# Vertical Stabilizer

The forces on the vertical stabilizer play a primary role in the yawing moment equilibrium equation but also appear as small participants in some of the others. Figure 8.18 shows the geometric relationships that are used in evaluating these forces.

TABLE 8.2

Horizontal Stabilizer—Example Helicopter

 Physical Parameters Aerodynamic Characteristics Parameter Symbol Value Characteristic Symbol Value Source Span Ьн 9 ft Slope of Lift Curve aH 4.0/rad Figure 8.6 Root chord с’н 2.34 ft Dynamic Pressure Ratio Чн/q .6 Figure 8.9 Tip chord с‘н 1.66 ft Rotor Downwash Ratio 1.5 Figure 8.11 Area лн 18 sq ft Fuse. Downwash Ratio dEh/da. .23 Figure 8.15 Taper ratio ** .71 Span Efficiency Factor .02 Figure 8.17 Half chord sweep angle Лс/2И 13° Zero Lift Drag Coefficient C°°H .0064 Figure 6.30 Aspect ratio A. R-н 4.5 Incidence -3° Horizontal distance from main rotor x/Rh -1.08 Vertical distance from main rotor z’/Rh .3 Zero lift angle of attack aLOH 0°

 Єр = aF + iH at intersections

 Fuse. Angle of Attack, deg. FIGURE 8.16 Wind Tunnel Results Used to Calculate Fuselage – Induced Downwash Ratio at Horizontal Stabilizer

The equations for the forces on the vertical stabilizer are:

Xv = – Dv cos[p + iMv + r|T|/ + – Lv sin[|3 + iMy + Лі> + Ляк]

Yy = Ly costf + rMy + rTv + тц,] – D„sm[p + + Лтк + Лtr]

Zv = Xv sin[© – (e% + EFy + y,)]

where (3 is the sideslip angle and T| is the sidewash angle at the vertical stabilizer induced by the other components of the helicopter.

The basic equations for lift and drag of the vertical stabilizer are:

Ly = J^}AyC

W

Each of the new terms in these equations will be discussed separately.