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  #1  
Old 07-22-2020, 08:57 AM
Mike Howard Mike Howard is offline
 
Join Date: Jan 2006
Location: Omaha, NE.
Posts: 7
Default Vibration after lift off

I have developed a strange engine vibration that occurs approximately 3 to 5 seconds after I lift off while at full throttle. The vibration started just after I replaced my nose gear leg and fork. I do not believe that it is related to an out of balance nose wheel because it does not happen until more that 5 seconds after the nose wheel lifts off.
Here is the strange part the vibration goes away completely if I pull the throttle back to about 50% for a second or two and then push it back in for full throttle. The vibration does not occur for the remainder of the flight for any throttle position.
I have checked the lower engine mounts where the new gear leg clamps to the firewall. I thought that the nuts might have bottomed on the bolt so I added a washer under the nut. The problem seems a little less but it is still there.
Anny ideas?
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  #2  
Old 07-22-2020, 09:13 AM
BlndRvtr BlndRvtr is offline
 
Join Date: Mar 2009
Location: NE Where
Posts: 430
Default

Could it be a harmonic set up by the new NG leg, fork and wheel assembly? More specifically, is it related to nose wheel tire rotation. As the tire stops spinning, the harmonic subsides? A camera aimed at the nose gear could be revealing.

George
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  #3  
Old 07-22-2020, 09:35 AM
kritsher kritsher is offline
 
Join Date: Feb 2007
Location: Stow MA
Posts: 175
Default nose wheel

I'd check the breakaway force on the nose wheel.
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  #4  
Old 07-22-2020, 10:09 AM
bobg56 bobg56 is offline
 
Join Date: Nov 2018
Location: Peachtree City, GA
Posts: 300
Default

You probably do this put I'll suggest it anyway, my RV12 has vibration after lift off but its the main wheels spinning, I apply the brakes and it stops.
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  #5  
Old 07-22-2020, 10:21 AM
cajunwings cajunwings is offline
 
Join Date: Jun 2007
Location: new iberia la
Posts: 948
Default Vibes

Sounds like the tire/wheel balance and itís worse when the weight is off and itís spinning down. Make a takeoff, donít touch anything and see if it stops in the same time frame. Tire balancing might be needed.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
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  #6  
Old 07-22-2020, 11:50 AM
Dgamble's Avatar
Dgamble Dgamble is offline
 
Join Date: Aug 2005
Posts: 873
Default

I get this too but it seems to occur more often after a touch & go than a normal takeoff. The only difference between the two is that the nosewheel is probably turning faster after the touch & go than it is after a normal takeoff.

My normal takeoff is stick full back until the nosewheel lifts, then just hold that attitude until it flies itself off the runway. That keeps the speed down for the nosewheel.

I bought the motorcycle wheel balancer from Harbor Freight and did find the nosewheel to be out of balance. I just live with it now because I donít trust modern wheel weights that are held on (barely) with double-sided tape, and they donít seem to be made out of lead anymore, so you have to use more of them.
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  #7  
Old 07-22-2020, 01:08 PM
cajunwings cajunwings is offline
 
Join Date: Jun 2007
Location: new iberia la
Posts: 948
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Quote:
Originally Posted by Dgamble View Post
I get this too but it seems to occur more often after a touch & go than a normal takeoff. The only difference between the two is that the nosewheel is probably turning faster after the touch & go than it is after a normal takeoff.

My normal takeoff is stick full back until the nosewheel lifts, then just hold that attitude until it flies itself off the runway. That keeps the speed down for the nosewheel.

I bought the motorcycle wheel balancer from Harbor Freight and did find the nosewheel to be out of balance. I just live with it now because I donít trust modern wheel weights that are held on (barely) with double-sided tape, and they donít seem to be made out of lead anymore, so you have to use more of them.
I balance my aircraft tires. Remove the double sided tape (belt sander or whatever) and use silicone or proseal to hold them on. Works great.

Don B
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  #8  
Old 07-23-2020, 06:04 AM
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dbhill916 dbhill916 is offline
 
Join Date: May 2013
Location: Westerville, OH
Posts: 185
Default

I was pretty sure that vibration as described by the OP was from my front tire spinning down because I could do a "wheelie" touch-n-go and have no vibration at all on climb out.

Ditto for Dave G's comments --On his advice, I bought the same tire balancer from Harbor Freight.

I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them. Works great. No vibration on regular take offs or wheelies.
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N76012
RV-12 #0760
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  #9  
Old 07-23-2020, 06:30 AM
Greg Arehart's Avatar
Greg Arehart Greg Arehart is offline
 
Join Date: Jul 2007
Location: Sequim, WA/Atlin, BC
Posts: 2,455
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Quote:
Originally Posted by dbhill916 View Post
I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them. Works great. No vibration on regular take offs or wheelies.
I would suggest that this may cause you issues down the road (so to speak) rubbing the tube. I balance my wheels similarly, but use pieces of old inner tube rather than anything rigid or with sharp edges. Less weight than metal weights but more flexible.
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  #10  
Old 07-23-2020, 08:21 AM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 10,187
Default

Quote:
Originally Posted by dbhill916 View Post
I solved the attachment issue by balancing the tire using tape to hold the weights on the outside of the tread, marked where they ended up and then disassembled the nose wheel. I took the weights and taped them to the inside of the tire and put the inner tube in very carefully to not dislodge them.
I would caution other RV owners against using this technique to balance aircraft tires.

The reason we liberally coat the surface of the tube and the inside of the tire with talc is for it to act as a lubricant because the tube is always moving slightly from the flexing of the tire. The RV-12 is a light airplane. Because of that we run rather lower pressure in the nose tire compared to most airplanes so that can potentially make the situation even worse.

Even the smallest amount of movement of the tube against the sharp corners of the typical wheel weight is going to, at the very least, cause a major inconvenience at some point, and possibly worse.
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Hubbard, Oregon
Formerly of Van's Aircraft Engineering Prototype Shop
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