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Vibration after lift off

Mike Howard

I'm New Here
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?
 
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
 
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.
 
Vibes

Sounds like the tire/wheel balance and it’s worse when the weight is off and it’s spinning down. Make a takeoff, don’t 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
 
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 don’t trust modern wheel weights that are held on (barely) with double-sided tape, and they don’t seem to be made out of lead anymore, so you have to use more of them.
 
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 don’t trust modern wheel weights that are held on (barely) with double-sided tape, and they don’t 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
 
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.
 
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.
 
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.
 
How I balance mine;
I have a 24" axle, (steel rod), that I put horizontally in the shop vise. With the wheel on the axle I spin it up with a die grinder and a 2" rubber wheel. I watch the vibration through all speeds at it winds down. With the wheel 12" out on the axle small imbalances are very noticeable. I use 2" patches of duct tape stacked and stuck to the tread to balance it and remove the vibrations. When I find the right amount and spot I weigh the stack and multiple x 3. Then use that amount of stick on tire weight on the inside of the rim. I remove the original tire weight foam tape and replace it with Scotch 411 tape, the grey stuff, it does not come off easily.

To clarify, I put the weight on the "outside" of the wheel on the surface facing the axle. Centrifugal force works to make the weight stick better.
 
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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.

Thanks for the input. Will definitely look at an alternative.
 
Follow up information on strange vibration.
I performed a test take off today with the stick full back. The nose lifted off very quickly with little or no nose wheel spin up. No vibration, problem solved? maybe?
This still doesn't explain why the vibration stops immediately after I reduce the throttle with a normal take off technique. Throttle position shouldn't have any impact on vibration caused by an unbalanced tire.
Also why did the vibration only start after I installed the new nose gear leg and fork? I didn't change the tire or wheel and it wasn't a problem before I installed the new pars.
 
Also why did the vibration only start after I installed the new nose gear leg and fork? I didn't change the tire or wheel and it wasn't a problem before I installed the new pars.

This is a new "system" and probably has different vibration frequency.

Professor Horton could explain it most likely.
 
I bit the bullet and bought some Michelin Pilot tires. I'm done with those cheap POS Aero Classics. No more vibrations and they make the nicest chirp too!!
 
I bought a motorcycle tire balance rig from Harbor Freight. It’s a rod with two conical pieces that when pushed together clamp the wheel on either side at the bore for the axle. The rod then acts like an axle and rests on two bearings so the heavy spot rotates to the bottom, and you can add weights until the wheel doesn’t rotate due to a heavy spot. I’ve found that you can balance really bad tires even on the aircraft axles and get a marked improvement.
 
Follow up information on strange vibration.
Throttle position shouldn't have any impact on vibration caused by an unbalanced tire..

I have to disagree with this. Things resonate when they get vibrated at a specific frequency, or multiple of that frequency. It is possible that as you throttle back your engine goes through some specific rpm as it slows down that interacts with the fork.

If you have a wheel out of balance on your car it doesn’t necessarily get worse as you go faster. It will get bad at a certain speed and be fine above or below that speed.

Gear shimmy and resonance issues are very common and tricky to fix on many types of airplanes. Nosewheel shimmy on cessnas is common. It will break the engine mount. Tailwheel shimmy will damage structure as well. Lots of modern fighter aircraft have had nosewheel shimmy issues. In the airliner world they do exhaustive testing on the runway to identify any potential issues by hitting a shimmy plate at different speeds with nose and main gears, which is just a means of exciting vibration. It is a tricky thing. It would not surprise me at all to find that there is an interaction with the nosewheel fork and engine rpm. So not impossible at all.
 
Vibration

I have the exact same problem since replacement of the nose leg.
The wheel is balanced and never had any vibration with the old leg.
It starts full throttle take off at about 2-300 feet @70 kts for 2-3 seconds.
Throttle back stops it immediately.

It seems related to a different stiffness of the leg.
 
Any further thoughts on the cause of this?
I have it too. Not every flight but on some of them a few seconds after lift off I get the vibration then it is gone as quickly. New nose gear.
Per the seller my break out force is lower than the instructions, I haven’t checked it yet, unsure how much lower.
 
Next time it happens, just touch the brakes and see if it stops.
If it does, one or both of the MLG tires might be out of balance. If it continues, it is likely the nose wheel.

If the vibration only lasts a few seconds, one solution is to call it a "feature", and not worry. ;)
 
To isolate front wheel as source of problem, perform a touch/go without letting nose wheel touch runway. Try to make landing nose-high and gentle as possible to not set cantilever nose gear in springing-oscillation. I do the touch/go without flaps to allow smoother departure. The idea is to have main wheels spin-up but not nose wheel. Small wheels spin fast so any out-of-balance is pronounced. I use automotive stick-on weights on the inside wheel rim with no problems. Also, keep in mind that static balancing is not as good as dynamic. You may have to move weight L-R to compensate for imperfection in tire/wheel assembly. A little trial and error go a long way…
 
Any more movement on this issue? I too am experiencing the same vibration. Occurs on climb out (150-300 ft AGL) for 2-3 seconds. I have a habit of tapping the brakes so I doubt it is the main gear. Nose tire seems the most likely culprit.
 
Me too

I experience the same vibration and believe it is the nose wheel. I balance it as best I could about three years ago but to me it could be better. Annual is coming up and I will rebalance then
 
Glad to know others are having the same issue. What is the best process for checking/adjusting the balance on the wheel?
 
No results for me yet
Tried most I could think of but nothing stops the vibration
Typical just after take off at 200-300 ft for 1-2 seconds.
Brakes make no difference, wheel perfectly balanced. Flaps or no flaps.
Anybody tried without nose wheel fairing ?
With the new fork the incident angle is quite different and it may induce lift
 
I also think the nose fairing could be an issue. I just recently purchased my RV-12is and the previous owners did not have the fairings installed. I had them installed before I picked up the airplane. I asked them about the issue and they hadn't experienced it. Which makes sense. They hadn't flown the new nose fork with the fairing installed.
 
I would almost guarantee it is the nose wheel balance. Here is a quick way to check.

Tilt your plane back and put it on the front saw horse only. This lifts the nose wheel off the ground. Remove the faring (if you have one).

Now spin the wheel up to rotation speed, about 50 mph. The easy way to do this is with a 3000 RPM variable speed drill motor. Put a 6" sanding disk backing plate in the chuck, (no sand paper). Run the edge of the disk against the tire tread to bring up the rotation speed of the tire. Then back away and let the tire spool down. If the tire is out of balance you will know. You will probably be afraid to fly once you actually see what is going on with an imbalanced tire.
 
Or, you can call it a "feature", and press on, as I did.

Now, if it DIDN"T shake briefly, I'd wonder what's gone wrong! :D
 
Or, you can call it a "feature", and press on, as I did.

Now, if it DIDN"T shake briefly, I'd wonder what's gone wrong! :D

Exactly. The wheel is mounted on the end of a long cantilever "stick". Nose gear is not stiff enough to dampen out oscillation from imbalanced wheel rotation.
 
Dynamic balance is very interesting but not easy to do. I assume you need to speed the wheels to a comparable speed so need some drive system. Handdril is slow I guess.

On the other hand there was no problem with the old leg even without any static balance. I did a good static balance which made no difference.

The difference is the stiffness of the new leg and the incident angle of the fairing.
When weather improves I will test without fairing first.
 
Dynamic balance is very interesting but not easy to do. I assume you need to speed the wheels to a comparable speed so need some drive system. Handdril is slow I guess.

The easy way to do this is with a 3000 RPM variable speed drill motor. Put a 6" sanding disk backing plate in the chuck, (no sand paper). Run the edge of the disk against the tire tread to bring up the rotation speed of the tire.


https://vansairforce.net/community/showpost.php?p=1482204&postcount=29
 
On the other hand there was no problem with the old leg even without any static balance. I did a good static balance which made no difference.

I do have wheel fairings.
My plane had vibration on take off I spun balanced the nose wheel, the vibration quit.
The original leg was replaced with the new design one on 6/8/20, there were no new vibrations.
I replaced that leg 120 hours later on 12/2/20 still no new vibrations.

I don't think the leg or the fairing is the issue.
 
Initially I had a bad vibration from the nosewheel after takeoff. I bought a static balancer from Harbor Freight intended for motorcycle wheels and epoxied motorcycle balance weights to the wheel rim. End of problem.
 
Another thought - -

I used a buffer with lambs wool pad. Spins it up nicely after static balancing. I posted about it years ago. Likely still someplace on here.
 
After months of trying to pinpoint the problem I ran out of ideas.
After replacing the nose gear leg and fork as per SB annoying vibrations started when climbing in take off or climbing from cruise.

I tried the following :
Checked the prop blade angles to be the same
Verified the tracking of the prop blade tips
Aligned the spinner.
Did a thourough dynamic prop balance
Did a thorough carb sync
Staticcally Balanced the nose wheel
Exited the nose wheel to high speed with a hand drill; no vibration or out of roundness

Nothing works untill I took the nose fairing off. No vibration at all.

As there is quite a difference in fairing incident angle between old and new fork which may result in lift when climbing , I have tried a number of angle with no results

The only thing that works is take the thing off

A fellow RV12 owner with exactly the same leg,fork and fairing has no problem at all.

The new leg is much stiffer than the old one but why do others not have this problem ?

Any suggestions or ideas ?
 
cruisaider

the fact that you encounter this both in climb after start AND at climbing in cruise, might suggest it isn't (entirely) to be pointed at the (new) fore wheel at all? That wheel does not spin during cruise, does it?
 
The new fork axle design uses “wave washers” that do not add very much rotational drag to front wheel. It’s possible the wheel might rotate in flight from air flow. My nose wheel vibrates as it slows to a stop after take-off. There is pretty good oscillation as plane reaches 300-500 feet altitude. Spinner can be seen jumping 1/8” relative to cowling. If I do a touch/go landing and keep nose wheel off the ground the whole time so it doesn’t spin – no vibration.
 
...Nothing works untill I took the nose fairing off. No vibration at all.

As there is quite a difference in fairing incident angle between old and new fork which may result in lift when climbing , I have tried a number of angle with no results
Here is my un-educated guess. There may be an angle at which airflow around the wheel opening causes buffeting. The old setup never saw that angle, the new one does. OR, maybe you changed the size or shape of the opening slightly while doing the other work. Maybe the answer lies in doing something to the wheel opening in the bottom of the fairing to eliminate the buffeting.

One way to test this might be to use a leaf blower at various angles and see if you can reproduce the vibration. You could hold the tail down to simulate a climb.

Just a thought.
 
Wad some newspaper and shove it up into the wheel pant so the wheel can’t spin freely and see if it goes away. Would at least confirm that’s the source.
 
The new fork axle design uses “wave washers” that do not add very much rotational drag to front wheel. It’s possible the wheel might rotate in flight from air flow. My nose wheel vibrates as it slows to a stop after take-off. There is pretty good oscillation as plane reaches 300-500 feet altitude. Spinner can be seen jumping 1/8” relative to cowling. If I do a touch/go landing and keep nose wheel off the ground the whole time so it doesn’t spin – no vibration.

This is ecactly what I see including the spinner jumping. It stops at abt 500 ft.
I agree the wave washers give hardly any drag but what is the difference when the fairing is off. It may spin a lot less when there is air flow top and bottom of the tyre without the fairing.
The gopro is still on but it is very difficult to see
I tried the fairing level as well as 10 degrees up and down with vibration in all cases.
I might try to increase the bearing drag some way to see if stooping the spinning helps.
 
This is ecactly what I see including the spinner jumping. It stops at abt 500 ft.
I agree the wave washers give hardly any drag but what is the difference when the fairing is off. It may spin a lot less when there is air flow top and bottom of the tyre without the fairing.

So, both of us have same observation. I’m inclined to ignore this vibration – it is a known quantity and repeatable. Vibration is accentuated because heavy nose wheel, and add’l weight of fairing, are cantilevered on a long spring arm (nose strut). Perhaps there is even a natural occurring harmonic frequency involved...
 
I spin mine to 1000 - 1500 rpm and let them spool down, if it shakes at all I balance. This can be done on the plane on the ground. If it does not shake there it will not do it in the air.

A lot of pilots don’t carefully balance wheels or do it static. I hear a lot of “it only spins for a few seconds on takeoff so why bother”, to each his own.
 
I spin mine to 1000 - 1500 rpm and let them spool down, if it shakes at all I balance. This can be done on the plane on the ground. If it does not shake there it will not do it in the air.

A lot of pilots don’t carefully balance wheels or do it static. I hear a lot of “it only spins for a few seconds on takeoff so why bother”, to each his own.

I had calculated that my tires rotate at:

2π x 6" tire= 37.7" circumference.
60,761"/minute (50kts)
66,837"/minute (55kts)

1611 rpm @ 50kts
1772 rpm @ 55kts

So a 1500rpm test is in the ballpark of what real-life is.

I can absolutely tell you that if you haven't balanced your tires with at least a cheapo Harbor Freight motorcycle tire balancer, you're missing out. Well worth the $40. Take your time doing the balancing. I was even able to get a few weights inside the nosewheel too.

One of my mains was soo far out of balance, that it used to be downright scary to touchdown. After balancing, there were a couple landings that I couldn't even feel that the wheels were on the ground and spinning.
 
I already did an accurate static balance.
I will try to spin it ar 1500 and see what happens

Thanks all
 
Just my 2 cents;

Static balance will get you close but….
For automobile tires static balance has been obsoleted and replaced with spin balance, there is a reason.
 
I replaced nosewheel with a new 5.00x5 Aero Classic LSA Tire & New Michelin ($156 :eek:) Air Stop Tube. 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. So, I ended up adding six pcs of automotive stick-on lead weights to get wheel assembly to balance statically. Lots of weight is needed because wheel hub is small compared to outside diameter of tire. Not a desirable situation…

First flights today are same as prior wheel assembly and also what I have experienced with other RV-12’s…. that is a vibration (oscillation) as the nose wheel coasts to a stop. So, nothing has changed... I think the long cantilever nose gear (long round tube with heavy wheel at the end) has a resonant frequency that goes bonkers at a certain rotational speed of the front wheel. High speed is no problem – low speed causes oscillation. Front wheel coasts through this oscillation at about 400’ elevation climbing out from hard surface takeoff.

Question: Has anyone dynamically balanced front wheel to fix this problem?
 
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