The manual shows you how to set your alignment with the plane up on jacks. It also mentions that you should try to get 10 degrees in this configuration. What they never tell you is that it should be 0, or perhaps 1 degree head in (contact surface out) camber with the weight on it. Mine had a bunch of camber, and probably a bit more toe in that they should, or at least when rolling the excessive camber probably was toeing the wheels in a bit too. The net effect was we had poor alignment, even though it tracked the centerline OK, but it was chewing our tires up. Especially since we’ve been pretty much test flying ever since we built it, with lots and lots of takeoffs and landings.
If you read the blog, you know that we also got a wicked vibration (I hesitate to call it shimmy, because it didn’t amplify, and was very speed related) at about 45 kias. I was worried that we may have broken a main gear bolt, or had a brake dragging, heating up, and then cupping and warping. We cut our gross weight testing short to figure out what was going on, but our initial inspection didn’t show anything, so we decided to pull the wheels off and check everything. In the meantime we’d go ahead and change the tires and realign the main gear.
Nearly three weeks later, it appears the shimmy was do either to the tire getting flat-spotted (going out of round or of of balance) or the internal bias plies parting. Over the course of that time we ground the original axle pads off of the gear legs, and completely cleaned the brakes. Then we got shims from harbor freight for both the large and small (AN5/AN6) axle bolts, pull Jerry’s laser and my inclinometer out and started re-shimming the axles.
The new wing jacks are really nice for this, you can just crank both sides up off of the ground very quickly and easily. This is a several iteration process, as the angle on one side can effect the other, and the airplane has to be level to really check the alignment. First we’d set the camber, and get the first cut at the axle pad set, as this was relatively easy to check. To get the toe, you have to mark the airplane’s centerline on the floor and measure from here to the outside of the wheel at the wheel and the nose, looking for 1″ toe in at the nose. Since you loose your centerline as soon as you jack the plane to shim it, this can be quite tedious. You also have to roll the plane back and forth a few feet to really get the legs to their “relaxed” position. A few more shots at this, and the final axle pad was set with flox.
Then we repacked the axles, changed the inner tubes and tires, and balanced all three wheels. I got the 6 ply Condors and “airstop” tubes. The tubes were probably good, and I’ll keep them as spares, but it seemed like cheap insurance to get new ones. I also liked the tire talc to help with aligning the tube stem with the heavy spot on the side of the tires. We used 1/4 oz stick on weights to get the wheels balanced. One of the mains was pretty close, but the other and the nose wheel took about a ounce and a half to balance. However, I think this and repacking the axle grease will pay out in the in. Finally I ran some brake fluid through both legs as there was at least one pocket of air in the line.
Jerry did a quick fast taxi and reported that the vibration is gone, and the alignment is quite good now, as is the wheel balance, so I hope that this will serve us well for a few hundred hours.
Next up, we’ll be replacing the pitch trim spring, but I hope to get a couple of flying hours in first. I prefer to change one thing at a time, just so if we have any issues it’s clearer what is causing them. Hopefully we can do that by the weekend and we can replace the spring over the weekend as it should only be a couple of hour job. We also have a fly-in this weekend at the airport, but that shouldn’t take too much time, but maybe we’ll do a quick fly-by before we open her up again.
Posted By: Brett FerrellMonday May 28th, 2012 at 7:47 PM