Horizontal Stabilizer

The lift and drag of the horizontal stabilizer play important roles in the longitudinal trim conditions of the helicopter. Figure 8.5 shows the conditions at the stabilizer, especially the relationships that define its angle of attack.

The lift and drag of the horizontal stabilizer enter into the longitudinal equilibrium equations as:

X„ = LH sin[0 – (e,„H + e, H + Y.-)] – D„ cos[0 – (e,„H + tfH + y,)]

Z„ = – L„ cos[0 – (ЄМн + Єрн + Y.)] – DH sin[0 – (Єд, н + s, H + Y.-)]

The basic equations for lift and drag are:

Lh =

LH = ^ ^qAH[a((l — CIlo)]h

and

These equations contain several types of parameters that must be evaluated. The first are the geometric terms, which are defined by the configuration description: stabilizer area, AH; stabilizer aspect ratio, ARH; incidence of the main rotor shaft with respect to the body axis, iM; incidence of the chord line of the horizontal stabilizer, iH and angle of zero lift of the airfoil used on the stabilizer, aLG. Three more parameters that may be found indirectly from the configuration description are the slope of the lift curve, aH, which is a function of aspect ratio and sweep of the stabilizer; the span-efficiency factor, 5,H; and the profile drag coefficient, CDq. Some methods for evaluating these will be given. The second set of parameters consists of the flight conditions: dynamic pressure, q, and the angle of climb, yf, which for most analyses are known beforehand. The third type are the environmental conditions in which the stabilizer operates: the dynamic pressure ratio qjq, and the downwash angles induced by the main rotor and fuselage, and eF{J. These terms must be evaluated by some more-or-less empirical methods based either on studies of previous designs or on wind tunnel tests of the configuration analyzed. Both types of methods will be discussed. The last set of parameters are the trim conditions, 0, arpp, and ax, which are to be solved for in the procedure to be oudined later.