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Question for Instructors

Flying Instructors & Examiners A place for instructors to communicate with one another because some of them get a bit tired of the attitude that instructing is the lowest form of aviation, as seems to prevail on some of the other forums!

Question for Instructors

17th May 2016, 13:36

Join Date: May 2016
Location: Buenos Aires, Argentina
Posts: 5
Question for Instructors

Hi, this is my first thread here, thanks for accepting me. I dont know if this is the right place to write questions of this type, so if someone needs to move this thread to another place please do it. Here goes the question:

During a level turn, once you begin rolling you got different vertical path described by the inner and outer wing, therefore you got different AOAs, related to the roll damping effect and lateral stability. That occurs while you keep your aircraft rolling. Once you stop rolling your aircraft (you stop increasing or decreasing your banks angle) there wont be a vertical motion now, cause even tought your plane is in a CONSTANT angle of bank, it is no rolling at all. So vertical speed at that time doesnt exist, and the only thing that you have is two wings travelling at different speeds but describing the same horizontal path, so there AOA must be the same.
Do you agree with me?.

What Im trying to find out is a reasonable explanation for the fact that in level turns both wings have (or not?) the same AOA.

Regards,

Agus.
19th May 2016, 05:59

Join Date: Jan 2007
Location: San Francisco, California, USA
Posts: 76
Yes, AOA difference between each wing is only changing during rolling motion on turn entry, once rate of turn is established and constant, AOA remains the same for each wing.
If the AOA was not constant during the turn there would be a constant rolling motion to the inside of the turn.

In a few years of flying, you'll look back on this question and ask yourself "why did I even care"! believe me.
20th May 2016, 00:00

Join Date: Oct 2012
Location: UK
Posts: 679
the only thing that you have is two wings travelling at different speeds but describing the same horizontal path, so there AOA must be the same
AOA remains the same for each wing.
If the AOA was not constant during the turn there would be a constant rolling motion to the inside of the turn
For a constant Angle of Bank the Lift generated by each wing must be the same. In a turn the outer wing will be traveling through the air fractionally faster than the inner wing, therefore the inner wing must have a higher Angle of Attack than the outer wing.

Here's one for the Boffins:

In order for an aircraft in a steady, banked, level turn to the left to maintain a constant flying attitude (as seen out of the front windscreen) it MUST, by definition, be continuously Yawing to the left, Rolling to the right and Pitching up.

Discuss...........
20th May 2016, 00:19

Join Date: May 2016
Location: Buenos Aires, Argentina
Posts: 5
"For a constant Angle of Bank the Lift generated by each wing must be the same. In a turn the outer wing will be traveling through the air fractionally faster than the inner wing, therefore the inner wing must have a higher Angle of Attack than the outer wing"

The outer wing does produce more lift because it is moving faster, thats why you have an overbanking tendency, but that doesnt mean it has a greater AOA.

On the other hand, what happens If you maintain a banked turn, cut thrust, and try to maintain altitude? Would the entire plane stall or would one wing fall first?

Last edited by Agus Rosales; 20th May 2016 at 01:41. Reason: I quoted a wrong post.
21st May 2016, 17:09

Join Date: Mar 2014
Location: froggylandia
Age: 71
Posts: 28
@ Agus Rosalex. If you remain coordinated (ball centred) and have a sound airplane (as did yesterday, in my CAP10b/k, en route from to Annecy from Avignon, the two wings stall at the same time. If you are in slightly uncoordinated flight (ball skewed left or right), the plane will snaproll, and you'll be in an incipient spin.

Last edited by formationdriver; 21st May 2016 at 19:21. Reason: typos
22nd May 2016, 02:05

Join Date: May 2016
Location: Buenos Aires, Argentina
Posts: 5
Let me expose something more:
I have never considered the fact that the ailerons surface changes the wing's AOA at that part of it. I mean, if you move the aileron it changes the position of the chord, thus you get different angles of attack.

So, in a 60º bank turn, you will be raising the outer wing's aileron to overcome the overbanking tendency, so this should result in a bigger AOA of the inner wing, in which the aileron is down. At this point, with no thrust and maintaining altitud and attitude during the turn, would the inner wing stall first?

Regards,

Agus.

Last edited by Agus Rosales; 23rd May 2016 at 14:00. Reason: .
26th May 2016, 19:39

Join Date: Mar 2008
Location: in the air
Posts: 46
Originally Posted by Agus Rosales
you have is two wings travelling at different speeds but describing the same horizontal path, so there AOA must be the same.
Do you agree with me?.
No,

They don't have the same horizontal path, and the AOA will not be identical. Does it make any difference? I don't know. Certainly from a flight instruction point of view I would suggest that it is irrelevant.

I'm not even sure if an aeronautical engineer can work out all the factors with 100% accuracy, hence the need for test pilots...

Not suggesting you should not try and understand the underlying physical phenomenon, just be aware your predictions may be wrong
27th May 2016, 13:49

Join Date: May 2016
Location: Buenos Aires, Argentina
Posts: 5
Originally Posted by vh-foobar
No,

They don't have the same horizontal path, and the AOA will not be identical. Does it make any difference? I don't know. Certainly from a flight instruction point of view I would suggest that it is irrelevant.

I'm not even sure if an aeronautical engineer can work out all the factors with 100% accuracy, hence the need for test pilots...

Not suggesting you should not try and understand the underlying physical phenomenon, just be aware your predictions may be wrong
Both wings have different horizontal speeds, this means that the outer wing travels faster in order to cover the same distance as the inner wing, so SAME horizontal path. Imagine two circles. One inside the other, therefore one smaller than the other one. Now place your airplane in a way you place one wing in each circles' border, and now start moving your airplane over the circles.
Both wings will be describing the same path over the circles, despite the outer wing will be doing it faster.

Agus.
27th May 2016, 15:28

Join Date: Mar 2008
Location: in the air
Posts: 46
Originally Posted by Agus Rosales
Both wings have different horizontal speeds, this means that the outer wing travels faster in order to cover the same distance as the inner wing, so SAME horizontal path. Imagine two circles. One inside the other, therefore one smaller than the other one. Now place your airplane in a way you place one wing in each circles' border, and now start moving your airplane over the circles.
Both wings will be describing the same path over the circles, despite the outer wing will be doing it faster.

Agus.
H'mm think it through... If the wings travel at 'different horizontal speeds' and for wings to remain attached to the fuselage, they can't follow an identical path... i.e. if you overlay the two paths they will NOT match.
28th May 2016, 00:17

Join Date: May 2016
Location: Buenos Aires, Argentina
Posts: 5
Originally Posted by vh-foobar
H'mm think it through... If the wings travel at 'different horizontal speeds' and for wings to remain attached to the fuselage, they can't follow an identical path... i.e. if you overlay the two paths they will NOT match.
Maybe I 've made a mistake while trying to explain. From your point of view, you are right, one path is bigger than the other one, that's why they would never match. But what I was trying to describe was the path's angle. You will see that this angle is constant for both wings during the whole path on each, this means that the relative wind will hit both wings with the same angle, so same AOA.
I hope you can understand what I tried to explain here. Anyway, I will wait for you answer and your point of view.
Thanks vh-foobar,

Agus.
28th May 2016, 11:04

Join Date: Mar 2008
Location: in the air
Posts: 46
Originally Posted by Agus Rosales
You will see that this angle is constant for both wings during the whole path on each, this means that the relative wind will hit both wings with the same angle, so same AOA.
Agus.
I would suggest that's not correct either, the AoA won't be and neither will the local slide slip angle. If your looking for a good example of the later, consider why large aircraft often have body gear steering.

Whether this effect is significant I don't know. Sorry not very helpful

I think your question was, though not sure

If you maintain a banked turn, cut thrust, and try to maintain altitude? Would the entire plane stall or would one wing fall first?
Neither, one section of the wing will start to stall before the other, typically the root. But does it really matter? At some point a significant reduction in lateral stability and roll damping will occur. I would suggest this is what really matters.

From a flight instruction point of view you must reduce the AoA.

That's probably enough from me
7th Jun 2016, 04:38

Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 3,496
Level Attitude said:
Here's one for the Boffins:

In order for an aircraft in a steady, banked, level turn to the left to maintain a constant flying attitude (as seen out of the front windscreen) it MUST, by definition, be continuously Yawing to the left, Rolling to the right and Pitching up.

Discuss...........
Not much to discuss.
If the machine did a totally flat turn (no bank) then it is ALL yaw.
If it turned at 90 deg bank, it is ALL pitch up.
A co-ordinated turn, (balanced and less than 90 degrees) then it will involve left yaw and pitch up.

But I can't see the roll - where does that come in?

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