Downwash Effect on the Unguided Rocket under Rotor Wake and External Wind

Abstract

Downwash effect is the interaction between rotor wake and a launched rocket. Since the effect alters the initial motion of the rocket, a comprehensive analysis of the effect is crucial in predicting the entire trajectory and range of the rocket. In addition, external winds affect the trajectory and range as the winds alter the downwash effect. Because the downwash affected ranges do not appear to be investigated sufficiently, this study aims to reveal the trajectory and range variance characteristics focusing on the downwash effect and external winds. Using an actuator model and six-degrees-of-freedom analysis, trajectories of the rocket due to the downwash effect are described. The range variance characteristics of an unguided rocket are investigated for a 3,000-lb class helicopter, and the rotor flow field database is analyzed using the CFD method while considering external wind effects. It is concluded that the effective angle of attack of the rocket in the rotor wake region varies along the wind direction, and the final reach range also changes accordingly. In particular, the range increased significantly when the rear wind is blown out. However, the range of the rocket is constant after a specified wind speed due to rocket acceleration.