ANALYSIS OF HELICOPTER AEROELASTIC CHARACTERISTICS IN HIGH-SPEED FLIGHT

Described is a general analytical method, which can be used for performance, stress, and vibration studies of helicopters and VTOL-type aircraft. The analysis is well suited for highspeed investigation, and applications are given for a helicopter in the flight regime from 80 to 160 knots. A sample problem is carried out at 150 knots. A rapidly convergent iterative procedure, which takes into account blade stall, is used to put the rotor in trim. Blade elemental lifts and drags are computed using wind tunnel airfoil data. Mach number effects are included. Blade motions are coupled to the aerodynamic excitation. Rotor blade dynamics are determined using a set of complex equations based upon an extension of Myklestad's analysis for rotating beams. The analysis assumes the blade infinitely rigid in torsion and takes into account 24 flatwise and 24 edgewise degrees-of- freedom with coupling due to builtin twist. There are provisions for handling rotor and propeller blades of all types: rigid, teetering, and articulated. Dynamics of the flexible blade are "married" to dynamics of the fuselage by matching blade root impedance to fuselage impedance at the rotor head. The resulting calculation gives the coupled blade-fuselage dynamic response at a particular airspeed.