The tail on Jonathan's plane sounds way too small to me--especially if you are using coupled flaps (are you?)
On the question of CG location, the larger the tail (or aft surface), the farther back you can (and must) locate the center of gravity. An extreme case would be a canard, where the rear "tail" (now the wing) is larger than the front surface and the center of gravity is located entirely behind the front surface (the rear "tail" being 200% bigger or whatever.)
On the comment of making the tail bigger and eliminating the "hop" in the corner, one thing that hasn't been mentioned here is the fact that a heavier airplane needs more flap (or wing for lift) and a lighter airplane needs less flap (or wing for lift). If the wing area remains the same and we are able to build a lighter airframe, then we can either shorten the flaps (make them so they are not full length) or taper them more in order to reduce their effective area. Alternately we can use the same amount of wing and flap but make the elevators bigger to give more elevator throw less movement of the flap or
We can use an adjustable elevator horn which allows us to make changes according to weight without having to resort to cutting into the model or modifying areas.
With an adjustable elevator horn, start with a 1:1 ratio of elevator to flap. If you have too much lift coming out of the corner (the tail isn't swinging, but the airplane is hopping), then crank in a bit more elevator. In effect the elevator movement will remain the same for a given amount of turn, but the flap movement will then become less.
This is another trim area that usually isn't covered in the trim charts, but should be included in any serious stunter. Trimming the flaps may work, but it is much easier to be able to simply adjust the amount of elevator throw in relation to the flap.
Leonard Neumann
