As the 21st century dawns, steam catapults are running out of steam. Massive systems
that require significant manpower to operate and maintain, they are reaching the limits of
their abilities, especially as aircraft continue to gain weight. Electromagnetic catapults
will require less manpower to operate and improve reliability; they should also lengthen
aircraft service life by being gentler on airframes.
The amount of steam needed to launch an airplane depends on the craft’s weight,
and once a launch has begun, adjustments cannot be made: if too much steam is used, the
nose wheel landing gear can be ripped off the aircraft; if too little, the aircraft
won’t reach takeoff speed and will tumble into the water. The launch control system
for electromagnetic catapults, on the other hand, will know what speed an aircraft should
have at any point during the launch sequence and can make adjustments during the process
to ensure the aircraft is within 3 mph of the desired takeoff speed.
Engineers test a prototype electromagnetic catapult at the U.S. Naval Air Warfare Center
in Lakehurst, New Jersey. Powered by electromagnetic energy, the prototype can accelerate
test articles — massive metal frames on wheels — to 165 mph in three-quarters
of a second on a track just 100 feet long. Electromagnetic catapults will eventually replace
the Navy’s current steam-powered aircraft launchers, taking up less space, weighing
less, and outperforming the equipment they replace.
The following 1½-minute film shows a full-scale test.
Electromagnetic Aircraft Launch System (EMALS) full-scale prototype test, Lakehurst NJ — 1½ minutes.
Excerpted from an article by Tim Wright in Air & Space Magazine:
George Sulich stands astride one of two 333-foot-long steam-powered catapults aimed down
the runway at the U.S. Naval Air Warfare Center in Lakehurst, New Jersey. The catapults,
identical to those that launch airplanes aboard Navy carriers, are used to tweak and test
the 1950s launch technology. But Sulich’s interest lies a few steps away, in a
concrete-and-steel trench more than 300 feet long, where a new catapult completed in 2008
became the first to use electromagnetics to launch manned aircraft.
As the Navy’s project manager for the Electromagnetic Aircraft Launch System
(EMALS), Sulich’s task is to move the newest catapult technology from development at
the research facility to ships at sea. A key instrument in the transition is a 1:12-scale
model of an electromagnetic catapult bolted to the concrete floor inside the lab. When the
power is turned on, a wave of electromagnetic force silently shoots an aluminum block to the
opposite end of the model at 60 mph. After a few keystrokes on a computer, the
electromagnetic wave reverses, gently returning the block to its starting position.
The scale model is a linear induction motor — an efficient way to generate thrust
with a minimum of moving parts. Shipboard electromagnetic catapults will be based on larger
linear induction motors made up of three main parts: two 300-foot-long stationary beams
(stators) spaced a couple of inches apart, and a 20-foot-long carriage (shuttle) sandwiched
between the two beams. Selectively energizing each beam’s segments generates an
attractive magnetic force at the carriage’s leading edge and a repulsive force at its
rear, creating the effect of a traveling magnetic wave.
The interface between carriage and airplane runs through the aircraft’s nose wheel
landing gear, using the same hardware employed by the current steam catapult system. After
releasing an aircraft at speeds approaching 200 mph, the carriage stops in only 20 feet,
its forward movement countered by reversing the electromagnetic forces. The same energy then
returns the carriage to its starting position.
An electromagnetic catapult can launch every 45 seconds. Each three-second launch can
consume as much as 100 million watts of electricity — about as much as a small town
uses in the same period. In shipboard generators developed for EMALS, electrical power is
stored kinetically in rotors spinning at 6,400 rpm. When a launch order is given, power is
pulled from the generators in a two-to-three-second pulse. In the remaining 42 seconds
between launches, the rotors spin back up to capacity, readying themselves to release
another burst of energy.
Care has been taken to make the launch process as similar as possible to current steam
systems. Pilots positioning their aircraft for a catapult shot won’t be able to tell
if they are launching with electromagnetics unless they happen to notice the absence of
steam escaping from the deck.
Electromagnetic catapult technology already has the ability to launch any aircraft now
in the Navy inventory and any the Navy has ordered. With the new launch system’s
potential to achieve acceleration forces reaching 14 G’s, human endurance may be one
of the few limitations it faces.
Related pages:
Cat Shots ·
Catapults ·
Magnetic Rail Gun
