NH90 blade tip shape

The NH90 helicopter is equipped with 4 composite material blades. Theirs ends have a parabolic form. Why ?

Aerodynamic optimisation of the blade tip shape allows a reduction in the strength of the shock waves on the advancing blade of a helicopter rotor flying at high speed, thereby decreasing rotor power required and the noise generated. By solving the fluid mechanics equations, the aerodynamic conditions of real flights are simulated on the computer. They are used to study and optimise various blade geometries. A parabolic blade tip was thus designed by ONERA (French Aeronautics and Space Research Center) and adapted by Eurocopter for the rotors of the Super Puma Mk2, Tiger, NH90 and High Speed Dauphin. The comparison by shock wave visualisation demonstrates the improvement over the traditional geometry.

Computation and optimisation : the shock wave is weaker on the blade with a parabolic tip, which is therefore better (doc. ONERA)