The R101 was a British Airship from the 1930s. It was designed and built by an Air Ministry-appointed team and was effectively in competition with the government-funded but privately designed and built R100. When built, it was the world's largest flying craft at 731 ft (223 m) in length, and it was not surpassed by another hydrogen-filled rigid airship until The Hindenburg flew seven years later.
After trial flights and subsequent modifications to increase lifting capacity, which included lengthening the ship by 46 ft (14 m) to add another gas bag, the R101 crashed and exploded in France during its maiden overseas voyage on 5 October 1930, killing 48 of the 54 people on board, resulting in the end of the British Airship program.
Among the passengers killed were Lord Thomson, the Air Minister who had initiated the program, senior government officials, and almost all the dirigible's designers from the Royal Airship Works.
The crash of R101 effectively ended British airship development and was one of the worst airship accidents of the 1930s. The loss of life was more than the 36 killed in the highly public Hindenburg disaster of 1937, though fewer than the 52 killed in the French military Dixmude in 1923, and the 73 killed when the USS Akron crashed in the Atlantic Ocean off the coast of New Jersey in 1933.
Background[edit | edit source]
R101 was built as part of a British government initiative to develop airships to provide passenger and mail transport from Britain to the most distant parts of the British Empire, including India, Australia, and Canada since these distances were too great for heavier-than-air aircraft of the period. The Burney Scheme of 1922 had proposed a civil airship development program to be carried out by a specially established subsidiary of Vickers with the support of the British government, but when the General Election of 1923 brought Ramsay MacDonald’s Labour administration to power the new Air Minister, Lord Thomson, formulated the Imperial Airship Scheme in its place. This called for the building of two experimental airships: one, R101, to be designed and constructed under the direction of the Air Ministry, and the other, R100, to be built by a Vickers subsidiary, the Airship Guarantee Company, under a fixed-price contract. This led to the nicknames the "Socialist Airship" and the "Capitalist Airship".
In addition to the building of the two airships, the scheme involved the establishment of the necessary infrastructure for airship operations; for example, the mooring masts used at Cardington, Ismailia, Karachi, and Montreal had to be designed and built and the meteorological forecasting network extended and improved.
Specifications for the airships were drawn up by an Air Ministry committee whose members included Squadron Leader Reginald Colmore and Lieutenant-Colonel Vincent Richmond, both of whom had extensive experience with airships, principally nonrigid ones. These called for airships of not less than five million cubic feet (140,000 m³) capacity and a fixed structural weight not to exceed 90 tons, giving a "disposable lift" of nearly 62 tons. With the necessary allowance of about 20 tons for the service load consisting of a crew of approximately 40, stores and water ballast, this meant a possible fuel and passenger load of 42 tons. Accommodation for 100 passengers and tankage for 57 hours' flight was to be provided, and a sustainable cruise speed of 63 mph (101 km/h) and a maximum speed of 70 mph (110 km/h) was called for. In wartime, the airships would be expected to carry 200 troops or possibly five parasite fighter aircraft.
Vickers' design team was led by Barnes Wallis, who had extensive experience of rigid airship design and later became famous for the geodetic framework of the Wellington bomber and for the bouncing bomb. His principal assistant (the "Chief Calculator"), Nevil Shute Norway, later well known as the novelist Nevil Shute, much later gave his account of the design and construction of the two airships in his autobiography, Slide Rule: Autobiography of an Engineer, first published in 1954. Shute's book characterizes R100 as a pragmatic and conservative design, and R101 as extravagant and over-ambitious, but one purpose of having two design teams was to test different approaches, with R101 deliberately intended to extend the limits of existing technology. Shute later admitted that many of his criticisms of the R101 team were unjustified.
An extremely optimistic timetable was drawn up, with the construction of the government-built airship to be begun in July 1925 and complete by the following July, with a trial flight to India planned for January 1927. In the event, the extensive experimentation that was carried out delayed the start of construction of R101 until early 1927. R100 was also delayed, and neither flew until late 1929.
Construction[edit | edit source]
The whole airship program was under the direction of the Director of Airship Development (DAD), Group Captain Peregrine Fellowes, with Colmore acting as his deputy. Lieutenant-Colonel Richmond was appointed Director of Design: later he was credited as "Assistant Director of Airship Development (Technical)" with Squadron Leader Michael Rope as his assistant, and the Director for Flying and Training, responsible for all operational matters for both airships, was Major G.H. Scott, who had developed the design of the mooring masts that were to be built. It was based at the Royal Airship Works at Cardington, Bedfordshire, which had been built by Shorts during the First World War and had been employed by the Admiralty to copy and improve on the latest German designs from captured rigid airships. It had been nationalized in 1919 but after the loss of the R38 (then in the process of being transferred to the US as ZR2) naval airship development was stopped and it had been placed on a care and maintenance basis.
R101 was to be built only after an extensive research and test program was complete. This was carried out by the National Physical Laboratory (NPL). As part of this program, the Air Ministry funded the costs of refurbishing and flying R33 in order to gather data about structural loads and the airflow around a large airship. This data was also made available to Vickers; both airships had the same elongated tear-drop shape, unlike previous airship designs. Hilda Lyon, who was responsible for the aerodynamic development, found that this shape produced the minimum amount of drag. Safety was a primary concern and this would have an important influence on the choice of engines.
An early decision had been made to construct the primary structure largely from stainless steel rather than lightweight alloys such as duralumin. The design of the primary structure was shared between Cardington and the aircraft manufacturer Boulton and Paul, who had extensive experience in the use of steel and had developed innovative techniques for forming steel strip into structural sections. Working to an outline design prepared with the help of data supplied by the NPL, the stress calculations were performed by Cardington. This information was then supplied to J. D. North and his team at Boulton and Paul, who designed the actual metalwork. The individual girders were fabricated by Boulton and Paul in Norwich and transported to Cardington where they were bolted together. This scheme for a prefabricated structure entailed demanding manufacturing tolerances and was entirely successful, as the ease with which R101 was eventually extended bears witness. Before any contracts for the metalwork were signed, an entire bay consisting of a pair of the 15-sided transverse ring frames and the connecting longitudinal girders was assembled at Cardington. After the assembly had passed loading tests, the individual girders were then tested to destruction. The structure of the airframe was innovative: the ring-shaped transverse frames of previous airships had been braced by radial wires meeting at a central hub, but no such bracing was used in R101, the frames being stiff enough in themselves. However, this resulted in the structure extending further into the envelope, thereby limiting the size of the gasbags.
The specifications drawn up in 1924 by the Committee for the Safety of Airships had based weight estimates on the then existing rules for airframe strengths. However, the Air Ministry Inspectorate introduced a new set of rules for airship safety standards in late 1924 and compliance with these as-yet unformulated rules had been explicitly mentioned in the individual specifications for each airship. These new rules called for all lifting loads to be transmitted directly to the transverse frames rather than being taken via the longitudinal girders. The intention behind this ruling was to enable the stressing of the framework to be fully calculated, rather than relying on empirically accumulated data, as was contemporary practice at the Zeppelin design office. Apart from the implications for the airframe weight, one effect of these regulations was to force both teams to contrive a new system of harnessing the gasbags. R101's patented "parachute" gasbag harnessing, designed by Michael Rope, proved less than satisfactory, permitting the bags to surge unduly, particularly in rough weather. This caused the gasbags to chafe against the structure, causing holes in the fabric. Another effect was that both R100 and R101 had a relatively small number of longitudinal girders in order to simplify the stressing calculations.
R101 used pre-doped linen panels for much of its covering, rather than lacing undoped fabric into place and then applying dope to shrink it. In order to reduce the area of unsupported fabric in the covering R101 alternated the main longitudinals with non-structural "reefing booms" mounted on kingposts which were adjustable using screw-jacks in order to tension the covering. The pre-doped fabric proved unsatisfactory from the start, with panels splitting because of humidity changes before the airship had even left its shed.
There were other innovative design features. Previously ballast containers had been made in the form of leather "trousers", and one or other leg could be opened at the bottom by a cable-release from the control car. In R101, the extreme forward and aft ballast bags were of this type and were locally operated, but the main ballast was held in tanks connected by pipes so that ballast could be transferred from one to another to alter the airship's trim using compressed air. The arrangement for ventilating the interior of the envelope, necessary both to prevent any buildup of escaped hydrogen and also to equalize pressure between the outside and inside, was also innovative. A series of flap-valves were situated at the nose and stern of the airship cover (those at the nose are clearly visible in photographs) to allow air to enter when the airship was descending, while a series of vents were arranged around the circumference amidships to allow air to exit during ascent.
Engines[edit | edit source]
Heavy oil (diesel) engines were specified by the Air Ministry because the airship was intended for use on the India route, where it was thought that high temperatures would make petrol an unacceptable fire hazard because of its low flash point. A petrol explosion had been a major cause of fatalities in the loss of the R38 in 1921.
Initial calculations were based on the use of seven Beardmore Typhoon six-cylinder heavy-oil engines which were expected to weigh 2,200 lb (1,000 kg) and deliver 600 bhp (450 kW) each. When the development of this engine proved impractical, the use of the eight-cylinder Beardmore Tornado was proposed instead. This was an engine being developed by Beardmore by combining two four-cylinder engines which had originally been developed for railway use. In March 1925 these were expected to weigh 3,200 pounds (1,500 kg) and deliver 700 bhp (520 kW) each. Because of the increased weight of each engine, it was decided to use five, resulting in overall power being reduced from 4,200 bhp (3,100 kW) to 3,500 bhp (2,600 kW).
Severe torsional resonance of the crankshaft was encountered above 950 rpm, limiting the engine to a maximum of 935 rpm, giving an output of only 650 bhp (485 kW) with a continuous power rating at 890 rpm of 585 bhp (436 kW). The engine was also considerably above estimated weight, at 4,773 lb (2,165 kg), over double the initial estimate. Some of this excess weight was the result of the failure to manufacture a satisfactory lightweight aluminum crankcase.
The original intention had been to fit two of the engines with variable-pitch propellers in order to provide reverse thrust for maneuvering during docking. The torsional resonance also caused the hollow metal blades of these reversing propellers to develop cracks near the hubs, and as a short term measure, one of the engines was fitted with a fixed-pitch reverse propeller, consequently becoming dead weight under normal flight conditions. For the airship's final flight two of the engines were adapted to be capable of running in reverse by a simple modification of the camshaft.
Each engine car also contained a 40 bhp (30 kW) Ricardo petrol engine for use as a starter motor. Three of these also drove generators to provide electricity when the airship was at rest or flying at low speeds: at normal flight speeds the generators were driven by constant-speed variable-pitch windmills. The other two auxiliary engines drove compressors for the compressed air fuel and ballast transfer system. Before the final flight, one of the petrol engines was replaced by a Beverly heavy oil engine. In order to lessen the risk of fire, the petrol tanks could be jettisoned.
Diesel fuel was contained in tanks in the transverse frames, the majority of the tanks having a capacity of 224 imp gal (1,018 l). A mechanism was provided for dumping fuel directly from the tanks in an emergency. By the use of tankage provided for weight compensation when traveling with a light passenger load a total fuel load of 10,000 imp gal (45,000 l) could be carried.