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LeadSpitter_
01-19-2004, 06:05 AM
it makes no sense of having csp in fb unless the variable props can damage thier engines, exceed oil pressure limits or over reving at alt which cant be done on russian a/c, bursting oil lines and damaging thier engines

it was an advantage to have csp but it is a disadvantage in FB not being able to slow down quickly and having to turn off magnetos or turn engine off before landing to slow down,100 pitch or 0 pitch and 0 trottle dont seem to slow you down quick enough but it is realistic because of the govenor

However with the variable props you can dive from 6000m + straight down at your runway reduce trottle put 100 pitch or turning off the engine makes you go from 700kmph to 200 in less the 3 seconds.

The british invented csp to reduce engine wear and mechanical problems that variable props had

An improvement in reality should not be a disadvantage in fb and defeats the purpose of having it in the game unless the problems of variable props are there.

Thoughts comments views discussion welcome.

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LeadSpitter_
01-19-2004, 06:05 AM
it makes no sense of having csp in fb unless the variable props can damage thier engines, exceed oil pressure limits or over reving at alt which cant be done on russian a/c, bursting oil lines and damaging thier engines

it was an advantage to have csp but it is a disadvantage in FB not being able to slow down quickly and having to turn off magnetos or turn engine off before landing to slow down,100 pitch or 0 pitch and 0 trottle dont seem to slow you down quick enough but it is realistic because of the govenor

However with the variable props you can dive from 6000m + straight down at your runway reduce trottle put 100 pitch or turning off the engine makes you go from 700kmph to 200 in less the 3 seconds.

The british invented csp to reduce engine wear and mechanical problems that variable props had

An improvement in reality should not be a disadvantage in fb and defeats the purpose of having it in the game unless the problems of variable props are there.

Thoughts comments views discussion welcome.

http://www.geocities.com/leadspittersig/LSIG.txt
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Jippo01
01-19-2004, 08:52 AM
My opinion is that I wouldn't complain about defiencies of CSP props at all as they are completely flawless right now. It should be possible to damage the engine also in SP plane, and at the moment on ly Brewster can be damaged. Adding throttle quickly from idle to full in high speed should blow the engine in CSP's too.

But in this field the game is not very complex anyway so I think it is ok.

-jippo

LeLv28 - Fighting for independency since 2002
http://www.lelv28.com

Falkster's Ju-88 fan site:
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Lazy312
01-19-2004, 09:36 AM
"posted 19-01-04 05:05
it makes no sense of having csp in fb unless the variable props can damage thier engines, exceed oil pressure limits or over reving at alt which cant be done on russian a/c, bursting oil lines and damaging thier engines"

I dont understand. All russian planes with the exception of TB-3 have CSP.

312_Lazy
312th Fighter Squadron
http://312.jinak.cz

Jaws2002
01-19-2004, 09:45 AM
It takes a lot of dedication and practice to be able to master the pitch manually on the 109.
I think whoever is flying the Bf-109 in manual mode and can do all this things effectively, deserves the advantage.

Just my two cents.

Stefan-R
01-19-2004, 10:05 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by LeadSpitter_:
it makes no sense of having csp in fb unless the variable props can damage thier engines, exceed oil pressure limits or over reving at alt which cant be done on russian a/c, bursting oil lines and damaging thier engines

<HR></BLOCKQUOTE>

Its possible to damage the engine with manual pitch by overreving the engine. (All german a/c have automatic prop pitch which must be disabled to have manual pitch.) [Note: except Ju 87 and He 111 which have const speed prop]
It is NOT POSSIBLE to damage the engine of a a/c with constant speed prop, even if the const speed prop is damaged and the engine is running at 5000rpm+ (except Bewster).

So in fact the engines of const speed prop a/c's are overmodeled, too. (except Bewster)

IV_JG51_Razor
01-19-2004, 02:50 PM
There is definitely something wrong with the modeling of the props in FB, but it's better than nothing. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Be careful what you wish for Leadspitter. If everything in FB were modeled correctly, it would take a long period of training for most folks to even be able to get around the traffic pattern without blowing an engine, let alone going into combat. http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif Some of the antics used by us in this sim to try to control speed, such as those you mentioned above, would result in a ruinned(sp?) engine for sure.

There comes a point where the developer has to decide between real life modeling, and playability. Witness all the discussions in here about icons, cockpit on/off, speed bar, etc, etc, etc.

For CSP equiped a/c in this game, there is no penalty for overboosting the engine, shock cooling, nor any tendancy to overspeed, which is a very real problem on any plane so equiped. On real a/c with csp's, the governor has only so much prop pitch to add or take away to maintain the desired RPM. If you have yours set to, say 2500, and let the nose drop. As the speed builds up, the gov will continue to increase the pitch until it's at the maximum available. After that, if you continue to accelerate, the RPM will climb. None of this is modeled in the game, and you should probably count your blessings that it isn't http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif Hells bells, just getting a round motor started without a fire, or hydraulic lock up is a trick in itself, not to mention pre-oiling, warmming up the engine oil sufficiently before takeoff, or worrying about mag timeing.

IMHO, it's better to let this sleeping dog lie.

Razor
IV/JG51 Intelligence Officer

"Good judgement comes from experience, and experience comes from poor judgement"

p1ngu666
01-19-2004, 03:24 PM
id like props to be in the damage model http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif
imagine blowing a blade off a prop, and the poor plane beeing shaken to bits http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif.
or shooting your own prop off on a 109. after someone shot the sync stuff, and u fell asleep on the fire button http://ubbxforums.ubi.com/infopop/emoticons/icon_biggrin.gif

JG14_Josf
01-20-2004, 09:52 AM
What happens with a CSP governor when the throttle is set to an idle yet the plane is flying at speed?

What happens to the prop pitch on a plane with a constant speed governor if the airspeed of the plane is greater than the speed at which the engine thrust can power it?

In an effort to maintain a set rpm when engine power is insufficient; the prop pitch angle of attack will reduce from a higher angle of attack toward a lower angle of attack.

Prop feathering, as far as I understaind it, is when the pilot is able to increase prop pitch beyond the maximum angle of attack to a possition where the prop blades present the least amount of resistance to air flow.

The prop feathered pitch angle will slow a plane down the least and as the prop pitch is turned to flatter or finer settings doesn't the prop drag then become progressively greater?

Going from full throttle in level flight to no throttle in a dive while the CSP prop governor remains set for the highest rpm possible will cause the engine and prop to no longer contribute to forward thrust. How can it? Why would the engine RPM be able to turn at a speed above an idle when the supply of fuel and air is reduced?

If the engine and prop are not producing thrust then the prop is either neutral; i.e. no net thrust and no net drag which is highly unlikely and certainly only momentary, or the prop is producing a drag force.

If the prop blades are anything but feathered then the CSP setting will be dialing in more drag as the blades go flatter.

It also makes sense, to me, that if the engine RPM's are high but not high as a result of burning fuel and air then something must be driving the blades and this force can only be drag and drag slows the plane down.

So, I think, if the problem, in the game, is that a plane with the engine set to idle does not slow down due to increases in the drag force of the prop then this problem includes planes with constant speed props.

Another way of looking at this is to consider what should happen when the throttle is closed, the engine is at an idle, and the plane is still on the runway. What happens to engine RPM as the pilot moves the prop lever fully one way and then fully the other way?

Nothing?

The governor will flatten the prop pitch in an effort to increase RPM. If the engine is less than the governed setting for example if the engine is at 500rpm and the lowest governor setting is 900rpm then the prop will be moved to the full flat pitch stop by the governor.
If the engine is at a 500rpm idle and the prop lever is moved to the highest rpm setting of 2700rpm then the prop remains at the full flat pitch setting. Nothing happens to the prop pitch while the pilot moves the prop lever on the ground with the engine at an idle. There is not enough fuel and air to turn the engine past 500rpm even if the prop were to be taken off the plane. Well it may rev up a little bit, but this effort on my part, here, is to communicate ideas.

How about adding a huge wind tunnel in front of the plane imagined above?

The engine is at an idle, the prop governor is set to the lowest setting say for example 900rpm. The wind tunnel is off, there is nothing available to turn the prop blades any faster than 500rpm so the prop pitch is fully flat.
Now turn on the wind tunnel.
What happens as more and more wind moves around the prop?

Would it be a good idea to tie the plane down?

effte
01-21-2004, 06:12 AM
What happens with a CSP governor when the throttle is set to an idle yet the plane is flying at speed?

The governor will move the propeller to finer pitch to maintain the set propeller RPM.

What happens to the prop pitch on a plane with a constant speed governor if the airspeed of the plane is greater than the speed at which the engine thrust can power it?

It will be at a rather coarse pitch, to keep it at the set RPM. If you bring the speed up way above the design speed envelope, the prop might hit the full coarse pitch stop and be unable to go any coarser. In that case, you have to reduce power to avoid a prop overspeed.

effte
01-21-2004, 06:15 AM
Prop feathering, as far as I understaind it, is when the pilot is able to increase prop pitch beyond the maximum angle of attack to a possition where the prop blades present the least amount of resistance to air flow.

It is when the blades move to or close to their zero-lift angle of attack for a non-moving prop, through operator interaction or automatically.

The prop feathered pitch angle will slow a plane down the least and as the prop pitch is turned to flatter or finer settings doesn't the prop drag then become progressively greater?

Correct.

effte
01-21-2004, 06:19 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Message Body is a mandatory field. You must enter a value for it.

Go Back<HR></BLOCKQUOTE>

And I'll post the rest as soon as someone explains to me how the **** I get around the above.

What a great system this is. I thought they'd switch to a proven board system. I guess that would have made too much sense.

/Fred

effte
01-21-2004, 06:25 AM
Going from full throttle in level flight to no throttle in a dive while the CSP prop governor remains set for the highest rpm possible will cause the engine and prop to no longer contribute to forward thrust. How can it?

I don‚'t see the problem? You stop feeding torque into the prop. It goes to a flatter pitch to maintain the set RPM. This means the angle of attack of the blades get lower and lower. Eventually, the combined lift and drag vector on the blades caused by the airflow over them will point in the direction of rotation. I e, the airflow will pull the propeller and engine around rather than the engine pulling the propeller around.

Why would the engine RPM be able to turn at a speed above an idle when the supply of fuel and air is reduced?

Since the airflow is turning the propeller, as per above. The engine is functioning as a large air pump, providing lots of resistance to movement.

If the engine and prop are not producing thrust then the prop is either neutral; i.e. no net thrust and no net drag which is highly unlikely and certainly only momentary, or the prop is producing a drag force.

What is your definition of neutral here?

If the prop blades are anything but feathered then the CSP setting will be dialing in more drag as the blades go flatter.

As the blades go flatter at a constant RPM and airspeed, they will absorb less torque and provide less thrust. Eventually, they‚'ll start producing drag and turning the engine.

It also makes sense, to me, that if the engine RPM's are high but not high as a result of burning fuel and air then something must be driving the blades and this force can only be drag and drag slows the plane down.

Correct.

So, I think, if the problem, in the game, is that a plane with the engine set to idle does not slow down due to increases in the drag force of the prop then this problem includes planes with constant speed props.

Correct.

Another way of looking at this is to consider what should happen when the throttle is closed, the engine is at an idle, and the plane is still on the runway. What happens to engine RPM as the pilot moves the prop lever fully one way and then fully the other way?

Nothing?

On the ground, the propeller is likely on the fine pitch stops when the engine is on idle so nothing should happen. Leave the RPM lever at the lowest RPM setting and increase the throttle. The RPM will increase initially. When the RPM stops increasing, the blades have come off the fine pitch stops and you will see something happen if you move the RPM lever.

The governor will flatten the prop pitch in an effort to increase RPM. If the engine is less than the governed setting for example if the engine is at 500rpm and the lowest governor setting is 900rpm then the prop will be moved to the full flat pitch stop by the governor.
If the engine is at a 500rpm idle and the prop lever is moved to the highest rpm setting of 2700rpm then the prop remains at the full flat pitch setting. Nothing happens to the prop pitch while the pilot moves the prop lever on the ground with the engine at an idle. There is not enough fuel and air to turn the engine past 500rpm even if the prop were to be taken off the plane. Well it may rev up a little bit, but this effort on my part, here, is to communicate ideas.

Exactly.

How about adding a huge wind tunnel in front of the plane imagined above?

The engine is at an idle, the prop governor is set to the lowest setting say for example 900rpm. The wind tunnel is off, there is nothing available to turn the prop blades any faster than 500rpm so the prop pitch is fully flat.
Now turn on the wind tunnel.
What happens as more and more wind moves around the prop?

The RPM will increase to the set RPM as the wind accelerates. You‚'ll rarely see a propeller in flight on the min pitch stops, even with the engine at idle.

Leadspitter, I have a good grasp on the workings of a CSP/VP, and I fail to see the problem you are trying to communicate. Exactly what is not working right in your opinion?

Cheers,
Fred

IV_JG51_Razor
01-21-2004, 07:34 AM
I think that this thread is about the problems in the sim with the modeling of drag produced (or lack of actually) by the prop when the throttle is at idle. You just don't seem to slow down as much as you'd think you should given that big flat faced fan out there in front of you http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif And the differences between the a/c equiped with CSPs and variable pitch props. It seems as though there is a big difference between the drag modeling of the two.

Razor
IV/JG51 Intelligence Officer

"Good judgement comes from experience, and experience comes from poor judgement"

JG14_Josf
01-21-2004, 12:41 PM
Neutral: When the prop contributes neither thrust nor drag. In otherwords the prop does not effect velocity.

Fred wrote:


Will the propeller be on the min pitch stop during an aerobatic maneuver such as a tail slide, or hammerhead, if the throttle is closed and while the plane is not moving relative to the atmosphere?

Suppose the prop was set for max rpm, the throttle is closed, the wind tunnel is turned off, and therefore the prop is fully fine or flat.

What happens to the prop pitch angle as the wind tunnel increases air flow?

Does the prop pitch stay at full fine until the engine reaches max rpm and then does the blade pitch move?

I think yes, because the force applied to move the blade pitch is controled by engine rpm.

Then what happens to the blade angle once enough wind has been applied to cause the blades to move?

They must move to a more coarse pitch, true?, since they were at the full fine stop before the wind tunnel was turned on and before engine rpm reached a speed where the governor reacted and caused a change in prop pitch.

Does the governor then "search" at a point where just enough wind is applied to cause the engine to rotate at max rpm?

What prop pitch angle creates the most lift as the air from the wind tunnel drives the engine with the prop, full flat, full fine, or a pitch somewhere in the middle?

Is it true that when the prop is at the pitch which generates the most lift caused by the air from the wind tunnel that the prop is then at the setting that causes the most drag?

Fly weight governors in some diesel engines tend to search when unloaded or neutral, so to speak, such as at low or high idle. Fuel flow is inconsistant and causes fluctuations in rpm.

It seems to me that the most drag or greatest lift pitch angle for props driven by wind will not be at the full fine stop, therefore it may be a very dynamic situation when the prop is right at that balance between not enough rpm to move the pitch and just enough rpm to move the pitch.

Thanks for the response, Fred, what would these boards be without the input from those in the know? Certainly much less informative.

JG14_Josf
01-21-2004, 12:47 PM
Cutting and pasting is a not working http://ubbxforums.ubi.com/infopop/emoticons/icon_frown.gif

ucanfly
01-21-2004, 03:36 PM
Overrevving of CSPs are modeled to some extent some of the US planes (P_39, P-40, P-51), but I totally disagree that the CSP should be able to keep 2800 RPM when idling and not in a dive or at high speed. That is just wrong and not realistic

WWMaxGunz
01-21-2004, 07:02 PM
Perhaps while running high rpms with engine at idle in the sim, the resistance of the engine to being driven and the efficiency of the prop to turn that engine are not being factored in? There should be drag and it should not be as much as acceleration since the prop is designed to pull the plane forward.

Still, I've seen many times in articles about why diving prop planes can't get to let alone break mach 1 (by experts, not just guessing) that the drag when thrust is exceeded gets to be the same as a solid disk the diameter of the prop. It's got to be something like that in a steep dive with the engine at idle considering in the record setting power dives the engines were not at idle.


Neal

effte
01-21-2004, 11:37 PM
Will the propeller be on the min pitch stop during an aerobatic maneuver such as a tail slide, or hammerhead, if the throttle is closed and while the plane is not moving relative to the atmosphere?

If it has time to get there, it will hit the min pitch stops again and you will see an RPM drop. Propeller pitch is a function of throttle setting and airspeed.

This is the way to get a non-feathering prop (such as installed on most singles) to stop windmilling if the engine has quit. Lift the nose until the airspeed drops off enough for the prop to not be able to pull the engine around anymore (and hope you don‚'t stall first). Once stopped, it will remain stopped even at somewhat higher airspeeds. This will reduce drag greatly, compared to having the propeller windmill.

Suppose the prop was set for max rpm, the throttle is closed, the wind tunnel is turned off, and therefore the prop is fully fine or flat.

What happens to the prop pitch angle as the wind tunnel increases air flow?

Does the prop pitch stay at full fine until the engine reaches max rpm and then does the blade pitch move?

Yes. As the prop is again able to turn faster than the current RPM setting at the current throttle setting, the CS governor will take the prop off the min pitch stops to keep the set RPM.

I think yes, because the force applied to move the blade pitch is controled by engine rpm.

Exactly.

Then what happens to the blade angle once enough wind has been applied to cause the blades to move?

They must move to a more coarse pitch, true?, since they were at the full fine stop before the wind tunnel was turned on and before engine rpm reached a speed where the governor reacted and caused a change in prop pitch.

Exactly.

Does the governor then "search" at a point where just enough wind is applied to cause the engine to rotate at max rpm?

The governor sets the pitch of the blades to whatever angle will cause them to maintain the set RPM at the given airspeed and throttle setting.

What prop pitch angle creates the most lift as the air from the wind tunnel drives the engine with the prop, full flat, full fine, or a pitch somewhere in the middle?

Maximum power is generally available at the maximum RPM. At one point, propeller efficiency will go down through e g the blade tips going into the transonic region.

I‚'m not sure about what you mean by max lift. Lift is defined as the part of the aerodynamic force perpendicular to the airflow. The airflow, as seen by the propeller blade, will be created by the velocity of the oncoming air and the rotational velocity of the blade itself. The lift generated will be broken down into thrust, pulling the aircraft through the air, and a component causing torque on the propeller. The drag is parallell to the oncoming airflow and will be broken down into torque and drag.

Is it true that when the prop is at the pitch which generates the most lift caused by the air from the wind tunnel that the prop is then at the setting that causes the most drag?

Fly weight governors in some diesel engines tend to search when unloaded or neutral, so to speak, such as at low or high idle. Fuel flow is inconsistant and causes fluctuations in rpm.

It seems to me that the most drag or greatest lift pitch angle for props driven by wind will not be at the full fine stop, therefore it may be a very dynamic situation when the prop is right at that balance between not enough rpm to move the pitch and just enough rpm to move the pitch.

The prop will generate the most drag when windmilling, idle throttle, at the maximum RPM and at whatever pitch it takes to create this situation. If you could get it to a higher RPM, it would generate even more drag from causing the engine to pump even more air. You‚'d be outside the design parameters though and risk overstressing things in the engine and/or prop assy.

ucanfly spake thusly:
Overrevving of CSPs are modeled to some extent some of the US planes (P_39, P-40, P-51), but I totally disagree that the CSP should be able to keep 2800 RPM when idling and not in a dive or at high speed. That is just wrong and not realistic

And on just what factual basis do you build this profound insight? Please tell, and we‚'ll see what can be done to lift the veils obscuring this particular aspect of the Hidden Secret of Constant Speed Propeller Operation.

Cheers,
Fred

effte
01-22-2004, 12:24 AM
As segments of the propeller blades approach sonic speeds, prop efficiency goes out the window.

In theory, I guess you could build a prop with supersonic profiles... http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif But bear in mind the directions of the lift and drag vectors as outlined in my previous post, and the L/D ratios required for the generated thrust to counter the drag, even when only considering the geometry, as the speed picks up.

Cheers,
Fred

[This message was edited by effte on Thu January 22 2004 at 12:01 AM.]

Ugly_Kid
01-22-2004, 01:49 PM
The prop modeling is mighty forgiving. At least the two cases of crossing controls should exist...high MP and coarse pitch, danger of detonation - low throttle setting fine pitch for high rpm prop is braking instead of pulling (airstream driving the prop). The effect should be large, instead of pull there is drag.

Then there are further effects of tip speed going supersonic. Governor hitting stops and prop overrevving. Too bad this was actually what I was expecting from this CEM stuff back then but I can also live without it, I guess. I regret only that the game gives a rather dim view about the control systems used by the Germans and others and the real historical advantages and disadvantages of cockpit load.

IV_JG51_Razor
01-23-2004, 02:58 AM
Does the prop pitch stay at full fine until the engine reaches max rpm and then does the blade pitch move?

Yes. As the prop is again able to turn faster than the current RPM setting at the current throttle setting, the CS governor will take the prop off the min pitch stops to keep the set RPM.

I think yes, because the force applied to move the blade pitch is controled by engine rpm.

Exactly.

Then what happens to the blade angle once enough wind has been applied to cause the blades to move?

They must move to a more coarse pitch, true?, since they were at the full fine stop before the wind tunnel was turned on and before engine rpm reached a speed where the governor reacted and caused a change in prop pitch.

Exactly.

Does the governor then "search" at a point where just enough wind is applied to cause the engine to rotate at max rpm?

The governor sets the pitch of the blades to whatever angle will cause them to maintain the set RPM at the given airspeed and throttle setting

Just to be perfectly clear on this Josef, make sure that you understand that it is engine oil pressure that is actually supplying the force to change the pitch of the propeller blades. The governor, which is connected to the RPM control lever in the cockpit, will meter the oil pressure into, or out of, the hub to achieve the desired RPM until such time as the blades hit their stops at either end. I believe that counter weights in the hub have a roll in all this too, but I'm not too clear as to what exactly. Fred??

Razor
IV/JG51 Intelligence Officer

"Good judgement comes from experience, and experience comes from poor judgement"

JG14_Josf
01-23-2004, 08:47 AM
Razor,

I am pretty sure based upon what someone sent to me on this board that the 109 airplanes used electric motors to drive prop pitch angle.
The controls included a fly weight speed sensing governor driven by engine rotation and electrical switches that turned the electric motor in the appropriate direction.

Effte,


This following question of mine concerned a situation where the engine was not driving the prop, but instead where relative wind from a wind tunnel (or the planes velocity through the air) drove the prop.

What prop pitch angle creates the most lift as the air from the wind tunnel drives the engine with the prop, full flat, full fine, or a pitch somewhere in the middle?

Instead of the wind tunnel example; how would the above question apply to a plane in a dive where the throttle is closed, where the velocity of air drives the prop then which prop angle would the governor stop turning the prop blades to maintain the highest RPM setting? In other words will a full fine prop setting allow for higher forces to turn the engine and pump air or coarse settings?

WB_Outlaw
01-23-2004, 09:01 AM
Some props control pitch with engine oil pressure, some use electric motors. I believe all countries used both types at some point or another.

-Outlaw.

effte
01-23-2004, 11:41 AM
Josf,
the prop will turn the engine faster (generate more torque) in a fine pitch setting. Fine pitch still means higher RPM.

Cheers,
Fred

effte
01-23-2004, 04:21 PM
Blank post due buggy forum software

effte
01-23-2004, 04:28 PM
OK, I decided to run a little test.

Hurricane MkIIc, 50% fuel. Approximate weight 2900 kgs.

I took it up to altitude and then measured the time for a stabilized dive from 1500 m to 1000 m at a constant speed of 300 km/h.

The total energy loss is Wt is 2900*500*g Nm. A local value for g of 9.82 m/s^2 is assumed.

Wt = 14.25e6 Nm

The time for the high RPM dive was 34 seconds.

The time for the low RPM dive was 49 seconds.

The power consumed by drag is the energy loss divided by the time. This gives a drag power of:

High RPM: 418.8 kW = 389.7 hp

Low RPM: 290.6 kW = 561.6 hp

The power difference, representing the loss incurred through propeller drag, is 128.2 kw or 171.9 hp.

Some of those will be consumed by propeller inefficiency and losses in the drivetrain, but a large part of it will reach the engine. How much power is needed to crank an aircraft engine around? If that difference, minus the losses, is the difference between cranking it at low vs high RPM, the model is perfectly valid.

I‚'d say that it is.

If you are looking for an airbrake, you‚'ll be disappointed.

Cheers,
Fred

BlindHuck
01-25-2004, 02:28 PM
If the prop is windmilling, then it is working at a negative angle of attack and producing REVERSE thrust. It is not possible for any amount of windmilling force to spin the crank at redline. A common tactic of the Germans that took Americans new to the theatre in '43 by surprise was the throttle chop. Pilots were instructed to watch the exhaust of the planes they were attempting to get guns on, usually high angle of attack-full power, because if they didn't spot the throttle chop and respond QUICKLY they would overshoot. A favorite tactic used against newbies all the time online (actually, I have yet to get it to work at all, but any day now!).

I have stated it - It is so. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

WB_Outlaw
01-25-2004, 05:07 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BlindHuck:
If the prop is windmilling, then it is working at a negative angle of attack and producing REVERSE thrust. It is not possible for any amount of windmilling force to spin the crank at redline.<HR></BLOCKQUOTE>

BH,
A windmilling prop produces drag, not reverse thrust. Although the effect is the same since drag and reverse thrust act in the same direction, it's not truly reverse thrust. Thrust reversal is only possible by turning the prop the other direction or reversing the pitch.

If the automatic pitch control is working properly then you are correct, however, fixed pitch props or porked pitch controls can easily overspeed the engine. That's why bomber engines that were losing oil had to be feathered before so much oil was lost that the pitch control quit working.

-Outlaw.

effte
01-26-2004, 01:04 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by BlindHuck:
If the prop is windmilling, then it is working at a negative angle of attack and producing REVERSE thrust.
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Affirm on the negative angle of attack, but negative on the reverse thrust, for reasons stated by WB_Outlaw. Reverse thrust = engine feeds torque into propeller, windmill = prop feeds torque into engine.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
It is not possible for any amount of windmilling force to spin the crank at redline.
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No. But it is possible for a finite amount of torque. Coincidentally, torque is just what a windmilling propeller is producing.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
A common tactic of the Germans that took Americans new to the theatre in '43 by surprise was the throttle chop. Pilots were instructed to watch the exhaust of the planes they were attempting to get guns on, usually high angle of attack-full power, because if they didn't spot the throttle chop and respond QUICKLY they would overshoot. A favorite tactic used against newbies all the time online (actually, I have yet to get it to work at all, but any day now!).
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While a non-newbie will get a solid burst in as the distance closes, pull up and grin at suddenly gaining an energy advantage.

Cheers,
Fred

effte
01-26-2004, 01:10 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by WB_Outlaw:
If the automatic pitch control is working properly then you are correct, however, fixed pitch props or porked pitch controls can easily overspeed the engine. That's why bomber engines that were losing oil had to be feathered before so much oil was lost that the pitch control quit working.
-Outlaw.<HR></BLOCKQUOTE>

Later, they (assuming you are thinking of the B17s) were fitted with additional means of feathering a stopped propeller. Frequently, multi-engine propellers are designed in such way that spring action will return the propeller to a feathered state if oil pressure is lost (with an RPM-dependent catch that will stop this on shutdown on recips, so they won't have to turn a feathered prop on starter when starting up).

Works well for single-acting propellers. For dual-acting props where there is no spring, solutions would include separate feathering pumps with an oil reservoir which can only be used for feathering, and counterweights pulling them to a reasonably coarse pitch should the oil be completely lost.

Cheers,
Fred

[This message was edited by effte on Mon January 26 2004 at 12:39 AM.]

JG14_Josf
01-26-2004, 10:25 AM
Effte,

I'm not sure what was shown with your in game tests, particularly the part where the dive speed was kept constant at 300kph.

To give an example of why it appears that prop drag modeling is odd in IL2/FB try diving an FW190A8 straight down into the ground from 3000 feet using the quick mission builder.
Start the session and dive ASAP during each test to limit the variables.

Dive with the engine on at an idle.
Dive with the engine off using the "I" key (engine start/stop toggle).
Dive with the engine off using the magneto's turned off.
Dive with prop on manual.
Dive with prop on Automatic.
Dive with manual 100 percent pitch
Dive with manual 0 percent pitch.

The slowest speed before impact (most drag) occured when the FW190A8 was configured with the engine off ("I" key) and manual prop set to 100. 600kph

The fastest speed and therefore least drag was done with the engine on at idle, auto prop reaching well over 700kph.

Turning the engine off makes a big difference in how fast the FW slows down.

Doing the tests described above a player may suppose that the game adds the prop drag only when the engine is turned off using the engine start/stop toggle or "I" key.

How much drag should an FW190A8 prop generate at 600kph engine on at idle?

I find it hard to believe that a combat pilot flying an FW190A8 would find it very usefull when forcing an overshoot to turn the engine off, such as is the case in IL2/FB.


The real pilots, as far as my reading goes, would not consider turning the engine off during a landing approach. Turning the engine off in IL2/FB makes landings easy compared to trying to land with the engine on as the glide slope then resembles that of a waxed sailplane.