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Vibration after lift off

Piper J3 said:
Question: Has anyone dynamically balanced front wheel to fix this problem?
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I dynamic balance all (3) of my wheels with the tires mounted, done properly it absolutely removes ALL wheel vibrations.
I have had instances where the nose wheel will shake on take off to 500’. When I spin it up on the ground it reveals itself. After rebalancing it is smooth.
 
see post #11 of this thread:
That was my early method, I have streamlined it a bit over the years.

To check balance on the plane, example nose wheel.
1) Add weight to the tail tie down hook to raise nose wheel off the ground.
2) Remove nose wheel pant.
3) Spin the nose wheel to 1500 RPM (there are many ways to accomplish this but this is approximately 60 MPH take off speed. If you can only get 700 RPM it will still probably show you the imbalance.
4) I use a 8" rubber backing disk on a corded drill and rub the edge of the disk to the tire tread.
5) Let the tire spin down to a stop and observe the shaking the airframe goes through. This is what you feel inside.

To adjust the balance, example nose wheel
1) Clean the tread area with rubbing alcohol all the way around
2) Put a mark on the tire as a reference to 12:00
3) Lightly turn the tire and see if it prefers to stop at a particular clock position.
4) I use a stack (2" squares) of duct tape starting with 4 layers onto the tread opposite the heavy side. Add more or less layers until it feels balanced statically.
5) spin the wheel up and let it spin down observing the shake. If it is better or worse. If it is vibration free go to #8
6) At this point it is trial and error for the correct position and amount of tape.
7) If you get completely lost start with a stack of 6 tapes at 12:00. Spin it up and if it is worse move the tape to 2:00, repeat the spin and move process. There will be a point in the "clock" that is noticeably better. At that location you can move the tape a little in either direction to center on the best spot, then start adjusting the number of tape layers until it spins down without any vibration.
8) Mark the location then remove the tape stack and weigh it. The ratio on the RV-12 wheels is about 3x, if the tape weighs 8 grams then the lead applied to the wheel will be 24 grams. Draw a line from the axle center to the center of where the tape was on the tread, where it intersects the wheel is where to put the weight.
9) I use lead tire weights but remove the tape they come with and replace it with 3M VHB tape. It is much better than what comes on the weights, plus I can reuse weights. I put the weight on the outer most lip of the wheel facing in. Centrifugal force works to keep the weight stuck better.
 
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That sounds like a lot of trial and error… I was hoping someone had figured out a balancer similar to prop balancing with use of accelerometer and position sensing to calculate amount of weight and radial position on wheel.
 
Piper J3 said:
That sounds like a lot of trial and error… I was hoping someone had figured out a balancer similar to prop balancing with use of accelerometer and position sensing to calculate amount of weight and radial position on wheel.
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I have the prop balancer and plans to build the fixture.
If I told you that method the response would be "that requires a $4000 balancer and a fixture I don't have", "I wish someone had a method easier to the common folk".::D
 
Thinking out of the box I asked one of my Go-Kart Racing patients what he uses. Very quick answer, 90 to 110 mph on 5 or 6 inch wheels they have to be dynamically balanced. So how do you do it, I ask? He said ask around at a motorcycle shop or bring the mounted tire and wheels to his shop and he would put them on his balancer, a Leo L9067. Appears the balancer cost about $1500. It takes a rim down to 1" and 2" wide. I haven't tried yet but I will take wheels and tires once finish kit shows up mid summer. Worth a try, I reckon. -JJR
 
Piper J3 said:
That sounds like a lot of trial and error… I was hoping someone had figured out a balancer similar to prop balancing with use of accelerometer and position sensing to calculate amount of weight and radial position on wheel.
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Harbor Freight sells a motorcycle wheels balancer for $50. They also sell stick on weights. That's what I used. Took about 45min to complete the process. Wheel hasn't shaken since.
 
WJaviation said:
Harbor Freight sells a motorcycle wheels balancer for $50. They also sell stick on weights. That's what I used. Took about 45min to complete the process. Wheel hasn't shaken since.
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I don't think they have it anymore. At least, I could not find it on their website.
 
Mike S said:
This is a new "system" and probably has different vibration frequency.
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And, it sounds like the system is most susceptible to vibration at a frequency that is near the frequency of full throttle prop pulses.
One way to advance toward a solution would be to use camera tech combined with nose fairing tufting to get definition of the aerodynamics in play.
Vans should have some interest in this phenomenon, as it could lead to something as simple as a small nose fairing modification for the RV-12 fleet.
 
I think everyone is overthinking this. It's simple. Buy one of these, ~$50. Spin it by hand and let it settle. Use those sticky auto weights on the inside race of the rim. NEVER place anything inside the tire where it could puncture the tube. I check the nose wheel every annual whether or not I've felt vibration. It's super easy.

There is really no need to balance the mains unless they're really gross. Bearing drag will stop them from rotating shortly after takeoff.

See this video if you don't believe me.

https://youtu.be/P5N8C4_f8eE
 

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Nice thread. I am chasing an intermittent vibration issue on my -7A, and I would not have thought to suspect gear legs or wheels.
 
Thought I would share my vibration issue. I have a original 12 with AM15 engine.
Also have experienced a shudder after lift off for a few seconds on every takeoff.
After reading this thread I checked my nose wheel and found it to be out of round and unbalanced. Fitted with a Vans supplied Aero Classic.

Not sure if it's a manufacture fault or from standing prolonged on the same spot during build.

I did not want to try balancing it like that so bought a new Goodyear.
Lined the valve up with the red dot and it was in perfect balance.

Test flight today with no vibration and shudder at all

Also found that the RHS fairing bracket had cracked due to this as well.
 
noting works

Bougth a new tyre (Michelin) which is even better quality than Aero Classic.
Balanced it dynamically up to about 3000 rpm. Perfect
Nothing changed. Bad vibration in take off and every time you climb.

The only thing that works is taking the pant off. All gone.

My guess
it seems like the wheel spins very fast with the pant and just the lower half sticking out to excite it.
Without the pant both upper and lower side get the same airflow which stops or reduces the spin.
To prove this I fitted a rubber flap rubbing against the tyre to add drag, which proved this point. The flap is gone after one flight so no permanent solution.
Not so easy to brake this wheel in a safe way

regards

Jack
Netherlanda
 
Hotscam said:
Bougth a new tyre (Michelin) which is even better quality than Aero Classic.
Balanced it dynamically up to about 3000 rpm. Perfect
Nothing changed. Bad vibration in take off and every time you climb.

The only thing that works is taking the pant off. All gone.

My guess
it seems like the wheel spins very fast with the pant and just the lower half sticking out to excite it.
Without the pant both upper and lower side get the same airflow which stops or reduces the spin.
To prove this I fitted a rubber flap rubbing against the tyre to add drag, which proved this point. The flap is gone after one flight so no permanent solution.
Not so easy to brake this wheel in a safe way

regards

Jack
Netherlanda
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Jack
I think the fact that others have totally resolved a vibration problem by balancing the nose wheel assembly of their RV-12, and since you have proven that your nose wheel rotating is causing your vibration, it proves that even though you say yours has been balanced, that it actually is not (unless your airplane has some amazing mods that allows to fly at Mach .9 or some other crazy fast speed ;))
 
Posting this to multiple balance threads so people don't go on the wild goose chase I just did:

Harbor Freight/Amazon cones (1 1/8") no longer fit the either with bearings (not best option) or even close to bearing races. According to another VAF'r if you purchase the "DC42 Parts" from here (http://www.marcparnes.com/Ducati_Motorcycle_Wheel_Balancer.htm#DU42) for $50 shipped you'll be able to use the $50 balancer. $100.

Another option which I wish I had seen before assembling the HF one is from Desser, $100 for a bubble balancer style desktop unit that doesn't have bearings that will rust out. (https://shop.desser.com/desser-ga-05dt-static-tire/wheel-a-ga-05/ecomm-product-detail/324692/). Another bonus is you don't have to pull out bearings to get a decent balance like you do with the HF type.

YMMV, hopefully not as many miles as I had.
 
FitzRX7 said:
Another bonus is you don't have to pull out bearings to get a decent balance like you do with the HF type.
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I have always balanced with the bearings still in place. They have enough friction from the rubber seal that they don't rotate. The cones included with the HF balancer fit in the bearings fine.

What is the reason for balancing with the bearings removed?
 
rvbuilder2002 said:
Jack
I think the fact that others have totally resolved a vibration problem by balancing the nose wheel assembly of their RV-12, and since you have proven that your nose wheel rotating is causing your vibration, it proves that even though you say yours has been balanced, that it actually is not (unless your airplane has some amazing mods that allows to fly at Mach .9 or some other crazy fast speed ;))
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Scot

That might be the case and will try again, but does mot explain to me why the old nose leg and fork did not have this problem at all
 
Maybe expand the possible list?

Hotscam said:
Scot

That might be the case and will try again, but does mot explain to me why the old nose leg and fork did not have this problem at all
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Jack, I don't know much about the 12, but I was flying with a friend and noticed his front gear was vibrating and the wheel turning in flight. He was happy to know as he was sorting an inflight vibration. Also, after sitting, my tires will have a flat spot and that affects the balance.
 
I installed a new nose wheel tire and Michelin AirStop ($150) during Annual Condition Inspection back in March. I did the wheel balance with the wheel installed on the nose fork and I’m not happy with outcome. I now balanced on a Harbour Frt balancer and had to add 2 oz more to get good balance.

Tire is 5.00x5 Aero Classic LSA. The tire did not have a painted dot to indicate light portion of tire. Normally the dot is placed to offset the weight of the valve stem and things work out pretty well. I now have 14 pcs of ¼ ounce lead weights placed inside the wheel hub and packed around the valve stem. This is wild... I used some Gorilla Glue to prevent weights from shaking loose when wheel spins up suddenly. I plan a test flight tomorrow.
-
 

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That really sucks, Jim. I’d have trouble finding space for all of those weights. I just signed off my CI yesterday and balanced my nose wheel for the first time at around 300 hrs. Still the Van’s supplied tire and tube. As a comparison, it only took 0.25 oz opposite the valve stem to get it within 2.6 g of balance. And yes, my tire has the red dot, positioned at the valve stem.
 

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If I had to add that much weight I'd try rotating the tire on the rim 180 degrees and then see how much weight is needed.
 
Per my post #70 above where I now have 14 pcs of 1/4 ounce lead weights to balance the new tire.... Today I flew to three outlier airports to test nose wheel balance. Looks really good... I spun-up the wheels a bit more than usual on takeoff and nose wheel was surprisingly smooth as it coasted to a stop. I checked to see if any weights shifted and appears hunky-dory. For now, I will run as is...
 
Just a quick "Me Too" that:
1. doing a soft field landing and keeping the nose off proved that the issue was the nose wheel spinning
2. using the harbor freight balancer and working until the wheel assembly was finally balanced fixed issue.
 
I had a Cessna 150 with bad shimmy on takeoff and landing. I took the wheel pants off, and the problem was gone. I worked with a friend who did composite work for the military. He looked at the wheel pant and saw some bad repairs, but the real problem was a manufacturing defect in the trailing cone, too much rosin and glass. He set up a rig to find the center of gravity based on the nose wheel. It took time but fix the problem.
 
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