can anyone help
i have a venture 50 and am having serious fuel foaming problems due to high frequency vibration.
the main and tail blades are all balanced perfectly
the motor is balanced to within 20 microns that obviously includes cooling fan and clutch
what is an acceptable spec on the balancing of these things?
is 20 microns way out of balance or am i missing something?
any advic would be appreciated.

how perfect is the flybar balance? Its very easy to forget to ballance the flybar... and that can create all kinds of vibration problems.

How well do the blades track? If the blades aren't tracking... you have a vibration from the wobble of the rotor disk.

And what no one ever checks do the flybar paddles track with each other?

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Other end of the heli... hows the balance and tracking of the tailrotor? (yes, the tailrotor can have the pitch of the 2 blades not adjusted for proper tracking.)

High freq. vibration from the engine causes fuel foaming because it's so close to the tank. It could come from the engine itself, the fan, clutch or start shaft that doesn't use a sprag. The tail blades spin very fast too but usually won't transmit the vibs back up the tail so much. Anything on the main shaft (head, blades, paddles etc.) will cause more of a visible shake, but not fuel foaming.
Sometimes on a new heli, the clutch liner can have a varying thickness letting the shoe sling out by different amounts causing an imbalance. As it seats-in, this will true itself or you can 'turn' the liner in a small lathe.
For best results, the fan and clutch should be balanced and then checked for 'run-out' to less than .002 in. (.05mm) after mounted to the engine. Most of these components are machined to tight specs and are self centering when mounted so that they run true enough to not cause a problem, but just because it runs 'true', doesn't mean it's balanced.
Being you still have a foaming problem, I would do both.
A good prop balancer or a high point balancer works good but be sure that the part is spinning 'true' in the cones before you start removing material. Always mark the heavy side and rotate it in the cones to see that the mark falls to the bottom repeatedly.
Be sure the clutch shoe gaps are equal and parallel before you check it.
Hope this helps...Good luck!!


Kirk

Can I ask what you used to measure the runout of your engine assembly down to 20 microns? That's .02mm, or .00079 inches (7.9 ten-thousanths).

I'll guess that you mean .020 inches (or 20 thousanths). That's a reasonable number, but still too much for your clutch stack. You should be able to get it around 2 thousanths, or .002 inches. A runout of .020 will cause the type of vibration you're having.

Ben

THE TAIL OUTPUT SHAFT COULD ALSO BE BENT SLIGHTLY.

Have you got training gear on it?

Venture 50's have had problems with the fuel tank rubbers being too thin, my mate had foaming problems that we just couldn't clear up, we spoke to the distributer who sent us some thicker tank mounting rubbers, this cleared up the problem, something to think about

thank you for the advice guys will try and implement suggestions just as a matter of interest
the figure of 20 microns is correct i use a dial guage that that measures 001mm per graduation on the dial very sensitive! any other ideas on the subject would be appreciated

Richard

Got me a Venture 30 - very neat machine! One problem, during my tenth flight, the muffler broke off - the tube between the engine and and muffler broke off where it meets the muffler. From the oil residue it seems as if it cracked off gradually. The supplier says that I mmust have serious vibration on the heli. When flying the helicopter, there is no foaming of the fuel in the tank. Is there any way of checking for vibration other than the fuel in the tank?

Jaco