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12-06-2018, 10:12 PM
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Join Date: Jan 2018
Location: Birmingham, AL
Posts: 207
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Prop/Engine Vibrations
I purchased my RV-13 last February with 338 hours on it. It now has 432 hours on it. This summer I started noticing that when I reduce power from cruise, around 4400 down to about 3800 I get a vibration. I think it started after I complied with the Service Bulletin on the cracks in the front of the propeller hub. I hear the vibration more that I feel it. Two other pilots who have ridden with me also think it is from the propeller or gear box. The engine runs smoothly at cruise and at idle.
About a month ago I rechecked the front hub for cracks, and found none, and reset the blade angles at 71.4 and 71.3. The vibrations continued. This last week I replaced the soft engine isolators with the new ones from Van's and replaced all the springs on the muffler.
When I flew the aircraft, it still has the vibrations. Today I rechecked the blade angles and they are still 71.4 and 71.3. I checked the torque on the bolts and they are fine. I looked all over the engine for anything loose that could be vibrating and didn't find anything.
The propeller was dynamically balanced at 105 hours.
So I am asking for ideas, suggestions on what might be causing these vibrations. Has anyone else experienced vibrations like this?
Thanks.
__________________
John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 240 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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12-07-2018, 05:30 AM
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Join Date: Apr 2014
Location: Port Orange, Fl
Posts: 931
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Dynamic prop balance? Also, I had a similar problem and I found one of my throttle cables was sticking slightly in mid-throttle range. I rerouted it slightly near the carb and secured it better so it wouldn't move. That worked for me.
__________________
Tom
Port Orange, Fl
EAA #51411
RV-12 N121TK ELSA #120845; first flight 06/10/2015; 700 hrs as of 02/2020
RV-12 N918EN ELSA #120995 Eagles Nest Project; first flight 05/18/2019
SPA Panther N26TK; First Flight 03/13/2020
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12-07-2018, 06:15 AM
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Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,657
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Hi John --
Which prop hub front did you install - D1 or F ? I understand that you can install the blades 'in' a little from where they should be with the 'F' hub. I think it has been discussed that after the new hub, assuming the blades were installed correctly, there still can be a balance difference. Be sure the blades are in there most outward position, and rebalance it. I did mine, and it helps a bunch.
__________________
John Bender
Flying RV-12 - Serial #120036
Paid in May ( 5-2020 )
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12-07-2018, 08:45 AM
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Join Date: Jan 2018
Location: Birmingham, AL
Posts: 207
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Vibrations
I just reinstalled the original hub after inspecting it. I am planning on ordering the new style hub and installing it.
__________________
John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 240 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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12-07-2018, 08:58 AM
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Join Date: May 2013
Location: Temecula, CA
Posts: 295
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John,
Did you really set the blades at different angles (71.4 and 71.3), or is that a typo in your post?
Alex
__________________
Alex Erdelyi
RV-9A Purchased
RV-12 Built and Sold
Paid through December, 2020
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12-07-2018, 09:00 AM
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Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,247
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Quote:
Originally Posted by pilotyoung
About a month ago I rechecked the front hub for cracks, and found none, and reset the blade angles at 71.4 and 71.3.
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Why tie difference? Was that just the closest you were able to get them to being the same?
Ha... Alex was faster on the keyboard than I was, I see.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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12-07-2018, 09:59 AM
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Join Date: Jan 2018
Location: Birmingham, AL
Posts: 207
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Vibrations
I set them both to 71.4 and after I got all the bolts finally torqued one was at 71.3 and one at 71.4. Since the tolerance is .2 I left them alone.
__________________
John D. Young, RV-12 Owner
Serial Number 120022, N6812Y
Bought it as a flying airplane in Feb. 2018
Just passed 240 hours flight time in RV-12, and 10,000 hours mostly in corporate jets. I am a CFI; CFII; MEI; and a advancd Ground Instructor, CFIG; and hoping to be able to help new RV-12 owners by doing some transition training for new builders and owners in RV-12's.
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12-07-2018, 10:39 AM
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Join Date: Dec 2007
Location: Brentwood, CA
Posts: 659
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Seeing you’ve already balanced the engine, and assuming you haven’t changed the spinner or prop pitch, it could be things like a mis-firing spark plug(s) or carburetor balance.
If you’ve taken the spinner off to inspect - be sure you put it back on in the same orientation. It’s only gram weights that make a difference and the spinner is a very common cause. I’d also look for things like missing washers.
Lastly, do another engine balance and look for 2nd or 3rd level harmonics. It could be something like the alternator - but the most likely is something more innocuous like the spinner or a washer on a spinner screw.
__________________
Ron Gawer
- RV10, Build in progress.
- RV12, N975G, "The Commuter"...many great hours and happy landings so far.
- Several others that are now just great memories for me.
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12-07-2018, 10:57 AM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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The carbs on the ULS tend to run the engine a bit on the rich side in the mid throttle range. If you have a float that is just beginning to get a bit heavy and floating a bit lower, it could be causing that carb to be even richer but possibly only show up at mid range throttle settings.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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12-08-2018, 06:24 PM
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Join Date: Jul 2009
Location: Coeur d'Alene, ID/Casa Grande, AZ
Posts: 654
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Quote:
Originally Posted by pilotyoung
I purchased my RV-13 last February with 338 hours on it. It now has 432 hours on it. This summer I started noticing that when I reduce power from cruise, around 4400 down to about 3800 I get a vibration. I think it started after I complied with the Service Bulletin on the cracks in the front of the propeller hub. I hear the vibration more that I feel it. Two other pilots who have ridden with me also think it is from the propeller or gear box. The engine runs smoothly at cruise and at idle.
About a month ago I rechecked the front hub for cracks, and found none, and reset the blade angles at 71.4 and 71.3. The vibrations continued. This last week I replaced the soft engine isolators with the new ones from Van's and replaced all the springs on the muffler.
When I flew the aircraft, it still has the vibrations. Today I rechecked the blade angles and they are still 71.4 and 71.3. I checked the torque on the bolts and they are fine. I looked all over the engine for anything loose that could be vibrating and didn't find anything.
The propeller was dynamically balanced at 105 hours.
So I am asking for ideas, suggestions on what might be causing these vibrations. Has anyone else experienced vibrations like this?
Thanks.
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I second what Scott has suggested; also, carb sync...it is amazing the difference it makes when done right in overall smoothness of engine performance. Took me numerous attempts before getting the hang of it....and not wanting to start a war on the forum (I disagree with Van’s sync instructions) PM me for phone#; and i’ll share a slick method that has worked on my -12 and many other 912 Rotax equipped a/c. The typical comment i’ve recieved after tuning their engines...i’ve never seen it run so smooth...
__________________
Ric Dickison
307 (CAB) Phantom
Search and Destroy (Can Tho RVN)
Distinguished Flying Cross Society Member
CH-47 & UH-1H "Driver"
Rotax 9 Series Service IRMT
RV-12 Kit#729 "N312RD" is now a full functioning fun machine!! Thanks Van for fulfilling my dream😎
2018 Dues Paid
Last edited by Phantom30 : 12-08-2018 at 06:42 PM.
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