Undercamber in aileron

[painless]

Group:

I am continuing to hunt down the cause of a heavy left wing. I am going through the processes as outlined by Van's, and have yet to test fly after repositioning my left aileron which was mounted so that its inboard edge was set lower than the outboard. Now both ailerons are mounted exactly the same.

After checking things over, I have noticed that I have an underchamber in my right aileron. The undercamber is located in the area on the bottom of the aileron where the skin wraps around the leading edge and extends about 4 inches or so aft to where it is riveted to the aileron spar. If I lay a straightedge on this portion of the bottom of the aileron, I see about 1/8th of an inch of space at the apex of the undercamber. Aft of the rivet line where the skin overlaps and is riveted to the aileron spar, the skin is perfectly flat. This making sense how I am describing it??!

Is it possible that this amount of undercamber in my right aileron is creating a slight amount of lift enough to make me roll to the left?

Thanks for any input/advice.


Regards,

[Bob Axsom]

You could adjust the right flap actuator linkage to raise the right flap trailing edge - say 1/16" and see if the flight characteristics improve. Then proceed from there based on the results.

Bob Axsom

[painless]

Thanks Bob. With all the checking and re-checking, I also noted that my left flap was retracted too much by about 3/32"(trailing edge past neutral of the aileron) which could have been rolling me left as well. I adjusted the linkage to bring it down just a tad.

I imagine that all the things I have found *could* be all contributing. Test flights will tell.........


Regards,

[Kevin Horton]

Originally Posted by painless

Is it possible that this amount of undercamber in my right aileron is creating a slight amount of lift enough to make me roll to the left?

The undercamber might be contributing to your problem, but the mechanism is slightly different than described.

The undercamber would be forcing the air to change directions as it tries to follow the contour of the aileron skin. Newton's first law tells us that the air won't change direction unless a force is applied to it. The required force comes from changes in air pressure at different parts of the aileron surface. If the contour of one aileron is different from the other, this leads to differences in the pressure patterns on the two ailerons. This difference in pressure will cause the ailerons to deflect a little bit even when you aren't inputting any lateral stick force. This small aileron deflection causes the aircraft to want to roll, and is felt as a wing heaviness.

I have a hard time trying to figure out whether an undercamber on one aileron would tend to make it deflect up or down. I think this would tend to make the right aileron want to deflect up, which would make a right wing heavy condition. But, this could have been masked by the effect of one aileron hinge being higher than the other, which may have been forcing the ailerons to deflect in the other direction, causing a left wing heavy condition.

[Bob Axsom]

Originally Posted by painless

I also noted that my left flap was retracted too much by about 3/32"(trailing edge past neutral of the aileron) which could have been rolling me left as well. I adjusted the linkage to bring it down just a tad.

Good catch. This is one of those tricky rigging jobs that starts with the big homemade full airfoil template tool with final tweaking to give a perfectly straight line from wing tip to root. In any case, the different flap orientation between left to right you describe will favor lift on the right side and the adjustment you made is in a correcting direction as I'm sure you know from reading your "ah hah" thoughts behind the words.

Bob Axsom