelerated by gravity, poke through the sand 2-3 inches, then should not the elephant sink farther? Does he have more mass, or not? Is not the sand less able to resist the higher mass of the bull male, and he sinks to his knees? http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:

If the two bullets were loaded with the same energy during the shooting straight up test, into the air, then the test would only test the constant force of gravity and the constant resitance of atmosphere.

Is it safe to say that both objects would go up the same distance?

Therefore the analogy would show that a P-47 full of fuel zooming next to a P-47 with 25 percent fuel would need to have less velocity at the start of the zoom to reach the same altitude. (Both planes chop the throttle at the start of the zoom)
<HR></BLOCKQUOTE>

Let's go back to our faithful bullets. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif The lighter one is fired faster than the heavier one. In fact, it's fired at just the right velocity to reach the same height as the heavier bullet. This tells us what? That inertia, "The resistance to change in state of motion which all matter exhibits" is dependent on not only mass, but motion as well. In this case, velocity. Your analogy doesn't really state anything to make a conclusion about. Two energy states, two masses, with the right amounts of each, produce the same results, based on physics. In reality, the heavier Jug will probably have more drag due to it's higher weight, and will lose to the lighter Jug. There's a reason sailplanes are made as light as possible, and not heavy. A Cessna generally has a better glide ratio than a 747 when their both out of gas.

As far as the rest, I'm 100% in agreement with H_Butcher, where he agrees, and where he does not. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif I hope all of our collective questions and curiosities can be satisfied. A fun and educational discussion is one of the main reasons I like this forum. People who share my enthusiasm for flying and physics is a rare treat. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/p47nh.jpg
What if there were no hypothetical questions?

JG14_Josf
06-09-2004, 11:28 AM
It may help to illustrate my questions with a chart. The following MS Paint construction asks a question. The idea is to identify what factors are in place that cause a difference in distance traveled between vehicles traveling through an atmosphere. The vehicles are all the same size and shape.

I ask this question to identify something specific and my hope is to find a specific answer.

The application of this information is secondary and unless you find a real need to jump ahead I am going to ask that this chore be delayed until the specific question is answered.

http://mysite.verizon.net/res0l0yx/Inertia.JPG

Perhaps it would be a good idea to ask some more specific questions and add one extra note.

Note: The starting speed for the vehicles going up is 500kph. The distance traveled for the fastest vehicle going down is marked at the spot where the fastest vehicle reaches 500kph. The fastest vehicle going down does not reach compressibility or in other words the fastest vehicle going down will continue to accelerate to 1000kph or so. The test is made to show differences in accelerate that are well under terminal velocity.

I may find time to construct another diagram to better show what I am looking; specifically the distance traveled between A and B on that chart.

It may help to put those distances next to each other instead of one going up the chart and the other going down the chart.

I ran out of time this morning.

Edit:
Chart had an error and has been edited

[This message was edited by JG14_Josf on Wed June 09 2004 at 10:51 AM.]

El Turo
06-09-2004, 12:05 PM
Bud, there's quite a few errors and assumptive fallacies that you've made in your chart there.

I don't have the energy (pun intented) to go through them all right this second in much detail, but a few short items:

Gravity effects all objects equally. There is no difference between high/low density objects in this regard. The ONLY thing that will effect each differently is the relationship between mass and drag.

For example, with your H and L mass objects falling under thrust, the L mass projectile will NOT reach a greater speed than the H mass projectile. The L mass projectile will accelerate at a greater rate initially but the H mass projectile will achieve a superior maximum rate of travel and pass up the L mass projectile. Of course, your chart doesn't discuss TIME.. so we're forced to speak in ultimates and eventualities instead of specifics. This gets back to the whole point about it not being a black/white answer for every conceivable generality when discussing the merits of a H or L mass projectile (with propulsion factored in).

Hint: It's the opposite when you're going straight up under power (beginning from equal velocities, anyway). The H mass will retain more velocity initially but the L mass object will have much greater velocity towards the top of the zoom climb because the thrust being applied to the H mass object is less able to offset the effect of gravity due to its having greater inertial resistance.

The H mass projectile loses the advantage it had in resisting drag at high velocity and begins incurring a penalty for having a poor thrust vs. mass ratio.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-09-2004, 03:56 PM
H_Butcher,

If there are errors and assumtive fallacies then please point them out.

If the low mass thrusted vehicle is going faster initially then how do you know when the low mass thrusted vehicle will pass up the high mass thrusted vehicle?

Couldn't the chart express a situation where the low mass thrusted vehicle is still within the initial stages of acceleration?

If so then where are the errors and the assumtive fallacies?

Is it possible even without specific information to get an answer to the question of what factors explain the difference between A and B on the chart?

For instance:

If 500kph is reached while the Low Mass Vehicle going down has more initial acceleration then A and B could be the same value. Because...

I tried building a better chart but ran out of time again.

El Turo
06-09-2004, 04:14 PM
If the low mass thrusted vehicle is going faster initially then how do you know when the low mass thrusted vehicle will pass up the high mass thrusted vehicle?

Exactly. That's where you really start getting into complicated curve intersection and aerodynamic calculations that I don't believe either of us is qualified to draw up nor solve.

Couldn't the chart express a situation where the low mass thrusted vehicle is still within the initial stages of acceleration?

Sure could, but it doesn't specifically express one way or the other.. which is why the conclusions (drawings) are assumptive.

Is it possible even without specific information to get an answer to the question of what factors explain the difference between A and B on the chart?

We've already laid those out. Initial acceleration vs. sustained acceleration. That's the whole thing in a concise remark.

!S

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-10-2004, 07:58 PM
El Turo wrote:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>We've already laid those out. Initial acceleration vs. sustained acceleration. That's the whole thing in a concise remark.
<HR></BLOCKQUOTE>

I didn't get very far before hitting a basic problem in my thinking.

If it is possible can anyone answer the following question:

In a vacuum chamber big enough to contain the USS Arizona; would it be possible for someone to move it? The vacuum chamber also has no gravity. A person has his back to a wall and the USS Arizona is within easy reach, there is no gravity.

If it is possible for someone to push the USS Arizona away, then how fast could a person move the USS Arizona in a vacuum with no gravity?

El Turo
06-10-2004, 09:42 PM
Yes, at a very small rate.. but yes, they would be able to.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-10-2004, 10:04 PM
EL Turo,

Thanks,

I am trying to picture this and would it be true to think that if someone wedged themselves between the wall and the USS Arizona that they would huff and puff and push with their legs for all they had just to get the USS Arizona to move at .000002KPH?

The actual speed is not important. I'm just wondering if this would be a situation where as the Carrier was motionless relative to the wall; the guy doing the pushing would find that there was a great resistance to movement.

Something with a small mass, I guess, could be accelerated as fast as the arm could swing it, no?

Once the USS Arizona or the small mass object left the human's touch the object would remain at that velocity, correct?

Cajun76
06-10-2004, 10:13 PM
I'd like to use the USS Iowa for my example, since the USS Arizona is lying at the bottom of Pearl Harbor as a shrine. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-sad.gif

Vacuum or no vacuum, and provided the USS Iowa is floating in zero G, then yes, it is possible. Simple 'human force' on a known mass will produce an acceleration. With no atmosphere, and a continuous force, then the Iowa will continue to accelerate at the same rate, provided our human doesn't get tired. For the sake of simplicity, if the Human can run normally at 10 km/h, then eventually, the Iowa will reach 10 km/h as well. (Simplistic modeling) And if the human gets the Iowa moving, it will take an equal amount of force and time to stop it as well.

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/p47nh.jpg
What if there were no hypothetical questions?

JG14_Josf
06-10-2004, 11:53 PM
Cajun76,

Thanks,

I'm working on that idea.

Three guys playing dodge ball with the USS Iowa.

Snap shot or Tracking shot? (http://mysite.verizon.net/res0l0yx/Snap%20shot.htm)

JG14_Josf
06-11-2004, 11:03 AM
Cajun,

Can we construct someting more instructive?

What would it be like to have a typical school gymnasium out in space where two player had a basketball and a basketball sized cannonball.

The floor is made of steel plate and the players have magnetic shoes that approximate the earths gravity. I guess they need to keep at least one foot on the floor at all times.

The Basketball is called Spitfire. The Cannonball is called P-47.

One player has the Spitfire and the other player has the P-47.

The players are standing 10 meters apart.

How does the Spitfire feel compared to the Cannonball?

Is the Cannonball difficult to move?

I can imagine that the Basketball would be just a little easier to move than it is on earth and I could throw it without too much trouble at a velocity of 10 kph.

If I used the same amount of energy to throw the Cannonball as I used to get the Basketball going 10kph then how fast would the Cannonball be thrown?

What happens when player A and player B both use the same amount of energy to throw thier balls at each other?

k5054
06-11-2004, 11:18 AM
No thought experiments are required here, this is all Newtonian physics, and has been known for 350 years. Get a book.

JG14_Josf
06-11-2004, 11:52 AM
k5054,

Perhaps it is unrealistic for me to expect much help.

Newton is dead, he is not going to read my posts and even if he was alive, even if he did read this post it is just as likely that he would see no reason to bother himself with someone so obviously ignorant.

Newton did pass on a whole lot of knowledge and his diciples exist today.

I guess they are as reluctant to waste energy toward a hopeless cause i.e. educating the ignorant.

Meanwhile I am trying to move my basketball sized cannonball in the gymnasium looking for another player.

If the moderators find my game to be innapropriate then they have the authority and the means to squash it.

http://mysite.verizon.net/res0l0yx/Looks%20good.jpg
http://mysite.verizon.net/res0l0yx/Heat.jpg

Snap shot or Tracking shot? (http://mysite.verizon.net/res0l0yx/Snap%20shot.htm)

JG14_Josf
06-11-2004, 12:43 PM
Back at the gymnasium:

It occurs to me that the player throwing the cannonball named P-47 is having a hard time.

His magnetic shoes won't hold him down.

What is down?

Now the player with the P-47 is centered on one wall looking up at the other player.

The player with the Basketball called Sptifre is centered on the opposite wall looking up at the player with the P-47.

Both players are held in place with shoes that are nailed to the walls.

Both players are squating down holding their balls.

Strike that last description.

It conjures up an image that may derail this thought experiment and bring in the thought police.

Instead both players are possitioning themselves in such a way as to be able to accelerate the round objects containing mass.

Each player is going to use their knees instead of their backs to lift these roundish bodies of mass toward the other player.

If both players are of the same strength and are equally able to use the same effective technique to accelerate the balls with the same amount of force then how fast will the Basketball named Spitfire travel and how fast will the Cannonball named P-47 travel?

El Turo
06-11-2004, 05:26 PM

In a vacuum, in the absence of gravity, and with equal force being applied to a high and low mass object, the low mass object will accelerate at a higher rate.

Here's one for you to visualize:

If you are standing on the deck of the USS Iowa (good call) in perfect vacuum with no gravity and you jump... what happens?

As you apply force downward into the USS Iowa to push off, the Iowa will actually move in the opposite direction but due to the insane difference in mass, you will rocket away in the opposite direction with probably 99.9% of the energy (as fast as your "jump" will propel you anyway).

As our esteemed K5054 stated.. basic Newtonian Physics.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-11-2004, 09:28 PM
El Turo,

Thanks http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

The player with the cannon ball starts to lift, or rather move the cannon ball toward the other player. Unlike the basketball which is easily moved the cannon ball is difficult to move.

I guess it is difficult for those of you who know all this stuff to imagine what it is like for someone who doesn't.

Knowledge is kind of like a one way door.

Anyway it helps me to write and to visualize these things in a relative manner. I am still having some trouble realizing what is going on exacty.

The cannon ball must not be as difficult to move in space as it is on earth. Gravity has an ability to glue the cannon ball down onto the ground.

Knowing and feeling the weight of something on earth is one thing. I am trying to imagine what it would be like to try and move that cannon ball without gravity, to know or feel its mass.

Lifting a basketball sized cannon ball against gravity would take more strength than I am able to muster. But without gravity, it seems to me, it would be at least a little easier to move the cannon ball in space without gravity.

Perhaps the cannon ball moves very slowly at first. I give it a real good pull upwards and sure enough I am able to lift on it some, however it tires me out so I let go.

I stand up to stretch my back.

The cannon ball continues upward.

It is now at my knees.

The basket ball zooms past my head bouncing off the plate at my feet.

I look up at the other player who is reaching for another ball.

Now the cannonball is at my waist.

I stoop under it and position my shoulder against it.

Pushing with all my might the cannonball moves a little faster.

I stand up again.

The cannonball is at eye level moving faster.

Another basketball goes by zooming and bouncing. (I guess they would bounce)

Looking up at the other player I have time to give the cannon ball another push with my hands. It goes slightly faster.

Then again the cannonball may be easier to move. I don't know.

It is a good game so far for me. The other player is having fun too. I can see him up there grinning.

Is it true then that he can only throw the basketball as fast as his arm will swing?

I can see him trying a wind up pitch type throw.

Cajun76
06-12-2004, 01:37 AM
Just a small correction, El Turo. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>El Turo wrote:
As you apply force downward into the USS Iowa to push off, the Iowa will actually move in the opposite direction but due to the insane difference in mass, you will rocket away in the opposite direction with probably 99.9% of the energy (as fast as your "jump" will propel you anyway).<HR></BLOCKQUOTE>

Although you might rocket away with 99.9% of the velocity, equal force is imparted to you and the Iowa. Equal inertia. The result is visually more dramatic as you rocket away, but to an impartial observer, the fact that a 40,000 ton battleship is moving slightly from the same energy would also be dramatic and interesting. It would take an equal amount of energy that your jump produced to stop the Iowa and yourself as well.

@ Josf:

One of the great things about working in zero G that's different than here on Earth is that any work you do is not wasted on overcoming or maintaining a force equal to or greater than gravity. The slightest pull upward on your cannonball will result in it moving upward. There's no gravity to work against, bleeding away the energy you've imparted to the cannonball.

Rolling something heavy on a flat level surface will produce a somewhat similar effect. Try a 16 lbs. bowling ball at the ally if you have a chance. Roll it one way and another, and stop it. Standing still, it doesn't want to move. Once it gets rolling, it doesn't want to stop. Since you're not picking it up, your dealing with it's mass, not it's weight. Your experiment in 2D, basically. In fact, having someone roll a 6 lbs. ball while you do the 16 lbs. and vice versa would probably be an excellent example. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR> Josf wrote:

1)Then again the cannonball may be easier to move. I don't know.

It is a good game so far for me. The other player is having fun too. I can see him up there grinning.

2)Is it true then that he can only throw the basketball as fast as his arm will swing?
<HR></BLOCKQUOTE>Numbers added by Cajun for clarity.

#1
To accelerate the cannonball takes the same amount of force as before. If you gave it a 25cm per second initial acceleration with 50 lbs of force, then it will take an equal amount of force to get it moving another 25cm per second faster. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

#2
Not so sure on the human powered side of things, but it stands to reason. To impart the velocity and energy, the hand/fingertips would have to be moving at same speed as imparted to the object. Disregarding imparting the inertia, the velocity a human arm/hand can travel forward will mean you'll never see a 200mph fastball for that reason. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/p47nh.jpg
What if there were no hypothetical questions?

El Turo
06-12-2004, 02:33 AM
Cajun,

Quite right.

Josf,

If you're searching for something tangible and "real" as a point of reference, just put yourself into a large swimming pool or lake for the purposes of imagining the effect of mass in a "weightless" environment.

Pushing against, say, a jetski while you float there is going to be much different than pushing against a 40ft yacht.

Same basic idea.

In fact, astronaughts TRAIN in underwater environments as a matter of fact.. for this very reason.

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-12-2004, 08:45 AM
El Turo,

Earlier I wrote this:

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Back at the gymnasium:

It occurs to me that the player throwing the cannonball named P-47 is having a hard time.

His magnetic shoes won't hold him down.

What is down? <HR></BLOCKQUOTE>

I had placed both players in the Space gymnasium on the same wall with magnetic shoes. The player with the Cannonball was having a hard time accelerating the Cannonball toward the other player. For this reason my players moved to opposite walls with thier shoes nailed in place.

Communication can be very difficult when an idea is not shared. If the idea is shared then communication is much easier.

By 'Feel' I mean feel not 'real'.

I can feel objects of high mass on earth. They are stuck to whatever they rest on.

My idea is to know what an object of high mass feels like, I want to know this feeling.

In order to accomplish this task there is a real need to learn.

To say that the cannon ball requires acceleration does not answer the question of how difficult would it be to accelerate it.

The cannonball resists movement on earth because gravity and friction hold it in place.

When the Cannon ball is floating in space next to me there is no gravity and no friction.

I possition myself between the cannon ball and the wall so that my shoulder is under the cannon ball, my knee's are bent and I give the cannon ball all my might to shove it away.

How difficult is it to impart acceleration into the cannon ball?

No friction and no gravity holds the cannonball in place.

The cannonball has no weight.

If it is difficult to accelerate then it is stuck somehow. If I have a hard time moving the cannonball, if it resists my moving it, then there is something inside of it that does not want to move.

If the cannonball is out in front of me motionless (remember my shoes are attached to the plate where I stand) How hard is it to place my hand on top of the cannonball and move my hand downward as if trying to pass my hand through the cannonball. How much does the cannonball slow down the progress of my hand as it is forced downward?

I looked up some Newton on the web and found this:

F=MA

What I need to know in order to 'feel' what is going on is the relationship between M and A.

I have an idea.

There is a device on earth known as a strain gauge.

The Strain Gage (http://www.omega.com/literature/transactions/volume3/strain.html)

I need to attach the Strain Gage between the Cannonball and my hand. Perhaps I can machine a flat spot to the cannonball and glue the Strain Gage to that flat spot. Then I put a handle on top of the Strain Gage.
The cannonball is back on the floor. My shoes are still attached to the floor. I pull on the handle with a force perpendicular to the floor.
Let's say the cannonball on earth weighs 200 pounds.

How much strain is recorded on the Strain Gage?

JG14_Josf
06-12-2004, 09:16 AM

Take two compressed stars and place then 4 feet apart in space.

Both stars are inert. They are cool. They are motionless.

Get between those two stars.

Can you move them?

Please don't get hung up on the gravity between the stars. They can be separated far enough that gravity is not a factor and then be connected with two towers (long towers) that almost touch leaving enough room for someone to push against the two towers.

The towers can even have strain gauges or scales on them.

Would the scales record an amount of weight equal to whatever the person was able to lift and the movement of the stars would be insignificant or nearly immesurable?

[This message was edited by JG14_Josf on Sat June 12 2004 at 09:30 AM.]

Cajun76
06-12-2004, 09:51 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by JG14_Josf:

Take two compressed stars and place then 4 feet apart in space.

Both stars are inert. They are cool. They are motionless.

Get between those two stars.

Can you move them?<HR></BLOCKQUOTE>

Disregarding the gravitational attraction of the two massive objects, http://ubbxforums.ubi.com/images/smiley/16x16_smiley-wink.gif yes, you could move them, a tiny bit. F = ma still applies. Or more properly, a = F/m

http://science.howstuffworks.com/fpte1.htm

This link may answer and explain a few things. Wasn't it Yoda that said, "You must unlearn what you have learned." http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

Good hunting,
Cajun76

http://img12.photobucket.com/albums/v30/Cajun76/p47nh.jpg
What if there were no hypothetical questions?

klower
06-12-2004, 01:51 PM
Josf,
Let me try to put F=ma into some perspective. Say you have a 1 lb mass. Say it's 1 lb of ground beef that is shaped like a me-109k4. If you put it on a frictionless table, say an air-hockey table, and applied 1 lb of force to one side for 1 second, the me-109k4 shaped beef would obtain a velocity of 32 ft/sec. In that one second, the me-109k4 shaped beef would move 16 ft. OK, you would have a hard time doing this unless the air hockey table was very long and you could run allong beside it.

Now let's say you had a scale model p-47 that weighs exactly 16 lb. If you applied the same force, 1 lb, the acceleration would be 1/16th as much. So, if you applied 1 lb for 1 second, the final velocity would be 2 ft/sec and the p-47 would have traveled 1 ft at the end of the second. If you stop pusing and no other force acts on it, it will keep moving at 2 ft/second for ever (or untill it hits the end of the air-hockey table, CRASH).

A mass that has a force applied to it will accelerate in accordance to the equation f=ma. Gravity is a force, that is proportional to the mass of the object, so that in the absence of friction, it will accelerate all objects at an equal rate of 32 ft/sec2 (here on earth at least, let's not talk about other planets, like the one you're from) (that is, the object will increase it's speed by 32 ft/sec for each second it is moving under the force of gravity only.

If a body is subjected to several forces in different directions, they can be resolved using vector addition to a single force vector. The object will accelerate in the direction of this force vector again as determined by the equation f=ma. This all gets quite complicated when the forces are aerodynamic forces that varry depending on the objects speed and angle of attack.

Anyways, remember the statement a few pages back that a bullet dropped will hit the ground at the same time as a bullet fired horizontally from a gun. This a a direct result of the same law of motion that I am describing to you here. For this problem, you can ignore the movement in the horizontal direction and only look at the movement in the vertical direction (assuming this all takes place in a vacuum, if we have an atmosphere, the statement is not exactly true, but that get's into the whole messy subject of fluid dynamics). Anyways, both the fired bullet and the dropped bullet start off with an initial velocity downward of zero. The only force acting in the downward direction on either bullet is gravity so they both accelerate at 32 ft/sec2 downward. So, if they start at the same height, and accelerate at the same rate(in the vertical direction)and have the same distance to drop, they will hit the ground at the same time. This is a classic classic introductory physics of motion example.

Oops, I'm rambling. Hope this helps you put some meaning behind the whole equation of motion thing. The next thing you should think about is concervation of energy and concervation of momentum. These are also very important in understanding the physics of motion.

Klower

El Turo
06-12-2004, 03:29 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>it's 1 lb of ground beef that is shaped like a me-109k4.<HR></BLOCKQUOTE>

Hehe.. for some reason this REALLY made me laugh out loud. Meat-erschmit?

http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif

Callsign "Turo" in IL2:FB & WWIIOL
______________________
This place
was once
a place
of worship
I thought,

~V.

JG14_Josf
06-12-2004, 04:54 PM
Thanks for all the help.

I must resist the tendency to move ahead before realizing the mass thing in more detail.

Unlearning is not a problem if I don't know anything.

I am trying to avoid learning something based upon an assuption.

The guys at work call me a turkey baster baby.
They said an alien being came down to earth and artifically inseminated my mom.

Ho ho ho what a funny bunch of guys http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

F=ma
a=F/m

I will read the link, it looks good. Then it will be back to the gymnasium for me.

I really want to move that cannonball in zero g. The other player is hammering me with Basketballs.

I think they eventually bounce themselves down to zero a.

JG14_Josf
06-12-2004, 11:12 PM
Time needs to be considered.