Roll Damping Contradiction

[chris]

Hey guys,

I have a question in regards to roll damping:

I realize that if there is a gust so as to lower one wing, that wing will face a higher AOA (as it lowers, the relative wind shifts, coming up at the wing more from below), and thus will produce more lift relative to the upgoing wing. This will restore the straight and level condition.

This is how it's explained in several books. It appears to make sense, but I see something contradictory in it, and I would like some feedback.

Now, when we want to bank the aircraft to the left, we move the yoke left. This lowers the aileron on the right wing and raises it on the left. Now, the right wing is supposed to be at a higher AOA because of the lowered aileron, which means it will be producing more lift, allowing the a/c to bank.

It just seems weird to me... in this case, the upgoing wing is supposedly at a higher AOA, while in the classic roll damping example, it is the downgoing wing that faces the higher AOA.

It also seems that the wing at a higher AOA will produce more induced drag, which would cause yaw. Aileron drag is clearly present at the initial stages of a bank, so the upgoing wing must be at a higher AOA. However, why doesn't aileron drag come into play in the roll damping example? At least it doesnt appear to be mentionned in any books.

Well, I hope someone can cure this confusion of mine.

Thanks in advance.

ps- tonight is the last day of classes at University for me! I will finish at around 8:30pm, then I will go watch some hockey... go wings go!! go sens go!!!

 

[MattB]

Devils Devils Devils

 

[SteveC]

[ QUOTE ]
...Now, when we want to bank the aircraft to the left, we move the yoke left. This lowers the aileron on the right wing and raises it on the left. Now, the right wing is supposed to be at a higher AOA because of the lowered aileron, which means it will be producing more lift, allowing the a/c to bank.

It just seems weird to me... in this case, the upgoing wing is supposedly at a higher AOA, while in the classic roll damping example, it is the downgoing wing that faces the higher AOA.

[/ QUOTE ]
In the roll damping model it is the action of the wing descending that causes the change in AOA.

In the banking model, you change the angle of attack by changing the cord line (from the front edge of the wing to the back end of the aileron) by lowering the aileron. This increases the *effective* angle of attack of the wing. When the wing begins to move up in response, the relative wind shifts, causing a decrease in the AOA, but not enough to counter the increased AOA caused by the cord line shift (i.e. aileron movement).

Confusing enough?

[ QUOTE ]

It also seems that the wing at a higher AOA will produce more induced drag, which would cause yaw. Aileron drag is clearly present at the initial stages of a bank, so the upgoing wing must be at a higher AOA. However, why doesn't aileron drag come into play in the roll damping example? At least it doesnt appear to be mentionned in any books.


[/ QUOTE ]
No aileron drag if you don't displace an aileron.

(Note to self, you answered that one pretty off-the-cuff. Let's see who finds the holes....)