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A gust striking from behind may, or may not affect the elevator flaps, this depending on their position at the time that the gust strikes. If the flaps are turned up, the rear end will be raised by the gust and the machine will head dive: if turned down, the gust will depress the tail, raise the head and tend to "stall" the machine. If the tail is of the lifting type, the rear entering gust will reduce the relative velocity, and the lift, and cause the tail to drop. On passing over the tail and striking the wings, the rear gust will reduce the velocity and cause a loss in lift. This will either cause the machine to head dive or drop vertically through a certain distance until it again assumes its normal velocity.

All of these variations cause a continually fore and aft upsetting movement that must be continually corrected by raising and lowering the elevator flaps, and in very gusty weather this is a very tedious and wearing job. It requires the continual attention of the pilot unless the action is performed automatically by some mechanical device, such as the Sperry Gyroscopic, or else by some arrangement of the surfaces that give "inherent" stability. Control by means of the elevator flaps (which raise and lower the body in a fore and aft direction, as shown) is known as "longitudinal control," and when the machine is so built that correction for the longitudinal attitude is obtained "inherently," the machine is said to be "longitudinally stable." Modern machines can be made very nearly longitudinally stable, and are comparatively unaffected by any than the heaviest gusts.