>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,
This is nearly a 10% decrease, maybe a little more than 'nominal'. With the
reduction in pin diameter your pin would be less than 70% the original
strength.
However, the point that needs addressing is - is the wire strong enough?
The answer is - probably yes but the authorities will want hard evidence of
course.
>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!)
The worst case to consider is probably not a flight load but the 'jammed
control' case where both pilots are applying a defined load on the control
column against a jammed aileron. With the amplification of load due to
leverage effects I'm glad that you are offering your finger, Tony, to act
as the pin!
> 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.
Yet another point to consider.
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.
We have to look at all of the components but in this situation we are only
wanting to substite the pin.
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)
Merry Christmas to you and yours - Andy
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