The pin goes through the hole in the slider in the Tom Morris control horn that is held in place by the cap screw noted at the bottom of the clevis. In this photo it is not tightened yet and the slider is all the way to the bottom (longest position).
I chose this solution because I think putting access holes on both sides of the fuselage weakens an already fairly weak and relatively heavily loaded section of the fuselage (torsionally), in a place where torsional stiffness is important!
Other opinions may vary!
Randy Cuberly
I should have been building with such adjustability features long ago. Only recently did I start due to the frustration of trying to get everything lined up properly: stab chord in-line with wing chord, no tilt in stab when viewed head-on, hinge line parallel to flap hinge line, etc. Even if I did get it very close, I usually needed some elevator adjustment relative to flap position.
One reason I avoided it was that I shared the concern about weakening the fuselage with cut-outs under the stab. But, I felt the adjustability feature was necessary and I would hope for the best. I put a radius on the corners of the openings and I added some 1/32 ply to the inside surface around the openings. I put openings on each side since I wanted the easier access. I am glad I put access on each side.
So far I have seen no indication that the hatches have caused any weakness in the aft fuselage. I do not have hundreds of flights on the one plane that I fly the most but it appears to be holding up.
I use an aluminum clevis that I can make myself. Or, I sometimes have a machinist make them if I have no time or desire to mess with it. I use a conventional horn. That is, no slider for adjusting elevator deflection with respect to flap deflection. I can only adjust the length of the pushrod by rotating the clevis. So far this has proved to be enough but I might look into a slider feature as well.
A turnbuckle is probably the ideal way to go since it gives unlimited adjustment. And, you do not have to remove any pins. With a clevis, the smallest adjustment is a half turn. How much that affects the elevator position is a matter of the horn throw and the thread pitch.
For the pin I use a piece of 3/32 wire with an "L" bend on one end and a wheel collar on the other. I worry about the collar vibrating off but I check periodically and it has not loosened. Maybe a better way is to drill a small hole in the pin and slip a piece of safety wire thru it and twist the safety wire ends. That is, if you can get in there to do that.
Even with two hatches access can be a bit of a hassle. But, once you have it set, you might not have to do get in there again.
Topic: Adjustable elevator control linkage (Read 4080 times)