Rougerie's patent of 1928 describes a simple trainer, fixed to the
ground, consisting of a students seat facing an instrument panel and two sets of
controls, one each for the student and instructor. The student's flight
instruments are directly connected to the instructor's controls. The student,
then, flies the trainer in response to commands from the instructor, who in turn
modifies the instrument indications according to the students actions - the
accuracy of the simulation depends entirely on the instructor. A further
development of this concept can be seen in a development by W.E.P. Johnson in
1931, an instructor at the Central Flying School, Wittering, and one of the
pioneers of instrument flying in Britain. He constructed his trainer from a
written-off Avro 504 fuselage. In the simplest form of this invention an
airspeed indicator, turn indicator, and bank indicator are directly operated by
wires attached to the sticks and rudder bars of student and instructor. Further
improvements included a throttle control affecting the airspeed indicator and
integrating devices for the display of altitude and heading. It is interesting
to note that a true simulation of accelerations due to aircraft motion was
suggested. However, it seems that this idea was not to be taken seriously for
more than twenty years.
Another early British instrument flight trainer is that described by
Jenkins and Berlyn of Air Service Training Limited, Hamble, in their patent
application of 1932. This ground-fixed apparatus used mechanisms similar to
Johnson's for linking the instruments to the controls. Rotation of the magnetic
compass was effected with a magnet, while transient deflections, were produced by
causing a rotary movement of the compass damping fluid in response to pitch and
throttle control changes.
The Link Trainers themselves were soon being fitted with instruments
as standard equipment. Blind flying training was started by the Links at their
flying school in the early 1930's and as the importance of this type of training
was more fully appreciated, notably by the U.S. Army Air Corps, so the sales of
Link Trainers increased. The newer Link Trainers were able to rotate through
360Deg which allowed a magnetic compass to be installed, while the various
instruments were operated either mechanically or pneumatically. Altitude, for
example, was represented by the pressure of air in a tank directly connected to
an altimeter. Rudder/aileron interaction was provided in the more advanced
trainers, as was a stall feature. The reproduction of aircraft behaviour and
dynamics was still produced in an empirical manner.
A further increase in the usefulness of the trainers was achieved with
the attachment of a course plotter. This consisted of tortoise like device, on
three wheels, which was self-propelled and steerable; the course of the simulated
flight was traced on a chart by means of an inked wheel. The plotter can be seen
in the picture on the instructors desk. By relating the
position of the student's aircraft to marks on the chart, the instructor was able
to manually control the transmission of simulated radio beacon signals to the
trainer. In the 1930's the device was produced in various versions and was sold
to many countries, including Japan, the USSR, France and Germany. The first Link
Trainer to be sold to an airline was that delivered to American Airlines in 1937.
The RAF also took delivery of their first Link in the same year. By the
beginning of the Second World War, many of the major air forces were doing their
basic instrument training on Links, or devices derived from them. The Link
Trainers continued to be manufactured into the 1950's, their principle of
operation remained the same.
Two of the first electrical flight trainers, both still based on
empirical designs, were Dehmel's trainer and Travis' "Aerostructor". Dr. R.C.
Dehmel, an engineer with the Bell Telephone Laboratories, became interested in
flight training in 1938. His first development was an automatic signal
controller for the generation of synthetic radio signals for a Link Trainer, thus
eliminating the need for the attendant who manually operated signal volume
controls during the training session. This was an important advance in
instrument flight training in that it enabled a closer match with the behaviour
of actual navigational aids. Following this, Dehmel developed the "flight"
portion of a trainer based on electrical circuits. This machine was never
manufactured, but served as a starting point for future developments.
The Aerostructor, developed by A.E. Travis and his colleagues in 1939/
40 also in the United States, was a fixed base, electrically operated trainer
with a visual rather than an instrument presentation. The visual system was
based on a loop of film and simulated the effects of heading, pitch and roll
movement. The trainer was widely demonstrated in the U.S., but was never
commercially produced. It was however, used in large numbers by the U.S. Navy in
a modified form as the "Gunairstructor".