AIM-9 Sidewinder
The AIM-9 Sidewinder is a short-range air-to-air missile. It entered service with the United States Navy in 1956 and the Air Force in 1964, and is one of the oldest, cheapest, and most successful air-to-air missiles. Its latest variants remain standard equipment in most Western-aligned air forces. The Soviet K-13, a reverse-engineered copy of the AIM-9B, was also widely adopted.
Low-level development started in the late 1940s, emerging in the early 1950s as a guidance system for the modular Zuni rocket. This modularity allowed for the introduction of newer seekers and rocket motors, including the AIM-9C variant, which used semi-active radar homing and served as the basis of the AGM-122 Sidearm anti-radar missile. Due to the Sidewinder's infrared guidance system, the brevity code "Fox two" is used when firing the AIM-9. Originally a tail-chasing system, early models saw extensive use during the Vietnam War, but had a low success rate. This led to all-aspect capability in the L version, which proved an effective weapon during the 1982 Falklands War and Operation Mole Cricket 19 in Lebanon. Its adaptability has kept it in service over newer designs like the AIM-95 Agile and SRAAM that were intended to replace it.
The Sidewinder is the most widely used air-to-air missile in the West, with more than 110,000 missiles produced for the U.S. and 27 other nations, of which perhaps one percent have been used in combat. It has been built under license by Sweden and other nations. The AIM-9 has an estimated 270 aircraft kills.
In 2010, Boeing won a contract to support Sidewinder operations through to 2055. In 2021 an Air Force spokesperson said that its relatively low cost, versatility, and reliability mean it is "very possible that the Sidewinder will remain in Air Force inventories through the late 21st century".
Design
The AIM-9 was a product of the US Naval Weapons Center at China Lake in the Mojave Desert. It features a lightweight, compact design with cruciform canards and tail fins. It uses a solid rocket motor for propulsion, similar to most conventional missiles, a continuous-rod fragmentation warhead, and an infrared seeker.The seeker tracks a difference in temperatures detected and uses proportional guidance to achieve impact. Older variants such as the AIM-9B with uncooled seeker heads could track only the high temperatures of engine exhaust, making them strictly rear-aspect. Later variants, however, featured liquid nitrogen coolant bottles in the launchers, allowing the missile to track any part of the aircraft heated by air resistance due to high-speed flight, giving modern Sidewinders all-aspect capabilities.
The nose canards provide maneuverability for the AIM-9, with the AIM-9X using thrust vectoring to augment this. The hot gases generated were used to actuate the nose canards in older models, while newer variants use thermal batteries.
To minimize the amount of energy devoted to actuating control surfaces, the AIM-9 does not use active roll stabilization. Instead, it uses rollerons, small finned metal discs protruding out of the aft end of the tips of the tail fins which are spun by the passing airflow as the missile flies through the air, providing gyroscopic stabilization.
The AIM-9 uses a passive infrared proximity fuze to detonate its warhead near an enemy aircraft, scattering fragments that aim to damage the aircraft, rendering it inoperable. The continuous rod warhead features rods welded together to form a cylindrical outer shell, with explosive filler inside. Upon detonation, the rods expand in a toroidal shape, ensuring that at least some portion of the shrapnel hits enemy aircraft.
Newer models of the AIM-9 sought to increase the range that the seeker head's gimbal can turn, allowing the missile to track aircraft at greater angles from its direct line of sight, or boresight. Models such as the AIM-9L, AIM-9M, and AIM-9X feature high off-boresight capabilities, meaning they are able to track targets at high seeker gimbal angles, or highly distant from the boresight.
Guidance
The Sidewinder is guided not by the actual position recorded by the detector, but by the change in position since the last sighting. So if the target remains at 5 degrees left between two rotations of the mirror, the electronics would not output any signal to the control system. Consider a missile fired at right angles to its target; if the missile is flying at the same speed as the target, it should "lead" it by 45 degrees, flying to an impact point far in front of where the target was when it was fired. If the missile is traveling four times the speed of the target, it should follow an angle about 11 degrees in front. In either case, the missile should keep that angle all the way to interception, which means that the angle that the target makes against the detector is constant. It was this constant angle that the Sidewinder attempted to maintain. This "proportional pursuit" system is straightforward to implement and offers high-performance lead calculation almost for free and can respond to changes in the target's flight path, which is much more efficient and makes the missile "lead" the target.History
Origins
During World War II, various researchers in Germany designed infrared guidance systems of various complexity. The most mature development of these, codenamed Hamburg, was intended for use by the Blohm & Voss BV 143 glide bomb in an anti-ship role. Hamburg used a single IR photocell as its detector along with a spinning disk with lines painted on it, alternately known as a "reticle" or "chopper". The reticle spun at a fixed speed, causing the output of the photocell to be interrupted in a pattern, and the precise timing of the resulting signal indicated the bearing of the target. Although Hamburg and similar devices like Madrid were essentially complete, the work of mating them to a missile had not been carried out by the time the war ended.In the immediate post-war era, Allied military intelligence teams collected this information, along with many of the engineers working on these projects. Several lengthy reports on the various systems were produced and disseminated among the Western aircraft firms, while a number of the engineers joined these companies to work on various missile projects. By the late 1940s a wide variety of missile projects were underway, from huge systems like the Bell Bomi rocket-powered bomber to small systems like air-to-air missiles. By the early 1950s, both the US Air Force and Royal Air Force had started major IR seeker missile projects.
File:F104-AIM9.gif|thumb|alt=Video vignette of an F-104 destroying a QF-80 target drone with an AIM-9 Sidewinder missile|A F-104 Starfighter test-firing an AIM-9 Sidewinder against a QF-80 target drone at Eglin Air Force Base
The development of the Sidewinder missile began in 1946 at the Naval Ordnance Test Station, Inyokern, California, now the Naval Air Weapons Station China Lake, as an in-house research project conceived by William B. McLean. McLean initially called his effort "Local Fuze Project 602" using laboratory funding, volunteer help and fuze funding to develop what they called a heat-homing rocket. The name Sidewinder was selected in 1950 and is the common name of Crotalus cerastes, a rattlesnake, which uses infrared sensory organs to hunt warm-blooded prey.
It did not receive official funding until 1951 when the effort was mature enough to show to Admiral William "Deak" Parsons, the Deputy Chief of the Bureau of Ordnance. It subsequently received designation as a program in 1952. Originally called the Sidewinder 1, the first live firing was on 3 September 1952. The missile intercepted a drone for the first time on 11 September 1953. The missile carried out 51 guided flights in 1954, and in 1955 production was authorized.
In 1954, the US Air Force carried out trials with the original AIM-9A and the improved AIM-9B at the Holloman Air Development Center. The first operational use of the missile was by Grumman F9F-8 Cougars and FJ-3 Furies of the United States Navy in the middle of 1956.
First generation rear-aspect variants
Nearly 100,000 of the first generation of the Sidewinder were produced with Raytheon and General Electric as major subcontractors. Philco-Ford produced the guidance and control sections of the early missiles. The NATO version of the first-generation missile was built under license in Germany by Bodenseewerk Gerätetechnik; 9,200 examples were built.AIM-9A (''AAM-N-7 Sidewinder I'') (USN)
AIM-9A was a pre-production of the Sidewinder, first fired successfully in September 1953. Missile production began in 1955, and the first models entered the Navy's fleet service in 1956. Generally, it was a prototype production run, with 240 pieces being produced, and mainly intended for training pilots in air combat techniques. The AIM-9A was initially called the AAM-N-7 before the tri-service designation change in 1962.The AIM-9A and AIM-9B were originally fitted with a non-propulsive attachment for their MK 15 and MK 17 rocket motors. If the motor accidentally ignited while kept in storage, during transport, or while it was fitted to the aircraft hardpoints, the NPA would direct the exhaust gases at right angles rather than straight back. In these cases, the missile would not move. While the NPA safety device itself suffered no failures, some ordnance men forgot to remove them after hanging the missiles in the hardpoints. When the pilots attempted to fire the missiles in flight, the hot exhaust gases were redirected directly towards the wings, severely damaging the aircraft. After losing three aircraft in this manner, the US Navy withdrew the NPA from use.
AIM-9B (''AAM-N-7 Sidewinder IA'') (USAF/USN)
The AIM-9B is very similar to the AIM-9A, but the "B" has a more sophisticated rear and more aerodynamical front fins. The AIM-9B is a very limited weapon, but it had no serious competitors and counters when it was introduced, causing it to be adopted by the USAF and NATO as a standard weapon, with around 80,000 units being produced from 1958 to 1962.The viewing angle of the AIM-9B's sensor was a minuscule 4 degrees, so at launch, the pilot had to accurately aim the aircraft's sight over or above the target. The speed of the conical scan was very slow, additionally, the uncooled missile had a low sensitivity and was liable to extraneous heat. The AIM-9B was recommended for use on non-threatening targets, only from behind and only with the sun behind or to the side of the launching aircraft.
It was famously the first Sidewinder variant to be fired in anger as on 24 September 1958, it achieved the world's first successful kill with an air-to-air missile, when Taiwanese F-86Fs shot down Communist Chinese MiG-15s using AIM-9Bs supplied and fitted by the U.S. Navy.