Gidday,
OK, now we are cooking. I had the fortune of flying with a fellow the other
day who has just gone into business to help out a friend, and the business
is the largest Stainless Steel Supplier in Sydney. This business is a member
of the Australian Stainless Steel Development Association, and consequently
he has access to a wealth of different information and testing results. I
already have looked at the specs for the locally sourced welding rod which
is a CIG rod known as 316L. This is basically the same as 316 Stainless
which seems to be an indusry spec, except the welding rod has 3% more
carbon. This reduces the mechanical properties by a nominal amount which is
316L (welding rod) 485 MPA
316 (standard?) 520 MPA
As you can see this is a nominal decrease, however has satisfied Australian
and FAA standards. (Australia is very conservative in terms of certification
and modifications).
He states in a recent fax that "all other properties for 316L compared to
316 are mainly the same. All I could offer is 316 but I believe the CIG
welding rod will easily satisfy your requirement." ( he had been asked to
supply details on the strongest type of stainless he could get his hands on)
I am going to research the shear load reduction between the original pin and
the reduced diameter pin-welding rod. However it does instinctively seem to
be a bit academic. What I mean is, lets face it, the flight controls are not
that big and consequently do not apply that much load when fully deflected.
The critical scenario is a sustained load at max control deflection
IAS(VM??, I used to know!)
I would hazard a guess that for ailerons, if hyperthetically the lug of the
hinge was big enough to accept your finger, at max deflection and max IAS,
you would probably have a very uncomfortable, but still intact finger! My
point is to highlight loads versus strength, and I feel the weak link is the
compressibility of the teflon i.e. its ability to distort under load, and
its shear capability when a smaller diameter pin tries to laterally cut or
pull through the sidewall. The teflon is pretty tough stuff I should add,
and if properly fitted to a new hinge will act with the replacement pin as 1
unit. The aluminium lug is obviously also a weak link in terms of strength
i.e. the pin is infinitely stronger irrespective of which diameter you
chose. The more I think about it the more I feel that if each component is
looked at in terms of its individual strength properties it will only
confuse the issue. The only real way would be to make up a test piece and
expose it to a destructive load and see what gives. If this load is 3,4 or
10 times the maximum flight control capable load then all is well. Lets face
it, if it wasn't a safe option it would no longer be allowed by FAA as no
doubt thousands of hours have already been flown in this configuration.
Does anyone know the aircraft manufacturer that uses this teflon sleeving
and any contact details???
Still on the case, as such, and will pick up the scent after Xmas. Safe and
Happy Xmas times to all who have persisted with this diatribe ( if thats the
way its spelt)
Reg
Tony Renshaw
Builder No. 236
>Hey guys, All I meant to say is just because somebody else is doing
>something doesn't mean it's a great idea. Not being sure about reducing the
>hinge pin diameter by .023" has kept me away from this idea. I for one,
>have no idea of the loads placed on these pins at 100mph/plus airspeeds. If
>anyone had any data about the strength difference from a .084" piano wire
>to a .061" stainless steel wire, I would like to hear it. If it is
>negligible and not to be worryied about, fine, tell us. As I have already
>bonded on all my hinges, that rules out the full length hinge option. So I
>would like to know with FACTS if this is a viable option.
> Jim Thursby
> N814AT
>
>
>> I wished to air this idea because not only do several thousand homebuilt
>>aircraft probably use this method, and now I'm told production aircraft
>>also, but I really don't want to have to replace the bonded hinge flange for
>>a long long time. If you have doubts that this method has floors or
>>compromises safety in any way just say so, and why. This message above is
>>only negative and nothing can be drawn from it.
>
>
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