Evaluating Stability Derivatives with a Linearised Frequency Domain Solver

Abstract

Efficient and accurate prediction of derivatives from aerodynamic forces and moments of aircrafts are crucial for their flight stability and control. This requires numerical methods that resolve aerodynamic forces and moments for the complete range of flow conditions encountered during an aircraft flight envelope. The talk starts with an overview and discussion of the flight mechanic principle. A linear, ordinary, differential equation emerges and is the basis for many well known problems. Subsequently, the forcing function and their treatment to obtain accurate stability derivatives from aerodynamic forces will be shown in more detail which leads to the linear frequency domain solver (LFD). The LFD is a small disturbance approach. After all, a complex valued linear system of equations has to be solved. If flow conditions reach transonic and detached conditions, this linear system usually gets stiff and preconditioning methods are necessary to solve the equations. We will focus on the derivation of the LFD’s equation and numerical methods to enhance robustness. An important concern is the accuracy in the linearisation procedure. Examples of misleading results are discussed which occur due to simplifications in the linearisation. Finally, an outlook presents alternative numerical approaches for determining stability data.