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Gear Leg Oscillation - Grove Gear

I have an RV-8 (approx 100 hrs). Not the original builder. If you look at the video you will see the left gear leg oscillate forward and backward just prior and after the wheels leave the ground. In the video, I kept the nose forward to accelerate as much as I can. Its definitely speed related.

Since this problem began we have re-torqued the gear attach bolts, repacked the bearings and check the brakes. The gear is the Grove Aerofoil gear, wheels and brakes are standard Matco.

Any recommendations?

https://drive.google.com/file/d/1LwuG92UpQP5eYXgSdqoOLRiS5KHE-XZ_/view?usp=sharing
 
Has anyone balanced these wheels? Have you found that the wheels can get unbalanced? How do you balance?


To balance the wheels, get the Harbor freight balancer for motorcycle tires. It has a mandrel and two cones. The wheel sits vertically, not the one that they also sell that sits horizontally. I haven’t tried that one yet. Anyway, you use stick on lead weights. You may have to go to an old tire shop for real lead.. they try to sell sink as wheel weights these days. I like to put a little pro seal over the weights to encapsulate them for extra security.

Be sure to check the mandrel and the cones for trueness.. I have seen the cones machined with a lot of runout.
 
Have you jacked the plane off the ground and checked the gear leg bolts for tightness? Also, that right wheel seemed to stop pretty quick, did you tap the brakes or is the wheel dragging? May have to make a shim for the caliper if it’s dragging..
 
Have you jacked the plane off the ground and checked the gear leg bolts for tightness? Also, that right wheel seemed to stop pretty quick, did you tap the brakes or is the wheel dragging? May have to make a shim for the caliper if it’s dragging..

It has been jacked up and all bolts have been checked. I did tap the brakes in that takeoff as I could really feel the shudder. Brakes have been thoroughly checked as well by AME. I also added some rudder peddle extensions to ensure that there is no pressure on the brakes. Next is to add the return springs on the master cylinders. Waiting for parts.
 
Cool video. Do you a closeup of the gear? It might be the angle, but those don't look like my Grove airfoil gear. I had started to video what's happening outside like you are doing, but I unfortunately lost a camera. :( I won't trust the sticky stuff any more. Which camera are you using?
 
Cool video. Do you a closeup of the gear? It might be the angle, but those don't look like my Grove airfoil gear. I had started to video what's happening outside like you are doing, but I unfortunately lost a camera. :( I won't trust the sticky stuff any more. Which camera are you using?

I looked at your site. They are the same gear. I used a GoPro Max attached to the tie down ring using the mount from ACS

https://www.aircraftspruce.com/catalog/avpages/mypilotpro13-18886.php
 
If not tire balance or dragging brake, then look to wheel toe in and camber. As you lift off a side load will be removed - so the wheel reflexes back.

Carl
 
Has anyone balanced these wheels? Have you found that the wheels can get unbalanced? How do you balance?

If nothing else, just remove the tire/wheel and have it balanced at your corner tire store. They’ll use the weights that attach to the wheel adhesively.

But there’s one other thing to check. Make sure the wheel bearings are properly greased. If not, the bearing drag can pull the wheel back as they impede wheel spin, then the leg will elastically snap the wheel forward. This cycle repeats, creating a fore/aft oscillation that feels like a shimmy. This is more common in A-model RV nose struts between 20-25 KGS, but I’ve heard of it on tail-dragger main legs.
 
If nothing else, just remove the tire/wheel and have it balanced at your corner tire store. They’ll use the weights that attach to the wheel adhesively.

But there’s one other thing to check. Make sure the wheel bearings are properly greased. If not, the bearing drag can pull the wheel back as they impede wheel spin, then the leg will elastically snap the wheel forward. This cycle repeats, creating a fore/aft oscillation that feels like a shimmy. This is more common in A-model RV nose struts between 20-25 KGS, but I’ve heard of it on tail-dragger main legs.

Hi Sid, the bearings were re-packed and are good. I think your description of what is happening is correct. But we have checked and double checked the brakes and bearings. I still have a concern that the left brake might be binding due to pressure on the pedals. I fabricated an extended extension at the base of the pedals and made sure that I was pressing on the extensions during take off. But it seems like the geometry of the rudder pedals in the 8 may cause inadvertent braking. I am going to install the springs on the master cylinders when i get the parts which should then eliminate the brake binding theory.
 
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