Tempest FAI Head problem

[Zilly]

I was suffering from a lot of vibration on the Stratus and after a lot of fiddling with the engine and head scratching (mine not the helis) I noticed when it was back on the ground for about the 6th time that there was a larger gap between one grip and the headblock than the other.

Upon closer inspection I noticed that one of the Damper orings was bulging out on one side, I took both blade grips off and this allowed a closer look however when I wobbled the blade axle around a bit it went back in to the head block as it should, I put it all back together again and flew for the first minute all was fine then the wobble returned and the blade grips were off to one side again.

I have only flown this head for perhaps 30 flights since I built it. I checked to ensure all the correct washers and shims are in place and nothing is missing.

I always felt that there seemed to be a lot of movement in the blade axel as when you grabbed a blade grip you can push and pull it in and out of the head block by a good couple of mm.

Any ideas?

z

[DavidH]

I would start by checking the balance of the blades? If one is heavier than the other or the spanwise C/G is out further on one than the other. This would cause the axle to pull to one side and the vibration problem.

Only thing I can think of right now. I have been flying the Tempest FAI rotorhead couple of years. Have not had a problem like you describe.

David

[Zilly]

Thanks for the quick reply David, do you have the in / out play i mentioned?

z

[DavidH]

Zilly,
I really don't have any noticeable in and out play in the head when pulling on the blade grips.

I did measure a spare blade axle I have. It is 138m from end to end. At least that is the measurement I got holder a ruler up next to it.

Here is the drawing of the head.
http://www.miniatureaircraftusa.com/support/kit_drawing_page.asp?kit='1022'&section='MRASM'&image='01E-01F'

You do have 0848-3 installed next to the .025mm shim at the dampeners?

Also 0840-10 between the thrust bearing and the radial bearing?

Other than those two items above. I don't know of anything else that would cause the in and out play your describing. Other than the blade axle being too long.

I know you probably have, but double check your assembly of the head against the drawing I posted.

David

[Zilly]

Having replaced the dampers and checked and double checked that I had all the right shims and spacers as per the drawing I got a chance to fly the head today and the problem immediately came back, i took some pictures to show you all what it looks like when I land.

If i grab the blade grip and psuh it back in I can re seat the orings however as soon as I fly the problem comes back.

z

The picture below gives you an idea of how far over the axle is...

[Zilly]

Here is a closeup showing how the Oring looks

z