© Wonders of World Aviation 2015-23  |  contents  |  site map  | contact us  |  cookie policy

Wonders of World Aviation

Mobile Site

Many famous types of amphibians and flying boats have been produced by Saunders-Roe Limited

The Saunders Roe London was designed as a general-purpose flying boat

EXTENSIVELY USED BY THE R.A.F., the Saro London was designed as a general-purpose flying boat, and proved to be one of the most successful flying-boat designs in the world. This photograph, taken at the manufacturers’ works at Cowes, Isle of Wight, shows in the foreground a turntable which is used to assist in manoeuvring the flying boats on to the slipway for launching.

THE development of Saunders-Roe, Limited, is one of the most notable instances of progress in the aviation industry. At East Cowes, Isle of Wight, on the eastern shore of the little town, world-famous for its links with yachting, flying boats are built in one of the most modern workshops in Europe. The flying boats are launched down a slipway and take off from the waters of the Solent.

Saunders-Roe, Limited, combines the interests of S. E. Saunders, Limited, famous for fast marine craft and aircraft, with those of Sir Alliott Verdon-Roe. The story of the firm of S. E. Saunders goes back to 1830, when Moses Saunders, grandfather of S. E. Saunders, founded a boat-building business at Streatley-on-Thames, Berkshire. He afterwards moved over to the Oxfordshire side of the river at Goring.

In 1901 S. E. Saunders moved to West Cowes, and in partnership with others formed the Saunders Patent Launch Building Syndicate. This partnership ended in 1906, when Mr. Saunders moved across the river Medina to East Cowes and set up business under his own name. The formation of S. E. Saunders, Limited, a private limited company, followed. The principal products of the firm were fast motor launches.

The design and construction of these craft provided valuable data and experience which were later useful in the production of flying-boat hulls. The firm claims to have built the first wooden launch to go faster than a steel boat and the first motor boat for the British Admiralty. In 1912 a Saunders hull was fitted to the Sopwith Bat, the aircraft which was the first successful amphibian. The Bat won the Mortimer Singer prize for a series of flights between land and water, alighting on the water and on land.

After the beginning of the war of 1914-18 the firm was engaged entirely on the production of land and sea aircraft. It was the first sub-contractor for aircraft to the British Admiralty and War Office, and built a large number of aircraft. The variety of the firm’s activities is indicated by the particulars of the work during this period. The firm built 201 Avro biplanes, 80 Short seaplanes, 24 Norman Thompson flying boats, 100 F.2.A flying boats, 50 F.5 flying boats, 116 flying-boat hulls, 389 seaplane floats, 416 aeroplane and seaplane parts, equal to about 200 aircraft, and eight gondolas for large airships.

This work necessitated considerable extensions to the works. After the Armistice the company turned to the development of flying boats of its own design. Among the most notable of these were the flying boats Valkyrie, Medina and A 7, which were prototypes for the Air Ministry.

Sir Alliott Verdon-Roe and the late John Lord joined the company in November 1928, and in the following year the name of the company was changed to Saunders-Roe, Limited. Among the amphibian aircraft and flying boats produced were the Saro Cutty Sark, the Saro Windhover, the Saro Cloud and the Saro London.


ALTERNATIVE ENGINES MAY BE FITTED to the Saro London, giving horse-powers up to a total of 2,400 without modification of the superstructure. The normally fitted engines are two Bristol Pegasus X engines, each of 820 horse-power at 2,250 revolutions a minute Armament may include a torpedo carried on rails fitted to the top of the hull, as shown in this photograph.

The Cutty Sark amphibian flying boat was designed for the private owner, flying boat training, navigational instruction and feeder air lines. With the wheels lowered, the amphibian can take off from any aerodrome and fly to a seaport or lake, upon which it can alight, with the wheels up, as a flying boat. It can taxi to a slipway and, after the wheels have been lowered, can taxi up the slipway. This ability of the amphibian to dispense with a wheeled undercarriage and a winch to haul it up a slipway is one of its chief advantages over a flying boat. Although the weight of the amphibian is slightly more than that of a flying boat of equal power, its other qualities amply compensate for the extra weight.

The Cutty Sark hull was built of “Alclad” (protected aluminium alloy) to the Saro patented design. The span was 45 feet, length 34 ft. 4 in., height (to top of engine cowling) 11 feet and wing area 320 square feet. Four seats were arranged in the cabin and the hull was divided by four watertight bulkheads into five compartments. The bow compartment was used for stowing marine gear. Moorings were picked up from an opening in the deck, which was normally covered with a sliding hatch. The main compartment forming the cabin, just forward of the wing, was enclosed. The front screens were of “Triplex” glass and the sides and roof of “Cellon” dope. The four seats were arranged side by side with a gangway between them.

Aft of the cabin was the luggage compartment. Access to the two engines was through a hatch aft of the luggage compartment. A fixed fin, built integral with the hull, carried a small trimming fin and the tail unit. The wing floats were of similar construction to the hull and had two watertight bulkheads. The floats were attached to the wing outboard of the amphibian undercarriage. All fittings on the outside of the hull were of stainless steel.

Flight Duration Four Hours

The monoplane cantilever wooden wings were formed by two spars of box section with spruce flanges and three-ply webs; the ribs were of three-ply with spruce flanges. The three-ply covering was specially stiffened near the engines to provide walkways. The wings were of sufficient buoyancy to support the aircraft if the hull were so damaged that the interior was flooded. They were attached to the hull by four stainless steel fittings, and were removed by unfastening the bolts of the fittings. The two engines were mounted above the wings so that all their parts were accessible while the aircraft was afloat.

The trimming fin, tailplane, elevators and rudder were of welded mild steel, covered with fabric. The elevators and rudder had horn balances. The two main fuel tanks carried sufficient fuel for four hours’ flight at cruising speed, and were mounted in the wings and interconnected with large balance pipes. Surface-cooled oil tanks were mounted in the nacelle behind each engine.

The amphibian chassis was a detachable unit, with a wide wheel track and ample shock-absorbing qualities. Axle and radius rods were attached to the side of the hull at the spar frames. The shock-absorbing leg sloped to the top corner of the hull at the front spar, where it was attached to a screw shaft, and was retracted along this to the centre of the machine. The wheels were well clear of the water for taking off. Control of the amphibian chassis was by a crank operated by the pilot and torque shafts aft, the chassis being wound up or down in about half a minute. An indicator showed the pilot when the chassis was fully lowered. Shock-absorbing was by patent stainless steel oleo legs, operated by oil and high-tensile steel springs.

A choice of engines provided a total horse-power of either 240 or 280, and another model was fitted with one engine giving 215 horse power. With two Gipsy Major engines the weight of the machine when empty was 2,670 lb, the disposable load being 1,180 lb, and the total weight 3,850 lb. By dispensing with the amphibian chassis the empty weight was reduced to 2,500 lb. and the disposable load was increased to 1,350 lb. The top speed of the amphibian was 103 miles an hour, cruising speed 85 miles an hour, climb 550 feet a minute and ceiling 9,000 feet. The flying boat model was ten miles an hour faster than the amphibian at maximum speed and cruising speed was five miles an hour greater. The rate of climb was increased by 50 feet, and the ceiling was 500 feet higher.

The larger and more powerful Saro Cloud, which was developed later than the Cutty Sark, has been adopted by the R.A.F. as the standard navigational training aircraft. The hull of this twin-engined amphibian is of similar construction to that of the Cutty Sark, all framing being of straight section. No plating has curvature in more than one direction, a feature which enables repairs to be carried out easily. The control cabin, which is entered by a sliding hatch forward of the screen, has two seats with a gangway between them, the pilot occupying the port seat.

The saloon cabin, which in the civil machine has seats for seven or eight passengers, has doors at either end. Forward there is full headroom, and aft, under the wing, the headroom is 5 ft. 3 in. The length of the cabin is 10 ft. 6 in., and there is a gangway between the two rows of seats. Aft of the passenger cabin is the luggage compartment, in which is the main companionway, with hinging doors and steps for access to the ground. The passenger cabin has a cubic capacity for freight of 300 cubic feet. Fin, wing float tail unit and wing are of similar design and construction to those of the Cutty Sark, although on a larger scale. The span is 64 feet, length 49 ft. 9 in., height (to top of engine cowling) 15 ft. 8 in., and wing area 650 square feet.

Low Water Resistance

There is a difference between the weights and performances of the flying boat and the amphibian. Total weight loaded of either is 9,500 lb; the empty weight of the flying boat is 6,070 lb. and the disposable load 3,430; corresponding figures for the amphibian are 6,720 lb. and 2,780 lb. respectively. Fitted with two engines giving a total of 680 horsepower, the flying boat has a maximum speed of 120 miles an hour, and a cruising speed of 103 miles an hour; the extra gear of the amphibian reduces these two speeds by ten miles an hour. The ceiling of the flying boat is 11,000 feet; that of the amphibian is 10,000 feet.

The Saro London general purpose flying boat is extensively used by the R.A.F. The prototype won the competition for a craft to replace obsolescent types. Because of this the aircraft was put into full quantitative production. It is designed for open-sea reconnaissance, coastal defence and

patrol, convoy and general purpose duties.

The qualities for which the London was selected were such that the type has proved to be among the most successful flying boats in the world. The first essential quality in a flying boat is seaworthiness. The hull must have a low water resistance (minimum skin friction of the submerged part), a clean design so that the water disturbance is the least possible at speed, an ample margin of stability when at rest or taxying, steady running characteristics, and the trim must enable the aircraft to adjust itself to rough, choppy or smooth water. A feature of the design of the London is the capacity of the machine to fly on a pair of medium-powered motors, and also to be equipped with engines of a maximum of 1,200 horsepower per engine if necessary. The cost of the conversion is less than one-quarter of that for other types, because no alteration of superstructure is necessary.

The Saro Cutty Sark was designed for the private owner, flying boat training, navigational instruction and feeder air lines

AN AMPHIBIAN FLYING BOAT can alight either on land or water. The Saro Cutty Sark was designed for the private owner, flying boat training, navigational instruction and feeder air lines. The totally enclosed cabin had accommodation for four people, including the pilot. The hull was metal-covered, and the wings were covered with three-ply wood. The range at cruising speed was four hours.

Other features of the London include the capability of handling an overload of about 4,000 lb., the great buoyancy due to the large hull, seaworthiness, freedom of movement of the crew in any part of the boat, and a comparatively flat wide deck which facilitates external movement on board. The wings are in seven units, the outer parts of the lower wing being small and easily replaced. Maintenance and repairs are easily made, especially to the hull, where complicated mouldings have been eliminated by the flat system of plating. The longitudinal stability enables the aircraft to be stable at extreme ranges of centre of gravity, and the airframe is well-balanced and sturdy.

The dimensions of this twin-engined unequal-span biplane are: span 80 feet, length 56 ft. 6 in., height 18 ft. 4 in. The upper plane is in three sections, the lower, the span of which is 56 feet, is in four sections. Each outer section of the bottom wings is joined at the base of the intermediate struts and can be removed without deranging the remainder of the structure. The overhang of these wing tips is short; detachable tips are provided on the spars so that local damage does not necessitate scrapping the whole spar. Ailerons are mounted on the top wing only, to avoid the risk of damage from the sea or from boats. The centre struts attaching the upper wing to the hull are anchored to the hull in special frames, widely spaced to absorb the heavy forward loads encountered when the aircraft alights in a heavy sea.

The wing floats have a sufficient reserve of buoyancy to permit the aircraft to be taxied across wind or in heavy weather conditions; the sturdy strutting arrangement ensures that the float cannot be damaged or lost. Suction pipes enable the floats to be pumped out while the machine is moored.

The hull is made of “Alclad” protected duralumin and has fittings of stainless steel. It is bulkheaded and any two of the three watertight compartments can be holed without loss of the aircraft; any water which may gain access to the bilge can be pumped or drained from one sump.

In the bow compartment there is a locker forward for stowing the anchor and chain, a roller lead being provided for the chain. Warps, hand lines, boathook and other gear also are stowed in the bow compartment. There are two towing bollards in the nose of the aircraft and cable towing strops are provided. The bow Scarff gun ring is fitted on sliding rails; below it is the bomb aimer’s station. The station is in a sheltered position and has a wind-balanced shield or door in the nose of the aircraft. Drums of ammunition and other military equipment are stowed in the bow compartment.

View in All Directions

Aft of the bow compartment is the pilot’s compartment, a bulkhead with a sliding door separating these two compartments. Pilot and second pilot or navigator sit side by side in the cabin with a gangway between them. The top of the cabin consists of a transparent sliding roof, which provides a view in all directions. Fuel jettison-valve releases are included among the controls and an automatic pilot can be fitted.

A partition divides the pilots’ compartment from the navigator’s compartment or officers’ cabin, which is entered through a door in the side of the hull; an internal sliding door separates the officers’ cabin from the rest of the hull. There are two bunks on the starboard side and a navigation table to port. Stowage for instruments and officers’ equipment is provided and the cabin is lighted by hinged ports on either side.

Behind the officers’ cabin are the engineer’s and wireless operator’s stations, and bunks for the crew. The engineer’s station is to starboard, with instrument boards and controls for all engine services, including the compressed-air starting unit for the engines. A ladder leads to the deck, access to which is through a sliding hatch. The galley, aft of the crew’s quarters, is provided with a cooking stove, an ice chest, a larder and lockers. The midships gunner’s post is behind this compartment ; the firing step is fitted with a vice and is used as a work bench. External access from this gun position enables the drogue box to be reached. Wet ropes and gear are stored in this and are not brought into the aircraft hull.


A CUTTY SARK AMPHIBIAN taking off. When the aircraft was used from water the landing wheels were wound up well clear of the water. The raising or lowering of the wheels could be effected in about half a minute. All metal parts used in the wheel chassis were of stainless steel, to prevent corrosion due to salt water thrown on to them.

Gear such as the rubber dinghy, bedding, maintenance platforms, spare airscrews and engine derricks are stored in the tail compartment. The rear gunner’s position is in the extreme end of the tail. The cockpit is fitted with a seat, and can be closed by a sliding watertight hatch. The control runs can be inspected easily, all cable runs being either open in the hull, or, as with the aileron controls, external to the wings. Access to the back of each engine is through a door beneath the engine cowling. Maintenance platforms hook on to the engine structure so that the cylinders can be reached; an inspection platform enables the propellers to be removed while the aircraft is on the water. A crane is provided for removing and changing the engines and there are attachments for lifting the entire aircraft.

The four fuel tanks are mounted in the top centre section, the total capacity being 548 gallons. A pump system assists the gravity flow to the engines. Auxiliary saddle tanks can be fitted on the deck of the hull to extend the range. The lubricating oil tanks are in the leading edge of the top plane; the oil is cooled by oil radiators slung beneath the engine cowling. In an emergency the fuel tanks can be emptied within two minutes by jettison valves.

Two Bristol Pegasus X engines, each of 820 horse-power at 2,250 revolutions are now standard equipment. They drive two three-bladed metal airscrews of 13 ft. 6 in. diameter. Spare engines and other material can be carried on deck and a torpedo can be carried on rails.

The three gun positions completely cover, between them, the entire field of fire, and the spaciousness of the hull enables a rapid interchange of gunners between stations. Bombs are hoisted into position when the aircraft is afloat or on shore by the Saunders-Roe patent hoisting gear, consisting of a direct lifting winch placed immediately over the bomb positions. The average time to prepare for loading and to load one 500-lb. bomb with the winch is 2 minutes 25 seconds on the slipway. The winch can be removed from port to starboard in a minute and a half; the time taken to load a 250-lb. bomb being also a minute and a half. At moorings in good weather four 250-lb. bombs can be secured in position from a dinghy in less than fifteen minutes.

Electrically Operated Bomb Carriers

All bomb carriers are electrically operated and are placed as follows: two to take bombs of from 50 to 550 lb. are fitted to the outer port and starboard positions on the underside of the bottom plane and two to take bombs up to 250 lb. are fitted in the inner positions; two light carriers are fitted inboard of these two larger ones to take either eight 20-lb. bombs, eight practice bombs, four Mark I four-inch flares, or four Mark I smoke flares. The bomb controls are operated electrically through twelve release selector switches and one bomb-aimer’s firing switch; there is also a pilot’s jettison release switch for the bombs. The controls are on the starboard side of the bombing officer’s station in the bow and any single bomb can be released. All switches and controls are protected by a hinged metal cover, so that there is no likelihood of inadvertent release of bombs by the gunner in the bow position.

The weight of the flying boat empty is 11,100 lb., the fixed military and service loads and the fuel and oil bringing the weight of the London in flying trim to 18,400 lb. Maximum overload weight is 22,000 lb. With the full normal load of 18,400 lb. and with two Bristol Pegasus X engines, the maximum speeds of the flying boat are, in miles an hour, 142 at sea level, 155 at 6,560 feet, 149 at 13,120 feet. The cruising speeds range from 128 miles an hour at 13,120 feet, on 60 per cent of power, through 134 miles an hour at 6,560 feet on 70 per cent of power, to 136 miles an hour at sea level on 80 per cent of power. The flying boat takes off in sixteen seconds in a distance of 310 yards. The service ceiling is 19,900 feet. The most economical cruising speed is 109 miles an hour at 5,500 feet on 45 per cent of power. This gives a range of 1,200 miles, the range at 70 per cent of power being 960 miles and at 100 per cent of power, 620 miles.

The Saro Cloud is a larger amphibian than the Cutty Sark, but is designed on similar lines

USED BY THE R.A.F. FOR TRAINING in navigation, the Saro Cloud is a larger amphibian than the Cutty Sark, but is designed on similar lines. None of the plating on the hull of this aircraft has curvature in more than one direction; this considerably simplifies repairs. The aircraft is available also as a flying boat; in this form it has a slightly better performance than when wheels are provided. The Flying Amo, illustrated here, has an auxiliary wing, the object of which is to reduce the landing speed. The aircraft's dimensions are: span 65 feet, length 49 ft. 9 in., height (on chassis) 17 feet.

The London was designed not for high performance but principally for strength, simplicity, seaworthiness and low maintenance costs, and because of these factors has proved a notable aircraft in service. Among the performances of the type are the first non-stop flight from Gibraltar to Plymouth in 1931 and the 30,000 miles’ formation flight completed in May 1938 by five flying boats of No. 204 (General Reconnaissance) Squadron R.A.F. Under the command of Wing Commander K. B. Lloyd, A.F.C., the five Londons took off from Mount Batten on December 2, 1937. Air Commodore S. J. Goble, C.B.E., Page 757 D.S.O., D.S.C., of the Royal Australian Air Force, who has flown round Australia in a seaplane, embarked at Plymouth as a passenger to Australia. The flying boats flew via Malta, Egypt, India, Singapore and Batavia to Australia, arriving at Darwin on January 17, 1938. They flew round Australia, left Melbourne on April 5, and returned to Plymouth on May 29, having flown more than 30,000 miles in about 400 hours’ flying time.

The London is one of the most comfortable aircraft, as the space and accommodation enable the crew to live on board. The transparent cover over the cockpits keeps out rain in flight, and prevents water from being shipped when the flying boat is taking off.

Quantity production necessitated the building of a new main workshop, which was completed at East Cowes in 1935. The building can house from ten to twelve flying boats in various stages of construction. This main erecting shop provides a clear space of 150 feet by 200 feet, with a height of 40 feet. This is achieved by means of main roof trusses spaced at 50-feet centres, which support secondary lattice girders and rafters carrying the corrugated asbestos-cement covering. To provide for future developments, the main stanchions on one side of the building are designed to support another similar 150-feet span roof. The doorway has an opening 150 feet wide by 40 feet high, and has six steel-framed sliding doors. Although each of the doors weighs 5 tons, it is easily opened or shut by one man operating hand gearing.

The main roof trusses support tracks for electrical travelling hoists. The galleries are under lean-to roofs of 30 feet span. On the East Gallery is the sheet metal working department, where petrol and oil tanks, wing tip floats and stowage fittings are made. The assembly fitting and mechanical testing department is on the ground floor. On the West Gallery are the sewing room and metal wing assembly; below are dope and covering shops for large wing components. The office block contains, on the ground floor, the finished parts store and other stores, the executive offices. The Aeronautical Inspection Department is on the first floor; the mould loft, parachute assembly department and lecture and school room are on the second floor. There are two grades of apprentices, ordinary and premium. Ordinary apprentices are selected from boys whose relatives are employed by the company or who live in the neighbourhood. These boys generally serve their time in a particular trade, and from them the most promising are chosen as selected ordinary apprentices to be given instruction in the drawing office and elsewhere. Premium apprentices receive instruction in the tool stores, and machine, detail fitting, metal wing and erecting shops before proceeding to the drawing office and technical departments.

When the slipway was built provision was made for future flying boats of 50 tons and requiring support for a maximum wheel load of 17 tons. Piles of 12 in. square section varying between 22 and 40 feet were used. The upper part of the slipway was built on the flat slab principle, and the part below half-tide level with precast units. Units weighing about 5 tons, each interlocking and attached to the tops of the piles, were used for the decking. The apron and the floor inside the building are of reinforced concrete supported on hard core filling. To prevent concrete dust from damaging machines in construction the floor was hardened and dustproofed.

An R.A.F Saro Cloud being taxied on to the slipway

ONE OF THE ADVANTAGES of an amphibian flying boat is that it can be beached easily. When the amphibian has taxied up to the slipway the wheels are lowered while it is still afloat. Taxying can then be continued right up the slipway, the wheels taking the weight as the hull comes clear of the water. This photograph shows an R.A.F Saro Cloud being taxied on to the slipway.

Click here to see the photogravure supplement to this article.

You can read more on “Floatplanes and Flying Boats”, “Flying Boats and Their Work” and “Seaplanes and Their Work” on this website.

Saunders-Roe Aircraft