Negative Stabilizers. A considerable amount of inherent longitudinal stability is obtained by placing the stabilizing surface at a slight negative angle with the wings. This angle generally varies from -2° to -6°. At small angles of wing incidence the negative angle of the tail will be at a maximum, and acting down will oppose further diving and tend to head the machine up. At large wing angles, the tail will be depressed so far that the tail angle will become positive instead of negative, and thus the lift on the tail will oppose the wings and will force the machine to a smaller angle of incidence. The negative angle can thus be adjusted to give longitudinal stability within the ordinary range of flight angles.
Stabilizer Shapes and Aspect Ratio. Stabilizers have been built in a great number of different shapes, semicircular, triangular, elliptical, and of rectangular wing form. Measured at the rear hinged joint, the span or width of the stabilizer is about 1/3 the wing span for speed scouts, and about 1/4 the wing span for the larger machines. Nearly all modern machines have non-lifting tails, or tails so modified that they are nearly non-lifting. Since flat plates give the greatest lift with a small aspect ratio, and hence are most effective when running over the ground at low speeds, the stabilizers and elevators are of comparatively low aspect. In general, an aspect ratio of 3 is a good value for the stabilizer. Vertical rudders generally have an aspect ratio of 1, and hence are even more effective per unit area than the stabilizers. This is particularly necessary in ground running.
Aileron Control Diagram of Curtiss JN4-B.
Elevator Control Diagram of Curtiss JN4-B.
Vertical Rudders. The calculation of the vertical rudders must take the moment of inertia and yawing moments into effect, and this is rather a complicated calculation for the beginner. As an approximation, the area of the rudder can be taken from 9 to 12 square feet for machines of about 40 feet span, and from 5 to 8 square feet for speed scouts.
Stick Control Used on the Caudron Biplane. Wing Warp Is Used Instead of Ailerons. Back and Forth Movement Actuates Elevator.
