By Andy Cooke
When looking at disasters in history that pushed OTL away from airships, the most common one to come to mind is the Hindenburg disaster.
However, the crash of the R101 is often a close runner-up, and is arguably more pivotal. I'm going into extra depth for this one (necessitating two articles), as it looks to me to be the more pivotal point. The event that destroyed the nascent future of airship travel throughout the British Empire.
Had things unfolded slightly differently, the most far-flung empire on the planet would have institutionalised airship travel by the mid 1930s.
What happened
It's all about the Imperial Airship Scheme. Coming late to the airship game, and impressed by the World War 1 Zeppelins (especially the flight of the Africa Ship, mentioned in the previous article), the British realised that air travel could improve communication throughout their far-flung Empire. At the 1921 Imperial Conference, it was proposed that airships could link up the farflung outposts of Empire in a far more convenient, timely, and cost-effective way than could sea-faring ships or aeroplanes. It would reduce transit times by more than a factor of three: instead of 17 days to Bombay, it would take five-and-a-half; instead of 35 days to Australia, it would take a mere 11. Aeroplanes were considered, but their limited range, small payload, and need for runways put them at a disadvantage. No, airships were the way. As well as passengers, mail could be routed quickly and easily.
The suggestion did not immediately gain funding. There were proposals and counterproposals - at one point, six airships, of similar size to the then-planned Graf Zeppelin in Germany, were to be constructed. The Government were largely favourable, but misgivings by the Treasury (and changeovers of Government in 1922, 1923, and 1924) delayed and altered the plans. The loss of the R-38 (mentioned in the last article) also hindered the programme, but some good appeared to have come of it: all British airships would, from then on, be subject to proper structural and aerodynamic analysis.
At last, in 1924, the Air Ministry decided to initiate construction of two prototype airships, from which lessons would be learned and future operational airships designed and built. This would build upon careful safety analysis and economic analysis, during which the two airships would be constructed to very different designs: a more conservative, conventional design and a more experimental and radical design. These were designated the R100 and R101 respectively.
The Airship Guarantee Company, at Howden in Yorkshire, would design and build the R100, under the design leadership of Barnes Wallis. The Royal Airship Works at Cardington would design and build the R101, under the design leadership of Lt Col Richmond.
Requirements
The core requirements were carefully agreed, and looked very sensible:
"The final objective of the present airship programme is the inauguration of a company to operate airships commercially. The stages to this end may be summarised as follows:-
(a) To demonstrate that airships of a reasonable size can fly successfully.
(b) To demonstrate that such airships can use a mooring tower for general operating purposes over a wide range of weather conditions.
(c) To demonstrate that the ship can operate with reasonable regularity.
(d) To demonstrate that the ship has a reasonable life and is not unduly expensive to maintain.
(e) To demonstrate that the ship can be handled on the ground in a practical manner.
(f) To demonstrate that 'prima facia' (at first glance) airships can be made a commercial proposition.
(g) To create an atmosphere in which the public will give financial support to an airship operating company.
(h) To find an individual or individuals who will accept the responsibility of floating and operating such a company."
A common specification was given: the airships were to have a gas volume of 5 million cubic feet with a structural weight not exceeding 90 tons (giving an anticipated 62 tons 'disposable lift'), a payload of up to 100 passengers, to be able to cruise at not less than 60 knots for 48 hours, and to have still air range of 2880 miles (chosen to allow one-stop flights to India via Egypt). Furthermore, given previous disasters occurring due to petrol vapour igniting (seen as a particular risk in the tropics), heavy oil or diesel engines were specified (although hydrogen-kerosene fuelled engines were also under development). allowing one-stop to India via Egypt. A decision was also made to use stainless steel rather than lightweight aluminium or duralumin, thinking about durability, ease of future manufacturing, and the long-term economics of the airship scheme.
Safety was crucial, and paramount (a great irony, seeing how the project finished). Difficulties with the development of reliable lightweight hydrogen-kerosene or diesel engines led to the R100 being given an exemption to use petrol engines (and then pencilled in for only non-tropical flights; it would focus on the transatlantic route, leaving the India, Africa, and Australia routes to the R101). Yes, despite the original requirements, it was understood that the R100 would inaugurate regular passenger services over the Atlantic, while the R101 would begin regular passenger flights to and from India.
After a prolonged discussion with the Air Member for Supply and Research, the Director of Airship Development (Group Captain Peregrine Fellowes) reluctantly accepted that:
“Finally it is understood that your wishes are that R.101 when first completed should contain all the features which will enable her to carry out the following functions:- Naval reconnaissance, ambulance, troop carrier and commercial services, and when she is modified, after her return from India, she will be able to carry a certain number of aircraft and to have her fuel system modified to give an extended range for reconnaissance.”
An alert reader will notice consider differences between these wishes (plus the passenger services that had somehow snuck in) and the original requirements of the project...
Putting it into practice
The 1926 Imperial Conference saw the publication of the official Imperial Airship Scheme details. Mooring mast specifics, airship basing requirements, timetables and routes were all laid out as the development continued - behind schedule. The difficulty of constructing such large airships - the largest ever built at the time - was considerable. The R100 was coming along a little faster, Barnes Wallis having come up with a design that allowed a mere 11 different types of girder to be used, and following a far more conventional process (albeit with an improved aerodynamic 'teardrop' shape). Delays to the diesel engines, which were then considerably overweight, hampered the R101. Governments changed over again and Lord Thomson returned to a programme in 1929 which was now considerably behind schedule.
The delays were unsurprising. As well as the chopping and changing of requirements and ebb and flow of support and funding, there were considerable innovations which needed to be developed. For the R101 alone, these included a new shape, which incorporated a "stiff ring construction" made of stainless steel with tubular girders. This meant that the standard wiring mesh system that restrained internal gasbags, preventing them from chafing against the hull, and transmitting their lift to the rest of the craft, could not be used. Squadron Leader Rope, an ingenious engineer on the programme, devised a "parachute harness" system that replaced this system safely.
The tapered teardrop shape was also new, as were the fins, the use of diesel engines, and even new valves on the gasbags (used to release pressure in fast climbs or unstable flight)[1]. Both ships pioneered an innovative rainwater collection system along the top of the hull, to accumulate water ballast to compensate for the loss of weight of the consumed fuel, keeping the weight of the ship constant, and preserving the hydrogen.
Further than this, the basic research into structural strength and aerodynamic pressures caused further delays: the airships were originally required to comply with safety standards that hadn't even yet been created.
As the prototypes finally drew towards completion as 1929 wore on, their gasbags being slowly and carefully inflated for the first time, over months, the Graf Zeppelin took off on its famous round-the-world flight. Comparisons were certain to be drawn, increasing the pressure on the project. The R101 was delayed due to building entire sections of test facilities to prove their structure against the safety standards; the R100 delays were partly due to their fixed-price contract - the safety-standard delays and other existing delays meant that they would run out of money at the initial pace and had to eke out their resources.
Late in 1929, both prototypes were finally completed - and both were overweight.
The R101 was supposed to weigh 90 tons; it weighed 110 tons (partly due to the heavier-than-anticipated engines, and partly due to the effects of the increased safety standards for material and aerodynamic strength). It was supposed to have a lifting capacity of 146 tons; it could only lift a little over 142 tons. This meant that fuel, ballast, crew, and passengers could each not be close to the desired scale. It would have a shorter range, less durability, fewer crew, and far fewer passengers. The R100 was also overweight, but to a lesser extent, having used less innovation and with proven, lighter petrol engines (although the R101 team pointed out that over long journeys, the markedly better fuel consumption of their diesel engines meant carrying a lot less fuel, offsetting some of the excess weight of the diesels).
Revisions
The R101's weight issues were unacceptable. An urgent weight-saving programme was embarked upon (transforming the R101-a into the R101-b), but this could not save enough weight. For the R101 to be able to fly to India with only one stop en-route[2], more drastic measures were needed. After some early flight-tests, it returned to the shed for major surgery to turn it into the R101-c: it was cut open and an entire new bay and gas-bag installed in the middle, to provide significantly increased lift. The existing gas-bags were "let out" to the maximum physical size available.
The latter changes meant that the gas-bags could now rub and roll against the exposed nuts, screws and rivets in the interior. These had not been covered or rounded off, as Rope's "parachute harnesses" previously prevented gas-bag movement close to the envelope. Inevitably, chaffing occurred, abrading the gasbag surfaces and causing multiple small holes, allowing leaks. Investigation identified these, and padding was added to relevant locations in the interior, partly addressing the issue. It was, though, deemed essential, as a lack of long-distance flights would drive public perception that the project had been a failure, regardless of the valuable technical knowledge gained (the original requirement).
One design difference between the two ships in regards to the cover pressurisation led to the R100 developing a kind of "standing wave" flapping on its cover, stressing the cover and harming aerodynamic stability. The R101 design avoided this by allowing an internal pressure space, further improving aerodynamic efficiency. The drawback with this design was that any hydrogen that leaked from the gasbags would not immediately escape to the outside, as on the R100, but would instead mix with the air inside the envelope.[3]
While the revisions were under way, it was found that the outer covers on both ships leaked in the rain, allowing the gasbags to become wet. Improvements in the material were to be pursued in future designs. Nevertheless, the life expectancy of the material was still measured in years - causing some alarm when the forward part of the cover was found to be split. Much of this was replaced and reinforcing strips added, but concern remained.
Test flights
The R101 had a series of test flights, in its original configuration and following revisions. Difficulties with the experimental engines prevented full-speed trials, and in the earlier configurations, its lift capacity was marginal.
One feature of these test flights that immediately ring alarm bells in retrospect was the tendency to allow non-essential staff on board to boost awareness and support. Lord Thomson himself was on board the second ever test flight. The fifth test flight was made solely for public relations purposes, with forty passengers including the Lord Mayor of Bedford. The weight of the passengers was such that the aircraft was pressurised to a height of only 500 feet and with minimal fuel and ballast, before "staggering around Bedford."
The sixth test flight, investigating the cooling system and gasbag alterations, included the Director of Civil Aviation and ten MPs amongst its 32 passengers. This emboldened the management, who invited no fewer than 100 MPs for a later flight. Rescheduled due to weather, they eventually embarked for a meal while moored at the mast. With a barometric low, the R101 did not have sufficient bouyant lift and only remained aloft thanks to dynamic lift over the envelope and fins (like an aeroplane's lift) caused by the 45 mph winds. Some of the crew and staff were very unhappy with the stunts.[4]
Following the full refits mentioned above, three more test flights were carried out, during which multiple holes and abrasions were discovered in the gasbags. Further padding was hurriedly added.
An eleventh test flight, starting on 1st October 1930, demonstrated significantly improved response and handling and boosted confidence.
This was fortunate, as the 1930 Imperial Conference was beginning in London and Lord Thomson was anxious to demonstrate the capability of this fully functional airship...
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Andy Cooke has written the sci-fi Endeavour trilogy (The End and Afterwards, Diamond in the Dark, Beyond the Sunset) and the political alternate history Lectern books (The Fourth Lectern, The Fifth Lectern), published by SLP