Cantilever wing spar design

[Bill Gaylord]

The 1/3 span rule and stab area calcs become less accurate for small models, especially our heavier r/c models in roughly the 20" and under span. I would imagine once the stab area becomes infinitesimally small, it becomes ineffective, regardless of the area/chord/span ratio. Your stab looks reasonable. The only issues I've had are with the really small 16" warbirds, where the speed has to be kept up to maintain reasonable control. Before changing to a lighter motor and using a lighter battery mounted further forward, I've flown the C150 per plan at over 6oz, and it wasn't bad at all. At 5 it flies like a trainer. One issue I have encountered with many of these small models, is that for stability they fly better a bit nose heavy and require that both the speed be kept up, and some up elevator fed in for landing.

[davidchoate]

I put a 3 axis Rx in it, and can compensate for any adverse characteristics, but I am trying to learn to fly without it.

[davidchoate]

I was tolda @deg positive setting on wing and stab and a zero thrust line will make it better too.

[Bill Gaylord]

I've found that the flat bottom section like Guillows uses works well with the flat bottom portion of the wing set parallel to the stab, and the prop set with 0 to 1 degree downthrust angle works well. That seems to be what you just described. Built with per plan incidence, they climb excessively as an rc model. The last time I deviated from that rule with a Miles M38, where I still had a decent flyer, but with some elevator down trim and somewhat balloning flap effect. Could program the climb conditions out, but would have preferred to get it right off the board. Same climb issue proved true with the Robin built to plan, where I simply matched the wing panels to the cabin roof formers. Flies fine, but would be better without the excess positive incidence.