Pilot Equalization with the Crossover Model

All airplane transfer functions, such as the pitch response to elevator and the roll response to aileron, have first – or second-order denominator functions, arising from mass or inertia. To satisfy the crossover model the pilot must supply a canceling numerator function over the same frequency range. This amounts to lead or anticipation, agreeing with common sense as to what is required for the error elimination in compensatory operation.

The amount of lead or compensation required by the pilot is a direct measure of workload. The pilot lead is reflected in the positive slope of the pilot model amplitude ratio in the Bode diagram, in the vicinity of the crossover frequency. A large positive slope corresponds to excessive lead, high workload, and poor pilot rating. A numerical connection can be made between pilot rating by the Cooper-Harper scale, discussed in Chapter 3, and required lead equalization (Figure 21.3).