The making of a gliding descent, or _vol-plané_, is an art all airmen learn; and the vital thing to remember in connection with it is, that the machine must always move swiftly forward. Sometimes, checking his glide too soon, a pupil at the schools will make what is called a “pancake” landing: that is to say, misjudging his height above the ground, he stops the glide of his craft, by a movement of the elevating plane, when he is still 15 or 20 feet in the air. The result is that the machine comes to a standstill, then drops flat upon its wheels; and in doing so it may break its chassis supports, and give the pupil a shaking. The art, in a gliding descent, is to lessen the steepness of the dive, by throwing up the elevating plane only a second or so before the landing-wheels make their contact with the ground. Then, its downward speed checked--in the same way that a bird checks itself, just before its feet touch earth--the wheels of the craft will meet the surface smoothly, and there will be no shock or rebound. [Illustration: A. Upper main plane; B.B. Lower main plane; C.C. Hinged flaps which act as air brakes. SEEN FROM ABOVE. AS VIEWED FROM ONE SIDE. 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. [Illustration: 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.