Pyro: how is prop drag modelled?

[StSanta]

I heard Pyro or HiTech say that modelling this was quite complicated. Now, I've heard several definitions of prop drag and they've differed some, so if anyone in the know would want to share the real definition, I'd appreciate it.

Someone said prop drag happens when the prop doesn't provide more thrust, but instead drags the plane. That would mean it should happen at quite high speeds. Another definition was regarding feathered/non feathered props when out of fuel.

What has me wondering is the behaviour of the 109G10 - HTC hasn'ytt made any changes to the FM, yet it is very different from what it used to be - accelerates slower, yinks to the left a little after vertical input and is a little more stall prone. It is especially noticeable at mid range speed of 200-300mph.

So could anyone explain what exactly it is, and could Pyro tell me how he and HT have modelled in AH? I sense something is not quite right if we go according to the two definitions I have heard, which might be totally wrong.

<S!>


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StSanta
JG54 "Grünherz"

[Udie]

 Well I know I'm defenately not the one to answer this, but since my 2nd to oldest cousin on my mohter's side is going for his phd in aerospace engineering at Texas A & M, I'll give it a shot  

 I think the drag is there constantly.  Regardless of thrust, which I believe is a product of engine output and prop angle.  Reduse the prop angle and reduse the drag, but also reduse the thrust because the prop doesn't grab as much air. So I think all planes should accelerate a bit slower after they added prop drag. There was no drag before, now there is, hence the slower acceleration. Also, the planes slow down alot faster because of it too  

 Not bad for a highschool drop out eh? I think I answered it, any of you physisist want to back me up?  

Udie

[This message has been edited by Udie (edited 07-31-2000).]

[Jigster]

 

Originally posted by StSanta:
I heard Pyro or HiTech say that modelling this was quite complicated. Now, I've heard several definitions of prop drag and they've differed some, so if anyone in the know would want to share the real definition, I'd appreciate it.

Someone said prop drag happens when the prop doesn't provide more thrust, but instead drags the plane. That would mean it should happen at quite high speeds. Another definition was regarding feathered/non feathered props when out of fuel.

What has me wondering is the behaviour of the 109G10 - HTC hasn'ytt made any changes to the FM, yet it is very different from what it used to be - accelerates slower, yinks to the left a little after vertical input and is a little more stall prone. It is especially noticeable at mid range speed of 200-300mph.

So could anyone explain what exactly it is, and could Pyro tell me how he and HT have modelled in AH? I sense something is not quite right if we go according to the two definitions I have heard, which might be totally wrong.

<S!>

Normally prop drag is not really noticable until the pilot pulls his throttle back and the prop is actually spinning slower then the air moving through it, and thus it creates alot of parasitic drag because the prop is making virtually a porus wall that the air must flow through.

It does effect acceleration though, because it is always producing some drag, and I think it actually increases P-factor.

- Jig

[Lizard3]

I hate it when that happens  

[StSanta]

Well, if it shouldn't be that noticeable, I wonder why it has changed the 109 fm quite much?

Hm, maybe I am missing something.



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StSanta
JG54 "Grünherz"

[buhdman]

I just wanted to ask this question.  After talking to a pilot of single-engine planes, he stated that standard procedure for engine failure is to bring the nose up until the prop stops windmilling to lessen the drag.  Will we ever see this?  I know I've tried to get the prop to stop but it just keeps on trucking.

Thanks!

buhdman, out

[Jochen]

Hmmm, maybe I do something wrong but I'm doing great on G-10! I have noticed the nose slew left/right on nose pitches up/down but I haven't bothered me too much.

I also think that if G-10 accelerates slower it also should climb slower and that would be quite easy to notice. Hmm, on the other hand, during acceleration prop goes trough many airspeeds unlike in climb where prop works on quite constant airspeed.

The truth is out there.

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jochen
Jagdflieger JG 2 'Richthofen' Aces High
Geschwaderkommodore (on leave) Jagdgeschwader 2 'Richthofen'  Warbirds

T-34/76 to Aces High!

Ladysmith wants you forthwith to come to her relief
Burn your briefs you leave for France tonight
Carefully cut the straps of the booby-traps and set the captives free
But don't shoot 'til you see her big blue eyes

[StSanta]

Jochen:

Hm, you're probably right. I do ok in G10 now again, after having abandonded it for the A5. But man, it takes *time* to get reused to the G10 - it has some rather odd qualities  .

I guess we might (or might not) learn more about how prop drag is modelled.



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StSanta
JG54 "Grünherz"

[Fishu]

I have only couple times flew 109G10 in testing purposes on MA, but I didn't personally see any problems, but that I couldn't adjust propeller pitch after engine was dead.
In offline I noticed that 109G10 can now do immelman pretty easily right after takeoff, what it didn't do like now in the past versions. (stall limit lower or something?)

Buhdman, you can lessen drag a bit by adjusting prop pitch, but you must do this before engine is knocked out, or you can't adjust it anymore.

[Renfield]

Wow - some big misconceptions here.

P-factor - has nothing to do with prop drag. P-factor is when the airplane itself is at a high angle of attack (i.e. slow flight, on takeoff, heavy) and the plane of the prop arc is not 90 degrees to the apparent wind (the airplane path). Picture a taildragger accelerating down the runway - the nose is high at first. If the pro rotates clockwise as viewed from the pilot seat, the blades on the right side of the plane will be at an effective higher pitch and take a bigger bite of air than the blades on the left side. This causes the airplane to veer to the left. It has nothing to do with prop drag, windmilling, etc.

There is no prop drag the way it seems others are describing it when the engine is throttled up. The only drag there is is that of rotation which produces a reaction that tries to rotate the airplane opposite to propeller rotation along the airplane longitudinal axis. This drag is strictly the drag of trying to move something through the air. As long as the prop is producing thrust, it is not slowing the plane down. Even if it is just a teeny amount, it won't be prop drag that slows the plane. But please note that I said as long as the prop is producing thrust.

When the engine quits or is throttled back to where it is driven and not driving is another story. Then prop drag gets real. Higher pitch settings (closer to feathered) will be better and should produce less drag.

But P-factor is completely different and has nothing to do with prop drag. Same thing for the prop gyroscopic effect that produces a force 90 degrees later (i.e. lift the tail on takeoff and the nose tries to swing left).

[Fishu]

 

Originally posted by Renfield:
Wow - some big misconceptions here.

P-factor - has nothing to do with prop drag. P-factor is when the airplane itself is at a high angle of attack (i.e. slow flight, on takeoff, heavy) and the plane of the prop arc is not 90 degrees to the apparent wind (the airplane path). Picture a taildragger accelerating down the runway - the nose is high at first. If the pro rotates clockwise as viewed from the pilot seat, the blades on the right side of the plane will be at an effective higher pitch and take a bigger bite of air than the blades on the left side. This causes the airplane to veer to the left. It has nothing to do with prop drag, windmilling, etc.

There is no prop drag the way it seems others are describing it when the engine is throttled up. The only drag there is is that of rotation which produces a reaction that tries to rotate the airplane opposite to propeller rotation along the airplane longitudinal axis. This drag is strictly the drag of trying to move something through the air. As long as the prop is producing thrust, it is not slowing the plane down. Even if it is just a teeny amount, it won't be prop drag that slows the plane. But please note that I said as long as the prop is producing thrust.

When the engine quits or is throttled back to where it is driven and not driving is another story. Then prop drag gets real. Higher pitch settings (closer to feathered) will be better and should produce less drag.

But P-factor is completely different and has nothing to do with prop drag. Same thing for the prop gyroscopic effect that produces a force 90 degrees later (i.e. lift the tail on takeoff and the nose tries to swing left).

In the game, if your RPM is in the maximum and you idle engine, speed loss is alot worse than when you have changed RPM to minimum..
It is tested.

When engine dies and its on maximum RPM, your plane begins to remind like flying rock and slow down if you dont pitch down, but if you have minimum RPM just before it dies, you can glide ALOT further.

(note; I am talking about in game in earlier post and now)

[Jigster]

 

Originally posted by Renfield:
Wow - some big misconceptions here.

P-factor - has nothing to do with prop drag. P-factor is when the airplane itself is at a high angle of attack (i.e. slow flight, on takeoff, heavy) and the plane of the prop arc is not 90 degrees to the apparent wind (the airplane path). Picture a taildragger accelerating down the runway - the nose is high at first. If the pro rotates clockwise as viewed from the pilot seat, the blades on the right side of the plane will be at an effective higher pitch and take a bigger bite of air than the blades on the left side. This causes the airplane to veer to the left. It has nothing to do with prop drag, windmilling, etc.

There is no prop drag the way it seems others are describing it when the engine is throttled up. The only drag there is is that of rotation which produces a reaction that tries to rotate the airplane opposite to propeller rotation along the airplane longitudinal axis. This drag is strictly the drag of trying to move something through the air. As long as the prop is producing thrust, it is not slowing the plane down. Even if it is just a teeny amount, it won't be prop drag that slows the plane. But please note that I said as long as the prop is producing thrust.

When the engine quits or is throttled back to where it is driven and not driving is another story. Then prop drag gets real. Higher pitch settings (closer to feathered) will be better and should produce less drag.

But P-factor is completely different and has nothing to do with prop drag. Same thing for the prop gyroscopic effect that produces a force 90 degrees later (i.e. lift the tail on takeoff and the nose tries to swing left).

More drag on one side of the prop then the other because of angle to relative wind. I doubt this would happen with a varible pitch prop, because the most of the time the blades flatten out during engine deceleration producing a more equal area then a fixed pitch.

Also the entire prop is not producing thrust, the sections that connect the lift surfaces to the hub are normally roundish and do produce drag, especially the flatter sections on props that are not lift surfaces like the Hamilton standards. For that reason there is always drag on any surface that is not producing thrust, and the lift-surfaces does produce drag but this meerly reduces it's thrust so I guess it could be said that a prop produces no "drag" because of overwhelming thrust.

- Jig

[Renfield]

Maybe I should have been careful to say "net" thrust and "net" drag. Just like a wing, lift is not produced all across the surface and is disturbed at the root.

[Renfield]

OK, maybe at very flat pitch moving very fast down the runway, one side might go into a no net lift (thrust) situation, but I doubt it. I'd bet one side is just producing more thrust than the other but both sides are working to pull the plane forward and neither is trying to slow it (i.e. drag).

[Jigster]

 

Originally posted by Renfield:
OK, maybe at very flat pitch moving very fast down the runway, one side might go into a no net lift (thrust) situation, but I doubt it. I'd bet one side is just producing more thrust than the other but both sides are working to pull the plane forward and neither is trying to slow it (i.e. drag).

There is always one side pulling harder then the other, I was just pointing out that the side with the lesser thrust as more potential for more drag (because of the angle) and would increase the effect of P-factor slightly.

Perhaps if the prop was at 1/3 degree pitch from flat, and the nose of the plane was at 89 degrees from relative wind one side would not pull...but I'm not going to try it  
Didn't mean to imply one side wasn't pulling  

- Jig