As our gear is very flexible the wheel alignment changes severely with the following: - Load the gear spreads giving positive camber. - As the load comes off during lift off we get negative camber. - Braking twists the gear leg giving toe out, as the axle is on the outside of the leg the braking forces on the wheel must twist the leg. - Angle of fuselage especially in tail draggers - Angle of legs in front of the vertical will effect the twist the leg gets when loaded.
When doing a wheel alignment there are 3 things to consider: 1) caster. Is used for steering geometry on the wheels that steer a vehicle and do not apply to aircraft. 2) camber is the tilt in or out of the vertical axis of the wheel, zero camber is best for aircraft to give best tyre wear. 3) toe in is what defines our stability when on the ground for aircraft. (Toe in and caster define stability for cars in a straight line) Most important note: Toe out is dangerous as it will make the aircraft/vehicle swerve and harder to straighten as once you start to track of one way both wheels are pulling in the same direction, giving over steer. With toe in the vehicle tries to straighten, giving under steer which is what we want, the aircraft will try to straighten. I would never run zero toe in as there will always force backwards when the aircraft is moving which would give slight toe out, especially when braking. My initial setup was done in the flying attitude. Because the legs are angled forward they twist and spread under load so I aligned them loaded with a slight toe in to allow for braking. With the tail on the ground there is less load on the mains and this gave me sever toe in and scrubbed my tyres and made steering hard, especially on paved surfaces. Worst time for bad steering is when the tail drops :-( Next modification was to do the alignment with the tail on the ground as 95% of the time that the aircraft is on the ground the tail is on the ground. Alignment was done loaded with my average flying weight (me plus some stuff = 95kg plus half a tank of fuel) and a slight toe in of about 1.5 degrees to allow for braking and full load. Beautiful steering when tail was on the ground and no noticeable problems with the tail up as the wings are taking the load and control is through the flying surfaces. In the example below the 2" over 12 foot is about 0.8 degree which is good. Just my two cents worth. (I have done wheel alignments on go-karts, super karts, stock cars, sports cars and offcourse the odd the family car) And offcourse the disclaimer: your results may vary depending on your setup, etc,etc,etc Regards Barry Kruyssen Cairns, Australia k...@bigpond.com http://www.users.bigpond.com/kr2/kr2.htm -----Original Message----- From: krnet-boun...@mylist.net [mailto:krnet-boun...@mylist.net] On Behalf Of Randy Smith 2" toe in is a lot. You will find that close to 0 is very good. --- Bernard McLean Sr <popsfl...@northboone.com> wrote: > > Jim Raleigh wrote: > > >When I back up the gear straightins up and the > tires are running as they should. I know that this means that the > wheels are castered outward. I tried putting some shims in the back > but it seems to only bend the thru bolts. You guys with the grove > gear got some ideas. > > > Jim; > Sounds like your main wheels are severely toed out. > Try looking at Mark Langford's web site on this topic. He has some > very astute comments and procedures there. > I installed the Diehl gear while the boat was still upside down on the > table and took extreme care to make sure that the gear leg ends were > equidistant from the floor (gear brackets attached!) and that the axle > bracket mounts were as parallel as possible. > Even with all this, I had to add .015" shims at the rear of the axle > brackets. This has resulted in a 2" toe-in over a distance of 12 feet. > I'm hoping I can live with this but am prepared to adjust the shims if > I get any handling anomalies or weird tire wear. I'm told that a > slight toe in is acceptable. > Hope this helps. > > Bernie McLean > Poplr Grove IL > KR 2
