Rotor Performance for Ideal Twist

The torque equation can be used to plot Cq versus CT—or, more conveniently, Cq/g versus CT/a, where:

C(/(T = Cp/a = у® (CT/a)}/’ + – j

The derivation of this equation has been based on ideal twist and a number of other simplifying assumptions and thus should not be used uncritically to compute the performance of all rotors. It does, however, provide a guide to interpreting actual performance data such as Figure 1.11, where Cq/g has been plotted against (CT/o)i/2 for whirl tower data from Reference 1.1. The theoretical line is based on the value of ~cd determined from Figure 1.10 as a function of the average angle of attack and the Mach number at the 75% radius. It may be seen that although there

image36

FIGURE 1.11 Comparison of Test Results with Simple Theory

is some discrepancy between the theory and the test points, the general characteristics of the theoretical line are the same as the test results. The reasons for the discrepancies that do exist will be discussed in a later section.