Q: Screws in fiberglass for -10 doors?

I might be over-thinking this...so if I am, please let me know. What concerns me is that the screws holding on the doors on the -10 are simply #10 flush screws into fiberglass. I've heard anecdotal evidence of screws and fiberglass not working well (wallowing out over time) in other locations (cowling, wheel pants, fairings, etc)...but haven't about the -10 door. So is this a big deal or not?






My preliminary mitigation plan involves epoxying Tinnerman washers into the fiberglass, but it doesn't come without second order effects.

Here are some facts:
Tinnerman washer is 0.114 tall, which includes the countersunk depression
Tinnerman "lip" is 0.030 tall
Fiberglass is two layers and a total of 0.100 thick

From the picture below, you can see my test piece and plan to router out the 0.030 thickness so that the washer fits flat. And although the math doesn't work, I can have the Tinnerman washer flush on the top, and the bottom doesn't extrude. So there is some variability in my measurements.



In the end, it should be something like this.



What do you all think of this plan? An absolute must do? Don't bother? For those who have already painted...did you paint the screws in place? Was it painted with the doors open or closed?

Thanks for the insight!

-Jim

Wait till you get to the wheel fairings........I just finished them, and the same problem comes up, just more acute. I am second guessing my decision to follow directions. As for the doors, with 20-20 hindsight, I would lay a couple more layers of fiberglass under this area, as I ended up making a shim to fit between hinge and door in order to make everything fit. But, everyone's doors fit a little different, so I don't know if this would work for you or not.

Thanks Andy. If you were to do it again, would you go through the hassle of putting in the Tinnerman washers on the door then? Thx! -Jim

You have certainly been thinking!

For structural reasons I understand spreading out the load under the screw heads.

I do believe that your test would probably work well with the fully inset illustration. However as you are making the under glass part a little thinner.

I think you would have the best structural situation by carefully countersinking the outside skin and having the countersunk large area washer be exposed.

The advantage would be that you only have to get the countersink to match the bottom of the washer and not need to do any other modification that changes the original door attachment except add the wide area countersunk washers.

See here for your material choices. http://www.gen-aircraft-hardware.com/images/pdf/specialwash.pdf

Thanks Tom, that is a good idea. I suppose I could do as you suggest, then fill and blend to make it smooth. Might be the strongest and cosmetically appealing option. Thx! -Jim

In a similar vein, do people put a layer of glass over the top and blend in once all the various fittings (front strut, doors, seat belts) are in the canopy?

I agree with Tom that countersinking the washer into the door is both helping and hurting, and that it would be better to simply add a countersunk washer and then blend with filler. That said, I haven't heard of any problems with these attachments.

Just me talkin' so feel free to ignore, but I wouldn't try to fill & blend. You'll have quite a bit of depth to blend and more importantly, suppose you want to take the door or strut off sometime like I just did to change a window.

Jim,

I have structural SS #10 holding my door. I don't/didn't see any problems associated with the screws holding the door on. Personally I believe there is enough thickness in the fiberglass there to not worry about it. I have pulled those doors off sooooo many times and the holes look the same.

My 2 cents

On my doors I left the screws per the plans and have seen no issues. I had considered epoxying an aluminum piece to the door on the mating surface but decided to stick with the plans. On the wheel pants I did go with the tinnerman washers after some screws pulled through and I lost a pant on rotation at takeoff.

I too had some concern about the screws pulling through a reduced glass thickness after you conuntersink so I put some carbon fiber in between the hinge and the door. Don't know if that will make any difference in the event of a door coming open and hope not to ever test it.

Relax

To my knowlege Door no screws have failed or loosened. There are many areas to improve things on the 10 kit but this maybe a solution looking for a problem to solve.

Gary Specketer

The bonded washers will probably work fine but bonding to metal can be a little tricky. My advice would be to put a lot of effort into surface preparations before you glue them in. Alternatively, there are some proven bonded fasteners on the market (Click Bond CG596, etc.) but they tend to be expensive.

I forgot where the carbon fiber is located on the door. In general, you want to make sure that you keep the carbon and metal apart to avoid corrosion. I'm not sure if this is a factor for the door handles.

Since your washers have a large flange, it might be possible to bond them in place, then put an additional ply of glass over them. You can fill them with clay, layup the glass, then knife trim the opening before it's fully cured.

thanks!

Thanks for all the ideas guys. Heeding your advice, I'll skip the tinnerman washers. However, I might coat the inside the the countersink with some pure epoxy...the epoxy should be tougher and more wear resistant than pink fiberglass by itself. Thanks again, -Jim