THE advantages offered by the large-scale flying boat for use on overseas air routes have long been recognized, and one of the most important and significant developments in British commercial aviation has been the recent adoption of this type of aircraft by Imperial Airways.

Imperial Airways have had a small number of flying boats in use for some years, but it was not until 1934 that it was decided that on their long trunk routes the flying boat class of craft. should be used as well as the land plane.

This re-equipment represents one of the boldest steps ever taken in British air transport. A contract was placed with Short Brothers, Ltd., of Rochester, Kent, for twenty-eight flying boats, the specification laid down being based on Imperial Airways' experience in flying over their scheduled routes between England and South Africa, England and Australia, and elsewhere.

The Short Empire flying boat has been the result. She is an all-metal cantilever monoplane powered with four engines. In design and construction the craft is full of ingenious and unusual features. Among modern aircraft she is a giant in size and in weight.

From tip to tip the main plane measures 114 feet. From nose to tail the length is 88 feet, and the overall height is 31 ft. 9-3/4in. Unladen, the boat scales 24,000 lb., and when fully loaded, 40,000 lb. Yet this great monster weighing eighteen tons can attain 200 miles an hour as a maximum all-out speed, or can cruise at 165 miles an hour with the motors throttled down. The normal range in still air is 760 miles, and after a take-off lasting only twenty-one seconds the boat can gain height up to a ceiling of 20,000 feet at the rate of 950 feet a minute. These figures, which must necessarily be baldly stated, cannot in themselves convey a true idea of the immense bulk of the craft, nor the impressiveness of her behaviour on the water and in the air.

The craft has to be boarded and viewed from inside and outside before one can realize what a masterpiece of aircraft construction her manufacturers have achieved. A factor that makes their venture all the more remarkable is that in many ways the design breaks away from orthodox practice. The only precedent was the Short Scion flying boat which was, in effect, a half-scale model of the new Empire class.

FIRST OF THE NEW FLEET to be completed, the Conopus measures 88 feet from nose to tail and has a wing span of 114 feet. Her overall height is 31 ft. 9-3/4 in. and she weighs 40,500 lb. when fully loaded. She has a range of 760 miles in still air.

Those who bore the main responsibility in producing the boats must have experienced some anxiety as the work proceeded, for here was a whole fleet of new craft steadily taking shape, their performance yet to be proved, while the date of delivery, as laid down in the contract involving thousands of pounds, grew inexorably nearer.

The work began in the designers' office, spread to the drawing office, then to the works and the big erecting shops. Seventy draughtsmen worked to produce some 12,000 drawings, tracings and blueprints, with every nut, bolt and rivet shown. Every part, component and unit was numbered and scheduled. So the task proceeded. Meanwhile all those difficulties of manufacture and erecting which might or might not arise were being weighed up, considered and prepared for.

When an aircraft is built to operate from the surface of a river or the sea, additional factors add to the complications that face the designer. One of the most difficult tasks is the design of the planing, bottom of the hull so that the craft will "unstick" easily in all conditions of loading and yet be stable while manoeuvring on the water and while landing. Hull design is not easy, even in small craft; imagine, then, the size of the task on the Empire boat with her all-up weight of 40,500 lb. She had to be strong enough to withstand tremendous shocks on alighting on a rough sea. Yet she had to be light.

Her interior capacity had to be such as to provide passenger accommodation not inferior to that in an up-to-date bungalow or flat. Yet the boat had to be aerodynamically correct in structure and contour to give adequate strength, control and the prescribed speed. All these factors, with a great many others, were meticulously considered, calculations were made, numerous scale models were tested in a tank, and finally the Empire boat's hull was evolved.

The Empire craft differs from the majority of British flying boats, in having a hull with a small beam-height ratio; her beam is narrow in comparison with the height from the keel to the top of the structure.

Throughout the hull, metal is used, with girders, sheeting and fittings riveted together. The main structure at the base consists of the keel and two chines, or "backbones." The keel is made of a built-up I-shaped beam with L-shaped sections located on either side and at the top and bottom edges of the flange to complete the I-section. The building of the keel is thus in itself an intricate piece of work which is further elaborated by the way in which holes are cut in the web to reduce the weight. Between the keel and the chines there is a series of transverse frames built up of other riveted girder members with horizontal channel members arranged transversely between the two chines. To this triangular arrangement are attached the vertical frame members of varied girder form, longitudinal members, diagonals, gussets, angle-brackets and stringers which go to make up the entire framework that is the basis of the great hull. Over the whole is fixed sheet alloy (known as "Alclad") planking. The "Alclad" sheeting is riveted to the longitudinal and vertical members with flush-headed rivets so as to complete the smooth surface.

The hull interior is divided into various compartments. In the bows there is a locker used for the stowage of marine equipment consisting of a retractable mooring bollard (a projection to which ropes and cables are secured), an anchor and a boat hook. This hold has a hatch in its turtle decking from which mooring operations are conducted. There is also a retractable landing light in this compartment Above the locker is the pilot's cabin, from which access is gained to the locker by a step ladder. The pilot's cabin is so large that the term "cockpit" would be a misnomer.

A RADIAL AIR-COOLED ENGINE of the type used in the Empire flying boats. Four of these nine-cylinder engines, each developing 920 horse-power, give the boats a cruising speed of 165 miles an hour and a ceiling (maximum height) of 20,000 feet.

Immediately behind the semicircular glazed front is the instrument panel, with its elaborate array of engine and navigation instruments. Mounted on the top of the panel are the four starter switches and ignition switches for the engines, and in the centre is the "auto" pilot, a wonderful piece of apparatus which automatically keeps the plane on a predetermined course. The other instruments include a rate-of-climb indicator, engine revolution indicators, sensitive altimeter, air speed indicators, homing indicator, directional gyro, artificial horizon and dual compasses. This complicated installation may seem bewildering, but every instrument is a vital and essential component. Combined with the special radio plant that is installed in another compartment, the entire equipment makes the great flying boat almost independent of the outside world when flying on her long and lonely routes.

Behind the instrument panel are the seats provided for the captain and his first officer. The flying controls consist of the orthodox control column and rudder-bar apparatus. The control column is surmounted by a wheel which operates the lateral controlling surfaces and forward or backward movement of the column actuates the elevators. These controls are duplicated, and between the two sets the engine control levers are grouped. These levers are centrally placed so that either pilot can operate them. They consist of four throttle levers, four mixture controls, a master switch for the automatic pilot and two "cut-out" levers. The "cutout" levers are for the purpose of making the engines dead after switching off.

Other controls disposed near the pilots' seats are the airscrew pitch controls, fore-and-after trimmer, rudder bias, fuel supply cocks and the switch for operating the wing flaps.

Arranged round the cabin behind the pilots' seats is further equipment. On the starboard side there is a panel containing gauges showing the temperature of the engines; on the opposite side there are the gyro pilot unit, auxiliary electric generators and the directional loop for the wireless direction-finding receiver, near which the radio operator is seated. Behind the starboard pilot's seat there is a skylight which can be opened. This allows the navigator to make his observations without difficulty, as the aperture is provided with a wind-screen which protects the navigator from the rush of air.

Radio Operator's Cabin

CONSIDERING the great size of the Empire flying boat, her immense power and her elaborate equipment, it is astonishing that one man can fly the machine single-handed. In regular operating conditions the duties are divided between various members of a crew, but on the initial test flight of the first Empire boat Shorts' test pilot, Captain J. Lankester Barker, was alone in the machine.

The pilots' cabin is partitioned off from the radio operator's cabin by a sloping bulkhead and door. The operator sits with his back to the pilots and is in charge of a transmitting set and a, receiving set which operate on wavelengths of 600-2,000 metres and 16-75 metres. The directional loop can be projected from or retracted into the compartment by a simple mechanism, the object being to reduce drag when it is not in use. There is also a trailing aerial which, when not in use, is wound on a drum. When it is drawn up an automatically-closing flap seals the aperture through which it passes. In addition to the trailing aerial there is another one arranged in a "V" on the top of the wing and the hull. By means of this aerial the radio operator is able to pick up signals and calls while he is transmitting, for as soon as he releases the key of his transmitter his headphones are connected to the receiver.

The pilots' cabin and the radio room are located in the upper deck—for the flying boat has two decks within her hull.

THE "BRIDGE" OF ONE OF THE EMPIRE FLYING BOATS. Between the seats for the captain and first officer are four throttle levers, four mixture controls and the switch for the "automatic pilot." At the top of the instrument panel are the starter switches and ignition switches for the four engines. The dials of the rate-of-climb indicator, air speed indicator, revolution counter, gyro compass, altimeter and homing indicator all face the pilots. Many other controls are arranged round the walls of the cabin.

Next to the radio compartment, in the aft direction, there is the mail compartment, which is combined with the office of the ship's clerk, whose desk and equipment are on the starboard side, the space for mail (or freight) being arranged on the port side. A sliding door in this compartment provides communication.

The clerk's office serves as headquarters for the internal lighting equipment of the whole craft, and beside the desk the main switch panel is fitted. This carries voltmeters, ammeters, fuses and switches not only for the ceiling and wall lights in the passengers' quarters but also for those in the radio cabin, pilots' cabin, mail and bunk stowage and loading hatch, and for the navigation lights as well. The top deck extends beyond the clerk's office to a hold in which is housed bedding for passengers' use during night nights. At the rear of the office there is a step ladder leading to the kitchen, which is on the lower deck between the midship cabin and a smoking cabin.

READY FOR LAUNCHING AT ROCHESTER. The Canopus, on her initial tests, was flown by a single pilot. Considering the great size of the craft, her immense power and her elaborate equipment, this is a striking tribute to the controllability of the machine. Unladen the Canopus weighs 24,000 lb., and with her motors throttled down she has a cruising speed of 165 miles an hour.

The smoking cabin is immediately behind the mooring locker in the bows, and is 6 ft. 6 in. long, 10 feet wide and 8 feet high, sumptuously furnished and decorated in green and white. It is only one of four compartments allotted for the accommodation of the passengers. Amidships is another saloon of similar size, which is connected by a passageway to the smoking cabin. This saloon contains chairs of a special design which can be adjusted to provide a reclining position or an upright sitting position. They are upholstered with air cushions. Near by are the steward's pantry and the lavatories. The pantry is lavishly equipped with compact and ingenious devices. There are plate racks, sink, draining-board, an ice chest and hot cupboards.

Two Ventilating Systems

FARTHER astern is a large cabin which, because its spaciousness permits passengers to "take a stroll," is known as the promenade cabin. This is an innovation in heavier-than-air craft, and one of considerable importance. One of the disadvantages associated with air travel in the past has been the lack of room. On long trips passengers became cramped. The promenade cabin in the Empire boat overcomes this difficulty. The midship cabin accommodates three passengers by day and four by night: the promenade cabin holds eight seated passengers and four resting occupants; and in the fourth cabin, which is far down the hull, there are six seats for use during the day, or accommodation for four sleeping passengers can be provided at night. The equipment and furnishing of these saloons, or cabins, does not cease at lighting, carpets, chairs and tables. There are also bunks, bell pushes for summoning the steward, hold-alls attached to the walls, luggage racks, cover flaps for the numerous windows and individual ventilation controls.

In all the cabins there are two separate ventilation systems. One consists of a series of ducts which have, their outlets at floor level. Air passes into these ducts and to a steam radiator. Steam is generated in a boiler fitted to the exhaust pipe of one of the engines, and by a control, which is operated by the pilot, the air stream that is warmed in the radiator can be supplied in varying degrees to the hull interior. The second ventilation system comprises a simple arrangement of louvered vents that call be adjusted by the passengers to suit their individual requirements.

There is one more compartment in the hull and this consists of a large hold wherein is stowed baggage, freight and mail. This hold is behind the after cabin and access is provided to it through a hatchway located on the cambered decking.

THE HUGE ADJUSTABLE LAUNCHING WHEELS of the Caledonia, shown at Rochester immediately before beginning her trial flights, give an impression of the great size of the new craft. The smooth finish imparted to the hull and wings by the use of sheet alloy and flush-fitting rivets is also clearly shown.

The cantilever wings of the Empire boat, as well as providing the lift and the lateral controlling surfaces, also house the four power units, the fuel and the oil tanks. The construction throughout is of metal and the main spars are built up in the form of a girder box. These "boxes" are tapered in depth as well as in plane towards their outer extremities. Round these spars are built a complicated system of struts, stiffeners and the tubular mountings for the engines.

The whole of the wing is covered with light-metal sheet. A novel feature of the wing assembly is the way in which the leading edge and the trailing edge (that is the front and rear portions of the wing) are built up as separate units and attached bodily to the central portion comprising the spars. When these units are removed the entire internal structure of the wing with all its intricate details is revealed. The hinged outer sections of the trailing edge which form the ailerons for lateral control are fixed in the usual way, and flaps are arranged between the inner ends of the ailerons and the hull.

The object of these flaps is to reduce the landing speed, and for this purpose they are lowered by the pilot as he makes his approach prior to alighting. The flaps are really retractable extensions of the trailing edge, and have a curved upper surface but are flat underneath.

The flaps move in curved tracks, run on roller bearings, and are extended and drawn into their recesses by a form of screw jack that is rotated by a small electric motor. When the pilot wishes to operate them he simply moves a switch. The flaps are moved down in sixty seconds and returned in ninety seconds. The four engines are of the Bristol "Pegasus" type and develop 920 horse-power each, yielding a total of 3,680 horse-power. They are of the radial air-cooled type having nine cylinders. Each engine is surrounded by a streamlined cowling and is fitted with a three-bladed De Havilland variable pitch airscrew, which is to the aeroplane as the gear box is to the motor car.

This device is controllable from the pilots' cabin so that at the take-off additional power is available, after which it can be adjusted to secure the most economical running while the machine is cruising. Alongside each engine there are two retractable platforms on which mechanics can stand to attend to the mechanism. The engines are started by electric starters and a hand turning gear is also incorporated.

The fuel tanks are placed behind each pair of engines and are embodied in the wing. The standard capacity is 600 gallons, but additional tanks are fitted in the machines designed for the transatlantic service.

On the under surface of the wing, at a point somewhat beyond the outer engine on either side, a float is attached on streamlined and wire-braced struts. These floats are to stabilize the craft when she is on the water; to prevent undue torsional loads reaching the wing, in the event of the floats being struck by broken water, the floats are fitted with shock absorbers.

The tail unit of the Empire boat is built into the stern of the hull. The construction of the tail plane, the rudder and the elevator is similar to that of the main wings. Rudder and elevator are equipped with trimming tabs.

These tabs are provided to set the altitude of the machine while in flight and to relieve the pilot of a proportion of the work of keeping the machine on her course. The tabs are operated by handle controls located in the pilots' cabin.

The first batch of the Empire flying boats was delivered in 1936, after having undergone all tests with complete success. The Canopus and the Caledonia were the first boats to be launched into the River Medway at Rochester, Kent. Early in 1937 the Centaurus, the Cambria and the Cavalier added their names to the Empire fleet of flying boats.

When the entire fleet is in service between Great Britain and South Africa, along the great England-Australia route and even across the Atlantic, these craft will be linking up the Empire as never before and another page will have been turned in the brief but eventful history of aviation.

BUILT TO OPERATE FROM THE SURFACE OF A RIVER, as well as from the sea, the Empire flying boats are designed for a take-off which lasts for only 21 seconds, and for a fast rate of climb. The hulls are designed to "unstick" easily in all conditions of loading, and yet are strong enough to withstand tremendous shocks when alighting on a rough sea. The Caledonia was one of the first of the Empire flying boats to be put into service.

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