The Aeroplane

by Claude Grahame-White; Harry Harper

SEEN FROM THE BOW,

showing the “stream-line” effect which is gained by tapering the body, also the simplification of the landing chassis, and the use of a minimum of wires.

VIEWED FROM ABOVE.

The shape of main-planes and tail are shown also the exact position of the pilot’s seat.

Fig. 62.—Racing Deperdussin Monoplane (160 h.p.).

What is needed, in the high-speed machine, is a power to vary its pace. If it will fly slowly, as well as at high speed, landing difficulties are overcome; and as a scouting machine it has the added advantage that, should he be passing over a spot where he wishes to make careful notes, the pilot can reduce his speed and so gain leisure in which to survey. In the provision of variable speed, aeroplane designers have achieved already a striking success. By constructing a machine lightly, increasing the efficiency of its planes, and reducing head resistance to a minimum, and at the same time by fitting an engine of ample horse-power, the modern builder has, in some instances, produced a craft which will fly at 90 miles an hour as its high speed, and at 30 miles an hour for a low, when its engine is throttled down.

Contributing to this efficiency, there is the study that has been made of the curve of planes. It will be remembered that, according to early experiments, there was a pressure below a cambered plane, and a vacuum or lifting influence upon the top. The first students of plane-curves reckoned that the pressure from below was the more important of the two. But modern and scientific research has shown that top suction is the really powerful influence. It has been proved that the upper part of a plane will yield a lifting effect which is from three to five times as great as the pressure from below. Hence, in the latest type of machine, the planes are given two separate curves or cambers. The one on the lower surface is designed to obtain a maximum up-thrust; while on the upper surface the plane is so shaped that, according to scientific research, it will extract the strongest possible up-lift as it passes through the air. The “hump” or arch, as advised by Phillips, is still preserved; but in many cases it is less pronounced, and is continued farther towards the rear of the plane. What modern builders do is to design a wing-curve, and then send it to a laboratory to be tested. Here it is put in a wind tunnel—a tube through which a current of air is driven by a fan—and its lifting influence tested by instruments of precision.

The pilot slackens his speed when flying by throttling down his motor, and so reducing the pull or thrust of his propeller; or he sets his engine at full power, and so attains his maximum speed. For military work such variation is, as has been said, of great importance. An air-scout needs to reach a given point quickly, and return to headquarters at high speed. Every moment’s delay in bringing the Commander-in-Chief some vital piece of news, may spell the difference between victory or defeat. It is here, in fact, that cavalry scouts have failed. They may obtain important tidings, but before they can make their way to headquarters and report, the aspect of affairs has changed, perhaps, and their news—which would have been valuable had it been received at once—has lost its significance through delay. An air-scout who can vary his speed will fly fast till he needs to make an observation; then he will slow down and study what lies below him; and, his survey completed, he will return at top speed to headquarters.

Wireless telegraphy, for communicating between an aeroplane in flight and its headquarters, is now adopted for urgent reports—a cypher being used to prevent messages being “tapped” by an enemy. At first poor results were obtained, signals being audible on the ground, when sent from a machine flying low, at a distance of only about a mile. This was due to the difficulty of producing a sufficiently light apparatus; but now, with transmitting mechanism weighing from 70 to 80 lbs., messages may be dispatched from an aeroplane to a land station 100 miles away, although problems still remain to be solved in regard to the tapping and jamming of signals. The dynamo generating the electric current is driven by a small petrol motor, which develops about 2¾ horse-power; and the antenna or aerial wire, by means of which the message is sent forth—a wave length of from 200 to 500 metres being adopted—may be arranged between the planes and tail, or unwound from a reel below the landing chassis when a machine is in flight, and allowed to trail earthward. Apparatus weighing 20 lbs., is also being tested, by means of which—using a magnifying receiver—an operator in an aeroplane may receive a message as well as send one. This allows communication, not only between a machine and an earth-station, but also between two craft when in flight.