Tony R., and Steve E. Thank you for the information. looks like I'll be
cutting out my hinge pins for replacment tommorow evening.
Jim Thursby
N814AT
>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
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