R101 Airship

R101 was one of a pair of British rigid airships completed in 1929 as part of a British government programme to develop civil airships capable of service on long-distance routes within the British Empire. 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 in length, and it was not surpassed by another hydrogen-filled rigid airship until the LZ 129 ''Hindenburg'' was launched seven years later.

After trial flights and subsequent modifications to increase lifting capacity, which included lengthening the ship by to add another gasbag,"R101".
Airship Heritage Trust via Airshipsonline.com. Retrieved: 23 July 2008. the R101 crashed in France during its maiden overseas voyage on 5 October 1930, killing 48 of the 54 people on board. Among the passengers killed were Lord Thomson, the Air Minister who had initiated the programme, 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 48 lives was more than the 36 killed in the much better-known ''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

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 the distances were then too great for heavier-than-air aircraft. The Burney Scheme of 1922 had proposed a civil airship development programme to be carried out by a specially-established subsidiary of Vickers with the support of the British government. The scheme drew support from the Air Ministry, which sought more airships and a base in India. The Admiralty added that it would forego some light cruisers of which it was very short. However, Prime Minister Lloyd George's government decided it could not afford to support the Burney Scheme.

When the 1923 general election brought Ramsay MacDonald’s Labour administration to power, the new Air Minister, Lord Thomson, formulated the Imperial Airship Scheme in place of the Burney Scheme. It 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. They were nicknamed the "Socialist Airship" and the "Capitalist Airship", respectively.

In addition to the building of the two airships, the Imperial Airship Scheme involved the establishment of the necessary infrastructure for airship operations; for example, the mooring masts used at Cardington, Ismalia, 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 V.C. Richmond, both of whom had extensive experience with airships, most of them non-rigid. They 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, as well as stores and water ballast, this allowed 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 and maximum speed of were called for.''Report of the R101 Inquiry'' 1931, p. 14. 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, later gave his account of the design and construction of the two airships in his 1954 autobiography, '' Slide Rule: Autobiography of an Engineer''. Shute Norway's book characterises R100 as a pragmatic and conservative design, and R101 as extravagant and overambitious, 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 Norway later admitted that many of his criticisms of the R101 team were unjustified.

An extremely-optimistic timetable was drawn up, with construction of the government-built R101 to begin in July 1925 and be complete by the following July, with a trial flight to India planned for January 1927. In the event, the extensive experimentation that was necessary delayed the start of construction of R101 until early 1927. R100 was also delayed, and neither flew until late 1929.

Design and development

The entire airship programme 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. 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. Work was based at the Royal Airship Works at Cardington, Bedfordshire, which had been built by Short Brothers 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. The Works had been nationalised 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 completion of an extensive research and test programme by the National Physical Laboratory (NPL). As part of this programme, 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 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 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, tearing 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 stress 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, the design 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.''Report of the R101 Inquiry'' 1931, p. 31.

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 build-up of escaped hydrogen and also to equalise 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 was arranged around the circumference amidships to allow air to exit during ascent.

Engines

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 R38 in 1921."Boulton and Paul – the R101."
''norfolkancestors.org.'' Retrieved: 27 August 2010.

Initial calculations were based on the use of seven Beardmore Typhoon six-cylinder heavy-oil engines which were expected to weigh and deliver 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, combining two four-cylinder engines which had originally been developed for railway use. In March 1925 these were expected to weigh and deliver each. Because of the increased weight of each engine, it was decided to use five, resulting in overall power being reduced from to .

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 with a continuous power rating at 890 rpm of .Masefield 1982, p. 69. The engine was also considerably above estimated weight, at , over double the initial estimate. Some of this excess weight was the result of the failure to manufacture a satisfactory lightweight aluminium 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 caused the hollow metal blades of the 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 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; 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 . A mechanism was provided for dumping fuel directly from the tanks in an emergency. By the use of tankage provided for weight compensation, when travelling with a light passenger load a total fuel load of could be carried.

Crewing and control

In normal service, R101 carried a crew of 42. This consisted of two watches of 13 men under the officer of the watch, this duty being divided among the three principal ship's officers. In addition there were the chief navigator, the meteorological officer, the chief coxswain, the chief engineer, the chief wireless officer and the chief steward, who were not assigned to watches but were on duty as necessary, and four supernumeraries (three engineers and a radio operator) who were available to provide relief watch keeping if necessary, and an assistant steward, a cook and a galley boy who were on duty as required between 06:30 and 21:30. The minimum crew requirement, as specified in the airship's Certificate of Airworthiness, was 15 men.

The control car was occupied by the duty officer of the watch and the steering and altitude coxswains, who respectively controlled the rudder and elevators using wheels similar to a ship's wheel. The engines were individually controlled by an engineer in each of the engine cars, orders being given by an individual telegraph to each car. These moved an indicator in the engine car to signal the desired throttle setting and also rang a bell to draw attention to the fact that an order had been transmitted.

Accommodation

The passenger accommodation was spread over two decks within the envelope and as first designed included 50 passenger cabins for one, two, or four people, a dining room for 60 people, two promenade decks with windows down the sides of the airship, a spacious lounge of and an asbestos-lined smoking room for 24 people. Most of the passenger space was on the upper deck, with the smoking room, kitchen and washrooms, crew accommodation, as well as the chart room and radio cabin on the lower deck."Airships: R101 Interior."
''Airship Heritage Trust'' via ''Airshipsonline.com.'' Retrieved: 27 August 2010. The control car was immediately under the forward section of the lower deck and was reached by a ladder from the chart room.

Walls were made of doped linen painted in white and gold. Weight-saving measures included wicker furniture and aluminium cutlery. The promenade windows were lightweight "Cellon" instead of the intended glass, and one set was removed as part of later weight-saving measures.

Operational history

Testing

1929

The lengthy process of inflating the R101's hydrogen gasbags began on 11 July 1929 and was complete by 21 September. With the airship now airborne and loosely tethered within the shed, it was now possible to carry out lift and trim trials. These were disappointing. A design conference held on 17 June 1929 had estimated a gross lift of 151.8 tons and a total airframe weight, including the power installation, of 105 tons. The actual figures proved to be a gross lift of 148.46 tons and a weight of 113.6 tons. Moreover, the airship was tail-heavy, a result of the tail surfaces being considerably above estimated weight. In this form, a flight to India was out of the question. Airship operations under tropical conditions were made more difficult by the loss of lift in high air temperatures: the loss of lift in Karachi (then part of British India) was estimated to be as much as 11 tons for an airship the size of R101.

On 2 October the press were invited to Cardington to view the finished airship. However, weather conditions made it impossible to take it out of the shed until 12 October, when it was walked out by a ground-handling party of 400. The event attracted a huge number of spectators, with surrounding roads a solid line of cars. The moored airship continued to attract spectators, and it was estimated that more than a million people had made the trip to Cardington to see R101 at the mast by the end of November.Masefield 1982, pp. 131–32

The flying programme was influenced by the Air Ministry's need to generate favourable publicity, illustrating the political pressures which weighed upon the programme. Noël Atherstone, the first officer, commented in his diary on 6 November: "All these window-dressing stunts and joy-rides before she has got an Airworthiness Certificate are quite wrong, but there is no-one in the RAW oyal Airship Worksexecutive who has got the guts to put their foot down and insist on trials being free of joy-rides". Atherstone's remarks were occasioned by a lunch held on the airship for delegates to a conference on empire legislation, but there were several similar occasions.

R101 made its first flight on 14 October. After a short circuit over Bedford, course was set for London, where it passed over the Palace of Westminster, St Paul's Cathedral and the City, returning to Cardington after a flight lasting five hours 40 minutes. During this flight the servos were not used, without any difficulty being experienced in controlling the airship. A second flight lasting nine hours 38 minutes followed on 18 October, with Lord Thomson among the passengers, after which R101 was briefly returned to the shed to enable some modifications to be made to the starting engines. A third flight lasting seven hours 15 minutes was made on 1 November, during which it was flown at full power for the first time, recording a speed of : even at full speed it was not found necessary to use the control servos. During this flight, it circled over Sandringham House, observed by King George V and Queen Mary, flew on to the previous Secretary of State for Air's country house near Cromer, then to Norwich over Boulton & Paul's works and aerodrome before returning by Newmarket and Cambridge. On 2 November the first night flight was made, slipping the mast at 20:12 before heading south to fly over London and Portsmouth before attempting a speed trial over a circuit over the Solent and the Isle of Wight. These trials were frustrated by pipe breakages in the cooling systems of two of the engines, a problem later solved by replacing the aluminium piping with copper. It returned to Cardington around 09:00, the mooring operation ending in a minor accident, damaging one of the reefing booms at the bow.

On 8 November, a short flight – purely for public relations purposes – was made, carrying 40 passengers, including the Mayor of Bedford and various officials. To accommodate this load, the airship was flown with only a partial fuel and ballast load and was inflated to a pressure height of . In Atherstone's words, it "staggered round the vicinity of Bedford for a couple of hours" before returning to the mast.

Two days later, the wind began to rise and gale

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