Head Wobble

[Steve]

Any suggestions gladly appreciated please.

I had an 'incident' with one of my helis a couple of weeks ago when th etail belt stripped most of its teeth off. So I've replaced the damaged parts, and took it up the field for a test fly yesterday evening. On spool-up it started to vibrate (head speed vibration, not high frequency tail vibration) and the tracking was a mile out. I then spent ages fiddling with the tracking trying to get it right, only to find that it would be ok at one head speed, and then miles out as the head speed increased. Needless-to-say, I never got it off the ground, and have spent this evening investigating.

Now, all the shafts are fine - main, feathering, flybar, and the tail shafts (not that this is a tail problem, it's a head problem). The blades grips are metal and they're fine, not bent etc. Everything is fine, none of the plastic bits are cracked, the ball joints are all ok, the push rods are all spot-on (but I've fine tuned them anyway this evening for an even more precise setup). The bearings are fine and alligned, the auto-rotation hub is fine etc etc etc.

I just cant find anything wrong, except that one of the extended balls on the one of the blade grips was ever-so-slightly loose. Not much, almost nothing, just not quite as tight as I might have liked.

Anyway, I've had it all apart and reassembled it again this evening and triple checked everything, so am out of ideas at the moment. I'm happy to go and test-hover it again when I next get a chance (probably next week sometime) but am really after any advice on anything else that I shoul dreally take a look at.

Cheers.

[AndersUK]

That phenomenon is usually down to parts rotating on the spindle or the spindle/feathering shaft itself.

Replace spindle anyway
Check dampers and head bearings - may want to replace anyway.
Ensure the main blades are fine and blade grip spacers are equal (if used)
Replace blade tracking ball links

Andy

[Steve]

That phenomenon is usually down to parts rotating on the spindle or the spindle/feathering shaft itself.

Replace spindle anyway
Check dampers and head bearings - may want to replace anyway.
Ensure the main blades are fine and blade grip spacers are equal (if used)
Replace blade tracking ball links

Andy

All of the above are fine and in excellent condition, so I am loathed to replace any of them at the moment. However, If it still happens when I next try it, then I'll certainly take thi sadvice gratefully.

[Steve]

Sorted it.

After replacing the dampers and thrust bearings in the grips, as well as checking and re-checking the whole control system for slop and/or bent stand-off balls and/or cracked plastic bits etc etc etc, I finally gave it a go with a different set of blades - hey presto, no more wobble.

I can't find the other thread about the TT blades along the same lines. In my case, it's the TT blades without question. The blades I bought are 620mm TTs, and when I put the 600 TTs off my Sceadu (never had a problem with these blades on that heli) onto the Airskipper, no more flapping about.

So the 620s will be going back to the shop and replaced with something eles.

I'm quite suprised that it's the blades really, and a bit disappointed, as I though they were good value for money.

[mchristyuk]

The Manager,

Another thing worth trying is static tracking to make sure nothing in the head block is distored.

I find the easiest way to do this is set the model on a flat surface and then have your transmitter next to it at the tip of the rotor blades. Extend the aerial up so that the 1st blade just brushes the top of the blade. Then rotate the head around 180 degrees and the 2nd blade should also just brush the top of the aerial. If the blade is more than a centimetre or so higher or lower then your head block is out. This can cause weird tracking issues.

The old original Xcell 60's (maybe even the current ones..) had holes in the block which had grubscrews in that pushed against the mainshaft to allow you to adjust the static tracking (another instance on that machine where everything was overly complex and adjustable because they couldn't make straight bits in the first place... but thats another matter...)

Cheers

Mark

[Philimon]

Dumb question: You did balance the blades correctly, by first setting their CG's to identical positions and then adding weight to the light blades at the CG?

Sorry if I'm stating the obvious...