Differential ailerons again

[Mark Kramer]

Something popped up on my screen and said ,what I was reading was old,and that I should start a new topic. I like the idea of differential ailerons. Found a drawing on the old pages which had the aileron arm, I’ll call it, canted over out of square to 10 degrees. I cut out my belcranks to those drawings. Before drilling my struts, I made a jig to see what happens. The first pic sets them up the way I assumed was correct. The 10 degree aileron arm tipped fwd. Now move the cable to stick arm and the aileron arms travel exactly the same distance in both directions. No differential action. Now set them up like the second pic and you get some differential movement. It’s exponential, the more you move it , the greater the differential movement. The problem with the 2nd setup is that it also provides uneven movement in the cables from the stick to belcrank. Tightening and loosening effect. Not good. Would love to hear some opinions on what I am missing here.

[Kamcoman77]

Try setting up your test linkage like this and see what happens. The portion of the bellcranks the cables attach to must be parallel to keep your cables reasonably snug.

[Mark Kramer]

Ok, think I have this figured out. You are absolutely correct in that the cable attach points must be parallel to each other. Its the only way the cables maintain constant tension. My mistake was I was measuring the travel of the aileron connection point, the hole in the arm, how much it moved in the arc of the circle it travels in. I should be measuring that connection point, the hole in the arm, how much it travels in a 90 degree direction from the strut centerline, not it’s travel in an arc. The 90 degree direction is how much it will push or pull the aileron horn. Flipping the arms over, pointing rearward towards the ailerons provides the same amount of differential, but in the wrong direction, more down than up. So they must angle the 10 degrees forward. I am so happy when someone responds to a question, as it helps me understand things
Thanks