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Hi Matt, I have a Glasair II-RG, so the gear setup may not be the same, but
generally you want 0deg of caster, toe and camber. Since we don't have nosewheel
steering you want this to be pretty close, I imagine.
An assumption: Toe in is measured from the longitudinal centerline. Use a plumb
bob from the tail and the spinner (with the wings level, connect the dots and
extend 20-30' to the front. Also establish a mark on that line that shows the
wheel centers; run a string between the axles to get that mark. At the forward
end of the line mark another line perpendicular to it and as long (a little bit
more) as the wheel base. You now have a Tee.
There are probably a couple ways to establish the toe-in. Either way you do it,
use distance to leverage the accuracy. Use two taut lines parallel to the brake
rotors (use a framing square on the rotor surface) extended forward for 20-30
feet (to the top of the Tee) and measure the distance between them and the
centerline. You don't just want to measure the distance between the
wheels/lines, what if they're both skewed in the same direction? You could be
real high tech and use a laser level to do the same thing -- just make sure the
laser target is perpendicular to the fuselage CL.
Measure the distance for the line to the "target", call it "H." Measure the
distance from the centerline (at the top of the Tee) to the mark on the target,
call it "O." Measure the distance from the axle mark on the centerline to the
target, call it "A."
Now you have everything you need to determine the shim value for the stub axles.
Just use trig. This is scary -- since I used tangent on the Glasair list a
couple weeks ago... <g>
Take some measurements, draw a picture than solve for the angle at the rotor to
figure the shim required. There should be very little SWAG with this method.
Disclaimer: I am not a mathematician or wheel alignment engineer.
Here's the relevant equations:
Tangent of the angle equals O over A.
Sine of the angle equals O over H.
Cosine of the angle equals A over H. (you shouldn't need this little gem)
Of course, if the "A" equals "H" on both sides of the centerline,
everything is good and you can put the old textbooks away.
Good Luck, and here's to many happy brake-less taxis!
Theo N180TG
Glasair Super-IIS RG
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