Dynamic analysis of a free-tip rotor

The flag-lag-torsion flutter of a constant-lift rotor (CLR) and a free-tip rotor (FTR) has been investigated in hovering flight. The CLR blade consists of a finite number of strips pivotally mounted on the spar; torsional stiffness of the strips is attained through the elastic axis offset from the aerodynamic center. It is shown that, with a suitable combination of lag damper and negative pitch-flap coupling, it is possible to design a CLR blade that is free of aeroelastic instability with suitable airfoil selection. The FTR blade, which consists of an inboard section similar to that of a conventional blade and a small outboard section freely pitching on its spar, is also free of aeroelastic instability.