Why is Yaw 2nd effect of Roll? (and explain Trim)
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I think its an interesting topic that isn't 100% clear cut which is why I asked the question in the first place. It's easy to explain on PPL level, but going into it further seems to cause alot of debate.
On a simplistic level, I say that when you roll (turn) the aircraft, the reletive air is now hitting the fuselage and fin which causes the yaw. It just seems that if you pitch up, this yaw doesn't occur but pitching up is not meant to prevent yaw is it?
Blobber 'C & G in Personal Development and Achievement' (Princes Trust)
On a simplistic level, I say that when you roll (turn) the aircraft, the reletive air is now hitting the fuselage and fin which causes the yaw. It just seems that if you pitch up, this yaw doesn't occur but pitching up is not meant to prevent yaw is it?
Blobber 'C & G in Personal Development and Achievement' (Princes Trust)
I say that when you roll (turn) the aircraft......
To get back to basics, we shouldn't be referring to the further effect of roll in any case but the further effect of aileron - Effects of Controls, remember?
If, in straight and level unaccelerated flight, the aileron is displaced and none of the other controls is moved, the aircraft will roll with the result that the lift vector will be displaced from the vertical causing sideslip. The directional stability of the aircraft will cause yaw and, if uncorrected, the aircraft will enter a spiral descent.
Roll => Sideslip => Yaw. What else is there to explain?
BB - No degree, just CFS A1/A2(H)
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If, in straight and level unaccelerated flight, the aileron is displaced and none of the other controls is moved, the aircraft will roll with the result that the lift vector will be displaced from the vertical causing sideslip. The directional stability of the aircraft will cause yaw and, if uncorrected, the aircraft will enter a spiral descent.
Roll => Sideslip => Yaw. What else is there to explain?
Roll => Sideslip => Yaw. What else is there to explain?
However!
Judging from many of the contributions on this thread, what else seems to need explaining is the mechanism for 'correcting the yaw to prevent a spiral descent' (if indeed that is what one does 
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In my mind the secondary or further effect of aileron is adverse aileron yaw.
The effect of being 'banked' is sideslip leading to yaw towards the lower wing, as might occur in turbulence.
If i roll an aircraft from being banked to straight wing level flight does yaw occur?
Adverse aileron yaw does.
What happens on say a MU-2 with wing spoilers for roll contol.
The effect of being 'banked' is sideslip leading to yaw towards the lower wing, as might occur in turbulence.
If i roll an aircraft from being banked to straight wing level flight does yaw occur?
Adverse aileron yaw does.
What happens on say a MU-2 with wing spoilers for roll contol.
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Here we go again with the sloppy terminology. Do you mean roll or do you mean turn? The two are not synonymous - you can roll an aeroplane without turning it just as you can turn an aeroplane without rolling it.
..the aircraft will roll with the result that the lift vector will be displaced from the vertical causing sideslip.
The directional stability of the aircraft will cause yaw and, if uncorrected, the aircraft will enter a spiral descent.
Blobber - Your total lack of uderstanding of the most basic principles of flight is utterly astounding. Please, please tell me that you are not an instructor.
When do you roll and not turn? - In any properly executed slow roll
I think you might be well advised to quit before you make yourself look an even bigger fool.
When do you roll and not turn? - In any properly executed slow roll
I always thought that directional stability creates yaw in the opposite direction [to the roll]
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Mate, you're taking the piss. Go and crawl under your rock you arrogant ****. I believe I have made a mistake in what I have said about directional stability I was thinking of something else, but so what! People are entitled to make a mistake about something about a subject they dont use every day. As for for the roll issue, I think you are just being an arse. I doubt you would talk that that to anyones face, and if you did to me kick **** out of you 
Last edited by blobber; 3rd Apr 2007 at 12:18.
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I have not read this post, cause it bores me……..boot the rudder what happens????????????????????????????????its the basics!!!! the aircraft yaws about the normal axis then it rolls…..every aircraft I have tried does the SAME THING!!
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I have not read this post, cause it bores me……..boot the rudder what happens????????????????????????????????its the basics!!!! the aircraft yaws about the normal axis then it rolls…..every aircraft I have tried does the SAME THING!!
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Now, before anyone bites my head off, I'm not challenging anything that's gone before!! And apologies for prolonging what looks to have been an agonising debate... 
This is one I've always had a bit of difficulty with, and now I have to explain it to babiators.
Ex 4.1 is effects of controls, not effects of attitude.
We all (presumably?) agree that there is no secondary effect of pitching with elevator. Certainly that is what I have been taught to teach. Change in IAS and ROC is a function of the pitch attitude we find ourselves in. We use elevator to achieve a given pitch attitude, but we don't consider what happens as a result of that pitch attitude to be a secondary effect of the controls.
Is not yaw which results from sideslip which results from bank the same thing, ie a result of aircraft attitude rather than a secondary effect of the controls?
In which case, is not Wikipedia's answer (though I hesitate to admit it) mentioned above the most accurate, in that while changing our angle of bank by rolling with aileron, we create sideways lift on the vertical stabliser / fin?
I admit that it would be bloomin difficult to demonstrate. In my experience the yaw is only noticeable once established at an angle of bank with no elevator input.
Come to think of it, none of my babiators have ever shown much interest in why, so maybe it isn't that important. On the other hand none of them seem too interested in flaring at the mo, so that's possibly no guide!
This is one I've always had a bit of difficulty with, and now I have to explain it to babiators.Ex 4.1 is effects of controls, not effects of attitude.
We all (presumably?) agree that there is no secondary effect of pitching with elevator. Certainly that is what I have been taught to teach. Change in IAS and ROC is a function of the pitch attitude we find ourselves in. We use elevator to achieve a given pitch attitude, but we don't consider what happens as a result of that pitch attitude to be a secondary effect of the controls.
Is not yaw which results from sideslip which results from bank the same thing, ie a result of aircraft attitude rather than a secondary effect of the controls?
In which case, is not Wikipedia's answer (though I hesitate to admit it) mentioned above the most accurate, in that while changing our angle of bank by rolling with aileron, we create sideways lift on the vertical stabliser / fin?
I admit that it would be bloomin difficult to demonstrate. In my experience the yaw is only noticeable once established at an angle of bank with no elevator input.
Come to think of it, none of my babiators have ever shown much interest in why, so maybe it isn't that important. On the other hand none of them seem too interested in flaring at the mo, so that's possibly no guide!
Last edited by FL8; 25th Apr 2007 at 22:42.
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We all (presumably?) agree that there is no secondary effect of pitching with elevator.
What more can one say?
Note to ones self: do stay in touch VFE!!!! Again, have I missed something apart from most of this thread?
'K.I.S.S.' anyone?
VFE.
We all (presumably?) agree that there is no secondary effect of pitching with elevator.
If by "secondary effect" you mean consequences, then... well, see above! I would suggest that looking at the consequences is more useful for the student.
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All very interesting. And it does presumably (must stop presuming things!) suggest my FIC instructor was being inconsistent describing the yaw resulting from sideslip as a secondary effect of controls but categorically refusing to say the same about the shrinking sheep and plummetting ASI needle resulting from elev application.
Semantic, I agree, but thought provoking. Thanks for the (control) input.
Semantic, I agree, but thought provoking. Thanks for the (control) input.
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All simplifications loose detail and accuracy, how much you are willing to loose and simplify depends on how much detail the student needs to understand what they are doing. It is fine to simplify for ab initio students roll=>sideslip=>yaw (fin effect) as succinctly stated by BEagle. However for advanced manoeuvres (aeros ie vertical rolls, STOL landing in high tail aircraft, spinning, etc) a more accurate understanding of effects of controls and aerodynamics is required to understand what inputs are required when. As an instructor you must know when to simplify the explanation, but not confuse the simplified explanation with the facts. Instructors should have the detailed, correct understanding required to expand simplified explanations if the students asks for more or requires more for advanced sequences.
While not important for basic student to understand that during a banked turn the aircraft is both yawing, pitching and rolling, instructors certainly should know it, and they should not deny the fact if queried. Otherwise you will finish up with very confused students and perpetuate some of the mis-information evident in this thread.
The original question was "Why is Yaw 2nd effect of Roll?". Answers for basic students are:
Adverse yaw is secondary effect of aileron roll due to increase in drag on wing going up.
Into turn yaw is secondary effect of bank due to sideslip and directional stability.
Expanded answer for inquisitive students to the second "secondary effect" goes something like this:
In a bank the lift vector is tilted sideways. Resolving it into vertical and horizontal components means there is a small vertical component of weight remaining, and a horizontal component in the direction of the bank. When combined these result in a sideslip vector toward the low wing. Directional stability caused by change in AOA on the tail fin results in into turn yaw. Note that increasing the wing loading with back stick to maintain the vertical component of lift equal to weight (and therefore mantain level), still results in a sideslip component, and therefore into bank yaw (and also gives us a pitch rate). The combination of the roll, yaw and pitch result in a turn. In a conventional design (dihedral and/or sweep back for roll stability) in a steady turn (constant rate of roll, pitch and yaw), there is a requirement to hold some into turn aeileron to maintain the AOB. This causes a (slight) adverse yaw, requiring into turn rudder to remain balanced.
More detail is required to explain variations caused by delta wing, high tails, spoilers, canards, high/low wing, etc, but there isn't room here.
Is that clear?
Edit: left out the constant pitch rate in steady turn.
While not important for basic student to understand that during a banked turn the aircraft is both yawing, pitching and rolling, instructors certainly should know it, and they should not deny the fact if queried. Otherwise you will finish up with very confused students and perpetuate some of the mis-information evident in this thread.
The original question was "Why is Yaw 2nd effect of Roll?". Answers for basic students are:
Adverse yaw is secondary effect of aileron roll due to increase in drag on wing going up.
Into turn yaw is secondary effect of bank due to sideslip and directional stability.
Expanded answer for inquisitive students to the second "secondary effect" goes something like this:
In a bank the lift vector is tilted sideways. Resolving it into vertical and horizontal components means there is a small vertical component of weight remaining, and a horizontal component in the direction of the bank. When combined these result in a sideslip vector toward the low wing. Directional stability caused by change in AOA on the tail fin results in into turn yaw. Note that increasing the wing loading with back stick to maintain the vertical component of lift equal to weight (and therefore mantain level), still results in a sideslip component, and therefore into bank yaw (and also gives us a pitch rate). The combination of the roll, yaw and pitch result in a turn. In a conventional design (dihedral and/or sweep back for roll stability) in a steady turn (constant rate of roll, pitch and yaw), there is a requirement to hold some into turn aeileron to maintain the AOB. This causes a (slight) adverse yaw, requiring into turn rudder to remain balanced.
More detail is required to explain variations caused by delta wing, high tails, spoilers, canards, high/low wing, etc, but there isn't room here.
Is that clear?
Edit: left out the constant pitch rate in steady turn.
Last edited by ghostwhowoks; 28th Apr 2007 at 00:14.
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Because the rate of roll in a steady level turn is very small, the adverse yaw associated with it is much less than when applying a large control input to demonstrate adverse yaw. But it is still there, and without designs such as differential ailerons and horns, some slight rudder will be required to remain balanced. Don't confuse this with there is NO rudder required in a steady turn. If rudder is not used, there will be a slight out of bank yaw, however this will be masked by releasing the back stick very slightly to remain level (but the aircraft will not be exactly balanced, and the rate of turn will be slightly lower than for a balanced turn).
If rudder is not used, there will be a slight out of bank yaw, however this will be masked by releasing the back stick very slightly to remain level (but the aircraft will not be exactly balanced, and the rate of turn will be slightly lower than for a balanced turn).
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Why You Have To Retrim - Simple
DONT EVERY FORGET:
POWER + ATTITUDE = PERFORMANCE
IF POWER REMAINS CONSTANT AND YOUR AIRSPEED IS CHANGING:
FOR 90KTS YOU WILL NEED A LOWER NOSE ATTITUDE TO REMAIN LEVEL, AND 80KTS YOU WILL NEED A SLIGHTLY HIGHER NOSE ATTITUDE AND AT 70KTS YOU WILL NEED A SLIGHTLY HIGHER NIOSE ATTITUDE AGAIN TO REMAIN LEVEL.
THE REASON WE TRIM IS TO NOT ONLY RELIEVE LOADS ON THE CONTROL COLUMN BUT TO SET THE REQUIRED AOA(I.E WE SEE ATTITUDE) WE NEED.
SO SIMPLY: AS SPEED CHANGES WE NEED A CHANGE IN ATTITUDE >> WE NEED TO RE TRIM.
HOPE THAT HELPSq!
POWER + ATTITUDE = PERFORMANCE
IF POWER REMAINS CONSTANT AND YOUR AIRSPEED IS CHANGING:
FOR 90KTS YOU WILL NEED A LOWER NOSE ATTITUDE TO REMAIN LEVEL, AND 80KTS YOU WILL NEED A SLIGHTLY HIGHER NOSE ATTITUDE AND AT 70KTS YOU WILL NEED A SLIGHTLY HIGHER NIOSE ATTITUDE AGAIN TO REMAIN LEVEL.
THE REASON WE TRIM IS TO NOT ONLY RELIEVE LOADS ON THE CONTROL COLUMN BUT TO SET THE REQUIRED AOA(I.E WE SEE ATTITUDE) WE NEED.
SO SIMPLY: AS SPEED CHANGES WE NEED A CHANGE IN ATTITUDE >> WE NEED TO RE TRIM.
HOPE THAT HELPSq!
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Sorry Apollo, but I beg to differ. You should never trim to set attitude. You should set the attitude, then trim to remove control forces. Is this just being pedantic? No.
If you use trim to set the 70 kt attitude while doing 90 kts, the aircraft pitching moment due to moving centre of pressure will require you to continue to trim to maintain the attitude as the speed decreases. If you don't the attitude will drop and the airspeed will finish up stabilised well above 70 kts. It is also a slow and inaccurate way to set an attitude, making it inefficient except for very small speed changes.
Remember: change, check, hold then trim!
Cheers
Edit: added old flying dictum
If you use trim to set the 70 kt attitude while doing 90 kts, the aircraft pitching moment due to moving centre of pressure will require you to continue to trim to maintain the attitude as the speed decreases. If you don't the attitude will drop and the airspeed will finish up stabilised well above 70 kts. It is also a slow and inaccurate way to set an attitude, making it inefficient except for very small speed changes.
Remember: change, check, hold then trim!
Cheers
Edit: added old flying dictum