Re: How to calculate the flat form of a flight of screw conveyor. Then the inside developed diamater, B = square root of [ (PI*d)^2+ (P)^2]. Value of PI = 3,... So the developed inside radius of the flight will be: r = Rb => b=Rr; b/r= (rR)/R 1º step R/r=A/B; (Rr)/r= (AB)/B 2º step consider that R is the developed outise radius.