R100

R100 at Cardington, April 1930. The German Graf Zeppelin is seen in the background.

Since wind tunnel tests showed that a 16-side transverse section had about the same drag as a circular one, both R100 and R101 used a smaller number of longitudinal girders than previous airships to simplify stress calculations. Even so, the calculations for the transverse frames required hand computation that took two or three months to produce a solution for each frame. The thoroughness of the stressing calculations was a consequence of new Air Ministry criteria for the strengths required of airships, formulated after the catastrophic structural failure of R38 in 1921. Fewer longitudinal girders resulted in larger unsupported panels of fabric in the envelope, and flight trials were to prove that the R100's covering was barely adequate. The envelope of R101 was also unsatisfactory and a failure in its cover was possibly a cause of its crash.

Barnes Wallis created the frame of the airship using only 11 standard components. The 16 longitudinal girders were formed of three tubes each, formed from strips of Duralumin wound into a helix and riveted together. These connected 15 polygonal transverse frames, which were held in shape by wire bracing connected to a central longitudinal girder running the length of the ship.[1] A further consequence of the new rules for airframe stress design was that a new way of harnessing the lifting force of the gasbags had to be found. Wallis's solution to this problem later led to his innovative geodesic airframe fuselage and wing design for the Wellesley, Wellington and Windsor bombers.

The elevators were aerodynamically balanced but the rudders were unbalanced. When the designers learned that R101 had been fitted with servo motors at a substantial cost in weight and money they thought that they had made a mistake and rechecked their calculations. They eventually concluded that their calculations had been correct: when R100 was flown the controls proved both light and effective, and its control characteristics were compared favourably with those of R101 by Nöel Atherstone, First Officer of R101.[2] R100 was built suspended from the roof of its shed. The individual transverse frames were assembled horizontally then lifted up and slung from roof-mounted trackways before being slid into position and attached to the adjacent frames by the longitudinal girders. The ship remained suspended until the gasbags were inflated with hydrogen.[3]

By mid-1929 the ship's structure was nearly complete and its gasbags were inflated. Following inflation of the gasbags, the outer covering of linen fabric painted with aluminium aircraft dope was put in place, and it was completed at the beginning of November.[3] Lift and trim trials were carried out on 11 November: empty weight was 105.52 long tons (107.21 t) and gasbag volume was 5,156,000 cu ft (146,000 m³), giving a standard gross lift of 156.52 long tons (159.03 t) and so a disposable lift of 51.00 long tons (51.82 t). Deducting 18 long tons (18 t) for the service load (crew, stores and ballast) this meant the weight available for fuel and payload was 33.00 long tons (33.53 t).[4]

It had originally been intended to design special engines for R100 which would be fuelled by hydrogen and kerosene but after a year's work it was realised that the engine would not be developed in time and it was decided to fit the Beardmore Tornado diesel engine that was being developed for the Air Ministry for installation in R101. At an early stage the Tornado was judged unsuitable because of its weight and other problems, and Wallis settled on the use of six reconditioned Rolls-Royce Condor petrol engines even though the fuel, with its lower flash point, was considered to be a fire risk under tropical conditions.[5] The engines were contained in three gondolas, each with one engine driving a 17 ft (5.18 m) diameter tractor propeller, a second driving a 15 ft (4.57 m) diameter pusher propeller, and a third smaller engine in the middle of the car driving a dynamo for electrical power. The engines driving the pusher propellers were fitted with a gearbox to provide reverse thrust for docking the airship.[6]

The passenger and crew accommodation were arranged on three decks occupying a single bay of the structure and entirely contained within the airship's envelope. The lower deck contained the crew accommodation. The second deck had a dining room, which doubled as the passenger lounge, plus the kitchen, 18 four-berth passenger cabins and a gallery on either side for passengers to enjoy the view through the windows built into the skin. The third deck consisted of a gallery running around the dining room and 14 two-berth cabins.[6]

R100 made its maiden flight in the morning of 16 December 1929. After departing Howden at 07:53, it flew slowly to York then set course for the Royal Airship Works at Cardington, Bedfordshire, running on five engines since one of the engines had to be shut down because of a cracked water jacket, and completing the mooring process at 13:40.[7] A second flight was made the next day, with the intention of making a flight to London, but shortly after slipping the mast, a strip of fabric became detached from the lower fin, and the flight was limited to a cruise around Bedfordshire to test control response, lasting 6hr 29 min. The following day, R100 was taken from the mast to No.2 shed at Cardington and work on modifying the wiring holding the cover in place begun: this took until 11 January 1930.[8]

During a test on 16 January 1930, R100 achieved a speed of 81.5 mph (131.2 km/h).[9] At speed, a problem with the outer covering became apparent: it tended to ripple and flap excessively in the form of a standing wave. During a fourth flight on 20 January, cine film was taken of this phenomenon, which occurred because of the large areas of unsupported fabric; it is also visible in some photographs.

A further short flight was made on 20 January before an endurance flight, starting at 09:38 on 27 January when R100 slipped the mast at Cardington and ending at 15:26 on 29 January after more than 53 hours in the air.[10] Following this flight, it was returned to the shed for work on the cover to be carried out. At the same time, the original reconditioned Condor IIIA engines were replaced by six new Condor IIIBs and some weight was eliminated by reducing the amount of passenger accommodation. The work was complete by the end of April, but on 24 April it was caught by a gust while being walked out of the shed, damaging the tail surfaces. The wind prevented it being replaced in the shed, so it was moored to the mast.[11] It was not possible to return it to the shed for repairs until the morning of 27 April. Repairs took longer than expected, and R100 remained in the shed until 21 May, when it made a 24-hour flight intended to test the new engine installation and modifications to the cover.

R100's contract had originally called for a demonstration flight to India. The decision to use petrol engines resulted in a change in destination to Canada, as it was considered that a flight to the tropics with petrol aboard would be too hazardous. All being well, it was planned to set off for Canada on 25 May. During the flight of 21 May, the conical tail section collapsed due to unexpected aerodynamic pressure, and it was returned to the shed where the original tail section was replaced by a hemispherical cap designed and made by the Royal Airship Works,[12] reducing the airship's length by 15 ft (4.6 m)

R100 over Canadian Bank of Commerce building in Toronto, Ontario, then the highest building in the British Empire (August 1930). The rippling of the airship's cover is visible.

R-100 Approaching mast, St. Hubert, Quebec after flight from Toronto. Aug. 1930.jpg

Shortly before R101's flights in June 1930, the Cardington engineers tentatively suggested that the long flights to Canada and India might be postponed until 1931 on the grounds that neither of the two airships was fit to make a lengthy flight at their current developmental stage.[13] The R100 team replied that their airship was perfectly capable of flying to Canada, and that the Canadian flight was a part of their contract.[14] R100 departed for Canada on 29 July 1930, reaching its mooring mast at the St-Hubert, Quebec Airport (outside Montreal) in 78 hours, having covered the great circle route of 3,300 mi (5,300 km) at an average ground speed of 42 mph (68 km/h). The airship stayed at Montreal for 12 days with over 100,000 people visiting the airship each day while it was moored there, and a song was composed by La Bolduc to make fun of the people's fascination with R100.[14]

It also made a 24-hour passenger-carrying flight to Ottawa, Toronto, and Niagara Falls while in Canada. The airship departed on its return flight on 13 August, reaching Cardington after a 57½ hour flight. Nevil Shute Norway later suggested in Slide Rule: Autobiography of an Engineer that the success of R100's Canadian flight indirectly led to the R101 disaster. Prior to the transatlantic flight, the Cardington team could suggest that neither airship was ready for a performance of such duration. However, when R100 returned in triumph they had to either make the flight to India or admit defeat – which would have meant discredit with the consequent danger of losing their jobs. He said that his team "guessed that their ship was a bad airship, but did not realise" (because of secrecy at Cardington) "how bad the other ship was."[14]

The tale of the design of R100 and its claimed superiority to R101 is told in Shute Norway's Slide Rule: Autobiography of an Engineer, first published in 1954. Although flawed and not quite as overwhelmingly superior as Shute Norway implied, R100 represented the best that conventional airship technology in Britain had to offer at the time. R101 suffered in comparison partly because of its many groundbreaking but ultimately dubious innovations, and also because of the weight of its diesel engines. In lifting efficiency, both dirigibles were inferior to the smaller LZ 127 Graf Zeppelin. After R101 crashed and burned in France, en route to India on 5 October 1930, the Air Ministry ordered R100 grounded. The airship was deflated and hung up in its shed at Cardington for a year whilst three options were considered: a complete refit of R100 and continuation of tests for the eventual construction of R102; static testing of R100 and retention of about 300 staff to keep the programme "ticking over"; or retention of staff and the scrapping of the airship. In December 1931, the R100 was broken up and sold for scrap. The framework of the ship was dismantled, flattened by a steamroller and cut up into sections[15] sold for less than £600.