I had an unfortunate incident in preparation for the first flight. While conducting a high speed taxi test, my nose wheel started to shimmy and I was not able to stop it by breaking or lifting the nose wheel. As I was pulling the mixture to stop the engine the nose dropped. In a split second I expected to see MT prop blades flying but the nose stopped short of hitting the ground. I rolled to a stop and got out to inspect.
Fortunately when the drag links to the nose strut failed, the drag link was pulled down by the springs and jammed against the strut precluding the gear from completely collapsing.
I had the plane towed back to my hangar and started taking things apart to see what needs fixing.
The cause I believe is important to all Glasairs with retract gear. I had set the friction on the collar some time ago and had not re-checked it. Last week I completed some taxi tests up to 60 knots with no issues. But a couple days ago I serviced the struts with nitrogen and in the process some hydraulic fluid spewed out and ran down the strut. I cleaned it up but didn’t think of the fluid in the friction collar. When I took it apart there was a good coating of fluid all through the collar. I believe this lubricated the friction collar and allowed the nose wheel to shimmy. Lesson here; if oil or hydraulic fluid gets in under the collar, you should take it apart and clean it and reset the proper tension.
I sent an email to Harry for some parts, and I hope they have them. I was
amazed at the damage. It wiped out the self-alignment bearings on the aft end of the drag brace, deformed the pivot pins at the top of the strut, and broke the clevis bolts that hold the small drag braces to the main brace.
Hopefully I can get it back together shortly and first flight will be soon.
Lory Ghertner adds:
We of the FT fame have a similar issue with the friction collar on our fixed nose wheel.
Oil running down the gear from the engine wants to collect there causing the shimmy of death. For those FT builders, I installed a fiberglass “plate” over the top of the fairing then attached it with RTV to totally seal the nose wheel gear from any oil dripping.
Ref; Don Yoakley’s nose wheel shimmy incident,
I had a similar event recently, but on landing on a grass strip, when the nose wheel touched down a violent shimmy collapsed the nose gear, followed by both mains as various events were happening!
The long and short of it that talking to Ian Baker at Mitagong ( AUST) who is the engineering manager for Advanced Aero Components Told me that the nose gear failure is designed such that the drag link fails downward! mine did the same and saved the prop. strike! He also said the insert in the shimmy clamp should be changed three monthly! It is age related!
Three monthly seems very short
Can worn scissor bushings cause the nose gear to shimmy?
I was also told that shims need to be installed to tighten the nose wheel bearings.
I’m not so sure about this!
Any advise?