The link trainer pictured is
a 1942 Model C-3, the term Link Trainer, also known as the "blue box," is commonly used to
refer to a series of flight simulators produced between the early
1930s and early 1950s by Edwin Albert Link, based on technology
he pioneered in 1929 at his family's business in Binghamton,
New York. The original Link Trainer was created in 1929 out of
the need for a safe way to teach new pilots how to fly by instruments,
using a radio range for determining an airplane's position in
instrument flight conditions and a subsequent let-down to a field
for landing. This primary navigation system was comprised of
sparsely located Adcock low-frequency range transmitters. Each
facility consisted of four legs which could be used as "beams"
for navigating either to or from a station on the airways or
for shooting low approaches for landing. Each range station emitted
audio signals comprised of four quadrants. Two quadrants provided
a Morse Code signal of "N" (dash-dot) while the opposing
quadrant emitted an "A" signal (dot-dash). Each quadrant
overlapped precisely to provide a three-degree leg or beam by
meshing the two audio signals to provide a continuous dash or
"on course" monotone signal.
These simulators became famous
during World War II, when they were used as a key pilot training
aid by almost every combatant nation. More than 500,000 US pilots
were trained on Link simulators, as were pilots of nations as
diverse as Australia, Canada, Germany, Great Britain, Israel,
Japan and the USSR.
The Link Flight Trainer has been designated as
A Historic Mechanical Engineering Landmark by the American Society
of Mechanical Engineers.
The Link was mounted on a base
which permitted the trainer to turn, tilt and bounce as the instructor
(who sat at a desk outside the trainer) created rough air and
put the pilot through simulated instrument flight conditions.
An operator sat at the desk and transmitted radio signals which
the "pilot" in the link heard though his ear phones.
The pilot "flew" the link through various turns, climbs,
and descents, and the link's "course" was traced in
red ink by the remote "bug" on a map on the table.
After a flight was completed, the pilot could study the red-line
course to determine his what he might have done incorrectly.
There was no AIR CONDITIONING in these
trainers... and on a hot west Texas day, it got pretty hot inside
this 'box'. Many a young trainee almost crashed and burned--not
from lack of flying skills, but from the heat!
In the late 20's Edwin A. Link learned to fly while working for
his father in Binghamton, New York who manufactured organs and
pianos. Because of the economic depression at that time, flying
lessons became too costly. Link got the idea to shorten the expensive
flying lessons by learning rudimentary piloting skills using
a ground aviation trainer. Drawing from his expertise in air-driven
pianos and pipe organs, Link used organ parts and compressed
air to build the first flight simulator.
In 1928, Edwin A. Link left his father's organ
building business to begin work on a "pilot trainer."
He designed the trainer using suction through fabric bellows
to cause motion. Organ bellows and a motor provided the means
for the trainer, mounted on a pedestal, to pitch, roll, dive
and climb as the student "flew" it. In 1931 he received
a patent on his "pilot maker" training device.
Most of his first sales were to amusement parks. In the beginning
there was very little interest by the flying community in Link's
trainer. Initially the trainer was meant
for instruction of visual flight, but in 1934, after a series
of tragic accidents while flying the air mail, the Army Air Corps
bought six Link trainers to assist in training pilots to fly
at night and in bad weather, relying on instruments. The second
customer for the Link trainer was the Japanese Imperial Navy
in 1935. Many Japanese pilots were trained in these Link trainers
and used their skill and knowledge in fighting the American planes
in World War II.
The need for pilots with instrument training in World War II
resulted, by the end of the war, in Link delivering 6,271 Link
trainers to the Army and 1045 to the Navy. The Link trainers
were also used by 35 foreign countries. Although Army Air Force's
aviation cadets flew various trainer aircraft, virtually all
took blind-flying instruction in the Link.
Movement of the trainer is accomplished by
vacuum operated bellows, controlled by valves connected to the
control wheel (or stick) and rudder pedals. An instructor sat
at the desk and transmitted radio messages which the student
in the Link heard through his earphones. Inside the "cockpit",
the student relied on his instruments to "fly" the
Link through various maneuvers while his navigational "course"
was traced on a map on the desk by the three-wheeled "crab".
Slip stream simulators gave the controls the feeling of air passing
over control surfaces, and a rough air generator added additional
realism during the "flight".
The Link Trainer holds a significant place in aviation
history. It was the first true flight simulator, and provided
safe instrument training to hundreds of thousands of student
pilots during the 1930s and 40s.
In 1993, the Western Museum of Flight (WMOF) initiated the restoration
of a 1942 Model C-3 Link Trainer. A crew of WMOF Volunteer Docent/
Restorers staffed the project. They had at their disposal an
inventory of donated obsolete and nonfunctioning parts of 1940s
era Link Trainers, that had been accumulated by the museum over
several preceding years. This inventory consisted of: two bases,
two octagons, an almost fully equipped fuselage, two blind flying
hoods, an almost complete set of Link Trainer operation, overhaul,
and maintenance technical manuals, and a sufficient amount of
spare bellows, valves, turning motors, telegon transmitters,
For the first phase of the project, the crew tore down the existing
components and meticulously drew up scale drawings that would
be used to rebuild the trainer and its various mechanical, electrical,
and pneumatic systems. All of the major valves, linkages, tubing,
bellows, and instruments were diligently taken apart, cleaned,
put together again, and/or fabricated per the technical orders
in the Link maintenance and overhaul manuals. The highly labor
intensive, time consuming, and skilled work would require two
years to accomplish. During this period, the process of putting
together and completely rewiring the Links base, central
column, vacuum compressor, and main electric panel were accomplished.
In addition, the Links octagon with its master climb/dive
and banking bellows was completely restored and work was initiated
on the restoration of the Instructors Desk, its radio and
automated flight tracking device.
In January 1995, the restored octagon was mounted
to the Links base. Once completed, the base was fully restored
with its now functioning vacuum compressor, wind/drift motor,
and main electric panel. Work now progressed rapidly on the restoration
of the Links fuselage. This required rebuilding the entire
frame of the fuselage on the octagon. Much of the original frame
was used, but many sections had to be completely rebuilt from
scratch, utilizing the great scale drawings that had been made
during the tearing down of the original and specifications laid
out in the technical manuals.
In March 1997, restoration of the Links fuselage was completed.
With the fuselage now sitting on the Links octagon, the
restored components were then carefully reinstalled. This included
all the major and minor valves, bellows, metal and rubber tubing,
rough air generator, linkages, springs, telegon transmitters,
turning motor, rudder pedals, control stick, altitude and airspeed
vacuum cans, vibration motors, air dampers, cockpit lights, air
circulating fan, and pilots radio. Although most of the
restored components were used, some parts had to be fabricated
on the spot. Once again, all this was done per the technical
manuals specifications, aided by the fine scale drawings
made during the first phase of this project.
The next step was the restoration and installation
of the Links instrument panel. The restored panel now contained
a fully functional magnetic compass, gyro-horizon indicator,
altitude meter, airspeed meter, turn and bank bubble, climb and
dive indicator, engine rpm meter, clock, radio beacon, glide
path indicator, fuel gauge, on/off switch, pitot tube heater
switch, and fuel switch.
In July 1997, the time consuming re-calibration
and testing of all of the Links major and minor valves,
electrical transmitters, mechanical linkages, vacuum chambers
and air dampers was completed. The partially restored pilots
seat was then installed in the cockpit. Now, with one of the
crew seated in the cockpit, the Link was given its first full
powered systems test per instruction in the Links technical
manuals. For all intents and purposes, the Link performed beautifully,
flying level, banking and turning, climbing, diving, and stalling.
A sign was affixed to the fuselage announcing to all who viewed
it that the Link had successfully had its First (post full
restoration) Flight on 3 July 1997.
In October 1997, Californias Santa Maria
Air Museum donated a usable set of Link Trainer wooden framed,
cloth covered wings, with movable ailerons, and wooden tail with
movable rudder and elevators. Restored Wings, Elevator and Rudder
In November 1997, disaster struck the project. Arriving at the
Museum to start work, the team found what they thought was sawdust
on the floor, outlining the Links fuselage and base. Upon
close inspection they also found several small piles of this
sawdust inside the Links fuselage.
It was finally deduced that evidently long dormant
termites in the old wooden framework of the fuselage had awakened
and become active again. The entire wooden fuselage frame and
floor were starting to crumble. This required a complete teardown
and removal of all the painstakingly installed Link components.
The affected fuselage was then removed from the octagon and destroyed.
Luckily the octagon had been spared, but, as a safety measure,
it was inspected and thoroughly treated with a termite inhibiting
spray. the Links Instructors Desk and Blind Flying
Hood/Canopies were inspected and treated.
In February 1998, March Air Force Base Air Museum
provided a usable Link Trainer fuselage. This fuselage was found
to be in fairly good shape. It had been denuded of all of its
internal hardware, access doors, seat and backrest, but would
only need a small amount of repair to bring it back into shape.
It was completely inspected for signs of termites. The fuselage
was quickly cleaned up, treated, mounted, and restored. Once
again all of the required restored hardware, electrical, mechanical,
and pneumatic systems were installed in the fuselage.
By years end, 1998, the work was finally completed and
the newly restored second Link fuselage was installed in a jury
rigged paint booth within the WMOF hanger and painted in the
1940s style Army Air Corp distinctive blue colored enamel.
Once again all the Links systems were re-calibrated and
tested and the Link performed per specifications.
In 1998, the Links wings and tail assemblies
were fully restored. The wings frames were repaired as
needed and their cloth coverings patched and sealed. The wooden
tail assemblies were cleaned and sanded. The wings ailerons
hinges, brackets, and cables, along with the tails rudder
and elevators hinges, cables, and brackets, were then restored
to full working order. These assemblies were then painted in
the 1940s style Army Air Corp trainer distinctive yellow
enamel. The restored wings and tail were installed on the Links
fuselage. A new fixture had to fabricated to attach to the restored
control stick assembly that would take, secure and activate the
wings ailerons, when the stick was moved from its center
position to the right or left. This was machined from a solid
block of aluminum and when fitted, performed its required function
perfectly. Now the Link began to look like a real little airplane.
During this year the restoration of the Links Instructors
Desk and radio were completed. Also restored was the electrical
and mechanical linkages from the desk to the Links base.
When the Link was operated, the desks automatic tracker
traveled across a copy of a 1940s era flight map on the
desk top, inking a dotted line to show the direction the Link
was flying. Remote instruments on the desktop
displayed the Links simulated attitude, airspeed, climb
and dive angles on its respective meters. The desk and its remote
instrument cabinet were painted the 1940s era Army Air
Corp olive drab colored enamel.
In 1999,the Links Blind Flying Hood/Canopy were completely
restored . All the old, rotted cloth covering had to strip off
and the wooden frame cleaned and strengthened . It was then recovered
with aircraft linen, hot ironed , primed, and finally repainted
in its 1940s era Army Air Corp trainer blue enamel, with
silver colored false windows. After installation of the hood,
newly acquired 1942 era Army Air Corp aircraft roundels were
affixed to the wings with red and white strips on the rudder.
Small red NO STEP and NO PUSH caution signs were painted
on the Links wings and rudder.
In June 1999, the Links metal-framed base was then fitted
with pegboard cover panels and painted with a black enamel. A
black cloth skirt was fashioned and affixed to the fuselage base
and anchored to the octagon. The covering protected the major
climb, dive, and bank bellows. The Link was now officially completely
restored, displayed in all its bright colors. Visitors to the
museum could now see the Link, as it would have been set up in
a typical World War II Army Air Corp training building. Its Instructors
Desk showed its radio, in its partially opened center drawer,
an aerial flight map positioned under its Automatic Tracker,
and its Instructors earphones and microphone displayed
on their holder awaiting use by the Instructor.
February 28, 2000, disaster struck again. While moving the Link
from an off site location it was inadvertently dropped. The entire
nose section of the Links fuselage, just forward of the
instrument panel, was ripped away. Both wings and one side of
the stabilizer were also damaged. Due to the shock of the fall,
all of the Links major valves were wrenched from their
settings and severe damage was done to the sensitive telegon
transmitter system that activated the airspeed and engine rpm
June 2000, restoration was started to repair the damage.The nose
of the damaged Link was replaced with parts taken from another
fuselage. The wings and tail were again restored. Once again
the Links systems were reset, re-calibrated, and tested.