Estimation of aircraft unsteady aerodynamic parameters from dynamic wind tunnel testing

TLDR

Current aerodynamic models lack the ability to directly incorporate frequency‑ and amplitude‑dependent data, making comprehensive testing of nonlinear unsteady aerodynamics time‑consuming and motivating the development of more general testing methods. This study proposes using Schroeder sweep inputs as an efficient alternative to single‑frequency forced‑oscillation testing for obtaining the frequency response of unsteady aerodynamic models. Schroeder inputs deliver a flat power spectrum across a chosen band, and the authors compare this approach to traditional single‑frequency inputs while presenting a data‑analysis method to identify suitable unsteady aerodynamic models. The authors discuss issues arising from the analysis and compare results obtained with Schroeder sweeps to those from traditional single‑frequency testing.

Abstract

Improved aerodynamic mathematical models, for use in aircraft simulation or flight control design, are required when representing nonlinear unsteady aerodynamics. A key limitation of conventional aerodynamic models is the inability to map frequency and amplitude dependent data into the equations of motion directly. In an effort to obtain a more general formulation of the aerodynamic model, researchers have been led to a parallel requirement for more general testing methods. Testing for a more comprehensive model can lead to a very time consuming number of tests especially if traditional single frequency harmonic testing is attempted. This paper presents an alternative to traditional single-frequency forced-oscillation testing by utilizing Schroeder sweeps to efficiently obtain the frequency response of the unsteady aerodynamic model. Schroeder inputs provide signals with a flat power spectrum over a specified frequency band. For comparison, experimental results using the traditional single-frequency inputs are also considered. A method for data analysis to determine an adequate unsteady aerodynamic model is presented. Discussion of associated issues that arise during this type of analysis and comparison of results using traditional single frequency analysis are provided.