What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Tinnermans always needed for fiberglass?

rightrudder

Well Known Member
Where the fiberglass thickness is sufficient for a full countersink, do you always need to use a Tinnerman washer, or can you simply use a countersunk screw? Without the washers, does vibration over time wallow out the holes?

It seems obvious to use them on thin fiberglass, like the empennage fairing, but less so in other areas like the wheel pants.
 
I have fiberglass attached without tinnerman washers. I have 400 service hrs so far with no problems. However, in a number of places that I thought were tough service locations, I used pan head screws (for the same reason as washers) instead of countersunk but there are still more countersunk screws directly in the glass in use than the pan heads. For instance, wing tips, tail intersection and some on the gear intersection fairings. I think if the parts fit well and there is little stress, then a no washer installation will last a good while.
 
They don't hurt

They won't cause you any problems buy using them. That way you have a wider flange on the glass and metal for the screw. They look pretty good too.
 
What I did

I used Tinnermans under any #8 screw into fiberglass (wheel pant attach brackets, cowl, spinner, etc). I used Tinnermans under certain #6 screws that hold the leg faring to the fuselage. Since there is some movement with the faring I thought it best to use the Tinnermans. However I didn't use Tinnermans under the #6 screws holding the empennage faring or wheel pants together.

Other then some chipped paint around the #6 screws (the ones without Tinnermans) from removing the screws for inspection, there no other issues at all (275 hrs).
 
SS and angles...

The alternative to tinnermans would countersunk finishing washers...tinnermans with a small OD.

4, 6, 8, 10's on this page:

http://www.clipsandfasteners.com/Finishing_s/206.htm

Yes, but those are most likely commercial 82 degree washers like the stainless steel ones from AC Spruce - the ones marked "flush" -

http://www.aircraftspruce.com/catalog/hapages/finishingwashers.php

A few whacks with the correct dies in your C-Frame should turn them into 100 degree washers for a better fit. :)
 
Thanks for all the input, and the link to the Clips & Fasteners page. That website is a gold mine for all kinds of great hardware.

For the wheel pants, I think I'll try screws without Tinnermans, at least at first. It's nice to know that there's no penalty for going with the Tinnermans later, with a slightly deeper countersink. Who knows, I might want to use them everywhere for uniformity, as I'm committed already for the empennage fairing. For the spinner I'll use the stainless low-profile pan heads with the plastic washers.
 
Last edited:
Another alternative is to drill out #6 tinnermans to #8. The washer is barely larger than a #8 screw, and is 100*
 
Back
Top