> > My formula was Drag = 0.5 x Cd x Rho x A x V^2 > > Rho = air density = 1.3 kg/M^3 > A = frontal area in metres > V = velocity i metres/second > Drag = drag force in Newtons (eg Kg x g ~~= 10 x kg). > Cd = coefficient of drag = improvement relative to a flat plate. > Nice simple formula! We could, of course, apply it backwards and develop the force on an object due to wind speed, then try to get energy out of the wind. If we let the "sail" go the same speed as the wind, force drops to zero, so we get no power (energy per unit time). So, what's the "maximum power point?" What fraction of wind speed should a sail be moving to recover the most power? Harold -- FCC Rules Updated Daily at http://www.hallikainen.com - Advertise on hallikainen.com - $100/year! -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist