Landing gear installation?

I'm starting construction on a Sig Super Chipmunk kit and one of the things I want to do is strengthen the landing gear mounting. What are your thoughts on how to do this? I've had several ideas but they all seem overly complicated or excessively heavy. I'm really looking for simple, light, durable...

Johnny Paris has one of those. He uses both the wing mount and added a fuse mount. That way he can change them when needed. I always liked the looks of the wing mounted gears, but if you push it in you're up the creek. Not and easy task repairing it.
Jay

I can't exactly recall how the Chipmnk anchors its gear, but the best you can do is to tie into the spars (and the sheeting). On my Pathfinder I made sure that the part which ties into the upper part of the torsion rod is very secure. The kit has some thin ply rib doublers--can't hurt. Realize that the normal forces here are pushing the top into the spar, while the lower part is being pushed away from the spar. However you have a good long glue joint here on the lower spar.

One of our club members has a Super Chipmunk, which is a bit on the heavy side, and so far he has had no problem landing on our grass field--but we do keep it mowed rathe short. I don't think there is anything you could do if the problem comes from a -1 inch pullout on an inside loop!

LAST EDITED ON Jun-30-03 AT 12:06 PM (CDT)
 
>I'm starting construction on a Sig Super Chipmunk kit and
>one of the things I want to do is strengthen the landing
>gear mounting. What are your thoughts on how to do this?
>I've had several ideas but they all seem overly complicated
>or excessively heavy. I'm really looking for simple, light,
>durable...

The "weak spot", I suppose would be the right description, is the anchor ends, which with time can wear away the sides of the holes. I bent my own gear legs on a similar LG setup to extend the anchor end past the gear block and added a thin aluminum cap to the top of the anchor end thinking that would show the wear much more slowly. I have one that I didn't improve, and that one needs fixing after almost no use at all.

I think that I will drill the hole round, to fit a stub of brass tube the size to fit the 1/8" wire, and epoxy that stub in place.

P.S. I have a recollection of a wing-gear assembly in a kit that used a similar grooved block (something softer than maple, certainly), but at the anchor end had a stub of the same material capturing a longer anchor end, making the block assembly into a short legged "L". I don't have any plans or reduced size plan collections at hand to go through looking for a reminder, but I don't think the Chip's gear had that feature. I think, however, my modification with a metal cap may have been inspired by the variation with the "long" anchor end.

.
Kiwi

As a follow-up to the anchor ends, that is the weak spot on the gear mount. Make new wire legs with longer ends sticking up through the mount, and then glue a couple of pieces of maple motor mount stock above the standard mount, one on each side where the gear legs protrude. Then drill up through the motor mount stock and that will anchor the gear in quite sturdily. The gear is still removable if you should need to bend it forward or back for whatever reason (or make longer gear legs.

I do like a fuselage mounted gear for flying off of grass, but if that is not your priority, the above will work fine.

Thanks for the comments... All of the things I had come up with would have added considerable weight: plywood doublers, etc. I would like to retain the removable/replaceable gear feature since I don't know the prop diameter for certain yet. And, yes, I will be flying over grass and hard surfaces... If the additional maple does the job, thats the route I'll take. Moveable leadouts and a tip weight box are the only other mods I'm considering at this time. The wing construction is a little strange to me (the half height spar...), but "do-able". The kit wood looks OK, I'll probably replace the sheeting. The fuselage wood looks to me to be harder than necessary but I'm worried about being nose heavy so I think I'll use it anyway. I am concerned that it'll come out too heavy to fly well, but I need something durable. I do plan only a "minimal" finish. So we'll see what comes out.

Another question about the design: the evelator has aerodynamic balances. I've seen only a few other designs with this feature (Accentor and Tanager, to name a couple). Was this done on the Chipp just to retain a scale look? or is there an aerodynamic need for them on this model to reduce the hinge moments or something?

David Fitzgerald did a stab/elevator comparison some years back in Stunt News, and as I recall, he had some nice things to say about the balanced elevator. Since he flew the Chipmunk way back when (as a Junior??), I think I would keep that feature.

Ive built a Chipmonk years ago and and isnt the landing gear mounted with ply doublers on the ribs? Mines stock has has taken a ton of landings. Just build it straight and you will have a ball.

> Ive built a Chipmonk years ago and and isnt the landing
>gear mounted with ply doublers on the ribs? Mines stock has
>has taken a ton of landings. Just build it straight and you
>will have a ball.

On my kit plans there is a hard wood bar with a groove and a short verticle piece for the LG wire. This is mounted in a square cut out in two ribs that are slightly reinforced with a balsa doubler. This would be OK except that the end that would constrain the torsion loads is not well braced. I think Leonard's "fix" is a good plan: extend this verticle piece upward to attach to the upper leading edge sheet. I think I'll also lengthen the horizontal part enough so that the verticle part can be attached to a rib and the spar. The plans don't show this verticle piece attached to a rib or the spar. Both ends of the horizontal hardwood mount are between ribs. I suspect it was done this way for "kit-ing" reasons. There will be some funky angles involved...

The ply doublers on the ribs might also be a good idea. But, may not be necessary with the other reinforcement.

Ron B.
F4Fguy

On all my torsion gear I make the vertical arm long enough to engage a short,grooved maple block glued to the top spar and the adjacent rib.This gives the longest possible lever arm consistent with removable gear.At the expense of a little additional weight,this block can be extended to the bottom gear block,making it almost bullet proof.

LAST EDITED ON Jul-01-03 AT 01:14 PM (CDT)
 
I would certainly replace the balsa rib doublers with thin (1/32) plywood. Brodak uses plywood half ribs as doublers on the Fancy Pants kit and it seems to work pretty well. The torsion stop on the top of the grooved blocks is a piece of motor mount material. It is glued to the top of the grooved block and drilled prior to gluing the blocks into the wing structure. When I get around to building my old Chipmunk kit, I plan to update it to an installation similar to the Fancy Pants.
Steve