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Fasteners for composite panels.

Fasteners for composite panels.

Fasteners for composite panels.

(OP)
I have to find suitable fasteners to hold the engine covers on a new, rear-engined, composite aircraft. The two mating surfaces are two layers of 300gram bi-directional glass thick. It would be preferable to have the fasteners flush with the surface if possible, but a small bump could be ok.
Has anyone had experience in this situation or could point me to a suitable source of info?
Thanks.
Gyro.

RE: Fasteners for composite panels.

Have you thought of the opportunity to use couter sunk discs?

RE: Fasteners for composite panels.

(OP)
Hello Kasper,
Well yes, something countersunk might be OK but how do you countersink into such a thin material? The laminate is only about a millimetre thick.
I have considered cutting a piece out of the surface to be fixed to and making a recess in it by glueing another piece behind it. Then this would give some space to add depth to the engine cover in a similar fashion. Perhaps I could then fit a countersunk washer? I have not heard of them previously. Where would I find details of them? If I could use a countersunk screw, perhaps I could utilise Tinnerman speed nuts. Have you had any experience with them? Will they stay tight and secure?
Thanks for your assistance, Gyro.

RE: Fasteners for composite panels.

Gyro,

The washers I ment are per standard DW (for example DW06SS). You do not sunk into material, the sunk is in washer.
By perhaps cutting out the bottom part a bit, as you mentioned, there should be enough room. By the way this solution provides dissipation of static electricity from fairing.
Try this:
http://www.ddaircraft.com/subcategory.cfm?Subcategory=DW&Category=WASHERS
Kasper

RE: Fasteners for composite panels.

gyro,
If it is possible at this time to modify the mould, or if a new mould is to be produced, why not mould the countersinks as part of the panel? You may also need to consider laying extra plies along the fastener line anyway to ensure you have adequate bearing strength in the cover to take the loads from the fasteners, or insetting the metallic countersunk washers at the moulding stage. Also consider dropping the height of the complete landing for the cover, rather than spending extra time 'repairing' it to take the countersinks. Seems like the fasteners should have been considered earlier in the design (but my hindsight was always known to be good...).

RE: Fasteners for composite panels.

(OP)
Thanks fellas,
As this is the prototype we are using the "tryit and see" approach to some of the design. If, after testing, the fasteners are ok - good, we will take steps to incorporate as necessary, into the moulds. Some things like this can be tricky and something new might need to be done.
The crucial factor is always weight and the engine area is always the heaviest. The covers are of a thickness that is fine for structural requirements, if we can fix them suitably without adding, we are on the winning side.
I am in sunny Australia and I don't have a listing on this c'sunk washer. I assume that it is stainless steel and that someone like Hawker Pacific would know it by that DW number.
I looked on the ddaircraft site but the listing didn't give dimentions.
I will try to track it down here.
Gyro.

RE: Fasteners for composite panels.

Gyro
    I know of a screw with a large diameter thin spring steel captive washer (with a very flattened M-profile) under the head to distribute load on composite surfaces. I believe it's called DAN169. More info on www.fairchildcorp.com

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