Comprehensive Maneuver Load Analysis of a Hingeless Coaxial Rotorcraft for Blade Structural Design

Abstract A coaxial compound rotorcraft may experience insufficient blade tip clearances during high-speed lift-offset level flight or high-g maneuvers such as bank turns. Therefore, the aeromechanical loads acting on the coaxial compound rotorcraft during free flight must be investigated. This paper presents a comprehensive analysis of the aeromechanical loads acting on the rotorcraft with a hingeless coaxial rotorcraft that is designed on the base of X2TD. Efficient modeling approaches were employed, including a beam cross-section analysis using the variational asymptotic beam sectional analysis tool, empirical airframe aerodynamic coefficient estimation using DATCOM, and Euler equation-based airfoil table generation using a multi-element sectional analysis. Subsequently, the aeromechanical features were implemented by modeling the main rotor, pusher propeller, fuselage, and empennage in CAMRAD II. Trim strategies for level flight and 2-g bank turns with different lift-offset levels and flight speeds were devised. The results showed that the coaxial compound rotorcraft could achieve a 2-g turn at cruise speeds of over 200 kt, while ensuring the structural integrity of the blade without any significant increase in the total engine power. A trade-off analysis revealed that reducing the lift-offset levels for a high-speed bank turn maneuver relieves the blade tip clearance but requires a higher engine power and a lower lift-to-drag ratio of the rotor.