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Hey Dudley,

Nice report. I am sure it will help some one else.
You might have mentined that the binding was only heard while
operating the flaps on the ground with the engine off.
Might be a good pre flight check monthly or so.
Hope to see you at the concert.
Take care,
Jerry

The machenist could not believe that the OD of the bearing surface was was larger than the ID of the bushing. The torque tube will go right into a lathe and was polished. This did not change the OD enough to measure.

Next, I used cloth paper on a drill to polish the inside of the bearing surface. Again, the diameter was not affected but the torque tube would fit easily and could be turned with minimal effort.

The IA used antisieze compound on the surfaces to prevent gnarling which might eventually bind up the surfaces again.

There was a black substance on the bearing surface before polishing. This may have been grease which had hardened over time.

============COMMENTS======================

4-22-02
Hi, Dudley

My younger sister always maintains that everything happens for a reason 
-
sometimes it's a wake-up call.  Glad you had the flap torque tube 
fixed.

A quote from Europe that you might get a chuckle from:
    "Indeed all these Marchettis are hand made, so it's difficult to
exchange one airframe part to another airframe."   Sounds like an
understatement to me.

Alex
Dudley,
What works for me is to move the flap on one side and see if the contralateral flap moves. Then try the other flap and see if it moves the first flap. If there is any significant binding the slop in the torque tube fittings will absorb any movement before it reaches the other flap.

Barry

Dudley,

I looked at the info on the web site on the flap torque tube binding. I think Teflon might be a good fix for that binding bushing but one would have to be careful about using Teflon there. If the stresses on the Teflon lining get too high, the stuff tends to extrude. Teflon is real bad about that and it can happen at bearing stresses as low as 1000 psi. I designed some bushings to replace the wallowed out bronze ones on our 16T wind tunnel compressor stator blades. I went with a metal matrix Teflon composite material that I believe is called Garlock DU or something like that. I will look it up and find out for sure what I used. That stuff has excellent wear and low friction properties like Teflon but can withstand bearing stresses around 45,000 psi or so without failure. I think they have been working well in service for about seven years now.

Another potential problem with bushings used on aircraft is binding due to differential thermal expansion between the bushing and the torque tube. You just have to make sure that the materials of the bushing and the torque tube have the same coefficient of thermal expansion, or that if they are different, that the worst case minimum clearance between the bushing and the torque tube is still a clearance and not an interference fit. I would open up the bushing I.D. to have a minimum worst case clearance of 0.001 inches with the torque tube bearing surface O.D.

Tom

Dudley,

I wouldn't use any anti-seize compound on bearing surfaces that still have relative motion. The main use for anti-seize compound is for highly torqued threaded fasteners to prevent seizing on eventual dis-assembly. Depending on just what is in the anti-seize compound, it could tend to kinda bunch up and bind. The bronze and copper based stuff can do that. If it was a molybenum disulfide based anti-seize compound, I don't think that would happen.

Tom 1