Control Anticipation Parameter

The idea behind CAP is that the initial pitch attitude response of the aircraft is useful in ascertaining the ultimate response of the flight path [10,11]. The initial pitch acceleration is sensed by the pilot. The load factor parameter being related to the flight path curve is useful in defining this criterion.

CAP1: This criterion is defined as

u0 2 v2P

—— (rad/s /g); an approximation of this is given as (for LOTF)—.

Anzs n/a

Here, the numerator is the initial pitch acceleration and the denominator is the steady-state change in the load factor.

CAP2: This criterion is defined as UmaxHODS (rad/s2/g), based on the maximum pitch acceleration.

TABLE 10.1 Handling Qualities Specified Minimum Values Level 1 Level 2 Level 3 Class of the Aircraft vsp Па vsp Па £sp Te I, II-C, IV 0.87 2.7 0.6 1.8 0.05 6 II-L, III 0.70 2.0 0.4 1.0 0.05 6 Source: Shaik, I. and Chetty, S. HQPACK User’s Guide, Vols. 1, 2. PC based SW package in MATLAB ver 5.2 for the prediction of handling qualities and pilot induced oscillation tendencies of aircaft. NAL Project document, PD-FC-9810, December 1998.

CAP3: This criterion is defined as based on the quasisteady-state pitch rate.

nzs

—2 –

CAP4: This criterion is defined as qmaxHODS based on the peak value of the

pitch acceleration for step command from the pilot. CAP4 is approxi­mately equal to the CAP1 approximation. The CAP values where applic­able are computed from the parameters of the LOTF or the HODS.

The CAP and the equivalent short-period damping Zsp should be within the HQ level bounds. Table 10.1 gives the minimum values for the Category C flight phase.

The product — spTU represents the phase lag at —sp. It is also an equivalent time delay between the pitch attitude response and the flight path response. If the two responses are adequately separated then the pilot gets a proper cue for controlling the outer slow path. This nondimensional equivalent parameter should fall within the specified HQ bounds. Other limits are the following: For Category A flight phase! Level 1, —sp > 1.0, and for Level 2, —sp > 0.6. For Category C, Table 10.2 gives the HQ specified requirements.

TABLE 10.2 Handling Qualities Specified Minimum Values for Time Constant Level Class Minimum (1 /Te) 1 I, II-C, IV 0.38 II-L, III 0.28 2 I, II-C, III 0.24 II-L, III 0.14 Source: Shaik, I. and Chetty, S. HQPACK User’s Guide, Vols. 1, 2. PC based SW package in MATLAB ver 5.2 for the prediction of handling qualities and pilot induced oscillation tendencies of aircaft. NAL Project document, PD-FC-9810, December 1998.

The time delay тв max limits are specified as the following: For Level 1 as 0.1 s, for Level 2 as 0.2 s, and for Level 3 as 0.25 s. The equivalent time constant is important in attitude dynamics as well as for the flight path. Additionally, the short-period frequency and the acceleration parameters are also evaluated. It is interesting to note here that the CAP1 approximation is related to the static margin. The vsp, boundaries for categories of flights and the levels are also specified in MIL-F-8785C.

The pitch acceleration, an important flight mechanics parameter, is related to pitch control derivative as

At high angle of attack a high value of the nose up pitch acceleration is encountered and adequate control recovery power is required to overcome this pitch acceleration.