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Advice needed

bernsbm

Active Member
Friend
Hi Everyone. I'm having a problem with my RV12 and am looking for some thoughts on how to resolve it. Some background first. My RV12 E-LSA is a Synergy Air quick built kit started in April 2016 and completed in Sept 2016. First flight was in October 2016. I now have ~30 hours on the plane, and love the way it flies. However, I have a disturbing low frequency vibration, almost a hum, the source of which I've been unable to isolate. I can easily feel it in the rudder pedals, engine controls, instrument panel and canopy.

Other observations:
Occurs at all engine RPMs, may be a little worse between 3000-4000 RPM
Occurs at all airspeeds while airborne
Is NOT present at any RPM while on the ground

Attempts to correct:
Pitched prop blades, identical to 0.1 degree
Carbs balanced by experienced Rotax repairman
Carb floats checked and all found to be ok (2.9gm each)
Gear box removed, checked and reshimmed to Rotax specs
Removed nose wheel fairing (no difference noted)
25 hour Rotax inspection completed with no problems found
Prop dynamically balanced
Checked Engine Isolators per Van's Notification 16-08-10 and found to be correct.
Prop blades returned to Sensenich and balance checked

Any thoughts on where else to look for the source of a bothersome vibration, neither airspeed or RPM dependent, only present while airborne?

Help much appreciated!

Barry
Mequon, WI
2017 Dues Happily Paid
RV12 Flying
 
Is the nose wheel balanced? It could be turning in flight. I doubt the mains will turn in flight because of disc brake drag.
 
Yes, I did my transition training in an S-LSA. Didn't feel anything like the vibration in my 12.
 
Could it be noise associated with airstream leakage? I assume your Synergy RV-12 was equipped with Van's canopy weather-proofing / sealing kit?
 
+1 for what Tony suggested. I think Tony may be on to something .... I've seen videos where the nose wheel spins while in the air. A spinning wheel not balanced would certainly induce a vibration into the air frame.

I would take the nose wheel off and check to make sure it is balanced as best as possible.
 
Last edited:
I had the front nose wheel 'problem' - -

I needed to add a little more toque on the front axle bolt. The wheel was spinning ( with wheel pant ). No noise, just a low freq vibration. Once the wheel stopped spinning in flight, went away.
 
From first start to about 35hrs I had a vibration noise. I search all kinds of places from engine to tail trying to figure out the problem. Noise was more of a hum on the ground and got worst at 3500-4000 rpm. While flying with my son I was in the right seat. He suggested I lean my foot against the aircraft skin just next to the rudder pedal. Sound stopped. I installed a stiffener and haven't had a problem since. Nothing to loose in looking at that area.
 
I had noises that I determined came from the instrument panel shelf, below the glove box and also some from the rear baggage bulkhead cover. Went to the Home Depot aviation store and bought a 3" wide roll of stick on insulation foam that is foil backed. (used for water line insulation) I put strips on panel shelf under glove box and that noise disappeared. Likewise for the baggage panel cover where I put it between the corrugations. Only a couple of $ and a few ounces for an easy fix. Still great after 100 hours.
 
?

Check the fiberglass layup on the canopy. I modified a part in my panel and canopy did not close all the way in the front and I got a harmonic vibration until i made an adj, fixed. ONLY A GUESS FROM WHAT I READ FROM YOUR POST. Good luck finding it.
 
Vibration

Thanks all for your many helpful suggestions. Thought I would provide an update on finding the cause of the vibration in my RV12. As background:

Pitched prop blades, identical to 0.1 degree
Carbs balanced by experienced Rotax repairman
Carb floats checked and all found to be ok (2.9gm each)
Gear box removed, checked and reshimmed to Rotax specs
Removed nose wheel fairing (no difference noted)
25 hour Rotax inspection completed with no problems found
Prop dynamically balanced
Checked Engine Isolators per Van's Notification 16-08-10 and found to be correct.
Prop blades returned to Sensenich and balance checked

Based on suggestions:
Removed nose wheel fairing and jacked up front of plane. Spinning nose wheel at a high speed (placing the edge of an orbital polisher on the tire) elicited a vibration that was transmitted throughout the airframe. The nose wheel was found to be both out of round and out of balance. Replaced tire and balanced nose wheel. Vibration could no longer be elicited by spinning the wheel, but vibration in flight was unchanged.

Completed installation of Van's weather proofing/seal kit, including canopy frame

Identified an area of "tin canning" on right fuselage side skin near firewall. Added stiffener eliminating tin canning.

I continue to experience vibrations in the rudder pedals but can also feel it in the canopy frame and panel. The vibration is strong enough that is is uncomfortable leaving my feet on the rudder pedals! Noted in flight only, seems more pronounced at cruise (not climb out), and somewhat less (but present) when operating at <5000 RPM.

Engine seems to be running smoothly, and after 35 hours on the Hobbs, I'm very happy with the way the plane flies. Any other thoughts on potential causes or approaches to identify a source would be greatly appreciated.

Barry
Mequon, WI
2017 Dues Happily Paid
RV12 N12BB Flying
 
To confirm that the vibration is from moving air and not the engine, climb up high and close the throttle. While descending, note the vibration at various air speeds. Have the Matco wheel bearings been adjusted per specs that require a certain amount of drag? Have you tried pressing the brakes while flying?
 
I know you have had a lot of suggestions so here's one more, sometimes something Attached to the engine can be touching motor mount or airframe transmitting vibration, could be something like a hose clamp or exhaust support it easy to check.
Jerry
 
Following up on Jerry's suggestion -- On the RV-12, potential vibration/touching-the-cowling points include: 1) the left front exhaust spring, 2) a left-side rocker box cover, 3) the exhaust pipe where it exits the cowling, and 4) a floppy lower-right-side oil line.
 
Will be interested to continue to hear updates on this one. Did the problem change at all when flying without wheel pants vs with them, after the wheel balancing?
 
Following up on Jerry's suggestion -- On the RV-12, potential vibration/touching-the-cowling points include: 1) the left front exhaust spring, 2) a left-side rocker box cover, 3) the exhaust pipe where it exits the cowling, and 4) a floppy lower-right-side oil line.

I agree with 4. above if DHeal is referring to the oil reservoir vent line. But, i would also check the hose vent line from the weep/drain off of the mechanical fuel pump. I had a similar sporatic vibration. Then, during an annual, I made a thorough inspection of all hoses, lines, etc. for abraision and saw how one or both of these vent lines were wearing at contact points against the firewall. So, I put some zip tie offset combos. and RTV where applicable between the lines and all possible contact points and have not noted recurrence of the vibration.
 
Another suggestion, a friend had a similar problem, turned out to be oil canning of the floor directly behind the baggage bulkhead. Mine was doing the same thing so we fixed it with a couple of strips of aluminum angle.
 
Thanks everyone, greatly appreciate the thoughtful suggestions and offers of help. I'll follow up on the possible sources of vibration and report back!

Barry
 
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
 
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.
 
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
 
Closure

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
 
Just came across this thread while looking for something else and thought I'd add a possible solution.

For anyone else that runs into a low-frequency vibration in the early RV-12 (legacy) in flight, check to see if the firewall Stiffener Retrofit is installed. Refer to KAI 54 (attached) and order the 12 STIFFENER KIT from Van's.

Also, be sure to have your prop balanced.
 

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