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Landing Gear Camber Angle...

Piper J3

Well Known Member
I’m in the middle of my Annual Condition Inspection and replaced tires and brakes. With airplane raised up, it is a real eye-opener to see how much camber angle is built into the landing gear. I measure 11 degrees camber…

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Hey Jim, or anyone, can you show me the formula to determine angle of the shim/s needed based on measurements from the centerline determining toe-in or toe-out.
I?ve done the measurements and need to figure sin or cosin or tangent and calculate degrees of angle needed to get as close to 0 toe-in.

Thanks
 
Depending on which measurements you took, it should be either ArcSine or ArcTangent. For these small angles, it shouldn't make much difference which one of those you use.

So, if x is the actual toe-in or toe-out you measured (in inches, mm or whatever), and y is the distance between your front and rear measurements (the measurements you took to determine x), then the angle is either arcSine(x/y) or ArcTangent(x/y).

If you wanted to be precise, use ArcTangent if the two measurements were measured along the centerline of the aircraft and use ArcSine if the two measurements were made along the axis of the tire.
 
I was taught a simple (too simple, so it couldn't possibly be accurate.. maybe) procedure from old guys I respect.

Plane on the ground in normal loaded state
- establish your center plumb line on the ground
- clamp a 3 ft or longer 3/4" angle to the brake rotor extending forward of the wheel
- measure distance from center line to angle near the wheel - and from a spot 36" forward from center line to the angle.
- 1" differential means 1 degree, obviously 0.5" would be a half degree. Simple method to determine what shim you need, or not.

For Camber adjustment - I'd simply look at the tire wear pattern & let that dictate if you need any shims.
 
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I was taught a simple (too simple, so it couldn't possibly be accurate.. maybe) procedure from old guys I respect.

Plane on the ground in normal loaded state
- establish your center plumb line on the ground
- clamp a 3 ft or longer 3/4" angle to the brake rotor extending forward of the wheel
- measure distance from center line to angle near the wheel - and from a spot 36" forward from center line to the angle.
- 1" differential means 1 degree, obviously 0.5" would be a half degree. Simple method to determine what shim you need, or not.

For Camber adjustment - I'd simply look at the tire wear pattern & let that dictate if you need any shims.

Hey Ralph,

FYI, 1" displacement, 36" from the axle gives me 1.59 deg. Someone please check my math.
 
Landing Gear Camber Angle

Jim,

Some people say those tires are much heavier than the original tires. Has that created any problems for you?

Thanks.

John
 
Hey Ralph,

FYI, 1" displacement, 36" from the axle gives me 1.59 deg. Someone please check my math.

That's what I got too. You need about a 5' straight angle, not 3', to get 1" = 1 Deg.
 
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Jim,

Some people say those tires are much heavier than the original tires. Has that created any problems for you?

Thanks.

John

Yup, mine were heavier. But, I got 265 landings on the original tires, over 900 on the Desser Retread Elites. Undoubtedly at least some of that is more experience with the aircraft but IMHO it was mostly the tires.
 

Interesting. I wonder how it works - it looks like it might depend on the side friction of a tire that isn't rolling exactly straight over the gauge. If that's the case, I wonder how well it would work on or aircraft tires - our tires have such a smaller footprint than auto tires, especially our high camber tires.
 
Interesting. I wonder how it works - it looks like it might depend on the side friction of a tire that isn't rolling exactly straight over the gauge. If that's the case, I wonder how well it would work on or aircraft tires - our tires have such a smaller footprint than auto tires, especially our high camber tires.

It measures scrub. There are two platforms separated by rollers so very little friction. There is a pointer attached to the top platform that indicated too much toe in or toe out. I've never tried it on the airplanes but it works well on my Lotus 7 with around 400 lbs/wheel.
 
If you are looking for a really long straight reference beam to measure toe-in/toe-out consider using two 4'-6' fluorescent light bulbs each placed against the side of each wheel hub or brake rotor. Be careful though -- the bulbs tend to shatter if mishandled.
 
That's what I got too. You need about a 5' straight angle, not 3', to get 1" = 1 Deg.

Yep You're all right! Shouldn't trust old guys, or should give them less beer.
The length should be 57.3" to get a 1" sweep to equal 1 degree.

General concept is still simple & easy to do though.
 
It should be 1/2? per wheel for the calculation since you want each wheel to the centerline , not to each other.

NO, we are not suggesting a 1 degree toe in or out. Was just suggesting a different way to determine each wheel's angle before shimming.
Yes, you would have to add the two results to set your desired overall toe in / out.
 
Remember that the toe value check is relative to the aircraft center line. Not the two wheels to each other.

It is not uncommon for the production tolerance to have one leg with toe in and the other with toe out. If checked in relation to each other, it may look like it is perfect but your airplane will move in a straight line yawed to one side.
 
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