[vlittle]

For those keeping count, another "a" model flipped over yesterday while landing at the fly-in at Reklaw. I believe it was a 7a. I didn't see it happen but saw the plane after it happend. Hundreds of planes showed up, everything from cessnas, pipers, beech, Rv's, etc. The strip is kinda rough towards the north end. Other "a" models landed there without trouble. Not sure who it was, but I think they're ok.

Tobin

I know Van's position on this topic: it's all about pilot technique. I think, however, there is some anecdotal evidence that the A's are prone to this problem.

I had a good look at a Grumman Cheetah today, which also uses a castering nosewheel. The gear is larger diameter, a presumably stronger. The gross weight of a Cheetah is higher than most of the A models.

What was substantially different, however, is that the top of the nose gear strut was hinged at the firewall attach point, and two small oleo struts were attached several inches below that point to provide support and shock absorbtion.

On a hard impact the strut is designed to absorb energy by collapsing vertically, with a minimum of backwards travel in the gear leg. This is in contrast to the Van's design that tends to tuck backwards on impact.

I believe that it is quite possible for Van's to build a similar system, and even make it retro-fittable to existing engine mounts. It would be heavier, of course, but the weight is ahead of the cg, which is beneficial.

I hope Van's is taking this issue seriously. I know with the RV-12 they are looking at a different system than they've used before. My hope is that they will put some energy into improving the existing design as well.

Vern Little
www.vx-aviation.com

 

[az_gila]

I had a good look at a Grumman Cheetah today, which also uses a castering nosewheel. The gear is larger diameter, a presumably stronger. The gross weight of a Cheetah is higher than most of the A models.

What was substantially different, however, is that the top of the nose gear strut was hinged at the firewall attach point, and two small oleo struts were attached several inches below that point to provide support and shock absorbtion.

On a hard impact the strut is designed to absorb energy by collapsing vertically, with a minimum of backwards travel in the gear leg. This is in contrast to the Van's design that tends to tuck backwards on impact.

Vern Little
www.vx-aviation.com

Vern... I own a Grumman Tiger (a Cheetah with a 180HP engine) and your statement is not quite correct.

The Grumman nose gear is designed to rotate about a torque tube that is just behind the firewall. It's not a hinge. The torque tube twist is the springing.

The two small shock struts were only added in 1977 and on models. I believe they are related to shimmy reduction, NOT the actual springing of the nose gear.

The Grumman nose gear leg is stiff, and all of it's movement comes from this torque tube...

A picture is at the bottom right of page 3 of this catalog section....
http://www.fletchair.com/onlineBrochure/32-39_Sec32.pdf

Many early Grummans had overshoot landings (don't come in hot...they float) and a typical failure was a snapping off of the nose gear leg.
I think the failure point is the bend in the nose gear leg. Each annual there is a check for ovality at the bend ....
Several did flip.... The baggage door has proved to be a way out .. if you are skinny...

gil in Tucson
Tiger N12GA coming out of the paint shop soon...

 

[vlittle]

nose gear

Vern... I own a Grumman Tiger (a Cheetah with a 180HP engine) and your statement is not quite correct.

The Grumman nose gear is designed to rotate about a torque tube that is just behind the firewall. It's not a hinge. The torque tube twist is the springing.

The two small shock struts were only added in 1977 and on models. I believe they are related to shimmy reduction, NOT the actual springing of the nose gear.

The Grumman nose gear leg is stiff, and all of it's movement comes from this torque tube...

A picture is at the bottom right of page 3 of this catalog section....
http://www.fletchair.com/onlineBrochure/32-39_Sec32.pdf

Many early Grummans had overshoot landings (don't come in hot...they float) and a typical failure was a snapping off of the nose gear leg.
I think the failure point is the bend in the nose gear leg. Each annual there is a check for ovality at the bend ....
Several did flip.... The baggage door has proved to be a way out .. if you are skinny...

gil in Tucson
Tiger N12GA coming out of the paint shop soon...

Gil, thanks for the clarification. For those interested, I took a picture of the Grumman set-up while I was helping with the wing spar AD. My AME said that the oleos are anti-porpoise dampers.

BTW, if any of your friends are doing the Spar AD, I have some tips. Contact me off-list.

Vern