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Longitudinal HQ Criteria
Evaluation of aircraft’s longitudinal HQ is very important [8]. This is more so for any fighter aircraft than a transport aircraft. Next we discuss several such important criteria.
10.4.1.1 Lower-Order Equivalent TF
An adequate lower-order equivalent TF (LOTF) is required to assess the longitudinal HQs of an aircraft for short-period performance, and this is done in terms of the equivalent parameters [1,9]: Zsp, vsp, 1/T0, тв. This is because the aircraft with feedback controllers (filters with gains and time constants) and other subsystem dynamics becomes a very higher-order dynamics system (HODS). Thus, it would be very convenient to reduce this HO aircraft-control dynamic system to an equivalent lower-order system and judge the adequacy of the parameters mentioned here in terms of evaluation specifications. The HQ evaluation then becomes easy in a manner similar to that for conventional aircraft, more so if the responses are of the conventional type. If the responses are not of the same type as the conventional aircraft, then this approach is not preferable. LOTFs are obtained in the following forms:
Ф) _ Ku(s + 1/T)e~TeS ^ nz(s) _
SeO) S2 + 2ZspVspS + V2p Se(s) S2 + 2Zsp VspS + v2p
The frequency range for fitting LOTF to HODS is taken as 0.1-10 rad/s. The procedure for obtaining the LOTF is explained in Section 10.10. The parameters of LOTF are better used in conjunction with another criterion known as control anticipation parameter (CAP) discussed next.
