The problem of stiff roll controls may not have anything to do with the tufnol
bearings at all. In my case the apparent stiffness of these bearings was the
symptom, not the cause.
For any of you that have bench assembled the yolk, torque tube and free
spinning tufnol bearings, only to discover an alarming reluctance to rotate
once the assembly is bonded into the cockpit module, read on..........
The torque tube is assembled to the yolk using Redux. As explained in the
manual, a large clearance in purposely left to allow the Redux to self centre
the torque tube, aligning it concentrically and axially. Nice theory....but in
practice this dosen't always happen. In my case (despite careful setting up)
the tube bonded in at an angle. The result of this is that the far end will try
to describe an arc, rather than rotating about it's axis. Bonding the aft
tufnol bearing in place will hold the end of the tube where the build
instructions say it SHOULD go....and not where it wants to go!
The result is a control the may well run freely in some positions, but
progressively stiffens as it is rotated.
If this is the case then no amount of lubrication or abrading will do any
good. The only solution will be to dismantle the system and rebuild it
correctly.
The worst thing you can do is to leave it, since the torque tube will
continually flex until it eventually fatigue fractures, or exert so much
lateral force on the tufnol bearing that the latter grinds it's way through the
tube.....with the same catastrophic results.
IMHO the design of the tube/yolk is should be changed. Simply by reducing the
clearance between these components to a smooth sliding fit, High strength
Loctite could be used instead if the bulkier Redux. This would force the tube
to locate concentrically and axially, and the problem would disappear.
If you see this Andy, I would appreciate your feedback. From a manufacturing
point of view it would cost no more to produce and from a builders point of
view, it would eliminate the possibility of a fatal error.
Nigel (147)
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