700 Tail Twist

[Steve]

I've had two flights of my 700 this afternoon and the tail has twisted by say 10-15 degrees clockwise (looking from the back) without any untoward contact. The heli is over 2 years old, has been flown regularly and more than any other in my fleet, has not been dinked in a year or more, and this has never happened before. It is still rock solid and tight to the touch and I can't twist it back by hand without undoing anything.

So, any ideas? I will of course straighten it up and make sure everything is tight etc, but I'm more curious about the underlying cause - might it be a sign of a main shaft bearing going notchy and causing small vibrations or some other similar cause.

If you've had this happen before, your advice and recommendations would be much appreciated.

Ta.

[Paulice]

Did you do any very hard stops from a fast piro?
The extra torque can cause it.
Make sure the little locking screw is fitted correctly in the boom clamp.

[Steve]

Just had it all apart - the horizontal fin hasn't budged, so I can assume it's the tail gear box that's moved on the boom rather than the boom turning in the main frames.

Found the system to be very 'gummy' just off centre with some very noticeable dead spots in certain parts of the slider travel - lack of maintenance So it's all been apart, cleaned, polished, shaft cleaned with oiled 1200 wet and dry, thrust bearings cleaned and greased and put back together - is now all silky smooth as a tail mechanism should be .

Explains why the tail was struggling when I was attempting my very limited backwards flying today.

I guess the torque suggestion is probably right as the gyro/servo were working too hard to overcome the mechanical failings in the system.

Thanks.

[SRH990]

With the design of the plastic peg that retains the tail gearbox, if the clamp is a little loose or the fin gets a sideways knock, the boom acts like a guillotine and chops the peg off. I've managed to do this a couple of times and now use the upgrade aluminium retainer.

[alex]

There is also a little play where the plastic peg fits in the hole in the boom, enough to let it rotate a bit- seen this on quite a few 700s now. You can get a metal upgrade, but I feel the plastic peg is a good sacrificial link if you do touch the tail down a bit firmly :P

I just check it every week as part of my mechanical check over.

[barney]

Hi Steve.

SRH the otherSteve..LOL is giving you the cause. The pin that locates the gearbox into the boom has sheared allowing the gearbox to twist..Its very common and is meant to be sacraficial

Brian