Is there a formula for arriving at the ideal moments of a stunt ship.....that is nose to leading edge trailing edge to elevator , size of rudder and elevator , ideal balance point etc.? or is it still just trial and error...……...

Is there a formula for arriving at the ideal moments of a stunt ship.....that is nose to leading edge trailing edge to elevator , size of rudder and elevator , ideal balance point etc.? or is it still just trial and error...……...

  There are a bunch of rules about this, but there's no particularly good basis for it aside from trial and error. The absolute value of the tail moment matters, it's not a ratio to anything else. The nose moment is technically irrelevant aside from the balance, which depends on how heavy your propulsion components might be, and how heavy you build.

    My airplanes have a 18" "tail moment" and a 10.5" "nose moment" and they tend to come out lighter than the target and nose-heavy. 10.5 is as short as I can make it and easily contain all the necessary parts, so I almost always wind up with substantial weight (1/2 oz - 1.5 ounces) in the tail. This amount of weight is negligible for these sorts of airplanes, irrelevant, so no harm done.

     I have used various "tail moments", as defined to drive Howard crazy, from hinge line to hinge line, of anywhere from 16" to 22" on full-size airplanes. I think the right answer is about 18" more-or-less. The reason it drives Howard crazy is that this measurement also has no technical relevance, it's the distance from the CG to the CP of the tail that matters. And it's also not a "moment" (which means torque), but a lever arm (which means distance). But with a typical set of other parameters, it's reasonably OK to compare hinge line to hinge line distance, since you really don't calculate any of the dynamics involved.

     Brett