RE: Correcting adverse yaw
 

At the speeds he was initially trying to fly it at a down only traveling aileron would most certaily have produced an instant tip stall if more than a whiff of stick was used. At a slightly higher speed where tip stalling would not be an issue then the wing would have lifted but the model would likely have dragged the nose to the outside/upper side of the turn all while banking into the turn. The final position would have been a tail low drag around the turn until the model straightened itself up since with no dihedral he only used aileron to roll into the turn and back out.

His thinking was to make his ailerons function more as spoilerons. But he didn't allow for the fact that at the angles he was using and the fact that they were not actual spoilers that they would produce a shift in lift rather than just drag. And because of the shift in the angle of attack on the deflected aileron side it left the other side operating in that high lift and high drag region which was enough drag to still produce the AY.

RE: Correcting adverse yaw
 

WoW! This thread has gotten a lot more technical than I had ever imagined. I'm learning a bunch by reading it. I don't want to cause the discussion to end, but I thought that it might be fun to let you all know that I've decided to not change anything as I get my Cub prepared for the upcoming flying season. I'll continue to correct the yaw with a little rudder input as I have always done.
All of the input has been helpful, though it just helped me make up my mind to not change anything. I hope the discussion continues as we have some very intelligent people involved. I'll continue to lurk, though the discussion has progressed to the point that I no longer have enough knowledge to actively participate. My thanks to all of you.

RE: Correcting adverse yaw
 

I can't agree with you there Harry.

I agree with BMathews who said
I've actually found that most science is whatever the particular book's authour felt like saying. Usually they won't say anything wrong but it's not at all unusual for some authours to present one part more fuly while downplaying or managing to avoid some other part

I think maybe that Harry is a victim of one of these New Age theorists who come up with a new theoretical explanation (often quite valid) but they feel compelled to tear down all the older theories so that their New one can be alone and resplendant on its pedestal for universal admiration.
The problem I have with this new theory (which I have read before somewhere) is that, as Harry says, it depends on the notion that "Adverse yaw comes from the rolling motion."

Back in the mists of time a flying instructor demonstrated adverse yaw. The aeroplane (I've no recollection what) was trimmed at some in-between speed and he applied just aileron. As instructed I watched the nose carefully.
AS the aileron was applied the nose yawed towards the downgoing aileron
THEN it started to roll towards the Up aileron
THEN it started to turn towards the Up aileron

The Adverse Yaw existed before the rate of roll existed. I was told by the instructor that in extreme cases the yaw caused by adverse yaw could be bad enough to PREVENT roll in the desired direction as it interacted with the lateral stability (rolling moment due to yaw). The point he was making was that we had to use bootfuls of rudder to help the aircraft into the turn.

I would also like to take issue with Harry's statement The cure is to use rudder to counter the advesre yaw. Use your tx to mix in enough to do the job.

It is best not to use Tx mixing because when turning what is needed is NOT aileron + 10% rudder, held constant.
Especially on something like a glider we need
aileron + quite a bit of rudder to establish a bank angle and turn rate.
Once the bank angle and turn are established, the aileron can be reduced, maybe even to neutral.
The rudder has to be maintained however throughout the turn. Tx mixing cannot achieve this pattern of control input, which is needed on the very aircraft that suffer most from adverse yaw.

I am inclined to agree with tomfiorentino who said I understand that both are correct; ailerons cause yaw and so does the tilting lift components due to roll.

RE: Correcting adverse yaw
 

I don't have anything intelligent to add to the cause side of this discussion, but I do know that the corrective action you've written is correct. On the cub that started this thread,:eek: at slow airspeed, adverse yaw can be so severe that not correcting it with rudder input can cause a stall. The bank, once established does not require any aileron input to maintain it, especially if rudder is being applied. Rudder, on the other hand, needs to be held relatively steady throughout the turn, releasing it only prior to returning to wings level. Mixing rudder with the aileron would only start the correction a touch earlier if I were slow on the left stick. I would still need to release the aileron while holding the rudder until the turn was complete.
What I am interested in trying the next time I have the Cub out is to release all input other than elevator in the middle of the turn. If I understand correctly, theory says that without additional aileron input the adverse yaw should not return, but as I go wings level, I should see yaw towards the inside of the turn. Is this correct?

RE: Correcting adverse yaw
 

I disagree Alasdair! You are mixing two different events together. The need for rudder against adverse yaw during rolling is different to the need for rudder once in the turn. You said that once the bank angle has been established the aileron can be reduced maybe to neutral thus proving that you are no longer talking about adverse yaw. You can't say I am wrong to use tx mixing to counter adverse yaw by giving an example which isn't adverse yaw!!!! There are times when rudder must be held in constantly in straight flight such as single engine prop plane in a climb, and rudder may be needed in the turn in the opposite direction to the turn. None of that denies that rudder may be needed to counter adverse yaw at the time aileron is applied. Using mixing doesn't prevent you from using rudder at other times you know! So it is entirely correct to use coupled aileron to rudder to counter adverse yaw. Don't confuse other rudder requirements such as when established in the turn, with adverse yaw during rolling.

H

RE: Correcting adverse yaw
 

BAe Systems actually, but if you want to think of them as new age theorists, that's your right!

RE: Correcting adverse yaw
 

I confess that I don't know the specific reasons behind adverse yaw. All I know is how to prevent it.

But, I can concur with alasdair on the "demonstration" aspects. I've demonstrated adverse yaw on many occasions to students and I used to say something along the lines of,

"Look straight ahead, over the nose of the aeroplane. Now, when I move the control column to the left, you will see the nose yaw to the right AND THEN, the aircraft begins to roll to the left." There was actually time to say this during the demonstration. Obviously, we would then move on to using the rudder to keep the aeroplane in balance ... at various angles of attack.

The Tiger Moth is extremely difficult to fly, using ailerons without appropriate rudder. Almost impossible.

RE: Correcting adverse yaw
 

Which was one of the points I was making, the Tiger has massive differential yet is renowned for its massive adverse yaw. Aileron differential doesn't cure adverse yaw.

RE: Correcting adverse yaw
 

And don't forget to re-read rmh's comment about an airplane accelerating vertically, and the differences in work. It is very practical.

As is usually the case with many of these discussions, its almost never one thing that causes something else. Just when you think you have isolated a cause and effect someone appropriately chimes in with "not when you are going vertical", or "not when you are in knife-edge", or "not at slow speed, fast speed, low wing loadings...etc.".

I guess we should qualify all comments with "it depends". http://www.rcuniverse.com/forum/js/f.../msn/72_72.gif

RE: Correcting adverse yaw
 

Re you adding elevator too?I know from flying real planes that a t that degree of bank you should be puulling the nose up to maintain altitude.You loose alot of lift in a bank as far as holding the plane up! Hope I was of some help Good Luck

RE: Correcting adverse yaw
 

Can you say top rudder? http://www.rcuniverse.com/forum/js/f.../lightbulb.gif

RE: Correcting adverse yaw
 

Yes, it does all depend on what aircraft we are talking about, what speed it flies and so on.
I have flown all kinds of models, and on jets, and aerobats with symmetrical sections, I have never observed adverse yaw.
I have flown Boing 757, 767, 747 and Lockheed Tristar and HS Trident and never noticed adverse yaw, never used the rudder (except on the ground or asymmetric).
But thinking back to the twin prop HS 748, rudder was used to help the turns and I have a notion that adverse yaw as I already described was present.

So my reply to Harry's statement "Adverse yaw comes from the rolling motion." is that, on a practical level, it is not sustainable without modification.

Adverse yaw has been demonstrated to me (and by bobeagle to others) to be caused by aileron deflection, WITHOUT a rate of roll. Therefore IN THIS CASE the adverse yaw is not caused by a rate of roll so your statement needs modified. You need to include a cause that does not involve a rate of roll, but only an aileron deflection. The yaw is there before the roll.

As for Transmitter mixing, use it by all means to help with adverse yaw, but you will still need to coordinate rudder into the turns. If you need to operate the rudder independantly anyway for coordination, then a fixed mix seems a bit pointless.
A turn can be sustained once the bank angle has been established, with the ailerons returned to neutral so adverse aileron drag cannot be blamed. Indeed I heard that some high aspect ratio gliders need slight opposite aileron to prevent the turn from tightening. The blame for that allegedly goes to the wing on the outside wing of the turn having a higher airspeed than the inner wing, and hence more lift, and more drag. The rudder counters the extra drag of the faster wing.

I am sure there are other ways of looking at it, maybe ways that fit computer modelling better or whatever, but I think it is premature to shoot down the idea that aileron deflection, up on one wing and down on the other, creates unequal drag.

RE: Correcting adverse yaw
 

Oooh, I hope that was tongue in cheek! :D

RE: Correcting adverse yaw
 

<span style="font-size: small"><span><span style="font-family: Tahoma">Sorry but Ihave flown and owned full scale aircraft and the do use differential. A Cessna 150 does not need rudder as much as a Cub because it uses aileron differential. Also because it has less wing. Low wing planes are affected just as much as high wings. Early Piper Cherokee's needs more rudder than the Cessna high winger aircraft. You can not completly rid the need for coordinated rudder in turns because there are other factors such as centrifigal force pusing the nose out requireing rudder to bring it back into the turn. This depends on speed and bank of course. And other factors brought up here as well. But full scale aircraft use differential if only because it decreases the possibility of a spin if it is stalled.</span></span></span>

RE: Correcting adverse yaw
 

Oh God yea..except we don't have a tongue-in-cheek smiley face!

Once again though the statement as made (with models anyway) is usually the case and I was basically ok with it in the context that it was made.You need some elevator in the turn to"keep the nose up".

But pulling the elevator alone in every instance isn't going to get you there and that's what I was getting at.Take three conditions. <u>ONE:</u>Most of the time we bank, pull elevator and head back the way we came. Fine! <u>TWO:</u> A long, gradual sweeping turn is going to require some top rudder to look more natural. Maybe noone cares! <u>THREE:</u> Sometimes we bank, pull elevator too hard and oops...the pavement bites us! I think we all care about those.

Where my head was anyway...

Tom

PS How about the NY Rangers!!!!!

RE: Correcting adverse yaw
 

I have a cunning plan.

Take a small model of an aeroplane ... perhaps made of card ... and arrange it so that it can rotate about its vertical axis on a wire.


Now, the ludicrous part. Stand on the seat of your car, with your body and model sticking out the sun-roof. Have the car driven slowly. (maybe a domestic fan would suffice, if the airflow is smooth-ish)

By altering the wing's angle of attack; and by altering the various aileron throws ... it should be possible to demonstrate that there is asymmetric drag developed by the ailerons. This would be manifest as yaw. The model would be unable to roll, owing to the arrangement of the wire through the vertical axis.



It should also be possible to demonstrate that, for a given A of A, a certain degree of "differential" will lead to a symmetry of drag. Or not.


Maybe.

RE: Correcting adverse yaw
 

On your second point if you mean rudder opposite the turn ie: rt turn lt rudder, to keep the nose from dropping then you are using too much bank angle for the turn rate or not enough elevator for the angle of bank. If you use rudder opposite then you are knife edging ( there is however one time it would be needed, that is if your past the neutral point and have to add opposite aileron to keep it from rolling more, but that would not be on a long gradual sweeping turn.) On your third point again if pulling elevator causes you to dive then you have banked too much, and rudder is not the way to correct.

RE: Correcting adverse yaw
 

Concerning the topic but slightly OT.

How does Y tail and V tail differ in adverse yaw situation with Cup's equivalent ?

RE: Correcting adverse yaw
 

"Top rudder" used to be known as "crossed controls" ... and is a concept which has led to the demise of many an aviator. In essence, the term means the application of, say, Left rudder and Right aileron. Or, the converse.


Basics. There are two requirements for a spin. Firstly, the wing must be at/near the stall; secondly, the aeroplane must be "out of balance" (yawing).


When you "cross controls", you are deliberately flying out of balance. Sometimes, that is done to initiate a sideslip. Sometimes, it is done in the mistaken belief that the nose of the aeroplane should be "held up" in a turn.


In the latter case, you have placed yourself in a very vulnerable situation because ...

1... you are flying "out of balance".
2 ... you are banking and turning; thus, your A of A is increased, placing the wing nearer to the stall.

So, you are initiating the two conditions which are necessary for a stall/spin. And, it would be an "accelerated" stall; therefore, more violent. For instance, a steep right turn can be transformed into an abrupt spin to the left. Very disorientating, especially if you have no idea of why it's happening.



As noted by others, if the aeroplane's nose is dropping, in a turn, the safe recovery is to first unload the wing (ie, reduce the A of A), then use the controls normally to reduce the bank angle.

To summarise ... only very naughty boys use "top rudder".

RE: Correcting adverse yaw
 

Maybe indeed! If that were true, how can you explain an aircraft that is renowned for its differential is also renowned as one of the worst adverse yaw planes (gliders excepted) that you can fly? The Tiger Moth. Huge differential, and huge adverse yaw. Ail Diff does not lead to its symmetry of drag.

RE: Correcting adverse yaw
 

Mmm, though sadly it is one of model flying's more enduring myths - nose drops in the turn, must need top rudder! You can understand why though, at very steep bank angles it seems the rudder has become the elevator and it is counter-intuitive to hold the nose up vertically by using elevator which seems to be operating horizontally at steep banks. I often help fellow fliers who complain their model dives or loses height in steep turns and who are wondering about using rudder, by encouraging them to simply pull back harder and harder. I think few model fliers realise that the amount of pull back goes up exponentially with bank angle, they expect more of a straight line relationship such as double the bank means double the pull whereas the increase in pull must rise faster especially as bank angles become very steep.

It reminds me of a curious problem and my solution to it when flying my Avonds F-104 Starfighter. The normal method of turning is to bank as needed and hold that constant and then pull back enough to keep the nose up and keep adjusting the elevator as required. I find that at many points in the circuit it is better the other way around with the F-104! I give it some bank, pull as hard as I think this turn needs and hold that pull constant and then adjust bank depending on whether it is climbing or diving. The reason is that with its very short span and anhedral, if the F-104 is at the far end of the circuit you can't see the far wing in a turn until it is very steeply banked, leading to over banking or even being beyond the vertical without realising it, at which point pulling back makes it dive and pulling back harder makes it dive even faster which causes a brown trouser moment the first time it happens! It is very hard to judge bank angles in those circumstances so that is why I bank a bit, pull as required and let the climb or dive tell me to roll in our out a bit. I hold on constant ele and nudge the ailerons back and for all the way around those turns.

RE: Correcting adverse yaw
 

Do I understand this phenomena correctly...

http://en.wikipedia.org/wiki/Adverse_yaw

If you have a Y tail plane like LF 2100 ( or the one in my avatar ) the underside rudder increases the adverse yaw ?

RE: Correcting adverse yaw
 

Yes, of course you are right. I understand this and you are probably right about the counter-intuitive part too.As youknow, the problem there would be based on not understanding the changes in the vertical component of lift associated with turning in the first place. Which goes to zero at 90 degree bank. Get your turning work done, then do you knife edge thingy. But there is always a spot where you are doing a little bit of both. A little bit.To much of anything isn't good right!


It reminds me of a curious problem and my solution to it when flying my Avonds F-104 Starfighter. The normal method of turning is to bank as needed and hold that constant and then pull back enough to keep the nose up and keep adjusting the elevator as required. I find that at many points in the circuit it is better the other way around with the F-104! I give it some bank, pull as hard as I think this turn needs and hold that pull constant and then adjust bank depending on whether it is climbing or diving. The reason is that with its very short span and anhedral, if the F-104 is at the far end of the circuit you can't see the far wing in a turn until it is very steeply banked, leading to over banking or even being beyond the vertical without realising it, at which point pulling back makes it dive and pulling back harder makes it dive even faster which causes a brown trouser moment the first time it happens! It is very hard to judge bank angles in those circumstances so that is why I bank a bit, pull as required and let the climb or dive tell me to roll in our out a bit. I hold on constant ele and nudge the ailerons back and for all the way around those turns.

[/quote]

Interesting perspective. Thanks for taking time to add that view.

Tom

RE: Correcting adverse yaw
 

It's to bad you can't see how coordinated your turns are .They have a ball similar to a level.By keeping the ball in the center while turning shows haw coodinated it is? Rudder is usually not needed for shallow turns but should be used in a steeper turns.If you get into a spin don't use airlerons to try and level out or come out of the spin.Use strickly rudder .The spin will tighten by the drag on the inside wing which has less lift in a spin!!

RE: Correcting adverse yaw
 

uh oh....I think some disagree on the notion that the ailerons cause drag which in turn contributes to Adverse Yaw; now we have ailerons causing drag and tightening a spin...http://www.rcuniverse.com/forum/js/f.../cry_smile.gif

Tom