I learned early on that the wheel alignment on gyros is quite important. I built a machine for a guy in the 90's, he came to me with a fiberglass axel beam he had made and wanted me to make a machine and put this beam axel on it. I took one of my frames and adapted it. When I test flew the machine, on the ground running it weaved slightly and seemed to want to do anything but go straight, it was worse once the nose wheel came up.... it was a sort of 'duck walk Very un nerving, I had never experienced it before.

Standing back and looking at the wheels, they seemed to toe in.... I got 2 pieces of frame alloy and clamped them horizontally to the outside of the wheels/tires, so about a yard was in front and a yard behind each wheel,, marked them evenly with the shortest and measured between the 2 pieces.... it turned out the distance at the front was about 3/4" toed in, confirming what my eyes were seeing.

I thought about it and took out the beam and reversed it, now they were toeing out at the front a little.... testing it again, it ran perfectly straight, no more duck walking. I considered filing the end to bring them parallel, but it ran so straight and predictably, I left it as it was with his agreement.


It turns out that I discovered something that I haven't heard mentioned before as being critical and thought it would be good to mention it here for other home builders to think about. The guy had made the mold from some 4" C section steel and he cut V's and bent it to the bow shape he wanted,, then tacked in some flat bar to make the ends taper in to about 2 and 1/2" where the flat for the axel came thru.... then he finished the mold so it would be a nice finish, then waxed it and layed in resin and cloth, til it was a bit over an inch thick. He had taken it out of the mold and drilled the holes for the axels. He showed me, looked ok, we mounted it on a board and piled about 300# of weight on it at the middle..... not much flex, no cracking noises.... seemed good, We shook the weights and he even stood on it as well as the weight, very strong. However, it turns out the mold ends were a tiny bit off, so the beam, with the wheels on, had the wheels toeing in.... great for a car, a few degrees toe in, but very unstable for a gyro. Naturally I had picked it up and put it on expecting them to be parallel and just put it on without any thought, but of course 50 - 50 chance, I got it toe in...... ending in duckwalking and a severe risk of rolling over. Having it slightly toe in, the wheels (especially on sealed runway) wanted to come together (even try to roll under the machine), making it very unsafe. With the wheels toeing out once I turned the beam around, the wheels want to run apart, not together, so it was very stable as a result. The tires do tend to wear more on the inside edge, but once the wear gets excessive (a long time unless always on sealed runways) you can turn the tire over on the rim, so the 'as new' side is now in contact with the ground, so you get twice the life of the tires. With the wheels toeing out, on landing, the wheels wanting to part, put a lot more stress on the bolt/pin/circlip that stops the wheel coming off, so one light circlip in a groove wont be real safe, A left hand thread on the left side, castellated axel nuts pinned, or a tube piece over the axel to the bearing with a bolt thru the axel, whatever, but strong and fail safe is key.

I just thought I would bring this up. If someone has a machine that seems to want to duck walk for no apparent reason, check the wheels are not toeing in... I personally would recommend a little toe out over dead straight ahead (just a tiny bit at least). Might be a good idea just to check your machine, just out of interest, just because you can.

Comments welcome.....

Very good post, and yes mostly overlooked and potentialy dangerous, automobile tires should be toed in, Aircraft should be toed out, for all the reasons that you mentioned.
Camel toe is something different all together.......

One more thing about wheels that people often overlook, is wheel balance.... The small tubes we use, or tubeless stems if no tubes used, usually make the small wheels out of balance. So what I hear you all say?.... well, gyros land pretty slow, so not really an issue there, but on takeoff, often the little wheels are asked to do 25mph..... sometimes more.... so just as you lift off, the out of balance wheels are flat out, then suddenly off the ground spinning like mad.... this is hard on bearings and we all know what nose wheel shimmy feels like.... often the nose wheel is smaller, so it is spinning even faster....

Ok, so jack your nose wheel off the ground, spin it and look for the tire on the rim properly (center of tire not rising and falling as it rotates) If it is more than a 3/16" 'out of round' mark the high spot, let the air out push the tyre off the bead, put soapy water on rim, put a few pounds of air in so it seats lightly on the rim, spin, look for high spot again and push and manipulate the tire to get it so there is the least run out of the tire on the rim.... then put your normal air pressure in. Spin the wheel and listen for dud bearings and put side load on the bearings each way to see if there is any play anywhere in the axel or bearings. Then spin the wheel a few times in a row and see where the wheel stops by itself each time.... 10 - 1 it will always stop with the valve stem down.... and sometimes it the wheel will actually go past valve at 6 oclock, then go backwards to 6 oclock,, that is seriously out of balance..... from a tire shop, buy a strip or 2 of stick on wheel weight... snap off a couple of squares and without peeling the sticky paper, tape on a square each side of the rim, spin again, if still valve down, tape on another square each side, spin again, now if it stops weights down, you have too much weight.... snip a corner off each of one weight on each side, spin again...... if it stops with the weight and stem at 3 oclock, 9 oclock, and you spin it over and over and it stops in any old place, it is pretty well balanced, so mark where the weights need to go, un tape them off the rim, clean the rim with some meths (not metal cleaner or polish) sit the weight on 2 drill bits lead side up and tap with a ball pein hammer so the weigh gets the aprox shape of the rim, then peel the sticky back and stick on permanently where it needs to go. Then spin the wheel a few more times.... if you think the weight might be a bit much, drill away some lead a little at a time with a 3/16" drill and spin again. You want the wheel to stop any old place every time and it shouldn't stop spinning and run backwards at all..... the bearings should sound 'happy' no change of sound or vibration as it slows....

Do the same with your main wheels, Jack up and spin..... I bet you are surprised how out of balance they can be, but the size of the wheel means a couple of grams is a lot, especially at speed. Sure it sounds pedantic, but that is my middle name.... you will notice the difference, I bet. New tires are not balanced either, so if you want to get really anal.... put the tire on but don't blow it up more than a little, add soapy water so the tire can slide on the rim, spin, move the tyre around on the rim, spin, see if you can find the heavy part of the tyre and put that opposite the valve... then make sure no run out, then do the weights, then see a psychologist (after doing 3 wheels you might need to)