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Vibration while taxiing...please help!

What-Now-Ski

What-Now-Ski

Member
Occasionally, when taxing with idle RPM there is a bad vibration in my RV-7. The airplane has 70 hours on it and has never done this before. It usually occurs after a wheel landing, and after the tail wheel is down and rolling along. And the whole plane keeps vibrating while taxiing in. An increase in speed usually increases the vibration. If I come to a stop and start taxing again, there isn?t a vibration until there?s a buildup in speed. No problems in flight at any RPM or any speed down to stall. Is this a wheel or brake issue? Please help!!!
 
Vibration while taxiing.

It usually occurs after a wheel landing, and after the tail wheel is down and rolling along. And the whole plane keeps vibrating while taxiing in. An increase in speed usually increases the vibration. If I come to a stop and start taxing again, there isn?t a vibration until there?s a buildup in speed.
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Sounds like tail wheel shimmy to me.
 
Raise the tail with a stand (so the tailwheel has no weight on it) and check your tailwheel for wear. If all of that checks out, put the tail back on the ground and make sure that the pivot point is straight. If it is angled back from top to bottom (negative castor), that could very well be your problem. This common if the tailspring becomes weak or bent.
I have dealt with this problem with my other plane that has a Scott tailwheel.
If you can, post a photo taken from the side of the tailwheel with weight on it.
Good luck!
 
I have a vibration also. I thought it was at a certain RPM and my engine was shaking badly. Turns out it is my right gear has a shimmy. A friend was taxiing behind me and noticed my right wheel pant shook badly.
 
Landing gear shimmy

I would bet you have a shimmy in one or both landing gear legs. Van's recommends reinforcing each gear leg with a wood brace wrapped to the rod landing gear leg with fiberglass cloth & resin. I used some oak door trim cut down & have no shimmy at all but I have seen many other RV's without the braces that do shimmy. This could be your problem as well.

Dick DeCramer
RV6 N500DD 400 hrs.
RV8 fuselage almost complete
Northfield, MN
 
In addition to wheel shimmy take a look under the cowl and if anything ie exhaust, heat muff or anything new vibrating on the cowl. Sometime the engine mount rubber sags and allows something to get to close to the cowl.
 
hydroguy2 said:
I have a vibration also. I thought it was at a certain RPM and my engine was shaking badly. Turns out it is my right gear has a shimmy. A friend was taxiing behind me and noticed my right wheel pant shook badly.
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This is very likely your problem also. If it happens pretty consistently, the best trouble shooting procedure is to have someone watch you make a landing. If it is one of the main gear legs or the tail wheel, inducing the vibration, someone viewing from the outside will be able to see it.

DickDe said:
I would bet you have a shimmy in one or both landing gear legs. Van's recommends reinforcing each gear leg with a wood brace wrapped to the rod landing gear leg with fiberglass cloth & resin. I used some oak door trim cut down & have no shimmy at all but I have seen many other RV's without the braces that do shimmy. This could be your problem as well.
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If you do find that it is one of the main gear legs, do not go to this extreme until you have tried the simple things first.

I have seen severe cases of this problem totally solved just by installing new tires and balancing the wheel/tire before installing it on the airplane.
If you do discover it is one of the gear legs, and the tires still have a lot of life in them, start with checking the roundness of the tires (jack up one side and turn the tire with some type of indicator positioned next to the tire surface). The tire should be nearly perfectly round as long as the airplane hasn't been sitting unmoved for very long. If the tires are round, then check the balance. My bet is that one of these (or a combination of the two) is causing your problem. Be sure to report back what you find.
 
That's the plan. I'll be doing my Conditional Inspection in the next few weeks. Rotate and balance the tires is on the list.
 
Check the bearing pre load.

Vans has used a thin walled steel spacer inboard of the bearing, and it is prone to wear.

First thing after you get the cotter pin out of the wheel mounting nut, try tightening the nut, and see if it takes up any slack.

Good luck.
 
Stiffeners available

I still have some gearleg stiffeners available for sale. Email me for info at:
[email protected]

Temporarily you could reduce your tire pressures to about 25lbs and see if this doesn't help. It sounds like you have the typical oscilliting gearleg problem.
 
Put the gear stiffeners on. Not only gets rid of the vibration witch can get very bad sometimes but dampens out the gear for much better landings. Gets rid of the pogo stick action also. Don
 
First check your tire inflation. If i put too much in mine (+38 psi) i get shimmy. With less pressure, no problem.

Mark
 
strahler13 said:
First check your tire inflation. If i put too much in mine (+38 psi) i get shimmy. With less pressure, no problem.

Mark
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Tire inflation is a major factor, don't hesitate to drop the pressure. After the tires have worn out of round a bit I find 24 psi will prevent most shimmy on my RV-6 and still perform safely.
 
check the air pressure. ?To much air will increase to landing gear shake. Less pressure means more friction and helps the gear track without the shake.

sam
 
I agree that tire inflation pressure is also important, but I didn't mention it in my previous post because a pressure adjustment should not be used to compensate for an out of round or out of balance condition that is causing leg shimmy.

First verify everything is working correctly with the tire/wheel, then use pressure adjustments if there is still an issue.
 
Shimmy

When I owned my Bingelis RV-3 it would shimmy in the 20-25 kt speed region while taxiing or after landing and lowering the tail wheel . It was happening because the springy gear legs wanted to track out then back in with the tail on the ground. It never happened with the tail off the ground. Solution was to put wooden stiffeners on the back of the gear legs and to balance the wheel pants. Once I did that the shimmy went away.
 
Sam Buchanan said:
Tire inflation is a major factor, don't hesitate to drop the pressure. After the tires have worn out of round a bit I find 24 psi will prevent most shimmy on my RV-6 and still perform safely.
Click to expand...

Goodyear specifies a service load rating of 800 pounds (per tire) at a 31 psi pressure for their 4 ply 5x5.00 tires.

If you are using the 4 ply tires at 24 psi it is way outside the manufacturer's service load rating.

Page 4 of this PDF file

http://www.goodyearaviation.com/resources/pdf/datatires.pdf

Interesting data here -

http://www.goodyearaviation.com/resources/pdf/engtechinfo.pdf

If you inflate when the plane is on the gear (i.e. loaded) you should add 4% to the inflation pressure...:) - just aim 1 or 2 psi higher...:)
 
Try this...

Dave,

This sounds like typical gear leg shimmy/vibration. As per the previous suggestions try these out:

- Ensure that the main tires are inflated to 25-28 PSI if using the original issued Aero Classic tires. If using a 'better' grade (Goodyear, Michelin, etc) you may be able to inflate them a smidge higher. Tire inflation pressure is the 1st defense against shimmy/vibration.

- Check for flat spots or other damage. This may be the reason the shimmy gets started in the first place. Balancing the tire may also help. (Are the valve stems aligned with the red dot on the tires?)

- Change runway surfaces... Does it happen on all paved surfaces? What about grass?

- Note what load condition the event starts at? Light or heavy?

- Gear leg stiffeners are typically a 'last resort'. Most of the time shimmy can be solved with proper tire inflation.

- Note what GPS ground speed this occurs at and operate outside of that range if possible. Slower taxi speeds tend to alleviate it.

Most of the time shimmy is a transient event and only occurrs at a specific speed range. This is a well known idiosynchasy of the taper rod gear leg. I have also seen some RV's that when one leg begins to vibrate, it will cause the other to follow. Give me a call at Van's if none of these solutions work...
 
I've dealt with this on three different RVs. If you PUT THE LEG STIFFENERS ON you won't have a problem. Mine doesn't shimmy a bit no matter what my tire pressure or wear is and it was terrible before. These are not a big deal to put on, you can do it in a couple of hours. Don
 
Thanks for the responses

I'm going to lower the tire pressure and go from there. I'll get back with the (hopefully positive) results..
 
As I have explained on many occassions, if you lower your tire pressures you create a scrubbing action that pulls the round gearlegs aft while landing or taxiing. This is OK but you will be replacing tires in less than 100 hours and increasing the risk of heat failure. Read Van's instructions that came with the kit.
 
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