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Link trainer in use at a British Fleet Air Arm station in 1943
The term Link Trainer, also known as the "Blue box" and "Pilot Trainer" is commonly used to refer to a series of flight simulators produced between the early 1930s and early 1950s by the Link Aviation Devices, Inc, founded and headed by Ed Link, based on technology he pioneered in 1929 at his family's business in Binghamton, New York. During World War II, they were used as a key pilot training aid by almost every combatant nation.
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. Ed Link used his knowledge of pumps, valves and bellows gained at his father's Link Piano and Organ Company to create a flight simulator that responded to the pilot's controls and gave an accurate reading on the included instruments. More than 500,000 US pilots were trained on Link simulators, as were pilots of nations as diverse as Australia, Canada, Germany, New Zealand, United Kingdom, Israel, Japan, Pakistan, and the USSR. Following WWII, Air Marshall Robert Leckie (wartime RAF Chief of Staff) said “The Luftwaffe met its Waterloo on all the training fields of the free world where there was a battery of Link Trainers.”
Link Trainer at Freeman Field, Seymour, Indiana. Freeman Field was a US Army Air Force field in World War II.
Edwin Link had developed a passion for flying in his boyhood years, but was not able to afford the high cost of flying lessons. So, upon leaving school in 1927, he started developing a simulator. The project took him 18 months. His first pilot trainer, which debuted in 1929, resembled an overgrown toy airplane from the outside, with short wooden wings and fuselage mounted on a universal joint. Organ bellows from the Link organ factory, the business his family owned and operated in Binghamton, New York, driven by an electric pump, made the trainer pitch and roll as the pilot worked the controls.
Link's first military sales came as a result of the Air Mail scandal, when the Army Air Corps took over carriage of U.S. Air Mail. Twelve pilots were killed in a 78-day period due to their unfamiliarity with Instrument Flying Conditions. The large scale loss of life prompted the Air Corps to look at a number of solutions, including Link's pilot trainer. The Air Corps was given a stark demonstration of the potential of instrument training when, in 1934, Link flew in to a meeting in conditions of fog that the Air Corps evaluation team regarded as unflyable. As a result, the Air Corps ordered the first six pilot trainers at $3,500 each.
Link and his company had struggled through the Depression years but after gaining Air Corps interest the business expanded rapidly and during World War II, the ANT-18 Basic Instrument Trainer, known to tens of thousands of fledgling pilots as the "Blue Box" (although it was painted in different colors in other countries), was standard equipment at every air training school in the United States and Allied nations. During the war years, Link produced over 10,000 Blue Boxes, turning one out every 45 minutes.
Link Trainer models
Several models of Link Trainers were sold in a period ranging from 1934 through to the late 1950s. These trainers kept pace with the increased instrumentation and flight dynamics of aircraft of their period, but retained the electrical and pneumatic design fundamentals pioneered in the first Link.
Trainers built from 1934 up to the early 1940s had a color scheme that featured a bright blue fuselage and yellow wings and tail sections. These wings and tail sections had control surfaces that actually moved in response to the pilot's movement of the rudder and stick. However, many trainers built during mid to late World War II did not have these wings and tail sections due to material shortages and critical manufacturing times.
The Pilot Maker was Link's first model. It was an evolution of his 1929 prototype and was used in Mr. Link's Link Flying School and later by other flying schools. During the Depression years versions of the Pilot Maker were also sold to amusement parks. In fact, his patent (US1825462 A) for the Pilot Maker was titled Combination Training Device for Student Aviators and Entertainment Apparatus.
The most prolific version of the Link Trainer was the ANT-18 (Army Navy Trainer model 18), which was a slightly enhanced version of Link's C3 model. This model was also produced in Canada for both the Royal Canadian Air Force and the Royal Air Force with a somewhat modified instrument panel, where its model designation was D2. It was used by many countries for pilot training before and during the Second World War, especially in the British Commonwealth Air Training Plan.
The ANT-18 featured rotation through all three axes, effectively simulated all flight instruments, and modeled common conditions such as pre-stall buffet, overspeed of the retractable undercarriage, and spinning. It was fitted with a removable opaque canopy, which could be used to simulate blind flying, and was particularly useful for instrument and navigation training.
The first major component is the trainer itself. The trainer consists of a wooden box approximating the shape of a fuselage and cockpit, which is connected via a universal joint to a base. Inside the cockpit is a single pilot's seat, primary and secondary aircraft controls, and a full suite of flight instruments. The base contains several complicated sets of air-driven bellows to create movement, a vacuum pump which both drives the bellows and provides input to a number of aircraft instruments, a device known as a Telegon Oscillator which supplies power to the remaining pilot and instructor instruments, and a Wind Drift analog computer.
The second major component is an external instructor's desk, which consists of a large map table; a duplicate display of the pilot's main flight instruments; and the Automatic Recorder, a motorized ink marker also known as the "crab." The crab is driven by the Wind Drift computer and moves across the glass surface of the map table, plotting the pilot's track. The desk includes circuits for the pilot and instructor to communicate with each other via headphones and microphones, and controls for the instructor to alter wind direction and speed.
The ANT-18 has three main sets of bellows. One set of four bellows (fore and aft and both sides of the cockpit) controls movement in the pitch and roll planes. A very complicated set of bellows at the front of the fuselage controls movement in the yaw plane. This Turning Motor is a complex set of 10 bellows, two crank shafts and various gears and pulleys derived from early player piano motors. The Turning Motor can rotate the entire fuselage through 360 degree circles at variable rates of speed. A set of electrical slip ring contacts in the lower base compartment supplies electrical continuity between the fixed base and the movable fuselage.
The third set of bellows simulates vibration such as stall buffet. Both the trainer and the instructor's station are powered from standard 110VAC/240VAC power outlets via a transformer, with the bulk of internal wiring being low voltage. Simulator logic is all analog and is based around vacuum tubes.
Procedural trainer that included only basic instruments.
Known as the C-2 by the United States Army Air Forces.
Developed from the C-3, it added landing gear, propeller pitch and flap controls. Also known as the AN-T-18.
A number of Link Trainers are known to survive around the world.
At least 22 ANT-18 trainers survive in Australia, in various states of repair. A number of these are in museums, but the majority are in the custody of the Australian Air Force Cadets, who were given them in the 1950s by the Royal Australian Air Force (RAAF). They were maintained until 1975 by the RAAF, and as a result many are still in relatively good condition, being either fully or partially operational. The number of operational ANT-18s has been boosted in recent years by the restoration of several machines.
The Millville Army Air Field Museum at the Millville Airport, Millville, New Jersey owns two Link Trainers, and has one, operational, on display in the World War II Link Trainer building.
A circa 1943 Link Trainer with instructor's desk is on display at NASA's Ames Research Center, Moffett Field, Mountain View, Calif. This trainer was physically and mechanically restored to full working order in 1992. This trainer did not originally have the wings and tail assembly installed. They were often omitted on trainers made during World War II. However, a set of "paddle style" wings and tail assembly was manufactured from original Link documentation specs, and added during the restoration. This trainer has been moved and is now on public display at the Moffett Field Historical Society Museum, Moffett Field, Mountain View, CA.