Bell 412 Full Flight Envelope Aircraft Simulation Model Development and Evaluation With Nonlinear Equations of Motion

Abstract

Flight models are used to accurately predict the aircraft performance and response and are used for aircraft development, engineering analysis, and pilot training. It is common practice to use linearized small perturbation equations of motion for the identification of the stability and control derivatives that form the basis of flight models using system identification. Due in large part to advances in computer technology and optimization techniques, it is feasible to use nonlinear equations of motion for time-domain system identification. This report compares two full flight envelope aircraft models that were developed with identical data: one developed using linearized equations of motion in a state space form, and the other with nonlinear equations. The global flight models were developed for the NRC Bell 412 helicopter in forward flight across its range of speeds, altitudes, and configurations. Use of the nonlinear equations of motion produced a model with less parameter variance and its corresponding global model had improved trim characteristics.

A physics-based neural network for flight dynamics modelling and simulation

“…where X, Y , Z, L, M, and N , are the forces and moments given in the body-fixed coordinate system, θ is the Euler pitch angle, and φ is the Euler roll angle. The time propagation of the numerical solution can be completed with a second-order Adams-Bashforth integration scheme, which was found to be sufficient for the helicopter dynamic simulations by Crain et al [54].…”

“…The linear model can then be identified using time-or frequency-domain methods. In the second approach, the non-linear equations of motion are used and combined with the first-order Taylor series of the forces and moments taken about 0 to form a grey-box system identification problem performed in the time-domain using the output-error (OE) method-this approach was used by Crain et al [54]. The dynamics of a rotor-craft in a any given flight regime (such as forward flight) are well established continuous functions, as are the forces and moments, but the collected flight data, as described in Sect.…”

“…The development of this global model using point modelling with polynomial regression is documented in References [54]. In this approach, the Taylor series is taken about 0 for all point models.…”

“…The identification of the point model derivatives used non-linear time-varying equations of motion with constant parameters. A full description of the modelling approach is available in References [54]. Once all flight dynamics models were identified, the global model was created using P d as the regressor.…”