In 1974, a French train smashes through a speed record,
exceeding 250 miles per hour.
But this train is unlike any other beforeit.
It doesn’t have wheels.
It hovers on a cushion of air, and because of that, it can travel efficiently at very high speed
Maybe you ’ ve never heard of hovertrains,
but by the 1970 ’ s, they were seriously being
considered as the solution to slow, antiquatedrailways which in many countries were in
In the 1960’s, railways were in trouble.
In developed countries, ridership was plummetingand railways were in decline.
In Britain, some routes were still servedby steam locomotives.
And the public was beginning to view rail as slow and outdated.
Trains now had to compete with newly built superhighways and intercity air travel.
And even Japan ’ s newly introduced Bullet Train,
a technical marvel for 1964, was initially
only running at speeds of up to 130 milesan hour.
Part of the problem was most rail lines
in the developed world, were built a half century earlier,
with their sharp twists and curves,
they just weren’t built for speed.
But the trains also had a problem.
And it had to do with the shape of their wheels.
Train wheels are not perfectly cylindrical,they’re cone-like in shape.
And this is what keeps them on their track, especially around curves.
While the wheels also have flanges,
these are really just a backup in case limits of
that conical shape are exceed.
The conical shape of train wheels is a brilliantinnovation.
But there’s a problem, and it’s called HuntingOscillation.
At higher speeds,
the cone-like shape causes a train to increasingly rock from side to side.
The flanges start hitting the track,
which increases resistance, making higher speeds
inefficient and causing wear and damage.
Given enough speed,
Hunting Oscillation can even cause a train to derail itself, on a
perfectly straight track.
This meant that trains essentially had a speed limit built right
into their basic design.
So in the 1960 ’ s,
the thinking was that maybe it was time to get rid of wheels all together.
The French have already built the Aerotrain.
Designed to reduce the running
friction problems of wheeled trains by doing away with the wheels.
It’s called a hovertrain.
By feeding high pressure air through lifting pads,
the train would float on a cushion of
air much like a hovercraft.
The track would act merely as a guideway.
Without the rolling resistance of wheels,
a hovertrain promised efficiency and much
And leading the way
for this promising technology was a French engineer named Jean Bertin.
By 1973, Bertin and his team had
built a hovertrain that could carry 80 passengers.
French officials and the media marveled at its combination of speed and smooth ride.
Bertin called his designs Aerotrains.
Over the years, he had worked tirelessly to develop several prototypes,
proving the viability
of the concept.
With each success, he secured a healthy doseof government funding.
The most advanced Aerotrain was powered bya turbofan.
pretty much straight off an airliner.
It produced over twelve thousand pounds ofthrust.
At the front,
a 400 horse power gas-turbine supplied high-pressure air to hover this twenty
tonne loaded train a quarter of an inch offits guideway.
And the guideway, was essentially poured concrete.
An Aerotrain could easily hover over imperfections.
That meant that hovertrain lines were
potentially easier to build than conventional rail and
cheaper to maintain.
On March 5, 1974,
an Aerotrain proved it could travel at nearly two hundred and sixty miles
And it might have gone even faster,
had its test track had been longer.
The success of Bertin ’ s prototypes led to plans
for Aerotrain links throughout France.
And just a couple months after the record breaking speed-run,
a contract was signed
to begin construction of the very first line.
Outside of France, the world was also takingnote.
The British, who had invented the hovercraft,
could see the enormous potential of hovertrain
They constructed their own hovertrain testtrack in 1970.
And in some ways,
Britain ’ s research into hovertrains was even more advanced.
Their prototype, the RTV-31 Tracked Hovercraft was designed around another important innovation.
The Linear Induction Motor.
Although Bertin also experimented with Linear Induction Motors,
most of his Aerotrains were
fan or jet propelled.
But a Linear Induction Motor is more efficient.
Instead of the rotary movement of a conventional motor,
it provides a linear force for forward
Without any of the noise or pollution of a turbofan running at ground level.
The British were aiming to build a transportation
system that could travel at two hundred and
fifty miles per hour.
The Americans, not ones to be outdone were also researching hovertrain technologies.
In 1965, the High Speed Ground TransportationAct was passed.
It was an effort to introduce faster railto America.
Funding was put towards developing new technologies and
even licensing Bertin ’ s Aerotrain designs.
Various hovertrain prototypes were developed,
some powered by Linear Induction Motors, others
But the most developed prototype was the Urban Tracked Air Cushion Vehicle.
With its sleek windowless cockpit and Blade Runner styling, it certainly looks fast.
It was designed to operate
in heavily travelled urban areas and had a top speed of about 150
miles per hour.
The Tracked Air Cushion Vehicle was
a fully developed prototype that underwent regular
testing on its track in Pueblo, Colorado.
At the start of the 1970 ’ s,
hovertrains looked poised to revolutionize rail.
But just a few years later,
not a single country was pursuing the technology.
Ambitious plans for Aerotrain links throughoutFrance never materialized.
All that’s left today are the abandonedtest tracks.
A global recession in the 1970 ’ s
pressured governments to cut funding for ambitious transportation
And some critical technical challenges werenever really worked out.
At high speeds,
hovertrains could travel more efficiently than conventional trains but at
low speeds, they wouldn’t stand a chance.
But that’s not really why they failed.
In the 1970’s, the first maglev train werealready in development.
They would use electromagnets to levitate
over a guideway instead hovering using high
And so Maglevs promised even greater efficiencyand speed over hovertrains.
But Maglev’s also failed to revolutionizerail.
After nearly four decades,
there ’ s only a handful of them operating in the world.
High speed rail today is still based largely on conventional wheeled trains.
It turns out that the problems
of railways were overcome not by one revolutionary leap forward,
but by incremental improvements.
Existing rail networks were modernized with sections
of track that could handle higher
New signaling technologies were developedalong with more advanced suspensions.
Precision machined wheels and yaw dampers allowed for train wheels with less cone angle.
And that reduced the hunting oscillation problem.
Instead of Aerotrains,
the French invested in their high speed TGV rail service, which
today routinely travels at 200 miles per hour.
The British came up with unique solutions
like a train that could tilt into corners
and take sharp curves more quickly.
The Americans, at least for the time being, mostly stuck with cars.
Hovertrains or Maglevs or any other
radical alternative to rail has to compete with nearly
a million miles of rail line already in existence.
With stations and infrastructure built-out in nearly every city in the world.
Turns out, it’s easier to adapt
new ideas to the existing world than to have the world
adapt to radical new ideas.
Which is why incremental improvements oftenwin out in the end. Although,
there’s a new solution in theworks.
A train runs in a new kind of track.
It ’ s actually a reduced pressure-tube,
so there ’ s less friction and air resistance.
Driven by linear induction motors and aircompressors.
It promises to travel at over 700 miles perhour.
It’s tube-like tracks could suspended or underground [voice fades out].
I used some conceptual terms in this video,
like friction, rolling resistance and magnetism.
These are foundational concepts,
the kind that is crucial to understanding how machines work,
whether it’s a hovertrain, or supersonicjet.
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