Читать книгу Aeroplane Construction and Operation онлайн

15 страница из 66

Fig. 8. Langley’s "Aerodrome," An Early Type of Tandem Monoplane.

The Aeroplane in Flight

Fig.9 shows an aeroplane in horizontal flight and lightly loaded, the machine traveling along the horizontal flight path F-F. With the light load, the angle made by the wings with the flight path is shown by (i), the tail and body remaining horizontal, or parallel to the flight path. With an increased load it is necessary to increase the angle of the wings with the flight line, since within certain limits the lift increases with an increase in the angle of incidence (i). Fig. 10 shows the adjustment for a heavier load (W₂), the angle of incidence being increased to (i'), and the body is turned down through a corresponding angle. The increased angle is obtained by turning the elevator flaps (T) up, thus causing a downward force (t) on the tail. The force (t) acts through the body as a lever arm, and turns the machine into its new position. It will be noted that when the angle of incidence is great that the rear of the body drags down and causes a heavy resistance. This position of a dragging tail is known to the French as flying "Cabré." With high angles cabré flight is dangerous, for should the propeller thrust cease for an instant the machine would be likely to "tail dive" before the pilot could regain control. This sort of flight is also wasteful of power. Cabré flight is unnecessary in a variable incidence machine, the wing being turned to the required angle independently of the body, so that the body follows the flight line in a horizontal position, no matter what the angle of incidence may be. In this type of machine the wings are pivoted to the body, and are operated by some form of manual control.