Tracked Hovercraft was an experimental
high speed train
High-speed rail (HSR) is a type of rail system that runs significantly faster than traditional rail, using an integrated system of specialised rolling stock and dedicated tracks. While there is no single standard that applies worldwide, lines ...
developed in the United Kingdom during the 1960s. It combined two British inventions, the
hovercraft
A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces.
Hovercraft use blowers to produce a large volume of air below the hull ...
and
linear induction motor
A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristic ...
, in an effort to produce a train system that would provide inter-city service with lowered capital costs compared to other high-speed solutions. Substantially similar to the French
Aérotrain
The Aérotrain was an experimental Tracked Air Cushion Vehicle
(TACV), or hovertrain, developed in France from 1965 to 1977 under the engineering leadership of Jean Bertin (1917–1975) – and intended to bring the French rail network to the c ...
and other
hovertrain
A hovertrain is a type of high-speed train that replaces conventional steel wheels with hovercraft lift pads, and the conventional railway bed with a paved road-like surface, known as the ''track'' or ''guideway''. The concept aims to eliminat ...
systems of the 1960s, Tracked Hovercraft suffered a similar fate to these projects when it was cancelled as a part of wide budget cuts in 1973.
History
Genesis at Hovercraft Development
It was noticed early on in the development of the hovercraft that the energy needed to lift a vehicle was directly related to the smoothness of the surface on which it travelled. This was not entirely surprising; the air trapped under the hovercraft will remain there except where it leaks out where the lifting surface contacts the ground — if this interface is smooth, the amount of leaked air will be low.
[Sandie Yang]
"Handling Hovercrafts: Designing a project curriculum to introduce girls to mechanical engineering"
MIT, June 2006, p. 14. This is the purpose of the ''skirt'' found on most hovercraft; it allows the fuselage to be some distance from the ground while keeping the air gap as small as possible.
The surprising discovery was that the amount of energy needed to move a given vehicle using hover technology could be lower than the same vehicle on steel wheels, at least at high speeds. Over , conventional trains suffered from a problem known as
hunting oscillation
Hunting oscillation is a self-oscillation, usually unwanted, about an equilibrium. The expression came into use in the 19th century and describes how a system "hunts" for equilibrium. The expression is used to describe phenomena in such diverse ...
that forces the flanges on the sides of the wheels to hit the rail with increasing frequency, dramatically increasing
rolling resistance
Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body (such as a ball, tire, or wheel) rolls on a surface. It is mainly caused by non-elastic effects; that is, not all the energy nee ...
. Although the energy needed to keep a hovercraft in motion also increased with speed,
[ this increase was slower than the sudden (and sometimes catastrophic) increase due to hunting. That implied that for travel above some critical speed, a hovercraft could be more efficient than a wheeled vehicle running on the same route.
Better yet, this vehicle would also retain all of the positive qualities of a hovercraft. Small imperfections in the surface would have no effect on the ride quality, and the complexity of the suspension system could be greatly reduced. Additionally, since the load is spread out over the surface of the lifting pads, the pressure on the running surface is greatly reduced — about the pressure of a train wheel, about of the pressure of a rubber tyre on a road.] These two properties meant that the running surface could be considerably simpler than the surface needed to support the same vehicle on wheels; hovertrain
A hovertrain is a type of high-speed train that replaces conventional steel wheels with hovercraft lift pads, and the conventional railway bed with a paved road-like surface, known as the ''track'' or ''guideway''. The concept aims to eliminat ...
s could be supported on surfaces similar to existing light-duty roadways, instead of the much more complex and expensive railbeds needed to support the weight on two rails. This could greatly reduce infrastructure capital costs.
In 1960 several engineers at Christopher Cockerell
Sir Christopher Sydney Cockerell CBE RDI FRS (4 June 1910 – 1 June 1999) was an English engineer, best known as the inventor of the hovercraft.
Early life and education
Cockerell was born in Cambridge, where his father, Sir Sydney Cocke ...
's Hovercraft Development Ltd. in Hythe, Hampshire
Hythe () is a town near Southampton, Hampshire, England. It is located by the shore of Southampton Water, and has a ferry service connecting it to Southampton. Hythe has a small shopping area, a pier, and a marina for yachts.
History
The name ...
, began early studies on the hovertrain concept. At the time, a major problem was selecting a suitable power source. As the hovercraft had no strong contact with a running surface, propulsion was normally provided by an aircraft-like solution, typically a large propeller. This limits the acceleration, as well as the efficiency of the system, a major limitation for a design concept that would compete with aircraft on the same routes.
Introducing the LIM
Through the same period, Eric Laithwaite
Eric Roberts Laithwaite (14 June 1921 – 27 November 1997) was a British electrical engineer, known as the "Father of Maglev" for his development of the linear induction motor and maglev rail system.
Biography
Eric Roberts Laithwaite wa ...
had been developing the linear induction motor
A linear induction motor (LIM) is an alternating current (AC), asynchronous linear motor that works by the same general principles as other induction motors but is typically designed to directly produce motion in a straight line. Characteristic ...
(LIM) at the University of Manchester
, mottoeng = Knowledge, Wisdom, Humanity
, established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univer ...
. By 1961 he had built a small demonstration system consisting of a LIM reaction plate and a four-wheeled cart with a seat on top. In 1962 he started consulting with British Rail
British Railways (BR), which from 1965 traded as British Rail, was a state-owned company that operated most of the overground rail transport in Great Britain from 1948 to 1997. It was formed from the nationalisation of the Big Four British rai ...
(BR) on the idea of using LIMs for high-speed trains. A November 1961 ''Popular Science
''Popular Science'' (also known as ''PopSci'') is an American digital magazine carrying popular science content, which refers to articles for the general reader on science and technology subjects. ''Popular Science'' has won over 58 awards, incl ...
'' article shows his Hovertrain concept using a LIM, the accompanying illustration shows small lift pads like those from the Ford Levapad concept, running on top of conventional rails. After moving to Imperial College London
Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...
in 1964, Laithwaite was able to devote more time to this work and perfect the first working examples of large LIMs suitable for transport systems.[''Laithwaite'']
LIMs provide traction through the interaction of magnetic fields generated on the vehicle and a fixed external conductor. The external conductor was normally made of plates of aluminium, chosen due to its high conductivity
Conductivity may refer to:
*Electrical conductivity, a measure of a material's ability to conduct an electric current
**Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution
**Ionic conductivity (solid state), elec ...
in relation to its price. The active portion of the motor consists of a conventional electric motor
An electric motor is an Electric machine, electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a Electromagneti ...
winding stretched out under the vehicle. When the motor windings are energised, an opposing magnetic field is induced in the nearby reaction plate, which causes the two to repel each other. By moving the fields down the windings, the motor pushes itself along the plate with the same force that is normally used to create rotation in a conventional motor.[ A LIM eliminates the need for strong physical contact with the track, requiring instead a strong reaction plate. It has no moving parts, a major advantage over conventional traction.
In Laithwaite's original designs, known as ''double-sided sandwich motors'', two sets of windings were used, positioned a few centimetres apart. They were positioned so that the aluminium stator plate would fit in the gap between the windings, sandwiching it between them. The advantage to this layout is that the forces pulling one set of windings toward the plate are balanced by the opposite forces in the other set. By attaching the two sets of windings to a common frame, all of the forces are internalised.][
]
Hovertrain
The Hovercraft Development team quickly picked up on the LIM concept as well. Their initial solution was a track shaped like an upside-down T, with the vertical portion consisting of a central concrete section with aluminium ''stator'' plates fixed on either side. Their first design concept looked like the fuselage of an airliner with two decks, riding above the stator beam, with the LIM centred in the middle of the body. Four pads provided lift, arranged two on a side fore and aft and riding on the horizontal surface of the guideway. Four more pads, above the lift pads, were rotated vertically to press against the centre beam and kept the craft centred. A test rig of this layout was built at Hythe, which was filmed in operation by British Pathé
British may refer to:
Peoples, culture, and language
* British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies.
** Britishness, the British identity and common culture
* British English, ...
in 1963, which also showed a model of the proposed full-sized version.(https://www.britishpathe.com/video/hovertrain/query/Hythe)
As development of the testbed design continued at HDL, the problem of high-speed loads on the guideway became obvious. In spite of its light weight compared to conventional train sets, the Tracked Hovercraft operated at such high speeds that its passage induced vibration modes in the guideway that needed to be damped out. This was a relatively new field for the civil engineers
This list of civil engineers is a list of notable people who have been trained in or have practiced civil engineering.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
...
that were working on the guideway design, as their field was more generally concerned with static loads.[Jim Platts]
"Dynamics of Hovertrain Tracks"
1971 The train layout was redesigned with a box-like main girder, with a top-mounted reaction plate being used for the LIM, and the vertical sides of the guideway being used for centring. Wing-like extensions extended down from the body of the train and covered the centring pads. A version with this layout was built as a scale model at Hythe, and featured in another Pathé film in 1966. This version was shown at Hovershow '66.
A further modification produced a guideway that looked like a rightside-up T, although the vertical section was a trapezoidal girder almost as wide as the top of the T. The reaction plate for the LIM was moved to the underside of the horizontal portion of the T on one side, extending vertically down, while the other side contained the electrical conductors that provided power. In such an arrangement, rain, snow and debris would simply fall off the plates. The new guideway design was simulated at the Atlas Computer Laboratory
The Atlas Computer Laboratory on the Harwell, Oxfordshire campus shared by the Harwell Laboratory was one of the major computer laboratories in the world, which operated between 1961 and 1975 to provide a service to British scientists at a time ...
.[ This work included the generation of films showing the vehicle in-action, using a Stromberg-Carlson SC4020 microfilm recorder.
]
Laithwaite joins
While the hovertrain was being developed, BR was running an extensive research project on the topic of high-speed wheeled trains at their newly opened British Rail Research Division
The British Rail Research Division was established in 1964 directly under the control of the British Railways Board, moving into purpose-built premises at the Railway Technical Centre in Derby. The intention was to improve railway reliability an ...
in Derby
Derby ( ) is a city and unitary authority area in Derbyshire, England. It lies on the banks of the River Derwent in the south of Derbyshire, which is in the East Midlands Region. It was traditionally the county town of Derbyshire. Derby gai ...
. This was the first group to characterise the hunting oscillation in detail. Their work clearly suggested that careful design of the suspension system could eliminate the problem. This would allow high-speed trains to be built using conventional steel-wheel technology.
Although high-speed travel would require new lines to be laid, expensive ones, such a train could use existing rail infrastructure at lower speeds. This would allow such a train to approach existing stations at lower speeds, greatly reducing capital costs of bringing the service into cities. The inter-city sections could be re-laid for higher speeds, where the infrastructure costs were generally lower anyway. BR also showed that the capital cost advantages of the hovertrain concept were offset by the higher vehicle costs; the tracked hovercraft concept made sense for a smaller number of vehicles or longer lines where the capital costs were concentrated in the tracks, but neither of these characterised BR's operations.
Meanwhile, having exhausted their research abilities using small models, the Hovercraft Development team had been petitioning their parent organisation, the National Research Development Corporation The National Research Development Corporation (NRDC) was a non-departmental government body established by the British Government to transfer technology from the public sector to the private sector.
History
The NRDC was established by Attlee's La ...
(NRDC), for additional funding to build a full-sized test track. NDRC was unsuccessful in raising new capital from the government and decided to put in £1 million from their own pre-assigned discretionary budget to start construction of a track, hoping that additional funding would be forthcoming from industry.[''Go-Ahead'' 1967, pg. 58]
On 1 April 1967, Hovercraft Development was officially transferred to National Physical Laboratory. Seeking to protect their investment, and finding little external funding, the NRDC decided to spin off the hovertrain group as Tracked Hovercraft Ltd. (THL). They also decided to spool out the funding over four years, starting with a £1 million grant for a single prototype vehicle and a short portion of the test track. Although this funding was enough only for the first stage of a track, the NRDC suggested it would be quite useful for testing low-speed intra-urban versions of the concept.[
Frustrated with BR's lack of interest in his hovertrain work, and their lack of funding, in 1967 Laithwaite severed his ties with BR and joined Tracked Hovercraft as a consultant. By this time the French government had started providing major funding for Jean Bertin's ]Aérotrain
The Aérotrain was an experimental Tracked Air Cushion Vehicle
(TACV), or hovertrain, developed in France from 1965 to 1977 under the engineering leadership of Jean Bertin (1917–1975) – and intended to bring the French rail network to the c ...
project, which was substantially similar to the Tracked Hovercraft in concept. Laithwaite, always described as persuasive, convinced the government that they were about to lose out on this burgeoning field of high-speed transit,[ and eventually won £2 million in additional funding.]
RTV 31
By the time construction was preparing to start in 1970, a new problem had appeared. Prior to construction most LIMs were test systems that had operated at low speeds, but as the speeds increased it was noticed that the mechanical forces of the LIM windings on the stator plate gave rise to a serious safety issue. Magnetic forces vary with the cube of distance, so any change in distance between the motor and stator plate caused it to be pulled more strongly to the closer side. At high speeds, the forces involved were so great that it was possible for the stator plate to crack along vertical joins in the plates, at which point it could strike the motor, or portions of the vehicle behind the crack point. Even without an outright failure, any mechanical motion in the plate due to the forces of the passing train could induce waves in the stator that travelled along with it. If the vehicle then decelerated these waves could catch up with it. Additionally, the passing of the train heated the plate, potentially weakening it mechanically. Laithwaite concluded that the double-sided LIM was "far too dangerous" to use.
Most systems using LIMs – there were dozens by this point – redesigned their tracks to use a single-sided LIM over a stator plate lying flat between the rails. This led to another redesign of the Hovertrain guideway as a square box girder with the LIM stator attached flat on the top of the box, and the electrical pick-ups below on either side of it. Power pick-ups extended from the rear of the vertical wing-like surfaces on either side of the vehicle, and the sparks they threw during operation are easily visible on test runs.["Video of RTV 31 test run"]
BBC News, February 1973
Starting in the 1970s, construction of test track started in the fens at Earith
Earith is a village and civil parish in Cambridgeshire, England. Earith lies approximately east of Huntingdon. Earith is situated within Huntingdonshire which is a non-metropolitan district of Cambridgeshire as well as being a historic county ...
in Cambridgeshire, supported by Tracked Hovercraft Ltd offices in Ditton Walk in Cambridge
Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge bec ...
city. The track was about off the ground, running along the earthworks between the Old Bedford River
The Old Bedford River is an artificial, partial diversion of the waters of the River Great Ouse in the Fens of Cambridgeshire, England. It was named after the fourth Earl of Bedford who contracted with the local Commission of Sewers to drain ...
and the Counter Drain just to its north, between Earith and the Denver Sluice. The first long section of the planned long track was laid to Sutton-in-the-Isle
Sutton or Sutton-in-the-Isle is village and civil parish in the county of Cambridgeshire in England, near the city of Ely. The "in-the-Isle" suffix refers to the fact that the village is part of the Isle of Ely, once an island in the Fens and ...
. Along the full length it was expected the train would reach .
On 7 February 1973 the first test train, Research Test Vehicle 31, or RTV 31, reached on a section, in spite of the short track and a headwind. The test was heavily publicised and shown on BBC #REDIRECT BBC #REDIRECT BBC
Here i going to introduce about the best teacher of my life b BALAJI sir. He is the precious gift that I got befor 2yrs . How has helped and thought all the concept and made my success in the 10th board exam. ...
...
news throughout the day. Much of the interest stemmed from rumours that the project was facing imminent cancellation. Aerospace Minister
to view the test. Heseltine said in an interview that he believed that the project would not be cancelled.