Roll Damping

[uwochris]

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!!

 

[Andy Neill]

May I add to your discussion the notion of dihedral. Due to the dihedral present in most aircraft, as the aircraft is upset in a left roll, the lift component on the left wing becomes more vertical while the lift component on the right wing (already tiled left) becomes less vertical and the vertical component of that lift diminishes.

The other points you raise concerning induced drag can be expained away by accepting the magnitude each element plays in the overall effect. In a pilot commanded left turn, the increased AOA of the right wing and decreased AOA of the left wing resulting from aileron movement overcomes the inherently self righting features of a descending left wig with a positive dihedral.