Shortcomings of modern control as applied to fighter flight control design

The road to applying modern control theory to fighter control design has been a very rocky one. LQR in its purest form has repeatedly been found unsuccessful. When it has worked, it has been so modified as to be unrecognizable. This paper presents the basic requirements for a flight control synthesis theory, plus reasons and examples are given revealing modern control theory to be highly deficient--in particular LQR, LQG, singular value theory, and eigenvalue/ eigenstructure assignment. In contrast, alternative techniques and theories are presented that address the real problems in flight control synthesis-coping with uncertainty and achieving specs. Frequency response has been found to be better suited to flight control design.