Fig. 61.—Single-seated Air Scout.
A. Propeller; B. Motor (partly hidden by shield); C. Pilot’s seat; D. Sustaining plane; E. Rudder; F. Elevating-plane; G. Chassis.
This scouting biplane is intended for detailed reconnaissance; for a careful flight above an enemy’s position, that is to say, in which every movement of troops is observed and noted. Another machine becomes necessary for the making of a quick and general survey—such, for instance, as that in which a pilot would be asked to fly to some definite point, and see whether a body of troops is stationary or on the march. Speed, for such a task, is the chief requirement. Hence there is a type of fast scouting monoplane, in which a pilot can ascend alone, and fly at 100 miles an hour. With such a craft, sweeping rapidly above an enemy’s position, the pilot-observer can return with his information at surprising speed. In [Fig. 61] an air-scout of this type is seen. The tapering, covered-in body will be observed; this is to reduce wind resistance as the machine rushes through the air. The Gnome engine is, for the same reason, covered by an aluminium shield, which only allows the lower cylinders to project; they must, of course, be exposed in some way to the air, or they would not cool themselves. The landing-carriage has been reduced to its simplest form; this, again, is to reduce wind resistance; and the pilot, sitting deep in the body, shows only his head as the machine flies. Here, again, apart from the greater comfort in being so shielded, the placing of the pilot within the machine spells a lessening of pressure. This question of the resistance of the air is vital in the designing of high-speed craft. Every projecting surface must be “stream-lined,” as it is called; it must, that is to say, have such a tapering shape as will offer least resistance as it passes through the air. The atmosphere is viscous—or, to use a commoner word, “sticky.” It clings to anything that is passed quickly through it, as treacle might adhere to the back of a knife; therefore the body of an aeroplane—like the hull of an airship—slopes away to a point astern, so that friction may be minimised.
What the pressure of the wind may mean, when high speeds are reached, one may prove by holding a hand from the window of an express, say while it is running at 60 miles an hour. The rush is so fierce that the arm will ache from the mere effort of holding it outstretched. Whereas the train is running at 60 miles an hour, a monoplane may be flying at more than 100 miles an hour. Therefore the thrust of the wind against wires, struts, and body may be imagined; it reaches the violence of a hurricane. Even the pilot, glancing above the wind-screen to steer his course, finds the pressure so tremendous that, in some racing machines, he is provided with a padded rest against which he can lean his head.
In the development of speed, some remarkable craft are built. Each year there is an international air race for the possession of the Gordon-Bennett trophy, and to win this designers build special craft. In tiny monoplanes, engines of high power are installed; and the sustaining wings are so reduced, to give a maximum speed, that the machines appear more like projectiles than flying craft. A purely racing-type monoplane is seen in [Fig. 62]. It represents a Deperdussin, which, with an engine of 160 horse-power, reached a speed of 130 miles an hour. How small this machine was, in relation to its engine-power, will be realised from the fact that the sustaining surface of its wings amounted to only 104 square feet—far less lifting area, in fact, than Lilienthal used in his gliders. Wires and struts are reduced to a minimum; the body is tapered and smoothed. Such a machine, although it carries speed to an extreme, and is in reality a “freak,” teaches useful lessons. But though it provides data for the construction of high-speed scouts, a monoplane of this type would be useless for cross-country flying; and for the reason that it cannot be manœuvred, prior to an ascent, upon anything save the smoothest of ground. Its wings being so small, to ensure a maximum of speed, the machine will not rise until it has run forward a long distance across the ground; and during this run it attains a speed of nearly 90 miles an hour. At such a pace, unless the ground below its wheels was level, it would leap, swerve, and probably overturn. When alighting from a flight, also, again owing to the smallness of its wings, the craft has to plane down so fast that its pilot could not land safely unless he had below him a surface that was absolutely smooth.
A. Propeller; B. Shield to lessen wind resistance; C. Sloping shield which encloses engine (also to minimise wind-pressure). Air passes between the shields B and C to cool the motor. D. Pilot’s seat; E. Padded projection against which, when at high speed, the pilot rests his head, F. Sustaining-plane, very slightly cambered; G. Rudder; H. Elevating-plane; I. Landing wheels.
