AWC Jeff
23rd Jun 2018, 23:36
For the experts. Replacing the elevator trim tab which blind rivet to use. Cherry or Cherrymax. C150.
If Cherrymax, what size.
Pilot DAR
24th Jun 2018, 01:02
The C 150 part catalog, and service manual do not seem to state which rivets to use. AC 43.13-1B, page 4-19 explains the use of Cherry rivets, and instructs that manufacturer's data is required to use them. So, to do it right, you're going to have to identify what Cessna used, and use that.
That said:
I avoid the use of Cherry max rivets, if Cherry rivets will do. For low stress, light skinned structure, Cherry rivets are usually appropriate. They are easy to install (use the proper tool), and low cost. More importantly Cherry rivets can be removed if necessary in the future, Cherry max are a total misery to remove. Careless removal of Cherry max rivets will certainly result in damaged/enlarged rivet holes. To remove Cherry max rivets (and I've taken out hundreds), it is necessary to file the steel stem smooth and square to the rivet head. Then I lightly center punch the center of the steel stem. I drill a very small center drill into the stem, and inspect it for concentricity. If I'm satisfied, I'll drill out the stem, taking great care to prevent the drill wandering off into the aluminum body of the rivet. With the stem drilled out, I can then drill out the body of the rivet, again, watching for the drill wandering. It could be necessary to hammer and punch out the stem or the rivet body. If so, be sure to back the inside skin (which will be hard, 'cause it's a blind rivet for a reason!), but if not backed, the inner joined skin may be deformed.
When I install Cherry rivets, I wash them in acetone prior to use, and then apply super glue to the stem just before I pull it. Once pulled, some stem will remain, Do not use side cutters to cut off the stem, the shock of the cut can drive the stem back down out of the rivet, and you'll have to replace it. Instead, I use a very fine razor saw to hand saw the stems close to the rivet head, and then carefully file them smooth. My STOL kit cuffs are installed with Cherry rivets, and only two have dropped out stems in 31 years I've owned the plane. If a Cheery rivet drops out a stem, it still has a little bit of hold until noticed, and is easily replaced as above.
AWC Jeff
24th Jun 2018, 20:45
Thank you for replying. I couldn't find any mention in the 150 Parts Catalog, or the 100 Series Maintenance Manual either. Left the AC43.15-1B in the hanger. I ordered some Cherry Rivets from Aircraft Spruce, different grip lengths and dia., so I'll have the manufacturer's data for the log entry. Thank's for the tip about using a fine tooth saw!
mikehallam
25th Jun 2018, 09:01
FWIW, apropos removing rivets.
The removal of a Pop rivet of the type with retained steel core from my Rans screen etc., was partly done as written above and too fraught with collateral damage risk to continue thus.
So I bought a Dremel, (It's an ultra high speed tool with optional bits including a tiny grinder).
With care one can grind the offending rivet, Ali and steel core, flush and after that gently push the remains back. (Yes if truly 'blind' the remains go inside ! )
Caveat - it generates lots of heat and for the sake of the screen material take it slowly and let cool. But for a few such it was the ideal solution.
mike hallam