Identification and Simulation Evaluation of a Combat Helicopter in Hover

Abstract

Frequency-domain parameter identification techniques were used to develop a hover mathematical model of the AH-64 Apache helicopter from flight data. The unstable AH-64 bare-airframe characteristics, without a stability augmentation system, were parameterized in the conventional stability-derivative form. To improve the model's vertical response, a simple transfer-function model approximating the effects of dynamic inflow was developed. The model, with and without stability augmentation, was then evaluated by AH-64 pilots in a moving-base simulation. It was the opinion of the pilots that the simulation was a satisfactory representation of the aircraft for the tasks of interest. The principal negative comment was that height control was more difficult in the simulation than in the aircraft.Nomenclature a x ,a y ,a z = longitudinal, lateral, and vertical applied specific force, ft/s 2 del = delayed j = complex variable, \/-I L, M, N = roll, pitch, and yaw applied specific moments, rad/s 2 Ion, lat, ped, col = longitudinal, lateral, directional, and vertical cockpit inputs, in. p,q,r = roll, pitch, and yaw angular rate perturbations, rad/s u,v,w = longitudinal, lateral, and vertical airspeed perturbations, ft/s X, Y, Z = longitudinal, lateral, and vertical applied specific force perturbations, ft/s 2 8 -control input, in. 0 = pitch angle perturbation, rad 0 = pitch rate perturbation, rad/s r = time delay, sec 0 = roll angle perturbation, rad 0 = roll rate perturbations, rad/s a) = frequency, rad/s o Introduction BTAINING accurate mathematical models of actual flight vehicles is important for many reasons. The models are used

Aircraft and Rotorcraft System Identification

“…Additional examples of helicopter state-space model identification with CIFER ® using quasi-steady (six-DOF) model structures include the Bo-105, 10 AH-64, 182 and Kmax. 173…”

“…11.7), resulting in a six-DOF identification model structure 10 as indicated in Table 1.2. The accurate modeling of the vertical response to collective inputs might require the inclusion of an additional state to account for dynamic inflow, as demonstrated in the seven-DOF model identification of the AH-64 helicopter by Schroeder et al 182 For helicopters with high flap stiffness, the rotor-body coupling becomes increasingly significant, as seen in Fig. 11.9, and the model structure must be extended.…”