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  #21  
Old 06-25-2017, 04:17 PM
Chopkins Chopkins is offline
 
Join Date: Mar 2012
Location: Birmingham, England
Posts: 35
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Hi Barry

Have you managed to find a reason for the vibration? I too have an RV12 and have experienced exactly the same symptoms since my build. I had a Rotax engineer do all of the checks that you have had done and he gave it a fine bill of health as with yours. The vibration/noise I experience comes and goes. Last weekend I did a 200 mile round trip and it started on the return journey. When it is happening, it looks like the top cowl vibrates too.

The only thing I can think of now is that it could be the front LH exhaust spring touching the lower engine cowling. Would be interesting to see if you got your sorted.

Anthony
G-RVTW
UK
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  #22  
Old 06-26-2017, 12:08 AM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 116
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Could you take some video and record this happening ?
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  #23  
Old 06-26-2017, 01:21 PM
bernsbm bernsbm is offline
 
Join Date: Nov 2015
Location: Mequon, WI
Posts: 22
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Hi Anthony,
I’ve approached my vibration issue from several perspectives, based on advice from forum members and others with similar problems. Not sure my experience will be helpful, but efforts included:

Engine induced vibration:
1 Carb balance
2 Prop pitch adjusted to be identical to 0.1 degree
3 Engine gearbox shim checked and adjusted
4 Prop static balance
5 Dynamic prop balance.
6 Spinner checked to confirm “true” while rotating

Engine vibration propagation/magnification:
1 Checked engine isolators to confirm correct (Notification 17-05-19)
2 Checked all hoses and wires that were connected to both the engine and airframe to confirm there was some play, minimizing vibration transmission between the engine and airframe
3 Checked for “oil canning”. Identified an area on both fuselage sides immediately behind the firewall that had the potential for oil canning, and installed additional stiffeners
4 Checked all engine component clearance from cowl

Non-engine induced vibration
1 Spinning nose wheel resulted in a significant vibration when tested on the ground. Attempted to balance wheel, but vibration persisted. Wheel found to be out of round, replaced, balanced and vibration associated with spinning the wheel resolved in ground testing
2 Braking did not impact vibration while airborne, suggesting spinning of main wheels was not contributing to the problem
3 Removal of wheel fairing did not impact vibration
4 Air seepage under canopy. Checked and added seals as needed.
5 Confirm/trim nose gear fairing to ensure it is not vibrating against bottom cowl

At this point it is clear the vibration is related to RPM (not airspeed), and is minimal at 4000-4800 RPM. I’m not sure which efforts were helpful, but the vibration has gradually improved to what I would now describe as a “buzzing” in the rudder pedals and canopy frame. At 65 hours total time, the issue is better, but not completely resolved. I would like to redo the dynamic prop balance (it was done at 4000 RPM with a relatively simple set up) with someone more experienced than me interpreting the results.

As your problem is intermittent, and unless you can relate it to select RPM, would be sure to check non-engine induced vibration, along with the usual carb balance, prop pitch etc.
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Barry Bernstein
N12BB RV12 flying since Oct 2016
Dues happily paid
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  #24  
Old 06-27-2017, 04:12 PM
Chopkins Chopkins is offline
 
Join Date: Mar 2012
Location: Birmingham, England
Posts: 35
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Barry

Thanks for your note. Bizarrely, I flew the a/c last night for a 110nm bimble around our local airspace and it was perfect throughout. It just purred along at 5000rpm @ 95-98knts and was happy as can be.

I might find a way of isolating the front LH exhaust spring from the lower cowl if it starts again.

Anthony
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  #25  
Old 07-30-2017, 03:49 PM
bernsbm bernsbm is offline
 
Join Date: Nov 2015
Location: Mequon, WI
Posts: 22
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Several forum members have asked me if the source of vibration in my RV12 was ever identified. As noted above, addressing a number of potential contributing factors appears to have helped. Today I had a dynamic prop balance performed by someone with considerable experience (Thanks Matt!) using a Dynavibe GX3.

After attachment of the balance weights, IPS improved from 0.41 to 0.03. In flight, vibration has resolved.

Thanks everyone for your thoughtful suggestions. Now it's time to sit back, relax, (grin) and enjoy the wonderful RV12 ride!

Barry
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Barry Bernstein
N12BB RV12 flying since Oct 2016
Dues happily paid
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  #26  
Old 07-30-2017, 04:43 PM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 614
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To add to your trouble-shooting efforts, here is a recent item re: ROTAX 912 vibration from rotax-owner.com:

http://rotax-owner.com/en/rotax-blog...vibration-help
__________________
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 560+ hours (as of Oct 2017)!
VAF donation through June 2018.
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