Instrument Flight Training


In the late 1920's the need was starting to be felt for the effective training of pilots in the skills of "blind" or instrument flying. Two methods were developed firstly the existing moving trainers, such as Link's, were fitted with dummy instruments and the means for their actuation, and secondly, non- movable devices were invented specifically for the task of instrument flight training.


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.


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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.


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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".



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