Jerzy Krasinski - TR-4 Cruiser

Aileron Drive Seal

I just finished the project of sealing the aileron drive between the fusealage and the wing. I did not see anybody describing a similar solution so you might consider it for your web site. Attached please find copies of the photographs.

Doing that I discovered that my aileron idler, done according to the manual, was in a wrong place. It was one inch too far forward, and it would not match to the wing's push rod. I think this was due to the fact that the front seat bulkhead was mounted in my plane at station 30 ( I got a fast built kit) while the manual's description of the idler is valid for the bulkhead at station 31. Only at that time I recalled that Ray Clegg wrote some time ago that the idler's description from the manual "does not seem to provide the correct geometry". I read it at some time but I did not know what was the meaning of that statement. Looking at the pictures of his plane I found that he had an identical problem.

To correct the problem I made a ~1 inch wide idler. The threaded rod is connected at the front side of the idler, while the long pushrod from the wing will be connected to the aft side of the idler, providing the necessary 1 inch difference (see Fig 2).

I made a box out of paper/foam/paper ~1/4 inch thick laminate that I got in Hobby Lobby. I got a flat black unpainted paper finish of the paper. I glued the whole thing with 5 minut epoxy, I saturated the paper with epoxy, and I put single ply BID on the seams. I made 2ply flanges around the box (see Fig 1) curing it later in position over a tape. It is all right after it all cured, but I feel that it was not the best idea to use that laminated foam/paper, I ruined one by overheating. If I had to do it again I would use a thin high quality plywood.

I have spent quite a time looking for a correct type of bellows to seal the opening. The problem is that there is a lot of motion of the threaded rod, while the distance from the rod to the front seat bulkhead is small. If you use a small diameter bellows you might get chaffing of the threaded rod against the rubber inside, for a large diameter bellows you get chaffing of the bellows against the bulkhead.

I selected mcmaster neoprene bellows cat# 5298K35 ($35.38). These are 1.5 inch ID , 2 5/8 OD and 10 inches long. I cut the bellows in half and that made two identical shorter bellows for the application. These bellows have large OD and they would chaff against the bulkhead. Luckily, there is plenty of ID, so I mounted them with a small ~1/4 inch or so offset away from the bulkhead as seen in Fig 2 where you can see a small wooden disc (goes inside the cuff) assymetrically attached to the threaded rod.

I glued the bellows to the boxes. I placed the box in place and I drilled a few holes through the flanges and through the fuselage (through the inner fuselage layer only). I increased the size of the holes in the fuselage wall so the heads of a #4 screws would go through. I filled the holes with flox/epoxy, pushed the screws in and after hardening I mounted the box with bellows. Seems to work just fine as seen in Fig 3. There is about 1/8 inch space between the bellows and the bulkhead, and the threaded rod does not chaff against the bellows.

Maybe it could be done with the smaller bellows of 1.25 inch ID and 10 inch length, but I did not check it

Jerzy