How do I tell if my main shaft is deformed and how much is acceptable?

[alex]

Says it all in the title really :P

I have had a great weekend with my first proper helicopter, but that also meant the first proper crash.

I now know the ins and outs of stripping the rotor head, all the way down to taking the main shaft out and have had every single piece of the rotor assembly in bits, mainly out of interest.

There is a fine, but pronounced vibration at 1900 RPM with the blades off, but the flybar in place. I am sure I can see a small amount of wobble in the top of the main shaft as it spins up, but also at high speeds, there is a slight blur of all the linkages.

Is this normal? I took the whole shaft out and ran it over a flat surface and it seemed fine, but I'm guessing that tiny deformities will not show up like this, but will be revealed at high RPM. Is there anyway of testing this, or am I best trying a new shaft and seeing the result?

Cheers

ALex

[sacko]

Take the head off, and spool it up...

...lbviously dont give it much throttle at all.

[ROCKET RONNIE]

hello mate, im new to this, but i hav had some crashes and every time ive been told for the sake of £5 change the main shaft, ive taken one out and rolled it on glass, could not c it bent or not, yet in the heli it was vibratring, new one in and all ok, hope this helps, Ronnie

[Fixxxer]

As ronnie says rolling on glass or a mirror will usual show up any bend, also check ur bearings. I'm guessing this is an electric heli ? if it's nitro then don't spool it up without blades as the engine requires a load.

[spunkmyer]

You can use a tin hammer to slowly knock it straight if it is a small heli (250,400 etc) but for the price just order a few and replace after each smack as even a small vibration at 1900rpm is putting huge strains and loads on other parts even the gyro can be up set with a slight vibration.

[alex]

Thanks for the replies- I have a new main shaft on order anyway, so will try it with that and see if there is any difference.

The crash involved a gust of wind ( which I should Have seen coming), about 2 meters altitude- it broke one blade and the blade grip, bent the fly bar a bit and the tail boom was a mess. The tail was dramatic, but easy to fix.

If there is a slight bend in the main shaft, it is too small to see with the naked eye. I tried spooling it up wthout the blades or the flybar too, but if there is a slight bend, the vibration will be far less noticable as there is less weight on the main rotor head to amplify and vibration.

I am learning fast

[stuartflys]

I've been so annoyed with vibration in the past that after any crash I nearly always replace the feathering shaft and flybar. Ifs its a good crash the main shaft as well. For a few quid its just not worth the hassle.

You cant really get away with any deformation in these shafts if you want a vibration free heli. Over time vibration will kill other components on the heli like bearings, electrics, etc..

[EtheAv8r]

Easy test for bent main shaft (and spindle) is to roll it on flat glass - no bend is acceptable - they are cheap, and must be straight and true. If you can see the wobble on the head, it is bent and must be changed. Yours might be straight from the sound of it and Innovator mainshafts are very strong.

When you do bend one, do not try to straighten it - you won't manage it and it won't be balanced.

If the flybar is bent or twisted, this will cause vibration, as will out-of-balance conditions. Also check for main gear teeth damage, anything here will cause vibration, as will too tight a mesh with the motor drive gear. Also check tail drive belt teeth, damage here will cause general vibration.