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bubiH
02-15-2006, 07:00 AM
I have just retested with 4.03 to confirm my old findings on this issue:

Planes dive the same whether loaded with 100% fuel or 25% fuel. These results prove that gravity is not completely modelled in this game, at least as far as dive performance is concerned.

Here are my figures from six consecutive tests in QMB on Okinawa map, starting at 5000m and diving to 3000m at 30 degrees of dive (in wonder woman view using the artificial horizon instrument), throttle setting maximum in P-51D20-NA.

SPEED ATTAINED AT 3000M

100% FUEL 793kph 791 793

25% FUEL 793 796 796

(Procedure was to increase throttle to max and and push into the dive immediately from spawn in QMB. I have also tested dive performance from high speed flight rather from the 300kph speed that QMB provides - the results are similar.)

From a tactical viewpoint, we can see that a heavy, fast plane like a FW-190 can gain no advantage by diving against a lighter, but still fast plane like a YAK 3. Your weight does not affect your speed!

I have not provided tracks; anyone who doubts these results can test for himself. I haven't seen this simple test in any of the learned discussions of performance we have seen on these forums. I wonder if Oleg's team are aware of this shortcoming in gravity-modelling?

Anyway, it's an amazing sim and more immersive and realistic than any other. Many thanks to Oleg for his continuing improvements.

Salute!

JG4_Helofly
02-15-2006, 07:46 AM
This problem is well known.
Also in the zoom you have no advantage with energy fighters.

The only thing I can say is: let's wait for Tbob and see if light planes can still retain the enery better than havy planes.

Bartolomeo_ita
02-15-2006, 07:47 AM
and see if light planes can still retain the enery better than havy planes.

IF

???????????????????

Stafroty
02-15-2006, 07:51 AM
Originally posted by Bartolomeo_ita:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">and see if light planes can still retain the enery better than havy planes.

IF

??????????????????? </div></BLOCKQUOTE>

in climb (slow speeds) i find that weight (fuel) matters. well i did find, now, i havent "tested" it.

JG4_Helofly
02-15-2006, 07:59 AM
What is the problem with "IF"? I maybe employed it the wrong way in the sentence? I can only repeat that my English is not so good, but I do my best http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

money_money
02-15-2006, 08:39 AM
I dont know much about physics, and I may be wrong, but I thought that things of different weights fall at the same rate.

<3 $

Aymar_Mauri
02-15-2006, 08:48 AM
Originally posted by money_money:
I dont know much about physics, and I may be wrong, but I thought that things of different weights fall at the same rate.

<3 $
That happens if you are only taking in to consideration gravity and no other forces aplied to the two bodies in study. If you take in to consideration drag caused by air you will have to calculate the influence of the aerodynamic flow of each object.

AKA_TAGERT
02-15-2006, 09:09 AM
Originally posted by Aymar_Mauri:
That happens if you are only taking in to consideration gravity and no other forces aplied to the two bodies in study. If you take in to consideration drag caused by air you will have to calculate the influence of the aerodynamic flow of each object. But money_money is correct, sort of, they don€t fall at the same rate due to gravity, the acceleration due to gravity is the same. It is the same for a feather as it is for a block of wood.

9.8m/s^2.

You are also correct, in that the consideration of drag and thrust must be taking into account. In that the drag of a feather is more than a block of wood.. There are other factors at play too.

But in light of the fact that the plane's shape did not change, thus the drag did not change, I would not expect the fuel load to have any effect on the dive speed. Thus I don€t know why the test was even done? Unless it was to prove something we already knew about physics?

The thing that is different, but, something you wont see on the IAS gauge is the TOTAL ENERGY. The kinetic energy of the plane with a larger fuel load will have a larger TOTAL ENERGY. That is all that I would expect, not a faster dive speed.

Thus, the conclusion drawn by bubiH, i.e.


Originally posted by bubiH:
These results prove that gravity is not completely modelled in this game, at least as far as dive performance is concerned.

From this testing is in error, in that this test does not prove that at all. If anything it proves that acceleration due to gravity is working perfectly in that it did not make a difference.

guderian_ente
02-15-2006, 09:31 AM
Let's wait for BoB and see if light planes can still retain the enery better than heavy planes.

Given the fact that most of the fighters in the Battle of Britain were lightweights (with the exception of the Bf 110, which was a pig) it may be a while before you get an answer. :)

OldMan____
02-15-2006, 09:43 AM
Plese. Stop with this "gravity is not completely modeled".

In every game gravity is applied in code lines soemthing like: forces= forces + 9.8*object.mass


So it is impossible to not model it completely. Or it is there or it is not. And we know it is there because we dive! If fuel makes difference in climb is AUTOMATICALLY does make difference in dive.


What we have is a game where trust is far stronger than gravity. So when you point nose down the acceleration from the egnien is more important than the dive itself. When we reach a certain speed the derag equals the force from gravity, from there only engine is capable of pushing you still faster.

OldMan____
02-15-2006, 09:46 AM
Originally posted by AKA_TAGERT:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Aymar_Mauri:
That happens if you are only taking in to consideration gravity and no other forces aplied to the two bodies in study. If you take in to consideration drag caused by air you will have to calculate the influence of the aerodynamic flow of each object. But money_money is correct, sort of, they don€t fall at the same rate due to gravity, the acceleration due to gravity is the same. It is the same for a feather as it is for a block of wood.

9.8m/s^2.

You are also correct, in that the consideration of drag and thrust must be taking into account. In that the drag of a feather is more than a block of wood.. There are other factors at play too.

But in light of the fact that the plane's shape did not change, thus the drag did not change, I would not expect the fuel load to have any effect on the dive speed. Thus I don€t know why the test was even done? Unless it was to prove something we already knew about physics?

The thing that is different, but, something you wont see on the IAS gauge is the TOTAL ENERGY. The kinetic energy of the plane with a larger fuel load will have a larger TOTAL ENERGY. That is all that I would expect, not a faster dive speed.

Thus, the conclusion drawn by bubiH, i.e.


Originally posted by bubiH:
These results prove that gravity is not completely modelled in this game, at least as far as dive performance is concerned.

From this testing is in error, in that this test does not prove that at all. If anything it proves that acceleration due to gravity is working perfectly in that it did not make a difference. </div></BLOCKQUOTE>

Things are not THAT simple. density matters on this subject, and weight does change it.

If you take a ball of thin plastic, of 1 meter of radius and weight 100grams. You may eb 100% sure it will dive slower than a ball of exactly same shape and size with 20 kg.

because drag force is the same. But force does not equal acceleration. Force equals to mass times acceleration. So the drag force is more effective in the body that weight less.

WB_Outlaw
02-15-2006, 10:30 AM
The acceleration due to gravity is constant (at 32.2 ft/sec^2) for all objects in FREE FALL. Free Fall is defined as the acceleration of an object under the influence of gravity ONLY. By definition it does not include drag force. Even if you only include gravity and drag (ie dead stick and neglecting windmilling prop effects) the same aircraft with a larger fuel load will accelerate faster in the dive.

--Outlaw.

Fillmore
02-15-2006, 10:44 AM
Test proves nothing, it is incomplete.

You need to show that the expectation is greater than the variance.

The variance in the tests looks to be about 1%

I want to see some numbers to show that the expected difference between 25% and 100% fuel should result in greater than a 1% difference USING THESE TEST CONDITIONS.

NonWonderDog
02-15-2006, 10:53 AM
High school physics -- a = F/m

Gravity applies a constant accelleration to every object, regardless of its mass.

Drag force is the same if shape doesn't change, but the accelleration component due to drag is inversely proportional to mass. Lighter objects will have less resultant accelleration in free fall, after drag is figured in.

BUT! -- The engine *also* provides a force -- a force rather larger than drag. Less weight means thrust causes greater accelleration. Thrust counteracts drag, so powered dive speed will not change very much due to a changing fuel load, and <span class="ev_code_YELLOW"> dive speed should actually increase as weight decreases if you're at full throttle.</span> I'm sure I could calculate how much it should change, but it's really not worth the time.


If you do the same test with the engine OFF, you should see the expected difference in dive accelleration. I wouldn't expect too much, though. The biggest (percentage) difference should be with engine off, full fine (100%) prop pitch, gear down, flaps down, arresting hook down, speed brakes out, carrying empty external tanks, and with the canopy open. If you do this on a winter map you should see slightly more disparity.


Originally posted by OldMan____:
What we have is a game where trust is far stronger than gravity. So when you point nose down the acceleration from the egnien is more important than the dive itself.
Right idea, but incorrect. If thrust was greater than gravity we could pull off indefinite vertical climbs. Rather, thrust is far stronger than *drag*. This makes sense -- if it wasn't, planes could never accellerate in level flight.

Jetbuff
02-15-2006, 11:53 AM
Horse-hockey!

If weight did not matter how come the draggier (but heavier) P-47D outdives the Spit IXe?

http://img105.imageshack.us/img105/3191/diveperf6bp.th.gif (http://img105.imageshack.us/my.php?image=diveperf6bp.gif)

Data from DeviceLink. The dive was engine off (0% fuel) from 0 airspeed at 6000m and 60? dive towards bomb marker. Tracks available.

As NonWonderDog pointed out. With engine on, you are adding thrust to the equation and that would favour of the lighter (but no less powerful) spitfire so it is a lot harder to 'isolate' the effect of weight. Even engine off, you cannot isolate the effect of weight from drag differences. However, since we can probably assume that the P-47 (due to greater cross-sectional area and wetted surface) has a greater drag than the Spitfire and yet it still out-dives the latter, it follows that:

Weight is most certainly modelled!

WWMaxGunz
02-15-2006, 12:29 PM
What prop setting was used?

At near 800kph the drag is very high. To gain 1% speed requires a lot of force more than
1% or even the square 1.01 x 1.01 as compression is modelled to some degree (not perfect
but mostly there).

If you just set pitch at 100 then you are adding a big source of drag that swamps the
difference in mass. At some speed you will anyway, P-51 is not so light empty that 75%
fuel difference is a major factor but it is some. Ummmm, does 100% include drop tank?

Jetbuff
02-15-2006, 12:35 PM
Are you talking to me Neal? Prop pitch was 0% for the P47 as per the graph if so. The Spit, having a system much like a Komandogerat, simply had a closed throttle. (requesting low rpm)

OldMan____
02-15-2006, 12:59 PM
Originally posted by NonWonderDog:
High school physics -- a = F/m

Gravity applies a constant accelleration to every object, regardless of its mass.

Drag force is the same if shape doesn't change, but the accelleration component due to drag is inversely proportional to mass. Lighter objects will have less resultant accelleration in free fall, after drag is figured in.

BUT! -- The engine *also* provides a force -- a force rather larger than drag. Less weight means thrust causes greater accelleration. Thrust counteracts drag, so powered dive speed will not change very much due to a changing fuel load, and <span class="ev_code_YELLOW"> dive speed should actually increase as weight decreases if you're at full throttle.</span> I'm sure I could calculate how much it should change, but it's really not worth the time.


If you do the same test with the engine OFF, you should see the expected difference in dive accelleration. I wouldn't expect too much, though. The biggest (percentage) difference should be with engine off, full fine (100%) prop pitch, gear down, flaps down, arresting hook down, speed brakes out, carrying empty external tanks, and with the canopy open. If you do this on a winter map you should see slightly more disparity.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by OldMan____:
What we have is a game where trust is far stronger than gravity. So when you point nose down the acceleration from the egnien is more important than the dive itself.
Right idea, but incorrect. If thrust was greater than gravity we could pull off indefinite vertical climbs. Rather, thrust is far stronger than *drag*. This makes sense -- if it wasn't, planes could never accellerate in level flight. </div></BLOCKQUOTE>


Ok think I used wrong words. I meant to say, trust is RELATIVELY much stronger when compared to grafvity than it should be. That is also sustained by the capabilities of planes climbign alot at very low speeds.

NonWonderDog
02-15-2006, 12:59 PM
Originally posted by WWMaxGunz:
If you just set pitch at 100 then you are adding a big source of drag that swamps the
difference in mass.

Other way around, isn't it? Larger drag forces should amplify the effect of changing mass.

(Very simplistically) accelleration should be something like:

a = g - F_drag / m

If drag force is low, you'll get only very slight differences in overall accelleration due to mass. Drag depends on speed of course, so this is a bit complicated. I'm not sure where the sweet spot is, but I don't think it's minimal drag config.

It seems to me that the largest percentage difference should be in high drag configuration. The speeds might be low enough that the numerical difference in mph/s or whatever would be hard to measure, though.

D'oh. You'd get the same result regardless, just at different speeds. It might be good to go as fast as possible (i.e. in lowest drag config) just to get a bigger range of measurements, but you wouldn't have much time to make them.


Seems a bit much just to prove that GRAVITY EXISTS, though. I think it's easiest just to say that dive speed is a function of engine power and drag coefficients, where weight is very much secondary.

WWMaxGunz
02-15-2006, 01:11 PM
Not really NWD. Large drag forces mean you hit the wall sooner.

If it takes X amount of force to reach a certain speed then it takes how much more to
increase that speed by 10%? What if X is into compressability?

How much difference does 10% more weight make?

From how I intuit it, less drag means a larger seperation in resulting speeds.

EDIT:
I see where we differ. I'm talking about speed not accel.

Here try this:
2 balls same size but different weights. One has terminal V at 100kph and the other 200kph.
What would the ratio of the masses be? I'm sure it is more than 1:2.

Jetbuff
02-15-2006, 01:16 PM
Originally posted by OldMan____:
Ok think I used wrong words. I meant to say, trust is RELATIVELY much stronger when compared to grafvity than it should be. That is also sustained by the capabilities of planes climbign alot at very low speeds.
I agree that that possibility has most definitely crossed my mind. See here:
http://forums.ubi.com/eve/forums/a/tpc/f/63110913/m/2721067114

Trouble is, this is a lot harder to verify.

NonWonderDog
02-15-2006, 01:24 PM
I wasn't really thinking about maximum dive speed, hold on.


Drag increases with V^2, all else being equal.
Gravitational force is proportional to mass.

You get, at F_drag = F_gravity, (vertical no-power dives are easiest http://forums.ubi.com/groupee_common/emoticons/icon_rolleyes.gif)
1/2*(rho)*V_max^2*S*C_D0 = m*g

V_max = sqrt(2*m*g/(rho*S*C_D0))

So, terminal dive speed is proportional to sqrt(m/C_D0).

...You should get about the same percentage difference due to chaging weight no matter your drag config, you just see this difference at different speeds. I should probably consider induced drag and lift so this works for other than vertical dives, but I'm far too lazy to think this hard in my spare time.


Now how do I go about forgetting wingarea in my drag equation...

WWMaxGunz
02-15-2006, 01:35 PM
If it takes the square of the difference in speed more force to increase speed,
ie 10% more speed requires 1.1x1.1=1.21 = 21% more force then how is increased
mass gonna increase speed linearly?

NonWonderDog
02-15-2006, 01:37 PM
Doesn't, speed would increase with the square root of mass.

It's just that speed would also decrease with the square root of the coefficient of parasitic drag.

You'll get a larger absolute difference at low drag, but the percentage difference should be constant.

WWMaxGunz
02-15-2006, 02:03 PM
Originally posted by NonWonderDog:
Doesn't, speed would increase with the square root of mass.

It's just that speed would also decrease with the square root of the coefficient of parasitic drag.

You'll get a larger absolute difference at low drag, but the percentage difference should be constant.

You mean with change in drag, not change in mass at the same drag?

And then we come to speed moving into compression speed range....

NonWonderDog
02-15-2006, 02:31 PM
In a vertical dive I mean change in mass at the same drag. The *percentage* difference between terminal dive speeds at two masses should be independent of drag config. The absolute difference would be most measureable at high speed, though, and high speed would be obtained in low drag config.

With a non-vertical dive it's a 4th order equation that I'm too lazy to work out at the moment. Maybe later. I'm sure I have the solution written down somewhere, too... I just don't expect increased drag to mask mass -- it doesn't make sense to me.

WWMaxGunz
02-15-2006, 02:51 PM
Originally posted by NonWonderDog:
In a vertical dive I mean change in mass at the same drag. The *percentage* difference between terminal dive speeds at two masses should be independent of drag config. The absolute difference would be most measureable at high speed, though, and high speed would be obtained in low drag config.

With a non-vertical dive it's a 4th order equation that I'm too lazy to work out at the moment. Maybe later. I'm sure I have the solution written down somewhere, too... I just don't expect increased drag to mask mass -- it doesn't make sense to me.

Not totally, no. But as you pointed out, the difference would be more at high speed
obtained at lower drag. Take the converse, the difference shrinks.

At 750+kph the P-51 is into compression and that parasite square of speed goes cubic and
then some. That's where I see a small mass difference as resulting in a much smaller
speed difference.

The first post example, he uses appx 30 deg dive so gravity assist at one-half vertical.

plumps_
02-15-2006, 04:14 PM
Originally posted by bubiH:
Weight Does Not Affect Dive Performance!
Planes dive the same whether loaded with 100% fuel or 25% fuel. These results prove that gravity is not completely modelled in this game, at least as far as dive performance is concerned.

Here are my figures from six consecutive tests in QMB on Okinawa map, starting at 5000m and diving to 3000m at 30 degrees of dive (in wonder woman view using the artificial horizon instrument), throttle setting maximum in P-51D20-NA.

...

(Procedure was to increase throttle to max and and push into the dive immediately from spawn in QMB. I have also tested dive performance from high speed flight rather from the 300kph speed that QMB provides - the results are similar.)
...
I have not provided tracks; anyone who doubts these results can test for himself. ...

Fuel load does have an influence on dive performance in FB 403m. I've made a little test mission that allows you to isolate the effect better than your QMB test does: Download (http://home.arcor.de/rayluck/sturmovik/divetest.zip)
Actually these are two almost identical missions; in one the P-51 D20 NA is loaded with 100% fuel, in the other one with 1%. Ammo is default in both missions. The aircraft's nose will be pointed vertically down right from the start.

My procedure is to start at 10000 m, shut off the engine immediately, and dive down vertically towards the bombing target below you. At 3000 m read the TAS speed gauge.

My results with 100% prop pitch were:

100% fuel - TAS at 3000 m 1109 km/h

1% fuel - TAS at 3000 m: 1079 km/h

I repeated each mission five times without significant differences.

I have no idea whether the 30 km/h difference between empty and loaded dive is realistic, but it's certainly not true that there is no difference at all.

Jetbuff
02-15-2006, 05:29 PM
Plumps, you may see a bigger difference (or the same difference earlier since the plane would probably break up sooner) if you use 0% pitch. Try it.

plumps_
02-15-2006, 05:59 PM
With 0% prop pitch the difference is still 30 km/h.

100% fuel, TAS at 3000 m: 1112 km/h

1% fuel TAS at 3000 m: 1082 km/h

(same conditions as before)

Note that with the engine shut down, the difference in speed between 0% and 100% pitch is much smaller than the difference in speed between 1% and 100% fuel.

IIJG69_Kartofe
02-15-2006, 06:08 PM
Weight doesn't affect dive performance...

YES !

It's well known since gallileo gallilei works !

http://www.fact-index.com/g/ga/galileo_galilei.html

FritzGryphon
02-15-2006, 06:19 PM
I can replicate Plumps' results. The difference is greater if you stretch out the dive for a longer period, by using a shallower angle.

Simply, the game does model grav force versus drag. I've tested as well that a FW-190 with a SC500 accelerates faster in an unpowered dive than one without a bomb.

But this is totally different than a P-47 vs. FW-190 comparison. The latter is a giagantic plane, with a much larger frontal area and wings. The former, a tiny plane. Their grav force/drag force ratio would be about the same (I'm guessing, since they dive so similar).

Were weight the only factor, a B-29 would outdive everything.

p1ngu666
02-15-2006, 06:40 PM
weight from fuel might not be well modeled. there is difference between different plane types tho http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

plumps_
02-15-2006, 06:51 PM
Originally posted by p1ngu666:
weight from fuel might not be well modeled. there is difference between different plane types tho http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif
Why would weight from fuel be modeled differently than any other kind of weight? I can't see any reason nor indication for this.

plumps_
02-15-2006, 07:06 PM
Originally posted by FritzGryphon:
The difference is greater if you stretch out the dive for a longer period, by using a shallower angle.

Simply, the game does model grav force versus drag.
That's something I just noticed myself. In a 45? unpowered dive from 10000 m to the ground not only the differences were greater, I also noticed that the P-51 reached its highest speed at 3000 m altitude. As it got closer to the ground it slowed down slightly, probably due to higher drag from the increasing density of air.

Jetbuff
02-15-2006, 07:11 PM
Originally posted by plumps_:
With 0% prop pitch the difference is still 30 km/h.

100% fuel, TAS at 3000 m: 1112 km/h

1% fuel TAS at 3000 m: 1082 km/h
Unless something has drastically changed between 4.01 and 4.03, you should also be attaining the speed faster. i.e. if you plot the speeds at various altitudes you should see a definite improvement in acceleration between the two - over 7000m, you've probably very close to terminal velocity.

But you are right, it is likely less than the effect of the weight difference.

AKA_TAGERT
02-15-2006, 09:12 PM
Originally posted by OldMan____:
Things are not THAT simple. density matters on this subject, and weight does change it.

If you take a ball of thin plastic, of 1 meter of radius and weight 100grams. You may eb 100% sure it will dive slower than a ball of exactly same shape and size with 20 kg.

because drag force is the same. But force does not equal acceleration. Force equals to mass times acceleration. So the drag force is more effective in the body that weight less. So what part of "There are other factors at play too" did you not understand?

plumps_
02-15-2006, 09:34 PM
http://forums.ubi.com/images/smilies/10.gif Let me guess. This is the part he probably didn't understand:


Originally posted by AKA_TAGERT:
But in light of the fact that the plane's shape did not change, thus the drag did not change, I would not expect the fuel load to have any effect on the dive speed. Thus I don€t know why the test was even done? Unless it was to prove something we already knew about physics?

...

If anything it proves that acceleration due to gravity is working perfectly in that it did not make a difference.

The-Pizza-Man
02-15-2006, 09:35 PM
Originally posted by FritzGryphon:
I can replicate Plumps' results. The difference is greater if you stretch out the dive for a longer period, by using a shallower angle.

Simply, the game does model grav force versus drag. I've tested as well that a FW-190 with a SC500 accelerates faster in an unpowered dive than one without a bomb.

But this is totally different than a P-47 vs. FW-190 comparison. The latter is a giagantic plane, with a much larger frontal area and wings. The former, a tiny plane. Their grav force/drag force ratio would be about the same (I'm guessing, since they dive so similar).

Were weight the only factor, a B-29 would outdive everything.

A plane with a bomb should accelerate faster in a dive than one without. The bomb presumably has a greater weight to drag ratio than the plane so it won't slow it down in a power off dive.

OldMan____
02-16-2006, 04:13 AM
Just some 2 cents. Drag does not increase with square of speed! It only increase at taht rate in 100% turbulent flow. At laminar flow it increases linearly. Sincce planes have a mix of turbulent and laminar flow (in several areas of plane), the drag increases between linear and quadratic.



TARGET: all the part, because you were completely unespecific and your statements let to the judgment that weight DOES NOT MATTER.

p1ngu666
02-16-2006, 07:50 AM
Originally posted by plumps_:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by FritzGryphon:
The difference is greater if you stretch out the dive for a longer period, by using a shallower angle.

Simply, the game does model grav force versus drag.
That's something I just noticed myself. In a 45? unpowered dive from 10000 m to the ground not only the differences were greater, I also noticed that the P-51 reached its highest speed at 3000 m altitude. As it got closer to the ground it slowed down slightly, probably due to higher drag from the increasing density of air. </div></BLOCKQUOTE>

well yes, but games/sims arent always logical http://forums.ubi.com/images/smilies/16x16_smiley-wink.gif

pretty cool that it slowed down

Stafroty
02-16-2006, 08:41 AM
Pingu, are you logical?

AKA_TAGERT
02-16-2006, 08:54 AM
Originally posted by OldMan____:
TARGET: all the part, because you were completely unespecific and your statements let to the judgment that weight DOES NOT MATTER. Not weight, mass.

Adding more fuel does:

1) NOT change the shape of the aircraft, therefore drag does NOT change.
2) NOT change the size of the engine, therefore thrust does NOT change.
3) NOT change the gravity constnat, therefore acceleratiion due to gravity does NOT change.

Thrust, Drang, and acceleration due to gravity have not changed. Therefore there should be no change in dive speed. The only thing that would change is the kintic energy.

All within reason mind you! For example, if you want to assume the *mass* of the moon was somehow cramed into the size and shape of the plane, then all bets are off in that your no longer talking about a real senario.

OldMan____
02-16-2006, 09:08 AM
Originally posted by AKA_TAGERT:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by OldMan____:
TARGET: all the part, because you were completely unespecific and your statements let to the judgment that weight DOES NOT MATTER. Not weight, mass.

Adding more fuel does:

1) NOT change the shape of the aircraft, therefore drag does NOT change.
2) NOT change the size of the engine, therefore thrust does NOT change.
3) NOT change the gravity constnat, therefore acceleratiion due to gravity does NOT change.

Thrust, Drang, and acceleration due to gravity have not changed. Therefore there should be no change in dive speed. The only thing that would change is the kintic energy.

All within reason mind you! For example, if you want to assume the *mass* of the moon was somehow cramed into the size and shape of the plane, then all bets are off in that your no longer talking about a real senario. </div></BLOCKQUOTE>

But that is exaclty what i answered about. No change in thrusts (lets imagine engines off just for sake of this). Same shape. Same gravity. So darg is same ok? Mass is different. Drag is same... this same drag force have less effect on a greater mass. Simple. Only that we were talking about. So fuel WILL change dive acceleration (but no effect at top speed)

Jetbuff
02-16-2006, 09:18 AM
Not sure what you're trying to say Tagert? Are you implying a change in mass does not affect speed and acceleration? Because it does. Like you said it does not change gravity or drag. However, the drag force required to slow down a more massive object is higher, provided drag coefficient is constant. Similarly the force of gravity acting on a more massive object is larger. (f = m*a, but a is constant for gravity)

e.g. Two feathers, one a normal one and the other an iron cast replica of the first are dropped, which one will accelerate faster and ultimately reach a higher terminal velocity?

Power on gets tricky, because at similar thrust acceleration of the more massive object is lower and yet it still takes more drag to ultimately stop acceleration.

WWMaxGunz
02-16-2006, 09:00 PM
Originally posted by AKA_TAGERT:

Thrust, Drang, and acceleration due to gravity have not changed. Therefore there should be no change in dive speed. The only thing that would change is the kintic energy.


That works for rockets in space but drag is a player all the way down and becomes -the-
major single player in a long enough, steep enough dive.

Forget the simplified acceleration formula. Apply force vs force stepwise in very small
increments and mass is a factor. Work it out in an infinite series if you want to spend
the time. Drag is there always, weight is the main force these planes have to overcome
it. Accel due to gravity in a falling object will not exceed 9.8m/s but with drag it will
=always= be less. A regular softball will fall slower than a softball with an iron core,
it will accelerate slower too.

I know you know this.

AKA_TAGERT
02-17-2006, 12:37 AM
Originally posted by WWMaxGunz:
That works for rockets in space but drag is a player all the way down and becomes -the-
major single player in a long enough, steep enough dive.

Forget the simplified acceleration formula. Apply force vs force stepwise in very small
increments and mass is a factor. Work it out in an infinite series if you want to spend
the time. Drag is there always, weight is the main force these planes have to overcome
it. Accel due to gravity in a falling object will not exceed 9.8m/s but with drag it will
=always= be less. A regular softball will fall slower than a softball with an iron core,
it will accelerate slower too.

I know you know this. Hmmmmm ok busted out the old physics book and found this


Two identical objects except with different masses are dropped from the same height at the same time. With air resistance set to zero, both balls strike the ground at the same time. As the air resistance is increased, the more massive object will strike the ground first. With enough air resistance the lighter ball is seen to reach a terminal velocity. Displayed is the distance vs. time, velocity vs. time, and the acceleration vs. time diagrams.

So, I was wrong!

Sum of the forces.. drag a constant, yet the force due to mass (aks weight) is now larger.. should have seen that.. makes since now, thanks guys! Sorry bubiH, Jetbuff, OldMan, etc for any confusionI may have caused!

Guess I have been working in aerospace too long.. Heavy on the space light on the aero! http://forums.ubi.com/images/smilies/35.gif

PS thanks WWMaxGunz for helping me pull my head out! http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

robban75
02-17-2006, 03:04 AM
A loooong discussion going on in this thread on the subject,http://www.acompletewasteofspace.com/modules.php?name=F...ile=viewtopic&t=7876 (http://www.acompletewasteofspace.com/modules.php?name=Forums&file=viewtopic&t=7876) , in case someone is interested. http://forums.ubi.com/images/smilies/16x16_smiley-happy.gif

OldMan____
02-17-2006, 04:07 AM
Unfortunately the only way to have precise data is to measure.


Does anyone here have scale models of FWs , Spits etc, and is willing to sacrifice them from the top of a building roof? :P

WWMaxGunz
02-17-2006, 04:18 AM
Originally posted by AKA_TAGERT:
Guess I have been working in aerospace too long.. Heavy on the space light on the aero! http://forums.ubi.com/images/smilies/35.gif

PS thanks WWMaxGunz for helping me pull my head out! http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif

Holy $#!+! Was that a Seal of the Apocalypse just broke?

Just be real happy to be doing what you do. IMO we all get tired and still keep moving.
At some point all the caffiene in the world don't help.

We keep getting these OLD CLAIMS dumped on us no matter how often they're disproved.

I was playing with the G-2 at idle clean stall. No VSI http://forums.ubi.com/images/smilies/16x16_smiley-sad.gif and not feeling patient either.
Anywho I did the pull-through idle thing and I'm not able to keep alt at, really before 180
kph just from watching the speedbar drop it's 10m increment. With lots of patience or using
UDPSpeed during a test I'm thinking that 240-250kph at idle will be at least CLOSE.

Finnish tests findable here (Google works to find posts here btw) give the idle pull through
at 175kph and idle clean stall speed at 240-250. They give full power stall speed 140-130kph.

IMO we have people running up the power in "stall speed tests" and comparing to idle stall
speed values. Not to mention, the same also have no problem with losing alt and still not
admitting they passed the point back a ways.

DaimonSyrius
02-17-2006, 07:15 AM
Originally posted by AKA_TAGERT:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Two identical objects except with different masses are dropped from the same height at the same time. With air resistance set to zero, both balls strike the ground at the same time. As the air resistance is increased, the more massive object will strike the ground first. With enough air resistance the lighter ball is seen to reach a terminal velocity. Displayed is the distance vs. time, velocity vs. time, and the acceleration vs. time diagrams.

So, I was wrong! </div></BLOCKQUOTE>
Galileo Galilei was the one who started all this. He started it from the top of the Tower of Pisa, specifically.

Unfortunately, he doesn't post much anymore http://forums.ubi.com/groupee_common/emoticons/icon_razz.gif

Cheers,
S.

WWMaxGunz
02-17-2006, 09:28 PM
Galileo was careful about his choices of what to drop. None of them had low enough density
to be affected by drag enough to show in that short drop.

What a shame Leonardo hadn't run the show!

Aaron_GT
02-18-2006, 02:50 AM
25% fuel - how much fuel weight?

100% fuel - how much fuel weight?

How much engine thrust?

At what point does drag becoming the limiting factor?

Really you need to do the tests with the engine off as it might be that the other terms (thrust and drag) dominate over the changes in weight.

WWMaxGunz
02-18-2006, 06:55 AM
Engine off and pitch at zero. Engine idle and pitch 100% is how I slow down CSP planes.
IMO it is forcing the plane to try and drive the engine at full rpms.

PikeBishop
02-20-2006, 06:27 AM
Dear All,
Bear in mind that I read this thread on friday and think that I have it clear..........
What I want to know is we have normal max speed of all aircraft in the sim. At this point the thrust equals the drag. Surely the terminal velocity would still be in the same ratio as the max speed of difference of each aircraft as the acceleration due to gravity is a constant. The resulting distance between to different aircraft would be modified by any initial??? acceleration differences peformed by said aircraft?

Best regards,
SLP

WWMaxGunz
02-20-2006, 03:28 PM
No you won't because due to drag the plane is not freely accelerating.
Not freefall. That is what terminal velocity is about, it's a drag I know but.....

Same plane but heavier should have a higher terminal velocity.
Maybe not much higher but the weight adds to the force pulling down.

Look at it another way. Potential energy is mass x height. More mass, more PE.

PikeBishop
02-21-2006, 04:32 AM
Dear Max.....
That is what I am not quite clear about.
My gut instinct tells me that the acceleration in the dive would be higher for the heavier aircraft, but the terminal dive speed??.....in the light of objects of varying density/mass still fall at the same rate in a vacuum. Does that not mean that it is the drag that matters most, combined with the thrust from the prop. The drag can of course be calculated from the inverse square law, but I am not sure that beyond max speed the prop is still effective and may even act as a break??
best regards,
SLP

PikeBishop
02-21-2006, 04:33 AM
sorry.....brake.

Jetbuff
02-21-2006, 04:44 AM
PikeBishop, there is another thread discussing how thrust should vary with speed: http://forums.ubi.com/eve/forums/a/tpc/f/63110913/m/2721067114

Back on topic though, yes terminal velocity would similarly be affected. As Gunz said, think of it as a summation of forces. One is drag and is similar for any two objects of the same shape and size. (e.g. same plane at 100% fuel and 0% fuel) It is trying to stop the plane from falling. The other is weight (m*g) and that is higher for a heavier aircraft. Since both these are forces, their vector sum will define the net acceleration of the aircraft. It is easy to see how the heavier plane will achieve a higher terminal speed. Its higher 'force of weight' must be counteracted by the exact same drag that acts on the lighter plane and a state of equilibrium (0 acceleration) is therefore reached at a different airspeed.

PikeBishop
02-21-2006, 08:58 AM
So.....what we are saying is that(not considering structural failure), if we can find quoted terminal dive speeds we should find that these speeds should be more or less in the same proportion as the maximum speeds. e.g.Ki841a TD was 595mph and max level was about 400mph, so this is a 50% increase. So it follows that the P47's was about 430mph and so the TD would be in the region of 430/2 plus 430mph i.e. 645mph.
I am aware that this is only a rough approximation but does anyone know what the terminal dive speed of the P47 was??
regards,
SLP

Professor_06
02-21-2006, 09:56 AM
Originally posted by PikeBishop:
So.....what we are saying is that(not considering structural failure), if we can find quoted terminal dive speeds we should find that these speeds should be more or less in the same proportion as the maximum speeds. e.g.Ki841a TD was 595mph and max level was about 400mph, so this is a 50% increase. So it follows that the P47's was about 430mph and so the TD would be in the region of 430/2 plus 430mph i.e. 645mph.
I am aware that this is only a rough approximation but does anyone know what the terminal dive speed of the P47 was??
regards,
SLP

The only dive test conducted of a P47 that I read was one in which stated the P47 didnt have a Vne but of course the prop spun off the test P47 when it reached 500mph in the dive. So this process is much more complicated then you could imagine. Simple formulas dont always work with machines.

Peace..

WWMaxGunz
02-21-2006, 10:01 AM
Originally posted by PikeBishop:
So.....what we are saying is that(not considering structural failure), if we can find quoted terminal dive speeds we should find that these speeds should be more or less in the same proportion as the maximum speeds. e.g.Ki841a TD was 595mph and max level was about 400mph, so this is a 50% increase. So it follows that the P47's was about 430mph and so the TD would be in the region of 430/2 plus 430mph i.e. 645mph.
I am aware that this is only a rough approximation but does anyone know what the terminal dive speed of the P47 was??
regards,
SLP

No, not at all. Flying level at high speed the amount of power going to keep the plane up is
very small compared to what is fighting the drag, esp at .5 mach and up. Weight becomes almost
a non-issue unless it is huge. There must be enough energy to keep the plane aloft but there
is far, far more making the speed so the heavy P-47 with over 2000HP that has not so great a
sustained climb will still roar along to a high top speed. More and more the trend went to
heavier planes with more power and higher level speeds.

Then you come to the dives and there you get changes in behaviour. As long as the plane is
under the top level speed it appears that thrust will totally counter or over-counter drag.
In that range there's an advantage to better power to mass, the lighter plane. JaRa did the
simple equation IIRC back in the fall/winter of 2002 the first time that "all planes dive the
same" was claimed though it was a false claim then and since. With thrust enough to overcome
drag you get the full accel due to gravity which is the same no matter weight.
However once past level top speed the drag will be eating into that accel and 9.8m/s will
become less and less. There's a calculus to it that's beyond my rust and beyond my knowing
the factors of even if I'd stayed on top of it all. The higher speed goes beyond level max,
the more that extra mass will be a benefit but the rate is not like twice the mass gets twice
the speed or even nearly so. Dives over 500mph I am sure are transonic enough that the drag
is increasing faster than by the square of the difference and into the cube. A lot of extra
weight in the same plane will still get real enough extra speed as P-47's with bombs in dives
were known to pass Vne which is real trouble, I dunno if dropping the bombs would even help.