The testing of rotorcraft, either in flight or in a wind tunnel, requires a consideration of the coupled aeroelastic stability of the rotor and airframe, or the rotor and support system. Even if the primary purpose of a test is to measure rotor performance, ignoring the question of dynamic stability introduces the risk of catastrophic failure of the aircraft. This computer program was developed to incorporate an analytical model of the aeroelastic behavior of a wide range of rotorcraft. Such an analytical model is desirable for both pretest predictions and posttest correlations. The program is also applicable in investigations of isolated rotor aeroelasticity and helicopter flight dynamics and could be employed as a basis for more extensive investigations of aeroelastic behavior, such as automatic control system design.
The program incorporates an analytical model which is applicable to a wide range of rotors, helicopters, and operating conditions. The equations of motion used in the model were derived using an integral Newtonian method, which provides considerable insight into the blade inertial and aerodynamic forces. The rotor model includes coupled flap-lag bending and blade torsion degrees of freedom, and is applicable to articulated, hingeless, gimballed, and teetering rotors with an arbitrary number of blades. The aerodynamic model is valid for both high and low inflow, and for both axial and nonaxial flight. Rotor rotational speed dynamics, including engine inertia and damping, and perturbation inflow dynamics are included in the aerodynamic model.
For a rotor on a wind-tunnel support, a normal mode representation of the test module, strut, and balance is used. The aeroelastic analysis for rotorcraft in flight is applicable to a general two-rotor aircraft, including single main-rotor and tandem helicopter configurations, and side-by-side or tilting proprotor aircraft configurations. The rotor model includes rotor-rotor aerodynamic interference and ground effect. The aircraft model includes rotor-fuselage-tail aerodynamic interference, engine dynamics, and control dynamics. A constant-coefficient approximation is used for nonaxial flow and a quasistatic approximation is used for the low frequency dynamics. The coupled system dynamics results is a set of linear differential equations which are used to determine the stability and aeroelastic response of the system. (NASA Ames Research Center)
This program was released by NASA through COSMIC as ARC-11150. The italicized text above is from the official NASA release.