Just wanted to post my recent experience with resolving the shimmy problem on my 7A. My shimmy/vibration was not so bad that I made it a high priority, but 50 hours after first flight, I decided to solve the problem. After spending considerable time reviewing the many previous posts and videos and varying my tire pressure and side breakout force (and refining my landing technique), I came to the conclusion that the breakout (side load) force is not the issue for the typically experienced "shimmy". I have not yet seen a video of a "fishtail" type movement (side to side) on the nose wheel. I have, however, seen many fore/aft shaking/shimmy videos and have observed this directly in taxi operations at my airport.
Also, I might note that the solution provided by Allan at ASA seemed to solve the problem with about 100 percent satisfaction. His solution has nothing to do with the side to side breakout force (or landing technique), but everything to do with bearing drag, wheel balance, and tire roundness. So, being one of those do it yourselvers (maybe one or two more out there), I decided to see what I could accomplish before I sent my wheel to ASA. By the way, I have Matco nose wheel with original split bushings, which if axle is tightened to prevent bushing spin produces a lot of drag.
Step 1. Per Matco tech bulletin, I removed the inner portion of the rubber seal. This reduces rolling drag buy maybe 50 percent.
Step 2. Trued tire (orig. Cheng Shin) with hand held belt sander, marker held steady using nose wheel fork (done with wheel mounted). About 30 min.
Step 3. Had wheel spin balanced at Spruce Creek FBO. $15.
Strep 4. Made alum. spacer (1" dia / approx. 1.3" long) using lathe (30 min.)to fit between the two bushings so axle nut can be tightned without affecting bearing preload. This accomplishes the exact same thing as the new type Matco axle. The last trimming of the length was done 1/1000th at a time to get the desired bearing preload.
Flight Test: Shimmy gone. (Don't leave plane without parking brake set now or it will roll off with mild breeze)
Also, I might note that the solution provided by Allan at ASA seemed to solve the problem with about 100 percent satisfaction. His solution has nothing to do with the side to side breakout force (or landing technique), but everything to do with bearing drag, wheel balance, and tire roundness. So, being one of those do it yourselvers (maybe one or two more out there), I decided to see what I could accomplish before I sent my wheel to ASA. By the way, I have Matco nose wheel with original split bushings, which if axle is tightened to prevent bushing spin produces a lot of drag.
Step 1. Per Matco tech bulletin, I removed the inner portion of the rubber seal. This reduces rolling drag buy maybe 50 percent.
Step 2. Trued tire (orig. Cheng Shin) with hand held belt sander, marker held steady using nose wheel fork (done with wheel mounted). About 30 min.
Step 3. Had wheel spin balanced at Spruce Creek FBO. $15.
Strep 4. Made alum. spacer (1" dia / approx. 1.3" long) using lathe (30 min.)to fit between the two bushings so axle nut can be tightned without affecting bearing preload. This accomplishes the exact same thing as the new type Matco axle. The last trimming of the length was done 1/1000th at a time to get the desired bearing preload.
Flight Test: Shimmy gone. (Don't leave plane without parking brake set now or it will roll off with mild breeze)
Allan Nimmo has been Great to work with!