Fig. 55.—An air brake.
In most cases, a machine with a good gliding angle is regarded with favour; but there are circumstances—such, for instance, as when a pilot seeks to alight in a small field—when a gradual descending angle is a disadvantage. The field may be bounded by trees; hence, if the machine prolongs its glide, and he cannot make a quick landing, the pilot may find himself threatened by a collision. To check the forward glide of a craft, when necessary, and bring it to earth at a steep angle, air brakes are now being tested, as illustrated in [Fig. 55]. When not in use, they form sections of the lower main-plane, and are operated by the pilot with a lever. Their action is simple: pivoted in the centre, they swing until they expose themselves at right angles; and their surface, when thus exposed, tends very materially to check the glide. The descent of a machine into a small field, with and without brakes, is shown in [Fig. 56]; and from this the value of the brake may be seen.
Fig. 56.—Action of an air brake.
A.A. Trees enclosing a small field; B. Gliding angle of a machine with an air brake; C. Angle of a machine without a brake.
The chief peril of the air, when pilots came to understand their risks, was seen to be this: that a machine might be caught by a wind-gust when flying near the ground, and dashed to earth before its pilot could check the helpless dive; and this peril still presents itself. Combating a breeze at first, then gusty winds, the airman has so progressed to-day that he will face a 60-mile-an-hour gale. When well aloft, indeed, he hardly cares how the wind may blow. It may turn him completely over, but he is not lost; as shown by “looping the loop,” in fact, a pilot can perform a somersault in the air and not lose control of his machine.
“Looping the loop,” which has made so great a sensation, has taught airmen one definite lesson; and it is this: no matter how their machines may be beaten and tossed by the wind, they need not fear a fall—provided they are high enough above ground. The movements of a machine, as it makes a series of “loops,” are shown in [Fig. 57]. The pilot reaches a high speed before he rears up his machine to begin the “loop,” and this downward velocity is attained by diving; then, when he estimates his pace sufficient, he pulls his elevating-lever back and the machine leaps upward, rearing itself vertically towards the sky, turning over on its back, then diving again and coming right-side-up—thus achieving a complete somersault. A skilled trick-flyer, also, will allow his machine to drop sideways or tail first, deliberately working the controls so that it shall do so. Then, just as it seems to spectators that he is falling to destruction, he will dive or twist, regain the mastery of his machine, and descend in a normal glide.
An airman, flying in a wind, is rather in the position of a man who puts to sea in a small boat when waves are high. Once he can clear the shore, the boatman feels at ease; but should a breaker catch him before he reaches the smooth, rolling billows a little distance from the beach, his craft may be overturned and dashed to pieces. So with the airman; his moments of peril, when flying in a gusty wind, come just as he is soaring from the ground, and when descending from a flight. Then an air-wave, like a sea-wave, may lift his craft and drive it with a crash to earth.
