Effect of Jet–Wake Interaction around a Tip-Jet Rotor in Torque-Balanced States

Tip-jet rotors operate in an equilibrium state between aerodynamic torque generated by rotations and jet torque by a tip-jet. This equilibrium state is denoted by the torque-balanced state and a corresponding tip speed is called as the equilibrium tip speed. As a noteworthy result, consistent jet-wake interactions (JWIs) cause similar flow structures that is independent of tip-jet flow condition at a specified collective pitch angle. Accordingly, the constant induced flow ratio leads to the constant net thrust coefficient nondimensionalized with the equilibrium tip speed. Furthermore, at the torque balanced state, trajectories of the tip-jet vortices remain unchanged irrespective of blade tip speeds. The net thrust coefficient in real situation primarily depends on the collective pitch angles and the momentum theory for conventional rotor analysis can be applied to the tip-jet rotor in the torque-balanced state.