December 15, 2019

Rudder Pedals and Evil Bushings!

I spent far too many hours this weekend trying to get various torque tubes that ride in bushings to turn smoothly. I gave up on the rear elevator torque tube for now, and decided to put in the rudder pedal hardware.

The rudder pedals are also torque tubes that sit in bushings… so I just can’t get away from this evil chore. After several hours and much trial and error, I finally got the rudder pedal tubes to move smoothly. I had to correct both the brackets themselves by
grinding away from the bushing brackets a little at a time, as well as the painted rudder pedal torque tube that had some oversprayed areas (the sections that rest in the bushings are supposed to be unpainted).

I did have a welcome distraction while I was working on the Sling. This past weekend the Wings of Freedom Tour visited my local airport KASH, flying in their B-17, B-24, B-25, P-40, and P-51. I didn’t go since I’ve seen these planes many times before, but they were offering rides for a donation, and I got to see the B-25 fly right over my house at about 1000′! I always get excited when planes fly over my house (it motivates me to work on my plane!), but this was pretty special… very unique sound as it approaches.

A WWII-era B-25 Mitchell flying right over my house!
Bracket for rudder pedals riveted into place
Problem #1 – the two brackets placed back-to-back don’t line up perfectly, which causes the bushings to be squeezed a little. I used a Dremel with a fine sanding disc to smooth this out
Problem #2: the factory masks off areas on tube that are designed to rest on the bushings, but masked areas weren’t quite at the right spot in a few places, causing paint to rub the bushings a little
Solution to problem #2: file away unwanted paint, then polish the tube smooth with a Dremel fine polish wheel
Finally!
Hardware installed for the linkages and stops

I also had to finish installing the joysticks, which again are torque tubes that rest on bushings. First, I needed to install the lock collars, after getting confirmation from TAF that I need to drill and install 4.0mm rivets in these collars. I figured this task would be easier to do in a drill press, so I removed the joysticks from their mounting brackets.

I used a drill press, a self-centering pipe jig, and a 3/32” drill bit to drill a pilot hole on either side on the lock collar, and then used a #20 reamer to open hole to its final size
4.0mm rivet installed, one on either side of the tube

After reinstalling the joysticks and re-securing the screws that hold the rear brackets to the main spar carry-thru, I was not happy with the amount of friction on the pilot side stick. I determined that the rear bracket (CF-BKT-007-X-C-, as shown on pg E2) was not bent to the correct angle, and was therefore twisting the bushing out of axial alignment with the tube, causing friction. At first glance it looked like this bracket is bent at a right angle, but I determined (again, by trial and error) that the correct angle is 95°, see photos below for detail. I used a bench vice and a hand seamer to bend the flange to the correct angle. I didn’t measure the original angle of the part, but I’m guessing it was about 92-93°, using my iPhone’s photo editor measurement tools. At first I bent it to 97° but that was too much; bending back to 95° seems right. After I reinstalled the bracket bent to this angle, the joystick now moves buttery smooth!

The angle indicated in this annotated photo is pretty critical to ensuring the joystick can move freely. This photo shows what the bracket looked like before I made adjustments; I didn’t use an angle finder for this case, but I estimate it was about 92-93°.
My first attempt at adjusting the bend on this angle; I went a little too far. At this point I had the idea to break out an angle finder and measure it
Angle finder tells me 97°, which was too much. I made a guess that it should be 95°.
After correcting the angle to 95 degrees, and re-installing the joystick, it now moves very smoothly

Lastly, I had to finishing putting in rivnuts to the center console brackets that the skins attach to. Pascal L. recommended that I buy a chucking reamer to open the holes for the rivnuts that go into these brackets. The rivnuts are nominal 6mm in diameter, but he recommended undersizing a little to ensure a good contact surface with the ribbed section of the rivnut. He recommended a size A reamer (0.2340″), but I couldn’t find one readily available from the usual sources (Amazon, Spruce, Brown, Cleaveland), so I went with a slighter bigger 15/64″ reamer (0.2344″ / 5.953mm) from Amazon, which is still smaller than a 6mm drill bit that I had been using. Results using this reamer on a test piece were very good; I could not get the rivnut to spin when I tested with an M4 screw.

My new spiral-fluted chucking reamer, size 15/64″, is perfect for the M4 rivnuts
Rivnuts installed. You can see my little experiment piece on the workbench; I use this to try out drill hole sizes for some of the common hardware I use, and record a little reminder to myself on which size I used
Brackets installed. There are two smaller ones I still need to put in, but I need to buy a hand rivnut tool; there’s not enough space to use my Astro Pnuematic drill-powered rivnut puller due to the joystick bracket

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.