Re: Tailplanes

[Graham Singleton <grasingleton@avnet.co.uk>]

>Is there a consensus as to the cause of eventual looseness?
>Rotational force against the pin in cruise should be zero, without any
>pressure on the stick.  Maybe some turbulent air and helical prop wash
>on the stabs, but is that enough to distort the steel to make the hole
>larger?  Aerobatics then?  Or is it in starting the engine, or turf
>bouncing on the monowheel, or engine runup in high winds from a
>certain direction on the tri-gear?
>Fred F.

I don't know of any conclusive answer to that. My own guess is that as Mark 
pointed out, the pins are loaded one way when on the ground by the weight 
of the tail being resisted (balanced) by the balance arm. If the airplane 
bounces on the ground that load will reverse. If there is any play in the 
holes at all this reversal of loads will cause slight hammering. The bigger 
the backlash the bigger the hammering effect. The problem is the very small 
contact area of the holes in the tube.

Graham