Flight Dynamic Stability Prediction with a Linear Frequency Domain Method

Each slight perturbation to a trimmed aircraft state causes additional aerodynamic loads on the aircraft, which is quantified with stability derivatives of forces and moments for a motion. Small disturbance approaches based on Navier-Stokes equations have become a solution to combine efficiency and accuracy for predicting stability derivatives. This approach leads to the presented linear frequency domain method, which is capable to resolve the first harmonic stability derivatives for the complete flight envelope of a transport aircraft. Its implementation involves the exact evaluation of the flux Jacobian including the turbulence model for reflecting the flow physics as well as the grid-node and grid-node velocity Jacobian. With forced rigid body motions, the proof for the good predictive accuracy of stability derivatives in comparison with fully time-accurate unsteady simulations is examined for various test cases. The importance for efficiently evaluating stability derivatives is demonstrated by a flight dynamics stability computation for an aircraft in subsonic and transonic flow. Flight dynamic stability prediction becomes feasible in practice with the derived frequency domain method. It achieves a speed-up of about two orders of magnitude in comparison with time-accurate unsteady simulations