R101 was a British rigid airship completed in 1929 as part of the Imperial Airship Scheme. After initial flights and two enlargements to the lifting volume, it crashed on October 5, 1930, in France, during its maiden overseas voyage, killing 48 people. Amongst airship accidents of the 1930s, the loss of life surpassed the Hindenburg disaster of 1937, and was second only to that of the USS Akron crash of 1933. The demise of R101 effectively ended British employment of rigid airships.
The story of the designs of R100 and R101, and the competition between them, is told in Shute's Slide Rule: Autobiography of an Engineer, which was first published in 1954 and in Airship Saga, published 1980 by Lord Venty.
Unlike the Vickers team who largely had to rely on their own resources the Royal Airship Works [RAW] had the help of other government departments: notably the National Physical Laboratory [NPL]. The Air Ministry funded the costs of refurbishing and flying R33 as a test ship in order to establish both the structural loads and airflows about a large ship. Some, but not all, of this data was supplied to Vickers.
A serious problem was whilst Vickers, under H.B. Pratt and later Barnes Wallis, his apprentice and successor, did have experience in original rigid airship design, no other corporation in the UK did. Cardington, which was owned by Short Brothers (Shorts) during WWI, was chiefly given contracts by the Admiralty to copy and improve on the latest German designs as captured rigid airships fell into allied hands.
The Shorts' engineers knew their business but in 1919 Cardington was nationalised and they left. So while Cardington, now the Royal Airship Works, had building experience it had no design team, except those from the then Naval Constructors Office who had no experience of rigid airships. Their first attempt to build one resulted in the R38/ZR2 disaster, after which the airship arm was closed down and Cardington was placed on a care and maintenance basis.
When the Imperial Airship Scheme was set up the newly appointed R101 design committee at Cardington was very weak except for the chief calculator, Roxbee Cox, later Lord Kingsnorth. The whole project for both ships was under the control of the Director of Airship Development [DAD], Wing Commander R.B.B. Colmore: by all accounts an excellent administrator. The head of the R101 design committee was Lt.Col V.C. 'Dope' Richmond and his assistant was Squadron Leader E.M. Rope.
But serious mismanagement and meddling by the Air Ministry threatened the whole project from the beginning. Thus the Committee for the Safety of Airships [CSA] under Professor Bairstow, 1924/5, had drawn up a specification for the new ships which were to have of hydrogen. They thought, and these figures were worked out very carefully, that the ship would have a total lift of 150 tons and a tare weight of 90 tons giving a disposable lift of 60 tons: and a cruising speed of , giving a still air range of with a payload of some 30 tons. As the record shows this was probably a very fair assessment of what could be done at that time.
In doing this calculation the CSA had allowed for a safety factor of 2 in the structural strength of the airframe but this was not sufficient for the Air Ministry who, for unaccountable reasons but perhaps because they were haunted by the R38/ZR2 disaster, increased it to 3. This meant that both ships would come out overweight by some 20-30 tons of unnecessary metal framework.
Similarly it was thought a hydrogen burning engine could be developed but attempts to do this failed: it does not appear to have occurred to anyone that Spark Ignition [SI/petrol/gasoline] engines are easily adapted to run on coal [town] gas, typically, about 45% methane, or better still pure methane, and that either of these are lifting gasses so the ship can be kept in balance by alternately burning petrol and gas. The point did not escape the Germans who used just such a technique for the Graf Zeppelin.
When the experiments with the hydrogen engine failed the Air Ministry ruled that Compression Ignition [CI/diesel] engines should be used: the reason supposedly given at the time being that in the tropics petrol [gasoline] was dangerously flammable whereas fuel oil is not. If so they amazingly failed to take into account that the ship would be full of explosive hydrogen and that petrol engined motor cars were even then, and still are, used in the tropics perfectly safely. It is of course true that a medium speed CI engine burns less fuel than an SI one and at that time fuel oil was becoming much cheaper than petrol.
It is not possible to get to at the reasons underlying this decision or some others because from the first the Air Ministry promoted its ship, the R101, by using press agents to keep up public interest, presenting the R101 as a great public enterprise: so the designers of the R101 became a prisoner of publicity and had to incorporate innumerable, heavy and useless gizmos simply because they had been announced to the press.
At the time, and even today, opinion about the R101, varies from the best airship ever designed to an appalling bad piece of engineering. This is largely because whilst the design was undoubtedly both elegant and ingenious, and the workmanship superb, the ship had basic flaws which were largely due to weaknesses in the design committee.
The major contradictions can be categorised as follows.
Uniquely the main airframe was unstressed, that is that instead of using tensioning wires as in all other rigid airships before and after it was made entirely of rigid tubes, girders and struts. A bold concept and one which worked very well in terms of weight and strength: and it was made of stainless steel rather than duralumin. But the need for reinforcing rings extending well inside the envelope limited the size of the gasbags so that the R101 had some half a million cubic feet less lifting gas than it should have done: and was consequently short of lift.
There were also serious problems with the wiring of the gasbags and the valves both of which were designed by Rope. The wiring although heavy was probably satisfactory when used as designed: but became dangerous when the ship was modified to increase its lift by letting the wiring out to expand the bags since it could no longer prevent the bags surging to and fro which made the ship even more unstable in pitch. And due to the arrangement of the wiring the bags were divided into two halves on either side of the central keel which again reduced their total volume and the ship's lift.
The valves were unsatisfactory from the first. Conventionally balloon and airship valves are used to adjust lift for handling and above all else to vent gas if pressure in the bag rises to the point that the bag might rupture. Traditionally they are simple, fairly coarse but progressive in response, and placed at the bottom of the bag so that the low density of the lifting gas opposes the outflow and thus limits the loss of gas.
But Rope's design was very sensitive, less than an eighth of an inch of water [gauge] and could only be either fully open or shut. Worse the valves were placed halfway up the gas bags venting into the central space: so in theory the slightest roll in flight would cause them to open. However airships don't roll very much so how much gas leakage was due to this is uncertain but from the initial trials the rate at which the R101 lost gas alarmed Richmond: as his official correspondence shows.
Again there were problems with the outer cover. In a conventional rigid hydrogen airship the constant seepage of hydrogen from the gas bags into the air inside the envelope creates a potentially explosive gas/air mixture. In the R 101 the cover was divided into a fore and after part with a loose vent on the upper side amidships, a low pressure region, and vents at the nose and stern, both high pressure regions. This was a most ingenious design which in theory should have created a continuous flow of fresh air through the inside of the envelope purging the ship of escaped hydrogen. Whether it did so is not known.
What is known is that the cover deteriorated very quickly. Conventionally linen is stretched over an airframe and then doped to shrink it but 'Dope' Richmond got his nickname because he invented a technique for doping linen before stretching it over the airframe. It may have worked for small aeroplanes in war time when the covering has to be replaced frequently but on an airship with some six acres [3 Hectare] of cover it proved unsatisfactory and by the time that she was extended it was apparent the whole cover had to be replaced although this was not completed before the crash.
There were other ingenious bits of design, traditionally ballast bags had been made in the form of a leather trousers and one or other leg could be opened at the bottom by a cable release from the control car: this was known as playing the organ. In the R101 the extreme forward and aft ballast bags were of this type but the main ballast was held in tanks connected by a pipe and vented from the control car so that by simply opening a valve either forward or aft ballast could be easily dropped to trim or lighten the vessel as required.
The design committee cannot be blamed for the decision to use CI engines or that these had to be British made ones. That was imposed on them by the Air Ministry and the Beardmore engine [see below], was totally unsuited to the task. Nor can they be blamed for the failure of the attempt to develop variable pitch, and so reversible, airscrews: however desirable the technology simply did not exist to build such enormous variable pitch propellors.
But their poor understanding of the dynamics of airships, which may have well led to the disaster, does show up in the design of the fins, rudders and elevators. Any airship has to be kept in balance with its lift and at that time, and indeed to the end of the rigid LTA era, this was done by constantly adjusting the pitch of the airship to use it as a wing to develop upward or downward thrust, nose up for dynamic lift, nose down for dynamic downforce. It was a job for the altitude coxswain and a very skilled one, it was said that you could tell who was at the elevator control by how the ship flew.
In the overall aerodynamic shape of the ship the design committee could call on the NPL and for the structural design on the Naval Constructors and on Boulton and Paul who designed and built the frames. But the fins, elevators and rudders were their own entirely and hopelessly unsatisfactory.
Due to a failed attempt to create hydrogen-powered engines and several other new design concepts, the project's completion was delayed from 1927 to 1929. The R101 was meant to have a useful lift of 60 tons but ended up only able to carry 35 tons.
The stability of R101 was doubtful, due to the insufficient span of its fins into the airstream. During its flight at the Hendon air show in 1930, it almost plunged to the ground, as well as repeatedly going into a dive during the return flight. Its gas bags also developed numerous leaks. The gas bag valves were of a novel design and placement. They showed a tendency to open slightly as the ship rolled thus causing a continual leaking of lifting gas and leading to constant decrease of lift in flight. The airship operated under a 'Permit to Fly', a restricted permit for experimental craft operating only in British Airspace and still used in a modified form today. Engineers lengthened the frame, added another gas bag, reversed propellers, and replaced the outer cover. After that, the ship was 777 feet (237 m) long with a total volume of 5.5 million cubic feet (160,000 m³) and a useful lift of just under 50 tons. In her new form she was given a temporary Permit to Fly after the Air Council had consulted Professor Bairstow, the structural expert for both the R101 and the R100. His advice was ambiguous. In the event she only carried out one test flight on the first of October in her new form in fine weather and at reduced speed because of the failure of the oil cooler in one engine. Despite the issue of a Temporary Permit to Fly the safety inspector, Wade, refused to issue a Certificate of Airworthiness citing the following causes: that her outer cover was in a poor state, that her gas bags were leaking badly, that the 4000 odd protection pads were not working. He also questioned the effect of lengthening her on her stability in pitch, which had had been always been very poor.
The Air Council, which had no members with any experience of airships, asked Cardington, the Royal Airship Works and builders about these matters and received an emollient reply. The record shows that despite Inspector Wade's objections a Certificate of Airworthiness was issued on 2 October; tradition has it that it was only handed to Captain Irwin an hour before her flight to India.
At completion, she was the largest flying craft ever built, surpassing LZ 127 Graf Zeppelin, which was of similar length but carried only 3.7 million cubic feet (100,000 m³) of lifting gas. Hindenburg exceeded this five years later, at a length of 804 feet (245 m) and volume 7 million cubic feet (200,000 m³).
R101 was fitted with five heavy diesel engines made by Beardmore. The engines were designed by combining two four cylinder railway transport units into the 8 cylinder Beardmore MkI Tornado engine. These were intended to give an output of at 1,000 rpm but in practice had a continuous output rating of only and, at 17 tons for the five, were 6 tons above design weight. The big end bearings were also found to be prone to early failure, and it was reported gold plating had to be used to lengthen their life. In additions, there were two critical vibration frequencies which coincided with idling and cruising speeds, to unfortunate effect. The engines were intended to have reversing propellers, but they failed. At one point during development, one engine was to be aimed astern and used only at the start and finish of flights, a decision that astonished Shute and the other engineers on the R100 team. This was later changed when two engines were made reversible.
The Air Ministry pressured the engineers to finish the project. The final trial flight of R101 was originally scheduled for September 26, 1930 but an unfavourable wind delayed it until October 1. She returned to Cardington after a flight of 17 hours.
R101 departed on October 4 at 6:24 p.m. for its intended destination to Karachi (then part of British India) via a refueling stop at Ismaïlia in Egypt under the command of Flight Lieutenant Carmichael Irwin. Passengers included Lord Thomson, Secretary of State for Air, Sir Sefton Brancker, Director of Civil Aviation, and Squadron Leader William Palstra, RAAF air liaison officer (ALO) to the British Air Ministry. On release from the tether mast, the nose of the R101 dipped alarmingly, forcing the airship to drop 4 tons of water ballast from the nose section bring the airship back to true. This used all the forward ballast and reduced usable lift by almost half.
In contravention of reports received from the airship about cruising height, observers both across the UK and in France, were amazed and alarmed to see the airship flying so low. Even though it was foul weather, observers reported that it was so close they could see people at the windows of the airship.
In France, the low and erratic flying pattern further alarmed observers with a number concerned that it was going to hit rooftops. (from witness reports at the formal inquiry held at the end of 1930).
Over France, R101 close to Beauvais ridge at a height estimated at went into a dive from which she slowly recovered. Rigger Church, who died three days after from his injuries, was sent forward to release the forward ballast bag but before he could do so the ship went into another dive and hit the ground. The cause of the first dive is not known, but after it, according to the surviving witnesses in the engine cars, the Officer of the Watch [OOW] rang for dead slow. Why he did so is a matter for conjecture because as he must have known without their thrust the ship would dive slowly into the ground, which it did. The Enquiry estimated the impact speed at some thirteen miles (19 km) an hour.
The Enquiry ascertained that there was no major structural failure in the ship, the only major fracture in the wreckage was at the rear of the new framework extension but it is unlikely this failed in the air: it was either broken in the impact or more likely cracked in the intense heat of the subsequent fire. The Enquiry was of the opinion that the forward cover ripped open causing the forward gasbags to fail: but again this is conjecture. As Inspector Wade had pointed out she was very unstable in pitch: and she was also badly overloaded and her cover rainsoaked.
Likewise it is not known why the R101 caught fire, several hydrogen airships had crashed in similar circumstances without catching fire. The Enquiry thought that it was due to the engines being torn away but these were diesels, hot certainly but with no sparks. Many suggestions have been put forward from the ignition of calcium flares in the control car to electrostatic discharge. What is certain is that she caught fire almost at once and burned fiercely: and that her combustible but supposedly not inflammable heavy fuel oil caught fire too so she took nearly twenty-four hours to burn out.
Forty-six of the fifty-four passengers and crew were killed immediately. Two men who survived the crash later died at the hospital bringing the total to forty-eight dead.
The Court of Inquiry concluded that there was evidence there had been a failure of the outer cover of the upper nose. This, it was postulated, led to the destruction of a gas bag, loss of the flammable hydrogen lifting gas, and caused the nose to drop. R101 had exhibited severe longitudinal instability in previous flights, and due to a unique design feature –- lack of any wire bulkheads to prevent gas cell surging –- they had been seen to move back and forth during flight.
During the Inquiry held into the disaster, all reports both from the Air Ministry and the government painted glowing reports of the airworthiness and competence of the airship prior to its flight to India. This was in direct contravention of the experiences of the technical and support crew who worked on the R101 and also the observations of those working on the sister ship, the R100. Technicians and other staff were intimidated into silence through the threats of loss of jobs and pensions. The true state of the construction only came to light in later decades as a number of technicians and also Neville Shute made public observations and details of the problems that had accompanied the airship's construction.
R101 was the end of British attempts to create lighter-than-air aircraft. Its competitor, R100, despite a more successful development programme, and a safe transatlantic trial flight, was mothballed immediately after R101 crashed and sold for scrap in 1931.