http://www.airdeglisse.org/
Authored and compiled by:Christopher Fitzgerald
Chairman, World Hovercraft Organization; President, Neoteric Hovercraft, Inc.
The
growth of civilization occurred within view of – and in many ways because of
– our seas and rivers. Since the beginning of human history, we have been
shaped by our ability to carry goods and people across water – our most ancient
highway.
Without a means of water transportation,
ancient mariners could not have explored the world or traded goods.
Civilizations that mastered ship building and sailing inevitably prospered as
centers of trade, culture and power, and the earliest cities were located on
seashores or rivers. The superiority of water transport over ground transport
was so apparent to even the earliest civilizations that canal building was one
of mankind's earliest engineering achievements.
In 1775 Adam Smith, the first economist,
recognized the importance of water transportation in his revolutionary book
An Inquiry into the Nature and Causes of the Wealth of Nations. In his
analysis of why some nations are more prosperous than others, Smith examined
the advantages of water over ground transportation - one ship with six or eight
men could carry as much as 50 wagons attended by hundreds of men and 400 horses
- and concluded that communication across water has always been the least
expensive form of transportation. Water travel requires less manpower than
overland travel and can accommodate far greater loads than wagons, animals or
more recent ground transport vehicles.
Breaking the Water Barrier
Throughout history, mankind has been
intent upon finding ways to transport larger loads and to increase the speed of
load movement. From their inception, ground and air transport vehicles have
dramatically and continuously increased their speed. Such is not the case with
vehicles that travel across water, because they have to contend with the strong
resistance of water – the water barrier.
One factor that creates the water barrier
is water density. The density of water is 815 times the density of air. As a
ship increases speed, the resistance of the water increases exponentially,
causing huge increases in power to achieve only small gains in speed.
One method of describing transport
efficiency is the movement of a specific load over a specific distance in a
specific time. Speed equals distance divided by time; therefore, transport
efficiency is the movement of a specific load multiplied by the speed at which
it can be moved.
When a load is moved via water, the
various resistances increase as the velocity times itself, and the energy
needed to affect an increase in speed rises more than the energy cubed, or
energy multiplied by itself three times (the exact power is 3.5.) This is a
huge number.
Another way to think of this problem is
to consider the lift-to-drag ratio. The load has to float or be lifted
by the water; this results in drag (resistance) when movement commences.
A boat has a lift-to-drag ratio about ten times lower than a steel wheel
rolling on a steel rail. The only way to improve the lift-to-drag ration of a
boat is to lift the boat's hull and load completely out of the water, which
reduces wave production and surface parasitic drag.
In a quest to break the water barrier, to
improve the lift-to-drag ratio and decrease the resistance of water, many
vehicles have been invented, especially during the last three centuries. It is
an old idea to pump air under a ship's hull in order to reduce resistance, but
the obvious and simple approaches to this idea do not work; the entire hull has
to be lifted off the surface. The majority of the modern inventions are based
on the idea of lifting the water displacement hull, or lifting the
load-carrying device out of the water. These include hydroplanes, hydrofoils
and air cushion vehicles. (The hovercraft is one type of air cushion vehicle.)
Among them, the air cushion vehicle has the best lift-to-drag ratio of any
device that travels across water when speeds exceed 35 mph.
1700 – 1900:
The Genesis of Air Cushion Vehicles
When it comes to flying machines, ideas
easily date back to ancient Greece. This is not the case with air cushion
vehicles. The first recorded design for such a vehicle was in 1716 by Emanuel
Swedenborg, a Swedish designer, philosopher and theologian. Swedenborg's design
appeared in the fourth edition of Sweden's first scientific journal, Daedulus
Hyperboreus, and is the first detailed technical description of a flying
machine of any type.
Swedenborg's man-powered air cushion platform,
basically a circular aircraft, resembled an upside-down boat with a cockpit in
the center or a "flying saucer." His manually operated device
required the would-be pilot to use oar-like scoops to push air under the
vehicle on each downward stroke in order to raise the hull out of the water. A
working model of the design was never built, because Swedenborg soon realized
that a human could not sustain the energy needed to power the oars. His concept
required a source of energy far greater than any available at that time. As
with many other forms of transportation, significant progress had to wait until
a lightweight motor was developed in the nineteenth century.
In 1865, William Fronde of the British
Admiralty sent a letter to B. J. Tideman, who was the Chief Constructor of the
Royal Netherlands Navy, proposing the principle of air lubrication. The letter
is on display at the David Taylor Model Basin in Washington D.C. and also
appears on page 109 of J. Scott Russell's book, The Modern System of Naval
Architecture, 1865, Vol. I.
In the mid-1870s, the British engineer
Sir John Thornycroft built a number of ground effect machine test models
based on his theory that an air cushion system would reduce the drag of water
on boats and ships. His theory was that if a vessel's hull were designed with a
concave bottom in which air could be contained between the hull and the water,
it would create significantly less resistance. He filed a number of patents
involving air-lubricated hulls through 1877. The internal combustion engine had
not yet been invented, however, so the technology required to power his
inventions still did not exist. In addition, no one had yet discovered a
practical solution to the problem of how to keep a cushion of air trapped so it
could not escape below a vessel.
In 1876, John B. Ward of San Francisco,
California USA, suggested an aluminum platform with rotary fans to drive air
down and backwards, but wheels would push the device along. He received US
Patents 185465 and 195860 for his "aerial machines."
The first patent for air lubrication in
Great Britain was issued to another Swedish engineer, Gustaf de Laval, in 1882
but because the method for retaining the cushion of air was not yet resolved,
de Laval was not successful with his experiments. British Patent 5841 details a
ship built with de Laval's ideas. Information on this ship can be found on
pages 33-34 in the book Speed and Power of Ships by Admiral D.W. Taylor,
published in 1933.
In 1888, James Walker of Texas was
granted US Patent 624271 in which channels along the underside of boats
contained air that would be captured in the adjacent channel as it tried to
escape. US Patent 608757, obtained in 1897 by Culbertson, includes an idea that
led to the first suggestion for sidewall air cushion vehicles.
Air lubrication has been applied to many
industrial processes and applications, including railways. The concept of a
"sliding railway," a train that rode on small hoverskirted pads using
water under pressure, was first proposed in 1868 by the French engineer
Monsieur Louis Girard. A working example was operated in 1886 for 900 miles in
the LeJouchere Park. After Girard was killed in the
Franco-German war, one of his assistant engineers, M. Barre, improved upon
Girard's ideas and constructed a sliding railway at London's Crystal Palace in
1891. The London News hailed the invention as "a marvelous
invention … a singularly original contrivance for enabling trains to run by
means of waterpower at speed hitherto undreamed of … something which may
eclipse the electric motors."
1900 – 1950:
The Evolution of Air Cushion Vehicles
Experiments with air cushion vehicles
began in earnest after a suitable power source, the engine, became a reality,
and after imaginations were fostered by the development of the airplane. As the
airplane evolved as a viable vehicle after the renowned Wright Brothers flight
in 1903, more attention was paid to the fact that additional lift was created
if an airplane flew close to land or water, creating a "funnel effect"
or cushion of air. This became known as ground effect.
Realizing that pressurized air reacts
against the surface of water and enables a vessel to skim over the water rather
than through it, naval architects patented several designs intended to solve
the problem of water resistance, or hydrodynamic drag. Onboard fans would force
compressed air into a chamber beneath, lubricating the hull with air from stem
to stern, which would raise it slightly above the water.
World War I brought the development of
the airplane as a military weapon which, in turn, fostered technological
interest, and scientists and innovators began exploring the ground effect/air
cushion effect in earnest.
Various forms of air cushion craft began
to evolve after the first working example was demonstrated in 1916. At that
time, Dagobert Muller von Thomamhul, an Austrian engineer, designed and built
an air cushion torpedo boat for the Austrian Navy, which used fans to pump air
beneath the hull to form a lubricating air cushion. Further development was
abandoned when World War I destroyed the Austrian Navy and the empire.
During this same period of time, there
were a number of prolific inventors of air-lubricated boats. F.W. Schweder
obtained British Patent 4131 in 1906 in which improvements upon De Laval's
ideas were proposed. In 1907 Joseph Clark received US Patent 989834 for an air
vehicle. Charles Theryc of France proposed yet another rail concept between
1902 and 1915, for which he received British Patent 5569. These trains rode on
air and many patents were issued that dealt with air edge seals. Two examples
are US Patent 1152451 and British Patent 9011 of 1915. Another French inventor,
M.A. Gambin, submitted British Patent Application 188648 in 1921 for a
sidewall-type air cushion vehicle.
James Porter, a British engineer,
received a series of patents dating from 1908, including British Patent 21216
and US Patent 1016359. In 1913, Porter suggested a machine with ideas very
similar to annular jet air cushion air supply systems, and received British
Patent 975 in 1914, which shows an annular duct quite similar to those of
present day hovercraft.
Also in 1908, Charles Worthington, an
American, suggested a vehicle supported on air but riding in a conduit. A
similar proposal was made in 1913 by A.F. Eells, also an American. Other early
air cushion vehicle inventors in the United States included F.G. Trask of North
Dakota, who patented a sliding railway in 1922; V.F. Casey of Minneapolis,
Minnesota; and Douglas Kent Warner of Sarasota, Florida.
In 1925, Casey received U.S. Patent
1621625 for the first air cushion recirculation concept. His design featured a
flat-bottomed vessel with a series of longitudinal air channels open on the
underside by which cushion air could be returned.
Warner, the head of Warner Research
Laboratories at Tamiama Trail, Sarasota, Florida, carried out considerable
research and development on air-cushioned boats in the 1920s and he held many
patents; examples are US Patents 1819216, 2277620 and 2365676
experienced wave-pumping problems, his machines incorporated the ram wing
concept. In 1929, Warner won boat races in Connecticut by the use of the
trapped air cushion or captured air bubble principle on his sidehull craft.
Warner's craft was the genesis of the surface effect ship (SES) of today.
A.U. Alcock, an electrical engineer in
Perth, Australia, built a working model air cushion vehicle, which was
demonstrated to the press and government officials in 1912. Alcock called his
invention "Floating Traction," for which he received Australian
Patent 14309. He later demonstrated other models at the Cricklewood Ice Rink in
1939.
In 1927, K.E. Tsiolkovski, a noted
Russian scientist, developed what today might be called the hovertrain. T.J.
Kaario of Finland built and tested a ground effect machine in 1935, and
received Finnish Patents 18630 and 26122. Other inventors of air-lubricated
boats during this period of history include J.C. Hansen-Euehammer of Denmark,
Henry Clay of London, Great Britain and C.J. Lake of the United States. There
were more than 100 patents on this subject filed before 1962.
Soon after heavier-than-air flight began,
it was discovered that flying close to the surface, within the width (cord) of
the wing, requires less energy to remain in the air. This became known as the
ground effect phenomenon. Ground effect is a function of the width of the wing;
to take advantage of the ground effect, any vehicle must fly above the ground
at an altitude less than the distance between the leading and trailing edge of
the wing.
The German Dornier DO-X twelve-engined
flying boat proved the reality of the air cushion ground effect in 1929 by
crossing the Atlantic Ocean entirely in ground effect at low altitude close to
the water. As a result, the aircraft's fuel consumption decreased. During World
War II, aircraft were flown to make use of air cushion ground effect in order
to extend reconnaissance flight range.
American aviator Charles Lindbergh is
reported to have flown in ground effect in order to conserve fuel during his
historic transatlantic flight in 1927. The challenge of flying along the wave
tops no doubt also served to stave off boredom during his long journey!
These and other beginnings formed the
foundation for the various forms of air cushion supported vehicles that later
appeared on the modern scene. Not until the 1950s, however, was a solution
found for the problem that had thwarted all previous attempts: how to retain the
cushion of air beneath the vessel.
1950 – 1964:
The Birth of the Air Cushion Vehicle/Hovercraft Industry
The successful use of the air cushion
effect in World War II aircraft inspired British, American, Russian and Swiss
engineers to seriously explore innovative ways to apply it. The many
experimental models that emerged prior to the 1950s were developed as flying
boats rather than true air cushion vehicles, and they were known as ram
wings as well as ground effect machines. The terms air cushion
vehicle and hovercraft were not used until the late 1950s.
Serious practical development of today's
hovercraft began in the mid-1950s in Great Britain, when Christopher Cockerell,
generally accepted as the inventor of the hovercraft, began to explore the use
of air lubrication to reduce hydrodynamic drag. Cockerell was a brilliant radio
engineer who was retired from the army and operated a boatyard on the Norfolk
Broads. During his lifetime, Cockerell was granted more than 70 patents for his
inventions, many of them dealing with hovercraft, and he was knighted for his
achievements.
Sir Christopher Cockerell's theory was
that instead of using the plenum chamber – an open-bottomed empty box
such as Thornycroft had devised – if air could instead be pumped into a narrow
tunnel around the perimeter of the underneath side of the craft, it would flow
toward the center, creating a more effective air cushion. This peripheral
jet would allow the air pressure to build enough to equal the weight of
the craft and, since the air would be trapped, the pressure would elevate the
craft off the surface upon which it traveled.
Cockerell tested his theory with a test
model constructed of two empty cans, an industrial air blower and a pair of
kitchen scales. By inserting a cat food can into a coffee can, and blowing air
through the gap between the two cans, he showed that it was possible to
increase the hoverheight and to construct a vehicle that could travel on a
cushion of air.
Originally, Cockerell had imitated
previous designs that used fans to force air down from the deck into the
chamber below, which meant that air had to be continually pumped back in to
replace the air that had escaped. He then devised a new system: he made the
hull of the craft concave and angled air jets from the circumference in toward
the center of the craft to create a continuous air current. This effectively
solved the problems of retaining the air beneath the craft, kept the air
pressure stable and raised the hoverheight.
In 1955, Cockerell built a working model
and was issued British Patent 854211 for a vehicle that was "neither an
airplane, nor a boat, nor a wheeled land craft." Cockerell described his
invention as "a very expensive motorcar tire with a permanent
puncture." He named it the hovercraft, which he registered as a
commercial name, so it was not available for general use until later when he
generously handed the name over to public domain.
This model, which illustrated his annular
peripheral jet system with inturned jets, led to the birth of the air cushion
vehicle/hovercraft industry. In his efforts to turn his invention into a
commercial product, Cockerell demonstrated it for British military officials in
1956, who immediately classified it as secret, effectively halting commercial
development for the next year.
As news filtered in that other countries
were pursuing hovercraft development, the government realized that Britain
would sacrifice its place as the world leader in this emerging technology if
development did not resume. Cockerell was then given permission to approach the
National Research Development Corporation (NRDC), a government-financed agency
who could back further development if the hovercraft could be freed from the
secret list.
In 1958, Cockerell's invention was
removed from the secret list, permitting hovercraft development for civilian
use; the value of the hovercraft for military use had yet to be demonstrated.
The NRDC then contracted the Westland Aircraft Company's Saunders-Roe division
to build a full-scale research hovercraft from Cockerell's concept, which was
named the Saunders Roe Nautical One (SR.N1).
On 25 July 1959 - fifty years to the day
that Louis Bleriot made the first crossing of the Dover Strait by airplane -
the world's first man-carrying hovercraft, the SR.N1, crossed the English
Channel from Calais, France to Dover, England. The press turned out in force,
and this amazing new invention captured the world's attention.
The SR.N1 carried only three passengers.
Cockerell traveled as moveable ballast; Commander Peter Lamb piloted the craft
and John Chaplin served as engineer and additional moveable ballast. Another
mechanic failed to wake up in time and was left in France. As of 2004, John
Chaplin is still living and resides in Virginia, USA.
Due to its low one-foot hoverheight, the
SR.N1 was plagued by wave impacts greater than one foot. Another British
inventor, C.H. Latimer-Needham, had followed Cockerell's developments. He
realized that the wave clearance problem could be solved with a rubber skirt to
contain the air cushion; a flexible skirt would collapse temporarily when it
impacted waves or obstacles, then return to its inflated shape.
The introduction of the flexible
hovercraft skirt was a crucial engineering breakthrough. The skirtless SR.N.1
of 1959 could only operate on calm seas at low speeds. After the SR.N1 was
fitted with a 4-foot flexible skirt in 1962, it could cope comfortably with
6-7-foot waves, cross marshland with gullies up to 4 feet deep and clear
obstacles over 3 feet high. In addition, the SR.N1 could now operate at twice
its original weight with no increase in lift power. Just one decade after the
introduction of Cockerell's hovercraft, its descendents, fifty times heavier
and three times as fast, would ferry a third of all passengers and cars across
the English Channel for some thirty years' duration.
The
Development of the Heavy Hovercraft Industry
With the introduction of the flexible
skirt, the term air cushion vehicle was first applied to this new and
fascinating invention, and ACV development was initially very rapid. The advent
of the flexible skirt launched hovercraft technology and practical usage, and
also defined the difference between hovercraft and all other types of air
cushion vehicles. The flexible skirt fostered the inception of the air cushion
vehicle/hovercraft industry worldwide, from the introduction of 300-ton
passenger/car ferries moving more than two million passengers per year, to the
construction of massive hoverbarges, to amphibious assault vehicles and LCACs
(Landing Craft Air Cushion). SR.N1s built in the US were first used by the
United States military in the Vietnam War.
In October of 2000, the Princess
Margaret and the Princess Anne, two of the world's largest
hovercraft, were retired after thirty years of ferrying tens of millions of
passengers across the English Channel. The Princess Margaret was
featured in the James Bond Film, Diamonds are Forever. Both Princesses
are now (2004) kept in service operational condition at the British Hovercraft
Museum at Gosport, Great Britain.
The
Development of the Light Hovercraft Industry
After the rapid advances of the late
1950s and early 1960s, the hovercraft industry began to develop into two
distinct categories: heavy (or large) hovercraft and light (or
small) hovercraft. For purposes of definition, size and payload (carrying
capacity) are used to distinguish light hovercraft from heavy hovercraft.
Although the distinction is somewhat arbitrary, generally a light hovercraft is
any vehicle that is wholly supported on a cushion of air and has a carrying
capacity that does not exceed 9.8kN.
The unique mechanical curiosity, called a
hovercraft by Sir Christopher Cockerell, excited the world's attention.
Saunders Roe continued to manufacture heavy hovercraft, and other companies
developed their own versions. But the media attention, particularly the heavy
coverage by the British media, also enlivened the imaginations of hobbyists and
mechanically minded enthusiasts everywhere.
Cockerell's hovercraft had all the
appearance of a safe and inexpensive new type of flying machine and many saw
the hovercraft as an affordable airplane. Experimenters who managed to
construct a hovercraft that could actually hover soon began to consider
manufacturing them as a business. This became a worldwide phenomenon and
occurred in university laboratories, backyards and basements.
The evolution of small hovercraft was
considerably influenced by local environments, and shared many similarities to
the development of the sport motorcycle. European hovercraft began to develop
into fast, single engine racing machines suitable for closed circuit racing,
similar to the Café Racer style motorcycle that also originated in Europe.
Hovercraft in the United States, however, followed a different course, much
like chopper classic street motorcycles. The wide open spaces and bounty of
long rivers in North America inspired hovercraft that were suited for traveling
in a straight line and cruising with comfort. This difference can still be seen
in today's hovercraft races: the European models excel on a tight, quick
course, where the American models excel on the straights.
Event though it was relatively easy to
construct hovercraft that would hover, they were still a long way from being
workable and even further from being designs that were capable of forming the
basis of a light hovercraft manufacturing business. Most entrepreneurial
enthusiasts soon lost their zeal. Until 1964, light hovercraft were still quite
crude, despite the major technical improvements documented in the general and
scientific literature. What then happened in terms of development, starting
with the world's first ground effect machine (hovercraft) race, was nothing
short of amazing.
The World's First Hovercraft Race
In 1964 Canberra, the picturesque capital
of Australia, was about to celebrate the opening of its new man-made Lake
Burley Griffin. As part of the Canberra Day celebrations on Saturday 14 March
1964, the Canberra Branch of the Royal Aeronautical Society planned and
promoted a commemorative hovercraft race. As N.F. Lamb, Chairman of the
Canberra Branch of the RAeS stated, "The Hovercraft was chosen as a
project because success is possible in this field by one man's personal efforts
at a very limited cost."
There were twelve entries in the world's
first hovercraft race, all of them from Australia. Eleven arrived at the site,
ten participated, and only five actually finished the race. As journalist Eric
Shackle reported, "Ten mostly backyard-built mechanical hares and
tortoises competed in the world’s first hovercraft race … One of the amphibious
hares sank, three had to be towed ashore, and a tortoise was first of only five
to cross the finish line. The 10th failed to start."
More than 30,000 spectators attended the
event, and it received extensive media coverage. Flight International magazine,
London, reported in its special supplement on air cushion vehicles:
March 14, 1964, may become a famous date in ACV
history, for on that day, at Canberra, the world's first competitive hovercraft
trials took place. They attracted 11 amateur entries from all over Australia,
ten of which were actual starters. An analogy may be drawn between the Canberra
trials of 1964 and the Rheims air meeting of 1909: both mark the beginning of
competitive development in their respective fields, with relatively primitive
machines conceived by enthusiastic experimenters. Personal ACVs stand now as
aeroplanes stood then, though enjoying the benefit of over 50 years'
development of reliable and lightweight engines.
The event was
a remarkable success, considering that Australia was remote from the technical
developments occurring at the time in Europe and the participants were largely
isolated with one another with little technical support or assistance. It was
well summarized by N.F. Lamb, who was also an official at the race: "The
trials were an outstanding success. They illustrated the ingenuity of the
individual to allocate sufficient time and a little money to have a worthwhile
hobby and make a first class machine. The ACV races have helped sustain a
personal interest in aeronautics, which is extremely difficult, considering the
high cost of aeroplanes."
The resultant
interest generated by the world's first hovercraft race can be considered the
initial stages of the light hovercraft industry.
Light
Hovercraft Development in Australia
The
"individual enthusiast" phase of the history of light hovercraft had
already begun in Australia prior to 1964. Harold Clisby, an early enthusiast,
owned an engineering company near Adelaide in South Australia, specializing in
small air compressors. During the 1960s he developed a simple single-fan
hovercraft with a 30 hp engine; it weighed about 230 lbs, was 7 feet in
diameter, and could hover 2 ½ inches above the ground.
Another early
experimenter, Chris Fitzgerald of Melbourne, was originally inspired by the
television news broadcasts about the SR.N1 crossing of the English Channel. He
began building model hovercraft with a group of friends, among them Rob Wilson,
Arthur Boyd, Dennis Markham, Sam Salario, Bernhard Sucher, Peter Kolf, and Eddy
Thomas, who called themselves Hovercraft Research Organization.
Through his involvement
in the Royal Australian Air Force Cadet Air Training Corps, Fitzgerald became a
cadet instructor and formed a group within the Air Training Corps to experiment
with rockets, gliders and hovercraft. The group met on weekends and established
a workshop in one of the members' backyards.
Through Arthur
Boyd, the group met David Atkins, as well as an American design student
studying for his Master's Degree at Melbourne University who was interested in
doing a study of hovercraft. Through him, the group became involved with the
Mechanical Engineering School at Melbourne University in 1962 and changed their
name to Australian Air Cushion Vehicles Development. At the same time, Chris
Fitzgerald became employed as a Technical Assistant with the Aeronautical
Research Laboratories in Melbourne, working full time on hovercraft-related
experiments.
When the group
learned that the Canberra Branch of the Royal Aeronautical Society was inviting
all hovercraft groups to participate in the world's first hovercraft race, they
decided to enter the experimental hovercraft being developed at Melbourne
University. Their hovercraft, however, was plagued by mechanical failure at the
race and did not place. After the race, it carried on as a useful research
machine until it was cannibalized and the remains were burned around 1972 in
Hastings, Victoria.
The group
built a series of experimental test models and in 1966 moved their enterprise
to the Fitzgerald family business location in Melbourne. In 1969, they built a
workshop in Hastings near the mudflats and adjacent to the western port
seashore.
As a result of
these activities and the publicity they generated, Chris Fitzgerald received a
Rotary Foundation Award in 1969 that enabled him to travel the world for two
years in order to research the state of hovercraft development in numerous
countries. During this time he studied aeronautical engineering at Farnborough
Technical School in England and worked as an intern at British Hovercraft for
several months.
Upon his
return to Australia, the group changed its name and incorporated Neoteric
Engineering Affiliates Pty. Ltd. A new design was initiated and a prototype,
called the Neova, was developed, which gave the company a salable
product. The company's first income was derived from the sale of an information
package and do-it-yourself plans and instructions.
Because the
Neova incorporated a number of technological improvements, a plan was
formulated to sell these innovations to the new hovercraft manufacturers
beginning to be established throughout the world. To facilitate the project,
Chris Fitzgerald moved to Terre Haute, Indiana, USA in 1975 to establish the
company’s headquarters.
By mid-1976,
it was evident that a hovercraft manufacturing market for the company's technology
did not exist, so the plan was modified to establish a manufacturing base in
Terre Haute to initially sell hovercraft kit components. This evolved into an
operation that manufactured and sold the entire vehicle: Neoteric Hovercraft,
Inc., the world's original light hovercraft manufacturer.
Light
Hovercraft Development in North America
Even though
Sir Christopher Cockerell of Great Britain is generally accepted as the
inventor of the hovercraft, there exists some controversy over whether the
first hovercraft was actually developed in Great Britain or in the United
States.
During the
1950s and early 1960s, at the same time as Sir Christopher Cockerell's
achievements in Great Britain, an American inventor was following a similar
path. Dr. William Bertelsen, a general practitioner in Illinois with an
engineering background, had been seeking a practical method of alternative
travel that would allow him to make house calls to his rural patients
regardless of the weather.
Dr. Bertelsen
first piloted his "flying aeromobile" in 1958, eight months earlier
than Christopher Cockerell's first flight, and he filed United States Patents
around the same time Cockerell Filed British Patents. Popular Science
magazine featured Bertelsen's invention as the front-page story in its July
1959 issue. Dr. William Bertelsen founded Aeromobile, Inc., still in operation
today, and continued to innovate and promote air cushion vehicles. In 1996, Dr.
Bertelsen and his creations were filmed by the Discovery Channel as part of
their Extreme Machines program. A great transportation inventor and
visionary, Dr. Bertelsen was the recipient of the 2002 World Hovercraft
Excellence Award.
The
geographical environment also influenced hovercraft development in North
America. In contrast with their British counterparts, enthusiasts were
scattered across great distances. Since both the United States and Canada
abounded in ideal hovercraft operating terrain, with vast river systems,
enthusiasts were not as prone to get together to share selected sites, as was
the case in Europe.
Communication
between enthusiasts was sporadic, typically duplicating those of British
publications. An Indiana USA enthusiast, Jan Eglen, formed the National
Association of Air Cushion Vehicle Enthusiasts and published a newsletter
called The Kestral. Eglen resigned in 1973 and another enthusiast, Rod
McKeighan, transferred the club to Michigan and changed its name to the
American Hovercraft Association.
The
Association was in disarray in 1975 when Chris Fitzgerald moved his operation
from Australia to Terre Haute, Indiana USA, where he had become acquainted with
Jan Eglen during his Rotary Foundation world study tour. In 1976, Fitzgerald
established and organized the Hoverclub of America, Inc., which has since
become the largest hovercraft club in the world.
During the
late 1960s and early 1970s, many attempts were made at commercialization.
Several hovercraft manufacturers collectively produced approximately 3,000
hovercraft, which were sold through dealers. Unfortunately, manufacturers
drifted away from their initial attempts to qualify dealers. Their hovercraft,
therefore, often fell short of customer expectations and a great many
hovercraft manufacturers did not succeed. Nevertheless, a few American
hovercraft manufacturers have survived. Two of the most well known are Neoteric
Hovercraft, Inc. and Universal Hovercraft.
In 1976,
Robert Windt formed Universal Hovercraft in Cordova, Illinois USA. The company
limited its sales to plans, propellers and fans, and along with Neoteric
Hovercraft, Inc. has survived over the decades since their beginnings. Today,
approximately 90% of all homebuilt hovercraft in the Hoverclub of America are
Universal Hovercraft designs. In 2003 Chris Fitzgerald established
DiscoverHover, a not-for-profit worldwide school hovercraft program in which
students can build a hovercraft and compete in established hovercraft racing
events. The free hovercraft plans provided by DiscoverHover are updated
versions of Windt's Universal Hovercraft plans.
Light
Hovercraft Development in Great Britain
In the early
1960s, the United Kingdom had an active group of light hovercraft
experimenters. Outstanding among these was Jeff Harding, a mechanical engineer.
In 1965 he proposed that an organization should be formed and a race meeting
should be held so that individual enthusiasts would have the opportunity to
compare ideas and to compete.
Europe's first
amateur hovercraft rally took place at Apethorpe Hall, Northants. Lord Brassey,
the owner of Apethorpe Hall, was quite interested in hovercraft. This was the
beginning of the Hoverclub of Great Britain.
The winner of
the race was Dan Reece. Reece had been the only British competitor in the
world's first hovercraft race in Canberra in 1964. Reece went on to become the
designer for Hover Air, Ltd., a company formed by Lord Brassey in 1966.
Although the company eventually failed, it produced more than 100 Hoverhawk
hovercraft, which were sold worldwide.
In the
development of light hovercraft, Great Britain had the distinct geographical
advantage of being a small country; enthusiasts lived within easy driving
distance of each other and could meet frequently to compare and exchange ideas
about their new machines. Great Britain, however, suffered a disadvantage in
comparison to other nations, in that there were very few suitable areas for
operating hovercraft. Most waterways and canals had incredibly low speed
limits, such as 5 km/h (3 mph) and were crowded by fisherman. Although coastal
regions were suitable for cruising hovercraft, the salt water meant high
maintenance for the craft.
As a result,
British Hoverclub members were forced to seek out suitable private estates and
regional government lands for their rally activities. Many of these locations
were subsequently developed into a national circuit for hovercraft racing, with
the better courses located on the grounds of stately homes. Regulations, safety
rules, points scoring, and classification were developed as courses were
established. Regular rallies, hover-ins and especially competitive trials set
the stage for development in the following decade. No other nation was so well
equipped for the evolution of the sport of light hovercraft racing than Great
Britain.
Technical Trends in Light Hovercraft
Engines
One of the
first questions asked about hovercraft is, "What kind of engine do they
have?" Engines are a natural fascination for anyone with a mechanical
bent. The availability of suitable lightweight engines has contributed much to
the development of light hovercraft.
Early
designers used engines that were readily available in their respective
countries. Great Britain offered a wide variety of small, lightweight,
two-cycle engines. A few builders used aluminum block automobile engines.
American builders tended to use chainsaw, lawnmower, snowmobile and air- and
liquid-cooled automobile engines.
The
power-to-weight ratio of an automobile engine is such that a fairly large
machine is required just to carry the engine; they also take up a great amount
of space. Early hovercraft designers and builders put an inordinate effort into
adapting engines and trying to persuade transmission and fan systems to stay
intact. During the late 1960s, since the United Kingdom was well equipped with
engines suitable for hovercraft, British designers and builders were able to
concentrate on operating and testing hovercraft. This yet another reason why
light hovercraft evolved more rapidly in the United Kingdom during that period
than in any other nation.
The 1970s were
the golden years of the snowmobile in America. In 1971, North American sales
soared to nearly half a million units. Engine manufacturers, primarily in
Japan, were developing snowmobile engines with a power-to-weight ratio suitable
for hovercraft. Reliability, dependability and ease of starting were improved
with the introduction of capacitor discharge ignitions, better materials and
manufacturing tolerances, and high performance resonance exhaust systems. These
engines began to find their way into hovercraft toward the end of the decade.
At the same time, trail bikes began to increase in popularity and their
engines, as well as those of go-karts, were also adapted for use in hovercraft.
Fans and Propellers
As with
engines, fans and propellers also fascinate hovercraft enthusiasts, in fact,
they represent a starting point for many a would-be hovercraft builder. In the
early days, much of the hovercraft theory that abounded dealt with fans and
propellers. With decades of hindsight, what works best is well known and most
builders use commercially available fans.
Some of the
heavier and larger light hovercraft use centrifugal fans for lift, similar to
those found in home heating and air conditioning units. The axial flow fan,
however, which can be found everywhere for cooling, venting and circulating
air, has been found to be particularly suitable for hovercraft because it efficiently
moves large volumes of air at low pressures.
All amphibious
light hovercraft are propelled by either fans or propellers. The quantity of
static thrust available to accelerate a hovercraft is important. One measure of
performance is thrust efficiency, or the ratio of thrust per unit of power. Air
devices are notoriously inefficient when compared to tracked vehicles or even
water propellers. The highest efficiency static thrust air devices are
helicopter rotors. Next on the efficiency scale comes propellers, followed by
ducted axial flow fans.
Safety
considerations now dictate that a propeller must be enclosed. A properly
constructed wire cage is heavy and does nothing for the appearance of a
hovercraft, so most designers prefer to enclose propellers in ducts. Since the
late 1980s, although both open and ducted propellers dominate the American
do-it-yourself market, ducted thrust fans are found on the vast majority of
light hovercraft in Great Britain and throughout the rest of Europe. The ducted
fan's universal appeal has much to do with safety considerations as well as
aesthetic considerations.
Power Transmissions
Many types of
power transmission have been employed in light hovercraft over the years, but
the most common is the toothed timing belt. A more refined version is the HTD
belt, which can be found on most of the larger commercially manufactured light
hovercraft. Practically all hovercraft today are directly coupled, except for
the heaviest models in which various types of clutches are utilized.
Controls
Larger
hovercraft sometimes employ skirt-shift controls, which move the inner skirt
attachments to change the air cushion's center of pressure and enable the craft
to roll or pitch. Such complications are unnecessary on lighter, smaller hovercraft.
Pilots and passengers in light hovercraft move about to adjust trim as desired.
This method, referred to as kinesthetic control, is extremely important in
small racing hovercraft. The pilot must constantly shift his/her weight about
to assist the craft in operation while accelerating, decelerating or banking
into turns in order to prevent it from nose-diving into the water
("plowing in") or becoming airborne.
All light
hovercraft are fitted with vertical rudder blades, which are mounted in the fan
or propeller slipstream, and controlled through a steering wheel, joystick, or
bicycle-style handlebar. Some craft have horizontal elevators for longitudinal
trim. These are especially useful for hovercraft in which the driver cannot
readily move about.
When a
hovercraft lift engine is separate from the thrust engine, precise control over
the air cushion is possible. Such control helps to reduce dust and spray,
minimizes skirt drag, and makes it possible to adjust the skirt drag for
braking. This configuration also makes stationary hovering possible (hovering
in place without forward motion).
Neoteric
Hovercraft, Inc. in the United States, owns the patent for reverse thrust
buckets, which not only improve control, but also allows Neoteric models the
distinction of being the only hovercraft manufactured with the effective
capability of braking, backing up and hovering in place.
Skirts
The flexible
skirt has had a profound effect on the practicality of hovercraft and are
essentially the base technology of hovercraft. Most of today's skirt know-how
was invented in Great Britain during the mid-1960s. In the United States, the
majority of homebuilt hovercraft tended to use the non-flow bag skirt, the
simplest of skirts and the most rugged. However, bag skirts have a tendency to
bounce. British hovercraft started out using bag skirts in the late 1960s, but
by the 1980s most were using segmented (finger) skirts constructed of
neoprene-coated nylon, which is superior to most other fabrics as hovercraft
skirt material.
Structures
The selection
of building materials for hovercraft followed a natural course. The first
builders began by using wood, which is still popular today. The majority of
American homebuilt hovercraft are made of wood. Some early builders used fabric-covered
structures, fiberglass (requiring expensive molds) and aluminum. Some of the
larger passenger-carrying hovercraft are aluminum; others are composite
fiberglass with a "foam sandwich" construction.
It is not
difficult to make light hovercraft structurally sound; over the years there
have been few examples of structural failures. Structural stiffness in light
hovercraft is not critical because the structure is supported evenly by the
cushion pressure. Even the crudest hovercraft will work; masterful
craftsmanship and design are not critical to their successful operation.
Today, most
manufactured light hovercraft are constructed from chopmat fiberglass. The hull
is constructed on a mold and then sandwiched between a urethane core and a
fiberglass body.
The Future of the Hovercraft
The
hovercraft, no longer considered an obscure, impractical vehicle, is in
operation today throughout the world for a great variety of purposes, including
leisure sport and racing, search and rescue, ice fishing, hunting, surveying,
flood control, environmental projects, agriculture, icebreaking, water
transportation, education and a myriad of other purposes.
The hovercraft
industry, however, is still a wide-open area for research and potential
breakthroughs. Technically, light hovercraft are poised to continue the
advances developed during the last few decades.
Small, light
hovercraft have the potential for becoming primary transport vehicles in many
undeveloped areas. They can be easily constructed onsite, and their versatility
suggests worldwide applications.
As the number
of light hovercraft continues to increase throughout the world, new
applications will be found. Because hovercraft are not as limited as
snowmobiles geographically, their use for racing, cruising, hunting and
commercial applications are likely to eventually exceed that of the snowmobile.
Light hovercraft should become a significant new vehicle in the marine
industry; their concept represents one of the few breakthroughs in marine
transportation since the hydrofoil or the very first boat.
The future of
light hovercraft for sport, recreation and racing should be assured. Hovercraft
racing has, not surprisingly, become an established and growing international
sport. Light hovercraft make spectacular and unusually safe racing vehicles,
and are inexpensive compared to wheeled racing vehicles. Natural tracks for
hovercraft races exist in nearly every city in the world, and a first-class
hovercraft race needs little more than some water and adjacent land, ice or
snow.
The hovercraft has come a long way from
the "flying machines" of ancient Greece and Sir Christopher
Cockerell's tin cans. In the present day, hovercraft are attracting reawakened
attention, primarily because technological developments have led to greater
reliability and ease of operation. The last forty years of development, in
particular, have taken hovercraft technology from the domain of great inventors
and put it into the hands of the public, from large corporations and the
military to young schoolchildren.
Anyone of any age who has ever dreamed of flying can now experience that dream.
Hovercraft kits are available for the do-it-yourselfer and, even though there
are still few hovercraft manufacturers compared, for instance, to automobile
manufacturers, personal hovercraft can be purchased for less than the price of
a good motorcycle. Hoverclubs for private hovercraft enthusiasts have been
established in most major nations, and hoverclub rallies and World Racing
events attract growing numbers of participants and spectators each year.
Hovercraft are featured in mainstream entertainment, such as James Bond films
and Junkyard Wars. Worldwide school hovercraft programs, such as
The history of the hovercraft continues to be written. Today and in the future,
however, that history is being written not only by inventors, engineers and
movie studios. The history of the hovercraft is now being written by your
neighbors building a hovercraft in their garage; by your local fire department
performing rescues; by your child building a hovercraft at school; and by you.
The opportunities may be slim for you to go down in history as the inventor of
a new vehicle or as an Olympics winner. In contrast, hovercraft today and
tomorrow are very much an equal opportunity, available to everyone. If you've
ever wanted to fly, if you've ever wanted to race, if you've ever wanted to
become a part of history, now is your time.
The British Hovercraft Museum Trust, an online
encyclopedia describing the history of hovercraft www.hovercraft-museum.org
The History of Air Cushion Vehicles
Kalerghi-McLeavy Publications,
1963; Leslie Herbert Hayward, author.
style='font-size:9.0pt'>
History of Hovercraft – Pioneering Vessels and People
Editor
Hovercraft Technology, Economics and Applications;
Christopher Fitzgerald, contributor
The Speed and
Power of Ships: A Manual of Marine Propulsionstyle='font-size:9.0pt'>; US Government Printing Office, 1933: Admiral David W.
Taylor, author.