Aerial scouting—Types of machines used—The high-speed monoplane—Steering across country—An airman’s map and compass.

When they could fly in high winds, and their motors were reliable, it was seen that aircraft would become vital factors in time of war; so vital, indeed, that no army or navy could afford to be without them. Successful aeroplane builders, consequently, such as the brothers Farman and Louis Bleriot, became busy with the construction of military craft. France threw herself with enthusiasm into the creation of an aerial fleet. Germany, more methodical, studied cautiously and yet thoroughly the problems involved; while in England, for several years, the subject received scant attention.

It was in the autumn of 1910, when one or two aeroplanes were used in the manoeuvres in France, that interest was first focussed upon their power as scouts. These machines were not built specially for military work, and there was little organisation or foresight in their use; but observers accompanied the pilots upon long cross-country flights, during which they hovered above the enemy, and noted the location and movements of troops. By being able to pass through the air, and evade the enemy’s patrols, these observers brought back news it would have been impossible to obtain by use of cavalry scouts; and, owing to the speed of their flight, they were able to glean such reports, and fly back with them to headquarters, in a far shorter time than would have been possible by any other means. These first observers were officers, who sat behind the pilots as passengers. They carried with them field-glasses and notebooks, and the pilot obeyed their orders as to the direction in which he should fly. Peering down upon the land that lay below, an observer made rough notes of all he saw; then, upon returning to his starting-point, he prepared and handed in such a report as is printed below:

This report was one actually prepared, after an early morning flight, by an officer-observer in the French manoeuvres of 1910, and it shows how successfully an air-scout may detect a movement of troops. The report has an additional significance. Before he sent out his aeroplanes, on this particular morning, the Commander-in-Chief had assumed, but could not substantiate, the theory that his opponent was retreating. And now this report by aeroplane, showing that nothing save cavalry and rear-guards had been seen over a specific tract of country, served to confirm the rumour that the enemy was giving ground.

Once the value of aerial reconnaissance had been proved, France proceeded to the development of a scouting aeroplane; and the need, in such a machine, is that the observer shall have a clear view ahead and below. The construction of machines was, for this reason, modified. The front elevating plane was moved to the rear, where it was fitted in the form of a flap—as in the case of monoplanes—and the pilot and observer placed in a covered-in body, which projected in front of the main-planes, as shown in Fig. 60. By placing the body before the planes, the observer has a clear view ahead and on either side; and even when he leans over the side, and looks directly downward, there is no surface to obstruct him.

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 manoeuvred, 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.

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.

Another ingenious system of signalling, from an aeroplane to its headquarters, when the former is flying within view, is by means of smoke signals from the exhaust of the engine. As the exhaust gases are shot forth into the air they are rendered black by the mixing with them of a powder, the admission of which to the exhaust pipes the pilot can regulate by a lever. In this way he is able to send black puffs of smoke into the air, and spell out a message in the Morse code, which an observer on the ground can read with field-glasses. A more simple method, when an observer wishes to communicate with those below, and yet avoid the delay of a descent, is to drop a written message in a little bag, to which a flag and a weight are attached. This is seen as it falls, and is retrieved and carried to headquarters.

A machine that has achieved success, owing to its power of varying speed, is the Sopwith military biplane, as shown in Fig. 63. Adopting a practice that has become general, its wings are fitted upon what is practically a monoplane body. Tail-planes and rudder are the same as in a monoplane. The top main-plane, as will be seen, is set slightly in advance of the lower. The system is called “staggering”; and the idea is that, by placing the upper plane ahead of the lower, the total lifting power will be increased. It has been proved a disadvantage of the biplane that, when the main-planes are placed one above another, there is a slight loss of lift owing to the fact that, acting upon the air as they do quite close to each other, a certain amount of interference occurs between them—one tending to disturb the air-stream in which the other moves. By “staggering” the two planes this interference is overcome; but some makers regard it as a small consideration, and build their planes in the ordinary way, allowing as large a gap as possible between them. In the Sopwith military machine, engine and propeller are in front of the main-planes; then come the places for pilot and observer. The pilot sits first, and the body of the machine is so high that only his head appears above it, while just in front of his face, to deflect the wind-rush from the propeller, there is a raised section of the hull which acts as a screen. Behind the pilot, sitting in a second opening in the hull, is the observer. He has a view forward, rendered the better by setting back the lower-plane; while at the point at which it joins the body of the machine, immediately below him, this plane is hollowed out, so that he can look directly upon the earth below. Small windows are also fitted upon either side of the hull. Through those in front the pilot may glance when descending from a flight, so as to judge his distance from the ground, while the others are utilised by the observer, as he turns to look from side to side. This biplane, and many others, is balanced against sideway roll by ailerons, and not by warping the wings. Constant warping, such as is necessary in the everyday use of machines, has been declared to strain a plane and render it weak; therefore the use of ailerons is now favoured.

To meet the demand for a purely scouting machine, in which pilot and passenger shall have a clear field for observation, both above and below, a monoplane has been designed which is called the “parasol.” This machine, a Morane-Saulnier, is shown in Fig. 64. The two sustaining wings, forming a single surface, are raised above the body so that its occupants have nothing to impede their view earthward; and they can also see above them—an advantage of course in time of war, seeing that an enemy might be hovering overhead.

The driver of a modern-type aeroplane, sitting snugly within its hull, has a wheel and instrument-board before him, as sketched in Fig. 65. As he flies across country he has many things to think of. Holding the control-wheel in both hands, his feet resting upon the rudder-bar, his eyes rove constantly among the instruments on the dashboard before him. He glances at the compass often, for it is by this that he steers; and when the air is clear, and the earth below plainly seen, he will every now and then glance over the side of the hull, so as to be on the look-out for a landmark that may tell him he is on his course.

But sometimes, when the air is thick and misty, or there are low-lying clouds and the earth is shrouded in a fog, the pilot flies in an empty void. Nothing is to be seen above, below, or on either hand; he must rely entirely upon his instruments. The altitude meter tells him whether he is rising or descending; his compass tells him he is flying accurately to his goal; while his own ear, and the tell-tale dial of the engine indicator, informs him that his motor is doing its work. So he sits within the hull of his craft, perhaps 5000 feet above the earth—unseen by those below, and himself seeing nothing of the land over which he flies. Should the wind be steady, he has little to do save keep an eye upon his instruments, and listen to the beat of his engine. But if there are gusts and eddies his hand-wheel is busy; each lurch must be corrected by a movement of the ailerons, each dive checked by a pull upon the elevator.

The aeroplane compass, nowadays, has been made accurate and reliable; but pioneers found it a dangerous instrument. Vibrations from the engine, and the nearness to the compass of such large masses of metal as the motor and its fittings, made the needle deviate and give false readings. Once, when upon a cross-Channel flight and out of sight of land, a pilot glanced down at his compass and saw that the needle, instead of pointing northward, was spinning slowly round and round; and so it continued until he had by guesswork groped his way to land. But experience showed how a compass may be mounted upon rubber shock-absorbers to guard it against vibration; how fittings that are near it, such as the steering-column and rudder-bar, can be made of brass, or some other non-magnetic metal; while, as to the attraction of the motor, the compass is corrected against this by introducing scraps of metal into its case, so that the needle can be drawn back to an accurate reading from any deviation it may show.

But, even with an accurate compass, the cross-country airman may have anxiety in his mind. He may be flying in a side wind; and this, should it be strong and steady, will have an insidious effect upon his path, tending always to drift him sideways even while he keeps his bow upon a compass course. Fig. 66 should make this clear. The airman seeks to fly from A to B, a distance say of 60 miles; so he sets his course due east and passes steadily across country at the rate of 60 miles an hour, the bow of his machine always upon its compass line. But while he is flying, a southerly wind blowing at the rate of 20 miles an hour is pushing him sideways; and, unless he corrects this leeway, he will find himself after an hour’s flying, not at the point B, towards which he imagined he had been making, but at C, 20 miles north of the spot at which he had wished to alight. The wind, blowing at 20 miles an hour across his course, has pushed him these 20 miles to the north, although he has steered accurately eastward.

When flying above land, the making of leeway may be nothing more than an annoyance; but should the pilot be passing above the sea, between coasts many miles apart, this side sweep of the wind may be a peril. One of the grim tragedies of aviation is attributed to leeway in a wind. Leaving France on a flight to England, Mr. Cecil Grace was driven from his course by a wind which blew up Channel towards the North Sea. There was fog, too; and as the pilot was using an early type compass, it may have failed to register accurately. At all events, he never reached the English shore. Seen once while in flight—and this by a fishing-smack—he was lost in the mist, flew wide of his course, and passed out to the North Sea instead of towards the cliffs at Dover. From that day to this his fate has been a mystery, although it is true that not long after he vanished his flying cap and goggles were washed upon the beach near Ostend—mute but tragic witnesses to the ending of his flight. But of the airman’s body, or of the wreckage of his machine, nothing was ever found.

It is possible, with a modern-type compass, to make an allowance for leeway. The airman studies a gauge before he ascends, ascertaining the strength at which the wind is blowing. Then he sets a pointer upon his compass by which he may correct, even while passing through the air, the sideway thrust of the wind; that is to say, should he be flying to some point due east of his starting-point, as was assumed in Fig. 66, and should the wind—blowing from the south across his path—tend to force him towards the north, then he would set his pointer so that he was steering not due east, but to a point a certain number of miles south of east. In this way, with the wind driving him always north, he would arrive not at the imaginary destination towards which he steered, but at the real point due east which he desired to make. The drawback of the method may be this: should the pilot leave ground in a 10-mile-an-hour wind, and should the strength of this wind increase say to 20 miles an hour, his allowance for leeway would be insufficient; but against this may be set the fact that the airman, becoming aware probably, by the increased rolling of his machine, that the wind was tending to strengthen, would steer still wider of his goal. Compasses are being tested, also, which allow pilots to make an accurate and mechanical allowance, even while in flight, for risings or fallings of a side wind. There is one, a form of transparent compass, made so that the airman can look down through it, and see the ground passing away below. Selecting landmarks with his eye which are a little distance apart, he is able to note—by contrasting his compass-course with that his machine makes when in relation with these objects—just how much drift he should allow for. Then he alters his leeway indicator and makes another observation later on, should he think the wind has changed again.

Vital to the equipment of a pilot is his map. In the infancy of flying, when airmen first began to venture upon journeys between cities, they had neither maps nor compasses, and contented themselves as a rule with following a railway—the metals of which, gleaming below and appearing as though ruled across the country, provided an excellent guide. But soon, making longer flights and passing perhaps over districts where there were no railways, pilots found they needed a map; but not an ordinary map, such as a tourist upon the earth might use. Flying thousands of feet high, the airman’s view of the land is bird-like. The country stretches away on all sides below, apparently almost flat, and with its hills so dwarfed that they hardly catch the eye (see Plates XI and XII).

A river, or a sheet of water, is a conspicuous guide, and must figure plainly upon the airman’s map. Main roads, too, are clearly seen—stretching like white ribbons across the country. Railways also, and woods; while churches, chimneys, and isolated buildings may be seen from great distances when a voyager is in the air.

So the airman’s map is made up of landmarks that are likely to catch his eye, remembering always his point of view from above—and remembering also that as he rushes through the air at a speed faster than an express train, he needs to identify quickly any feature of the landscape below. A sketch showing what an airman’s map is like, will be seen in Fig. 67. Here we have railways, roads, rivers, lakes, and woods all made to show plainly, and with a large building or chimney indicated here and there. With such maps, and aided by a compass, a pilot will fly for hours without losing his way. When long flights are undertaken, and it would be inconvenient for an airman to change from one map section to another, he uses a narrow strip-map, mounted upon a couple of rollers, and fitted in a case with a transparent cover. As he passes across country he unrolls his map, section by section, so that the district he is traversing lies always before his eye.