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Hi Bob,
> I would draw your attention to a simple fact that when the flaps are
> extended at 82 knots a large proportion of the aircraft weight is
> carried on the flap hinges.
Yes, but this load is in the opposite direction and from quite a
different nature, and most likely in an angled direction whereas the
flap exerts a "straight" line of load.
Many of us have a "no push" or "no step" mark on the flap, while it is
very unlikely that someone weighs more than the lift potential of the
flap. Apparently some people feel that not all loads are of a similar
nature. I'm a bit cautious, I have to admit, I couldn't help wondering
about this. I just prefer to limit the use of critical parts to their
intended usage.
> With regards to receiving snatch blows through the aircraft "bucking
> about" this is entirely without foundation since on tying down through
> these points it is possible to load up and deflect the main gear legs
> to ensure the system is constantly in tension.
We all know what happens with the doors when they are in constant
tension by the support springs: they deform. I can imagine when you load
up the structure of the aircraft while being parked in the sun that it
may deform a bit over time. Maybe just a millimeter, but that said,
while building the airplane I did the measurements down to a precision
of better than 1 millimeter. So if I tie down the aircraft I make sure
not to tie any load on the wing. Downside of course is that if the
airplane rocks in the wind that it will jerk on the tie downs. But I
don't use the flap hinges as tie down points. But who knows? Maybe your
method is better. We are just guessing here, aren't we?
> In conclusion I can advise that G-PTAG has always been tied down in
> this manner and has withstood some severe gusting wind conditions
> without any damage ensuing what or where ever over it's 900 hours life
> time.
It is impressive, but no guarantee by itself that it could never have
any negative consequences. You are probably right but I had an uneasy
feeling when I red about it. If it was about a bicycle I would have
ignored it, but we are talking airplanes here and I feel that if any of
us has an uneasy feeling about something that he should bring it up.
> May I thank Neville Eyre for his kind intervention on this matter and I
I hope I didn't irritate you, I was just wondering whether using a
critical aircraft part outside the scope of its intended usage would be
safe by definition. I have to admit that I would never have thought that
just a pencil mark would compromise the strength of that part either.
I think it is a good thing if we discuss the safety of some ideas before
they become common practice. I would really hate to read someday that
one of us lost his flap during flight and that a hinge with an eyebolt
was discovered some distance away from the wreckage... Especially if I
remember having questioned it silently and never brought up the subject.
I guess we won't be able to obtain a definite verdict on this matter,
everyone should make his own decision. It is probably ok to use the flap
hinge for this but you can't know for sure I think.
Frans
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