|
Statistics
|
| Length |
164ft |
| Diameter |
45.9ft |
| Height |
61.3
ft |
| Speed
|
70
mph |
| Engines |
2
x 200 bhp Porsche air cooled piston engines. Cruise power
150bhp |
| Volume |
181,200
cft |
| Total
Lift |
5.16
tonnes |
| Disposable
Lift |
1.93
tonnes |
Shell
Gas Transportation Airship
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.
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
Aerospace
Developments AD 500
The first of the new Era.
|
