No. 17 (Beta) also saw active service, as she was based for a short period early in 1915 at Dunkirk, and was employed in spotting duties with the Belgian artillery near Ostend.
The Gamma and the Delta were both lying deflated at Farnborough at the outbreak of the war, and in the case of the latter the car was found to be beyond repair, and she was accordingly deleted. The Gamma was inflated in January, 1915, and was used for mooring experiments.
The Eta, having been inflated and deflated several times owing to the poor quality of the envelope, attempted to fly to Dunkirk in November, 1914. She encountered a snowstorm near Redhill and was compelled to make a forced landing. In doing this she was so badly damaged as to be incapable of repair, and at a later date was deleted.
No. 8, which was delivered towards the end of 1914, was also moored out in the open for a short time near Dunkirk, and carried out patrol in the war zone of the Belgian coast.
So ends the story of the Naval Airship Service before the war.
With the submarine campaign ruthlessly waged by the Germans from the spring of 1915 and onwards, came the airship's opportunity, and the authorities grasped the fact that, with development, here was the weapon to defeat the most dangerous enemy of the Empire. The method of development and the success attending it the following chapters will show.
NAVAL AIRSHIPS.—THE NON-RIGIDS—S.S. TYPE
The development of the British airships of to-day may be said to date from February 28th, 1915. On that day approval was given for the construction of the original S.S. airship.
At this time the Germans had embarked upon their submarine campaign, realizing, with the failure of their great assaults on the British troops in Flanders, that their main hope of victory lay in starving Great Britain into surrender. There is no doubt that the wholesale sinking of our merchant shipping was sufficient to cause grave alarm, and the authorities were much concerned to devise means of minimizing, even if they could not completely eliminate the danger. One proposal which was adopted, and which chiefly concerns the interests of this book, was the establishment of airship stations round the coasts of Great Britain. These stations were to be equipped with airships capable of patrolling the main shipping routes, whose functions were to search for submarines and mines and to escort shipping through the danger zones in conjunction with surface craft.
Airship construction in this country at the time was, practically speaking, non-existent. There was no time to be wasted in carrying out long and expensive experiments, for the demand for airships which could fulfil these requirements was terribly urgent, and speed of construction was of primary importance. The non-rigid design having been selected for simplicity in construction, the expedient was tried of slinging the fuselage of an ordinary B.E. 2C aeroplane, minus the wings, rudder and elevators and one or two other minor fittings, beneath an envelope with tangential suspensions, as considerable experience had been gained already in a design of this type.
For this purpose the envelope of airship No. 2, which was lying deflated in the shed at Farnborough, was rushed post haste to Kingsnorth, inflated and rigged to the fuselage prepared for it. The work was completed with such despatch that the airship carried out her trial flight in less than a fortnight from approval being granted to the scheme. The trials were in every way most satisfactory, and a large number of ships of this design was ordered immediately. At the same time two private firms were invited to submit designs of their own to fulfil the Admiralty requirements. One firm's design, S.S. 2, did not fulfil the conditions laid down and was put out of commission; the other, designed by Messrs. Armstrong, was sufficiently successful for them to receive further orders. In addition to these a car was designed by Messrs. Airships Ltd., which somewhat resembled a Maurice Farman aeroplane body, and as it appeared to be suitable for the purpose, a certain number of these was also ordered.
About this period the station at Farnborough was abandoned by the Naval Airship Service to make room for the expansion of the military aeroplane squadrons. The personnel and airships were transferred to Kingsnorth, which became the airship headquarters.
The greatest energy was displayed in preparing the new stations, which were selected as bases for the airships building for this anti-submarine patrol. Small sheds, composed of wood, were erected with almost incredible rapidity, additional personnel was recruited, stores were collected, huts built for their accommodation and that of the men, and by the end of the summer the organization was so complete that operations were enabled to commence.
The S.S., or submarine scout, airship proved itself a great success. Beginning originally with a small programme the type passed through various developments until, at the conclusion of the war, no fewer than 150 ships of various kinds had been constructed. The alterations which took place and the improvements effected thereby will be considered at some length in the following pages.
The envelope of the experimental ship S.S. 1 was only of 20,500 cubic feet capacity; for the active-service ships, envelopes of similar shape of 60,000 cubic feet capacity were built. The shape was streamline, that is to say, somewhat blunt at the nose and tapering towards the tail, the total length being 143 feet 6 inches, with a maximum diameter of 27 feet 9 inches.
The gross lift of these ships with 98% pure gas at a temperature of 60 degrees Fahrenheit and barometer 30 inches, is 4,180 lb. The net lift available for crew, fuel, ballast, armament, etc., 1,434 lb., and the disposable lift still remaining with crew of two on board and full tanks, 659 lb.
The theoretical endurance at full speed as regards petrol consumption is a little over 8 hours, but in practice it is probable that the oil would run short before this time had been reached. At cruising speed, running the engine at 1,250 revolutions, the consumption is at the rate of 3.6 gallons per hour, which corresponds to an endurance of 16 1/2 hours.
With the engine running at 1,800 revolutions, a speed of 50.6 miles per hour has been reached by one of these ships, but actually very few attained a greater speed than 40 miles per hour.
The envelopes of S.S. airships are composed of rubber-proofed fabric, two fabrics being used with rubber interposed between and also on the inner or gas surface. To render them completely gastight and as impervious to the action of the weather, sun, etc., as possible, five coats of dope are applied externally, two coats of Delta dope, two of aluminium dope and one of aluminium varnish applied in that order.
One ripping panel is fitted, which is situated on the top of the envelope towards the nose. It has a length of 14 feet 5 inches and a breadth of about 8 inches. The actual fabric which has to be torn away overlaps the edge of the opening on each side. This overlap is sewn and taped on to the envelope and forms a seam as strong and gastight as any other portion of the envelope. Stuck on this fabric is a length of biased fabric 8 1/4 inches wide. These two strips overlap the opening at the forward end by about three feet. At this end the two strips are loose and have a toggle inserted at the end to which the ripping cord is tied. The ripping cord is operated from the car. It is led aft from the ripping panel to a pulley fixed centrally over the centre of the car, from the pulley the cord passes round the side of the envelope and through a gland immediately below the pulley.
The nose of the envelope is stiffened to prevent it blowing in. For this purpose 24 canes are fitted in fabric pockets around the nose and meet at a point 2 1/4 inches in front of the nose. An aluminium conical cap is fitted over the canes and a fabric nose cap over the whole.
Two ballonets are provided, one forward and one aft, the capacity of each being 6,375 cubic feet. The supply of air for filling these is taken from the propeller draught by a slanting aluminium tube to the underside of the envelope, where it meets a longitudinal fabric hose which connects the two ballonet air inlets. Non-return fabric valves known as crab-pots are fitted in this fabric hose on either side of their junction with the air scoop. Two automatic air valves are fitted to the underside of the envelope, one for each ballonet. The air pressure tends to open the valve instead of keeping it shut and to counteract this the spring of the valve is inside the envelope. The springs are set to open at a pressure of 25 to 28 mm.
Two gas valves are also fitted, one on the top of the envelope, the other at the bottom. The bottom gas valve spring is set to open at 30 to 35 mm. pressure, the top valve is hand controlled only.
These valves are all very similar in design. They consist of two wooden rings, between which the envelope is gripped, and which are secured to each other by studs and butterfly nuts. The valve disc, or moving portion of the valve, is made of aluminium and takes a seating on a thin india rubber ring stretched between a metal rod bent into a circle of smaller diameter than the valve opening and the wooden ring of the valve. When it passes over the wooden ring it is in contact with the envelope fabric and makes the junction gastight. The disc is held against the rubber by a compressed spring.
The valve cords are led to the pilot's seat through eyes attached to the envelope.
The system of rigging or car suspension is simplicity itself and is tangential to the envelope. On either side there are six main suspensions of 25 cwt. stranded steel cable known as "C" suspensions. Each "C" cable branches into two halves known as the "B" bridles, which in turn are supported at each end by the bridles known as "A." The ends of the "A" bridles are attached to the envelope by means of Eta patches. These consist of a metal D-shaped fitting round which the rigging is spliced and through which a number of webbing bands are passed which are spread out fanwise and solutioned to the envelope. It will thus be seen that the total load on each main suspension is proportionally taken up by each of the four "A" bridles, and that the whole weight of the car is equally distributed over the greater part of the length of the envelope. Four handling guys for manoeuvering the ship on the ground are provided under the bow and under the stem. A group of four Eta patches are placed close together, which form the point of attachment for two guys in each case. The forward of these groups of Eta patches forms the anchoring point. The bridle, consisting of 25 cwt. steel cable, is attached here and connected to the forepart of the skids of the car. The junction of this bridle with the two cables from the skids forms the mooring point and there the main trail rope is attached. This is 120 feet long and composed of 2-inch manilla. This is attached, properly coiled, to the side of the car and is dropped by a release gear. It is so designed that when the airship is held in a wind by the trail rope the strain is evenly divided between the envelope and the car. The grapnel carried is fitted to a short length of rope. The other end of the rope has an eye, and is fitted to slide down the main trail rope and catch on a knot at the end.
For steering and stabilizing purposes the S.S. airship was originally designed with four fins and rudders, which were to be set exactly radial to the envelope. In some cases the two lower fins and rudders were abandoned, and a single vertical fin and rudder fitted centrally under the envelope were substituted. The three planes are identical in size and measure 16 feet by 8 feet 6 inches, having a gross stabilizing area of 402 1/2 square feet.
They are composed of spruce and aluminium and steel tubing braced with wire and covered by linen doped and varnished when in position.
The original rudders measured 3 feet by 8 feet 6 inches. In the case, however, of the single plane being fitted, 4-feet rudders are invariably employed. Two kingposts of steel tube are fitted to each plane and braced with wire to stiffen the whole structure.
The planes are attached to the envelope by means of skids and stay wires. The skids, composed of spruce, are fastened to the envelope by eight lacing patches.
The car, it will be remembered, is a B.E. 2C fuselage stripped of its wings, rudders and elevators, with certain other fittings added to render it suitable for airship work. The undercarriage is formed of two ash skids, each supported by three struts. The aeroplane landing wheels, axle and suspensions are abandoned.
In the forward end of the fuselage was installed a 75 horse-power air cooled Renault engine driving a single four-bladed tractor propeller through a reduction gear of 2 to 1. The engine is of the 8-cylinder V type, weighing 438 lb. with a bore of 96 mm. and a stroke of 120 mm. The Claudel-Hobson type of carburettor is employed with this engine. The type of magneto used is the Bosch D.V.4, there being one magneto for each line of cylinders. In the older French Renaults the Bosch H.L.8 is used, one magneto supplying the current to all the plugs. Petrol is carried in three tanks, a gravity and intermediate tank as fitted to the original aeroplane, and a bottom tank placed underneath the front seat of the car. The petrol is forced by air pressure from the two lower tanks into the gravity tank and is obtained by a hand pump fitted outside the car alongside the pilot's seat. The oil tank is fitted inside the car in front of the observer.
The observer's seat is fitted abaft the engine and the pilot's seat is aft of the observer. The observer, who is also the wireless operator, has the wireless apparatus fitted about his seat. This consists of a receiver and transmitter fitted inside the car, which derives power from accumulator batteries. The aerial reel is fitted outside the car. During patrols signals can be sent and received up to and between 50 and 60 miles.
The pilot is responsible for the steering and the running of the engine, and the controls utilized are the fittings supplied with the aeroplane. Steering is operated by the feet and elevating by a vertical wheel mounted in a fore and aft direction across the seat. The control wires are led aft inside the fairing of the fuselage to the extreme end, whence they pass to the elevators and rudders.
The instrument board is mounted in front of the pilot. The instruments comprise a watch, an air-speed indicator graduated in knots, an aneroid reading to 10,000 feet, an Elliott revolution counter, a Clift inclinometer reading up to 20 degrees depression or elevation, a map case with celluloid front.
There are in addition an oil pressure gauge, a petrol pressure gauge, a glass petrol level and two concentric glass pressure gauges for gas pressure.
The steering compass is mounted on a small wooden pedestal on the floor between the pilot's legs.
The water-ballast tank is situated immediately behind the pilot's seat and contains 14 gallons of water weighing 140 lbs. The armament consists of a Lewis gun and bombs. The bombs are carried in frames suspended about the centre of the undercarriage. The bomb sight is fitted near the bomb releasing gear outside the car on the starboard side adjacent to the pilot's seat. The Lewis gun, although not always carried on the early S.S. airships, was mounted on a post alongside the pilot's seat.
S.S. MAURICE FARMAN
For this type of S.S. the cars were built by Messrs. Airships Ltd. In general appearance they resemble the Maurice Farman aeroplane and were of the pusher type; 60,000 and in later cases 70,000 cubic feet envelopes were rigged to these ships, which proved to be slightly slower than the B.E. 2C type, but this was compensated for owing to the increased comfort provided for the crew, the cars being more roomy and suitable for airship work in every way.
The system of rigging to all intents and purposes is the same in all types of S.S. ships, the suspensions being adjusted to suit the different makes of car.
In these ships the pilot sits in front, and behind him is the wireless telegraphy operator; in several cases a third seat was fitted to accommodate a passenger or engineer; dual rudder and elevator controls are provided for the pilot and observer.
The engine is mounted aft, driving a four-bladed pusher propeller, with the petrol tanks situated in front feeding the carburettors by gravity. The engines used are Rolls Royce Renaults, although in one instance a 75 horse-power Rolls Royce Hawk engine was fitted, which assisted in making an exceedingly useful ship.
S.S. ARMSTRONG WHITWORTH
The car designed by Messrs. Armstrong Whitworth is of the tractor type and is in all ways generally similar to the B.E. 2C. The single-skid landing chassis with buffers is the outstanding difference. These cars had to be rigged to 70,000 cubic feet envelopes otherwise the margin of lift was decidedly small. A water-cooled 100 horse-power Green engine propelled the ship, and a new feature was the disposition of petrol, which was carried in two aluminium tanks slung from the envelope and fed through flexible pipes to a two-way cock and thence to the carburettors. These tanks, which were supported in a fabric sling, showed a saving in weight of 100 lb. compared with those fitted in the B.E. 2C.
For over two years these three types of S.S. ships performed a great part of our airship patrol and gave most excellent results.
Owing to the constant patrol which was maintained whenever weather conditions were suitable, the hostile submarine hardly dared to show her periscope in the waters which were under observation. In addition to this, practically the whole of the airship personnel now filling the higher positions, such as Captains of Rigids and North Seas, graduated as pilots in this type of airship. From these they passed to the Coastal and onwards to the larger vessels.
As far as is known the height record for a British airship is still held by an S.S.B.E. 2C, one of these ships reaching the altitude of 10,300 feet in the summer of 1916.
The Maurice Farman previously mentioned as being fitted with the Hawk engine, carried out a patrol one day of 18 hours 20 minutes. In the summer of 1916 one of the Armstrong ships was rigged to an envelope doped black and sent over to France. While there she carried out certain operations at night which were attended with success, proving that under certain circumstances the airship can be of value in operating with the military forces over land.
In 1916 the design was commenced for an S.S. ship which should have a more comfortable car and be not merely an adaptation of an aeroplane body. These cars, which were of rectangular shape with a blunt nose, were fitted with a single landing skid aft, and contained seats for three persons.
The engine, a 100 horse-power water-cooled Green, was mounted on bearers aft and drove a four-bladed pusher propeller. The petrol was carried in aluminium tanks attached by fabric slings to the axis of the envelope.
Six of these ships were completed in the spring of 1917 and were quite satisfactory, but owing to the success achieved by the experimental S.S. Zero it was decided to make this the standard type of S.S. ship, and with the completion of the sixth the programme of the S.S.P's was brought to a close.
These ships enjoyed more than, perhaps, was a fair share of misfortune, one was wrecked on proceeding to its patrol station and was found to be beyond repair, and another was lost in a snowstorm in the far north. The remainder, fitted at a later date with 75 horse-power Rolls Royce engines, proved to be a most valuable asset to our fleet of small airships.
The original S.S. Zero was built at a south-coast station by Air Service labour, and to the design of three officers stationed there. The design of the car shows a radical departure from anything that had been previously attempted, and as a model an ordinary boat was taken. In shape it is as nearly streamline as is practicable, having a keel and ribs of wood with curved longitudinal members, the strut ends being housed in steel sockets. The whole frame is braced with piano wire set diagonally between the struts. The car is floored from end to end, and the sides are enclosed with 8-ply wood covered with fabric.
Accommodation is provided for a wireless telegraphy operator, who is also a gunner, his compartment being situated forward, amidships is the pilot and abaft this seat is a compartment for the engineer.
The engine selected was the 75 horse-power water-cooled Rolls Royce, it being considered to be the most efficient for the purpose. The engine is mounted upon bearers above the level of the top of the car, and drives a four-bladed pusher propeller.
The car is suspended from an envelope of 70,000 cubic feet capacity, and the system of rigging is similar to that in use on all S.S. ships. The petrol is carried in aluminium tanks slung on the axis of the envelope, identically with the system in use on the S.S.P's. The usual elevator planes are adopted with a single long rudder plane.
The speed of the Zero is about 45 miles per hour and the ship has a theoretical endurance of seventeen hours; but this has been largely exceeded in practice.
The original ship proved an immediate success, and a large number was shortly afterwards ordered.
As time went on the stations expanded and sub-stations were added, while the Zero airship was turned out as fast as it could be built, until upwards of seventy had been commissioned. The work these ships were capable of exceeded the most sanguine expectations. Owing to their greater stability in flight and longer hours of endurance, they flew in weather never previously attempted by the earlier ships. With experience gained it was shown that a large fleet of airships of comparatively small capacity is of far more value for an anti-submarine campaign than a lesser fleet of ships of infinitely greater capacity. The average length of patrol was eight hours, but some wonderful duration flights were accomplished in the summer of 1918, as the following figures will show. The record is held by S.S.Z. 39, with 50 hours 55 minutes; another is 30 hours 20 minutes; while three more vary from 25 1/2 hours to 26 1/4. Although small, the Zero airship has been one of the successes of the war, and we can claim proudly that she is entirely a British product.
During the year 1917, designs were submitted for a twin-engined S.S. airship, the idea being to render the small type of airship less liable to loss from engine failure. The first design proved to be a failure, but the second was considered more promising, and several were built. Its capacity is 100,000 cubic feet, with a length of 164 feet 6 inches, and the greatest diameter 32 feet.
The car is built to carry five, with the engines disposed on gantries on the port and starboard side, driving pusher propellers. This type, although in the experimental stage, is being persevered with, and the intention is that it will gradually supplant the other S.S. classes. It is calculated that it will equal if not surpass the C Star ship in endurance, besides being easier to handle and certainly cheaper to build.
"COASTAL" AND "C STAR" AIRSHIPS
The urgent need for a non-rigid airship to carry out anti-submarine patrol having been satisfied for the time with the production of the S.S. B.E. 2C type, the airship designers of the Royal Naval Air Service turned their attention to the production of an airship which would have greater lift and speed than the S.S. type, and, consequently, an augmented radius of action, together with a higher degree of reliability. As the name "Coastal" or "Coast Patrol" implies, this ship was intended to carry out extended sea patrols.
To obtain these main requirements the capacity of the envelope for this type was fixed at 170,000 cubic feet, as compared with the 60,000 cubic feet and, later, the 70,000 cubic feet envelopes adopted for the S.S. ships. Greater speed was aimed at by fitting two engines of 150 horse-power each, and it was hoped that the chances of loss owing to engine failure would be considerably minimized.
The Astra-Torres type of envelope, with its system of internal rigging, was selected for this class of airship; in the original ship the envelope used was that manufactured by the French Astra-Torres Company, and to which it had been intended to rig a small enclosed car. The ship in question was to be known as No. 10. This plan was, however, departed from, and the car was subsequently rigged to the envelope of the Eta, and a special car was designed and constructed for the original Coastal. Coastal airship No. 1 was commissioned towards the end of 1915 and was retained solely for experimental and training purposes. Approximately thirty of these airships were constructed during the year 1916, and were allocated to the various stations for patrol duties.
The work carried out by these ships during the two and a half years in which they were in commission, is worthy of the highest commendation. Before the advent of later and more reliable ships, the bulk of anti-submarine patrol on the east coast and south-west coast of England was maintained by the Coastal. On the east coast, with the prevailing westerly and south-westerly winds, these airships had many long and arduous voyages on their return from patrol, and in the bitterness of winter their difficulties were increased ten-fold. To the whole-hearted efforts of Coastal pilots and crews is due, to a great extent, the recognition which somewhat tardily was granted to the Airship Service.
The envelope of the Coastal airship has been shown to be of 170,000 cubic feet capacity. It is trilobe in section to employ the Astra-Torres system of internal and external rigging. The great feature of this principle is that it enables the car to be slung much closer to the envelope than would be possible with the tangential system on an envelope of this size. As a natural consequence there is far less head resistance, owing to the much shorter rigging, between the envelope and the car.
The shape of the envelope is not all that could have been desired, for it is by no means a true streamline, but has the same cross section for the greater part of its length, which tapers at either end to a point which is slightly more accentuated aft. Owing to the shape, these ships, in the early days until experience had been gained, were extremely difficult to handle, both on the landing ground and also in the air. They were extremely unstable both in a vertical and horizontal plane, and were slow in answering to their rudders and elevators.
The envelope is composed of rubber-proofed fabric doped to hold the gas and resist the effects of weather. Four ballonets are situated in the envelope, two in each of the lower lobes, air being conveyed to them by means of a fabric air duct, which is parallel to the longitudinal centre line of the envelope, with transverse ducts connecting each pair of ballonets. In earlier types of the Coastal, the air scoop supplying air to the air duct was fitted in the slip stream of the forward engine, but later this was fitted aft of the after engine.
Six valves in all are used, four air valves, one fitted to each ballonet, and two gas valves. These are situated well aft, one to each of the lower lobes, and are fitted on either side of the rudder plane. A top valve is dispensed with because in practice when an Astra-Torres envelope loses shape, the tendency is for the tail to be pulled upwards by the rigging, with the result that the two gas valves always remain operative.
Crabpots and non-return valves are employed in a similar manner to S.S. airships.
The Astra-Torres system of internal rigging must now be described in some detail. The envelope is made up of three longitudinal lobes, one above and two below, which when viewed end on gives it a trefoil appearance. The internal rigging is attached to the ridges formed on either side of the upper lobe, where it meets the two side lobes. From here it forms a V, when viewed cross sectionally, converging at he ridge formed by the two lobes on the underside of the envelope which is known as the lower ridge.
To the whole length of the top ridges are attached the internal rigging girdles and also the lacing girdles to which are secured the top and side curtains. These curtains are composed of ordinary unproofed fabric and their object is to make the envelope keep its trilobe shape. They do not, however, divide the ship into separate gas compartments. The rigging girdle consists of a number of fabric scallops through which run strands of Italian hemp. These strands, of which there are a large number, are led towards the bottom ridge, where they are drawn together and secured to a rigging sector. To these sectors the main external rigging cables are attached. The diagram shows better than any description this rigging system.
Ten main suspensions are incorporated in the Coastal envelope, of which three take the handling guys, the remaining seven support the weight of the car.
The horizontal fins with the elevator flaps, and the vertical fin with the rudder flap, are fixed to the ridges of the envelope.
The car was evolved in the first instance by cutting away the tail portion of two Avro seaplane fuselages and joining the forward portions end on, the resulting car, therefore, had engines at either end with seating accommodation for four. The landing chassis were altered, single skids being substituted for the wider landing chassis employed in the seaplane. The car consists of four longerons with struts vertical and cross, and stiffened with vertical and cross bracing wires. The sides are covered with fabric and the flooring and fairing on the top of the car are composed of three-ply wood. In the later cars five seats were provided to enable a second officer to be carried.
The engines are mounted on bearers at each end of the car, and the petrol and oil tanks were originally placed adjoining the engines in the car. At a later date various methods of carrying the petrol tanks were adopted, in some cases they were slung from the envelope and in others mounted on bearers above the engines.
Wireless telegraphy is fitted as is the case with all airships. In the Coastal a gun is mounted on the top of the envelope, which is reached by a climbing shaft passing through the envelope, another mounting being provided on the car itself.
Bombs are also carried on frames attached to the car. Sunbeam engines originally supplied the motive power, but at a later date a 220 horse-power Renault was fitted aft and a 100 horse-power, Berliet forward. With the greater engine power the ship's capabilities were considerably increased.
Exceedingly long flights were achieved by this type of ship, and those exceeding ten hours are far too numerous to mention. The most noteworthy of all gave a total of 24 1/4 hours, which, at the time, had only once been surpassed by any British airship.
Towards the end of 1917, these ships, having been in commission for over two years, were in many cases in need of a complete refit. Several were put in order, but it was decided that this policy should not be continued, and that as each ship was no longer fit for flying it should be replaced by the more modern Coastal known as the C Star.
The record of one of these ships so deleted is surely worthy of special mention. She was in commission for 2 years 75 days, and averaged for each day of this period 3 hours 6 minutes flying. During this time she covered upwards of 66,000 miles. From this it will be seen that she did not pass her life by any means in idleness.
"C STAR" AIRSHIP
After considerable experience had been gained with the Coastal, it became obvious that a ship was required of greater capabilities to maintain the long hours of escort duty and also anti-submarine patrols. To meet these requirements it was felt that a ship could be constructed, not departing to any extent from the Coastal, with which many pilots were now quite familiar, but which would show appreciable improvement over its predecessor.
The design which was ultimately adopted was known as the C Star, and provided an envelope of 210,000 cubic feet, which secured an extra ton and a quarter in lifting capacity. This envelope, although of the Astra-Torres type, was of streamline form, and in that respect was a great advance on the early shape as used in the Coastal. It is to all intents and purposes the same envelope as is used on the North Sea ships, but on a smaller scale. An entirely new type of fabric was employed for this purpose. The same model of car was employed, but was made more comfortable, the canvas covering for the sides being replaced by three-ply wood. In all other details the car remained entirely the same. The standard power units were a 100 horse-power Berliet forward and a Fiat of 260 horse-power aft. The petrol tanks in this design were carried inside the envelope, which was quite a new departure.
These airships may be considered to have been successful, though not perhaps to the extent which was expected by their most ardent admirers. With the advent of the S.S. Twin it was resolved not to embark on a large constructional programme, and when the numbers reached double figures they were no longer proceeded with. Notwithstanding this the ships which were commissioned carried out most valuable work, and, like their prototypes, many fine flights were recorded to their credit. Thirty-four and a half hours was the record flight for this type of ship, and another but little inferior was thirty hours ten minutes. These flights speak well for the endurance of the crews, as it must be borne in mind that no sleeping accommodation is possible in so small a car.
The Coastal airship played no small part in the defeat of the submarine, but its task was onerous and the enemy and the elements unfortunately exacted a heavy toll. A German wireless message received in this country testified to the valiant manner in which one of these ships met with destruction.
THE "NORTH SEA" AIRSHIP
The North Sea or N.S. airship was originally designed to act as a substitute for the Rigid, which, in 1916, was still a long way from being available for work of practical utility. From experience gained at this time with airships of the Coastal type it was thought possible to construct a large Non-Rigid capable of carrying out flights of twenty-four hours' duration, with a speed of 55 to 60 knots, with sufficient accommodation for a double crew.
The main requirements fall under four headings:
1. Capability to carry out flights of considerable duration.
2. Great reliability.
3. The necessary lift to carry an ample supply of fuel.
4. Adequate arrangements to accommodate the crew in comfort.
If these could be fulfilled the authorities were satisfied that ships possessing these qualifications would be of value to the Fleet and would prove efficient substitutes until rigid airships were available. The North Sea, as may be gathered from its name, was intended to operate on the east coasts of these islands.
The first ship, when completed and put through her trials, was voted a success, and the others building were rapidly pushed on with. When several were finished and experience had been gained, after long flights had been carried out, the North Sea airship suffered a partial eclipse and people were inclined to reconsider their favourable opinion. Thus it was that for many months the North Sea airship was decidedly unpopular, and it was quite a common matter to hear her described as a complete failure. The main cause of the prejudice was the unsatisfactory design of the propelling machinery, which it will be seen later was modified altogether, and coupled with other improvements turned a ship of doubtful value into one that can only be commended.
The envelope is of 360,000 cubic feet capacity, and is designed on the Astra-Torres principle for the same reasons as held good in the cases of the Coastal and C Star. All the improvements which had been suggested by the ships of that class were incorporated in the new design, which was of streamline shape throughout, and looked at in elevation resembled in shape that of the S.S. airship. Six ballonets are fitted, of which the total capacity is 128,000 cubic feet, equivalent to 35.5 per cent of the total volume. They are fitted with crabpots and non-return valves in the usual manner.
The rigging is of the Astra-Torres system, and in no way differs from that explained in the previous chapter. Nine fans of the internal rigging support the main suspensions of the car, while similar fans both fore and aft provide attachment for the handling guys. Auxiliary fans on the same principle support the petrol tanks and ballast bag.
Four gas and six air valves in all are fitted, all of which are automatic.
Two ripping panels are embodied in the top lobe of the envelope.
The N.S. ship carries four fins, to three of which are attached the elevator and rudder flaps. The fourth, the top fin, is merely for stabilizing purposes, the other three being identical in design, and are fitted with the ordinary system of wiring and kingposts to prevent warping.
The petrol was originally carried in aluminium tanks disposed above the top ridges of the envelope, but this system was abandoned owing to the aluminium supply pipes becoming fractured as the envelope changed shape at different pressures. They were then placed inside the envelope, and this rearrangement has given every satisfaction.
To the envelope of the N.S. is rigged a long covered-in car. The framework of this is built up of light steel tubes, the rectangular transverse frames of which are connected by longitudinal tubes, the whole structure being braced by diagonal wires. The car, which tapers towards the stern, has a length of 85 feet, with a height of 6 feet. The forward portion is covered with duralumin sheeting, and the remainder with fabric laced to the framework. Windows and portholes afford the crew both light and space to see all that is required. In the forward portion of the car are disposed all the controls and navigating instruments, together with engine-telegraphs and voice pipes. Aft is the wireless telegraphy cabin and sleeping accommodation for the crew.
A complete electrical installation is carried of two dynamos and batteries for lights, signalling lamps, telephones, etc. The engines are mounted in a power unit structure separate from the car and reached by a wooden gangway supported by wire cables. This structure consists of two V-shaped frameworks connected by a central frame and by an under-structure to which floats are attached. The mechanics' compartment is built upon the central frame, and the engine controls are operated from this cabin.
In the original power units two 250 horse-power Rolls Royce engines were fitted, driving propellers on independent shafts through an elaborate system of transmission. This proved to be a great source of weakness, as continual trouble was experienced with this method, and a fracture sooner or later occurred at the universal joint nearest to the propeller. When the modified form of ship was built the whole system of transmission was changed, and the propellers were fitted directly on to the engine crankshafts.
At a later date 240 horse-power Fiat engines were installed, and the engineers' cabin was modified and an auxiliary blower was fitted to supply air to the ballonets for use if the engines are not running.
In the N.S. ship as modified the car has been raised to the same level as the engineers' cabin, and all excrescences on the envelope were placed inside. This, added to the improvement effected by the abolition of the transmission shafts, increased the reliability and speed of the ship, and also caused a reduction in weight.
The leading dimensions of the ship are as follows: length, 262 feet; width, 56 feet 9 inches; height, 69 feet 3 inches. The gross lift is 24,300 lb.; the disposable lift, without crew, petrol, oil, and ballast, 8,500 lb. The normal crew carried when on patrol is ten, which includes officers.
As in the case of the Coastal, a gun is mounted on the top of the envelope, which is approached by a similar climbing shaft, and guns and bombs are carried on the car.
These ships have become notorious for breaking all flying records for non-rigid airships. Even the first ship of the class, despite the unsatisfactory power units, so long ago as in the summer of 1917 completed a flight of 49 hours 22 minutes, which at the time was the record flight of any British airship. Since that date numerous flights of quite unprecedented duration have been achieved, one of 61 1/2 hours being particularly noteworthy, and those of upwards of 30 hours have become quite commonplace.
Since the Armistice one of these ships completed the unparalleled total of 101 hours, which at that date was the world's record flight, and afforded considerable evidence as to the utility of the non-rigid type for overseas patrol, and even opens up the possibility of employing ships of similar or slightly greater dimensions for commercial purposes.
N.S. 6 appeared several times over London in the summer months of 1918, and one could not help being struck by the ease with which she was steered and her power to remain almost stationary over such a small area as Trafalgar Square for a quite considerable period.
The flights referred to above were not in any way stunt performances to pile up a handsome aggregate of hours, but were the ordinary flying routine of the station to which the ships were attached, and most of the hours were spent in escorting convoys and hunting for submarines. In addition to these duties, manoeuvres were carried out on occasions with the Fleet or units thereof.
From the foregoing observations it must be manifest that this type of ship, in its present modified state, is a signal success, and is probably the best large non-rigid airship that has been produced in any country.
For the purposes of comparison it will be interesting to tabulate the performances of the standard types of non-rigid airships. The leading dimensions are also included in this summary:
Type S.S. Zero S.S. Twin Coastal North Star Sea Length 143' 0" 165' 0" 218' 0" 262' 0" Overall width 32' 0" 35' 6" 49' 3" 56' 9" Overall height 46' 0" 49' 0" 57' 6" 69' 3" Hydrogen capacity (cubic feet) 70,000 100,000 210,000 360,000 Gross lift (lb.) 4,900 7,000 14,500 24,300 Disposable lift (lb.) 1,850 2,200 4,850 8,500 Crew 3 4 5 10 Lift available for fuel and freight (lb.) 1,370 1,540 4,050 6,900 Petrol consumption at full speed (lb. per hour) 3.6 7.2 18.4 29.8 Gals. per hour 0.36 0.72 2.05 3
NAVAL AIRSHIPS.—THE RIGIDS—RIGID AIRSHIP No. 1
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 No. 1, 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 No. 9 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.
No. 1 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 No. 9
Rigid Airship No. 1 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 No. 9.
No. 9 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 No. 1, 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 No. 1, 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 No. 9 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 No. 9 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.
No. 9 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 "
No. 9 having finished her trials was accepted by the Admiralty in Mar. 1917, 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 No. 23 CLASS
After the decision had been made in 1915 that work on No. 9 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 No. 9, 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 3,000 feet starting from nearly sea level.
As will be seen later this class of ship, although marking a certain advance on No. 9 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, No. 24 by Messrs. Wm. Beardmore and Co., at Glasgow, and No. 25 by Messrs. Armstrong, Whitworth and Co., at Selby, Yorkshire.
In many respects the closest similarity of design exists between No. 9 and No. 23, 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 No. 9 was 520 feet, was increased in No. 23 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 No. 9, with a disposable lift under specification conditions of 5.7 tons as opposed to 3.8 tons.
The longitudinal shape of No. 23 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 No. 9, 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 No. 23 are somewhat different. In No. 9 it was intended to be sufficiently strong to support all the main vertical bending moments and shearing forces, but in No. 23 it was primarily intended to support the distributed weights of water ballast, petrol tanks, etc., between the main transverse frames. Unlike No. 9, 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 No. 9, but the system of rudders and elevators is totally different. In place of the box rudders and elevators in No. 9, 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 No. 9. 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 No. 9. 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 No. 9, 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 No. 9, 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 No. 9, 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 No. 9, 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 No. 9 was to provide a structure sufficiently strong to support all the main vertical bending moments and shearing forces, and that in No. 23 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 No. 31 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.Z. 85, 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.