Boulton and Paul - the R101

The following information was extracted from the book 'Boulton and Paul Aircraft - since 1915' written by Alec Brew and this is provided with his permission

By 1925, John North was acknowledged to be the leading authority in Britain on metal aircraft structures, and Boulton & Paul the most advanced manufacturers. This expertise led to them being given the contract for the detail design and construction of the structure of what was to become the largest airship in the world, the R101.

All British airship development had been halted by a Cabinet decision at the end of July 1920. Plans to use existing airships to operate a commercial service to India had been rejected on the grounds of cost, and no immediate need was seen for them in military circles.

The complete structure of R101. facing towards the nose.

From the outset R101 was designed with two main guiding principles. It was to be the most advanced airship ever built, with construction only starting after an extensive programme of research and development, and full-scale practical experiments, for which R33 was made available. In this respect R101 was always an experimental ship, whereas R100 was always envisaged as a more pragmatic design, using tried and tested technology wherever possible. The second principle inherent in RlOI's design, was to be safety. In fact that was the foremost principle, the main criteria against which all details of the design would be tested.

Early in 1925 it was decided that Boulton & Paul would be sub-contracted to complete the detailed design and to build the structure. This was an almost inevitable decision, with Vickers building the other ship, and Shorts unlikely to he interested in helping the Government to build an airship in their former works, a facility for whose loss they considered they had not been justly compensated. Boulton & Paul were the only other company in the country with extensive experience in building metal aircraft structures. John North was appointed as consultant to the Director of Airship Development, with the princely remuneration of £262 a year plus expenses.

The experimental work, which continued into 1925 had determined that R101 would have a streamlined, fat cigar shape, of continuous curvature, rather than the long thin form of earlier ships such as R33. The length to diameter ratio for R101 was 5.5:1, whereas for earlier ships it had been about 10:1. This would lead to far less drag, and therefore less power to achieve the required cruising speed. It also meant that a much larger volume airship could be built within the dimensions of the shed at Cardington.

To achieve as near a circular cross-section as reasonable, the airship would actually take the shape of a thirty sided polygon, increasing to thirty-six sides near the tail to facilitate the fitting of the four tail fins. This shape led to an airship 732 ft long, with a maximum diameter of 132 ft, enclosing a total volume of 5.755 million cu ft, including accommodation and air spaces. To create the thirty sided polygon shape, the structure was to consist of fifteen longitudinal girders around fifteen ring-shaped transverse frames. A further fifteen reefing booms, or intermediate girders, created the necessary thirty sides.

It was estimated that this hull shape would require about 2,000 hp to achieve the design cruising speed of 63 mph, and that therefore at least 4,000 hp should be installed to give a safety margin of 50 per cent on installed engine power. Mainly because of the horrific deaths caused by the petrol fires in the R38, it was decided at an early stage that only compression ignition engines would be considered.

The procedure which was agreed with Boulton & Paul was that Cardington would inform the company of the general arrangement of each structural component and the stresses it was required to sustain. The company's drawing office then designed the component, and when the drawings had been approved, the girder, or whatever piece of the structure it was, would he manufactured, under AID inspection, and delivered to Cardington for assembly.

One of the 70ft long special twisted longitudinal girders for R101 in its assembly jig

A large proportion of the structure was to be of high-tensile steel strip, rolled into tubular form in Boulton & Paul's patented locked joint system. Duralumin was used for bracing pieces, but the wire bracing, and gas-bag support wiring was also of steel. The structure required 27 miles of steel tubing in total, plus 11 miles of bracing wires. The decision to use steel strip, instead of light alloys like duralumin, which was normal airship practice, was largely because of the design input of John North, and the tried and tested experience of the company in its use. It was estimated that the use of steel strip for 65 percent of RlOl's structure saved 3 tons in structural weight, because steel had a higher specific strength than any light alloy in the thicknesses they were able to specify.

The transverse ring frames were triangular in shape, able to absorb all relevant stresses without bracing pieces. The challenge Boulton & Puul successfully overcame was to produce these triangular girders, up to 45 ft in length, some with both curvature and twist, to a finer tolerance than ever contemplated in an airship structure, plus or minus 0.03 in. A new bolted joint was designed to replace the traditional riveted plates, so that when the parts were delivered to Cardington, they could be just bolted together on simple trestles, and then lifted into place. This greatly reduced the amount of work which had to be accomplished high above the ground. So successful were they at achieving the fine tolerances required that no structural component was returned to Norwich because it would not fit, a remarkable performance considering that there was nearly fifty tons of the main structure.

The Boulton & Paul mathematician to whom the complicated three dimensional geometry of the structure was entrusted was A H Adkins. His task was made more difficult because of the shape of R101. Every transverse ring frame was of different diameter, so that they all had to be separately designed, unlike previous airships of regular cross section, whose transverse frames could he virtually mass produced.

The triangular shape of the girders was also useful in that it provided a handy place within them to install fuel and ballast tanks, and other equipment. The intermediate reefing girders were fitted to telescopic kingposts and screw jacks, so they could push out the fabric outer cover to the required taut cross-section. The rival R100 had a simpler and more conventional way of keeping the outer cover taut, by pulling it in with wires.

The four cantilever tail fins were triangular in shape, and fitted to frames 14 and 15. They had been designed after extensive wind-tunnel research, and the rudders and elevators were fitted with specially designed servos operated by hydraulics driven by a small electric motor. Revealingly Barnes Wallis saw no need to install servos on R 1 00.

Rather extravagantly a complete bay of the structure was ordered from Boulton & Paul solely for test purposes. This money-no-object approach was to be a feature of RlOl's construction. The first components of this bay were delivered to Cardington in April 1926. First one transverse ring was assembled and tested in both horizontal and vertical positions, with varying loads. Then the complete bay was assembled and loaded to its design limits. When it had proved capable of sustaining the required load, the appropriate gas bag of 500,000 cu ft, was installed, as well as ballast bags, all relevant equipment, and then the outer cover was fitted. Further tests were made, all successfully, and then in December the bay was dismantled, and each component tested to destruction.

This testing revealed that the structure was not just probably the strongest of any airship yet built, but was really too strong. In view of the weight problems which R101 was to run into, hindsight revealed that the safety-first dictums of the Cardington team had worked against themselves.

The test bay of the R101, complete with its gas-bag, which was eventually tested to destruction.

In erring on the side of safety in the strength of the structure they found themselves having to trim weight elsewhere.
In January 1927 manufacture of the components of the actual airship was able to begin. By the end of the year the first ring frame had been delivered from Norwich, bolted together and lifted into place, and by July 1928 frames 4 to 11 were fully assembled at Cardington. By now Boulton & Paul had completed all the detail drawings and they had all been approved by the Royal Airship Works.

By the end of 1928 the bow structure, forward of frame 4 had been delivered and joined up, and much of the outer cover had already been fitted. In March 1929 Boulton & Paul delivered the last of the structure, and the assembly and fitting of the fins began. The basic structure of the ship was complete in June 1929 and the installation of the engines and the final fitting out went ahead.

In June 1929 the Labour Government of Ramsay MacDonald came back to power, and Lord Thomson returned as Secretary of State for Air. Within ten days of taking office he was on the train to Cardington, to sec the results of the scheme he had set in motion five years before. He was to find serious problems with R101, and even the enthusiasm of the Royal Airship Works staff could not hide them.

Almost every aircraft ever built exceeds its designer's estimate of empty weight. In the case of airships, this is even more critical than in heavier-than-air machines. Every pound of excess weight means a pound less disposable load. Even the dust lying within such a huge structure can make a significant difference. By June 1929 it was discovered that R101 was in serious trouble because it was 15 tons over the original estimate of 90 tons. This meant that it only had a disposable load of 47 tons, instead of 63 tons, and would only be able to carry 24 passengers and one ton of mail over the route to India with a single stop in Egypt. This was seriously below the original specification. The main structure contributed 5.05 tons to this increase, but 5 tons of this was entirely due to the extra reefing girders not having been included in the original proposal.

There were other serious problems with the ship. It had been intended to use new steel reversible-pitch propellers, for use in mooring, but they had not been able to stand up to the vibration produced by the Tornado engines, and so two-blade wooden fixed-pitch propellers had to be fitted. For mooring one engine had to have a reverse-pitch propeller, so this engine could not be used in normal forward flight, a dead weight of 4,733 Ib, which in itself was twice the original estimate for each engine. This also meant that there were now only four engines available for forward flight, and because of the problems with vibration they were experiencing they were having to be run at reduced rpm, giving only 450 hp for cruising.

Worse was to come. When the gas bags were fully filled and the ship brought to equilibrium floating within the shed on 30 September, it was found that the gross weight was 3.3 tons higher than had been estimated, 23.4 tons more than the original design estimate. It was clear that weight reductions would have to be found together with extra lift if possible, if R101 was to be able to operate to India with a reasonable load.

A comprehensive examination of possible weight saving measures, replacing the Triplex windows with Plexiglas, removing twelve sleeping cabins, two lavatories, and two water ballast tanks, and cutting weight in other areas, seemed to indicate that about 2[/i tons might be clawed back. If the gas bag restraining wires were let out, they might hold up to another 100,000 cu ft of hydrogen, generating another 3 tons of lift; though some way would have to be found to stop the bags rubbing on the structure. Already the safety first doctrine was being compromised at every turn.

On 12 October, 1929, R101 was walked from the shed for the first time, and secured to the mooring mast. Two days later she made her first flight, a 5 hr 40 min journey to the centre of London and back. On the second flight on 18 October Lord Thomson was aboard, and waxed lyrical to the Press on his return. Everyone who had seen RlOI's superb passenger accommodation, and had seen her in the air. all agreed what a marvellous flying machine she was. Only the experts knew the truth. She was in deep trouble, weight had to be saved, and more lift secured; maybe even two more mooring masts would have to be built, at Malta and Basra, to enable her to refuel three times on the route to India.

Five more flights were made up to 18 November, and though they were seen with huge enthusiasm by the general populace, they only confirmed the pessimistic indications of the staff at Cardington. On the third flight, on 1 November, R101 flew over East Anglia, and over the Boulton & Paul Works so that the work-force there could admire their handiwork.

There were further problems experienced, including trouble with the engines' steam-cooling system, and an alarming, and continuous leakage of gas, over and above that lost during venting, when climbing, but it was the lack of sufficient disposable load which was putting a large question mark over the entire programme. As things stood, RIOI would only be able to lift enough fuel at Karachi, given the local conditions, for 24 hours flying time; and that was with a reduced crew. Even the weight saving programme, and letting out the gas bag restraining wires would not be enough.

By now RJ 00 had completed her lift and trim trials at Howden, and was found to weigh just over 8 tons less than RIOI in prepared-for-service form, including crew. Their empty weights, less engines, were almost identical; however, despite the far more lavish passenger accommodation on RIOI. This seemed to vindicate the highly innovative structural design, for which John North bore a considerable measure of credit. The fact that it had proved to be built too strong, also augured well for the future, the next Cardington airship could be built with a substantially lighter structure.

The weight troubles RIOI was experiencing could be laid entirely at the door of the power plants. The five Tornado diesels in RIOI weighed 17.96 tons, whereas six Rolls-Royce Condor petrol engines on RIOO only weighed 10.19 tons. There could be no prospect of changing to petrol engines on RIOI, that was the most fundamental safety dictum in the design. The only answer seemed to be fitting an extra bay

On 18 December it was announced that an extra bay of 500,000 cu ft capacity would be installed in RIOI, giving an extra 15.5 tons of lift for only 5 tons installed weight. Boulton & Paul were given the contract to construct the longitudinal girders, but the frame girders would be made in the workshops at Cardington. In addition the restraining wires on the existing bags would be let out to provide another 130,000 cu ft of capacity. Various weight saving measures would also be implemented, including removing the servo motors on the rudders and elevators as they had proved to be entirely unnecessary. By March a way had been found to obviate the need to haul around an engine which was only available for reverse thrust. A simple modification enabled the Tornado to run backwards. With fixed-pitch wooden propellers now fitted on all five engines, enough thrust was available from just one propeller running backwards for mooring purposes.

While waiting for Boulton & Paul and the Cardington workshops to complete the construction and delivery of the new bay, the other modifications were made to RIOI, including letting out the gas bag restraining wires. Further test flights were made, and the airship flew over the RAF Air Display at Hendon on
successive days. These flights revealed further problems. Gas was leaking to an even more alarming degree and it was found that the gas bags were rubbing the structure and were being holed. In addition severe problems were being experienced with the outer cover, rips were becoming frequent, and much of it was found to be rotten.

A section of R101 under construction at Cardington.

It was discovered that it was not just the holes in the gas bags which were leaking. The Royal Airship Works had decided to design their own side valves for the ship, rather than purchase the normal top valves from Germany, as the pragmatic team at Howden had done for the R100. These valves were designed to remain closed at anything up to a roll of three degrees, but it was discovered that R101 rolled much more than this, and so the valves were continuously leaking.

Even before the gas bag restraining wires were let out it had been discovered when the bags were removed and examined in November 1929, that many holes had appeared, as many as 103 in one bag. Up to 4,000 pieces of padding had been applied to all projecting pieces of the structure, but this was clearly not working well.

The latest test flights over Hendon had produced data which indicated that, because of the gas leakage experienced. R101 would be forced to make a forced landing after only 23 hours at cruising speed. Something drastic had to be done. Lord Thomson wished to fly to India and back during the Commonwealth Conference in the first week in October, and as it stood R101 was not just incapable of making the trip, it was not even airworthy.

Even with the new bay fitted, the extra lift provided by letting out the gas bag restraining wires was still needed. The gas bags would have to be replaced and repaired where appropriate, and reinforced in places most susceptible to damage. New padding would have to be applied, which was both thicker and less likely to slip, as the gas bags rubbed against it, and much if not all of the outer cover would have to be replaced.

After the Hendon flights R101 had been moved into the shed with its stern only 3 ft from the end, so that only the forward part need be moved when the ship was parted at frame 8. This was achieved on 29 July, and by 7 August Boulton & Paul had delivered all the parts for which they were contracted. The new frame (8A), constructed at Cardington, was lifted into place on 14 August and on the 25th the structural work in fitting the new bay was complete. The RlOl was now 777 ft long, the largest British airship ever built. Work continued on fitting the new padding and outer cover. The pressure was still being applied to fly to India in the first week in October, and this would leave time for only one long test flight, but everyone was confident that the schedule could be met.

At 6.30 a.m. on 1 October R101 was removed from its shed and moored to the mast. In the late afternoon she slipped her moorings and flew south for a test flight which was to last 16hr51 min. Everything went perfectly, except that the oil cooler in one of the engines failed, so that a full-speed trial with all five engines at maximum revolutions could not be made, to test the outer cover.

The flight to India would start on 4 October with 42 crew and 12 passengers including Lord Thomson. Capt Dawson Paul of Boulton & Paul had tried hard to get a place on the flight, but there was no room. It was to prove one of the luckiest failures he ever experienced.

The first stage of the journey was 2,235 nautical miles to Egypt, which it was hoped to accomplish in 48 hours. The second stage was 2,125 nautical miles, to Karachi, which it was hoped to accomplish in 46 hours. The airship had never been tested in the conditions it was to experience, the heat, and the humidity, it had never been tested at full speed, and its suspect outer cover had never even been tested in conditions other than clear skies with no turbulence. A Certificate of Airworthiness was issued over the head of the Inspector on the spot, and with a verbal assurance that the full-speed trial would be held on the flight to India. If anything was not entirely satisfactory, assurance was given, that R101 would be turned round and flown home.

It was a sign that everyone's confidence and pride in the project had welled up so much, they had washed away all thoughts of caution. It was felt that the new modifications that had been applied would solve all the problems that had dogged the ship.

By 6.20 p.m. on 4 October, 1930, all passengers and crew were aboard RlOl and all five engines were running. Sixteen minutes later the airship was free of her mooring and a cheer went up from the watching crowd. The ship slowly slid backwards, and then with the engines at half power slowly turned and climbed away into the gathering darkness, bound for Egypt.

Lord Thomson, and the Labour Government, who had initiated the scheme, had a great deal of political kudos riding on its success, and being socialists it was essential that the Government ship would prove superior to the private-enterprise R100, which had already flown to Canada and back, and was itself having a new bay fitted in the shed which R101 had just vacated. The staff at the Royal Airship Works were convinced that R101 was the finest flying machine ever built, it was certainly the biggest. Many of them had spent six years bringing this moment to fruition, and they all felt that the troubles of R.101 were behind her, she was an experimental ship, much had been learned, and things augured well for the future. The next generation of airships were already being planned, the R102 and R103.

R101. Showing the streamlined continuously varying cross-section.

Boulton & Paul also had their future hopes riding with R101. It had been an immense job, and had been completed in exemplary fashion. Of all the problems associated with R101, none of any significance had been concerned with the structure. The company had high expectations that a great deal more airship work, over many years would be coming their way.

Studies had begun in the spring of 1929 to decide the size and configuration of the next two airships to be built for the Imperial routes. Data collected from the flights of R100 and R101 caused the ideas of the design department, which consulted extensively with John North, to change several times. In the end it came down to a choice between a 9,500,000 cu ft airship which would achieve all that R101 had originally been intended to, and a more conservative 7,500,000 cu ft design, which would be able to operate the route to India refueling at two new mooring masts in Malta and Basra.

In the end the vast extra cost of the larger ships, not least in needing to build a much larger shed at Cardington. mitigated against them, and it was decided that R102 and R103 would be of 7.500.000 cu ft capacity. They would be built at Cardington. once more in association with Boulton & Paul, but disappointingly for the company, far less of the work would be sub-contracted to them.

The R101 contract had been worth £202,500 to Boulton & Paul, made up as follows: design £7,000, direct labour £45,000, materials £47,000, overheads £53,000, jigs and tools £13,000, plant and equipment £4,500. delivery £1,000, ex-gratia payment £14,000, profit £18.000. Total £202,500.

The value of the work on the next two airships which was likely to come their way was possibly to be considerably less, but they were bigger ships, and there were to be two of them, and in hard times any work was very welcome. In addition the R104 class of airship was already being penciled in for construction after the R102 and R103 were in service by 1935. This would be the very large 9,500.000 cu ft class of airship.

All these hopes and plans were to come to nothing of course. In the early hours of 5 October. 1930, R101 crashed at Allone near Beauvais, and shortly afterwards the British airship programme was cancelled, and R100 was broken up in her shed. Of all the factors which led to the crash, none could be laid at the door of Boulton & Paul, it was just their bad luck that they were associated with such a tragic project, a project marred by governmental interference, and over-optimistic and muddled planning by the protagonists of the airship
.
The crash was most likely caused by a failure of the outer cover in the nose section of the ship. RI01 had suffered very bad weather as it crossed France at low altitude, strong headwinds and turbulence, and also heavy rain which added tons of weight. The suspect cover, which had not been renewed in the nose section, almost certainly failed, causing the gas bags in the immediate area to deflate. When the airship went into a dive, it was the natural reaction of the crew to throttle hack the engines, but this caused all dynamic control to be lost, and at low speed the elevators became ineffective, sealing the fate of R101. When it hit the ground calcium flares stored in the control cabin ignited and the airship was burnt out. Of those on board only eight managed to get clear of the burning wreck, but two of these died later of their injuries. Lord Thomson was one of those who died in the crash.

Lying within the storeroom of Boulton & Paul Joinery in the Riverside Works at Norwich is one small girder from the wreck, presented to them after the inquiry, one .solitary item from a programme in which the company and country had placed such great store. Many other pieces of the wreck were taken by souvenir hunters, one small piece somehow coming into the possession of my own grandmother in Wolverhampton. A souvenir of the end of a different age.