As 1/2A R/C Texaco progressed, guys resorted to running 10-3 props on .049s to stretch out the fuel run. For those who don't know, 1/2A Texaco is an R/C discipline where one flies replica old time free flight models down sized for .049 power, guided by two channel R/C, and timed to a 15 minute max. The 10-3 trick stretched the fuel run out immensely, so one would have to rely less on thermal catching ability. It was a very slow run and took almost the whole 15 minutes to get any appreciable altitude. The practice was later banned and the fuel capacity was cut to a normal size baby Bee tank and prop size limited to 8 inches, I believe. I don't think you will ever get a .020 to swing a 9" prop, even with low or no pitch. At least not well enough to make any kind of useful thrust. to test a theory, just bush out any wood IC 9-4 or 9-3 prop, if you can find any, bolt it on and see what happens. Probably a lot of popping and not much else.
Type at you later,
Dan McEntee