Early efforts to Develop Hovercraft

There
have been many attempts to understand the principles of high air pressure below
hulls and wings. To a great extent, the majority of these can be termed
“ground effect” or “water effect” vehicles rather than
hovercraft. The principal difference is that a hovercraft can lift itself while
still, whereas the majority of other designs require forward motion to create
lift. These active-motion “surface effect vehicles” are known in
specific cases as ekranoplan and hydrofoils.

The first
mention in the historical record of the concepts behind surface-effect vehicles
that used the term hovering was by Swedish scientist Emanuel Swedenborg in
1716.

The
shipbuilder Sir John Isaac Thornycroft patented an early design for an air
cushion ship / hovercraft in the 1870s, but suitable, powerful, engines were
not available until the 20th century.

In 1915,
the Austrian Dagobert Müller (1880–1956) built the world’s first “water
effect” vehicle. Shaped like a section of a large aerofoil (this creates a
low pressure area above the wing much like an aircraft), the craft was
propelled by four aero engines driving two submerged marine propellers, with a
fifth engine that blew air under the front of the craft to increase the air
pressure under it. Only when in motion could the craft trap air under the
front, increasing lift. The vessel also required a depth of water to operate
and could not transition to land or other surfaces. Designed as a fast torpedo
boat, the Versuchsgleitboot had a top speed over 32 knots (59 km/h). It was thoroughly tested
and even armed with torpedoes and machine guns for operation in the Adriatic.
It never saw actual combat, however, and as the war progressed it was
eventually scrapped due to the lack of interest and perceived need, and its
engines returned to the Air Force.

The
theoretical grounds for motion over an air layer were constructed by Konstantin
Eduardovich Tsiolkovskii in 1926 and 1927.

In 1929,
Andrew Kucher of Ford began experimenting with the “Levapad” concept,
metal disks with pressurized air blown through a hole in the center. Levapads
do not offer stability on their own. Several must be used together to support a
load above them. Lacking a skirt, the pads had to remain very close to the
running surface. He initially imagined these being used in place of casters and
wheels in factories and warehouses, where the concrete floors offered the
smoothness required for operation. By the 1950s, Ford showed a number of toy
models of cars using the system, but mainly proposed its use as a replacement
for wheels on trains, with the Levapads running close to the surface of
existing rails.

In 1931,
Finnish aero engineer Toivo J. Kaario began designing a developed version of a
vessel using an air cushion and built a prototype Pintaliitäjä (Surface Soarer), in 1937. Kaario’s design included the modern
features of a lift engine blowing air into a flexible envelope for lift. Kaario
never received funding to build his design, however.[citation
needed
] Kaario’s efforts were followed closely in the Soviet
Union by Vladimir Levkov, who returned to the solid-sided design of the Versuchsgleitboot. Levkov designed and built a number of similar craft during the 1930s,
and his L-5 fast-attack boat reached 70 knots (130 km/h) in testing.
However, the start of World War II put an end to Levkov’s development work.

During
World War II, an engineer in the United States of America, Charles Fletcher,
invented a walled air cushion vehicle, the Glidemobile. Because the
project was classified by the U.S. government, Fletcher could not file a
patent.

Christopher Cockerell

The idea
of the modern hovercraft is most often associated with a British mechanical
engineer Sir Christopher Cockerell. Cockerell’s group was the first to develop
the use of an annular ring of air for maintaining the cushion, the first to
develop a successful skirt, and the first to demonstrate a practical vehicle in
continued use.

Cockerell
came across the key concept in his design when studying the ring of airflow
when high-pressure air was blown into the annular area between two concentric
tin cans, one coffee and the other from cat food. This produced a ring of
airflow, as expected, but he noticed an unexpected benefit as well; the sheet
of fast moving air presented a sort of physical barrier to the air on either
side of it. This effect, which he called the “momentum curtain”,
could be used to trap high-pressure air in the area inside the curtain,
producing a high-pressure plenum that earlier examples had to build up with considerably
more airflow. In theory, only a small amount of active airflow would be needed
to create lift and much less than a design that relied only on the momentum of
the air to provide lift, like a helicopter. In terms of power, a hovercraft
would only need between one quarter to one half of the power required by a
helicopter.

Cockerell
built several models of his hovercraft design in the early 1950s, featuring an
engine mounted to blow from the front of the craft into a space below it,
combining both lift and propulsion. He demonstrated the model flying over many
Whitehall carpets in front of various government experts and ministers, and the
design was subsequently put on the secret list. In spite of tireless efforts to
arrange funding, no branch of the military was interested, as he later joked,
“the navy said it was a plane not a boat; the air force said it was a boat
not a plane; and the army was ‘plain not interested.’

SR.N1

SR.N1
general arrangement

This lack
of military interest meant that there was no reason to keep the concept secret,
and it was declassified. Cockerell was finally able to convince the National Research Development Corporation to fund
development of a full-scale model. In 1958, the NRDC placed a contract with Saunders-Roe
for the development of what would become the SR.N1, short for
“Saunders-Roe, Nautical 1”.

The SR.N1
was powered by a 450 hp Alvis Leonides engine powering a vertical fan
in the middle of the craft. In addition to providing the lift air, a portion of
the airflow was bled off into two channels on either side of the craft, which
could be directed to provide thrust. In normal operation this extra airflow was
directed rearward for forward thrust, and blew over two large vertical rudders
that provided directional control. For low-speed manoeuvrability, the extra
thrust could be directed fore or aft, differentially for rotation.

The SR.N1
made its first hover on 11 June 1959, and made its famed successful crossing of
the English Channel on 25 July 1959. In December 1959, the Duke of Edinburgh
visited Saunders-Roe at East Cowes and persuaded the chief test-pilot,
Commander Peter Lamb, to allow him to take over the SR.N1’s controls. He flew
the SR.N1 so fast that he was asked to slow down a little. On examination of
the craft afterwards, it was found that she had been dished in the bow due to
excessive speed, damage that was never allowed to be repaired, and was from
then on affectionately referred to as the ‘Royal Dent’.

Skirts and other improvements

Testing
quickly demonstrated that the idea of using a single engine to provide air for
both the lift curtain and forward flight required too many trade-offs. A Blackburn
Marboré for forward thrust and two large vertical rudders for directional
control were added, producing the SR.N1 Mk II. A further upgrade with the Armstrong
Siddeley Viper produced the Mk III. Further modifications, especially the
addition of pointed nose and stern areas, produced the Mk IV.

Although
the SR.N1 was successful as a testbed, the design hovered too close to the
surface to be practical; at 9 inches (23 cm)[citation needed]
even small waves would hit the bow. The solution was offered by Cecil
Latimer-Needham, following a suggestion made by his business partner Arthur
Ord-Hume. In 1958, he suggested the use of two rings of rubber to produce a
double-walled extension of the vents in the lower fuselage. When air was blown
into the space between the sheets it exited the bottom of the skirt in the same
way it formerly exited the bottom of the fuselage, re-creating the same
momentum curtain, but this time at some distance from the bottom of the craft.

Latimer-Needham
and Cockerell devised a 4 feet (1.2 m) high skirt design, which was fitted
to the SR.N1 to produce the Mk V, displaying hugely improved performance, with
the ability to climb over obstacles almost as high as the skirt.[citation
needed
] In October 1961, Latimer-Needham sold his skirt patents
to Westland, who had recently taken over Saunders Roe’s interest in the
hovercraft. Experiments with the skirt design demonstrated a problem; it was
originally expected that pressure applied to the outside of the skirt would
bend it inward, and the now-displaced airflow would cause it to pop back out.
What actually happened is that the slight narrowing of the distance between the
walls resulted in less airflow, which in turn led to more air loss under that
section of the skirt. The fuselage above this area would drop due to the loss
of lift at that point, and this led to further pressure on the skirt.

After
considerable experimentation, Denys Bliss at Hovercraft Development Ltd. found
the solution to this problem. Instead of using two separate rubber sheets to
form the skirt, a single sheet of rubber was bent into a U shape to provide
both sides, with slots cut into the bottom of the U forming the annular vent.
When deforming pressure was applied to the outside of this design, air pressure
in the rest of the skirt forced the inner wall to move in as well, keeping the
channel open. Although there was some deformation of the curtain, the airflow
within the skirt was maintained and through natural factors such as escape of
air and balance of pressure within the skirt.

Team Principal smiley

27th May 2015

#peterhulbert
#f1hoverpod
#f1hoverpodracing.