Troubleshooting Shake/Vibration

BDavis

Newbie
Joined
Jun 17, 2020
Messages
9
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Inman, SC
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Parsons Trainer
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50
New gyro pilot/owner here...having fun working on adjustments for vibration, but seem to be going in circles (pun intended). If you had simultaneous stick shake (increasing with rrpm), cabin shake (horizontal plane, increasing with rrpm) and cabin hop (vertical plane, increasing with forward speed), which would you attack first, and why?

From the advice I've pieced together here, do I understand correctly that the order should be (assuming blades are strung correctly), 1) cabin shake by adjusting static balance with blade tip weights, 2) cabin hop by correcting dynamic blade tracking/angle of attack with shims on the rotor bar, and finally 3) stick shake by adjusting the left-right cord on the teeter bolt?

And for those who will recommend special equipment, I don't want to fly to Florida or pay $800 for a tester yet!

Thx, Ben
 

wolfy

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Dec 19, 2013
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western australia
Tracking affects balance but balance does not affect tracking.
Always tracking first.
The fastest way to success is with a balancing machine.
Ground tracking (via pre rotator and visual aids) will give limited results if your rotors are divergent in pitch (go further out of track with airspeed). In flight tracking with a balancing machine will give you the best compromise.
Blades can be in perfect visual track but not give the smoothest ride, track to lower vibration only.
Track and balance is a compromise.

wolfy
 

XXavier

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Ben, I suggest that you make a search of the forum with the keyword 'Goodrich'. Mike Goodrich is an expert on autogyro vibrations who has written many memorable posts here...

Good luck...
 

ckurz7000

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Balancing gyro blades is a black art. There are a lot of things affecting it, and not all rotor/rotor head/mast combinations can be tracked and balanced to a satisfactory end result.

Without a vibration analyzer like the PB4 you are running through a swamp at night with eyes closed and hands tied behind your back. Even with such a gadget it requires experience and knowledge. I wouldn't recommend you do it by yourself if you haven't balanced a lot of rotors before.
 

Chris Burgess

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"running through a swamp at night with eyes closed and hands tied behind your back"

Man, were you in my Army "Escape and Evasion" training exercise at Ft Stewart GA?

"Black art" has some truth to it. One thing to note if you go at it alone, make sure you "reference" mark "everything". If you goof later an unknowingly move something 180 degrees, all previous work will be lost.
 

BDavis

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Jun 17, 2020
Messages
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Inman, SC
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Parsons Trainer
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Ben, I suggest that you make a search of the forum with the keyword 'Goodrich'. Mike Goodrich is an expert on autogyro vibrations who has written many memorable posts here...

Good luck...
Will do! Thx.
 

BDavis

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Joined
Jun 17, 2020
Messages
9
Location
Inman, SC
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Parsons Trainer
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50
Tracking affects balance but balance does not affect tracking.
Always tracking first.
The fastest way to success is with a balancing machine.
Ground tracking (via pre rotator and visual aids) will give limited results if your rotors are divergent in pitch (go further out of track with airspeed). In flight tracking with a balancing machine will give you the best compromise.
Blades can be in perfect visual track but not give the smoothest ride, track to lower vibration only.
Track and balance is a compromise.

wolfy
Very helpful, and sounds consistent with what I have read. Have red and white reflectors now and will give it a shot at 150 rrpm with my pre-rotator and a flashlight. Suspect I will still have some velocity-correlated cabin hop in flight at 330 rrpm, but should be able to increase or decrease shim thickness on the rotor bar to find a decent compromise. I do find it hard to compare vibration levels from flight to flight, so will be trying the AMC Vibration Isolator Pro app to help quantify it.
 

BDavis

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Joined
Jun 17, 2020
Messages
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Location
Inman, SC
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Parsons Trainer
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50
Balancing gyro blades is a black art. There are a lot of things affecting it, and not all rotor/rotor head/mast combinations can be tracked and balanced to a satisfactory end result.

Without a vibration analyzer like the PB4 you are running through a swamp at night with eyes closed and hands tied behind your back. Even with such a gadget it requires experience and knowledge. I wouldn't recommend you do it by yourself if you haven't balanced a lot of rotors before.
Like a pig looking at a wristwatch!
 

BDavis

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Inman, SC
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Parsons Trainer
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"running through a swamp at night with eyes closed and hands tied behind your back"

Man, were you in my Army "Escape and Evasion" training exercise at Ft Stewart GA?

"Black art" has some truth to it. One thing to note if you go at it alone, make sure you "reference" mark "everything". If you goof later an unknowingly move something 180 degrees, all previous work will be lost.
Good advice. I stumbled through a version of SERE myself back in the day.
 

BDavis

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Parsons Trainer
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I think those vibration apps will give you a false sense of hope, I wouldn't take there results for gospel.

wolfy
I agree, but it would be nice if I could have something in addition to my highly-calibrated buttocks (not!) to help me detect an increase or decrease.
 

Mike G

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Ben
I'm glad you found my post in Greg's thread about slinging or stringing, I'd forgotten I'd written all that so it has saved me writing it again. There is another thread I wrote a few years back which gives a fairly in depth description of some of the balancing process but I think the illustrations will have disappeared because at the time all my photos and sketches for the RWF were on Photobucket and since then they decided I had to pay so I removed everything. If you have Facebook I put some documents (including that thread write up) on the "Files" section of the "Gyrocopter Pilots" group page.

Rotor track and balance is only a black art to the uninitiated. It's really pretty straight forward nowadays with a dynamic balancer but like anything it needs you to read and understand the manual or get training. If you decide to buy one buy it as a group, there's a good chance that one of the group will actually read the manual. On your own you probably won't get enough use out of it to justify the investment, divided between 4 or 5 it's not much more than a calibrated torque wrench and if you balance a few FW props it could nearly pay for itself.

If time isn't money (or you have none) the old classic method works but as I said it takes time and as you said it's difficult to get calibrated buttocks

Xavier is right the app (that I often recommend) can be very deceiving. As mentioned in another thread the only value I see in these apps is to be able to compare the 1/rev to 2/rev vibration to get a feel for if you have a track and/or balance problem but that requires a fair bit of experience and the results are always shrouded in weasel words like "should be", "perhaps", "maybe" etc.

I'm working on a solution that I hope will allow guys like you to get a cheap and more accurate fix on whether you have a vibration problem or not.

Mike G
 

BDavis

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Inman, SC
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Parsons Trainer
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Ben
I'm glad you found my post in Greg's thread about slinging or stringing, I'd forgotten I'd written all that so it has saved me writing it again. There is another thread I wrote a few years back which gives a fairly in depth description of some of the balancing process but I think the illustrations will have disappeared because at the time all my photos and sketches for the RWF were on Photobucket and since then they decided I had to pay so I removed everything. If you have Facebook I put some documents (including that thread write up) on the "Files" section of the "Gyrocopter Pilots" group page.

Rotor track and balance is only a black art to the uninitiated. It's really pretty straight forward nowadays with a dynamic balancer but like anything it needs you to read and understand the manual or get training. If you decide to buy one buy it as a group, there's a good chance that one of the group will actually read the manual. On your own you probably won't get enough use out of it to justify the investment, divided between 4 or 5 it's not much more than a calibrated torque wrench and if you balance a few FW props it could nearly pay for itself.

If time isn't money (or you have none) the old classic method works but as I said it takes time and as you said it's difficult to get calibrated buttocks

Xavier is right the app (that I often recommend) can be very deceiving. As mentioned in another thread the only value I see in these apps is to be able to compare the 1/rev to 2/rev vibration to get a feel for if you have a track and/or balance problem but that requires a fair bit of experience and the results are always shrouded in weasel words like "should be", "perhaps", "maybe" etc.

I'm working on a solution that I hope will allow guys like you to get a cheap and more accurate fix on whether you have a vibration problem or not.

Mike G
All good stuff! I found the docs on FB and read through them. One I had read before somewhere. Also enjoyed the one written by John Potter that mentions your work. Looks like I'm on the right track with my 28' Dragon Wings. Stringing is still good; I get no indication of mass imbalance. Mainly want to fix the cabin hop that increases with forward velocity. Been fiddling with tracking for the last 10 flights by using shims on the rotor bar, but need a better way to measure results (i.e. visually and physically). Plan to use the AMC Vibration Isolator Pro you mention on my next flight. My electric pre-rotator only gets me to ~125 rrpm, so I think ground testing won't do a good job of duplicating in-flight blade position at 330 rrpm. Tried the reflector & light method before sunrise this morning, but was hard to see very well at low RPM and light gusts. Not comfortable manipulating a big lamp in flight with an open cockpit. May have to try the UK Smart Avionics tip lights if they are still sold. I hope the over-wing bracket will work on one of the little Phillips screws on the blade tip-top. No screws on the end of Dragon Wings, as you likely know. Will post any progress on this thread. Thx again for all the kind advice for this newbie.
 
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