An analytical investigation into the possible improvement of aircraft propeller performance that may be obtained by employing high strength filamentary composite materials to modify the elastic characteristics of the blades was conducted. The orientation of the individual fibers with respect to the axis of the blade was chosen to induce a coupling between the centrifugal force acting on the blade and the shearing strain in the plane of the blade cross section. The shearing strain changes the pitch of the blade as the rotational speed of the propeller is varied. This change in pitch is then optimized to broaden the band of flight speeds over which the propeller operates efficiently.
Results for the analytical model indicate that the efficiency of non-controllable pitch propellers may be improved by 5% at the design condition and as much as 20% at off-design conditions. Furthermore, the results indicate a significant increase in the band of flight speeds over which the propeller operates efficiently. In addition, a 5% increase in efficiency throughout the applicable range of flight conditions was determined for controllable pitch propellers employing composite blades in place of rigid blades.
