| Chapter 9 |
| Landing Gear & Landing Brake |
Axles, Wheels and Brakes
Another lesson in geometry...great. Well I decided to use the plans method for setting the toe for the axles. After making sure everything was level, I re-checked the dimensions on the axle attach points (supposed to be at F.S. 110). I found that the right side was set perfect and the left was out 1/4". After moving the attach point forward 1/4" all my measurements were coming together and I was ready to set the toe. This turned out to be an interesting ordeal since the paragraph was so short without explanation. This was especially frustrating when Nat says that it is critical to do this correctly. So this is what I ended up doing right or wrong. I positioned the fuselage 13' from a wall and hung strings down at the aft and fwd centerlines. Then I hung a piece of printer paper on the wall with a large X on it so the center of the X was at the same height as the bottom of the gear legs. I aligned the paper so when I stood at the rear of the tub both strings were in line and the center of the X was directly in line with the strings. I measured the distance for my gear spread at the mount point to be 68.125". Half of that was 34.0625 plus 1/2 of the tube diameter (.125) ended up at 34.1875". From that I could remove the toe in distance which was (.1" for every 2 ft) .65", and marked the wall at gear leg height this distance from the center of the X. With my sighting tube I could easily move it to sight this mark, but it was moving everywhere on the camber of the strut. I did the 3 bid layup on the strut and let it cure for about 3 hours, then took and floxed my backup pad to the inboard side. Then I heaped way too much flox on the outboard side and placed a straight 4x4x1" pine board (covered with duct tape) on the strut so the top of the board and gear leg were flush and the board was parallel to the floor. I used C Clamps to hold it all together. I aligned my site tube on the inboard edge of the board and adjusted the C clamps until the mark on the wall was centered in the tube, then scraped up the excess flox. After cure this left me with two very flat surfaces aligned perfectly with the marks on the wall.
I had purchased the Matco brakes and read on Brian Deford's page and Marc's page on how they installed them. I used a technique that was similar to both to mount my brakes. I made a paper template, carefully noting the center line of the axle. I then aligned the template on the strut on the FS 110 mark and cut the strut. The calipers were mounted toward the leading edge of the strut and I made sure to give clearance for pad wear (so the calipers would smoothly move without interference from the strut (please note that this was done PRIOR to making the flox pad in the previous paragragh). Also I wanted the caliper near to vertical as I could make it to allow for bleeding later. Then I clamped the axles to the flox pad and drilled out the holes and bolted everything together. For whatever reason, I had to use extra long bolts to get enough grip length. I ended up with AN-25A's which are 3/8" longer than the -22's Nat used in the plans (perhaps the Matco axles have a thicker base flange).
When I mounted the wheel and began tightening the rotor to the wheel, I realized that something was wrong. As the bolts tightened the rotor starting dragging against the stationary pad on the caliper. This was very puzzling, and I could not figure out what was going on. I checked everything, but it all seemed right, but it was still dragging. I called Matco in the morning and eventually spoke with George (the current owner), I told him what was happening expecting this to be something common and stupid. No luck, he was mystified as why this would happen. I took my digital camera out and snapped a bunch of pictures and emailed them to him. After a while he called back and told me that he could see that there was a huge alignement problem with the wheel, but no idea why. Then we started measuring everything. As it turns out the bearing stop on the axle was 1/4" further away from the backing plate than the distance from the rim of the wheel to the bearing race. But why? I called the guy that I purchased the brakes from, and he said he never had any problems with them. But it turns out that he was using a Cessna axle, and the brakes themselves were several years old. Apparently, when the triple puck brakes were introduced by Matco they used the standard axles (available from Wicks). But at some point they started manufacturing their own axles and changed the distance from the backing plate to the bearing stop. I called George back with this information and he created two spacers for me that fit under the backing plate and in front of the base flange that were .25" thick. With new nuts and bolts I reassembled everything and viola, no drag.
After the wheels were safetied, I (with a lot of helpers) flipped the fuselage onto it's feet and ran the brake lines. It should be noted that you have to tighten the connectors to get the tubing inserts to deform and make a tight connection with the brake line. Whew, I was done with Chapter 9!
