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No adverse yaw?

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MtrHedAP

Lurker
Joined
May 17, 2005
Posts
52
If you do an aileron roll while the airplane is unloaded is there adverse yaw? I went up for an intro to aerobatics and that is what he told and showed me. I am trying to wrap my head around this. Since the lowered aileron creates more lift and drag, and causes the airplane to roll, i dont see why it matters if the aircraft is unloaded or not there would still be adverse yaw.

Anybody able to clarify?
 
adverse yaw is still there but is less visible because the when the airplane is "unloaded", ZeroG, the angle of attack is as close to 0degs as its ever going to be. so with a 0 deg angle of attack (or 0 Alpha for the brits) both ailerons are equaly effected.

the above is only 100% true if the wing is completly semetrical and the ailerons move up as much as they do down. but even with an unsemetrical wing and ailerons that move up say 12 degs and down 9 degs the principal is the same.

Clear as mud?
 
Ok thanks. That clarifies some things, it does make sense. By the way it was in a Pitts and he took me for a hell of a ride. I had a real good time and definately started to grey out at times.:eek:
 
Another way to look at this: In order to have adverse yaw the wing must be creating lift. If you unload the wing to zero lift........ it want be there.
On a vertical line (up or down) you have no wing lift and no adverse yaw. If you do get adverse yaw when vertical, then you not at zero lift or perfice vertical.
If the wing is not creating lift theres no HP air on the bottom side....so the down going aileron has the same amount of drag as the up going aileron.
The wing must be creating lift to get adverse yaw.
 
Another way to look at this: In order to have adverse yaw the wing must be creating lift. If you unload the wing to zero lift........ it want be there.
On a vertical line (up or down) you have no wing lift and no adverse yaw. If you do get adverse yaw when vertical, then you not at zero lift or perfice vertical.
If the wing is not creating lift theres no HP air on the bottom side....so the down going aileron has the same amount of drag as the up going aileron.
The wing must be creating lift to get adverse yaw.

Anytime an aileron is deflected you are creating lift, that is how an aileron works (local changes in angle of attack). The ailerons on a Pitts deflect more in the up direction than in the down direction (at least visually, I have never measured it). Therefore even at zero lift, you will still have some adverse yaw. It may not require much attention, but I'd bet if you are doing vertical rolls, you are good enough to counteract it instinctively.

My question is: Why was your instructor talking about this on an intro flight? :eek: If you end the slow roll off heading, chances are you need (more) opposite rudder through the first three quarters of the roll. The roll should be uncoordinated. Its all about how it looks to the judges...
 
I think he was talking about an aileron roll, or balistic roll. your correct about the local change in angle of attack but un like in level flight the 0 alpha means no high press air under the wing. so when both ailerons are deployed neither gets any high press air and neither gets any low press air. the lack of the difference at 0 alpha = no adverse yaw. the only way you can get adverse yaw at 0 alpha is when the airplane is set up so the ailerons move in one direction more than the other. say the left aileron deflects upward 10 degs and the right deflects down only 7 degs. the only "adverse yaw" would be a function of the extra drag produced by those 3 degs of difference. this is not really adverse yaw in the true sence though, more just differences in wing drag.

this kinda talk on an intro flight is OVERKILL. just go fast, pull up, unload, stick left, give a yah hoo, and recover.
 
your correct about the local change in angle of attack but un like in level flight the 0 alpha means no high press air under the wing. so when both ailerons are deployed neither gets any high press air and neither gets any low press air.

We are definitely splitting hairs, but the ailerons change the camber of the wing, which creates lift. If you are exactly at zero lift, one aileron will be creating lift in one direction, and the other aileron will create lift in the other direction. A change in lift equals a change in drag - specifically induced drag. Differential drag from one wing to the other is the definition of adverse yaw. Being at zero lift doesn't stop adverse yaw.

My brain hurts...
 
Most aerobatic instructors, that I know, do teach this on the first ride.
They will express that to do a slow roll, that scores well, you must use both rudders and elevator.
For a first roll it's a balistic roll because it's simple. The aircraft does not yaw - it just finishes more nose down than it started.
 
Interesting thoughts from everybody. I did not think it was too much to learn on an "intro" flight. I am not really interested in learning aerobatics at this time I just wanted to go on a good ride. Afterwards it got me thinking as I am a instructor and I always teach adverse yaw anytime ailerons are deflected, so I guess I was wrong in this case. So is it just action - reaction in this case for the ailerons?
 
I we need an aerodynamic physicist stat. d.fitz you are a formitable opponent, but the battle has already started.
...the ailerons change the camber of the wing, which creates lift. If you are exactly at zero lift, one aileron will be creating lift in one direction, and the other aileron will create lift in the other direction...
lets think about this. d.fitz is very correct that the change in camber creates lift and drag. duh. but the change in camber and there for lift and drag on one wing is going to be equal to the change in camber, lift and drag on the other wing. lets put it in to numbers (that may be very far) off to show my point. At 0G (and 0 alpha) a crazy half drunk "stunt" pilot punches the stick left. this changes the relaive alpha of the left wing to -2degs and changes to relitive alpha of the right wing to +2 degs. the net of the alpha change is 0 degs( -2 + +2=0 ) back to where we started. because there is no difference in alpha between the two wings there is no more lift or drag on one side of the airplane. and dare I say it... no adverse yaw. Gulp.
ps my iespell is not working and my computer is doing the thing where it deletes letters when you try to add some to the text. so deal with it.
 

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