Avid Flyer Nose Dragger wheel shimmy?

[nlappos 413]

A friend has experienced some nose wheel shimmy on roll out after landing. Any advice or observations? Is there a friction point on the gear shaft to help damp shimmy?

[Richard Smith 32]

Ive never had this issue but at what speed is the shimmy starting 

[marcusofcotton 51]

Which nose gear? Free castering rv6a style has nut with Belleville washers. Supposed to tighten it to require 20 lb of pressure to swivel wheel.

[nlappos 413]

His wheel is a simple pipe mount with an inner rotating sleeve that extends to the wheel (with no springs at the bottom.) The top has a simple kind of arrow that mounts some centering springs. There doesn't seem to be any friction device.

The shimmy starts at about 40 mph or so

[EDMO 1078]

Is he sure that it is not his tire out of balance?  Out of round?   Some have put stronger springs on the Avid nosegear.  Does he only have a steering rod on the right pedal or both sides - That can make a huge difference.  Any slack in linkage can let it shimmy.  Is there a way to put a shimmy damper on it?  The 20 lb force on tire to turn wheel can easily be overcome by your legs - they will hardly notice it.  EdMO

Edited 25 Jan 2018 by EDMO

[nlappos 413]

certainly not balance, the wheel twists violently. Only one steering rod, to the right side. Damper is a good idea, anyone try one?

[Guest]

What are the weight and balance numbers? A forward CG will not allow the pilot to "carry" the nose wheel AND will force faster landings. A terrible combination. The nose wheel should never see 40 MPH. 

Not saying there isn't something wrong or broken with the nose wheel setup, but the 40 MPH number has me spooked.

On my plane for example, the weight and balance is far enough back that I can lift the nose wheel within a few feet of beginning the takeoff roll, and can land and carry the nose wheel from touchdown thru taxiing and not set it down until it is time to stop. If the pilot cannot do that (pretty easily), his weight and balance is too far forward.

Dean originally designed the Avid with a nose wheel and placed the main gear very close to the balance point so the nose wheel really has nothing to do with takeoff or landing other than a third point to balance on when the plane is stopped.

One way to tell if his plane is in the ball park  is if he pushes the tail down to the ground is should stay there or be very close to staying down. Of course the best way to tell is by weighing and balancing :-)

Chris

[EDMO 1078]

What are the weight and balance numbers? A forward CG will not allow the pilot to "carry" the nose wheel AND will force faster landings. A terrible combination. The nose wheel should never see 40 MPH. 

Not saying there isn't something wrong or broken with the nose wheel setup, but the 40 MPH number has me spooked.

On my plane for example, the weight and balance is far enough back that I can lift the nose wheel within a few feet of beginning the takeoff roll, and can land and carry the nose wheel from touchdown thru taxiing and not set it down until it is time to stop. If the pilot cannot do that (pretty easily), his weight and balance is too far forward.

Dean originally designed the Avid with a nose wheel and placed the main gear very close to the balance point so the nose wheel really has nothing to do with takeoff or landing other than a third point to balance on when the plane is stopped.

One way to tell if his plane is in the ball park  is if he pushes the tail down to the ground is should stay there or be very close to staying down. Of course the best way to tell is by weighing and balancing :-)

Chris

Totally agree Chris - I could do almost the same thing with my Cessna 150 - With full up elevator and power, the plane would almost be on the tail with  or without brakes set - soft field takeoffs were on the mains only.  The Ercoupe was the opposite - it was nose heavy, and the nosewheel had to be kept on the ground for steering until ready to rotate.   Both had shimmy dampeners.   EDMO

Edited 25 Jan 2018 by EDMO

[Richard Smith 32]

I also agree

[nlappos 413]

Refresh me, what’s the stall speed of a speedwing?

[Richard Smith 32]

Mine stalls between 46 and 50 mph 

[EDMO 1078]

Even though the wings have stalled on landing there should be enough elevator power to keep the nose wheel off the ground at lower speeds - with power on, the nose should be able to raise long before stall speed is reached on takeoff.  EDMO

[Richard Smith 32]

As soon as I touch the throttle i can lift my nose wheel off the ground