Stuka Stunt Main Forum · 7 of 7 known posts recovered
I plan to use plywood or electric circuit board for bellcrank itself.
What's a good off-the-shelf product for the pivot and bushing?
I've made plywood bellcranks for F2d's before, but the expected life span wasn't so long on those.
I made my own. It's molded carbon fiber/epoxy with a bronze bushing (from a local parts supply place-Tacoma Screw). Pretty easy overall once the mold was made. The plug was machined on my mill out of aluminum.
Nice work, Randy, but "just milling a plug" and formulating a carbon fibre bellcrank is a bit beyond my technology.
Lou's suggestions are good ones.
I've been making my own bellcranks out of sheer orneriness for years. (Sheer orneriness is a home-grown item, not available in stores.) Happened upon a bunch of the old Perfect(R) brass bellcranks with 2-part bushings and real wimpy bellcrank plate thickness. (Price was right.) Pop the brass out of the aluminum plates and I have *excellent* bushings for up to a hefty 0.065 thick home-made unit...
Ah, but you are thinking thicker wood or phenolic-type plate...
One way could be to tap the center for 6-32 or 8-32 (even 10-32 if you put a big bear on the leash.) Run a higher quality bolt of appropriate thread into it and epoxy or thread-lock bolt and matching nuts above and below the plate. That's your 'axle'.
For bearings, nicely fitted nuts of that thread soldered to a plate just big enough to bolt to plywood caps at the wing surface - a la foamie hanging bellcranks. It's like the old threaded kingpin Ford front ends. Only needs some care during installation that both nuts allow the axle to turn freely - if they're as little as 1/4 turn off, they'll drag...
Or, aluminum book-binding nuts are threaded - I believe - 8-32. These look like elongated-stem blind nuts without the points bent in. The 'stem' (think mushroom shape?) is about 5/8" long at about 0.20" diameter. The flange ('cap'?) is about 0.40" wide. Cleaned well in say acetone, possibly scuffed with some 60 grit, these should epoxy into the bellcrank plate very permanently. I b'lieve I've seen these in ACE Hardware or major office supply outlets - should be available.
Way to use the bookbinding nuts should be obvious: epoxy into the plate and hang the assembly threaded onto a matching bolt between plywood caps at/near wing skin surface. Again, the pivot surface is threaded, and won't need spacers to keep it located vertically. Might pay to chase a tap through the threads after epoxy cures, in case any got into them.
\BEST\LOU
It didn't last very long. Fortunately, the airplane was used up before the bellcrank bolt.
The idea of K-balling old Perfect BC's sound pretty good.
Also, I have a nice Wakefield (F1b) motor peg made out of hard aluminum tubing that would be a dandy axle, assuming I can find a suitable bearing for the BC.
If you use linen base phenolic, an a steel axle like 1/8 music wire, no bearing is required. Make the BC thick enough to get some bearing length. The linen will hold some oil or gease.
If you want a dry lube setup, I've used Delrin or UHMW shoulder bushing into whatever material you want to make the BC from.
I can make up a couple bushings for you if you give me a sketch. I have the material and the machine.
Curt
PS:
If you use circuit bd material beware: If it is glass fiber reinforced, it can be VERY abrasive on the leadouts.
And some of the paper based phenolic ckt board material has very little strength.
3/16-1/4" phenolic is the cat's meow and works pretty much like plywood. ie you can saw it on a scroll saw, file it etc.