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Old Nov 08, 2012, 06:28 AM
PeterVRC is offline
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Australia, VIC, Melbourne
Joined Nov 2006
13,926 Posts
Interesting issue......

The final Su-35 repair/upgrade/maintenance was to go over all aspects of the plane to be sure it was all 100% fine. Which then reminded me of seeing the TV Rudder servo stalling now and then... fairly often really. The servo itself had worn the screw holes due to the pressure against it!

When I undid the TV nozzles, the right hand one was 'medium tight' and the left hand one was 'quite TIGHT' when moving through various position combinations. I found that if it was DOWN and the rudder tried to move it, that it was under high duress and unable to move it correctly - thus the servo mount issue.

After a lot of moving it around, I figured out a 'peak' in the friction/resistance that suggested the 'ball' had some high spots in it. It is not perfectly round!
The right hand one was the same, but just not as tight to matter as much - but it was unacceptable in one combination angle/position.
But the left hand one was highly unacceptable!!!

After a LOT of 'total manouevering around' through all angles, for 10 minutes or more - to get the friction to wear it down a bit (???) - I decided it was fruitless. The right hand one did improve a bit, but it wasn't that bad to start with.

But all the moving made rub marks as clues to where the issues were.
Then out came the 'somewhat fine' wet and dry paper.... and I sanded away merrily. Testing... sanding..... testing... sanding... yawn.... testing.... sanding.....
For over one hour in total across the two of them!!
End result... NICE 100% free moving, but no slop, TV "balls"!!

I had never thought about that before..... that they could be 'sub-standard', like most part of any PNF are, so I should have checked that from the start too really!!

Seeing the servo screw holes in the plywood plate were wrecked, I decided to put an MG servo in there, because it drive two TV's, whereas the other 'vertical travel' servos only drive one each. The MG servo being 5mm longer got me past the worn screw holes.

So now all is free, smooth and perfect!!! Yay!! But it took quite a while in total !! (2.5hrs or so!)

Inspection completed and passed......
I will take it out one morning this week, or at worst on the weekend.
I actually didn't "fill and finish" the repaired areas, as I want to see it FLY again FIRST.... plus the damages aren't that bad and they don't stand out much at all after 1metre or so. But I will do it all fully next week - if it is still alive after these next flights!!

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