toe-in or toe-out with gear deflection under load???

[Dana]

First, I can not even imagine how toe-in helps aesthetically. Are you confusing camber with toe-in?

I think he's talking about the gear attach points on the fuselage, and how it would look better if the gear leg pivot axis wasn't parallel to the aircraft centerline and/or to each other... in this case the toe would change as the gear leg pivots.

 

[wsimpso1]

When I set up the main gear on a Long EZ I first snap a chalk line on the floor under the exact center of the plane. Then Put an 8' straight edge on each wheel and toe it in 1/8" (in 8'). they always track straight and true. I had one Long EZ that liked to wander a bit. I guessed on toe out and I was right. I fixed it.

Long EZ’s have tricycle gear, and so you are talking the aft axle. A tad of toe-in is the norm for back wheels on cars too, and tends to make them track straight. Taildraggers are different. The mains are forward of the CG, and so need attention all the time, like a shopping cart being pushed backwards. The effort runs toward making it respond to rudder inputs quickly while making it slow to deviate into a ground loop.

Billski

 

[Pops]

Drive a fork truck fast and let go of the steering wheel and it will ground loop. Better do it slower at first

 

[raytol]

If in doubt ...go toe out!

 

[Pops]

If in doubt , try one wheel with toe in and the other with toe out.

 

[David L. Downey]

I think he's talking about the gear attach points on the fuselage, and how it would look better if the gear leg pivot axis wasn't parallel to the aircraft centerline and/or to each other... in this case the toe would change as the gear leg pivots.

you nailed Dana. As stated in the original post, tail wheel with trailing brace from firewall. The firewall measures less in width than the fuselage station where the main leg is hinged. The whole trailing brace tube is so much less attractive than one in compression (Tiger Moth aside...) but it solves several other problems. I have the geometry compromised now to greatly reduce/totally eliminate the change in toe with bungee stretch other than that induced by simultaneous off heading forces.
this conversation has been very profitable to me!
to wsimpos1: unfortunately I sold that cub! Tire wear was quite uniform so I think it was pretty straight.

 

[wsimpso1]

Gear hinge line on the fuselage does not make toe-in or toe-out at your planned weights. Look at Pops' posts. He made a fixture to hold his axles co-linear with each other, he sets his gear legs at about the middle of where they will sit with his typical flying weight, and then he welds the axles to the arms. They gotta be darned close to zero camber and zero toe that way.

Now if the hinge line is not parallel to the long axis of the fuselage, you will get what the car guys call "bump steer". The toe changes as the suspension moves through its travel. A little time with some trig and you can work out how much that will change within your operating range and for that matter while it strokes and rebounds during a hard landing. Then you can set it up so that it is never toed-in.

Take another page from Pops and set the gear up so it preloaded to near your empty weight, and the gear will not swing much at all during a gentle wheelie landing. That keeps you from having much bump steer between touch down and carrying static weight.

 

[Lendo]

I believe there was a recent article by Barnaby Wainfan in Kitplanes on this subject.
George

 

[Pops]

One well know early model of an airplane doesn't have the Cub type LG legs attach points parallel to the long axis of the fuselage. The fuselage is 1" wider at the rear LG attach station than the front attach station . So it not only has bump steer the top of the shock strut attaches to the fuselage at the center of the rear station, so due to the geometry it also has a bind in it somewhere in the LG travel. Having a rod end bearing in each end of the stock strut takes the bind out but the bump steer is still there. Later models were changed.
Picture of the rod end at the top and bottom of the shock strut. Also notice the use of a round tube in the stock strut instead of the streamline tube for a side load increase from 3150 lbs to 12, 900 lbs, on a 2700 lb GW aircraft.

My 1981 Chevy 3/4 ton truck also has bump steer. There is a rack and pinion steering kit for it to take the bump steer out. Common on older vehicles.

 

[Turd Ferguson]

cessna 100 series thru 172 with flat spring gear specifies 4°- 6° of positive camber with a toe-in of 0 - .06" (about 1/16") with the plane empty and no fuel. Then it says that will give zero camber and zero toe at gross weight.
When I had a C-120, I set it to the Cessna specs and the max tire wear was just outside center. Not sure if tire scrub or camber was responsible for the wear because I rarely flew it at gross wt. and did a lot of TO's and landings.

 

[Pops]

I sold a 1966 C-150 to a student pilot and bought it back 3 years latter when he got his 4th X wife. The left LG was bent at the lower bend in the flat spring gear. The one wheel had about 3/8" toe in. No damage to the gear box in the fuselage. I ask how did it get bent that bad. He said a very hard landing in a large crab. Think I would call that almost a crash. Installed a new gear leg.

 

[Dan Thomas]

When I had a C-120, I set it to the Cessna specs and the max tire wear was just outside center. Not sure if tire scrub or camber was responsible for the wear because I rarely flew it at gross wt. and did a lot of TO's and landings.

In flight, that gear hangs down some and the camber increases, so that the outer tread on the tire is the tread that gets ground off on touchdown regardless of gross weight. We used to take those wheels off when that outer tread was 2/3 gone and turn the tires around to get the most hours out of a tire. Airplanes flown by students go through a lot of tires. And some owners go through a lot of tires because they're in the habit of landing fast and flat and using the brakes to try to fix the problem.