Rudder Effectiveness

Figure 16.7 shows the rudder effect when varying the control angle. Varying the wind speed shows no effect on the general trend. The lift is not affected by the rudder, while the drag increases with the rudder deflection, as expected. The pitching moment is slightly affected because of the rudder drag effect. More important are the effects on the side force, yaw, and roll. The side force and yaw moment are AoA-independent, but vary with the rudder control angle as expected. However, note that a rudder setting of 0° does not correspond exactly to zero side or yaw results because of a slight misalignment of the rudder with respect to the control settings. At high AoA, the rudder effectiveness is reduced by the wake from the fuselage and wing. The side force coefficient range is about ±0.1, which translates into a force equal to ±34 N. Roll is affected by the rudder because the lift application point on the fin is above the wing centerline. This is more evident at lower AoA when the fin is not affected by the wing and fuselage wake. At very high AoA, the stall changes the trend because of the asymmetry of the stall behavior.

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