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Divisions of Service. In the army and navy, aeroplanes are used both for offensive and defensive operations. They must carry out their own work and intentions and prevent hostile craft from carrying out theirs. In offensive operations the machines fly continuously over the enemy's country and attack every hostile craft sighted, thus creating a danger zone within the enemy's lines where no opposing machine can work without being threatened with an overwhelming attack. The offensive also includes bombing operations and the destruction of supply depots and transportation centers. Defensive aerial operation consists in driving out the enemy craft from our own lines, and in protecting working machines when on photographing or observation trips. With a powerful offensive there is of course little need for defense. The former method is a costly one, and is productive of severe material and personal losses.

At the present time there are eight principle functions performed by military aeroplanes:

1 Offensive operations against enemy machines.

2 Reconnaissance, observation, special missions.

3 Bombing supply centers, railways, etc.

4 Photography.

5 Spotting for the artillery.

6 Signalling for infantry operations.

7 Submarine hunting.

8 Patrol and barrage.

Fig. 1. Curtiss "Baby". Biplane Speed Scout. Equipped with 100 Horsepower Water Cooled Motor.

Probably the most important service of all is performed by machines under heading (1). If a successful offensive can be maintained over the enemy's lines he is unable to intelligently direct his artillery fire, and can obtain no information regarding reinforcements, or troop concentrations for an impending attack. With fighting aeroplanes clearing the way for our own observation machines and artillery spotters, the enemy is not only blinded, but is blocked in any attempt to attack or concentrate his forces. The fact that the French aerial offensive at Verdun was so efficiently and well maintained accounts for the failure of the heavy German artillery. Driven far back over their own lines, the German aviators were seldom able to observe the placing of the shells, and as a result their gunners were practically trusting to luck in reaching their target. An immediate and accurate bombardment always followed one of the very infrequent German air raids over the French lines. Whenever the French, partially abandoned their aerial offensive in favor of a defensive campaign, they soon lost their mastery of the air. As long as enemy machines can be kept back of their own lines, new trench systems can be constructed, transportation lines can be extended and ammunition dumps arranged, undertakings that would be highly precarious with enemy observation machines continually passing overhead.

Fig. 1. Italian "Pomilio" Two Seater Biplane. Courtesy "Flying."

To maintain an effective offensive places a tremendous strain on both the men and the machines, for though the aeroplanes do not penetrate far beyond the lines they usually meet with superior numbers, and in addition are continually in range of the anti-aircraft guns. In an attack over hostile country a slight mishap may cause the loss of a 'plane, for usually the distance from its base is so great as to prevent a gliding return. Over its own lines an engine failure is usually only a temporary inconvenience. Fighting aeroplanes, for the offensive, are small high powered machines generally of the single seater type, and are capable of high horizontal and climbing speeds. The armament consists of a machine gun of the Lewis type, and occasionally a few light bombs may be included in the equipment. As they do not carry out operations far to the rear of the enemy's lines they are provided with fuel for only two or three hours, and this reduced fuel load is necessary for the high speeds that must necessarily be attained. The area is limited to permit of quick maneuvers in attack and escape, and at the same time to reduce the head resistance and weight. The horizontal speed may run up to 150 miles per hour, with a climbing velocity that may exceed 1,000 feet per minute. Such machines are variously known as "Speed Scouts," "Chasers," or "Pursuit Type" (French "DeChasse"). At the beginning of the war the chasers were largely of the monoplane type, but at present the biplane is in almost exclusive use.

Fig. 2. Machine Gun Mounting on Morane Monoplane. Gun Fires Directly Through the Propeller Disc. The Deflecting Plate Attached to the Root of the Propeller Blade Protects the Propeller When in Line of Fire. Ammunition in This Gun Is Furnished in Straight Strips or "Clips."

The aeroplane employed for surveys of the enemy country and battle front (2) are of an entirely different type and are much larger and slower. These "Reconnaissance" machines are generally of the two-seater type, the personnel consisting of an observer and the pilot, although in some cases a third man is carried as an assistant to the observer, or to handle a machine gun against an attack. Since their speed is comparatively low, they are generally provided with an escort of chasers, especially when employed on distant missions, this escort repelling attacks while the observations are being made.

Fig. 2-a. Machine Gun Mounting on S. P. A. D. Biplane. Gun Is Rigidly Attached to Fuselage Top in Front of Pilot.

For accurate observation and mapping, the speed of an observation machine must be necessarily low, and as they are additionally burdened with a wireless set, an observer, a large fuel reserve, and other impedimenta, they have a comparatively great area and are therefore lacking in the maneuvering qualities of the chaser. The span will average about 40 feet, and the weight carried per horsepower is greatly in excess of that of the chaser. From a number of examples, the reconnaissance type will average from 16 to 18 pounds per horsepower, while the loading of the scout is from 8 to 12. This means that the former has comparatively little reserve power for rapid climbing. The present reconnaissance type is always armed, and must not be confused with the early machine by that name, which, in fact, was merely an enlarged training machine and had neither offensive nor defensive powers. The Observer acts as gunner, and is located at a point where he has the greatest possible range of vision, and where the angle of fire is as little obstructed as possible.

The radius of action, or the distance traveled per tank of fuel, is greater with the reconnaissance than with the chaser, present machines having a capacity of from 10 to 12 hours on a single filling at normal flight speed.

In bombing operations (3), the loading is very heavy and consequently a "Bomber" must be a weight lifter to the exclusion of all other qualities. Not only is the bomb load requirement severe, but the fuel load is also of great importance, since bombing is usually carried out at considerable distances from the base. Such machines may carry from three to six men. All this calls for a tremendous area and a large power plant. The Handley-Page "Giant," and the Caproni Triplane are examples of Allied machines of this type while the German "Gotha," used in the London air raids, is an equivalent enemy machine. As an example of the weight carrying capacity of a typical bomber, the Handley-Page has carried a test crew of 21 men, or a personnel load of 3,570 pounds. The total weight, fully loaded, has been given as 11,500 pounds with a power plant of 540 horsepower. The maximum speed is 90 miles per hour with a climbing velocity of about 330 feet per minute. Duration is about 5% hours at normal speed and full load.

Fig. 3. Handley-Page "Giant" Bombing Type Biplane. Courtesy "The Aeroplane."

Fig. 4. Curtiss Twin Motor Biplane-Type JN.

Bombing is of great importance, not only because of the damage caused to munition factories, transportation lines, store houses, etc., but also because of the moral effect on both the enemy troops and the civil population. A well-timed bombing raid will do more to disorganize an army than almost any other form of attack, and this is attended with a much less loss of life, and with less cost and equipment. Points in enemy territory that could be reached in no other way are readily attacked by bombing planes with all the disastrous effects of heavy artillery fire. The aeroplane is better adapted for this service than dirigibles of the Zeppelin type, for they require fewer men for their operation, and in addition cost less to operate and build.

Fig. 4a. Curtiss "Wireless" Speed Scouts (S-2). By an Ingenious Arrangement of the Interplane Struts There Is No Exposed Wire or Cable.

Bombing operations against well protected objectives are best made at night since there is less chance of loss through anti-aircraft gun fire, and also because of the difficulty that the defense machines have in locating the raiders. Even when well equipped with searchlights and listening stations, it is not the easiest thing in the world to pick out and hold the location of an attacking squadron, for the searchlights immediately betray themselves and can then be put out of action by fire from the invaders. With the searchlights out of commission, it is almost impossible for the defending chasers to locate and engage the raiders, even before the bombs have been dropped. After the bomb dropping has been accomplished (and with comparative accuracy because of the flares dropped by the bombing party), the raiders are lightened of a considerable portion of their load, and are correspondingly increased in their ability to climb and to evade the enemy chasers.

Fig. 5. Sopwith Speed Scout or "Chaser."

Fig. 6. Nieuport Biplane Scout with Machine Gun Pivoted Above the Upper Wing. This Gun Fires Above the Propeller.

Night flying in squadrons always introduces the danger of collision, and to minimize this danger, by decreasing the number of machines, the size and carrying capacity of the bombers has been continually increased. Again, bombing requires the steady platform that only a large machine can give, and for accuracy the span and area must be greater than that of the reconnaissance type. In night flying a large machine is safer to handle owing to its lower landing speed and ability to come to rest quickly after landing, and this is of the greatest importance when landing outside of the aerodrome. For daylight work at comparatively short distances the smaller bomb carrier used at the beginning of the war is probably preferable as it has better maneuvering qualities, and as the bombs are divided among a greater number of machines they are not so likely to be defeated before accomplishing their object. Because of their great size, these bombing aeroplanes are nearly always of the "twin motor" type with two, or even three, independent power plants. The use of a twin power plant is an added insurance against forced landings in hostile country, or over unsuitable ground, and even with one dead engine the machine can be flown home at a fair speed.

Fig. 8. Fokker Synchronized Machine Gun. The Gun Is Driven by the Motor in Such a Way That the Bullets Pass Between the Propeller Blades. "L’Aerophile."

"Spotting" for the guidance of the artillery is a duty usually performed by the reconnaissance type, or small bombing type, and is usually done under the escort of chasers. Their duty is to direct the battery as to the placing of shots. The ideal machine for such a purpose would be the direct lift type similar to a helicopter which could hover over one particular spot until its object had been accomplished in making measurements, and plotting enemy positions. Since no such machine is at present available, the duty must be performed by a low speed aeroplane, that is large enough to provide a fairly steady platform and at the same time has sufficient speed for a quick getaway. A dirigible has the necessary hovering qualities but lacks the speed necessary for avoiding attack from even the slowest of aeroplanes, and in addition is a magnificent target for anti-craft guns if kept at an altitude low enough for accurate observation. A large speed range is a desirable characteristic in such service.

Photography is of the greatest importance in reconnaissance, since the camera distinctly records objects on the terrain, so small and obscure that they may entirely escape the eye of the observer. Again, the photograph is a permanent record that may be studied at leisure in headquarters, or may be used in comparisons with photographs taken at an earlier date in the same territory. Thus changes in the disposition of enemy batteries, trenches, and troops can be quickly identified. With modern aeroplane photographic equipment, a vast territory may be investigated and mapped out by a single machine in a few hours. Camouflage has but few terrors for the camera, and the photographs often clearly reveal that which has been passed over time and time again by the observers. When sent out on a specific mission, the aeroplane returns the films in an amazingly short length of time, and within a few minutes they are developed and are ready for the inspection of the officers in charge. The analysis of these photographs has rapidly developed into a science well worthy of a Sherlock Holmes. Changes in the position of shadows, suspiciously sudden growths of underbrush, changes in the direction of paths, and fresh mounds of earth all have a definite meaning to the photographic expert.

Fig. 9. Types of Aeroplane Bombs. The Tail Surfaces Guide the Bomb So That It Strikes on the Firing Pin and at the Same Time "Safeties" the Bomb So That it Will Not Explode Until it Has Fallen for Some Distance. In Falling, the Tail Blades Rotate and Release the Firing Mechanism After the Bomb Has Fallen Clear of the Aeroplane. Courtesy of "Flying."

Fig. 9-a. Curtiss "JN" Twin Motor Biplane. Observer Is Seated in Front.

In the navy the aeroplane has proved of much value in scouting and particularly in defense against the submarine. Because of its great speed it has a daily radius of action many times that of a torpedo boat, and because of its altitude the effective range of vision is still further increased. At a fair height the observer can easily detect a submarine even when submerged to a considerable depth, a feat impossible when near the sea level. For disclosing the conditions existing in an enemy harbor the aeroplane is fully the equal of the dirigible since it can approach and retreat rapidly, and without much danger at comparatively low altitudes. While the dirigible can float indefinitely at one point, it must be done at an altitude that is safely out of range of the enemy guns, and this is usually at a point where observation is a difficult proposition. It does not take long to get the range of such a target as a hovering dirigible, yet at a much lower altitude it is difficult to handle naval anti-aircraft guns effectively against a speeding aeroplane. The smaller scouting seaplanes can report the position of a submarine to a torpedo boat or "sub-chaser," while the larger machines are perfectly capable of dealing with the submarine at first hand. On the large bombing type, a three-pounder gun and a number of large bombs can be carried, either of which would be sufficient for the purpose.

Fig. 10. Explosion of a German Aeroplane Bomb Near Mesopotamia. Courtesy of "Flying."

In land defense chasers and fighters are used for patrol, and to maintain a barrage against the entrance of enemy machines into our lines. The patrol machines work along the front line trenches, while the machines maintaining the barrage are generally arranged in two parallel lines back of the trenches, the first being about five miles, and the second about ten miles from the front. All three lines are generally placed between the enemy and the principal stations and railroad centers to insure protection from enemy bombers and reconnaissance machines. Should the first line patrol fail to keep raiders from crossing the first line trenches, they will have to pass through at least two more zones of organized fighting squadrons before reaching a vulnerable spot in our lines. The machines used for patrol and barrage are of the high speed and fast climbing chaser type. The response to an attack involves rapid climbing, and a high degree of maneuvering.

Fig. 11. Caproni Triplane with Three Independent Power Plants. The Motor in the Central Body Drives a Pusher Propeller, While the Other Power Plants Are Mounted in the Two Outer Bodies and Drive Tractor Screws. This is an Example of the Larger Bombing Aeroplanes. The Gun Is Mounted in the Front of the Center Body. Courtesy "The Aeroplane."

Except for the bombers and battle planes, the machine gun or "Mitraleuse" has been the only form of arm in common use on aeroplanes. These use ammunition approximating service rifle caliber and are furnished in bands, strips or drums according to the type of gun. With larger guns, the weight of the ammunition has been found excessive with all but the largest bombing machines, and the recoil of a large caliber gun has also been difficult to overcome. In a modern American aeroplane gun of large caliber the recoil has been reduced to almost a negligible degree, even up to the four-pounder size, by a system of balanced projectile reactions. This gun has met successful tests, but whether it has met with general adoption would be difficult to say at the present time. In Europe, large caliber aeroplane guns have been used on large "battle planes" or "gun planes" for shelling dirigibles, or in destroying searchlight stations in bombing raids. The battle planes are nearly always of the "Twin" type with the gun mounted in the front end of the fuselage.

Summary of Types. To sum up the types required in military operations, we have: (1) High speed "Chaser" or "Scout" (Single seater), (2) High speed "Chaser" (Two-seat type), (3) Reconnaissance type, (4) Bombing type, (5) Gun or Battle Planes. This does not include the training machines of the two place and "Penguin" types, but as these are simply unarmed modifications of the two place reconnaissance and single seat machine, respectively, we will not go into further details at this point regarding their construction.

The Chaser or Pursuit Type. The most important factors in the design of a chaser are speed and maneuvering ability. The speed must be at a maximum in both the horizontal and vertical directions, for climbing ability is fully of as much importance as horizontal speed. Second in importance is the maximum altitude or "Height of ceiling" to which the machine can ascend. This maximum "Ceiling" generally goes hand in hand with the climbing speed, since a fast climber generally has a correspondingly high maximum altitude. The combination of weight and head resistance must be such that the climb interferes as little as possible with the forward velocity.

De Havilland. V. Single Seat "Chaser" or "Speed Scout" with a Single Rigidly Mounted Machine Gun on Top of Hood (To Left). It will Be Noted That the Top Wing is Staggered Back Instead of Forward as in the Usual Type, Thus Allowing the Pilot to Look Directly Up and in Front of the Top Wing. Dimensions Are in Millimeters.

Great climbing ability means a large power reserve, hence the weight carried per horsepower is reduced to from 8 to 12 pounds on the fastest machines, against the 16 to 18 pounds carried on the larger and slower reconnaissance types. Strength must be sacrificed to meet these conditions, so that instead of having a safety factor of from 8 to 12 as in the larger machines, it is cut to about 5.5, or in other words, the strength is relatively only half that of the usual type of aeroplane. This great reduction in strength calls for careful handling, especially in landing, and also painstaking care in the design and choice of materials.

High speeds and maneuvering ability both call for small wing areas and short spans, the areas being so adjusted that the resistance is at a minimum at the highest speeds. The short spans have a minimum of exposed interplane bracing and thus indirectly reduce both the head resistance and the weight. Unfortunately, the most favorable areas at high speeds are too small for safe landing speeds. With a fixed area, the minimum landing speed is only a little less than one-half of the maximum flying speed, hence with a maximum of 150 miles per hour the minimum will probably be little less than 70 miles per hour. The most efficient wing sections, and the greatest refinement in the body design, bracing, and chassis are necessary at speeds of over 100 miles per hour. All other conditions being equal, the resistance varies as the square of the velocity, hence at 150 miles per hour, the resistance is 2.25 times that at 100 miles per hour.

The following table gives approximately the apportionment of the head resistance producing items in a typical speed scout or chaser.

Body (Fuselage)	68 per cent
Chassis, wheels, struts, etc.	15 per cent
Tail, rudder, fin, elevator	5 per cent
Wing structure, struts, wire, fittings.	12 per cent

The aerodynamic drag due to the lift of the wings is not included in the above, the useless or parasitic resistance alone being considered. It will be noted that the body causes by far the greater part of the resistance, and as a result, the body of the speed scout requires the most careful attention in regard to streamline form. Fortunately this is possible with the short stumpy body of the chaser, since a true streamline form approximates the average body dimensions of the scout. In the larger machines, the body resistance is not as great in proportion to the other items since there are more struts and stay wires, the chassis is larger, and the tail surfaces are of greater area. The chassis is the next largest item and is one of the most difficult items to reduce. It has been suggested by several people that the chassis could be stored away in the body while in flight, but this adds additional mechanism and weight, and any automatic mechanism for folding up the chassis members would likely prove unreliable.

Chaser Armament. A single seat chaser is provided with one or two machine guns mounted on top of the fuselage, and directly in front of the pilot, the length of the barrel being parallel with the fore and aft center line. They may either be fixed rigidly to the fuselage top, or so that they can be pointed up, and over the top of the upper wing. With the machine guns fixed rigidly to the body, as in the early chaser monoplanes used by Garros and Vedrines, it was necessary at all times to fire directly through the disc area swept out by the propeller.

Two plans were tried for preventing the propeller from being broken by the bullets. The first consisted of a device operated by the motor that stopped the gun whenever the propeller blade came within the path of the bullets. This early mechanism proved unreliable, since the frequent stopping, with the propellers running 1200 revolutions per minute, soon put the apparatus out of order. Soon after the failure of this method, designers mounted curved protective steel plates on the inner portions of the propeller blades at points where they were likely to be struck with bullets. According to calculations in probability and chance, only one bullet out of every eighteen will strike the protective plate on the propeller blade, and hence only one out of eighteen bullets will be wasted. This, however, was a makeshift, and on modern machines the gun is driven, or "Synchronized" with the motor so that the bullets pass between the blades.

Curtiss Biplane in Flight. Taken from Another Machine. Courtesy "Aerial Age."

Many modern single seat chasers have the gun pivoted to the top of the fuselage so that the pilot can fire above the top plane and to either side of the body. This does away with the difficulty of keeping the machine headed directly at the enemy when in action, a method that is imperative with the fixed type of gun. Two seater chasers are generally arranged so that the gunner is seated back of the pilot, and the gun is so pivoted and supported that it can be swung through a wide radius both toward the front and on either side. This freedom of gun action at least partly compensates for the slower maneuvering qualities of the two seater type, since the gun may be swung with the target through quite a range of field, and without changing the flight direction of the machine. A gun of this type is provided with stops which prevent the gunner from shooting into the outlying parts of his own machine. The gun mounting in many cases of two seater construction consists of a light circular track that runs around the edge of the cockpit opening. The gun standard runs on this track, and the gun is pivoted at the upper end of the standard so that the muzzle can be raised or lowered. The gun turns in a horizontal plane by sliding on the track, and can be followed around by the gunner who is seated in the center on a pivoted seat. With this mounting it is possible to guard against a rear attack, to shoot straight up, or nearly straight down over the sides of the fuselage.

In a few machines of the two seater type, two machine guns are provided, one pivoted gun in the rear, and one gun rigidly fastened to the fuselage in front of the pilot. It is very seldom that both guns can be brought into action at once unless engaged with a number of enemy machines, although the front gun is handy in pursuit, and at a time when the rear gun is ineffective because of the pilot in front of him. Even with the double equipment, the superior maneuvering qualities of the single seater makes matters more even than would commonly be supposed. An added advantage of the single seater is that it is smaller and therefore more difficult to hit.

English speed scouts have largely adopted the American Lewis gun. The cartridges in this gun are arranged radially in a circular drum, and are fed to the gun as the drum revolves. The drum is mounted on the barrel near the breech and is operated automatically by the successive explosions. This feeds the cartridges and rejects the empty shells without the attention of the pilot. It fires about 600 shots per minute. When one drum is exhausted, another drum of new cartridges can be quickly and easily inserted. The French use the belt system to a large extent. In this system the cartridges are attached side by side on a cotton web belt as in the older types of army machine guns. As in the Lewis gun, the cartridges are fed automatically by the recoil of the explosions, and the belt moves through the breech with a step by step movement until the ammunition is exhausted. This is not nearly as compact an arrangement as the Lewis gun, and is more difficult to pivot on account of the dangling belts.

On the right hand side of the Nieuport body there is a drum on which the belt with the loaded cartridges is wound. The empty end of the belt is wound on a drum at the left, this drum being provided with a spring to keep the belt taut. The empty cartridges are discharged through a tube that passes through the side of the body. On the 1916 Fokker the gun is of the Maxim type, and is immovably fastened above the engine cowl and slightly to the right. To fire the gun, the pilot presses down a small lever fastened to the control column, and from this lever the connecting Bowden wire closes the motor clutch and starts the gun. A cam is fixed to the motor shaft in relation to the propeller blades. When firing, the elevator control is locked fore and aft, while the lateral control movement is operated by the pilot's knees. Steering is by the action of his feet on the rudder bar. Thus the pilot can balance laterally, and steer with his hands free for the manipulation of the gun, but he cannot change his elevation.

Aeromarine Training Seaplane

Power Plant of the Chaser. In the smaller speed scouts, the motor is of the rotary air cooled type, the output ranging from 80 to 110 horsepower, but as the power demands increased the water-cooled motor came into use, and at the present time has found favor with a large number of builders. When the power exceeds about 120 horsepower it is difficult to thoroughly cool the rotary engine, and although the Gnome, Clerget and Le Rhone are extremely desirable on a chaser because of their light weight, they cannot be used profitably on the larger scouts. Up to the present time, the Nieuport and Sopwith use the Clerget and Le Rhone rotary motors, but the S. P. A. D. and several others have adopted the water-cooled type. Nearly all of the German chasers, such as the Roland and Albatros, are water-cooled. Such motors must weigh well below 3 pounds per horsepower if there is to be sufficient power reserve for fast climbing. The Curtiss scouts are also water-cooled, although the rating is only 100 horsepower. The French and German machines are very heavily powered, motors of 175 horsepower being very common, even on single seaters. The fuel capacity is very limited, probably not exceeding 2.5 to 3 hours in any case.

General Dimensions of Scouts. The following table will give a better idea of the principal characteristics of these machines. It gives the overall dimensions, power, speed, climb, etc. It will be noted that the Nieuport biplane scouts have a smaller lower chord (*). The speeds given are the sea level speeds since a great change in altitude affects the performance to a marked degree.

Reconnaissance Type Arrangement. These machines are almost invariably of the two seater type, and are equipped either with one machine gun for the observer, or with a rigidly fixed gun for the pilot and a pivoted gun at the rear for the observer. In the majority of cases the observer is seated in the rear cockpit (Tractor types), and at a point where he has a greater visual radius and field of fire. With the pusher type, the observer is, of course, seated in the extreme front of the body, where he has an extremely wide angle of vision. The pilot in the rear seat of the pusher is effectually screened from any gun action, either from the front, side or rear, as the propeller cuts off the field at the back and the observer and interplane bracing blocks the way at the front and sides. The observer's cock-pit is equipped with the signalling apparatus, photographic equipment, map boards, etc., as well as the ammunition for the gun. The pilot's compartment contains the navigating instruments and controls.

Armament. At the beginning of the war nearly all of the French two seaters were of the pusher type, this arrangement, of course, resulted in almost a completely dead angle of fire in the rear, and a front horizontal angle that was practically restricted to 160 degrees. Owing to the forward position of the gun the vertical angle was quite good, 230 degrees or even better. In the tractor two seater, with a single movable gun mounted "En barbette" at the rear, the horizontal angle is about 180 degrees, but the vertical angle is less than with the pusher type. When the rear gun is supplemented with a front rigidly mounted gun, there is some protection at the front, but the rigid gun is far from being as effective as the pivoted rear gun. The front gun of course fires through the propeller. This armament is used by the German machines "Aviatic," "Rumpler," "Albatros," and "L. V. G." The forward rigid gun is usually of the infantry type, while the movable rear gun is lighter. The latter is fed by drums, or rolled bands on spools, so that reloading can be performed in the wind stream.

With the two seater type used in reconnaissance, artillery spotting, or photography, the power is generally in the neighborhood of 220-260 horsepower, and the speed varies from 85 to 100 miles per hour. The area is approximately 400 to 480 square feet. A single engine is generally used.

General Dimensions and Speeds. Reconnaissance machines of various types and makes are listed in the following table. A pusher is indicated by (P) and a tractor by (T). The German aeroplanes (G), and the Allied aeroplanes (A), are both listed for comparison: It will be noted that several types of machines have been made by the same firms, and that in some cases the same machines have different power plants. The Albatros C-III has been furnished with both the 170 and 220 Mercedes motor. The Ago biplane has a tapering wing, and the chord width (*) given is taken at the body. While very recent machines cannot be described, because of certain restrictions, the horsepower of the latest two seaters will average about 240 horsepower. If the dates and power items are noted, it will be seen that the machines used in 1917 have much larger motors than those built in 1916. The weight per square foot of surface will average about 6.5 pounds. The loading per horsepower rarely exceeds 17.0 pounds.

Bombing Type Aeroplanes. These large aeroplanes are fitted with either two or three independent power plants. The German bombers are represented by the Gotha, A. E. G., Friedrichshafen, and Rumpler G, while the Allied bombers are the Caproni, Handley-Page, Farman, Voisin, etc. The speed is about that of the reconnaissance type, and will seat three or more men. The motors average 500 560 horsepower per power plant, and the wing area is usually well over 1,000 square feet. The small two seaters are generally equipped with two pivoted machine guns, while the three seaters have a third machine gun arranged so that it can be lowered and fired through a trap door in the bottom of the body. Defense may thus be had from the rear, or below. In some of the pusher types, a rapid fire gun of comparatively heavy caliber is mounted at the front of the body in place of the usual machine gun. This is usually the case with the sea planes used for submarine chasing.

In addition to bombing operations, these large machines are also used for the protection of "spotting" aeroplanes, or for the direct protection of the lines against land attacks. These heavily armed bombers are very difficult to attack, even for the smaller and more agile "Chasers," as they can fire from below as well as from the front, top, or sides. In the bombers which have only a single gun in the rear, the gunner is working at a disadvantage if his adversary forces him to continually raise and lower his gun from the top of the body to the lower trap door. This is very tiring to the rear gunner, and if the chaser's tactics are carried out for a sufficient length of time, it can wear out the gunner by continually rising and dropping at the tail of the bombing plane. In regard to the front gun, the twin motor type offers many of the advantages of the pusher, and as a whole, the twin arrangement will nearly double the field of fire of either the tractor or pusher.

The bombing planes must have a very large radius of action, particularly those that are used in night bombing operations. The Gothas in bombing London fly several hundred miles from their base, and recently a Handley-Page bombing plane flew from London to Constantinople, Turkey, making only a few stops on the way. Starting out from Hendon, England, the Handley-Page machine flew to Paris, down the Rhone valley to Lyons and Marseilles, and then to Pisa, and Rome (Italy), where they landed. From Rome the machine passed over Naples, over Oranto and then over the Albanian Alps to the base at Salonica. Making preparations at this base they flew the final stage of the trip to Constantinople, a distance of 250 miles over hostile country. The bombing of the Turkish capital was done at night after a flight of 2 1/2 hours from Salonica. When over the sea of Marmora, the ship "Goeben" was bombed, and in addition a hit was scored on the two submarines lying at her side. Four bombs struck the "Goeben" directly, from an altitude of 800 feet. Two more bombs were dropped on the German ship, "General," which was the headquarters of the German staff. Finally, after 30 minutes over the city of Constantinople, the Turkish War Office was the recipient of two more bombs. In the words of the Turkish communiqué this "Was not entirely destroyed." On its return to Salonica it was found that the machine had been struck by 26 shrapnel bullets. This disabled one of the power plants so that the greater part of the return journey was made on a single motor.

From London to Salonica five men were carried. In addition was their luggage, bedding, two tool boxes, spare parts equivalent in weight to one engine, and two 11'-6" spare propellers. Complete, the machine weighed over 6 tons, with a useful load of about 6,000 pounds. In crossing the Albanian Alps the machine frequently was at an altitude of 10,000 feet. The power plant consisted of two 275 horsepower Rolls-Royce motors, and even at this high altitude, and with the heavy loading, no trouble was experienced. During the bombing, only three men were carried, the remainder of the useful weight being made up of bombs and other ammunition. While this record will probably be beaten before this book goes to press, it will at least give an idea as to the requirements and capabilities of the bombing type aeroplane.

Military Training Machines. The military training machines used in the United States are generally of the two seater tractor type, similar in external appearance to the reconnaissance type machines already described. They are low powered, 90 to 125 horsepower, and will have an average span of 40'-0". The controls are in duplicate so that the student's controls move in unison with the instructor's.