R22 Vibration Levels & Cyclic Control
Thread Starter
R22 Vibration Levels & Cyclic Control
Am in the middle of a course of which I am running the same R22, have noticed over ther past 2-3hours on it that vibration levels have increased significantly.
Have noticed it through the floor and back of seat, as my students are doing the majority of the flying with little input from me on the controls. When I have flown, the controls appear normal with regards to vibration, however the cyclic tends to stay in the same position if you let go of it throughout the speed range, never met this in an R22, any ideas? (I am maybe worrying about nothing).
The vibrations tends to change significantly at approx 70KIAS, I have asked engineering to track and balance on the next maintenace flight in a few hours.
Any suggestions welcome.
TiP
Have noticed it through the floor and back of seat, as my students are doing the majority of the flying with little input from me on the controls. When I have flown, the controls appear normal with regards to vibration, however the cyclic tends to stay in the same position if you let go of it throughout the speed range, never met this in an R22, any ideas? (I am maybe worrying about nothing).
The vibrations tends to change significantly at approx 70KIAS, I have asked engineering to track and balance on the next maintenace flight in a few hours.
Any suggestions welcome.
TiP
Last edited by TiPwEiGhT; 11th Oct 2007 at 00:57.
If you're in OZ, i'd buy a new one. 
Are they high or low frequency vibes? Main Rotor, Tail, engine?
Cyclic staying in place can be something as simple as a student not undoing the cyclic friction knob.
Let us know what engineering find but I wouldn't neccesarily wait until next inspection. Get it done asap especially if the check is just about due.
Are they high or low frequency vibes? Main Rotor, Tail, engine?
Cyclic staying in place can be something as simple as a student not undoing the cyclic friction knob.
Let us know what engineering find but I wouldn't neccesarily wait until next inspection. Get it done asap especially if the check is just about due.
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Just a thought, try cleaning bug splatter from the rotors. This may be increasing advancing blade turbulence or reducing retreating blade stall AOA (transition from laminar to turbulent flow). If no joy do the track and balance, and let us know what you find. If no cyclic, i would guess balance more than track - anything starting to wear like an elastomeric bush? Any chance of a bolt allowing some slipage?
Last edited by Graviman; 11th Oct 2007 at 15:49.
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R,T & B is a pain on these things due to the nature of the threads on the pitch change links fella. Your men need to be delicate and precise, I suggest a locally made clip on pointer and graduated scale sticker wrapped around the PCL to help. My learned colleague below (3Top) describes the whole procedure perfectly
Also check balance the fan on the back of the engine, when the fan is out of balance it shakes like buggery through the floor and seat backs.
As a previous poster said, depends on the vib freq. One more thing, I have had problems with an R44 which turned out to be driveshaft originated due to incorrect set up of the rear drive shaft belt tensioner.
Any pedal buzz??
Hope that helps.
Also check balance the fan on the back of the engine, when the fan is out of balance it shakes like buggery through the floor and seat backs.
As a previous poster said, depends on the vib freq. One more thing, I have had problems with an R44 which turned out to be driveshaft originated due to incorrect set up of the rear drive shaft belt tensioner.
Any pedal buzz??
Hope that helps.
Last edited by Alloa Akbar; 11th Oct 2007 at 14:55.
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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
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
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If your not the only pilot to fly, look out for overspeeded Main Rotor, it causes the pitch change bearings to stretch and then you find your self in very unfriendly areas, then again I am paranoid about this one because some jerk did it to me a few years back and never wrote it up in the Tech log, I was lucky to get back onto terra firma ( in one piece).
Peter R-B
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Peter R-B
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TIPwEIGhT,
If you are worried about the vibrations have an engineer to check up the track and balance of the M/R and the T/R, and also the balance of the fan. And if you are seriuously worried about the vibrations have the engineer to do it today.
If these actions doesn´t help have the engineers to check the "clearance" for the valves in the engine (stucked valve). We have had some times problems with valves and they might give you some indications of low frequency vibrations.
Also an overspeed can be the reason, usually indicated as vibrations thrue the cyclic due to the spindle bearings, also can be reqognised with cracks of the weldings at the fan of the engine.
But anyway, before the next flight: take your time and do a really good pre-flight, check that there is no cracks in the blades etc.
Cheers,
If you are worried about the vibrations have an engineer to check up the track and balance of the M/R and the T/R, and also the balance of the fan. And if you are seriuously worried about the vibrations have the engineer to do it today.
If these actions doesn´t help have the engineers to check the "clearance" for the valves in the engine (stucked valve). We have had some times problems with valves and they might give you some indications of low frequency vibrations.
Also an overspeed can be the reason, usually indicated as vibrations thrue the cyclic due to the spindle bearings, also can be reqognised with cracks of the weldings at the fan of the engine.
But anyway, before the next flight: take your time and do a really good pre-flight, check that there is no cracks in the blades etc.
Cheers,
Thread Starter
Other pilots do fly the aircraft and it does cross my mind what happens on flights ie, problems encountered, overspeeds etc.
Engineering is doing a detailed inspecton of the aircraft today before a flight with myself and one of the engineers.
MR and TR blades are OK as I am very particular about checking them before every flight and also cleaning if required. Engineering confirmed this also.
Keep you posted and thanks again for all your assistance.
TiP
Engineering is doing a detailed inspecton of the aircraft today before a flight with myself and one of the engineers.
MR and TR blades are OK as I am very particular about checking them before every flight and also cleaning if required. Engineering confirmed this also.
Keep you posted and thanks again for all your assistance.
TiP
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Tipweight,
The problem with the overspeed causing the spindle bearings to stretch or distort is that you cannot really see what has happened, it relies on the honesty of the Pilot or FI who was incharge at the time of the overspeed, the example I cited was caused when a young low hours pupil was allowed under supervison to enter an Auto rotation to power recovery, the young FI didnt keep a tight grip on what was happening and the pupil attained 116% to 120% overspeed on the main rotor, alas nothing was reported.
I came along to SFH with the same machine, I am renowned for being picky on my walkround pre-flight but dispite this even though I looked and touched the hub and spindle boxes nothing seemed untoward, the problem only became apparent at Transitional flight speed by this time it was nigh on impossible to direct the R22 anywhere where I wanted it to go, I could bore you with many more details but to say this occurance changed my way of trusting people is a slight understatement,
ASK THE ENGINEER TO LOOK!!
Peter R-B
Vfrpilotpb
The problem with the overspeed causing the spindle bearings to stretch or distort is that you cannot really see what has happened, it relies on the honesty of the Pilot or FI who was incharge at the time of the overspeed, the example I cited was caused when a young low hours pupil was allowed under supervison to enter an Auto rotation to power recovery, the young FI didnt keep a tight grip on what was happening and the pupil attained 116% to 120% overspeed on the main rotor, alas nothing was reported.
I came along to SFH with the same machine, I am renowned for being picky on my walkround pre-flight but dispite this even though I looked and touched the hub and spindle boxes nothing seemed untoward, the problem only became apparent at Transitional flight speed by this time it was nigh on impossible to direct the R22 anywhere where I wanted it to go, I could bore you with many more details but to say this occurance changed my way of trusting people is a slight understatement,
ASK THE ENGINEER TO LOOK!!
Peter R-B
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Well if the overspeed goes off the scale, there is some major work ahead (Worst case: overhaul)!!
A slight over speed may brinell the spindel bearings (rpm still ON the scale - rpm needle free to move. Once it is at the top stop you don't know where the rpm went!).
Maintenance would turn the spindels to move the brinelled area.
But as was mentioned it takes that the pilots who had the incindent to have the guts and report....
Otherwise, a experienced Robby mechanic may be able to find a rough spindel by disconnecting the pitchlink, raising the MR blade off the droop stop and move it pitchwise by hand. To go more sensitive he might have to empty the spindel bearing area and remove the boot.....
Good luck!
Curious what it was! (.... will have been?)
3top
A slight over speed may brinell the spindel bearings (rpm still ON the scale - rpm needle free to move. Once it is at the top stop you don't know where the rpm went!).
Maintenance would turn the spindels to move the brinelled area.
But as was mentioned it takes that the pilots who had the incindent to have the guts and report....
Otherwise, a experienced Robby mechanic may be able to find a rough spindel by disconnecting the pitchlink, raising the MR blade off the droop stop and move it pitchwise by hand. To go more sensitive he might have to empty the spindel bearing area and remove the boot.....
Good luck!
Curious what it was! (.... will have been?)
3top
The only time i've seen a cyclic not move when you let it go in an R22 was the one which had its blade almost split in half about 10 flying hours later.
The main rotor teeter friction was very obviously too high, you couldn't tilt the head when pushing it from below.
It had a very odd vibration in flight and when you lowered the lever in flight the cyclic would come back at you.
The Crack was a scary sight, I have some photos somewhere I'll see if I can find them.
GS
The main rotor teeter friction was very obviously too high, you couldn't tilt the head when pushing it from below.
It had a very odd vibration in flight and when you lowered the lever in flight the cyclic would come back at you.
The Crack was a scary sight, I have some photos somewhere I'll see if I can find them.
GS
Thread Starter
Track and balances on rotor and engine fan were well within limits which was a surprise!
As for the "steady" cyclic, well that has baffled most people, a full control linkage check has been done with no problems found.
As for balde cracks... I'll be having a good look tomorrow morning again!
Another pilot came forward the other day and reported similar occurrences, so there is much curiousity from both engineers and pilots.
Will keep you posted, am curious to see these picture of the rotor crack.
TiP
As for the "steady" cyclic, well that has baffled most people, a full control linkage check has been done with no problems found.
As for balde cracks... I'll be having a good look tomorrow morning again!
Another pilot came forward the other day and reported similar occurrences, so there is much curiousity from both engineers and pilots.
Will keep you posted, am curious to see these picture of the rotor crack.
TiP
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Check for peeling main rptor tape
Check for peeling main rotor weartape..? it lifts and settles back depending on angle of attack/load of blades... symptoms: vibration and slightly more MP required.. plus cyclic control anomalies. It may not be visible.... surely your engineers would have thought of this one but thought it worth mentioning for the idea-pot. It happened to me recently and kicked off a panic of instrument checks and possible eol fields. Is any tape missing?
Another thing is the recent directive on blade delamination near the tips/underside.. tap tap with finger nail..?
Another thing is the recent directive on blade delamination near the tips/underside.. tap tap with finger nail..?
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tape
TipWght
I have not seen it on the R22 first hand. It was removed by the time I next flew the specific craft. To fill you in: For me it happened at a climb out from 500ft to 800ft and disappeared as I eased collective down and levelled out. I was about to make a precautionary landing but as there were no warnings and it had been a low rpm vibration I elected to continue to the field, albeit very watchful of all indicators. It didn't appear again but I relayed the incident and could find nothing myself. Later the lifting tape was found as the answer, found by the cfi who had an inkling from previous experience with the same and plastic flotsom etc.. I have flewn it since and it runs smoothly.
Not sure what BladeTape is (if that is different), perhaps I should not have used that term if it is applied to something else specific? It must be weartape? I have seen it on the 206... for leading edge wear protection etc.
I have not seen it on the R22 first hand. It was removed by the time I next flew the specific craft. To fill you in: For me it happened at a climb out from 500ft to 800ft and disappeared as I eased collective down and levelled out. I was about to make a precautionary landing but as there were no warnings and it had been a low rpm vibration I elected to continue to the field, albeit very watchful of all indicators. It didn't appear again but I relayed the incident and could find nothing myself. Later the lifting tape was found as the answer, found by the cfi who had an inkling from previous experience with the same and plastic flotsom etc.. I have flewn it since and it runs smoothly.
Not sure what BladeTape is (if that is different), perhaps I should not have used that term if it is applied to something else specific? It must be weartape? I have seen it on the 206... for leading edge wear protection etc.
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TiPwEiGhT,
If your engineers are equiped to do it, then you could fly with an accelerometer stuck to the fuselage. This could be inside the cockpit, near where you felt the vibration, to avoid any complications. The idea is to convert the signal into a frequency plot, to understand the cause. It works because engine, main rotor and tail rotor are geared to rotate at different frequencies.
You haven't mentioned tail rotor by the way - any constraints on flapping? Is drive shaft running out of balance?
For general vibration work, with variable RPM, a Campbell diagram is a great way to pinpoint the source of a vibration
If your engineers are equiped to do it, then you could fly with an accelerometer stuck to the fuselage. This could be inside the cockpit, near where you felt the vibration, to avoid any complications. The idea is to convert the signal into a frequency plot, to understand the cause. It works because engine, main rotor and tail rotor are geared to rotate at different frequencies.
You haven't mentioned tail rotor by the way - any constraints on flapping? Is drive shaft running out of balance?
For general vibration work, with variable RPM, a Campbell diagram is a great way to pinpoint the source of a vibration