CHAPTER VI

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.

S.S.B.E. 2C

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.

S.S.P.

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.

S.S. ZERO

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.

S.S. TWIN

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 us d 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 moot 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 progaramme, 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 see,, 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: