СоФ1соа AS A HANDLING QUALITIES PARAMETER

The ratio а>фІ(оа is a significant parameter when studying lateral-directional handling qualities. If [соф, = [<wd, £d] then the quadratic factors in the numerator and denominator of (12.9,1) cancel. Or, to put it another way, the associated poles and zeros exactly cancel. The major consequence of such an occurrence is that the ф response to aileron becomes non-oscfflatory, a very desirable circumstance. Another consequence would be the disappearance of the valley-peak sequence in the frequency response for ф/да, as illustrated in Fig. 10.12c. When this special circumstance is not the case, then aileron inputs produce oscillatory responses. The cancellation of the quadratic

factors depends mainly on the values of а>ф and cod and less on 1,ф and ‘(d. Hence the importance of (0фІ(0а as a parameter.

Detailed analysis shows that for (оф/соа > 1 favorable yaw is generated, the opposite being true for (oJcod < 1. The yaw that occurs determines the amount and direction of rudder deflection needed to execute a coordinated turn. In addition, closed-loop bank angle control is difficult when софІсоа > 1. The general trend of pilot rating with софІ(ол is shown in Fig. 12.21. The general and marked preference for ojJo)d = 1 is apparent. Figure 12.22 gives typical pilot iso-opinion curves for a range of (о)ф1<оа)2 and £й. These curves indicate that, depending upon the value of £й, the optimum value of o>Jojd may differ from unity.

ROLL CONTROL SYSTEM CHARACTERISTICS (“FEEL”)

The roll control system dynamics are important in establishing the handling qualities of an aircraft. From the small amount of research performed in this area the following general remarks apply:

1. Full aileron deflection with a wheel-type control should not require a rotation exceeding 90°.

2. Control sensitivities as high as 0.5 deg/sec rate of roll per degree of wheel displacement can be satisfactory.

3. The force required to apply full control should be about 40 lb.