Efficient Computational Tools for Nonlinear Flight Dynamic Analysis in the Full envelope

Abstract

Equilibrium analysis for an aircraft is very important for control law design and development. Computation of equilibrium point is also required to initialize the aircraft model in flight simulation. This equilibrium point is obtained by solving for the zeros of the right hand sides of the aircraft equations of motion simultaneously. Mathematically, this is achieved using the conventional numerical optimization methods which are iterative and require more number of iterations. The typical flight envelope of a fighter aircraft ranges from 20% to 200% of the speed of sound and sea level to 15 km in terms of altitude. This places significant computational demand to generate hundreds of linearized aircraft mathematical models needed for control law design and evaluation. The Approximate Trim calculations, proposed in this paper, provide good initial guess values throughout the flight envelope for the conventional optimization methods resulting in faster convergence. Thus the time and effort required to generate the aircraft mathematical models is reduced. The aerodynamic database is obtained by wind tunnel testing. To reduce the wind tunnel testing costs, the aerodynamic database with respect to angle of attack is generated within the aircraft performance limits. This results in a reduction in the range of the aerodynamic data with respect to angle of attack as speed increases. Therefore, only three points are available for the interpolation at the extreme points in the flight envelope. In order to solve this problem, we propose barycentric (triangular) interpolation in combination with the conventional rectangular interpolation for these two dimensional tables