Does anyone have a good system or way of determining how much throw to put in a control surface of a new design?
Glenn

Yep, it's called 'SIAS'. Suck It And See. Or, for the mathematical minded, big surface, small movement, small surface, big movement. Fast plane, small movement, slow plane, big movement. Of much more concern is the initial balance set-up. Start at 25% MAC, fly it, you have a proportional radio, if there is too much control, move the stick less, not enough, move the stick more. If it is not balanced correctly, none of the above will matter.
Evan, WB #12.

Blunt and good advice. However, I thought "SIAS" was really "TLAR." "That looks about right."

If you can put in exponential I prefer a lot of control and about 50% exponential. With exponential, you can use small stick movements if the plane is quite sensitive yet have access to full throw if needed.

There are just so many possible variables that there is no actual forumula other than using about as much on the last model you flew that was about the same size, expected flying speed and style of model as you have had already.

For a lot of older designs, +/- 25 degrees or so was about right to start with. As was said above, the TLAR method works, as does copying the throws a previous model that was similar.

Aileron and rudder throw are entirely up to the individual flyer. Elevator throw, however, is a bit more involved. In my view, for normal (non-3D) flying, elevator throw should be just adequate to stall the wing, and no more. This ensures that the elevator is able to persuade the wing to develop its maximum lift, without excess danger of stalling. Excess elevator throw can produce an inadvertent snap roll at very inconvenient times, such as during a panic pullout from a low-level steep dive, resulting in loss of control and a crash.

To adjust elevator travel, I give the airplane full power and full elevator, while flying at a safe height. If the airplane performs several consecutive loops with no indication of stalling, it needs more elevator throw. If it immediately stalls and wanders around drunkenly, it has excess throw.

I find the ideal to be 1/2 to 3/4 of a loop before the airplane rolls and wanders with full up or full down elevator. If it goes wonky before finishing 1/4 loop, it has too much elevator travel. Application of full elevator in a dive pullout may result in disaster. I do the same exercise with both up and down elevator. Airplanes often require different up and down throws.

I prefer to test it by easing into a power off stall. If you have enough elevator to ease into a stall at idle you will have more than enough at high speed. The opposite may not be true, you may have enough to stall your plane at high speeds with full elevator but not enough at slow speeds. This can make landings difficult to say the least. It is also possible that at high speeds if you pull up fast enough you can stall the tail before the wing has a chance to reach its critical AOA, and this may lead you to believe that you need more throw, although this is less likely in short coupled aircraft.