What causes the yawing tendency with change in power settings?

[JozMk.II]

When changing power settings in straight and level flight, what causes the Mustang to want to yaw? I don't think it's P-factor, since P-factor shouldn't take effect in level flight; and I don't think it's torque, since torque is responsible for rolling tendencies, not yawing tendencies. The only other possible cause, I believe, is the propeller-induced slipstream that curves around the fuselage of the Mustang and strikes the vertical stablizer.

 

Is my assessment correct?

[WildBillKelsoe]

You are forgetting the wind.

[Anatoli-Kagari9]

It's mostly slipstream, and the asymmetry with which the wings and fuselage are "Hit" by the spiraling flow created by the prop.

 

On a CW rotating prop you can easily make a sketch and see how it hits the left side of the fuselage, as well as of the vertical fin & rudder, and the underside or the left wing to (and the upside of the right wing) thus helping to counteract roll due to torque.

 

Roll moments caused by torque, even if counteracted by asymmetric slipstream under most flight situations, can nonetheless create yaw (roll-induced yaw).

 

P-factor on S&L flight is not a factor there (well, it would be if we were talking MSFS where we have to use it to overcome the absence of proper slipstream simulation....).

 

There are other interesting pictures in the net:

 

- Like this one

Edited March 8, 2013 by jcomm

[Yo-Yo]

When changing power settings in straight and level flight, what causes the Mustang to want to yaw? I don't think it's P-factor, since P-factor shouldn't take effect in level flight; and I don't think it's torque, since torque is responsible for rolling tendencies, not yawing tendencies. The only other possible cause, I believe, is the propeller-induced slipstream that curves around the fuselage of the Mustang and strikes the vertical stablizer.

 

Is my assessment correct?

 

Does level flight goes with zero AoA? If no, there is P-factor always.

By the way, the slipstream effect becomes less noticable with speed, P-factor depends on AoA and not so dependable on speed.

 

But all side effects diminish with the speed because of increasing stabilising effect of the airframe due to increased dynamic pressure.

Edited March 8, 2013 by Yo-Yo

[Anatoli-Kagari9]

But all side effects diminish with the speed because of increasing stabilising effect of the airframe due to increased dynamic pressure.

 

And this is what fails to be correctly modelled on about every sim I have used, with the exception of DCS :-)

 

I was assuming he says S&L = Zero geometrical AoA... Of course slipstream or any other prop effects are reduced when the q in q * CL * S becomes the dominant factor...

 

I wish other sim maker could learn, and implement, such a BASIC concept :-/

 

Well, at least "the q effect" is acceptably modelled in MSFS, and in FlightGear 2.10 with JSBsim too, probably in Aerofly FS too, although all fail to model slipstream effects and asymmetry...

Edited March 8, 2013 by jcomm

[Yo-Yo]

And this is what fails to be correctly modelled on about every sim I have used, with the exception of DCS :-)

 

I was assuming he says S&L = Zero geometrical AoA... Of course slipstream or any other prop effects are reduced when the q in q * CL * S becomes the dominant factor...

 

I wish other sim maker could learn, and implement, such a BASIC concept :-/

 

Well, at least "the q effect" is acceptably modelled in MSFS, and in FlightGear 2.10 with JSBsim too, probably in Aerofly FS too, although all fail to model slipstream effects and asymmetry...

 

Frankly, the P-factor is a result of uneven AoA at blades situated at opposite sides of prop disk, so it's due to the vector sum of incoming air and blade linear velocity due to rotation. So even if you reduce plane AoA to maintain 1 G flight when the IAS grows P-factor remains almost the same (I can not say now exactly how constant is it but as far as I remeber my calculations it is significant degree).

[JozMk.II]

And this is what fails to be correctly modelled on about every sim I have used, with the exception of DCS :-)

 

I was assuming he says S&L = Zero geometrical AoA... Of course slipstream or any other prop effects are reduced when the q in q * CL * S becomes the dominant factor...

 

I wish other sim maker could learn, and implement, such a BASIC concept :-/

 

Well, at least "the q effect" is acceptably modelled in MSFS, and in FlightGear 2.10 with JSBsim too, probably in Aerofly FS too, although all fail to model slipstream effects and asymmetry...

 

What are these three variables, q, CL, and S?

[Anatoli-Kagari9]

q = dynamic pressure

CL = coeficient of lift

S = wing planform area

 

https://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/lift_formula.html bearing in mind that q = 1/2 * d * v^2, d being the air / fluid density in kg/m^3

Edited March 8, 2013 by jcomm

[Exorcet]

I don't think it's torque, since torque is responsible for rolling tendencies, not yawing tendencies.

Roll leads to yaw. They're coupled. Rolling reduces lift on one wing, increases it on the other. This reduces drag on one wing and increases it on the other.

[WildBillKelsoe]

I think it's predominantly torque of engine. OP asks with "change of power setting"

[Der_Fred]

It's actually all the forces, to varying degrees. You have to think in 3D with each change of control that you apply.

 

Simple example: If you pull back on the stick.

 

=> Higher AOA = More drag = You slow down = more Propwash and torque effects = more yaw ... dah dah dah.. you stall and spin.