That's a very violent 'shimmy' to be sure - When you called it a shimmy I wasn't expecting anything that bad! Looking at several other Cozy built aircraft that I follow, your geometry appears much different from all the others. When deployed, your strut is certainly more vertical than everyone else's and the wheel assembly looks more vertical in it's attachment to the strut too. On all other aircraft that I'm familiar with, the wheel axle trails the strut by lots more than yours does - With the axle further behind the strut and the strut angled back a few degrees more I'm pretty sure your problem would disappear. Check out the nose gear on several other planes and I'm sure you'll see the differences. Hope this helps ...
crazy!!! glad you got that on video... i was expecting to see some slight turning of the wheel putting vibration on the front... not holyshit, spin in every direction, freak out wheel!!!
What is the break free force you've measured on the pivot? I fought with this for a while, after I rebuilt my nosegear using Nate's new machined fork. I had too much stiction (force required to break free and begin to caster the fixture) which meant I was dragging a brake on takeoff because I couldn't get it to track straight (it was twisting the strut instead of the caster pivot). If I loosened it off to reduce stiction, it then would shimmy, because the friction was too low once it did start to move. I tried oiling the oilte washers, but this didn't work. What I ended up doing to solve it was using high-molybdenum grease (specifically, Honda M-77 paste) on the load bearing surfaces. This leaves a lubricating layer of molybdenum even after the carrier grease gets squeezed out. I then tightnened the Belleville stack until I got 8-9 lbs of stiction, measured at the wheel axle. This solved it for me.
Seems like there is an induced asymmetry between the nose wheel & either of the rear landing strut wheels.. A dragging brake on either of the rear wheels might cause this but in any case it is a dynamic event that probably will disappear at deceleration. Measuring the distance from either rear strut wheel to the nose wheel will probably not manifest the the event.
Definitely used to it from time to time with theGrumman Cheetah… 🤷🏽♂️
That's a very violent 'shimmy' to be sure - When you called it a shimmy I wasn't expecting anything that bad!
Looking at several other Cozy built aircraft that I follow, your geometry appears much different from all the others. When deployed, your strut is certainly more vertical than everyone else's and the wheel assembly looks more vertical in it's attachment to the strut too. On all other aircraft that I'm familiar with, the wheel axle trails the strut by lots more than yours does - With the axle further behind the strut and the strut angled back a few degrees more I'm pretty sure your problem would disappear. Check out the nose gear on several other planes and I'm sure you'll see the differences.
Hope this helps ...
I will do that at or next fly in coming up soon.Thanks
crazy!!! glad you got that on video... i was expecting to see some slight turning of the wheel putting vibration on the front... not holyshit, spin in every direction, freak out wheel!!!
You and me both!
Great video! Really look forward to solving this issue. Mine does the same about every 6mo
Thanks Russ. Ive noticed mine will happen usually on very rough runways only
What is the break free force you've measured on the pivot? I fought with this for a while, after I rebuilt my nosegear using Nate's new machined fork. I had too much stiction (force required to break free and begin to caster the fixture) which meant I was dragging a brake on takeoff because I couldn't get it to track straight (it was twisting the strut instead of the caster pivot). If I loosened it off to reduce stiction, it then would shimmy, because the friction was too low once it did start to move. I tried oiling the oilte washers, but this didn't work. What I ended up doing to solve it was using high-molybdenum grease (specifically, Honda M-77 paste) on the load bearing surfaces. This leaves a lubricating layer of molybdenum even after the carrier grease gets squeezed out. I then tightnened the Belleville stack until I got 8-9 lbs of stiction, measured at the wheel axle. This solved it for me.
Seems like there is an induced asymmetry between the nose wheel & either of the rear landing strut wheels.. A dragging brake on either of the rear wheels might cause this but in any case it is a dynamic event that probably will disappear at deceleration. Measuring the distance from either rear strut wheel to the nose wheel will probably not manifest the the event.
I still haven't measured it.. We can play with it at Rough River though