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RVers search for answers in nosewheel mystery

by Bob Collins

The flip-over over an RV-7A in the U.K. a few weeks ago has reignited the controversy over the nosewheel designs on Van's airplanes. But this time, something different is happening; RVers are looking for solutions rather than trying to convince others that there's a problem in the first place.

I've always wondered why, given the varied backgrounds of RVers, nobody has tried to organize an engineering response to the nosewheel design. Most threads on most bulletin boards have usually resulted in a "there's a problem" vs "bad piloting" approach.

Alex Peterson, an RV-6A pilot in Minnesota, started an engineering thread on the Van's Air Force site last weekend.  "I have concerns with the current nose wheel bearing/axle setup. My understanding of the current nose wheel setup is that there are two axle adapters, which are against the roller bearings. The bearing preload is determined by how tight the bolt is/isn't," he said.

"It would seem that this system is not overly rigid. Under loads, the bolt will attempt to flex somewhat. When this flexing occurs, there is an increase in the bearing load on the load side, and an unloading on the opposite side. The deflections could be very, very small, yet still have a large effect.

"Is it possible that runaway bearing drag is contributing to the nose-over incidents? It is not hard to imagine that there is a whole range of states of bearing pre-load out there, from sloppy to tight."

The trick may be being sure the bushing -- not the bearing --  turning. This is a modification that Wisconsin RVator Roberta Hegy tried. She "staked" the outer bearing bushing, allowing her to set the correct bearing preload.

"Preloading the bearing as Van's instructs was meant to create enough friction to prevent the bearing 'mushrooms' from turning and prematurely wearing. This also created excessive drag on the wheel, which slowed the acceleration of the wheel on touchdown. It was supposed to free up with time, but often does not," Hegy wrote on VAF earlier this year.

"The excess drag, as the wheel touches down, causes deflection of the leg and deformation of the tire, much like landing with a nosewheel brake applied. Low tire pressure and/or close fitting wheel pants adds to the problem as the tire can splay out and grab the wheel pant, creating a jamming situation that can literally flip the plane on it's back."

"Staking the mushrooms allows you to properly load the bearings. This allows the wheel to rotate more freely and not tend to grab as hard on touchdown."

"Proper tire pressure, adequate tire/ pant clearance, a wheel that is free to spin up properly on touchdown, and good technique will help ensure that your prize bird keeps the canopy side up on landings. And takeoffs."

Meanwhile, the rvsqn Yahoogroup list continues to kick around the nose gear design and whether it has been responsible for the spate of flip-overs. Several of the posters relayed first-hand experience.

"MY RV9A G-CCZT suffered a bent nose leg  12 hours into its life back in 2005. I was undergoing transition training at the time under the PFA scheme and had just completed a satisfactory landing on Bicester’s rather bumpy grass," Neil Henderson wrote. "On roll out at no more than 15 kts we encountered a wave like depression that pitched the nose up into the air. We continued the landing roll although it seemed to slow rather quickly. There was no feeling of being tipped up on its nose, it wasn’t until I attempted to taxi that it became apparent something was amiss. The nose wheel had curled under. The ground was soft and the undulation caused by settlement over an old ground drain. Not a narrow rut but a depression about 5ft wide and 6” deep. Old style fork but with spat fitted."

Henderson says even after years of practice, he's not sure improved technique would have prevented his mishap.

On that list, there is an intriguing discussion of beefing up the underside of the wheel pant cover (or "spat" in the UK).

Related Link(s):
Hotline archive: The nose-gear debate


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