Moving the axle forward

[herman pahls]

I could land shorter in my Model 4 Kitfox if I could brake sooner and harder.
I saw this gear extension on a Cessna 140 and am considering trying the same idea on the Grove gear.
I can usually land in 200 feet but am wanting to get in shorter at times.

I have 2 concerns regarding this modification.

1. Would the Grove gear legs, the attach brackets to the longerons and the longerons be up to the loads?

2. Without doing the calculations, any idea how much the weight and balance will be effected moving 29" Bushwheels with Matco brakes forward 4"?

I would appreciate any ideas or comments before I waste any time trying this.

Years ago when I was considering a Just Highlander (which are too expensive for me), I was told by Troy the owner of Just that the main reason Highlanders land shorter than Kitfox's is the the gear is pushed forward placing more weight on the tail.
I have been told that Highlanders weigh 120 pounds on the tail which is close to twice the weight of a Kitfox Model 4 tail.

Thanks
Herman

[jiott]

Herman,

This mod would definitely put a torsional twisting load on the Grove gear. Probably not a problem except for the occasional hard landing. If it was me, I would send a dimensional sketch with your anticipated worst case loading to Grove and ask for an analysis. They may charge something for the calculations, but then you will know for sure.

As far as W&B, it should be fairly easy to treat the wheels and tires as loads at the associated arm. Subtract the existing moment and then add in the new moment. The Kitfox website spread sheet makes this sort of thing easy to do. You will first need to level the plane in flight attitude and measure the existing CG location of the wheels and tires with respect to the datum (wing leading edge at the root) to get the arm. The new arm would be 4" forward of this. Probably will need to remove one wheel/tire assembly to get its weight. You probably already know all this, but I don't know any easier way.

After all this, assuming the Grove gear can handle it, there will still be an unknown, and that will be-can the Kitfox attach brackets and longerons handle the increased twisting loads? No doubt the reserve strength for hard landings will be reduced.

Jim

[herman pahls]

Jim
Thanks for your ideas and I will contact Grove.
I was also considering asking John at Kitfox for his opinion.
Herman

[mscotter]

Yes, definitely get this change in front of landing gear and/or airframe manufacturer's eyes. As mentioned, you're changing the loading on the landing gear. For that matter, you're changing the loading on the landing gear attachment points too.

[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?