AS350 - 3R Vibration

[OverTq]

One of our Squirrels has developed a marked 3 R vibration, which we have not come across before. Head, tail and drive-shaft are all OK, and can't think what could be causing this. Any ideas, please?

[wrench1]

OT,

Check the tuning weights under the floor per the work cards.

W1

[OverTq]

Thanks wrench. They are regularly checked, and show no sign of the cracking problem, Also, they don't seem to have shifted from their original position.

[alouette3]

This might make absolutely no sense ,technically ,but check the condition of the uni ball.
Alt3.

[Fred Bound]

Have a look at the condition of the rubber bushes on the 'dog bone' link under the transmission. It's a bit of a bugger to get out and in, but it's accessible, just, above the fuel tank.

We had 3r with a 350 in low autos/low power descents caused by these bushes.

Good luck.

[Hawkrx]

OverTq;
Have a good look at the windshield screws, loose screws are a primary cause of a sudden pronounced 3per. Also would have a look at the MRH Frequency adapter bearings, landing gear springs, vertical fin attachment screws, M/R blade trim tabs, AVA attachment screws, and Fuel tank strap tension. Double check your inflight NR set to 390 to get the smoothest ride. Best of luck, I know chasing a phantom 3per can be a real pisser . -HawkRX

[OCTANE100]

Hawks is on the money....

A couple of additional ones I have come across are the MGB support struts rod-end bearings worn (it takes only a tiny bit of wear to make a real rumble which you may pick up as a 3 per) and wear on the (bottom primarily) rod-end bearing of the M/Rotor Hyd servos.

By far the most common is the M/R freq adapter spherical bearings....

I wouldn't start adjusting the hammers until you are totally out of other options.......Have you inspected the airframe around the attachment for cracking..?

The lower br'g on the M/R vib absorbers ok ? top shaft attachment screw (to the weight)is still in place?? Can also do a dimension check on the springs if the aircraft has a few hours on it....

Cheers

[OverTq]

Thanks guys - the aircraft is only recently off a C check, but will get the 'spanners' to check those things you've suggested.