Study of Contra-rotating Coaxial Rotors in Hover, A Performance Model Based on Blade Element Theory Including Swirl Velocity

The purpose of this study is to create a simple model to evaluate the performance of a counter-rotating coaxial rotor system. As it is based on the blade element theory, it could be used as a design tool where the engineer can modify all parameters - rotor radius, blade pitch distribution, tip velocity, rotor spacing, number of blades, blade chord, and airfoil\u27s shape through its lift coefficient versus angle of attack slope. Different blade pitch distributions are tried and are assessed based on the power required to hover at the same weight. Also, the impact of the swirl velocity induced by the upper rotor is included and discussed. In order to verify the credibility of the model, results are compared to what was obtained from other researches. The main result is to compare performance of the current AH-64 Apache single rotor system with the optimal coaxial rotor model