Trim Tab Drive Screw - STRIPPED!!

M

mplstim

New member
Bellanca Drivers:

I'd recommend a thorough inspection of the threaded shaft that actuates your trim tab. I got a scare today when I was flying. I was happily cruising along at 130 IAS and suddenly the yoke did a rapid cycle out and back in, pitching the nose up and down. I returned home to check things out, noticing that the trim was behaving differently - too much up at my usual settings. It turns out that the drive screw was stripped toward one end and causing the tab to slip/flap in the breeze.

The trim tab is actuated a lot like our Cruisair gear is retracted. Out at the tab, the drive shaft rotates like a jack screw inside a brass threaded insert. Giuseppe must have liked the jack screw concept. It really is a beautiful design - if the threads don't get stripped. The shaft threads had been worn down and flattened out to the point that the insert could slip in certain places. I removed the shaft and insert and plan to have new ones made at my work's machine shop.

My preflight normally has me look at the connections and tug on the trim tab. This didn't reveal the problem. I'll check it out more carefully from now on..

Tim
 
Take note that is not just an all thread. I have seen a few planes with an allthread in them. The threads are revesed to get more travel with less turns.. I had to replace mine at rebuild. :lol: :lol:
 
I tried Alexandria Aircraft and they didn't have any of the original shafts for the Cruisair. So, I'm having a machinist friend make me a shaft and left handed bronze nut for the price of the left handed 10-32 tap and die. If you want a new shaft and/or nut, contact me and I'll forward you his contact information. He is using my old one as a sample so it will be a legit part under the "Owner Produced Parts" ruling. It will be to original spec, with RH threads on the front end and LH threads on the back end. My original one was just mild steel. The new one will be a zinc-plated steel for better corrosion resistance.

Tim
tbriggs3@mn.rr.com

FYI Alexandria Aircraft didn't have an old Parts Catalog for the 14-13 series. Some 14-13 parts are compatible with the 14-19 series. They apparently have an old card file with some of the 14-13 part numbers. I plan to fly up there one of these days and give them a copy of my parts catalog for them to reference.
 
I'd like a replacement for my Cruisair. Feel free to contact me at cruisair@hotmail.com and let me know what I owe you :D
 
Tim, I live 8 miles from Airlake. Let me know if you want to get together and fly the old birds. Mark
 
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