Electronic Flight Simulation

A major advance in simulation during the war period was the use of the analogue computer to solve the equations of motion of the aircraft. The analogue computer, or differential analyser, as it was then known, enabled simulation of the response of the vehicle to aerodynamic forces as opposed to an empirical duplication of their effects. It is difficult to make a complete separation of these two types of simulation as both may be present in the same device. However, certain devices clearly were true analogues and a number of these are the direct ancestors of the modern simulator.

The first known discussion of the computer method of flight simulation is that of Roeder in his 1929 German Patent Specification. Roeder treated the general problem of the instrument control of vehicles freely movable in space, such as airships, aeroplanes or submarines. His outlines of the requirements of a simulator for such a task could almost refer to a modern simulator. As an example of his technique he described the dynamic simulation of an airship height control system and a fluid-operated analogue computer suitable for this. No successful training devices are known to have resulted from this work. In 1939 Mueller, at MIT, described an electronic analogue computer for the faster-than- real-time simulation of aeroplane longitudinal dynamics. His interest was in aircraft design and the solution of the equations of motion, but as a postscript to his paper he mentioned the possibility of extending the time scale of the simulation and of including a man in the loop.

In 1941 an electronic simulator was designed and built at the TRE to serve as the "flying unit" for their AI radar trainers. This computer was based on the ideas of F.C. Williams, famous for his later work on digital computers, and used the velodyne, another TRE invention, for integration. The d.c. method of computing was used in the simulation of the simplified fighter aerodynamics. The first model of this computer (the Type 8 Part II) was constructed by Dynatron Radio Limited in 1941 and many were used throughout the war. Later, in 1945, a more advanced flying unit including feel forces was designed by A.M. Uttley for use in a new AI visual crew trainer. This, however, never saw service.

Also in Britain at about this time an electromechanical analogue computer for the simulation of aircraft longitudinal dynamics was proposed by G.M. Hellings, then working at the Ministry of Supply. Non-linear functions were generated with shaped cams, and it was sufficiently general to allow the characteristics of any chosen aircraft type to be represented. A mechanical version of this device, the Day Landing Trainer, was manufactured by General Aircraft Limited and used at the Empire Central Flying School. This trainer simulated longitudinal motions and had a pitch motion system with an endless belt, directly viewed visual model. Further development of the device was carried out after the war at Air Trainers Limited.

In 1941 Commander Luis de Florez, of the U.S. Navy, visited Britain and wrote his "Report on British Synthetic Training". This report was highly significant and influenced the establishing of the Special Devices Division of the Bureau of Aeronautics, the predecessor of the present Naval Training Equipment Center. Also in this year the Silloth Trainer concept was brought to the United States and one was erected at the Mohier Organ Plant at Hagerstown, Maryland. After evaluation it was decided to build an electrical version of the trainer as instability of adjustments due to humidity, temperature and ageing made the system unmanageable. The task of producing the new trainer was given to Bell Telephone Laboratories who produced an operational flight trainer for the Navy's PBM-3 aircraft. This device, completed in 1943, consisted of a replica of the PBM front fuselage and cockpit, complete with controls, instrumentation and all auxiliary equipment, together with an electronic computing device to solve the flight equations. The simulator had no motion system, visual system or variable control loading. A total of 32 of these electronic flight trainers for seven types of aeroplane were built by Bell and the Western Electric Company during the war years. It has been stated that the PBM-3 was "probably the first operational flight trainer that attempted to simulate the aerodynamic characteristics of a specific aircraft" but this is debatable.

Since the development of his electrical instrument flight trainer Dr. Dehmel had gained experience in analogue computing techniques through his work on Bell's M-9 anti-aircraft gun directors. He applied this knowledge to the design of an instrument flight simulator based on an analogue computer. He was then able to interest the Curtiss Wright Corporation in the manufacture of these devices in 1943. After the development of a prototype trainer, the U.S. Air Force ordered two trainers from Curtiss Wright for the AT-6 aeroplane; this trainer was named the Z-1 and is shown in the photo. These were followed by production examples designated the Z-2, -3 and -4.

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