Unexplained wobbling in the yaw plane

[darren_uk]

Hirobo Shuttle Z-TS

I fly rarely (e.g., had a gallon of fuel since 1998, not used it all yet).

My proficiency: I'm up to the hovering around in a tail-in figure of eight, and can transition to forward flight and bring it back to a hover some way away from me. Can do sideways on hovering just about but not nose-in.

GETTING TO THE QUESTION NOW:

The helicopter was set up by a competition flyer / shop owner (and has flown beautifully).

I dusted it off this weekend after not flown for 18 months. Flew nicely. Flew one tank of fuel.

Got back home - noticed one of the exhaust bolts had been lost (due to natural engine vibration). Put in another one and whilst I was at it put some fresh UHU (the 200degC stuff that you mix up) to keep them secure and to use as a gasket.

THE QUESTION:

Flew it this morning: It was as if I had an over-ambitious gyro. It was yawing left to right. Wasn't due to gusts of wind, this was wobbly in the yaw plane.

Anyone with experience of the Hirobo that might suggest what problem could have developed? It wasn't there on my last flight 2 days ago.

First rule of pre-flight (for those that do it....), make sure everything is tight.

The wobble could be a few things-

Over sensitive gyro
Loose control arm linkage at the tail or servo end
Loose part on the tail itself
Bad servo
Battery not charged fully

I've had the problem several times and it's always something loose at the tail end. I don't remember if the Shuttle's use bearing type connections at the linkage ends, but the default way Kyosho does it is to have the linkage slip into a servo horn type structure. Over time this hole gets reamed out and lots of play is introduced.

Hope that helps!

BTW- I've lost my muffler and starting cone a few times due to loose screws-nothing like seeing something fly off the heli while in flight but have no idea what it was! I've ended up with nuts on the end of the screws for the muffler (lock tite type stuff strips the screws)....I keep telling myself, pre-flight, pre-flight....

[administrator]

Sounds like a gyro sensitivity set too high. But if the problem wasn't there before, then I suspect vibration causing the gyro to pick up unwanted noise.

Try adjusting the gyro gain down a little to see if you get the wobble.

By the way, is your a pizeo type gyro or conventional mechanical one?

good point- traditional gyros do wear out- the use bushings to hold the spinning part and when the bushing wears in the same spot it can wiggle....

Also make sure the gyro itself is firmly seated. Most people I know use doublesided foam tape. Fuel eats this stuff alive and can wobble the gyro loose too.

[darren_uk]

HI again,

It's a piezo gyro. Mounted on the double sided foam like your said. It seems secure at the moment (no fuel corrosion)

I suspect, like yourself, it could be something else that's because loose thus introduced some noise.

And I supposed that because of the inertia of the main rotor then I wouldn't detect this in the cyclic, hence only saw a problem in the rudder.

I'll continue to monitor at the next flight, although goodness knows when that will be...

TAIL ROTOR: One thing I have noticed: there seems to be some for/aft movement, to the tube of 1 mm, in the tail rotor attachment to the boom - maybe this is just an engineering thing (can't pull it out further than 1 mm because the belt drive then retains it) or perhaps the belt has stretched over time (on so few flights?). Tightening up the bolts has made no difference - perhaps time to get the UHU out again...

[Daz(DJLFlapper)]

Hi I have had this problem with my heli and could not find the cause till I was forced to go looking harder buy the heli spining uncontrolably just as i got it off the deck.
For me it turned out to be a dry solder joint in the gyro itself. The black wire had come loose and was touching intermitently. This had the affect of turning the gyro off and on.
I was lucky and got the heli down without dammage. I opened the casing on the gyro and saw the wire at fault, I re soldered this wire and have had no problems scince.
I'm not saying this is the problem but if this carries on then it could be something to look at.
All the best,
My gyro is a peizo PG03

the advise i was given concerning the tail on any model heli at all is first of all check all is tight ada in good order ie; tail drive ,push rod etc. if problem is still there then change your tail bearings yes your tail bearings , this accounts for at least 90 percent of tail problems.if problem is still there then last of all look at the gyro or tail servo as being the problem. If I get a tail problem and we all do these are the rules that I stick to and yes its saved me pounds
hope this helps.
Nigel