MR vibration (low frequency) or high (TR or fan)?
T&B is no big deal if you get the pitchlink adjustment sorted:
Don't try to "measure the changes" with pitchlink rodend against pitchlink rodend.
The only change you make and register is the big self-locking nut on the pitchlink barrel. To do that you loosen one (generally the upper) rodend completely, adjust the barrel nut and re-tighten the rodend - hold the lower rodend so that it touches one end and tighten the upper one in the same position - touching the same side. This way both rodends have their max moving range and are always in the same position.
You mentione that vibration changes above 70 kts.
Does it the same in a hover and just gets stronger with speed or is it not there at all in a hover?
You get a rather strange shaky vibration when the friction in the MR head bushings (main bolt and/or coning hinge bolts) looses or tightens...
Part of this problem comes from mechanics touching the bushings and shims with their hands, introducing small amounts of grease which shows effect only after about 15 to 50 hrs.
Friction values generally stay putt for a long time if done correctly.
But of course everything wears.
Loss of friction does not mean that the bolts have to be loose! They be better be not!!
Do a friction test with 2 brooms, according to the manual - it might show right there!
3top
