MD 500 vibration
 

Guys

Help needed from those who have played with the beasts !
MR ips in hover under .1 ips , tr .05ips as ac accelerates to 60 kts tr .2 ips, 80 kts .4 ips 120 kts 1.2 ips
the problem area appears to be something between 235 to 245 rpm causing an intermix between main rotor and tail rotor, any ideas before we set fire to it ???:ugh::ugh::ugh:

TR Vibe?

Which model? C or D/E?

2 blade TR or 4?

Above 1.2 it will probably depart the aircraft eventually.

If a T tail machine - check for damper weights fitted between H/Stab and Tip Plates. Yes with 2 blade TR, No with 4 blade TR.

The damper weights will mask a large imbalance. Hence balancing at GI on the T tail. If unsure remove H/Stab and check balance at FI.

Are both TR pitch links the same and correct length. D is longer than C but will fit and I have seen them intermixed - don't ask how!

235 to 245? Do you have a spectrum analysis with harmonics visible?

What changed immediately before the issue - it should be pretty obvious.

P.S. Before you burn it I will give you 5 bucks for it! :rolleyes:

2 blade tr
D model
Tip weights when removed ips is lower
Normally balance when t tail removed then replace t tail remeasure and ips gets better
The buzz through the feet gradually getting worse however if in perfectly balanced flight no buzz as soon as you pressure a pedal buzz would come back.
Last 200 check tr box making metal not enough to set of chip detector. However replaced gearbox with a zero timed from oh
At same time mr blades back to htc for disbonding at the grips. Balance on tr now dreadful, back to shop put back old gearbox that has been overhauled better result but not acceptable ( info as per original post ) last time had this output shaft on box had gone undersized. Currently replaced swashplate and pitch links.

One area where I have previously had odd main rotor vibrations (500D) that come and go was worn main rotor pitch change/flapping bearings and pins. These are the bearings (spherical) that are bolted to the pitch change cases 5 off (excuse terminology long time since I touched a 500) and the pins 5 off attached to the hub by nuts. A 500C would obviously have 4 of each.

To check remove blade and try to lift the pitch case keeping it horizontal feeling for play.
They can give a rough ride while exhibiting a fairly good track.

The teflon inner lining of the bearings wears out and the metal to metal contact wears and steps the pins.

When looking at a visual tracking picture you see one or more blades moving up and down for no apparent reason.

Be very wary of 500 blades that are manufactured by PMA that will not track or balance.....the possibility of a broken spar could be a reason. We had this happen a few years back in Canada that caused an in flight breakup that of course killed a pilot.

Eric thanks but all have been changed !
Helilog the PMA blades tracked ok so don't think it is that but thanks

Still there then checked for cracks in roof plate just a thought as there is not much left to check or change.

235-245 RPM? Check the scissor link for play.

500 guy sorry that was 2450 to 2550 so a 5 to 1 vibe from main rotor . The vibe is from the airframe not any rotating item. Vibe gets worse with speed. accelerometer on tr box. reads 0.2 ups at 60 lys 0.4 at 80 1 at 100kts and 1.2 at 120 so goes up with airspeed

How do you know it is from the airframe? 2500 sounds like a 5 per on the MR, MR. Plungers and striker plates often make a 5 per at ground idle but should go away in flight.


Have you tried mounting it on the MR and seeing if it still sees the vibe? if not that rules out the MR.