Maximum likelihood identifier refinements for F-8C adaptive control

This paper presents design refinement for the baseline F-8C adaptive flight test control laws described in Reference [1]. The baseline laws consist of simplified quadratic-optimal model-following control structures in the pitch and lateral-directional axes. Both axes have variable gains which are adjusted adaptively by an explicit on-line maximum likelihood parameter identifier. The identifier operates in pitch only, using pitch rate, normal acceleration, and elevator position measurements. It consists of five parallel computing channels which evaluate the likelihood function at discrete points in parameter space. The best of these points (the "min-L" channel) is selected and a single (modified) Newton-Raphson step is taken from there to estimate the aircraft's surface effectiveness ( Mδ ), pitching moment due to angle-of-attack ( Mα), and air speed (V). Control gains are then adjusted as a function of Mδ. A simplified diagram of this identifier is shown in Figure 1, where the baseline design includes all elements above the dotted line.