Attaching Fiberglass Hardware

[SPB W10]

Working on Van's, wheel pants and putting in AN507C632R8 screws with the nut plates per print.
Some photos of flying airplanes show an additional A3236-SS-012 CSK washer under the screw heads on fiberglass wheel pants, cowling etc.
How have these fiberglass parts worn on airplanes that have been in service for a while?
Looking for input on just the screw or the screw with the washer, reasoning.
Checked section five and did not find any directions there.

 

[fixnflyguy]

You definitely want the washers! Mine show zero sign of wear after 400 hrs. , and the key is making sure the screws are all snugged up well. Ill fitting CSK washers and worn out loose nutplates or alternative hardware using Tinnerman nut plates and Sheetmetal screws will end in worn holes in short order.

 

[Ironflight]

I have twenty (plus) years and 2300 hours on the RV-8 now. The screws that hold the front of the wheel pant to the rear are countersunk, with no “Tinnerman” washers, and the fiberglass show no wear at all. The four screws that mount the pants to the brackets have Tinnermans (to spread the load), and there is a little (but not much) wear in the holes.

Similar wear on our 15-year-flying -3 and the 35+ year flying -6….

Just a couple of data points for you.

 

[Scott Hersha]

I have twenty (plus) years and 2300 hours on the RV-8 now. The screws that hold the front of the wheel pant to the rear are countersunk, with no “Tinnerman” washers, and the fiberglass show no wear at all. The four screws that mount the pants to the brackets have Tinnermans (to spread the load), and there is a little (but not much) wear in the holes.

Ocular wear on our 15-year-flying -3 and the 35+ year flying -6….

Just a couple of data points for you.

Same results as Paul (another data point) on my wheel pants and also on my empennage fairing. (pictured). My thoughts are, if the holes start to show wear I can install the tinnermans at that time, but after 300 hours there is no wear showing at all. Same results on all of my RV’s.

 

[Steve Ashby]

For what it is worth, the Evoke aircraft paint shop, which has turned out several Lindy winners, does not use tinnerman washers and their paint jobs are beautiful and durable.

 

[JonJay]

Same as above. As Paul noted, the bracket screws can benefit from tinnemans. Mine started to wear through after several hundred hours. Did what Steve suggests and simply added the washers with no additional work and they have been fine since.

 

[RV7 To Go]

As stated above. No washers and no issues for over 8yrs and 800 hrs on my 7. Add the washers later if you do find worn holes.

 

[DanH]

Not to buck a happy herd, but an AN526 screw with a nylon washer means the hole in the fiberglass is cylindrical...no knife edge at the bottom. Trust me, it will not cause your airplane to be slow, and the glass can actually achieve full bearing strength. They don't wear the hole or chip paint.

I try to reserve flathead screws for dimpled or countersunk holes in metal.

 

[JonJay]

Not to buck a happy herd, but an AN526 screw with a nylon washer means the hole in the fiberglass is cylindrical...no knife edge at the bottom. Trust me, it will not cause your airplane to be slow, and the glass can actually achieve full bearing strength. They don't wear the hole or chip paint.

I try to reserve flathead screws for dimpled or countersunk holes in metal.

View attachment 109572

I don’t think you’re bucking the heard, just not blindly following the plans.
I did the same with my spinner (but did t you do a blind fastener there?)
I would follow your lead on future wheel pants.

 

[DanH]

Some photos of flying airplanes show an additional A3236-SS-012 CSK washer under the screw heads on fiberglass wheel pants, cowling etc.

For those who insist on countersunk screws in glass, wear can be improved with trim washers rather than suffering the ugliness of tinnermans.

I did the same with my spinner (but did t you do a blind fastener there?)

No external screws.

 

[bjdecker]

For those who insist on countersunk screws in glass, wear can be improved with trim washers rather than suffering the ugliness of tinnermans.



No external screws.

View attachment 109674

The #6 trim washers fit #8 screws perfectly.

 

[wirejock]

+1 for button head screws and nylon washers.