Link Trainer

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. These simulators became famous during World War II, when 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. A former organ and nickelodeon builder, Link used his knowledge of pumps, valves and bellows 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, United Kingdom, Israel, Japan, Pakistan, and the USSR.

The Link Flight Trainer has been designated as a Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers. The Link Company, now the Link Simulation & Training division of L-3 Communications, continues to make aerospace simulators.

Origins
Edwin Link had developed a passion for flying in his boyhood years, but was not able to afford the high cost of flying. So, upon leaving school in 1927, he started developing a simulator, an exercise which took him 18 months. His first pilot trainer, which debuted in 1929, resembled a 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.

The Link company 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 colors other than blue 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 the 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.

Pilot Trainer
The Pilot Trainer was Link's first model, and was an evolution of his 1929 prototype.

ANT-18
The second and most prolific version of the Link Trainer was the ANT-18 (Army Navy Trainer model 18), which was in its turn, 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.

ANT-18 design and construction
The ANT-18 consists of two main components.

The first major component is the trainer itself. The trainer consists of a wooden box approximating the shape of a cockpit and forward fuselage section, 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 simulate movement, a vacuum pump which both drives the bellows and provides input to a number of aircraft instruments, and a device known as a Telegon Oscillator, which controls the remaining instruments.

The second major component is an external instructor's station, which consists of a large map table, a repeated display of the main flight instruments, and a moving marker known as a "crab." The crab moves across the glass surface of the map table, plotting the pilot's track. The pilot and instructor can communicate with each other via headphones and microphones.

The ANT-18 has three main sets of bellows. One set of four bellows (one under each corner of the cockpit) controls movement in the pitch and roll planes. A very complicated set of bellows at the front of the cockpit controls movement in the yaw plane. This complex set of 10 bellows, two crank shafts and various gears and pulleys comprised the turning motor. This motor could turn the entire cockpit in continuous 360 degree circles. This was possible since a series of electrical slip ring contacts in the lower base compartment, supplied electrical continuity between the cockpit and the base.

A third set 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.

Survivors
A number of Link Trainers are known to survive around the world. Many ANT-18 simulators survive around the world today.

Australia
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. One such unit is on static display at Fighterworld, adjacent to the Williamtown RAAF base outside Newcastle Australia, another in working condition is housed near the Redcliffe Aerodrome at Shapcott Base, home of 212 (City of Redcliffe) Squadron Australian Air Force Cadets.

Canada
A fully functional Link Trainer is owned and operated by the Canadian Harvard Aircraft Association of Tillsonburg, Ontario. Other Link Trainers are on display at the Canadian Air and Space Museum, the Western Canada Aviation Museum, the Canadian War Museum, Commonwealth Air Training Plan Museum, the Bomber Command Museum of Canada, and the Canadian Bushplane Heritage Centre. There is also a Link Trainer on display at the North Atlantic Aviation Museum in Gander, Newfoundland, Canada; it was used in the television series Above and Beyond (2006). Another Link Trainer is on display at the Claresholm Museum in Claresholm, Alberta, where the No. 15 Service Flying Training School was situated during World War II.

Czech republic
The Aviation Museum at Kbely, Prague has a Link Trainer.

Portugal
The Museu do Ar (Air Museum), located in Sintra, has one on display, used by TAP Portugal.

Serbia
At least three examples are known to exist out of which Aviation Museum in Belgrade owns one and Aeroklub Valjevo, Valjevo owns one example that was still operational in the '80s, nowadays it requires new set of vacuum tubes but otherwise it is in a good state.

United Kingdom
A number of Link Trainers are known to exist in Britain. Known survivors are located at:
 * Brooklands Museum (ANT-18)
 * Boscombe Down Aviation Collection at Old Sarum
 * The Welford Museum
 * No. 424 (Southampton) Squadron Air Training Corps
 * No. 195 (Grimsby) Squadron Air Training Corps which is fully operational after being restored around the turn of the millennium
 * No. 1349 Woking Squadron Air Training Corps which is fully operational
 * No. 328 (Kingston) Squadron Air Training Corps (ANT-18)
 * No. 130 (Bournemouth) Squadron Air Training Corps
 * No. 1063 (Herne Bay) Squadron Air Training Corps Not functional.
 * Wellingborough School CCF RAF Section
 * Imperial War Museum Duxford
 * Caernarfon Airport Aviation Museum, North Wales
 * Brenzett Aeronautical Museum, Kent
 * Manston History Club, Kent
 * Rochester Airport, Kent
 * Tangmere Aviation Museum, West Sussex
 * North East Aircraft Museum, Sunderland
 * Montrose Air Station Heritage Centre, Angus, Scotland
 * Montrose Air Station Heritage Centre, Angus, Scotland

USA
The Roberson Museum and Science Center in Binghamton, New York, contains an exhibit on Edwin Link including a Link Trainer in a typical classroom setting. The Greater Binghamton Airport, Link Field, also has a Link Trainer on display and another is at the Wings of Eagles Air Museum in nearby Elmira, New York. The CT&I Techworks! facility, also in Binghamton, has a trainer returned to functionality as well as numerous parts available.

The British Flight Training School Museum located on the grounds of the Terrell Municipal Airport in Terrell, Texas has a complete Link Trainer assembly with attached instructor's station on display at the museum dedicated to the 2,000 Royal Air Force Cadets were trained in Terrell from August 1941 through the end of World War II as a part of the Lend-Lease Act that allowed British aviation cadets to be trained in the US by civilian aviators.

A Link trainer used to train the Tuskegee Airmen is on display at the Museum of Aviation at Robins AFB near Warner-Robins, Ga. The National Museum of the United States Air Force has a Link Trainer on display; it was the museum's "Aircraft of the Week" during the first week of 2009.

One Link Trainer is in Post Mills, Vermont, owned by Balloonist and collector Brian Boland of Boland Balloons and can be viewed in his flight museum at Post Mills Airport.

Another Link Trainer in working condition is on display at the Commemorative Air Force Airpower Museum in Midland, Texas. Randolph Air Force Base, Texas, home of the United States Air Force's Air Education and Training Command (AETC), also has a Link Trainer on display. Likewise a Link Trainer is displayed at the Cavanaugh Flight Museum in Addison, Texas. The Museum at Hill Air Force Base, Utah has a Link Trainer on display. The Jimmy Doolittle Air & Space Museum, located at Travis AFB in CA, exhibits a Link Trainer.

Two Link Trainers are on display at the Museum of Flight restoration facility at Paine Field near Seattle, Washington. One is in fully functional condition with the adjoining instructors table.

A "Blue Box" is on display at the United States Army Aviation Museum at Fork Rucker, Alabama. It was added to their collection in 2006.

There is a Link Trainer on display at the Melbourne Airport in Melbourne, Florida. The Naval Air Station Fort Lauderdale Museum also has one on display in its Link Trainer Building #8, which is on the U.S National Register of Historic Places.

A Link Trainer is on display in the Golden Age of Flight Gallery at the San Diego Air & Space Museum. There is a light inside so visitors can see the instrument panel. In August 2009, Edwin Link's granddaughter visited the museum and shared her stories with the volunteer docents. One of the volunteer docents trained in a Link Trainer and shares his experiences with visitors and tours.

A complete Link Trainer assembly, including an instructor's station, is on display at the Prairie Aviation Museum in Bloomington, Illinois.

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.

The Valiant Air Command Warbird Museum in Titusville, Florida has a Link Trainer with instructor station in its collection.

There is a Link Trainer with instructor station on display at the Tri-State Warbird Museum.

There is a restored Link Flight Training Simulator on display in the United Airlines Flight Training Center in Denver, Colorado.

There is a preserved but unrestored Link Trainer on display at the American Treasure Tour in Oaks, Pennsylvania. Although its surface paint is white, the blue of the "Blue Box" is distinctly noticeable underneath it, which may indicate it dates to the late-war era.

The Silent Wings Museum in Lubbock, Texas has a Link Trainer on display including the chart table.

The Evergreen Aviation & Space Museum in McMinnville, Oregon has a "Blue Box" Link Trainer on display underneath the wing of the Spruce Goose in the Aviation section of the museum.

There is a restored Link Trainer at CAE Dallas in the lobby. They also have the first Singer Class "C" trainer, which is still in operation training pilots on the Learjet 35.