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  #1  
Old 12-06-2018, 11:12 PM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 56
Default 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.
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  #2  
Old 12-07-2018, 06:30 AM
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tomkk tomkk is offline
 
Join Date: Apr 2014
Location: Port Orange, Fl
Posts: 798
Default

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.
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Port Orange, Fl
RV-12 N121TK ELSA #120845; first flight 06/10/2015
RV-12 N918EN ELSA #120995 Eagles Nest Project
SPA Panther N26TK in progress
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  #3  
Old 12-07-2018, 07:15 AM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
Posts: 1,603
Default 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.
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  #4  
Old 12-07-2018, 09:45 AM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 56
Default Vibrations

I just reinstalled the original hub after inspecting it. I am planning on ordering the new style hub and installing it.
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John D. Young
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Serial Number 120022
Bought it in Feb. 2018
90 flight time in it
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  #5  
Old 12-07-2018, 09:58 AM
alexe alexe is offline
 
Join Date: May 2013
Location: Temecula, CA
Posts: 253
Default

John,
Did you really set the blades at different angles (71.4 and 71.3), or is that a typo in your post?
Alex
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  #6  
Old 12-07-2018, 10:00 AM
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DaleB DaleB is offline
 
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Location: Omaha, NE (KMLE)
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Quote:
Originally Posted by pilotyoung View Post
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.
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.
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[i][size="1"]Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
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Previous RV-7 project (sold)
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  #7  
Old 12-07-2018, 10:59 AM
pilotyoung pilotyoung is offline
 
Join Date: Jan 2018
Location: Birmingham, AL
Posts: 56
Default 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.
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Serial Number 120022
Bought it in Feb. 2018
90 flight time in it
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  #8  
Old 12-07-2018, 11:39 AM
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rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
Posts: 349
Default

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.
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- RV10, N1530G (reserved). Empennage in progress.
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  #9  
Old 12-07-2018, 11:57 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,874
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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.
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  #10  
Old 12-08-2018, 07:24 PM
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Phantom30 Phantom30 is offline
 
Join Date: Jul 2009
Location: Coeur d'Alene, ID/Casa Grande, AZ
Posts: 651
Default

Quote:
Originally Posted by pilotyoung View Post
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.
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...
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Tho RVN)
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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😎
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Last edited by Phantom30 : 12-08-2018 at 07:42 PM.
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