Countersink washers on fiberglass; assistance needed

[Brian Vickers]

I'm wondering how to properly attach the fiberglass fairings with the countersunk washers. Another good question; are you all using the countersink washers? The empennage intersection fairing is nice and thin; light weight. Do you open up an enlarged countersunk hole for the washer to nest in? It appears to me that for the assembly to fit well, the hole would be much larger than the shank of the machine screw. Or just let the fiberglass flex down into the countersink nutplate (K1000-08 or 06)? Tips, recommendations and suggestions welcome.

Sincerely,

[grover]

i'm countersinking until it looks about right. have done so on some of the thicker parts (wheel fairings, cowl, etc) so far with good results. am using various sizes of tinnerman washer.

[Tom Martin]

I would not reccomend using countersunk washers on glass parts. I have found that they often leave a large circular mark in the final paint that is worse than marks left around holes that do not have washers. Washers can always be added at a later date.
Places where I will use washers are in high wear areas like wheel pant attach points and areas of movement on the upper and lower gear leg farings.

[JonJay]

....anywhere. I countersank for appropriate screws and left it at that. Many of Van's machines have hundreds of ours on them with no problem.
This includes wheel pants, intersection fairings, empenage fairings, cowl inlet screws, spinner, etc....
I believe much of the hold over for the large washers where from the day of poly glass parts. Now that all of those parts are epoxy, they are much tougher.
No sign of any problem or wear after 80 hours. If I ever do see them start to wear, I will add in the washers then.