Comprehensive Analysis of a Coaxial Ultralight Rotorcraft and Validation with Full-Scale Flight-Test Data

Abstract

The results of full-scale flight testing in combination with comprehensive analysis of an ultralight counterrotating coaxial rotorcraft are presented. The CoAX 2D was developed and manufactured by edm aerotec in Geisleden, Germany. The helicopter features two-bladed, 6.5-m-diameter upper and lower rotors in teeter configuration with uniform airfoil sections and linearly twisted blades. The focus was on the development of a comprehensive analysis model using CAMRAD II, its validation with measured flight-test data, and results evaluation from both measurements and analysis. The CoAX 2D's power consumption, tail loads, hub loads, teeter angles, and blade-tip clearance were evaluated for both hover and forward flight. Performance and thrust correlated well between the analysis and the measurements. Effects from rotor-fuselage interference dominated the measured 2/rev hub load and 1/rev teeter angle harmonics. The numerical model also matched well with the measured vibrations during forward flight in terms of hub loads, teeter angles, and resulting blade-tip clearance. Minimal rotor-rotor blade-tip clearance occurred at low flight speeds because of dominating effects from rotor-rotor interference.