Airshipsonline : Airships : AD 500

Aerospace Developments

AD 500
The first of the new Era.

Introduction

Roger Munk was a qualified marine and naval engineer, which was an excellent foundation for an airship designer. It was in 1971 that a company formed, named Aerospace Developments, a partnership of an airship enthusiast, John Wood, and Roger Munk, naval architects. Later on in that year, the company was awarded a study by the Shell Oil company to develop a large rigid airship capable of transporting pressurised natural gas.

Shell Gas Transportation Airship

He originally had been engaged for 5 year upon designing Shell's large Rigid Airship, and set up a project to study the transportation of Natural Gas (NG) by airship from the Middle East to the UK. The company had been looking at a series of design concepts. Shell planned to use the airship to transport natural gas in gaseous form, eliminating the costly equipment associated with shipping liquefied natural gas by sea and, in particular, the need for large amounts of fixed plant in politically unstable countries. Barnes Wallis, who was probably our most experienced and most successful airship designer, had been involved in the airship project in its early stages but withdrew due to problems with his design for a very large non-rigid.

The natural gas would have functioned as the primary lifting gas on the loaded voyage, with a small amount of helium, plus hot air from the airship's (gas-fuelled) engines, supporting it on the empty return leg. The ship's structure would have been "of a semi-monocoque type" of stressed metal/skin honeycomb sandwich construction. The conceptual length was for an immense ship of some 1,800ft long.

However in 1974, after a major budget review arising from the sharp escalation of oil prices, Shell resolved to cut back their long term research and development expenditure, and accordingly the airship gas transporter project was shelved. As a result of this the Monk/Wood partnership was free to design and build their own airship prototype, albeit on a modest scale. Aerospace Development's work showed that the Shell concept was impracticable, however the advantage was that Aerospace Developments came into contact with the latest materials and ideas

AD-500 Design Concept

Aerospace Developments concept had first took shape on the drawingboard in 1976 as a small non-rigid airship of 120,000cft. It was originally designed to meet a need foreseen by Roger Munk's partner, John Wood, as a general purpose vehicle for operations in Peru. Later negotiations were made with potential customers in Venezuela. A ship of this size was felt as a better investment risk for potential financiers than the vastly bigger rigid airship of the type which had been designed for Shell. Accordingly Airship Developments decided to start small, at the time, and ease their way in to a new field and gather knowledge. However Roger became aware of the necessity to create a general purpose vehicle with adequate reserves of speed and endurance, the size of the prototype ship gradually crept up to it's 180,000cft.

The AD-500 might have been relatively small, "only" about the bulk of a Boeing 747, Roger Munk was determined that whatever it's role, it would incorporate every possible advantage that modern materials and technology could provide. Using his 5 years experience from the Shell project, he felt his was in a good position to achieve this. Munk also wanted to the make the best use of the experience and knowledge of built up in the earlier generations of airships, and apart from the documentary evidence available at the time, he also obtained invaluable help from some of the early airship pioneers. A typical example of this was the use of vectored thrust, in the AD-500's design, whereby the propellers, or ducted fans, can be tilted in pitch plane to drive the airship upwards or downwards; in a similar principle to the V/STOL BAe Harrier aircraft operated. The basic concept was employed on the Willows airships circa 1910. In practice, the resulting blend of modern technology with an old concept worked perfectly first time, surprising many who had forecast major development problems. With the contract, it was agreed that funding for the project would only be released when certain key stages or milestones had been completed.

Construction

Materials used in the ship included thin single-ply polyester, coated with titanium dioxide-doped polyurethane, for the envelope; Kevlar for the cables suspending the gondola from the top of the envelope; a Kevlar nosecone moulded in the same manner as glass-reinforced plastic; and a 30ft gondola moulded by Vickers–Slingsby from Kevlar-reinforced plastic. The use of Kevlar on the gondola achieved a significant reduction in costs and weight with very little in the way of accompanying problems. Similarly the tailfins were developed and patented a rather ingenious system of interlocking one piece honeycomb ribs and spars, which again reduced cost and weight while improving durability. Other new innovations featured in the AD500 included simplified controls and thrust vectoring, taking an old airship idea from the earlier British Rigids, and revived the concept, linked via inboard-mounted Porsche engines driving vectoring ducted fans

Propulsion

One of the main and most important features of the new ship was the propulsion system. The designers carried an idea which had been utilised in the earliest days of the airship programme, the use of vectored thrust engines.

The propellors were in fact ducted fans,containing a set of 5 bladed variable pitch propulsors, tilted in order to drive the airship upwards or downwards; a principle very similar to the Harrier Jump Jet V/STOL applies to maximum advantage. The propulsion ducts allowed the units to swivel through 200 degrees rotation allowing full maneuverability of the ship. Unlike previous airship designs, by putting the fans in to "cowels" this gives the advantage of low propellor noise and improved safety to passengers boarding the ship. The engines were twin air cooled Porsche piston engines, mounted transversely inboard at the rear of the car. The propulsors are driven by Westland Lynx helicoptor transmission shafts and 90 degree drive reduction gearboxes.

Gondola Design

The influence of Roger Monks maritime background would be seen in the design of the large gondola. This was constructed of kevlar, making it a giant reinforced plastic shell, being not only sturdy but also offering design flexibility, ease of manufacture and also very low maintenance.

The gondola itself is suspended from the top of the envelope by a fail safe system of 14 kevlar suspension cables and a sheer collar for horizontal restraint. The load of the gondola is spread along four arched parabolic load curtains bonded to the top of the envelope. The layout of the gondola is for maximum comfort with the skyship 500 able to carry 9 passengers and 3 crew.

The large windows could be opened and offered spectacular views for those who enjoyed the flights. The nose of the gondola offered a spectacular view for the pilots who could see almost 180 degrees unimpeded disability by the large windscreen.

Even though the ship has 2 seats in the cockpit, the Skyship was developed for one pilot operation. The control is offered by twin control yokes which operate all of the control surfaces, as there are no rudder pedals as in conventional aircraft. The engines are operated by single lever control mounted on a central control console.

Prototype AD 500

It was not until July 1977 that Aerospace Developments finally managed to agree terms for the first ship and get construction underway. The company was immediately faced with constructing a vast amount of special tooling, which was always expensive in a new project, and also the expensive and time consuming composite materials. The company's objective was to build a production ship, rather than a prototype. By March 1978 all the major components had been assembled in the No1. hangar at Cardington, a fitting place for the rebirth of the airship as it was the same hangar which had assembled the R100 some 50 years earlier. Initially there was a problem with the vital gas control valves used inside of the envelope. Originally the company had been lead to believe that they would be able to use the well proven 20 inch Goodyear valves, but at the very last moment, it became clear that this was not possible. The design of airship valves is highly specialised and the company did not, at the time, feel confident about tackling the design of these themselves. The team were forced t to find an alternative supplier of a proven value. A company was tracked down in the UK which manufactured valves which had been used on barrage and meteorological balloons and it was necessary to mount these in an alternative configuration on the envelope. However immediately the valves were tested, it became obvious that they leaked badly from their seals, and were unserviceable. Airship Developments then had to completely redesign the valves, resulting in delaying the programme by four months, as during this time, they were unable to inflate the envelope. The positive to emerge from this as that the company learnt all about airship valves and this enabled them to design their own valves with better performance for the AD 500. During this delay time, it also meant that other changes could be adapted. Some modifications to the tailfin skin cladding meant that they could save some further weight.

The envelope, with new valves was able to be inflated in the summer of 1978. More details and further changes were found once the envelope was inflated, and further testing could be undertaken. This lead to slowing the project even further, exacerbated by there were no proper workshop facilities in the hangar. Each month delay, the financial position of the company worsened due to overhead costs. The winter of 1978 was one of the worst for many years and the conditions in the hangar was particularly bad. On one occasion, they were so concerned that the water in the ships ballast tanks that Bruce Reid, one of the Aerospace Developments team, had to spend a night to watch floating night lights in the tanks to prevent ice building up and splitting the ballast tanks.

By January 1979, many hours of engine and propulsion system testing had been completed. Roger Munk had carried out several vectored thrust vertical take off's and landings with the ship on loose tethers fore and aft. The ship had been held in hover at 551kg heavy for many minutes on end. During these tests, further prototype issues were found as excessive friction on the control circuit, and a temperamental pitch change, despite these, the ship behaved well, and it was already seen to the team that vectored thrust would give the ship a considerable extra degree of safety.

First Test Flight

February 1979, and the worst of the winter weather had cleared. With all of the problems fixed on the ship, on 2nd February, the Permit to Fly from the Civil Aviation Authority was received. The CAA had maintained a very close relationship with Aerospace Developments, and had offered advice and help. The CAA was taking particular interest as the newly registered ship, G-BECE as the first airship to be built to the new Section Q of British Civil Airworthiness Requirements. It was abundantly clear that if the ship did not take off on Saturday 3rd February then in all probability the Aerospace Developments would go in to liquidation as the company was under enormous pressure and could only last a few more days, without a further injection of capital, which the Venezuelans were understandably reluctant to commit without seeing a demonstration of the ship. Furthermore, the weather reports indicated that the gap in the winter weather they would need for the first flight, would be very short lived.

On 3rd February, it was originally noted that the flight had been canceled for weather reasons, however two additional independent checks of the weather and wind conditions showed that the wind strength was quite low. Roger Munk gave instructions that the original flight programme should go ahead, although delayed for several hours, and for the ship to be moved on to it's mobile mast and out to the mouth of the hangar. The limit for the day's flight, was that it needed to be taken by sunset, which in the winter was at 16:51pm. The team were able to get the ship out of the hangar without a problem. The Aerospace Developments Chief Inspectors, Ray Hall, pronounced himself satisfied with the ship and ready for it's first flight. So with the pilot, Giovanni Abratti, John Wood, Ray Hall, Dick Cox, the Aerospace Developments electrical engineer, and Roger Munk himself, boarded the ship. The Porsche engines fired up perfectly and within 10 minutes permission to take-off was granted. The AD 500 left the ground at and climbed away at a 45 degree angle with a very fast climb, and about five degrees nose up trim. At 500 they leveled off and cruised over Shortstown. AD 400 was cruising at about 50 mph, close to the maximum cruise speed. The ship soon turned and returned to the Cardington airfield, and lined up in the wind to come up to their landing point. Vectoring the engines, allowed the ship to come down for a perfect landing.

The AD500 was then linked up to the mobile mast, just as nightfall was descending, and the whole area was lit up by the floodlamps of the TV crews and press illuminating the crowds of well-wishers. Part of the crowd were the Venezuelan bank managers who had come to see their investment fly. Once the ship had returned to the shed, the whole assembly retired to The Bell pub at Cotton End, to celebrate the successful first flight.

It was decided by the Venezuelan financial backers, not to implement the original plan of refinancing the company by selling a large proportion off via the City Merchant banks, now that the first flight had been successfully completed. It was decided t hat Aerospace Development were to wait for two months, had elapsed and the company had undertaken a Royal Navy trial lease, before going to the City banks. The idea of this would be to double the selling price of the shares in the company. Despite this being a good theoretical idea, it went against the original plan. With marginal funding over the next few months, the company was aware of it's worsening financial position. It was agreed to continue to press on and get the ship through it's flight test programme for it's air worthiness certificate, some 40 hours flying.

The Royal Navy had arranged a lease via the Department of Naval Warfare, nominally for two months but with an option for an optional extension. The Venezuelan's considered it excellent PR to wait until after the Navy evaluation.

Second Test Flight

A further test flight was planned, and on 7th March 1979, in weather conditions which were acceptable, but not ideal, the ship was taken out of the hangar. The following morning on 8th, in a wind gusting 15 to 20 knots, the ship took off with members of the design team on board, including Ian Reid, Godfrey Lea and Roger Munk. Again the vectored thrust worked perfectly. Some turning trials were undertaken as the ship flew at 600ft. The ship managed a perfect landing, this time in more difficult conditions. By the time the ship was docked on to the mobile mast, the wind had increased to 25 knots, and thus delaying returning the ship to the hangar.

Storm Damage

Despite the wind increasing, it was decided it was better to leave it on the mast outside rather than try and manhandle the ship in to the hangar. As the day wore on the wind straight increased and it became clear that a lull was not going to happen before the following day. It was agreed that a permanent watch be undertaken on the ship during the time moored. At 0100 hrs the wind had increased to very heavy gusts. Roger Munk was on watch in the cabin of the mobile mast. He heard a loud crumpling sound the masthead, immediately around the mobile mast cab. Fearing the worst he climbed the ladder to the top of the mast.

At the top he could not see any visible damage, but during a gust, a second crumpling sound could be heard, and it became apparent that that some part of the ships nose cone, a 9ft diameter glassfibre moulding was collapsing under the compressive loading during the strongest gusts, when the ship rode forward on the mast. At 01:20hrs Roger called for extra staff and the RAE duty balloon crew to provide extra men, and to open the doors of number 1 hangar in case an emergency attempt to be made to get the ship inside. With 20 minutes most of the Aerospace Developments crew and Cardington Balloon crew had arrived. With 43mph gusts, the nose cone began to break up slowly.

With no sign in a break in the weather for the next 12 hours, it was evident by now that the nose cone would fail. Roger Munk realised that leaving the ship where it was would cause a disaster, but they could try and improve the situation, and move the ship in to a more sheltered position or even in to the shed. Ian Reid went to reconnoiter the area behind the hangars in an attempt to find shelter for the ship, in their lee, but returned to say that the ground was too soft for the mobile mast. It was agreed that if the mobile mast was driven extremely slowly, less than 1mph, then there would be no added load on the cone, and the ship could be manoeuvred at least into a position directly upwind of the open hangar doors. The ship was moved in to positioned ot the wind behind the mobile mast, and the stern approximately 240ft from the open hangar doors.

The hangar flood lights were all switched on, and the meteorological balloons inside were moved to clear a path into the hangar. To pin the tail of the ship down, the ship was hitched to Roger Munks Land Rover. He told the mobile mast diver to wait for a lull, and then "drive like hell" for the hangar entrance. Roger would maintain station below the ships tail and try to keep the stern line taut. The Mobile Mast drove forward and Roger followed in the Land Rover. The Land Rover was beginning to be lifted by the tail of the ship, when the stern line broke, as had been designed.

It was then deemed to risky to try another attempt to get through the doors due to the extreme eddies which were being caused. Shortly afterwards, the nose cone collapsed as a rigid structure and it became apparent that a broken part of it had pierced the ships hull. At 02:30am Stan White and Roger Munk agreed, the only responsible thing to do was to deflate the ship by operating it's rip system before the ship broke away. During the deflation process the envelope was badly damaged by the wind. Despite never being operated before, the deflation system worked perfectly.

The End of Aerospace Developments

The loss of the AD 500 caused the financial collapse of Aerospace Developments as a company, however the ship, G-BECE was eminently repairable. However, over the next two years, the company, through a merger with Major Malcolm Wren's Thermoskyships, and and subsequent de-merger, the creation of the company known as Airship Industries, the design crew were back together. The team used the AD 500 prototype design to create the Skyship 500 series. Success came within two and a half years following the AD 500 first flight, when at 08:30 on Monday 28th September 1981 that the Skyship 500 G-B1HN was launched from Cardington.

Special thanks to Alastair Reid and Den Burchmore in help compiling this page and providing the unique historical photographs