Airplanes are not like automobiles. They travel at a
high rate of speed and move forward and backward and also from side to
side and up and down. They are difficult to operate and require hundreds
of hours of training. They are also a threat both to their occupants and
people on the ground if they experience problems in the air. Because of
this, innovators and engineers have long sought ways of training people to
operate an airplane without actually having to fly one. They have
developed machines called flight simulators that today are highly
sophisticated and important tools, useful for training, learning safety
procedures, and even for aircraft design and development.
Aviation simulators generally serve three major
functions. First, they are used to train pilots in many of the basic
operating procedures. Their primary advantage is that they are relatively
cheap to operate compared to flying an actual airplane. Second, they are
used for advanced training, particularly in emergency procedures. Numerous
emergency procedures cannot be practiced in the air, either because they
would be too dangerous or because there is no way to recreate the
emergency. Finally, simulators are used in the design process for new
aircraft.
The Wright brothers experimented with a primitive form
of a simulator to teach their aviation students to fly. They used the
centre section of an old plane on a mount, which someone on the ground
would move based on the student's actions with the controls. But the first
true simulator was designed by Edwin A. Link. While learning to fly
airplanes in 1927, Link learned about a French training technique called
the "penguin system" that had been used during World War I to train many
U.S. pilots. In this system, the novice pilot would taxi a plane on the
runway, gaining some limited feel for the controls. Link wondered if it
was possible to build a training system that would simulate the feel of an
aircraft's controls. He began designing a machine that used forced air to
exert pressure on a control stick and rudder pedals, and in April 1929
filed a patent for his pilot training device, called the Link Aviation
Trainer. His early trainers came complete with fake wings sticking out of
either side. He also established a ground school classroom in the basement
of his Link Piano and Organ Company. Link managed to sell a few of the
trainers to the military. But the onset of the Depression led to hard
times and Link ended up marketing his trainers to amusement parks as
rides.
Over the next several years, Link improved his
trainers, adding instruments that responded to the control inputs. The
Link Model 45 was a fully integrated trainer where the movements and
instruments worked together; if the pilot pulled back on the control
stick, the altitude indicator would show that the plane was climbing as
the speed indicator showed that the plane was decelerating. The fuel gauge
would eventually go to empty, and the engine noise would become erratic if
the engine temperature rose. By World War II, Link was selling thousands
of basic pilot trainers to the Army Air Forces and U.S. Navy.
Gradually trainers became more sophisticated and other
companies, such as the Curtiss-Wright Corporation, entered the business.
Motion trainers, which moved the trainee in response to control inputs,
fell out of favour as the military sought to train students to rely on
instruments. Analogue computers were also incorporated into trainers and
over time, people started to refer to these training devices as
"simulators." In 1944, the Massachusetts Institute of Technology (MIT)
started work on one of the most important early computer projects, known
as Whirlwind. Whirlwind was a computerized flight simulator. It was the
first interactive computer that responded immediately to inputs from the
user. Later, its features were incorporated into other flight simulators.
Starting in World War II, trainers were also developed
for aviation purposes other than simply teaching flying as gunnery, radar,
and navigation trainers were also built. By the early 1950s, Link produced
the C-11B jet flight trainer, the first basic jet simulator for all
branches of the military.
Link also began developing simulators for specific
aircraft. The B-47B flight simulator was the first simulator for a modern
jet bomber. The F-4C Weapon System Trainer allowed an F-4 Phantom crew to
learn how to operate its missiles and radar system. Virtually all new
American military aircraft and helicopters soon had dedicated simulators.
The military operated simulators for everything from fighters to bombers
to helicopters to cargo transports.
The military was the primary customer driving the
demand for new and more capable simulators. Because military aircraft
often operate at the edge of their performance envelope and include many
sophisticated systems, it is easier, cheaper, and safer for pilots and
aircrew to gain experience on the ground, where they can "crash" a plane
repeatedly while learning. Link and other companies also continued to
build simpler simulators for the general aviation market, primarily for
basic flight training for private pilots. But by the 1950s, commercial
airlines began expressing an interest in simulators for their passenger
jets. In particular, they wanted to simulate in-flight emergencies such as
engine fires or control system failures. Soon Link developed simulators
for the DC-8, 707, and DC-10. Other companies also entered the commercial
aircraft simulator business, including Redifon and CAE.
Simulators had different capabilities. Instrument
simulators were stationary and often did not require any imagery displays.
But commercial airlines in particular wanted simulators that provided a
pilot with an image of the airfield through the cockpit window. For many
years, this was often provided by moving a TV camera over a scale model
and projecting the image onto a series of television screens in front of
the cockpit window. By the 1970s, several companies were using computers
to generate basic imagery.
The X-15 research aircraft, which first flew in 1959,
also marked an important milestone in the development of flight
simulators. The X-15 was the first aircraft where a simulator was used to
practice flight manoeuvres before they were tried in the aircraft,
whereas previous simulators had been developed only after the plane's
flying characteristics were already known. There were two simulators
developed for the X-15. The first was used to prove its reaction control
system, which used jets to change the attitude of the aircraft. The second
simulator was more sophisticated and enabled a pilot to gain a sense of
how the aircraft would respond as it was made to do things that had not
been accomplished before.
During the 1960s, aircraft designers became much more
interested in seeking ways to improve an aircrew's performance. They began
studying the best ways to present information to the pilot and to design
controls so that an aircrew could use them effectively. This resulted in
the creation of engineering simulators used in aircraft design. The one
major problem with such simulators is that they are only as good as the
data provided to them. For a new aircraft that has not flown yet, data on
how it will perform is limited and could be flawed.
Simulators also played a major role in training
astronauts. The Apollo Mission Simulator allowed astronauts to simulate
the operation of what was then the most sophisticated vehicle ever built,
the Apollo spacecraft. In the late 1970s, Link also developed a Space
Shuttle Mission Simulator that simulated launch and landing of the
Shuttle.
In some cases, aircraft companies added simulators to
aircraft themselves to improve the quality of the simulations. First done
in the 1950s, it was then the only way to provide realistic visual and
motion inputs to a pilot. Sometimes the pilot in the in-flight simulator
had no control over the aircraft. In other cases, the simulator had some
degree of control over the aircraft, although a backup set of flight
controls and a second pilot were always included. A pilot working in a
conventional cockpit could take the aircraft to a predetermined point and
then let someone in the simulator take over, testing new control systems
and information displays. In-flight simulators were used in the
development of the F-16, F-18, A-10, B-1 airplanes and the Space Shuttle.
During the mid-1980s, Sikorsky Aircraft equipped an S-76 helicopter with
an additional "evaluation cockpit" that protruded in front of the nose of
the helicopter and was equipped with various display and control systems
to help develop advanced technologies for other helicopters.
Today it is rare for any major aircraft to enter
production before designers build a cockpit simulator. The plane is
"flown" hundreds of times before it ever leaves the ground, allowing
designers to rearrange cockpit instruments and improve information
displays, as well as providing them with some sense of the aircraft's
handling qualities. This saves money by avoiding design mistakes that
might normally become apparent only after the equipment has been built.