NAVAL AIRSHIPS.--THE RIGIDS--RIGID AIRSHIP N

The responsibility for the development the Rigid airship having been allotted to the Navy, with this object in view, in the years 1908 and 1909 a design was prepared by Messrs. Vickers Ltd., in conjunction with certain naval officers, for a purely experimental airship which should be as cheap as possible. The ship was to be known as Naval Airship N, and though popularly called the Mayfly, this title was in no way official. In design the following main objects were aimed at:

1. The airship was to be capable of carrying out the duties of an
aerial scout.

2. She was to be able to maintain a speed of 40 knots for
twenty-four hours, if possible.

3. She was to be so designed that mooring to a mast on the water
was to be feasible, to enable her to be independent of her
shed except for docking purposes, as in the case with surface
vessels.

4. She was to be fitted with wireless telegraphy.

5. Arrangements were to be made for the accommodation of the crew
in reasonable comfort.

6. She was to be capable of ascending to a height of not less
than 1,500 feet.

These conditions rendered it necessary that the airship should be of greater dimensions than any built at the time, together with larger horse-power, etc.

These stipulations having been settled by the Admiralty, the Admiralty officials, in conjunction with Messrs. Vickers Ltd., determined the size, shape, and materials for the airship required. The length of the ship was fixed at approximately 500 feet, with a diameter of 48 feet. Various shapes were considered, and the one adopted was that recommended by an American professor named Zahm. In this shape, a great proportion of the longitudinal huff framework is parallel sided with curved bow and stern portions, the radius of these curved portions being, in the case of the bow, twice the diameter of the hull, and in the case of the stern nine times the same diameter. Experiments proved that the resistance of a ship of this shape was only two-fifths of the resistance of a ship of the same dimensions, having the 1 1/2 calibre bow and stern of the Zeppelin airships at that time constructed.

A considerable difference of opinion existed as to the material to be chosen for the construction of the hull. Bamboo, wood, aluminium, or one of its alloys, were all considered. The first was rejected as unreliable. The second would have been much stronger than aluminium, and was urged by Messrs. Vickers. The Admiralty, however, considered that there was a certainty of better alloys being produced, and as the ship was regarded as an experiment and its value would be largely negatived if later ships were constructed of a totally different material, aluminium or an alloy was selected. The various alloys then in existence showed little advantage over the pure metal, so pure aluminium was specified and ordered. This metal was expected to have a strength of ten tons per square inch, but that which arrived was found to be very unreliable, and many sections had, on test, only half the strength required. The aluminium wire intended for the mesh wiring of the framework was also found to be extremely brittle. A section of the framework was, however, erected, and also one of wood, as a test for providing comparisons. In the tests, the wooden sections proved, beyond all comparison, the better, but the Admiralty persisted in their decision to adopt the metal.

Towards the end of 1909 a new aluminium alloy was discovered, known as duralumin. Tests were made which proved that this new metal possessed a strength of twenty-five tons per square inch, which was over twice as strong as the nominal strength of aluminium, and in practice was really five times stronger. The specific gravity of the new metal varied from 2.75 to 2.86, as opposed to the 2.56 of aluminium. As the weights were not much different it was possible to double the strength of the ship and save one ton in weight. Duralumin was therefore at once adopted.

The hull structure was composed of twelve longitudinal duralumin girders which ran fore and aft the length of the ship and followed the external shape. The girders were secured to a steel nose-piece at the bow and a pointed stern-piece aft. These girders, built of duralumin sections, were additionally braced wherever the greatest weights occurred. To support these girders in a thwartship direction a series of transverse frames were placed at 12 feet 6 inches centres throughout the length of the ship, and formed, when viewed cross-sectionally, a universal polygon of twelve sides. For bracing purposes mesh wiring stiffened each bay longitudinally, so formed by the junction of the running girder and the transverse frames, while the transverse frames between the gasbags were stiffened with radial wiring which formed structure similar to a wheel with its spokes. The frames where the gondolas occurred were strengthened to take the addition weight, while the longitudinals were also stiffened at the bow and stern.

Communication was provided between the gondolas by means of an external keel which was suspended from extra keel longitudinals. In this design the keel was provided for accommodation purposes only, and in no way increased the structural stability of the ship as in N and later ships. This keel, triangular in section, widened out amidships to form a space for a cabin and the wireless compartment. The fins and rudders, which were adopted, were based entirely on submarine experience, and the Zeppelin method was ignored. The fins were fitted at the stern of the ship only, and comprised port and starboard horizontal fins, which followed approximately the shape of the hull, and an upper and lower vertical fin. Attached to these fins were box rudders and elevators, instead of the balanced rudders first proposed. Auxiliary rudders were also fitted in case of a breakdown of the main steering gear abaft the after gondola. Elevators and rudders were controlled from the forward gondola and the auxiliary rudders from the after gondola.

The gasbags were seventeen in number and were twelve-sided in section, giving approximately a volume of 663,000 cubic feet when completely full. Continental fabric, as in use on the Zeppelin airships, was adopted, although the original intention was to use gold-beater’s skin, but this was abandoned owing to shortage of material. These bags were fitted with the Parseval type of valve, which is situated at the top, contrary to the current Zeppelin practice, which had automatic valves at the bottom of the bags, and hand-operated valves on the top of a few bags for control purposes. Nets were laced to the framework to prevent the bags bulging through the girders.

The whole exterior of the hull was fitted with an outer cover; Zeppelin at this time used a plain light rubber-proofed fabric, but this was not considered suitable for a ship which was required to be moored in the open, as in wet weather the material would get saturated and water-logged. Various experiments were carried out with cotton, silk and ramie, and, as a result, silk treated with Ioco was finally selected. This cover was laced with cords to the girder work, and cover-strips rendered the whole impervious to wet. Fire-proofed fabric was fitted in wake of the gondolas for safety from the heat of the engines.

Two gondolas, each comprising a control compartment and engine-room, were suspended from the main framework of the hull. They were shaped to afford the least resistance possible to the air, and were made of Honduras mahogany, three-ply where the ballast tanks occurred, and two-ply elsewhere. The plies were sewn together with copper wire. The gondolas were designed to have sufficient strength to withstand the strain of alighting on the water. They were suspended from the hull by wooden struts streamline in shape, and fitted with internal steel-wire ropes; additional wire suspensions were also fitted to distribute the load over a greater length of the ship. The engines were carried in the gondolas on four hollow wooden struts, also fitted internally with wire. The wires were intended to support the gondolas in the event of the struts being broken in making a heavy landing.

Two engines were mounted, one in each gondola, the type used being the 8-cylinder vertical water-cooled Wolseley developing a horse-power of 160. The forward engine drove two wing propellers through the medium of bevel gearing, while the after engine drove a single large propeller aft through 4 gear box to reduce the propeller revolutions to half that of the engine. The estimated speed of the ship was calculated to be 42 miles per hour, petrol was carried in tanks, fitted in the keel, and the water ballast tanks were placed close to the keel and connected together by means of a pipe.

N was completed in May, 1911. She had been built at Barrow in a shed erected on the edge of Cavendish Dock. Arrangements were made that she should be towed out of the shed to test her efficiency at a mooring post which had been prepared in the middle of the dock. She was launched on May 22nd in a flat calm and was warped out of the shed and hauled to the post where she was secured without incident. The ship rode at the mooring post in a steady wind, which at one time increased to 36 miles per hour, until the afternoon of May 25th, and sustained no damage whatever. Various engine trials were carried out, but no attempt was made to fly, as owing to various reasons the ship was short of lift. Valuable information was, however, gained in handling the ship, and much was learnt of her behaviour at the mast. More trouble was experienced in getting her back into the shed, but she was eventually housed without sustaining any damage of importance.

Owing to the lack of disposable lift, the bags were deflated and various modifications were carried out to lighten the ship, of which the principal were the removal of the keel and cabin entirely, and the removal of the water-trimming services. Other minor alterations were made which gave the ship, on completion, a disposable lift of 3.21 tons. The transverse frames between the gasbags were strengthened, and a number of broken wires were replaced.

On September 22nd the ship was again completed, and on the 24th she was again to be taken out and tested at the mooring post. Unfortunately, while being hauled across the dock, the framework of the ship collapsed, and she was got back into the shed the same day.

Examination showed that it was hopeless to attempt to reconstruct her, and she was broken up at a later date. The failure of this ship was a most regrettable incident, and increased the prejudice against the rigid airship to such an extent that for some time the Navy refused to entertain any idea of attempting a second experiment.

RIGID AIRSHIP N

Rigid Airship N having met with such a calamitous end, the authorities became rather dubious as to the wisdom of continuing such costly experiments. Most unfortunately, as the future showed and as was the opinion of many at the time, rigid construction in the following year 1912 was ordered to be discontinued. This decision coincided with the disbanding of the Naval Air Service, and for a time rigid airships in this country were consigned to the limbo of forgetfulness. After the Naval Air Service had been reconstituted, the success which attended the Zeppelin airships in Germany could no longer be overlooked, and it was decided to make another attempt to build a rigid airship in conformity with existing Zeppelin construction. The first proposals were put forward in 1913, and, finally, after eleven months delay, the contract was signed. This airship, it has been seen, was designated N.

N experienced numerous vicissitudes, during the process of design and later when construction was in progress. The contract having been signed in March, 1914, work on the ship was suspended in the following February, and was not recommenced until July of the same year. From that date onwards construction was carried forward; but so many alterations were made that it was fully eighteen months before the ship was completed and finally accepted by the Admiralty.

The ship as designed was intended “to be generally in conformity with existing Zeppelin construction,” with the following main requirements stipulated for in the specification:

1. She was to attain a speed of at least 45 miles per hour at the
full power of the engines.

2. A minimum disposable lift of five tons was to be available for
movable weights.

3. She was to be capable of rising to a height of 2,000 feet
during flight.

The design of this ship was prepared by Messrs. Vickers, Ltd., and as it was considered likely that owing to inexperience the ship would probably be roughly handled and that heavy landings might be made, it was considered that the keel structure and also the cars should be made very strong in case of accidents occurring. This, while materially increasing the strength of the ship, added to its weight, and coupled with the fact that modifications were made in the design, rendered the lift somewhat disappointing. The hull structure was of the “Zahm” shape as in N, a considerable portion being parallel sided, while in transverse section it formed a 17-sided polygon. In length it was 526 feet with a maximum diameter of 53 feet. The hull framework was composed of triangular duralumin girders, both in the longitudinal and transverse frames, while the bracing was carried out by means of high tensile steel wires and duralumin tubes. Attached to the hull was a V-shaped keel composed of tubes with suitable wire bracings, and in it a greater part of the strength of the structure lay. It was designed to withstand the vertical forces and bending moments which resulted from the lift given by the gasbags and the weights of the car and the cabin. The keel also provided the walking way from end to end of the ship, and amidships was widened out to form a cabin and wireless compartment.

The wiring of the transverse frames was radial and performed similar functions to the spokes of a bicycle wheel. These wires could be tightened up at the centre at a steel ring through which they were threaded and secured by nuts.

In addition to the radial wires were the lift wires, which were led to the two points on the transverse frames which were attached to the keel; on the inflation of the gasbags, the bags themselves pressed upon the longitudinal girders on the top of the ship, which pressure was transferred to the transverse frames and thence by means of the several lift wires to the keel. In this way all the stresses set up by the gas were brought finally to the keel in which we have already said lay the main strength of the ship.

The hull was divided by the transverse frames into seventeen compartments each containing a single gasbag. The bags were composed of rubber-proofed fabric lined with gold-beater’s skin to reduce permeability, and when completely full gave a total volume of 890,000 cubic feet. Two types of valve were fitted to each bag, one the Parseval type of valve with the pressure cone as fitted in N, the other automatic but also controlled by hand.

To distribute the pressure evenly throughout the upper longitudinal frames, and also to prevent the gasbags bulging between the girders, nets were fitted throughout the whole structure of the hull.

The whole exterior of the ship was fitted with an outer cover, to protect the gasbags and hull framework from weather and to render the outer surface of the ship symmetrical and reduce “skin friction” and resistance to the air to a minimum. To enable this cover to be easily removed it was made in two sections, a port and starboard side for each gasbag. The covers were laced to the hull framework and the connections were covered over with sealing strips to render the whole weathertight.

The system of fins for stabilizing purposes on N were two vertical and horizontal. The vertical fin was composed of two parts, one above and the other below the centre line of the ship.

They were constructed of a framework of duralumin girders, covered over with fabric. The fins were attached on one edge to the hull structure and wire braced from the other edge to various positions on the hull. The horizontal fins were of similar design and attached in a like manner to the hull. Triplane rudders and biplane elevators of the box type were fitted in accordance with the German practice of the time. Auxiliary biplane rudders were fitted originally abaft the after car, but during the first two trial flights they proved so very unsatisfactory that it was decided to remove them.

Two cars or gondolas were provided to act as navigating compartments and a housing for the engines, and in design were calculated to offer the least amount of head resistance to the wind. The cars were composed of duralumin girders, which formed a flooring, a main girder running the full length of the car with a series of transverse girders spaced in accordance with the main loads. From each of these transverse girders vertical standards with a connecting piece on top were taken and the whole exterior was covered with duralumin plating. The cars were suspended in the following manner. Two steel tubes fitting into a junction piece at each end were bolted to brackets at the floor level at each end of the transverse girders. They met at an apex above the roof level and were connected to the tubing of the keel. In addition, to distribute the weight and prevent the cars from rocking, steel wire suspensions were led to certain fixed points in the hull.

Each car was divided into two parts by a bulkhead, the forward portion being the control compartment in which were disposed all instruments, valve and ballast controls, and all the steering and elevating arrangements. Engine-room telegraphs, voice pipes and telephones were fitted up for communication from one part of the ship to the other. The keel could be reached by a ladder from each car, thus providing with the climbing shaft through the hull access to all parts of the ship.

The original engine equipment of N was composed of four Wolseley-Maybach engines of 180 horse-power each, two being installed in the forward car and two in the after car. As the ship was deficient in lift after the initial flight trials had been carried out, it was decided to remove the two engines from the after car and replace them with a single engine of 250 horse-power; secondly, to remove the swivelling propeller gear from the after car and substitute one directly-driven propeller astern of the car. This as anticipated reduced the weight very considerably and in no way lessened the speed of the ship.

The forward engines drove two four-bladed swivelling propellers through gear boxes and transmission shafts, the whole system being somewhat complicated, and was opposed to the Zeppelin practice at the time which employed fixed propellers.

The after engine drove a large two-bladed propeller direct off the main shaft.

The petrol and water ballast were carried in tanks situated in the keel and the oil was carried in tanks beneath the floors of the cars.

The wireless cabin was situated as before mentioned in a cabin in the keel of the ship, and the plant comprised a main transmitter, an auxiliary transmitter and receiver and the necessary aerial for radiating and receiving.

N was inflated in the closing days of 1916, and the disposal lift was found to be 2.1 tons under the specification conditions, namely, barometer 29.5 inches and temperature 55 degrees Fahrenheit. The contract requirements had been dropped to 3.1 tons, which showed that the ship was short by one ton of the lift demanded. The flight trials were, however, carried out, which showed that the ship had a speed of about 42 1/2 miles per hour.

The alterations previously mentioned were afterwards made, the bags of the ship were changed and another lift and trim trial was held in March, 1917, when it was found that these had had the satisfactory result of increasing the disposable lift to 3.8 tons or .7 ton above the contract requirements, and with the bags 100 per cent full gave a total disposable lift of 5.1 tons.

Additional trials were then carried out, which showed that the speed of the ship had not been impaired.

For reference purposes the performances of the ship are tabulated below.

Speed:
Full            45 miles per hour
Normal   = 2/3  38    "  "  "
Cruising = 1/3  32    "  "  "

Endurance:
Full     18 hours =   800 miles
Normal   26   "   = 1,000  "
Cruising 50   "   = 1,600  "

N having finished her trials was accepted by the Admiralty in Ma, and left Barrow, where she had been built, for a patrol station.

In many ways she was an excellent ship, for it must be remembered that when completed she was some years out-of-date judged by Zeppelin standards. Apart from the patrol and convoy work which she accomplished, she proved simply invaluable for the training of officers and men selected to be the crews of future rigid airships. Many of these received their initial training in her, and there were few officers or men in the airship service who were not filled with regret when orders were issued that she was to be broken up. The general feeling was that she should have been preserved as a lasting exhibition of the infancy of the airship service, but unfortunately rigid airships occupy so much space that there is no museum in the country which could have accommodated her. So she passed, and, except for minor trophies, remains merely a recollection.

RIGID AIRSHIP N CLASS

After the decision had been made in 1915 that work on N should be restarted, the Admiralty determined that a programme of rigid airships should be embarked upon, and design was commenced.

Several ships of the same class were, ordered, and the type was to be known as the 23 class. Progress on these ships, although slow, was more rapid than had been the case with N, and by the end of 1917 three were completed and a fourth was rapidly approaching that state.

The specification, always ambitious, laid down the following main stipulations.

(1) The ship is to attain a speed of at least 55 miles per hour
for the main power of the engines.

(2) A minimum of 8 tons is to be available for disposable weights
when full.

(3) The ship must be capable of rising at an average rate of not
less than 1,000 feet per minute, through a height of 3,
feet starting from nearly sea level.

As will be seen later this class of ship, although marking a certain advance on N both as regards workmanship and design, proved on the whole somewhat disappointing, and it became more evident every day that we had allowed the Germans to obtain such a start in the race of airship construction as we could ill afford to concede.

We may here state that all of the ships of this class which had been ordered were not completed, the later numbers being modified into what was known as the 23 X class; four in all of the 23 class were built, of which two Nos. 23 and 26 were built by Messrs. Vickers, Ltd., at Barrow, N by Messrs. Wm. Beardmore and Co., at Glasgow, and N by Messrs. Armstrong, Whitworth and Co., at Selby, Yorkshire.

In many respects the closest similarity of design exists between N and N, especially in the hull, but it will be of interest to mention the salient differences between the two ships.

The length of the hull, which in N was 520 feet, was increased in N to 535 feet, and the number of gasbags from seventeen to eighteen. This gave a total volume of 997,500 cubic feet compared with 890,000 cubic feet in N, with a disposable lift under specification conditions of 5.7 tons as opposed to 3.8 tons.

The longitudinal shape of N is a modified form of “Zahm” shape, the radius of the bow portion being twice the diameter of the parallel portion, while the stern radius is three times the same diameter.

In design the hull framework is almost a repetition of N, particularly in the parallel portion, the same longitudinal and transverse frames dividing the hull into compartments, with tubes completely encircling the section between each main transverse frame. The system of wiring the hull is precisely the same in both the ships, and nets are employed in the same way.

The triangular section of keel is adhered to, but its functions in N are somewhat different. In N it was intended to be sufficiently strong to support all the main vertical bending moments and shearing forces, but in N it was primarily intended to support the distributed weights of water ballast, petrol tanks, etc., between the main transverse frames. Unlike N, the keel is attached to the main transverse frames only. The cabin and wireless cabin are disposed in the keel in the same manner, and it also furnishes a walking way for the total length of the ship.

The stabilizing fins, both vertical and horizontal, are similar to those attached to N, but the system of rudders and elevators is totally different. In place of the box rudders and elevators in N, single balanced rudders and elevators are attached to the fins; they have their bearing on the outboard side on the external girders of the fins, which are extended for the purpose. The elevators and rudders are composed of a duralumin framework, stiffened by a kingpost on either side with bracing wires.

The bags, eighteen in number, are made of rubber-proofed fabric lined with gold-beater’s skin. It is interesting to note that the number of skins used for the bags of a ship of this class is approximately 350,000. The system of valves is entirely different from that in N. The Parseval type of valve with the pressure cone at the bottom of the bag is omitted, and in the place of the two top valves in the former ship are a side valve of the Zeppelin type entirely automatic and a top valve entirely hand controlled. The side valve is set to blow off at a pressure of from 3 to 5 millimetres. The outer cover was fitted in the same manner as in N. Two cars or gondolas, one forward, the other aft, each carry one engine provided with swivelling propellers and gears. They are enclosed with sides and a fireproof roof, and are divided into two compartments, one the navigating compartment, the other the engine room. The cars are in all respects very similar to those of N, and are suspended from the hull in a similar manner. The remaining two engines are carried in a small streamline car situated amidships, which has just sufficient room in it for the mechanics to attend to them. Originally this car was open at the top, but it was found that the engineers suffered from exposure, and it was afterwards roofed in.

The engine arrangements in this ship were totally different to those of N, four 250 horse-power Rolls Royce engines being installed in the following order. Single engines are fitted in both the forward and after cars, each driving two swivelling four-bladed propellers. In the centre car two similar engines are placed transversely, which drive single fixed propellers mounted on steel tube outriggers through suitable gearing.

The engines are the standard 12 cylinder V-type Rolls Royce which will develop over 300 brake horse-power at full throttle opening.

The engine is water cooled, and in the case of those in the forward and after cars the original system consisted of an internal radiator supplied by an auxiliary water tank carried in the keel. It was found on the flight trials that the cooling was insufficient, and external radiators were fitted, the internal radiator and fan being removed. In the case of the centre car no alteration was necessary, as external radiators were fitted in the first instance.

The engines are supported by two steel tubes held by four brackets bolted to the crank case, these being carried by twelve duralumin tubes bolted to the bearers and transverse frames of the car respectively. The drive from the engine is transmitted through a universal joint to a short longitudinal shaft, running on ball bearings. This shaft gears into two transverse shafts, which drive the propellers through the medium of a gear box to the propeller shafts, making five shafts in all.

The engines in the centre car being placed transversely the transmission is more direct, the engines driving the propellers through two gear wheels only. The propeller gear box is supported by steel tube outriggers attached by brackets to the framework of the car. The petrol is carried in a series of tanks situated beneath the keel walking way, and are interconnected so that any tank either forward or aft can supply any engine, by this means affording assistance for the trimming of the ship.

Four-bladed propellers are used throughout the ship.

Water ballast is carried in fabric bags also situated beneath the keel walking way, and a certain amount is also carried beneath the floor of the car.

Engine-room telegraphs, swivelling propeller telegraphs, speaking tubes and telephones, with a lighting set for the illumination of the cars and keel, were all fitted in accordance with the practice standard in all rigid airships.

The lift and trim trials taken before the initial flight trials showed that the ship possessed a disposable lift under standard conditions of 5.7 tons. The original disposable lift demanded by the specification was 3 tons but this was reduced by 2 tons owing to the machinery weights being 2 tons in excess of the estimate. Since then these weights had been increased by another half-ton, making a total of 2 1/2 tons over the original estimate. It was evident that with so small a margin of lift these ships would never be of real use, and it was decided to remove various weights to increase the lift and to substitute a wing car of a similar type to those manufactured for the R 33 class for the heavy after car at present in use.

R 23 carried out her trials without the alteration to the car, which was effected at a later date, and the same procedure was adopted with R 24 and R 25. In the case of R 26, however, she had not reached the same stage of completion as the other two ships, and the alterations proposed for them were embodied in her during construction. The gasbags were of lighter composition, all cabin furniture was omitted and the wing car was fitted in place of the original after car. This wing car is of streamline shape with a rounded bow and tapered stern. The lower portion is plated with duralumin sheets and the upper part is covered with canvas attached to light wooden battens to give the necessary shape. This effected a very considerable reduction in weight. The original 250 horse-power Rolls Royce engine was installed, now driving a single large two-bladed propeller astern. A test having been taken, it was found that the disposable lift under standard conditions was 6.28 tons. It was therefore decided that all the ships of the class should be modified to this design when circumstances permitted. Speed trials were carried out under various conditions of running, when it was found that the ship possessed a speed of 54 1/4 miles per hour with the engines running full out.

To summarize the performances of these ships as we did in the case of N, we find:

Speed:
Full               54 miles per hour
Normal   =2/3      48   "  "  "
Cruising =1/3      33   "  "  "

Endurance:
Full       18 hours = 1,000 miles
Normal     26   "   = 1,250  "
Cruising   50   "   = 1,900  "

The production of the rigid airship during the war was always surrounded with a cloak of impenetrable mystery. Few people, except those employed on their construction or who happened to live in the immediate vicinity of where they were built, even knew of their existence, and such ignorance prevailed concerning airships of every description that the man in the street hailed a small non-rigid as “the British Zeppelin” or admired the appearance of R 23 as “the Silver Queen.” The authorities no doubt knew their own business in fostering this ignorance, although for many reasons it was unfortunate that public interest was not stimulated to a greater degree. In the summer months of 1918, however, they relented to a certain extent, and R 23 and one of her sister ships were permitted to make several flights over London to the intense delight of thousands of its inhabitants, and a certain amount of descriptive matter appeared in the Press.

From that time onwards these large airships have completely captured the popular imagination, and many absurd rumours and exaggerations have been circulated regarding their capabilities. It has been gravely stated that these airships could accomplish the circuit of the globe and perform other feats of the imagination. It must be confessed that their merits do not warrant these extravagant assertions. The fact remains, however, that R 23 and her sister ship R 26 have each carried out patrols of upwards of 40 hours duration and that, similarly to N, they have proved of the greatest value for training airship crews and providing experience and data for the building programme of the future. At the present time highly interesting experiments are being carried out with them to determine the most efficient system of mooring in the open, which will be discussed at some length in the chapter dealing with the airship of the future.

RIGID AIRSHIP 23 X CLASS

During the early days of building the airships of the 23 class, further information was obtained relating to rigid airship construction in Germany, which caused our designers to modify their views. It was considered a wrong policy to continue the production of a fleet of ships the design of which was becoming obsolete, and accordingly within ten months of placing the order for this class a decision was reached that the last four ships were to be altered to a modified design known as the 23 X class. As was the case with the ships of the preceding class when nearing completion, they were realized to be out of date, and special efforts being required to complete the ships of the 33 class and to release building space for additional larger ships, the construction of the second pair was abandoned.

The main modification in design was the abolition of the external keel, and in this the later Zeppelin principles were adopted. This secured a very considerable reduction in structural weight with a corresponding large expansion of the effective capabilities of the ship.

It has been seen that the purpose of the keel in N was to provide a structure sufficiently strong to support all the main vertical bending moments and shearing forces, and that in N this principle was somewhat different, in that the keel in this ship was primarily intended to support the distributed weights of petrol, water, ballast, etc., between the transverse frames.

In this later design, namely, the 23 X class, it was considered that the weights could be concentrated and suspended from the radial wiring of the transverse frames and that the keel, incorporated in the design of the former ships, could be dispensed with.

For all practical purposes, apart from the absence of the keel, the 23 X class of airship may be regarded as a slightly varied model of the 23 class. The main dimensions are nearly the same, and the general arrangement of the ship is but little changed. The loss of space owing to the introduction of the internal corridor is compensated by a modification of the shape of the bow, which was redesigned with a deeper curve. The hull structure was also strengthened by utilizing a stronger type of girder wherever the greatest weights occur. In these strengthened transverse frames the girders, while still remaining of the triangular section, familiar in the other ships, are placed the opposite way round, that is, with the apex pointing outwards.

The walking way is situated at the base of the hull passing through the gas chambers, which are specially shaped for the purpose. The corridor is formed of a light construction of hollow wooden struts and duralumin arches covered with netting.

In all other leading features the design of the 23 class is adhered to; the gasbags are the same, except for the alteration due to the internal corridor, and the system of valves and the various controls are all highly similar.

The arrangement of gondolas and the fitting of engines in all ways corresponds to the original arrangement of R 23, with the exception that they were suspended closer to the hull owing to the absence of the external keel. The substitution of the wing car of the 33 class for the original after gondola, carried out in the modifications undergone by the ships of the 23 class, was not adopted in these ships, as the wireless compartment installed in the keel in the former was fitted in the after gondola in the latter.

The disposable lift of these ships under standard conditions is 7 1/2 tons, which shows considerable improvement on the ships of the former classes.

Summarizing as before, the performances appear as under

Speed:
Full            56 1/2 miles per hour
Normal          53       "  "  "
Cruising        45       "  "  "

Endurance:
Normal          19 hours = 1,015 miles
Cruising        23 1/2 " = 1,050   "

The two ships of this class, which were commissioned, must be regarded within certain limits as most satisfactory, and are the most successful of those that appeared and were employed during the war. Escort of convoys and extended anti-submarine patrols were carried out, and certain valuable experiments will be attempted now that peace has arrived.

In spite of the grave misgivings of many critics, the structure without the keel has proved amply strong, and no mishap attended this radical departure on the part of the designers.

RIGID AIRSHIP N CLASS

The airship known as R 81 was a complete deviation from any rigid airship previously built in this country. In this case the experiment was tried of constructing it in wood in accordance with the practice adopted by the Schutte-Lanz Company in Germany.

It must be frankly acknowledged that this experiment resulted in failure. The ship when completed showed great improvement both in shape, speed and lifting capacity over any airship commissioned in this country, and as a whole the workmanship exhibited in her construction was exquisite. Unfortunately, under the conditions to which it was subjected, the hull structure did not prove durable, and to those conditions the failure is attributed. Under different circumstances it may be hoped that the second ship, when completed, will prove more fortunate.

In length R 31 was 615 feet, with a diameter of 66 feet, and the capacity was 1 1/2 million cubic feet.

In shape the hull was similar to the later types of Zeppelin, having a rounded bow and a long, tapering stern. The longitudinal and transverse frames were composed of girders built up of three-ply wood, the whole structure being braced in the usual manner with wire bracings. It had been found in practice with rigid airships that, if for any reason one gasbag becomes much less inflated than those adjacent to it, there is considerable pressure having the effect of forcing the radial wires of the transverse frames towards the empty bag. The tension resulting in these wires may produce very serious compressive strain in the members of the transverse frames, and to counteract this action an axial wire is led along the axis of the ship and secured to the centre point of the radial wiring. This method, now current practice in rigid airship construction, was introduced for the first time in this ship.

As will be seen from the photograph, the control and navigating compartment of the ship is contained in the hull, the cars in each case being merely small engine rooms. These small cars were beautifully made of wood of a shape to afford the least resistance to the air, and in number were five, each housing a single 250 horse-power Rolls Royce engine driving a single fixed propeller. Here we see another decided departure from our previous methods of rigid airship construction, in that for the first time swivelling propellers were abandoned. R 31 when completed carried out her trials, and it was evident that she was much faster than previous ships. The trials were on the whole satisfactory and, except for a few minor accidents to the hull framework and fins, nothing untoward occurred.

At a later date the whole ship was through fortuitous circumstances exposed to certain disadvantageous conditions which rendered her incapable of further use.

R 33 CLASS

September 24th, 1916, is one of the most important days in the history of rigid airship design in this country; on this date the German Zeppelin airship L 33 was damaged by gunfire over London, and being hit in the after gasbags attempted to return to Germany. Owing to lack of buoyancy she was forced to land at Little Wigborough, in Essex, where the crew, having set fire to the ship, gave themselves up. Although practically the entire fabric of the ship was destroyed, the hull structure most fortunately remained to all intents and purposes intact, and was of inestimable value to the design staff of the Admiralty, who measured up the whole ship and made working drawings of every part available.

During this year other German rigid airships had been brought down, namely L 15, which was destroyed at the mouth of the Thames in April, but which was of an old type, and from which little useful information was obtained; and also the Army airship L., which was destroyed at Salonica in the month of May. A Schutte-Lanz airship was also brought down at Cuffley, on September 2nd, and afforded certain valuable details.

All these ships were, however, becoming out of date; but L 33 was of the latest design, familiarly called the super-Zeppelin, and had only been completed about six weeks before she encountered disaster.

In view of the fact that the rigid airships building in this country at this date, with the exception of the wooden Schutte-Lanz ships were all based on pre-war designs of Zeppelin airships, it can be readily understood that this latest capture revolutionized all previous ideas, and to a greater extent than might be imagined, owing to the immense advance, both in design and construction, which had taken place in Germany since 1914.

All possible information having been obtained, both from the wreck of the airship itself and from interrogation of the captured crew, approval was obtained, in November of the same year, for two ships of the L 33 design to be built; and in January, 1917, this number was increased to five.

It was intended originally that these ships should be an exact facsimile of L 33; but owing to the length of time occupied in construction later information was obtained before they were completed, both from ships of a more modern design, which were subsequently brought down, and also from other sources. Acting on this information, various improvements were embodied in R 33 and R 34, which were in a more advanced state; but in the case of the three other ships the size was increased, and the ships, when completed, will bear resemblance to a later type altogether.

As a comment on the slowness of construction before mentioned, the fact that while we in this country were building two ships on two slips, Germany had constructed no fewer than thirty on four slips, certainly affords considerable food for reflection.

The two airships of this class having only just reached a state of completion, a detailed description cannot be given without making public much information which must necessarily remain secret for the present. Various descriptions have, however, been given in the daily and weekly Press, but it is not intended in the present edition of this book to attempt to elaborate on anything which has not been already revealed through these channels.

It is regrettable that so much that would be of the utmost interest has to be omitted; but the particulars which follow will at any rate give sonic idea of the magnitude of the ship and show that it marks a decided departure from previous experiments and a great advance on any airship before constructed in Great Britain.

It is also a matter for regret that these two ships were not completed before the termination of hostilities, as their capabilities would appear to be sufficient to warrant the expectations which have been based on their practical utility as scouting agents for the Grand Fleet.

In all its main features the hull structure of R 33 and R 34 follows the design of the wrecked German Zeppelin airship L 33. The hull follows more nearly a true streamline shape than in the previous ships constructed of duralumin, in which a great proportion of the total length was parallel-sided. The Germans adopted this new shape from the Schutte-Lanz design and have not departed from this practice. This consists of a short parallel body with a long rounded bow and a long tapering stem culminating in a point. The overall length of the ship is 643 feet with a diameter of 79 feet and an extreme height of 92 feet.

The type of girders in this class has been much altered from those in previous ships. The hull is fitted with an internal triangular keel throughout practically the entire length. This forms the main corridor of the ship, and is fitted with a footway down the centre for its entire length. It contains water ballast and petrol tanks, bomb stowage and crew accommodation and the various control wires, petrol pipes and electric leads are carried along the lower part.

Throughout this internal corridor runs a bridge girder, from which the petrol and water ballast tanks are supported. These tanks are so arranged that they can be dropped clear of the ship.

Amidships is the cabin space with sufficient room for a crew of twenty-five. Hammocks can be slung from the bridge girder before mentioned.

In accordance with the latest Zeppelin practice, monoplane rudders and elevators are fitted to the horizontal and vertical fins.

The ship is supported in the air by nineteen gasbags which give a total capacity of approximately two million cubic feet of gas. The gross lift works out at approximately 59 1/2 tons, of which the total fixed weight is 33 tons, giving a disposable lift of 26 1/2 tons.

The arrangement of cars is as follows: At the forward end the control car is slung, which contains all navigating instruments and the various controls. Adjoining this is the wireless cabin, which is also fitted for wireless telephony. Immediately aft of this is the forward power car containing one engine, which gives the appearance that the whole is one large car.

Amidships are two wing cars each containing a single engine. These are small and just accommodate the engine with sufficient room for mechanics to attend to them. Further aft is another larger car which contains an auxiliary control position and two engines.

It will thus be seen that five engines are installed in the ship; these are all of the same type and horse-power, namely, 250 horse-power Sunbeam. R 33 was constructed by Messrs. Armstrong Whitworth Ltd., while her sister ship R 34 was built by Messrs. Beardmore on the Clyde.

In the spring of 1918, R 33 and R 34 carried out several flight trials, and though various difficulties were encountered both with the engines and also with the elevator and rudder controls, it was evident that, with these defects remedied, each of these ships would prove to be singularly reliable.

On one of these trials made by R 34, exceedingly bad weather was encountered, and the airship passed through several blinding snowstorms; nevertheless the proposed flight of some seventeen hours was completed, and though at times progress was practically nil owing to the extreme force of the wind, the station was reached in safety and the ship landed without any contretemps. This trial run having been accomplished in weather such as would never have been chosen in the earlier days of rigid trial flights, those connected with the airship felt that their confidence in the vessel’s capabilities was by no means exaggerated.

The lift of the ship warranted a greater supply of petrol being carried than there was accommodation for, and the engines by now had been “tuned up” to a high standard of efficiency. Accordingly it was considered that the ship possessed the necessary qualifications for a transatlantic flight. It was, moreover, the opinion of the leading officers of the airship service that such an enterprise would be of inestimable value to the airship itself, as demonstrating its utility in the future for commercial purposes.

Efforts were made to obtain permission for the flight to be attempted, and although at first the naval authorities were disinclined to risk such a valuable ship on what appeared to be an adventure of doubtful outcome, eventually all opposition was overcome and it was agreed that for the purposes of this voyage the ship was to be taken over by the Air Ministry from the Admiralty.

Work was started immediately to fit out the ship for a journey of this description. Extra petrol tanks were disposed in the hull structure to enable a greater supply of fuel to be carried, a new and improved type of outer cover was fitted, and by May 29th, R 34 was completed to the satisfaction of the Admiralty and was accepted. On the evening of the same day she left for her station, East Fortune, on the Firth of Forth. This short passage from the Clyde to the Forth was not devoid of incident, as soon after leaving the ground a low-lying fog enveloped the whole country and it was found impossible to land with any degree of safety. It having been resolved not to land until the fog lifted, the airship cruised about the north-east coast of England and even came as far south as York. Returning to Scotland, she found the fog had cleared, and was landed safely, having been in the air for 21 hours.

The original intention was that the Atlantic flight should be made at the beginning of June, but the apparent unwillingness of the Germans to sign the Peace Treaty caused the Admiralty to retain the ship for a time and commission her on a war footing. During this period she went for an extended cruise over Denmark, along the north coast of Germany and over the Baltic. This flight was accomplished in 56 hours, during which extremely bad weather conditions were experienced at times. On its conclusion captain and crew of the ship expressed their opinion that the crossing of the Atlantic was with ordinary luck a moral certainty. Peace having been signed, the ship was overhauled once more and made ready for the flight, and the day selected some three weeks before was July 2nd.

A selected party of air-service ratings, together with two officers, were sent over to America to make all the necessary arrangements, and the American authorities afforded every conceivable facility to render the flight successful.

As there is no shed in America capable of housing a big rigid, there was no alternative but to moor her out in the open, replenish supplies of gas and fuel and make the return journey as quickly as possible.

On July 2nd, at 2.38 a.m. (British summer time), R 34 left the ground at East Fortune, carrying a total number of 30 persons. The route followed was a somewhat northerly one, the north coast of Ireland being skirted and a more or less direct course was kept to Newfoundland. From thence the south-east coast of Nova Scotia was followed and the mainland was picked up near Cape Cod.

From Cape Cod the airship proceeded to Mineola, the landing place on Long Island. All went well until Newfoundland was reached. Over this island fog was encountered, and later electrical storms became a disturbing element when over Nova Scotia and the Bay of Fundy. The course had to be altered to avoid these storms, and owing to this the petrol began to run short. No anxiety was occasioned until on Saturday, July 5th, a wireless signal was sent at 3.59 p.m. asking for assistance, and destroyers were dispatched immediately to the scene. Later messages were received indicating that the position was very acute, as head winds were being encountered and petrol was running short. The airship, however, struggled on, and though at one time the possibility of landing at Montauk, at the northern end of Long Island, was considered, she managed after a night of considerable anxiety to reach Mineola and land there in safety on July 6th at 9.55 a.m. (British summer time). The total duration of the outward voyage was 108 hours 12 minutes, and during this time some 3,136 sea miles were covered. R 34 remained at Mineola until midnight of July 9th according to American time. During the four days in which she was moored out variable weather was experienced, and in a gale of wind the mooring point was torn out, but fortunately, another trail rope was dropped and made fast, and the airship did not break away.

It was intended that the return should be delayed until daylight, in order that spectators in New York should obtain a good view of the airship, but an approaching storm was reported and the preparations were advanced for her immediate departure. During the last half-hour great difficulty was experienced in holding the ship while gassing was completed.

At 5.57 a.m. (British summer time) R 34 set out on her return voyage, steering for New York, to fly over the city before heading out into the Atlantic. She was picked up by the searchlights and was distinctly visible to an enormous concourse of spectators. During the early part of the flight a strong following wind was of great assistance, and for a short period an air speed of 83 miles per hour was attained. On the morning of July 11th the foremost of the two engines in the after car broke down and was found to be beyond repair. The remainder of the voyage was accomplished without further incident. On July 12th at noon, a signal was sent telling R 34 to proceed to the airship station at Pulham in Norfolk as the weather was unfavourable for landing in Scotland. On the same day at 8.25 p.m., land was first sighted and the coast line was crossed near Clifden, county Galway, at 9 p.m. On the following morning, July 13th, at 7.57 a.m. (British summer time), the long voyage was completed and R 34 was safely housed in the shed, having been in the air 75 hours 3 minutes.

Thus a most remarkable undertaking was brought to a successful conclusion. The weather experienced was by no means abnormally good. This was not an opportunity waited for for weeks and then hurriedly snatched, but on the preordained date the flight was commenced. The airship enthusiast had always declared that the crossing of the Atlantic presented no insuperable difficulty, and when the moment arrived the sceptics found that he was correct. We may therefore assume that this flight is a very important landmark in the history of aerial transport, and has demonstrated that the airship is to be the medium for long-distance travel. We may rest assured that such flights, although creating universal wonder to-day, will of a surety be accepted as everyday occurrences before the world is many years older.