Of all the different types of rides that can be found at an amusement park, there’s very
few that can deliver the same terrifying thrills as a drop tower.
These impressive machines allow riders to experience a straight freefall from dizzying
heights, coming to a safe controlled stop just moments before reaching the ground.
This type of attraction packs a big punch given its small footprint, with the tallest
rides extending to heights in excess of 120 metres, or 400 feet.
Modern drop towers also come in a wide range of design styles with some clever twists that
make them even more thrilling, including the most recent innovation of tilting riders forward
so they fall face first.
Despite all the variations that exist today, the original design concept for the freefall
ride can be traced back to a single attraction that was built for the New York World’s
Fair in 1939.
This ride was known as the Parachute Jump, and it consisted of a 250-foot steel tower
with 12 parachutes suspended from a large frame with steel cables.
Riders would hang below the parachutes in canvas seats that were hoisted to the top
by an electric motor, and a drop mechanism would release them into a controlled fall
as the parachutes slowed the descent.
A similar type of wooden structure was used to train military paratroopers in the Soviet
Union as early as the 1920’s, but the technology was later patented in the United States where
it was modified for civilian use as a thrill ride.
This ultimately led to the development of the first free fall type attraction which
was popularized by Swiss ride manufacturer Intamin in the 1980’s, and they later improved
the concept by introducing the first modern drop tower in 1995.
Fast forward to today, and there are now many ride manufacturers that produce different
variations of the drop tower, however they all rely on one of two fundamental principles;
Either electromagnetism, or pneumatics.
The original design from Intamin employed an electromagnetic system, and we’ll start
by taking a look at this type of ride first.
The tower itself usually consists of a cylindrical steel structure that is anchored to a large
concrete foundation, and this is topped off with a machine room that houses the electric
lift motors.
Depending on the configuration, there may be a single ride gondola that wraps all the
way around the tower, or there may be several smaller gondolas equally spaced around the
circumference as shown here.
The vehicles travel along rails that are fixed to the exterior of the structure, and each
one is paired with a catch car that is mounted on the same set of rails above.
The catch cars are suspended from the top of the tower with steel cables, and they can
be moved up or down independently using the lift motors.
When the ride is ready to begin, each catch car is lowered onto the corresponding gondola
where a mechanical latch automatically engages to lock them together.
They are then hoisted up to the top of the tower, and when given the all clear, the latches
are disengaged to release the vehicles from the catch cars.
After a brief freefall, the gondolas are brought to a safe and controlled stop by a magnetic
braking system, which is both the most important and most innovative part of the whole ride.
At the bottom of the tower, there are 2 rows of inert metal plates that run parallel to
each set of rails, and these align with permanent rare earth magnets that are mounted to the
ride vehicles.
Each gondola has 4 strips of magnets, and they are arranged in pairs to create 2 thin
gaps that are just wide enough for the plates to pass through.
When a gondola drops down the tower, the moving magnetic field induces closed loops of electric
current in the plates called Eddy currents, and these generate their own temporary magnetic
field that opposes the motion of the permanent magnets.
The result is a magnetic drag force that acts on the gondola opposite to its direction of
travel, which is similar to the repulsive force that you can feel when trying to push
two magnets together with matching poles.
The magnitude of the drag force is directly proportional to the amount of current flowing
through the plates since this determines the strength of the opposing magnetic field, and
the amount of current is proportional to the speed of the vehicle.
What this relationship tells us is that the braking force will be highest when the permanent
magnets just begin to pass over the plates, and the force will decrease linearly as the
gondola loses speed, thus providing a smooth non-linear deceleration.
This method of magnetic braking is commonly referred to as Eddy current braking, and it
is used quite frequently in the amusement industry because it converts kinetic energy
directly to heat without any need for moving parts or frictional wear.
The system is also completely fail-safe because it does not rely on an external power source,
and the brakes will still function in the event of a power outage.
The only real downside is that magnetic brakes cannot bring the ride to a complete stop all
on their own, since there will be a point during the deceleration when the magnetic
drag force perfectly balances the force of gravity, and the gondolas will continue to
move downward at a slow but constant velocity.
In order to prevent a hard landing on the ground, the ride vehicles simply touch down
on hydraulic cylinders that are positioned around the base of the tower which absorb
the remaining kinetic energy.
Overall, this type of electromagnetic drop tower is a safe and dependable ride that is
still popular today, however it wasn’t long after Intamin introduced it that American
ride manufacturer S&S developed their own system using compressed air.
These towers usually have a steel truss structure with a square cross-section, and the ride
gondola travels along the 4 corners with small guide wheels so there is no need for external
rails.
Inside the tower is a massive air accumulator, which is basically a storage tank that can
hold air under high pressure, and it is surrounded by 4 smaller pneumatic cylinders called shot
tanks.
Each cylinder contains a piston that can travel up and down, and this is connected to a steel
cable that exits through small seals at the top and bottom.
The cable passes around a sheave at each end of the tower where it then connects to the
gondola, thus forming a closed loop around the outside of the structure.
As the 4 pistons move in one direction on the inside of the tower, they pull the cables
around the sheaves and drive the vehicle in the opposite direction on the outside.
When the system is depressurized, the gondola will naturally rest at ground level while
the pistons are raised to the top of the shot tanks, and this is how each ride cycle begins.
Once passengers are loaded, a small amount of air is moved from the accumulator into
the top of the pneumatic cylinders, which pushes the pistons down and lifts the vehicle.
The ride computer then weighs the vehicle by measuring how much air pressure is required
to balance it, and this determines how much air will be used to achieve the desired speed
and g-force.
Additional air is then released into the cylinders to lift the gondola to the top of the tower,
where it locks into a mechanical brake that holds it in place before the drop.
At this point, the accumulator is pressurized to its full operating pressure by moving air
from an external receiver tank, which is paired with a large air compressor and drying system
in a separate building.
When the ride is launched, the compressed air in the accumulator is released into the
bottom of the shot tanks, which shoots the pistons upward, releasing the holding brake
and driving the gondola down towards the ground.
As the pistons approach the top of the tower, the air in the top portion of the shot tanks
becomes compressed, thus absorbing the kinetic energy and slowing the gondola down before
bouncing it in the reverse direction just like a compressed spring.
The pistons and gondola then oscillate up and down several times as the motion is dampened
by slowly releasing air from the cylinders, and the vehicle is lowered back to the starting
position once the system in depressurized.
One of the benefits of using compressed air for a drop tower is that the entire ride is
controlled by a single pneumatic system that does not require separate mechanisms for lifting
and braking, yet the redundancy of multiple cylinders and cables still ensures that the
ride is fail-safe.
The intensity of the ride can also be adjusted by varying the amount of air that is used
for each launch, making it possible to achieve a drop that is nearly twice as fast as a free
fall.
The launch can even be reversed by releasing compressed air into the top of the shot tanks
instead of the bottom, shooting the gondola up the tower with an acceleration in excess
of 4 G’s.
Regardless of the underlying ride system, electromagnetic and pneumatic drop towers
both offer intense thrills that are unmatched by any other ride, making them popular installations
at amusement parks all around the world.
And while the experience of riding a drop tower may be terrifying, you can be assured
that these rides are always designed with guest safety in mind first.
Safety is the number one priority at any amusement park, and the same is also true for today’s
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