R101 - Operational History - Testing

Testing

The lengthy process of inflating the R101's 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 was estimated to be as much as 11 tons for an airship the size of R101.

R101 was first walked out from her shed by a ground-handling party of 400 on 12 October 1929 and two days later made a 5 hr 40 min journey to London and back. A second flight followed on 18 October. On 1 November, R101 flew over East Anglia including Norwich and the Boulton and Paul works there. This was followed by a flight to the Isle of Wight. By 18 November, seven flights had been made. The seventh had been an endurance trial of nearly 31 hours, carried out over England, Scotland and Ireland.

While the initial flight trials were being carried out, the design team examined the lift problem. Studies identified possible weight savings of 3.16 tons. The weight-saving measures included deleting twelve of the double-berth cabins, removing the reefing booms from the nose to frame 1 and between frames 13 to 15 at the tail, substituting the glass windows of the observation decks with Cellon, removing two water ballast tanks and removing the servo mechanism for the rudder and elevators. Letting the gasbags out would gain 3.18 tons extra lift, although Michael Rope considered this unwise, since there were thousands of exposed fixings protruding from the girders; chafing of the gasbags would have to be prevented by wrapping these in strips of cloth. To further increase lift, an extra bay of 500,000 cu ft (14,000 m3) capacity could be installed. This would deliver an extra nine tons disposable lift. On 30 November R101 was taken from the mast and walked back into the shed to prepare for the modifications, and after much consultation, all these proposed measures were approved in December. Letting out the gasbags and the weight-saving measures were begun. Delivery by Boulton Paul of the metalwork for the extra bay was expected to take place in June.

The outer cover was also giving cause for concern. An inspection by Michael Rope and J.W.W. Dyer, head of the Fabric Section at Cardington, undertaken on 20 January 1930 revealed serious deterioration of the fabric on the top of the airship in areas where rainwater had accumulated, and a decision was made to add reinforcement bands along the whole length of the envelope. Further tests undertaken by Rope had shown that its strength had deteriorated alarmingly. The original specified strength for the cover was a breaking strain of 700 lb (320 kg) per foot (30 cm) run (10 kN/m): the actual strength of samples was at best 85 lb (39 kg) (1.24 kN/m). The calculated load at a speed of 76 mph (122 km/h) was 143 lb (65 kg) per foot run (2.09 kN/m). A further inspection of the cover on 2 June found many small tears had developed. An immediate decision was taken to replace the pre-doped cover with a new cover which would be doped after fitting. This would take place following the flights which had been planned for June with the purpose of displaying R101 to the public at the Hendon Air Show. For these flights the cover would be further reinforced. Confirmation of the poor state of the cover came on the morning of 23 June when R101 was walked out of the shed. It had been at the mast for less than an hour in a moderate wind when an alarming rippling movement was observed and shortly afterward, a 90 ft (27 m) tear appeared on the right-hand side of the airship, shortly followed by a second tear 940 ft (290 m) long on the left-hand side. It was decided to repair these at the mast and to add more strengthening bands. This work was complete by the afternoon of the 25th.

R101 made three flights in June, totalling 29 hours 34 minutes duration. On 26 June a short proving flight was made, the controls, no longer servo-operated, being described as "powerful and fully adequate". At the end of this flight the R101 was found to be "flying heavy" and two tons of fuel oil had to be jettisoned in order to lighten the airship for mooring. This was initially attributed to changes in air temperature during the flight. On the following two days R101 made two flights, the first to take part in the rehearsal for the RAF display at Hendon and the second to take place in the display itself. These flights revealed a problem with lift, considerable jettisonining of ballast being necessary. An inspection of the gasbags revealed a large number of holes, due to the fact that the letting out of the gasbags had allowed them to foul projections on the girders of the framework.

Concern was also raised over the possibility of loss of gas through the valves, which were of an innovative design by Michael Rope. Airship valves are intended primarily to automatically vent gas if pressure in the bag rises to the point that the bag might rupture; they are also used to adjust lift for handling. Some concern was expressed over the valves opening because of either the airship rolling heavily or localised low pressure caused by the outer cover flapping, but after an examination of their operation F.W. McWade, the Air Inspectorate Department inspector at Cardington, concluded that their operation was satisfactory and they were not likely to be the cause of any significant loss of gas.

As an experimental aircraft R101 had been operating under a temporary "Permit to Fly", the responsibility of McWade. On 3 July, he wrote a letter to the Director of Aeronautical Inspection, Lieutenant-Colonel H.W.S. Outram, expressing his unwillingness to recommend either an extension to the permit or the granting of the full Certificate of Airworthiness which would be necessary before the airship could fly in the airspace of other countries. His concern was that the padding on the framework was inadequate to protect the gasbags from chafing, the harnessing having been let out so that they were "hard up against the longitudinal girders", and that any surging of the gasbags would tend to loosen the padding, rendering it ineffective. He also expressed doubts about the use of padding, considering that it made inspection of the airframe more difficult and would also tend to trap moisture, making problems with corrosion more likely. Outram, who knew little about airships, reacted to this by consulting Colmore, at that point the Director of Airship Research, from whom he received a reassuring reply. The matter was taken no further.

R101 entered her shed for the extension on 29 June. At the same time the gasbags were given a complete overhaul, two of the engines were replaced by the adapted engines capable of running in reverse and most of the cover was replaced. The original cover was left in place between frames 3 and 5 and in two of the bays at the tail. These parts of the cover had been doped after fitting and were therefore thought to be satisfactory, even though an inspection by McWade had found that some areas where reinforcements had been stuck on with a rubber solution were seriously weakened: these areas were further reinforced, using dope as an adhesive.

A schedule was drawn up by the Air Ministry for R101 to undertake the flight to India in early October, in order that the flight would be made during the Imperial Conference which was to be held in London. The entire programme was intended to improve communication with the Empire, and it was hoped that the flight would generate favourable publicity for the airship programme. The final trial flight of R101 was originally scheduled for 26 September 1930, but high winds delayed the move from the shed until 1 October. That evening, R101 slipped the mast for its only trial flight before setting off for India. This lasted 16 hours 51 minutes and was undertaken under near ideal weather conditions; because of the failure of the oil cooler in one engine, it was not possible to carry out full speed trials. The flight was curtailed because of the need to prepare the airship for the flight to India.

Despite the lack of full endurance and speed trials and the fact that a proper investigation of the aerodynamic consequences of the extension had not been fully completed by the N.P.L, a Certificate of Airworthiness was issued on 2 October, the Inspectorate expressing their complete satisfaction with the condition of the R101 and the standards to which the remedial work had been carried out. The actual certificate was handed over to Captain Irwin only on the day of her flight to India.