How the fighting powers of modern machines are continually being increased
THE THICKENED CENTRE SECTION of the lower plane accommodates the bombs of the Handley Page Heyford Mark II long-range night bomber. Each bomb and rack is in a separate cell closed by spring doors. The bombs are fused and fired electrically. Three machine guns are carried, one in the nose and two aft of the wings—one above and one below the fuselage. The lower rear gun is carried in a retractable turret.
IT has frequently been predicted that those responsible for the equipment of air forces would follow the alleged example of naval architects and turn their attention from the aeroplane to its armament. There has, however, as yet been no definite concentration upon aeroplane armament, although the beginnings of such a concentration are in sight.
The aircraft itself is still capable of great advances and it is unlikely at present that the guns it carries will be given more than secondary attention. Yet the past few years, if they have seen no major changes, have seen several important armament improvements. Today there are a variety and an ingenuity in the armament arrangements of most first-line aeroplanes that these aeroplanes did not have a few years ago.
Probably the most important change is in the increasing use of large-calibre machine-guns of the Oerlikon type. The use of these guns, or “cannon”, as they are conveniently called, has spread on the Continent, and it is possible that in the near future a number of military machines will be fitted with them. The cannon are of 20 mm. or 37 mm. calibre and they fire shells weighing about 0·5 kilogram (about 1 lb.).
It is essential to distinguish between the large-calibre gun, as tried during the war of 1914-18, and the cannon in its modern form. The old guns were not automatic. Georges Guynemer, the great French fighting pilot, who mounted two machine guns in his Spad, changed them during a short period for a single 37 mm. cannon mounted on the engine. But it fired single shots and had to be reloaded by hand between them. Despite this serious disability, Guynemer was such a brilliant marksman that he succeeded in obtaining with this cannon at least one victory over a German machine. The modern cannon, though it may be mounted in the engine, when it is known as the motor-cannon, is a quick-firing, automatic gun resembling a machine-gun, except that it fires small explosive or incendiary shells. The rate of fire may be 400 rounds a minute.
The cannon has a high muzzle velocity of perhaps 880 metres (962 yards) a second. Thus the range at which a shot can be fired with only a small allowance is greatly increased — a matter of some importance in aerial combat.
When large-calibre guns were first tried in aircraft it was thought that the recoil might seriously damage the aircraft structure. To guard against this possibility, elaborate precautions were taken or low muzzle velocities were used. One precaution consisted of the use of small shot or sand for taking the recoil reaction. The gun fired its projectile out of one end and small shot or sand out of the other. The limitations of such a method were obvious. The first people to tackle the problem of recoil on a rational and a practical basis were the Hispano-Suiza Company. That company’s engineers anchored their large-calibre cannon to the engine, mounting it between the cylinder banks and causing it to shoot through a hole in the middle of the airscrew shaft. This shaft was high because the engine was of the geared type. The magazine was placed round the gun and carried 60 rounds. This method of mounting has had much success abroad and is in use in more
than one air force today. It is not at present used in the Royal Air Force. British aircraft makers, however, have used it successfully in machines intended for export.
The essential point about the motor-cannon is that the gun, being anchored to the engine, is in effect on a firm mounting, a mass weighing perhaps 450 kilograms (992 lb.). A high muzzle velocity can therefore be used without any risk of damage to the aeroplane.
Since the motor-cannon came into use, various other mountings have been tried. With modern methods of metal construction it is contended by some designers that a gun can be mounted to the aeroplane structure with perfect safety. These designers state that the structure will take the force of the recoil without damage and with sufficient firmness for the purpose of obtaining accurate shooting. Exactly how far the wing-mounted cannon or the fuselage-mounted cannon falls behind the engine-mounted cannon in accuracy is a matter which is still being argued by armament authorities. Both methods of mounting are used today for cannon. The practical difficulties have been overcome but it remains to be seen how far the cannon will encroach on the machine-gun’s province.
The fighting aeroplane must be considered first, because the cannon has not so far been used extensively in the bombing aeroplane. The single-seater fighting aeroplane relies on fire brought to bear in a forward direction by a fixed gun or guns. It does not normally have movable guns (see the chapter “Fighter Design”).
The cannon will thus fire forward in the line of flight. If there is more than one cannon they will all fire forward. Only two positions are therefore available to them, unless an attempt is made to synchronize them with the airscrew blades.
Clusters of Machine-Guns
The first position is in the wings, where the cannon are beyond the disk swept by the airscrew; the second position is in the engine, where they can fire through the airscrew shaft in the manner originated by the Hispano-Suiza Company. With the motor-cannon firing through the airscrew shaft there is room for only one cannon. With the wing position there is room for two or more. There is little doubt that weight of fire is of supreme importance in aerial battle. Each fighting machine must therefore be able to bring to bear the greatest possible weight of fire consistent with the maintenance of a good performance.
If one motor-cannon is used, several machine-guns will be fitted in wings and fuselage to supplement it. If two cannon are fitted they will be supplemented with fewer machine-guns. In modern fighter designs provision is made for four, six and eight machine-guns or, alternatively, for a cannon and six machine-guns or for two cannon and four machine-guns.
The pilot is able to use the cannon or pair of cannon for long-range work, and then, when there is in-fighting to be done, he can use the machine-guns. The arguments for and against the cannon are fairly clearly defined.
For the cannon it is argued that one shell, having struck the enemy machine, will do sufficient damage to bring it down, whereas an aeroplane can be pierced by large numbers of machine-gun bullets without being brought down or even interrupted in its task. Further, the cannon is able to strike at a longer range. It has been suggested that the effective range of a cannon may be about twice that of an ordinary small-calibre machine-gun.
For the machine-gun it is argued that the supreme consideration in aerial fighting is not range or weight of projectile, but speed of fire. Aerial fighting is so swift that the accuracy of aim required for useful work with a large-calibre gun is said to be unattainable, and so a gun is required which shoots at the highest possible rate, even with a small projectile.
Only a gunnery authority can attempt to decide between the two views, and among gunnery authorities there is a sharp cleavage of opinion. Yet the cannon is attracting more and more attention and it may be increasingly used in the future.
AN ARMOURED SHIELD to protect the gunner is provided on this gun turret for two-seater fighters. The gun turret is seen in position on a Hawker Demon aircraft. The gun turret is power-operated and can be raised, lowered or swung laterally by the movement of a handle.
For the moment most British fighting aeroplanes are fitted with clusters of machine-guns mounted in the fuselage and in the wings. The machine-guns in the fuselage are synchronized to fire through the field swept by the airscrew blades; the machine-guns in the wings are Beyond the field swept by the airscrew blades. A panel is arranged in the cockpit with appropriate switches or cocks which enable the pilot to select the gun or group of guns he wishes to fire. The firing is then done by means of the trigger on the top of the control column.
Sighting methods have improved during recent years. Single-seater fighters have for long used the Aldis tube sight, which is often erroneously known as a “telescopic” sight. This is merely an optical tube containing a glass with hair lines or circles on it. These lines or circles give some assistance in estimating the speed of the machine aimed at and in placing it correctly. Ring sights are popular because they are proof against the kinds of trouble which occasionally afflict tube sights. One of these troubles is fogging up.
Great pains have been taken in seeking to prevent the fogging up of tube sights, but to ensure reliability a standby ring and bead sight is often provided. The recent change in fighter design, whereby the pilot is entirely enclosed in his cockpit, has in some ways aided and in some ways hampered sight design. The latest devices, details of which may not yet be given, are an advance on previous sights and simplify the problem presented to the pilot.
Single-seater fighter armament, then, consists in clusters of guns, with or without cannon or motor-cannon among them, fixed firmly to the machine and arranged to fire directly in the line of flight. Weight of fire and speed of fire are obtained. The single-seater has only to place itself in the correct position for an instant to be able to pour out such a stream of projectiles that it could scarcely fail to bring down the biggest and heaviest bomber.
For larger, multi-seater machines, the armament problem is more complex than for the single-seater. Gunners’ cockpits are now becoming almost as complex as naval gun turrets, and almost every week the machinery and equipment in them are being increased.
In the smallest multi-seater machines there may be only one gunner’s cockpit. It will have to perform the same general functions as the many cockpits that are to be found in a larger machine. The cockpit must protect the gunner from the slipstream, and must contain an appropriate gun mounting with apparatus for swinging the gun and for sighting it. Again, the cockpit must give the gunner as good an outlook as possible in all directions.
A large amount of experimental work has been done recently with mechanically-operated gun turrets. Various sources of power have been tried for rotating the turret, including hydraulic power and electrical power. The reason that power is wanted is that the gun barrels must project, even if only for a short distance, from the turret and the slipstream, with a modern high-speed machine capable of flying at about 300 miles an hour, is sufficiently strong to prevent the turret from being moved easily by hand.
Turrets have been designed for hand use. In one which was applied to a Vickers aircraft, the turret was swung on a horizontal instead of on a vertical axis. The turret formed a sort of round cap on the front of the aeroplane. A slit enabled the guns to project and the gunner was seated on a small bicycle-saddle type of seat mounted on an arm projecting out into the centre of the turret from the main part of the fuselage.
It was possible for the gunner to swing this turret on its horizontal axis by hand alone. The design was generally abandoned and was replaced by turrets of a more advanced design. With turrets turning on a vertical axis, power is essential for swinging. The Frazer-Nash turret is in extensive use in the Royal Air Force. This turret provides for the mounting of a pair of machine-guns with a sight. The gunner is seated near the centre of the turret and operates it with two handles which resemble the twist grips of a motor cycle.
THE CONTAINERS BELOW THE WINGS of these Vickers Wellesley long-range bombers are streamline containers for the bombs. These aircraft are built entirely on the geodetic principle, which is described in the chapter “Fixed Wing Machines”. The aircraft has two guns, one fixed in the wing and operated by the pilot, and the other in the rear cockpit. The rear gun is mounted on a movable carriage.
A turret of this kind can be swung rapidly and without any physical exertion on the part of the gunner. It provides for accurate shooting and has been fitted to the nose, tail and midway positions in various multi-seater aircraft.
One variety of turret which is in use in the Royal Air Force and which is British-built is placed in the nose of the fuselage. This variety of turret comprises a cylinder with domed ends and covered almost entirely with transparent material. The turret is mounted at the base in a bearing carried from a bracket built into the front fuselage frame, and is further supported by a special roller
bearing that only partly surrounds the upper extremity of the cylindrical body.
Inside the turret is a pivoted gun arm, carrying a Lewis gun. The barrel of this gun projects through a vertical slot extending the whole depth of the turret and allowing the gun to be moved over the entire vertical range. The gunner sits in the turret on a seat supported on a hydraulic ram, which is connected to a pair of smaller rams coupled to the elevating gun arm. The two sets of rams and the leverage of the second are placed about the gun arm; the seat and gun arm move in opposite directions. Adjustment of the leverage of the rams, coupled to the gun arm, permits accurate control of the degree of balance between gunner and gun, to cover variations in the gunner’s weight.
LARGE-CALIBRE MACHINE-GUNS or “cannon” are the latest addition to aircraft armaments, although experiments with such guns have been made for a long time. This photograph illustrates the gun which was tried in 1933 on a Blackburn Perth flying boat. The gun fired 1½-lb. 37-mm. shells at the rate of 100 a minute. A modern aircraft cannon may fire as many as 400
rounds a minute. Modern shells are of 20 mm. Or 37mm., but the weight may be only about 1 lb.
A reversible pneumatic motor, geared to the turret, provides power to rotate the turret in its bearings, thereby training the gun in response to pressure exerted on the handle by the gunner as he follows his target through the gun sights. In this way rapid movement of the gun vertically and horizontally automatically follows the small muscular efforts applied by the gunner in the normal processes of training his weapon on the target. The gun projects through a slot three or four inches wide; little will give the gunner a clear view, yet be draught comes into the turret through it and the turret is warmed with hot air drawn from a heater muff on the engine exhaust pipes. Power to drive the turret is supplied by an engine-driven six-cylinder air compressor, which keeps a set of compressed air bottles charged to a pressure of 200 lb. per square inch. The turret can be rotated at the rate of about twelve revolutions a minute. This is fast enough for the gun to be trained on the fastest moving aeroplane.
One of the problems attending the use of gun turrets is that of providing for an emergency exit by the gunner. Considerable ingenuity has been exercised in devising schemes whereby he can leave quickly.
In the tail turret of one aircraft, part of the underside forms a cap which can be released quickly and through which the gunner can dive with a parachute. In another turret the top can be forced off.
Another problem, satisfactorily solved now, is that of producing a material suitable for use in gun turrets which give the gunner a clear view, yet be sufficiently strong to resist all the aerodynamic and other forces that may normally act against it. Transparencies of various kinds have been tried. A form of plastic is now available which has the necessary strength, gives a good view and can be so moulded that it is optically satisfactory. This point is of the utmost importance when sights are used from within the turret, so that the gunner is looking through the material of the turret at the machine at which he is directing his fire. Unless the optical properties are good there is distortion, causing inaccuracy of view and of aim.
Apart from the Lewis gun, the machine-guns used in the Royal Air Force are mainly of the Vickers or Browning type. The Vickers is not the same as the war period gun, but of another pattern, which was adopted by the Royal Air Force in 1936. The Browning is an American gun, but arrangements have been made for its manufacture in Great Britain.
A REVOLVING GUN TURRET in the nose of a special Bristol Bombay bomber transport monoplane. A second enclosed gun turret is provided in the tail of the machine. For bombing flights a crew of four is carried in the Bristol Bombay, and internal storage is provided for the bombs. The crew consists of pilot, navigator-bomber, radio operator and gunner.
A machine-gun is operated by two forces. These forces are the explosion of the charge in the cartridge which forces the recoiling parts backwards, and a strong spring which produces the opposite movement.
The bullets are carried in 250-round belts of the disintegrating link type, the cartridges themselves holding link to link. Rates of fire of over 1,000 rounds a minute are obtainable with machine-guns.
Bomb sizes range upwards from 8-lb. practice bombs, but the mainstay of bombing armament consists of the 112-lb. and the 500-lb. Bombs.
Bombs were formerly carried on open racks under wings and fuselage. Modern bombers can carry the bombs internally. The racks consist of a single attachment at the point of balance of the bomb. The bomb carries a small eyelet; through this goes the pin which holds the bomb’s weight. There are steadying arms in front and behind to keep the bomb quite still. Fins are used at the tail of the bomb to assist steady flight when the bomb has been launched. There is a safety device, which often takes the form of a small spinner, which unwinds itself as the bomb is falling. The bombs will not explode until the spinner has detached itself. A bomb should be “safe” until it has been released and has fallen a predetermined distance from the aircraft.
When a bomber takes off with full load every possible precaution has to be taken to see that, if it is forced to land for any reason, it can do so without risks other than those attaching to a normal forced landing.
Methods of releasing the bombs have varied, but most of those now used in the Royal Air Force include electrical circuits. In some aircraft, release is electric in the first instance, but at the bomb rack, where the pin for holding the bomb is situated, there is a device holding a cartridge. When the bomb aimer closes the appropriate electric circuit, the cartridge is fired and a plunger forces out the pin which holds the bomb. This system is used so that the release of the heavy bomb may be as nearly instantaneous as possible.
There are other forms of bomb release which use solenoids, or electrically activated magnets, for withdrawing the holding pins. In all instances, the action by the bomb aimer is merely that of pressing a button. He has previously selected the bomb, or group of bombs, that he wishes to fire and fused them with other switches. He can fire one bomb at a time or salvos of bombs.
Bomb aiming is taught in the Royal Air Force by a “teacher” which uses an image moving on the floor of a shed. The image represents a patch of ground and is formed by a photographic plate, a lens and a source of light. The image can be made to move so as to give the effects of drift and height. With standard types of Royal Air Force bomb sights, the pupils are able to practise bomb aiming and it is possible to assess the accuracy of their work. Future armament developments will almost certainly centre in guns of larger calibre than those hitherto in use.
TORPEDO-CARRYING AIRCRAFT of the Vickers Vildebeest type. The forward gun, which is synchronized to fire through the propeller, can be seen on the side of the fuselage. The pilot’s sights are on top of the fuselage where they are in line with his windscreen. There is a movable gun provided in the rear cockpit for the observer.