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The Link Trainer

The world's first flight simulator

Courtesy ASME*

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Prior to the invention of the Link Trainer, a pilot learned how to fly by instruction from another pilot. Learning to fly was expensive, time consuming and dangerous.

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When, after several years of training, Ed Link received his pilot’s license in 1927, he began to think about better ways to learn how to fly. Using his experiences from flying and working in his father’s piano and organ company, he put together a flight trainer. A patent application filed March 12, 1930, was granted September 29, 1931.

The trainer was based on the vacuum technology used in automatic musical instruments of the 1920s. In fact, the earliest trainer sat on a series of organ bellows, which would inflate or deflate to various heights to cause the trainer to bank, climb, and dive. In 1930, Ed Link organized the Link Flying School in Binghamton, New York. The trainer allowed him to reduce the cost of flying lessons by providing a way for the student pilots to learn some flying skills on the ground.

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In 1929 instrument flying was introduced, and by 1933 Ed Link had upgraded his trainer so that it could be used for instrument training. Interest in the flight trainer grew slowly; in fact, in its early days it was more popular as a carnival ride than a practical trainer!

The first significant interest for use of the trainer for instrument flight training occurred in 1934. Earlier that year the U.S. Army Air Corps was ordered to take over airmail service in response to mail fraud from private contractors. However, there were a number of highly publicized crashes as a result of pilots not being able to fly on instruments during bad weather or night flying. These accidents were costly both in the loss of human life and the loss of aircraft. The Army became interested in the Link Trainer and ordered six trainers to improve the mail pilots’ skills.

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The Link Trainer came into widespread use during World War II when over 10,000 “blue box” trainers were used to improve safety and shorten training time for over 500,000 pilots. The trainers were used as a step preceding actual flight training and as an opportunity for experienced pilots to sharpen their skills.

The legacy of the Link Trainer is visible today, with flight simulators being an integral part of pilot training. Link simulators have been used in many historic applications including the training of the Apollo astronauts for the moon landing and the training of space shuttle pilots.

Technology

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The Link Trainer provided a pilot with a realistic replication of actual flying. This was done by providing a responsive movement in the trainer when the pilot operated the trainer’s controls. The basic trainer offered the pilot a control column, control wheel, two foot pedals, and various flight and navigation instruments. The trainer sits on four pneumatic bellows which are located on a cross frame.

The Link Trainer consists of a scaled-down fuselage that is mounted on a universal joint and control base. The trainer is designed so that the pilot can simulate banking, pitching, and turning. The flight trainer is designed so that responses to movement of the control stick or pedals will result in a fluid movement of the trainer, similar to that which would be experienced in actual flight.

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Control of the flight trainer is provided by four bellows mounted on the end positions of a rotating cross-arm. Clockwise or counter-clockwise turning of the cross-arm platform is accomplished by an electric motor which uses a belt-drive connected to the cross-arm. The motor operates on a vacuum signal that is generated in response to operation of the control stick and foot pedals.

The control system relies on four valves. The rudder valve consists of two pieces, a fixed bottom and a rotating upper section. As the control wheel is turned clockwise or counter-clockwise, vacuum will shift accordingly, driving the turning motor in the correct direction. Similarly, movement of the upper half of the aileron valve controls banking. Alternate bellows on the right and left side of the trainer will then expand and contract as required in response to the pilot’s movement of the wheel and cause the trainer to bank to the right or left. Two other valves, a turn tightening valve and an elevator valve, work to bring movements of the control surfaces into a smooth response. For example, a banking manoeuvre will also cause the turntable to rotate.

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The Link Trainer also provided for a pilot’s effectiveness in instrument flying, which could be gauged by having the pilot follow a predetermined set of directions to reach a destination. The cover of the trainer would be closed so that the pilot had no visual reference of where he was going. The pilot’s path would be traced out on a map as he proceeded, and the results would be compared against the objective to determine if the pilot was capable of instrument flying.

The Inventor

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The life of Edwin A. Link spanned most of the twentieth century during a period of explosive technological progress.

Ed Link was not merely a witness; he was a mover and a creator, for he had one of the restless, inventive minds that could perceive a problem or an opportunity and find a practical solution.

He began as a technician in his father’s automatic piano and organ factory, but while his hands were busy with automatic musical instruments, his heart was in the sky.

At first the stubby-winged, one-person trainer was successful only as a coin-operated carnival ride. Gradually it began to be used in flight schools, and in 1934 the Army Air Corps purchased six trainers, primarily for training the military pilots who at the time were carrying mail for the postal service.

As the Second World War approached, Link trainers were built for governments around the world. At peak wartime production, the Link factories in Binghamton and Canada were producing 80 trainers per week, and the now famous "blue box" was preparing men from all backgrounds for service as pilots.

The company also built a celestial navigation trainer for training bomber crews and navigators, and a bubble sextant for making navigational sightings aboard aircraft.

Beginning in the 1950s, Ed Link began to phase himself out of the aerospace business and into a career in underwater exploration.

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Ed Link and his wife, Marion, began with simple, recreational treasure hunting, diving off their sailboat, the Blue Heron. Soon, however, the lure of the unexplored ocean made them dissatisfied with their sailboat and its equipment. As treasure hunting gave way to serious underwater archaeology, they outfitted a large twin diesel-powered boat as a sea-going laboratory. By 1962 the Links had conducted excavations in the waters off Jamaica, Mexico, Israel, Greece, and Sicily.

In 1960 Link designed and built a Submersible Decompression Chamber (SDC) to allow divers to return to the ship's deck quickly from the ocean depths and then to decompress slowly on board. As his interest shifted from archaeology to ocean science, Link developed equipment to allow man to work and live under water for extended periods of time.

He designed a Submersible Portable Inflatable Dwelling (SPID) in 1964, and a mini-sub in 1967. The mini-sub was the first submersible with a lockout system that could send out a diver to work on the ocean floor. Link then designed a second lockout submersible, which introduced the use of acrylic and aluminium for deep-sea vessels and had removable components. He helped design the Cabled Observation and Rescue Device (CORD), one of the first successful remotely operated vehicles, that allows the crew on a surface ship to use television cameras and lights for underwater reconnaissance. Its claws and cutters can free a trapped submersible.

Late in his life, Ed Link became interested in antique steam engines, alternative sources of energy, and finding new uses for energy from the wind and sun.

Edwin A. Link died September 7, 1981.

*The Link Trainer is an American Society of Mechanical Engineers (ASME) International Historic Engineering Landmark. The text of this story appears by agreement of the ASME. Go to http://www.asme.org/Communities/History/Landmarks/Link_C3_Flight_Trainer_ca.cfm for more on this Landmark.

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