8.1.2 Main Wheel Alignment

This entry is part 6 of 8 in the series 08 - Wheels / Axles

This is definitely a two-person job.

The wheels on the main landing gear have to be aligned.  Simply put, they need to point slightly in toward the nose. Here’s the procedure:

  1. With the plane on the ground, roll it backward 15′ and then forward 15′.
  2. Using a plumb-bob, define the centerline of the fuselage by marking a point on the floor at the nose and the center of the prop at the rear.
  3. Measure out from the centerline to the outside of the left and right wheels.
  4. Measure out from the centerline at the nose left and right the distance obtained from the previous step.
  5. Using a wicked-ass long I-Beam, place it against the tire and see what distance it is from the centerline at the nose. It should be 1″ (closer to the nose) than the measurement from step 2.

To change the toe-in, shims are placed between the axle mounts at the front or rear depending on whether you want to move the line in or out. And you have to jack the plane up to do this. Which means when you put it back on the ground, you’ve got to do the 15′ back and forth rolling thing.

Malcolm swore that the geometry of the landing gear is such that there won’t be any difference in the measurements with the plane on the ground or on jacks. I didn’t buy that. So we tested it. Measured the alignment on the ground and then jacked up with the wheels off the ground.  Exactly the same. That’s going to save a ton of time!

The next deviation is to not trust the tire being perfect. Instead of placing the alignment device (wicked-long I-beam) against the tire, I used a block of 1″ x 2″ x 6″ aluminum that allowed me to use the metal wheel as the basis for the measurement.

Then I didn’t have a long I-Beam, so I used my 2′ long laser level.

I held the laser level against the block which was against the wheel while Malcolm marked where the laser hit the line at the nose. It looking about 1″ of toe-OUT on each side.

So I pulled the two rear mounting bolt and put in a washer. That got one side close but the other side went in the opposite direction!?!?  Pulled the washers on that side, put it back together, checked it again and it was almost where it needed to be in the first place. Then I discovered that by changing order that the bolts were tightened changed the results wildly.

I completely removed the axle assembly and discovered the gear leg did not have a flat surface in the first place. The result it that I was trying to attach a flat object (axle) to a rounded surface (gear leg). I could have played with the torque on the bolts and the order that I tightened the bolts until I got it where I wanted it, but then a bump could move it out of alignment.  So I mixed up some epoxy/cabo, applied it to the gear leg and bolted everything back together. Once it cured, I had a perfectly flat mounting surface.

New, flat mounting surface.

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After that it was just a matter of determining the correct shims for the two wheels to get the required 1″ of toe-in.

Once that was done I could repack the wheel bearings, bolt together and safety wire the brakes and wheels.

No pictures of the process since there were only the two of us and I was holding the laser and Malcolm was marking the dimensions.

Brake calipers torqued and safety wired.

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Disc bolted, torqued and safety wired to the wheel.

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Wheel mounted, torqued with cotter pin installed.

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Done!

Series Navigation<< 8.1 Matco Brake Upgrade8.1.2 – Wheel Alignment, Part II >>