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-   -   How to repair a broken All moving tail pivot (https://www.wattflyer.com/forums/showthread.php?t=73920)

solentlife 06-19-2014 12:55 PM

How to repair a broken All moving tail pivot
1 Attachment(s)
My Lanxian F16 has a plastic pivot system for the All Moving Tail.

Fuselage sides have plastic plates - one each side - with a 5mm rod horizontally for about 30mm .. with a groove near the end. This slides into a mating plastic tube in the stab, which has a screw that winds in to slot into the groove ... stops the stab from coming of but allows the stab to rotate round that rod. The tube has the control horn as part of the moulding.

The rod snapped of in a landing and I have since cut the stabs into fixed and hinged parts. She flies but an F16 looks strange with elevators and fixed stab.

The plastic parts are shot and nothing can be done with them.

How to fix and re-instate AMT ?

I thought about a tube across the fuselage and fixing rods into the stabs ... but it's an EDF and that tube would cross the centre of the exhaust tube.

How can I do it ? Would there be a way to fix a tube each side into fuselage .. fix a bolt into each stab ... the bolt being a size to fit the tube ... then a nut used on the inside of fuselage to pull up the stab till it's near tight but free enough to rotate ? Maybe the nut in the stab with head of bolt in fuselage ? Could use a GFN (Glass filled Nylon) bolt to give strong fixing but able to sheer in event of strike ?

Anyone else had to fix similar ? (see attached...)


fhhuber 06-19-2014 04:48 PM

The strongest way is the tube or a music wire straight through. That will present some drag in the air stream inside the fuselage but I think you'll find its relatively minor.

This is the ONLY way I have ever done a "flying stab".

I imagine you could use a blind nut and bolt for a pivot pin if the fuselage wall is strong enough. Possibly with a plywood doubler inside the fuselage to spread the load. Blind nut to the outside and you may also want a "fender washer" inside

solentlife 06-19-2014 06:44 PM

The original was two separate pivots .. one each side. So there is more than enough strength in the fuz wall.




As you see ... separate each side.

I think I would need to have similar flat plate as the old has to increase the area of support ...

The stabs are glued on at present with the mounts full of epoxy, fuselage rods missing etc.

So I could cut away the stabs .. rejoin them to elevator sections ... drill out the old plastic plates ... glue in CF rods or alloy ... maybe even use the old tubes in the stabs ? Or fit new with self-tappers through to dremel slots in rods ??

mmmmm tricky one ...

Like I say - she flies with the fixed versions I changed to as a quick fix ... but it just doesn't 'feel' right !


solentlife 06-19-2014 06:53 PM

The model in question was the F16 'Freebie' I received couple year back from a pal after he smashed her up. There's a rebuild thread here about her.



fhhuber 06-19-2014 06:57 PM

Thin ply "rib" laminated along the fuselage's root of the stab each side to spread load... and a CF tube that extends inward just to the air passage will be stronger than original.

The original plastic tubes mounted in the stabs might be fine... might need to be changed out to get a good fit with the available CF tube sizes.

Biggest issue I see now is setting up for the pivoting. The molded parts look like you probably had a groove for that set screw in the horiz stab to prevent the stab from falling off while allowing it to pivot. that is not as easy to do when you are replacing the molded parts with CF (or other material) tubes.

The pictures help a lot in figuring what might be appropriate.

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