Re: [Phys-L] Explaining Gyro Force to Motorcyclists

[John Denker <jsd@av8n.com>]

On 1/14/22 9:51 PM, Bill Norwood via Phys-l wrote:

> That’s when the wild oscillations in the handlebars started.

There are a lot of things that can cause a wheel to shimmy,
but gyroscopic precession is way, way down on the list (if
it makes the list at all).

> > Since shimmy frequency is independent of bike speed, gyroscopic
> > effects "are clearly not essential to the phenomenon."[2] The top
> > five influences on wobble have been found to be lateral stiffness of
> > the front tire, steering damper, height of bike center of mass,
> > distance of bike center of mass from rear wheel, and cornering
> > stiffness of the front tire.[3][9]

https://en.wikipedia.org/wiki/Speed_wobble
  See also references therein.


================

Back when I started taking flying lessons, it was at
a nearby small airport which was very unfancy. All the
Cessnas had terrible problems with nose-wheel shimmy,
which they blamed on improper pilot technique.

Then I read a magazine article that said that the
phenomenon really wasn't supposed to happen. It also
said that the problem was virtually never with the
hydraulic shimmy-damper cylinder, but rather with the
linkage that connects the cylinder to the wheel, in
particular looseness in the N joints in the linkage.
And sure enough, it was easy to see that the joints
were ridiculously loose. And the shimmy was stressing
them and making them progressively looser.

They really did not like a student pilot telling them
what to do, and they never conceded that I was right,
but they did shortly thereafter overhaul the linkages.
The problem went away.

https://www.cessnaflyer.org/media/k2/items/cache/3e04fb9a1a5c2d0e8729e590da1f436a_XL.jpg

https://www.cessnaflyer.org/maintenance-tech/item/1166-shake-rattle-roll-fixing-a-cessna-nosewheel-shimmy.html