LATERAL-DIRECTIONAL HANDLING QUALITIES

Generally speaking, lateral-directional control is more complex than longitudinal control. This, of course, is due to the fact that two axes of rotation are involved, leading to cross-coupling effects and the use of two primary control surfaces. As a result many groups of parameters are presently being studied to determine their correlation with pilot ratings. The following is intended to introduce the reader to some of these handling qualities parameters and to indicate the trends of research.

The primary lateral-directional control task facing the pilot is the control of bank angle through the aileron control system. The transfer function relating bank angle response to aileron input can be derived from (5.11,10) by putting ДLc = Ls ASa, ANc = Ns ASa and solving for the ratio <f>/A5a. The
result is

Here the factors in the denominator represent the spiral mode (time constant Ts), the roll mode (time constant TH), and the lateral oscillation of radian frequency (o)a) and damping (ld). The values of these four constants come from the solution of the eigenvalue problem, discussed at some length in Chapter 9, where approximate solutions for them are also given. The user of the approxi­mations should note their restricted range of validity. The numerator constants are given below with the aerodynamic transfer functions replaced by the corresponding stability derivatives, and with Yv = Yr = yc = 0.

where

(d)

(e)

A partial list of parameter groups used in handling qualities studies includes <*>ФІша, Ійсяй, TR, Ts, фІ0, ф/пЕ, andp where (vE = Wp/p0)-

SPIRAL MODE

The spiral mode time constant, Ts, determines the aircraft’s tendency to maintain a given course when cruising. It is generally found that in the case of a divergent spiral mode, pilots will rate the aircraft as satisfactory provided that |TS| > 20 sec.