
Chicken gun

A chicken gun or flight impact simulator is a large-diameter, compressed-air cannon used to fire bird carcasses at aircraft components in order to simulate high-speed bird strikes during the aircraft's flight. Jet engines and aircraft windshields are particularly vulnerable to damage from such strikes, and are the most common target in such tests. Although various species of bird are used in aircraft testing and certification, the device acquired the common name of "chicken gun" as chickens are the most commonly used 'ammunition' owing to their relative abundance.
History.
The first recorded chicken gun was built in 1942 by the US Civil Aeronautics Administration in collaboration with the Westinghouse Electric and Manufacturing Company. Built at Westinghouse's High Power Laboratory in Pittsburgh, it was capable of firing bird carcasses at up to , although most tests were conducted with muzzle velocities around . The tests conducted with this cannon were the first of their kind, and showed that the glass used in the windshields of common passenger aircraft such as the Douglas DC3 were extremely vulnerable to bird strikes; panels were penetrated completely by a bird traveling at only . Subsequent testing showed that laminate panels made of glass interleaved with polyvinyl chloride were far more resistant.
The device was used at the High Power Laboratory until November 1943. In early 1945, the device was moved to a CAA research & development location in Indianapolis, called the Indianapolis Experimental Station, where it was used to test components for various commercial aircraft manufacturers. The device was retired at some point in 1947. A similar device was independently developed by the de Havilland Aircraft Company in the United Kingdom in the mid 1950s. The UK's Royal Aircraft Establishment built a chicken gun in 1961, and in 1967 the Canadian National Research Council's Division of Mechanical Engineering used that device as a basis for their "Flight Impact Simulator Facility", based next to Ottawa airport. This gun remained in frequent use until 2016, at which point it was donated to the Canada Aviation and Space Museum and replaced by a pair of more modern devices. The replacement guns can accommodate different sized birds more easily through the use of a modular barrel.
In the 1970s, Goodyear Aerospace developed a chicken gun that stored compressed air behind a ceramic diaphragm and used a cardboard sabot to center and stablize the chicken. When fired, a needle struck the diaphragm, rupturing the seal and allowing the air to propel the projectile down the barrel. A metal ring on the muzzle stopped the sabot, but allowed the chicken to escape the barrel.
The United States Air Force built the AEDC Ballistic Range S-3 at Arnold Engineering Development Complex in 1972 to test the canopies and windshields of military aircraft. The gun was later used in the development and certification of multiple US military aircraft, including the F-4, F-111 and A-10. the gun was still in operation.
Use in aircraft certification.
Both the US Federal Aviation Administration and the European Aviation Safety Agency require that aircraft engines and airframes be resilient against bird strikes to a certain degree as part of the airworthiness certification process. In general, an engine should not suffer an uncontained failure after impact with a suitably-sized bird, and a bird strike to the airframe of a craft should not prevent "continued safe flight [and a] normal landing".
Chicken guns are routinely used in the process of proving compliance. Given the complexity of the devices and the expertise required to operate them, an aircraft manufacturer will typically contract with a facility that operates a device to perform a test against a given standard. The component to be tested is mounted securely on a frame, the cannon fires a bird at it, and the results are examined for compliance with the relevant standards. Most tests are performed with the cannon pressurized to around this results in a bird being launched at around , approximately the resultant velocity in a collision between a bird and an aircraft at take-off or landing.
The FAA do not specify the species of bird that should be used for testing, but do state that the birds should not be frozen - as this would not accurately reflect the reality of a strike. Chickens are used as they are cheap, and readily available.
There have been efforts to develop artificial bird analogs for use in impact tests, to replace the use of carcasses. The motivations for this range from ensuring that results are easily reproducible across the industry, cost, and sensitivity to the views of animal rights activists. However, concerns have been expressed by some engineers that tests with artificial birds do not accurately represent the forces involved in real bird strikes as the analogs lack bones. Some go further and state that the farm-raised birds commonly used in tests are also unrepresentative owing to the lower density of their muscle tissue.
Notable uses.
During the development of the Boeing 757 in the 1970s, the cockpit roof was subjected to a bird strike test wherein a chicken was fired at into a stationary cockpit. To the surprise of the Boeing engineers, the chicken penetrated the skin of the aircraft. As a result the cockpit of the 757, and that of the 767, which shared the same design, to be reinforced. Several 767s were already in service, and had to be recalled for retrofitting of the reinforcements. Later in the 757's development process a bird strike test was conducted on the aircraft's windows, again by firing a chicken at them. The UK Civil Aviation Authority's certification requirements at the time were more stringent than the FAA's, and required the metal around the windows to also resist a bird strike. The 757 failed this test, requiring further re-engineering.
After the Space Shuttle Columbia disaster in 2003, the chicken gun at AEDC Ballistic Range S-3 was repurposed to test the resistance of various components of the Shuttle orbiter and launch fuel tanks to impacts from insulating foam. The intent was to discover the exact cause of the disaster, and establish whether any modifications to the Shuttle were required.
Urban legend.
An apocryphal tale surrounding chicken guns has been in circulation since at least 1988. The specifics vary depending on the telling, but the essence is that an engineering team from one country borrows a chicken gun from another country to test a new vehicle design. They use the gun, only to have the chickens easily penetrate the item under test, causing catastrophic damage. They appeal to the donor country for help, only to be told simply to "thaw your chickens". The tale is usually told in order to mock the intelligence of the nation that supposedly borrowed the apparatus. In the most common retelling, the donors are American and the borrowers British. No evidence exists to show that such an event ever occurred.