Late last year we developed what we thought was a nose gear shimmy on our RV-7A. The aircraft has 1000 flight hours. It started as a light amplitude shaking noticed on roll out when we were going slow prior to exiting the runway. We had a friend watch us land and roll out. He noted that the motion of the nose wheel was vertical (nose strut bending along the longitudinal axis) and not horizontal (shimmy). We then jacked the aircraft and inspected and found the nose landing gear attach bolt near the firewall had lost torque. We replaced the bolt and retorqued. The joint seemed tight.
We were planning a panel upgrade so we went down then for the next five months. While we were down we removed and repacked the nose wheel bearings and conducted the pull test. All was well.
Fast forward post panel up ? Things got worse. If we did not consciously hold the nose off on landing roll out, we would get a violent motion that shook the entire plane on landing deceleration at slow speed. We then conducted taxi tests and determined that at 24 knots ground speed while decelerating we would get the vertical motion/shake. This vibration never happens on take-off most likely due to off-loading of the nose gear during acceleration.
Last night we tied the tail down (nose off the ground) and banged the nose strut both vertically and horizontally. Horizontally it is extremely well damped. Vertically it looks like a tuning fork that eventually damps but rings noticeably for a period of time. Obviously, we have looked for a cracked engine mount and cracked gear leg with no findings. Additionally, we have the AntiSplat nose job installed however, we operate from hard surface runways and only have about 10 grass field landings in 1000 hours.
Things we had done in an attempt to remedy the situation;
Replaced nose tire with new one ? No change
Reduced nose tire pressure to 30 psi ? No change
Rechecked the pull test on the fork ? No change
Replaced main tires, rebuilt right brake caliper (it appeared to be sticking a little, repacked main wheel bearings, replaced brake pads ? Have not flown this configuration yet.
Has anyone experienced this and more importantly what is the corrective action? The new nose gear damper appears promising but is a big job.
Thanks
We were planning a panel upgrade so we went down then for the next five months. While we were down we removed and repacked the nose wheel bearings and conducted the pull test. All was well.
Fast forward post panel up ? Things got worse. If we did not consciously hold the nose off on landing roll out, we would get a violent motion that shook the entire plane on landing deceleration at slow speed. We then conducted taxi tests and determined that at 24 knots ground speed while decelerating we would get the vertical motion/shake. This vibration never happens on take-off most likely due to off-loading of the nose gear during acceleration.
Last night we tied the tail down (nose off the ground) and banged the nose strut both vertically and horizontally. Horizontally it is extremely well damped. Vertically it looks like a tuning fork that eventually damps but rings noticeably for a period of time. Obviously, we have looked for a cracked engine mount and cracked gear leg with no findings. Additionally, we have the AntiSplat nose job installed however, we operate from hard surface runways and only have about 10 grass field landings in 1000 hours.
Things we had done in an attempt to remedy the situation;
Replaced nose tire with new one ? No change
Reduced nose tire pressure to 30 psi ? No change
Rechecked the pull test on the fork ? No change
Replaced main tires, rebuilt right brake caliper (it appeared to be sticking a little, repacked main wheel bearings, replaced brake pads ? Have not flown this configuration yet.
Has anyone experienced this and more importantly what is the corrective action? The new nose gear damper appears promising but is a big job.
Thanks