OK, I have all the all the proportions done and the fuse is built and the wing cores have been cut. The plane has a wingspan of 150 inches, and I have read some info on this forums that the landing gear has to be 25 % of the wingspan. That would mean 37.5 inches between the wheels. the problem being that I can`t get a landing gear that size down here so... would it be impossible to handle the plane with a 27 inch landing gear? The fuse is 106 inches including the engine and rudder. The wings.. well 150 inches. the elevator and stab are 45 inches (span) and the fin and rudder are about17 inches tall.
Any comments are welcome
John

To my knowledge, there is no specific formula for landing gear size. The main criteria for landing gear size is that it supports the weight of the plane. Secondary criteria are that the LG should be the proper width and properly located on the fuselage for good ground handling. It should also be tall enough to prevent prop strikes under normal landing conditions.

All that being said (and I get wordy at times), you should use the TLAR system (That Looks About Right).

Dr.1

DR.1 has it right. The landing gear has no width requirement. You can use a single wheel under the fuselage with outrigger wires or wheels to keep it from dragging a wing. Normally, though, the landing gear should be wide enough to keep the airplane from being too "tippy" when on the ground.

A tri-gear plane needs the mains just aft of the balance point so that it will keep the nose on the ground at rest, but still be able to rotate for takeoff. Put the mains too far aft, and the model won't rotate, and a gear that's a bit aft of ideal will tend to hug the ground until you put in a lot of "up" elevator and then it will "leap" into the air with a too-high nose-up attitude.

Tail-draggers need the width the same...so the plane's not to "tippy", and have the axles of the main wheels at about the leading edge of the wing when the plane's in the flight attitude. Slightly forward of that won't hurt.

In all cases the model must track dead-straight when allowed to roll. The mains must be absolutely parallel to start. Toe-in or toe-out is a controversy best discussed elsewhere.