HighPlains is absolutely correct and stating as a formula to use for gear placement in a percentage is just about impossible. Or about like suggesting there is only one size prop for any given engine with no consideration given to type airframe, pilot skills and types of performance being attempted. Most important of all and the best indicator is the distance forward or to the rear of the actual flight CG.

Here is just one of the compromise in play here: Main gear relationship with CG. The very easiest location for the main gear (in the case of a taildragger) in terms of bounce free and simple landings is directly at the actual CG. As were almost all earlier full scale post war gliders/sailplanes but there is a problem when we hang an engine on. Now when we slow down and perhaps are lazy of poorly trained with elevator skills guess what the nose is going to drop and we destroy the propellors.

The obvious solution is to move the mains back a short distane from the CG and put the third wheel under the nose. Remember though we are talking about a taildragger in this example --so-- the solution is instead to move main gears footprint forward of the CG quite a bit. Lets go back now to that perfect main gear footprint/CG relationship which is directly at the flight CG but now we know we must move the main gears footprint forward to protect that pesky propeller.

Moving that main gear footprint forward introduces another problem though that is when simply stated is: The further forwar this footprint is from the CG the greater will the tendency for this gear arraignment to bounce and cause the airplane to bounce excessively and be what I term as a: Boinger on landing. There have been a number of otherwise good airplanes but ones that were very difficult land well because the mains were just to far forward.

Building/designing airplanes, full scale or models to rigid formulas just does not allways work well.

John