Landing gear camber

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george7105
Posts: 4
Joined: Wed Apr 12, 2017 7:59 pm

Landing gear camber

Post by george7105 »

I'm ready to final weld the cub style (springs) landing gear. The fuselage is upside down and I'm trying to figure out how much to lift the axles [what degree of tilt] so when on gear and at weight the wheels are vertical. Thanks for any help.

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taildrags
Posts: 367
Joined: Tue Mar 07, 2017 10:39 pm

Re: Landing gear camber

Post by taildrags »

Wow. I'm not sure there is any formula or estimating method to help with that. It would be difficult to calculate the estimated compression of the springs and the resulting change of geometry of the gear legs, although it could be attempted by geeks like me if we knew the k factor of the springs and the anticipated max gross weight of the airplane when it's completed. It might also be that someone with jack stands and a landing gear similar to yours could measure the angular deflection of the axle backing plate with a level after the plane is hoisted up to remove the weight from the gear. I have done this in a pinch by lifting the tail of the airplane and having a helper slide a padded sawhorse crosswise under the belly of the airplane. Lowering the tail using the sawhorse as a fulcrum, the gear can be made to come off the ground but it is stressful on the belly of the plane. Alternatively, the nose of the plane can be lifted using a chain hoist overhead till the tires lift off and the angle of the backing plates can be measured.

The way it was taken care of on my airplane was with tapered shims. These are available from Aircraft Spruce and other suppliers as axle camber or toe-in/out shims in varying tapers of 1/2 or 1/4 degree, and in combinations. Both my axles needed a little tweaking but both are tracking nicely now. The original builder had used plain washers for this and it was not an elegant solution because it leaves a wedge-shaped gap that collects dirt and water and is very inexact. You can see how I did it here: http://www.flysquirrel.net/piets/axle.html

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

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taildrags
Posts: 367
Joined: Tue Mar 07, 2017 10:39 pm

Re: Landing gear camber

Post by taildrags »

PS, if you'd like for me to try, I'd be happy to try the sawhorse trick with my airplane to see how much the angle of the axle changes when the airplane weight is removed from the gear. Let me know...

-Oscar

Elton Hanneman
Posts: 4
Joined: Tue Dec 04, 2018 8:41 pm

Re: Landing gear camber

Post by Elton Hanneman »

Hi George
If you still have the fuslage upside down do this. Knock the wood plugs out of the axel stubs. You can either sight through the axel's to see the towin alingment or slide a pice of 1" od tube through to get both tow in and camber alined . Then masure your shock units at half travel then you need to set the cabane attach point to that length. I find that on a stock cub gear leg length and bungee units you need to raise the attach points about 4". I have seen more then one Piet includeing GN1's haveing negatine camber with the wheels off the ground. Then they all think I need more bungees. If you need more information just ask.
Elton
I just am finishing a Piet fuslage and welded up a new cub gear for it. should fly in a month. N1940

Elton Hanneman
Posts: 4
Joined: Tue Dec 04, 2018 8:41 pm

Re: Landing gear camber

Post by Elton Hanneman »

Hi George
Friday I rolled my aircamper out to take pictures the first time I had moved it since building new fuslage and landing gear. I discovered it was hard to push out and when I pushed it back in the wheels spread out. Tow out! I had set it to 0 degrees it in level fuslage pitch. In 3 point it is 3/4" tow out.I rechecked it in level and yes it still is zero. My plan is now to hang the airplane from the hoist with the shock struts removed shim under the tires to 0 camber. Lay a headed beam in front of the tires stick bars through the axel's chain the bar on the out side of the wheel to the beam then jack from the beam to the bar on the inside of the wheel I have disk brakes and use stright edges to ck from. I have set the shock strut mount to give me 0 camber at half travel. At full load and tail up I will have tow in. with tail down where most of the tire use is I want 0 with tail up you also get rudder help so tow in isnt that much of a factor. I guess building a gear with the airplane upside down turned me brain upside down. Will let you know how it comes out.
Elton

george7105
Posts: 4
Joined: Wed Apr 12, 2017 7:59 pm

Re: Landing gear camber

Post by george7105 »

Thanks Oscar and Elton for the response. I've built the gear as in Bingalis' books. I have to get it right because there are no shims in the design.
The springs can compress at 900lbs. per first inch. I'm thinking maybe try to compress the spring a 3/8 in. which would be about 338lbs. Close to what the plane should weigh at the tire. ?

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taildrags
Posts: 367
Joined: Tue Mar 07, 2017 10:39 pm

Re: Landing gear camber

Post by taildrags »

George;

My Air Camper with Cont A75 has 307 lbs on one tire and 304 on the other, in the level configuration for weighing, but mine is pretty light (636 lbs empty). Sounds like you are on the right track. Not sure about the spring rate/compliance on my shock springs, but just as another data point for you, the ones that William Wynne used on Bob Lester's Corvair-powered Piet conversion from bungees to die springs are rated k=1100 lbs/inch.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

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