R22 Vibration Levels & Cyclic Control
Thread Starter
Grav,
You have just sprung a thought into my mind sir!
Could excessive wear in the TR elastomeric bearing (but within limits according to engineering) cause this strange vibrations?
I have asked them on several occassions about the condition of the bearing, which is starting to debond on the outer edge, but as I mentioned it is apparently within limits.
I'll try get a picture tomorrow of it.
Thanks.
You have just sprung a thought into my mind sir!
Could excessive wear in the TR elastomeric bearing (but within limits according to engineering) cause this strange vibrations?
I have asked them on several occassions about the condition of the bearing, which is starting to debond on the outer edge, but as I mentioned it is apparently within limits.
I'll try get a picture tomorrow of it.
Thanks.
Brinneled pitch change bearings are difficult to detect with the blades installed. If nothing else is found and the problem persists I would whip the blades off and check the spindles by hand.
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TiPwEiGhT, like EricFerret says.
It makes sense that this could be the problem, since most others have been eliminated. You describe increased vibration in cruise, which suggests that when the tail rotor is asked to flap there is some non-linear behaviour in the tail rotor bearing. In flight it would be under load while moving, so could judder. Vibration would be almost at the low frequency end of audible - haven't got Prouty to hand so don't know TR RPM...
From ground vehicle design experience i know that elastomeric bearings fail by splitting the rubber. It takes a long time to start splitting, but once started does not take long to break up (from my experience that is not immediately catastrophic, but the bearing does start to float).
It makes sense that this could be the problem, since most others have been eliminated. You describe increased vibration in cruise, which suggests that when the tail rotor is asked to flap there is some non-linear behaviour in the tail rotor bearing. In flight it would be under load while moving, so could judder. Vibration would be almost at the low frequency end of audible - haven't got Prouty to hand so don't know TR RPM...
From ground vehicle design experience i know that elastomeric bearings fail by splitting the rubber. It takes a long time to start splitting, but once started does not take long to break up (from my experience that is not immediately catastrophic, but the bearing does start to float).
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R22 vibration levels and cyclic
Would it be reasonable to assume that if the machine die not have full and free cyclic movement whilst on the ground one would refuse to fly it!
Thread Starter
The machine does have full and free control movement on both the ground and in flight. The cyclic simply remains very steady in flight and maintains a pretty good attitude... have I just discovered a stab system for the robbo?
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R22 Vibration levels and cyclic
Graviman . Honest, not me guv, never mentioned delta 3 . Just got the impression from the first post that the cyclic stuck a bit and it sounded a bit dangerous. Heres an interesting question though. As the Robinson relies on a stack of bearings to take the centrifugal forces on the blades, does to load get distributed throughout the five (from memory) bearings or is it taken on one bearing. Bug
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Sorry Bug, dumb comment on my part (post now deleted). As well as friction off full and free check, i assume that track and balance would have picked up on any unexpected friction in the MR feathering bearings. Under load friction could be higher though.
TiPwEiGhT are you sure pitch bearings OK?
Not familiar enough with design details to answer question. Pics of main rotor:
http://www.b-domke.de/AviationImages....html#Robinson
Couldn't find tail rotor images either.
TiPwEiGhT are you sure pitch bearings OK?
Not familiar enough with design details to answer question. Pics of main rotor:
http://www.b-domke.de/AviationImages....html#Robinson
Couldn't find tail rotor images either.
Track and balance is often ok.
Pitch bearing brinelling tends to come through as a "rough" feel in the controls.
The point graviman makes about flight loads is spot on.
What does not feel like much by hand is very much worse with a few tons of centifugal force thrown into the equation.
Pitch bearing brinelling tends to come through as a "rough" feel in the controls.
The point graviman makes about flight loads is spot on.
What does not feel like much by hand is very much worse with a few tons of centifugal force thrown into the equation.
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Hey guys, I just flew an acceptance flight in an R22 and am getting a very similar vibe and centerd cyclic. The cyclic seems to center itself in forward flight and in a hover almost like a trim. I've never experienced this before. Good range of motion before start up and nothing binds up or feels even remotely rough.
Also, at about 70-75knts I'm getting a good bit of stick shake. More than I'm used too. Almost perfectly smooth in a hover. Nice and smooth up to about 65knts and starts to shake, not bad but noticeable. At 70 it starts to get rough.
Little background. New -4 MRB, new tail blades, new engine mounts, new lower sheave, new belts, new longitudinal bungee.
Another thing was that in a hover the ship twitched to the left a couple times. The mech said that the lower plugs may be fowler since the engine was pickled for a while. Has new mags and carburetor.
Any help would be great, thanks!
D
Also, at about 70-75knts I'm getting a good bit of stick shake. More than I'm used too. Almost perfectly smooth in a hover. Nice and smooth up to about 65knts and starts to shake, not bad but noticeable. At 70 it starts to get rough.
Little background. New -4 MRB, new tail blades, new engine mounts, new lower sheave, new belts, new longitudinal bungee.
Another thing was that in a hover the ship twitched to the left a couple times. The mech said that the lower plugs may be fowler since the engine was pickled for a while. Has new mags and carburetor.
Any help would be great, thanks!
D
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Get the engineer to check the T &B a few times in between a few flights up to 75 KIAS and ensure the same result is achieved without any adjustments.
I had an increasing vibration over a period of a week and as I was the only instructor flying the helicopter I could account for it not been oversped etc. Then on one flight half way through the student making a steep turn there was an unusual increase in vibration etc and the cyclic felt different. I made a precautionary landing and when I could not find an issue and having discussed with the engineer I flew back to base at 60 KIAS without incident. A full check was carried out and we concluded the T & B was within limits but decided to make it as smooth as possible so made an adjustment. After a few quick flights and small adjustments we found our selves making changes but with no improvement and the plot moving very randomly around the graph. After 4 moves the engineer said he thought he knew what the problem was - we checked the flapping hinge tension which whilst within limits did not feel right so we pulled the pins and sure enough the bushes were very stuffed. We replaced these, tracked it up and it has flown 600 trouble free hours since. The worn bush has clealry moved under load but the vibration was not felt until above 65 to 70 KIAS.
I had an increasing vibration over a period of a week and as I was the only instructor flying the helicopter I could account for it not been oversped etc. Then on one flight half way through the student making a steep turn there was an unusual increase in vibration etc and the cyclic felt different. I made a precautionary landing and when I could not find an issue and having discussed with the engineer I flew back to base at 60 KIAS without incident. A full check was carried out and we concluded the T & B was within limits but decided to make it as smooth as possible so made an adjustment. After a few quick flights and small adjustments we found our selves making changes but with no improvement and the plot moving very randomly around the graph. After 4 moves the engineer said he thought he knew what the problem was - we checked the flapping hinge tension which whilst within limits did not feel right so we pulled the pins and sure enough the bushes were very stuffed. We replaced these, tracked it up and it has flown 600 trouble free hours since. The worn bush has clealry moved under load but the vibration was not felt until above 65 to 70 KIAS.
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Unexplained vibration levels on r22 is cause to ground the machine until you know what the problem is. A senior pilot and instructor were killed in Australia from this very problem. Engineers had tried numerous times to balance the main rotor without disassembly, crack in retention bolt hole propagated and blade departed the machine.
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Be scared
Unexplained increase in vibration level on the R22 is cause to ground the machine.
Senior pilot and instructer were killed in Australia from this issue.
Engineers had tried unsuccessfully numerous times to balance the Main Rotor. Crack in blade retention bolt hole propagated until a blade departed the helicopter in flight
http://www.atsb.gov.au/publications/...302820_001.pdf
Senior pilot and instructer were killed in Australia from this issue.
Engineers had tried unsuccessfully numerous times to balance the Main Rotor. Crack in blade retention bolt hole propagated until a blade departed the helicopter in flight
http://www.atsb.gov.au/publications/...302820_001.pdf
Last edited by owen meaney; 21st May 2013 at 23:16.
