Duncan,
Thanks for posting this, I have been meaning to post something similar so
you have saved me the trouble of going into the detail.
Jacques, the only thing I would like to add is that ideally you need to use
the same cloth that was used in the original construction. In this case it
might prove difficult because pre-preg bid was probably used in
manufacture. The reason you need to do this is that using a material that
is significantly different means that this material may carry more (or
less) of the required load and become a source of stress in of its self.
I would see if you can get a response from Nev or Ivan to to find out how
many layers of material were used and what sort of cloth was used. I know
that when I did a repair on my wing I was fortunate enough to be able to
get the exact cloth that was not pre-preg'd. Ask them is it the same cloth
that was used in the wing. If it was then I have a small amount of this
and I can send it to you.
Failing that, it wouldn't be horrible if you can't match the cloth, but do
try and find out how many layers were in the original construction.
Paul
On Sun, Aug 26, 2012 at 3:11 AM, Duncan & Ami <ami-mcfadyean@talktalk.net>wrote:
> ami-mcfadyean@talktalk.net>
>
> <<..Any advice is welcome. .>>
> OK, I'll bite!
>
> During a monowheel collapse, the weight of the aircraft (less tailwheel and
> outrigger loads) is transferred from the monowheel in to the top of the
> 'tunnel'. Thereafter, the stress-path from the tunnel is mostly both
> forwards and aftwards. In the aft direction the tunnel distributes loads in
> to the seatback bulkhead then further in to the fuselage skin. This means
> that the area that has cracked (being at along this stress-path is taking
> abnormal loads and this is a possible cause of the cracking, as you have
> surmised, compounded by the holes that have been cut at that point.
> Assuming there is no evidence of any other overstress in that area, the
> repair needs to put back the strength lost. This means replication of the
> original strength of composite in that location, which can be determined by
> counting the number of plies present. Allow a minimum 1/2 inch per ply
> overlap on to the surrounding unaffected area (presuming a bond shear
> strength of 500psi and cloth strength of 250lbs/in) with staggered edges.
> If
> the holes must be recut, then double the reinforcement and cut the holes as
> ellipses (at a length:width ratio of 1.414:1, if you want to be pedantic!).
>
> Too much or overdesigned reinforcement may make the area too stiff and
> introduce other issues, and makes the aircraft heavy too!
>
> Your respective airworthiness and/or design authority will be the final
> arbiter of any repair, which might be along the lines of the above.
>
> Duncan McF.
>
>
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