Moving the axle forward

[cgruby]

Another thing one should be prepared for, moving the gear forward has an additional destabilizing effect on directional control, i.e., ground loops are easier to establish and control. The effect can be such that a docile airplane turns into a monster, or it can be hardly noticeable.

Cheers,

[Monocock]

Forgive me for saying, but surely if you're having to brake so hard that you risk nosing over, then you're either landing in a strip that's simply too short, or you're coming in too fast.

Modifying the airframe to enable you to stamp on the brakes seems rather excessive.

Or maybe I'm just misunderstanding your point.

[jiott]

Chuck, maybe I'm wrong, but I thought that a longer wheelbase would have the effect of Stabilizing the airplane with respect to ground loops rather than the other way around.

[Monocock]

It's more the fact that you're effectively shifting more of the overall weight behind the main axles than in front of them, therefore you have more rearward mass trying to overtake the forward mass.

[jiott]

OK, that makes sense. So you have two opposite things occurring: More weight aft of the mains is destabilizing but a longer wheelbase is stabilizing. I can see why it may be hard to predict what the overall effect will be, as Chuck said.

[wannafly]

Im thinking if you can land and stop in 200 feet you are just fine. Why complicate things. I would wonder if the tail wheel, springs, frame can take the extra load on the back end?

[cgruby]

OK, that makes sense. So you have two opposite things occurring: More weight aft of the mains is destabilizing but a longer wheelbase is stabilizing. I can see why it may be hard to predict what the overall effect will be, as Chuck said.

Back in my heyday building experimental airplanes, I saw a lot of guys who moved their gear forward to eliminate the nose-over tendency just to find they had created themselves a real monster to control. A good example, look at a sailplane, the wheel is just about on the cg. Did you ever hear of anyone ground looping a sailplane?

[Dusty]

Has anyone measured the position of the axle with the bungy to highwing cabane conversion? I suspect it may be slightly forward.
No adverse handling!
Better coordination between brakes elevator and throttle would be the best prevention from nose over!
I don't have the power of a 912 but a rearward position for me would be better as I have trouble getting the tail up before rolling and need nearly 2/3 throttle hard breaking and stick forward progressively applied on landing to keep the tailwheel up in the rough.

[Esser]

Sailplanes have a rudder the size of a sheet of plywood too. Many times they have a skid or forward wheel to fall onto when the brakes are applied.

[HighWing]

Has anyone measured the position of the axle with the bungy to highwing cabane conversion? I suspect it may be slightly forward.
No adverse handling!
Better coordination between brakes elevator and throttle would be the best prevention from nose over!
I don't have the power of a 912 but a rearward position for me would be better as I have trouble getting the tail up before rolling and need nearly 2/3 throttle hard breaking and stick forward progressively applied on landing to keep the tailwheel up in the rough.

Dùsty,
That is an interesting question. When we designed that gear our intent was to give the airframe a 2" rise at the firewall and wider stance. The purpose of the rise was for better angle of attack on the take off run.

This was all done while the airplane was in flying attitude so the gear when the fuselage is rotated back into three point does move forward a bit relative to the aft rotating fuselage. I just measured mine and when in level flight attitude the leading edge of the wing is about 2-3/4" forward of the center of the axle. When in three point, the wing leading edge is about 9-1/2" aft of the leading edge. It would seem that this would add a bit of weight at the tail wheel in three point attitude.

The factory cabane gear has a profile that suggests they lengthened the gear leg while in three point while maintaining the fore/aft location of the axle. This is just supposition on my part, however.

We have always maintained that installing our gear did not make the airplane a "Bush" plane, but was intended to make the airplane easier to handle on improved strips and to eliminate the need for periodic bungee replacement.

It has long been my thought that the frequent stories of original bungee gear collapse in the early days was a design feature. The airframe was designed to be light weight and the gear, by design, the easier component to replace in case of stress damage in a hard landing. I think Larry is trending in the right direction. All the gear alternatives are quite robust. It is the air frame in the attachment area that typically remains the same while we ever increasingly challenge it. Again just one guy's opinion.