Thanks for the advice, that helps me quite a bit! It reminds me that Ed Cregger once pointed out ([link=http://www.rcuniverse.com/forum/fb.asp?m=6866271]here[/link]) that a stable forward c/g was common. The Sun Fli could be one example. Like the Kwik-Fli, it may have a symmetrical airfoil and about 0.5 degrees wing incidence to make up for the forward c/g. Maybe now it would climb at full power, but that is prevented by the downthrust. Only drawback would be that it's neutral only upright and not inverted.

As to the thrust/weight ratio, even with a Schnürle ported .60 from the 1970s (1.27 hp) the Kwik-Fli Mk III has only 0.94 T/W at 6.5 lb weight (estimate with a 11x7" prop), but it's still quite fast (70 mph). With a crossflow .60 from the 1960s (optimistic 1 hp) it has 0.8 T/W at 6.0 lb weight (and 0.5 degrees wing incidence but no down thrust, 65 mph) and won the w/c. The Kwik-Fli Mk II (1965) was even designed for a .45 (0.65 T/W at 5.5 lb weight, 55 mph) and was boosted as "the hottest competition machine you've ever flown", even though it was often flown with a .60. The Kwik-Fli Mk I (1964) was designed for a .60 and had the exact same wing loading and T/W as the MK II. It only was bigger and maybe looked too slow but not "hot" in the air (66" wingspan instead of 60", 0.66 T/W at 7.25 lb weight, 63 mph). These figures may be somewhat incorrect, but they are comparable (estimated using the same procedure).

Unfortunately, I don't have a pattern model with semi-symmetrical airfoil in the simulator yet (not even the Taurus), but I tried with the Kwik-Fli Mk II: At 7 lb weight (instead of 5.5 lb!) with a .45 (0.51 T/W) it's still aerobatic, despite the symmetrical airfoil, and needs only 0.8 degrees wing incidence and a suitable balance to be trimmed neutral (upright, needing substantial down elevator inverted). It takes off from grass, looks quite right in the air (a tiny bit nose-up), and still has 25 m/s (55 mph) top speed.

The P-63 should be even better and nicer! Unfortunately, we won't know that because Chris will make his a modern stunter, like an old car with a modern engine turned into a dragster. (Sorry Chris, couldn't resist, and I'm helplessly nostalgic.)