My Arion Lightning has a Vans style nose gear leg out front. I cant comment on materials used because I have not handled the Vans nose gear legs in person. It starts with a thin wall CrMo tube as part of the engine mount. Then bolted to that tube is an aluminum nose gear leg that is hollow (drilled) at the upper end that attaches to the engine mount. The mounting bolt is 1/4" in diameter. At the lower end of the nose gear leg is a weldment which is again pinned to the nose gear leg with another 1/4" bolt. The lower part of the weldment has the pivot for the castoring nosewheel assembly. The bushing material for the castoring axis is a fiberglass/phenolic matrix and the method of creating the bushing diameter for the nosewheel pivot is by using a holesaw. It sounds none too precise to my mind.
The airplane has had long standing problems with the gear. While with the previous owner it lost one of the main gear axle/wheel/brake assemblies while on a takeoff roll and departed the runway into the grass. Last year, the airplane, after basic repairs was flown to the Lightning factory in TN where both of the mains and the nose landing gear was replaced, amongst other issues that were addressed at the same time. I bought the airplane in late June and have been working through all the squawks.
There are no complaints regarding the mains, but there has been a consistent shimmy problem with the nose gear. When I investigated it I found the fit of the nose gear leg inside the engine mount tube to be sloppy (diameter fit = loose). I also found that the hole for the 1/4" bolt to be wallowed out which was allowing the nose gear leg to rotate a few degrees in either direction. With this changing the castor angle, that seemed like a major problem. To remedy, I bushed the fit of the nose gear tube in the engine mount tube by wrapping aluminum foil tape around the gear leg to close up the fit. I found I needed about 3 turns of the aluminum tape to take up most of the gap and it then took a significant force to insert the gear into the engine mount tube.
The hole that had previously been drilled in the engine mount tube was so worn from the nose gear tube twisting from side to side that I felt it was too far gone to be fixed by simply drilling from 1/4" to 5/16" and using a larger bolt. Thus I re-installed the old bolt and centered the leg as well as I was able to judge and then drilled a new hole a few inches away in 3 steps to 5/16" and installed a new bolt. This resolved the sloppy fit in the engine mount tube and the twisting I had seen before.
Next, moving on to the weldment on the end of the gear leg. I found the weldment was held on with a single 1/4" bolt. The weldment has a female taper and the nose gear leg a male taper and no doubt the 2 are meant to fit snugly together, but due to some problems in execution the nose gear taper was bottoming out on the bore in the weldment before the surfaces of the taper were making contact. Apparently neither supplier has gauges to inspect the dimensions before shipping... And the builder (Orion factory that fitted the new gear) apparently cant understand the implications of the incorrect fit. Needles to say the weldment was prevented from twisting by the bolt, but was otherwise a floppy fit since the conical surfaces were not making contact. To remedy, I removed the bolt, shimmed the upper and lower diameters with the aluminum tape until the 2 parts had to be driven together and the bolt hole re-aligned by using a tapered pin punch. Original bolt re-installed. No more slop.
Next step was to take a look at the wheel and axle, since i found that I could rotate the axle bolt by hand very easily, despite the cotter pin being installed. Im assuming the shimmy that had been taking place had caused wear in the bearings since with the nut tightened a little the wheel tracked true and showed minimal lateral movement. I re-installed the cotter pin followed by the wheel pants and fairing. Flight testing has shown that while the shimmy is greatly improved it is not gone.
Only a few items remain for investigation.
Replace the tire
Replace the wheel
Rework the castoring pivot/bushing
Does anyone have any experience with resolving shimmy with this (popular) style of nose gear leg ? It seems to be found on a lot of different airplanes ?
Thanks for suggestions.
The airplane has had long standing problems with the gear. While with the previous owner it lost one of the main gear axle/wheel/brake assemblies while on a takeoff roll and departed the runway into the grass. Last year, the airplane, after basic repairs was flown to the Lightning factory in TN where both of the mains and the nose landing gear was replaced, amongst other issues that were addressed at the same time. I bought the airplane in late June and have been working through all the squawks.
There are no complaints regarding the mains, but there has been a consistent shimmy problem with the nose gear. When I investigated it I found the fit of the nose gear leg inside the engine mount tube to be sloppy (diameter fit = loose). I also found that the hole for the 1/4" bolt to be wallowed out which was allowing the nose gear leg to rotate a few degrees in either direction. With this changing the castor angle, that seemed like a major problem. To remedy, I bushed the fit of the nose gear tube in the engine mount tube by wrapping aluminum foil tape around the gear leg to close up the fit. I found I needed about 3 turns of the aluminum tape to take up most of the gap and it then took a significant force to insert the gear into the engine mount tube.
The hole that had previously been drilled in the engine mount tube was so worn from the nose gear tube twisting from side to side that I felt it was too far gone to be fixed by simply drilling from 1/4" to 5/16" and using a larger bolt. Thus I re-installed the old bolt and centered the leg as well as I was able to judge and then drilled a new hole a few inches away in 3 steps to 5/16" and installed a new bolt. This resolved the sloppy fit in the engine mount tube and the twisting I had seen before.
Next, moving on to the weldment on the end of the gear leg. I found the weldment was held on with a single 1/4" bolt. The weldment has a female taper and the nose gear leg a male taper and no doubt the 2 are meant to fit snugly together, but due to some problems in execution the nose gear taper was bottoming out on the bore in the weldment before the surfaces of the taper were making contact. Apparently neither supplier has gauges to inspect the dimensions before shipping... And the builder (Orion factory that fitted the new gear) apparently cant understand the implications of the incorrect fit. Needles to say the weldment was prevented from twisting by the bolt, but was otherwise a floppy fit since the conical surfaces were not making contact. To remedy, I removed the bolt, shimmed the upper and lower diameters with the aluminum tape until the 2 parts had to be driven together and the bolt hole re-aligned by using a tapered pin punch. Original bolt re-installed. No more slop.
Next step was to take a look at the wheel and axle, since i found that I could rotate the axle bolt by hand very easily, despite the cotter pin being installed. Im assuming the shimmy that had been taking place had caused wear in the bearings since with the nut tightened a little the wheel tracked true and showed minimal lateral movement. I re-installed the cotter pin followed by the wheel pants and fairing. Flight testing has shown that while the shimmy is greatly improved it is not gone.
Only a few items remain for investigation.
Replace the tire
Replace the wheel
Rework the castoring pivot/bushing
Does anyone have any experience with resolving shimmy with this (popular) style of nose gear leg ? It seems to be found on a lot of different airplanes ?
Thanks for suggestions.
