Aircraft stability and departure prediction using Eigenvalue Sensitivity analysis

Abstract

A stability analysis and departure prediction method has been developed and coded in a MATLAB®-based software package called the Stability And Departure Analysis Tool using Eigenvalue Sensitivity (SADATES). Using eigenvalue and eigenvector analysis, SADATES is capable of performing a full-envelope stability analysis, returning both quantitative and qualitative data regarding the stability of the airplane at a static reference condition. SADATES not only supplies the analyst with information describing where and when an aircraft is likely to depart, but also information about the departure characteristics, enabling the analyst to design for better departure resistance. While the eigenvalue and eigenvector approach is straightforward, it is a broader approach than many traditional stability parameters, yielding more accurate and reliable results than traditional methods. SADATES also analyzes the aircraft dynamics from a standpoint of eigenvalue sensitivity. Using this feature, the analyst may directly study the impact of data uncertainty and non-zero angular rates on the nominal stability of the aircraft. Of particular interest are the effects of the dynamic damping derivatives, as these derivatives are particularly difficult to estimate. In addition, the effect of an unsteady reference condition may be examined by studying the sensitivity of the eigenvalues to changes in angular rates, thereby using a static approach to give answers to a dynamic problem. Given the development of eigenvalue sensitivity data, the analyst is able to determine the margin of error on nominal aircraft stability. The utility of the SADATES package is tested using aerodynamic data of the McDonnell-Douglas F / A-18C Hornet. Bare airframe, controls fixed stability is analyzed, and its sensitivity to data uncertainty and to non-zero angular rates is examined. The Hornet's bare airframe stability characteristics are then compared to those using an active feedback control system to drive an automatic leading and trailing edge flap schedule, demonstrating the accuracy and versatility of the program.