Helicoidal pitch

Helicoidal pitch is the pitch defined by the true helical (screw) surface a blade section sweeps, P = 2 pi r tan(phi) at radius r, where phi is the angle between the local pitch line and the propeller disk plane. The reference helix is the nose-tail or face pitch line of the section, so helicoidal pitch is the geometric, no-slip advance per revolution for that radius. On a radially varying or warped blade the pitch differs section to section, and a single quoted figure is the mean or the 0.7R value. The helicoidal surface is the datum from which skew, rake, and section camber are measured.