Ninjak2k,

Larry Dudeck procided the power formula;from that you could compute your 200 watt example and how RPM decreases with increase in prop diameter. Static thrust, Ts=CT0*Rho*(RPM/60)^2*(Dia/12)^4. Where Ts is static thrust in lbs,CT0 is the static thrust coefficient,Rho is the air density in slugs/ft^3,RPM is the prop speed in revs per minute and Dia is the prop diameter in inches. The CT0 is measured imperically for a family of props that depends on power coefficient. Anyway, the static thrust varies as a function RPM^2 times Dia^4; you can play with that relationship keeping a constant 200 watts.

Yours,

Dick Huang