Bandwidth Criterion

The HQs of an airplane, in a closed loop, can also be determined from its stability margins [12]. The bandwidth (BW) is taken as the lesser of the gain (6 dB) and phase (45°) margins’ frequencies. A phase delay parameter characterizes the phase roll off, and it is very similar to the equivalent time delay parameter. The phase delay is defined as

T v180_______________

ph ~ 57.3 x 2w180

v180 is the frequency at which the phase is —180°, f2vi80 is the phase at twice the v180 frequency. These parameters are computed from the Bode diagram of the pitch attitude TF. The phase delay vs. BW HQ level bounds are specified. The BW is also an important control design criterion. Higher BW would be preferable, but it might cause increased ‘‘dropback.’’ The unified BW criterion (UBC) considers the flight path dynamics and it is useful for the landing task [13]. It considers pitch attitude BW, phase delay, flight path BW, pitch attitude dropback, and the pitch rate overshoot. HQ level boundaries are defined for these parameters. The UBC also checks for the dropback.

10.4.1.2 Neal-Smith Criterion

Neal-Smith criterion is used for assessment in terms of the pilot workload [14]. The aircraft is flown in closed loop as shown in Figure 10.4. The first block is the pilot model. It is assumed that the pilot performs the closed loop pitch attitude control

task, and hence the pilot’s compensation is a measure of the pilot’s workload. The HQ level boundaries are specified in terms of the closed loop response (resonance) amplitude and the pilot’s compensation. The pilot model parameters are tuned to obtain minimum closed loop resonance. The droop allowed is up to —3 dB. The lead/lag compensation used by the pilot (determined from the pilot’s control – theoretic model) is used in the HQ level boundaries. The point of this criterion is that it evaluates the closed loop performance.