Fighter Wing: A Guided Tour of an Air Force Combat Wing

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AIM-9 Sidewinder Missile

The first experiments with guided AAMs were done in Nazi Germany during World War II. In an attempt to keep their fighters out of range of the defensive machine guns of the massed air fleets of bombers and fighters attacking their homeland, the Germans developed a series of air-to-air missiles. Luckily for the Allied air forces, the Ruhrstahl X-4 came too late to make it into service. This compact, wire-guided missile was designed to be 'flown' by the pilot of the firing aircraft using a small joystick. It was a halting step on the way to the AAMs of today, but it was a first step nevertheless.

Following the war, a number of nations began to develop SAM and AAM designs, hoping to knock down the fleets of nuclear bombers that were expected to dominate the next major conflict. Most were designed to use the new technology of radar that had matured during World War II. The problem with radar-guided missiles was that they were relatively heavy, vastly complex, and required the firing aircraft/battery to track the target with its own radar. In order to allow the missile to get within lethal range of the target aircraft, you had to either 'illuminate' the target with a radar beam (called a fire-control radar), or track the outgoing missile in flight and radio flight commands (called command guidance or 'beam riding'). Early fighters equipped with these bulky systems had to be large, placing aircraft designers of the day under great pressure to build aircraft with performance equal to their smaller, gun-armed competitors. It seemed for a time that designers of missile-armed fighters would just have to grit their teeth and wait for technical advances in power plants, electronics, airframes, and computers to make the promise of air-to-air missiles a reality.

Then suddenly, out of a brilliant, unorthodox scientist's garage laboratory in the high desert of California, came an elegantly simple solution to the problem of missile guidance. The scientist was Dr. William B. McLean, at the Naval Ordnance Test Station (NOTS) at Inyokern, California (today the Michelson Laboratory of the U.S. Naval Weapons Center at China Lake, California). In the late 1940s, in his home garage workshop and on his own time, he built a simple device that could track an aircraft by the heat emissions from its power plant. This meant that a missile seeker could be developed to track a target without any sort of radar guidance from the firing battery or aircraft.

The key was a small electronic detector, called a photovoltaic cell, which was capable of detecting heat — or infrared radiation emissions in the short-wavelength region of the electromagnetic spectrum. The early infrared seekers used detectors based on lead sulfide, a material whose electronic characteristics are altered when it becomes saturated by infrared radiation. These seekers were not looking for the heat given off by the exhaust gases of a jet engine (as mistakenly reported for decades). On the contrary, what the tracking elements of the first-generation heat-seeking missiles were looking for was hot metal, or more specifically, the infrared radiation given off by the hot metal of jet or piston engine exhaust ports. The major technical advantage of infrared seekers is that they can be more compact, lighter, and cheaper than radar missile seekers. This allowed Dr. McLean and the engineers at NOTS to design a missile, initially known as Local Project (LP) 612, that only weighed about 155 lb./70.45 kg., in a tubular body only 5 in./12.7 cm. in diameter. To save money (which he did not have anyway), McLean used airframes from unguided 5 in./12.7 cm. High Velocity Artillery Rockets (HVARs), into which he packed the motors, warheads, and electronics. At the rear of each of the fixed tail fins is a small device that looks like a metal pinwheel. This is called a rolleron, and is used to stabilize the weapon while it is in flight. It's one of the tricks thought up by Dr. McLean and his team to help keep the Sidewinder on a stable course, and uses the missile's own slipstream through the air to generate gyroscopic motion to dampen any oscillations induced by the guidance system. The rolleron was on the first missile, and is still there today. LP612 also had the advantage of being a 'fire-and-forget' weapon — the pilot does not guide the weapon after firing. Tactically, this means the firing aircraft is free to maneuver or evade once the weapon is launched.

When the first test launches of what would become the Aerial Intercept Missile Nine (AIM-9) were conducted in 1953, the missile's snakelike flight path towards the test targets provided the name it would carry for the next half century of service, the Sidewinder. From its first tests against target drones, it was a favorite of the pilots at China Lake, because of its high reliability and deadly accuracy. In addition, it could be rapidly and cheaply retrofitted on older aircraft, so a whole generation of existing fighters could enjoy the benefits of AAMs, without the weight penalty of a massive air-intercept (AI) radar for guidance. Sidewinder was quickly adopted by the Navy and U.S. Marine Corps as the standard short-range AAM of the day.

The effectiveness of the little AIM-9 missile was demonstrated in 1958, when the Eisenhower Administration supplied the Republic of China (ROC)/ Taiwan with Sidewinder AAMs and launchers to equip its F-86 Sabrejets. The ROC Air Force was fighting daily air battles with MiG-17s of the People's Republic of China, over two small islands in the Formosa Straits, Quemoy and Matsu. While the AIM-9s were responsible for shooting down only a small percentage of the MiGs destroyed in the battles (most were still shot down by the.50-caliber machine guns of the ROC F-86s), their impact was immense, and the word quickly spread around the fighter world about the deadly little AAM named after a rattlesnake.

^{Loral Aeronutronic AIM-9L/M Sidewinder air-to-air missiles loaded onto their launch rails. The seeker is contained in the rounded nose of the missile, and the fins are designed to provide good maneuvering control and minimize drag.}

^{Loral Aeronutronic}

Over the next ten years or so, the early models of the AIM-9 (usually the AIM-9B variant) fought in theaters all over the world. In the skies over the Indian subcontinent (the 1965 India-Pakistan War), North Vietnam (1965 to 1973), and the Middle East (the June 1967 Six Day War), the Sidewinder was the most effective AAM in service. It shot down more enemy aircraft than any other AAM of the period, and put the longer-range, heavier, and more costly radar homing AAMs like the AIM-7 Sparrow to shame. So effective was the early AIM-9, that when several fell into Communist hands in the late 1950s and early 1960s, the Soviet Union produced an exact copy, the R- 13/AA-2 Atoll, for use on its own fighter aircraft.

For all its successes, the Sidewinder had some significant limitations and shortcomings. Many of these became evident in Vietnam. For instance, the early-model AIM-9B Sidewinder was a relatively short-range (about 2.6 nm./ 4.75 km.) missile, and its seeker could only 'acquire' a target and 'lock' onto it if the firing aircraft was behind the target (within a 90deg arc centered on the target's line of flight). It also was susceptible to being decoyed by flares, infrared jammers, and even the sun. (If you fired at a target within about 20deg of the sun, the missile would ignore the target and lock onto the sun.) The biggest problem, though, was the pilots' lack of in-depth understanding of the missile's performance 'envelope' (aviator jargon for things like, 'How fast can it turn, climb, or dive at different altitudes and velocities?'). In addition, the early electronics technology of the day (vacuum tubes) simply lacked the reliability to survive the shock of aircraft carrier landings and the tropical heat and humidity of Southeast Asia. As a result, several efforts were initiated by the U.S. military to improve the Sidewinder and other air-to-air missiles.

In 1968, a U.S. Navy study, the 'Ault Report,' examined the poor performance of U.S. fighter, radar, and missile systems in Southeast Asia. One of the first results of this study was better training of U.S. pilots, to teach them how to maneuver their aircraft into the 'heart' of the missile's lethal envelope, thus maximizing the chances of a kill. The development of Dissimilar Air Combat Training courses (DACT, practice dogfights against fighters with different flying characteristics from your own aircraft, using electronic scoring systems that simulate the performance of real missiles) in the USAF and USN, particularly the Navy's famous Top Gun school, did much to improve the performance of U.S. pilots in combat. As for the Sidewinder, there already was a series of product improvement programs in the works to remake the little AAM.

The first of these programs produced versions of the missile for the USAF (the AIM-9E) and the USN/USMC (the AIM-9D). Both versions, fielded in the mid-1960s, featured improved seekers that were cooled (thermoelectrically in the case of the AIM-9E, gas cooled for the AIM-9D). The — E models were converted from earlier AIM-9 B-model Sidewinders, and provided better low-altitude performance than the — B model. In addition, the — D had a more powerful rocket motor for greater range (up to 11 nm./20.11 km.) and an improved warhead. Later, the USAF further modified the — E model Sidewinder to the AIM-9J configuration, with improved aerodynamic