A numerical method based on highefficient trim strategy and moving overset grid technique was developed to predict the aerodynamic characteristics of rigid coaxial rotor. To simulate the rotors flowfield

the Reynoldsaveraged NavierStokes equations were discretized by Roemonotone upstreamcentered schemes for conservation laws(MUSCL) scheme with SpalartAllmaras turbulence model. A delta trim method was implemented. Researches on the aerodynamic interaction and trim characteristics of a coaxial rigid rotor model were conducted. Results indicated that the delta method consumed much less time than the conventional trim method with the same accuracy. The aerodynamic interaction of rigid coaxial rotor

with a smaller rotors distance

was much stronger than that of normal coaxial rotor. In hover condition

the lower rotor required greater collective pitch while providing less tensile force due to the upper rotors downwash; in low speed forward flight

the aerodynamic interaction brought about a more asymmetrical airflow on the rotors disks

leading to greater difference of cyclic pitches. In addition

the rotors power efficiency can be improved by a proper lift offset.