23-05: Aileron Bellcrank

The aileron bellcranks were a bit of a fun exercise. The plans are fairly straightforward - they are essentially a bronze bushing which is bolted and clamped between 2 aluminium brackets bolted to the spar. The bellcrank has an axle tube which rotates around this bronze bushing. The steel tube needs to be very slightly shorter than the bronze bushing so it can rotate freely. 

This however would mean the end of the steel tube would be riding directly on the aluminium spar brackets. This is apparently no issue ("hundreds of flying RV's etc") however it did not sit well with me. So i decided to slightly modify this arrangement by shortening the bronze bushing a little to allow a thin washer to fit on the end of each bushing, This also meant the steel tube needed to be shortened. I shortened it just a little bit more than the bronze bushing. I think this was a worthwhile modification.

However, before we get to this! You need to make sure than the AN4 bolt would fit inside the bronze bushing. To do this i used a 1/4" reamer inside the tube while it was mounted in the vice. 

I then tried to put the bushings into the steel tubes. Both did not fit, and needed a little sanding to slide in. One went in fine all the way, but one would not go in all the way - it would get stuck in either direction at around the 2/3rd position. It was like the tube was bent or something. Looking inside, i noticed some scoring marks inside the tube. I used some files (including chucking one up in the drill press) to remove these score marks, and this got the bronze bushing to go in nicely. 

Hard to get on camera, but there was some scoring in one of the tubes.

Yes, this was as dangerous as it looked. 

Once i was able to get the bronze bushing to go in, i was able to take the bushing to the wing and remove some length very slowly with a file, so it would fit between the brackets with a thin washer on each side. I placed tape on each one before filing, so i was able to file square, and also did not go too far. I then took them back to the bellcranks, and filed the bellcrank steel tubes down to allow them to be about 1/64th at each end shorter than the bushing. All edges were deburred.

The tape was placed just shy of the end, then i could file back to the tape to keep the end square, and also not go too far.

The steel tubes were also filed so they were very slightly shorter than the bronze bushing, 

Once this was done, i did a few other things such as installing a nutplate on the right ballcrank for the autopilot servo (note there is an error on the plans relating to how many holes need to be countersunk). I also final drilled all the bolt holes. 

I was then able to lube the bellcrank bushings with LPS2 lubricant, and install in the wing. The nuts were torqued to 95 in/lbs (85 in/lbs plus 10 in/lbs of drag). For the most part they were completely free and rotated well, however both had a little drag when getting vertical.  You can see this in the video below. 

As a final note, this drag was of no issue and was well past the location where the bellcrank needs to rotate once the pushrods were installed.