Flightline: 52/TBD

"user314" (user314) 09/23/2020 at 11:00 • Filed to: flightline, Planelopnik, planelopnik history, USAF, u.s. navy

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A USAF YF-104A, on loan to the USN, carrying an AIM-9C missile

!!!error: Indecipherable SUB-paragraph formatting!!! , CA, 29 July 1960

Established in 1943, NAWS China Lake is a large (China Lake’s two ranges cover 1.1 million acres, larger than Rhode Island) installation for weapons and armaments research, development, acquisition, testing and evaluation (RDAT&E). Founded jointly with Caltech during WWII for the test and evaluation of rockets as well as ordnance, including the !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! , !!!error: Indecipherable SUB-paragraph formatting!!! and !!!error: Indecipherable SUB-paragraph formatting!!! rockets. A new airfield was constructed as part of the Manhattan Project, and was used by B-29s !!!error: Indecipherable SUB-paragraph formatting!!! for the atomic bomb. After the war, China Lake was involved in the development and testing of the !!!error: Indecipherable SUB-paragraph formatting!!! and !!!error: Indecipherable SUB-paragraph formatting!!! rockets, !!!error: Indecipherable SUB-paragraph formatting!!! and !!!error: Indecipherable SUB-paragraph formatting!!! anti-radiation missiles, and !!!error: Indecipherable SUB-paragraph formatting!!! (JSOW) and !!!error: Indecipherable SUB-paragraph formatting!!! (JDAM).

One of the earliest, and perhaps the most famous, post-war weapons developed at China Lake was the AIM-9 Sidewinder IR guided missile. Originally intended as a potential guidance and fusing module for the Zuni rocket, the system was eventually developed into an entirely new missile.

F-104 test firing an AIM-9 Sidewinder against a QF-80 target drone.

China Lake developed an IR seeker featuring a mirror about the long axis of the missile, which would allow the the Sidewinder to calculate the target’s flight path and “lead” it, giving a better chance of intercept:

The detector was mounted in front of the mirror. When the long axis of the mirror, the missile axis and the line of sight to the target all fell in the same plane, the reflected rays from the target reached the detector (provided the target was not very far off axis). Therefore, the angle of the mirror at the instant of detection ( w1 ) estimated the direction of the target in the roll axis of the missile.

The yaw/pitch (angle w2 ) direction of the target depended on how far to the outer edge of the mirror the target was. If the target was further off axis, the rays reaching the detector would be reflected from the outer edge of the mirror. If the target was closer on axis, the rays would be reflected from closer to the centre of the mirror. Rotating on a fixed shaft, the mirror’s linear speed was higher at the outer edge. Therefore, if a target was further off-axis, its “flash” in the detector occurred for a briefer time, or longer if it was closer to the center. The off-axis angle could then be estimated by the duration of the reflected pulse of !!!error: Indecipherable SUB-paragraph formatting!!! .

The Sidewinder also included a dramatically improved guidance algorithm. The Enzian attempted to fly directly at its target, feeding the direction of the telescope into the control system as it if were a joystick. This meant the missile always flew directly at its target, and under most conditions would end up behind it, “chasing” it down. This meant that the missile had to have enough of a speed advantage over its target that it did not run out of fuel during the interception.

The Sidewinder is not guided on the actual position recorded by the detector, but on the change in position since the last sighting. So if the target remained 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 “ !!!error: Indecipherable SUB-paragraph formatting!!! ” system is very easy to implement, yet it 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.

This arraignment, however, precluded spinning the missile to stabilize it, as this would interfere with the guidance system detecting and tracking a target. The solution was a set of “rollerons” in the missile’s fins, which acted as gyroscopic stabilizers.

Rolleron tab on a modern Sidewinder.

Essentially a toothed wheel set in a tab on the fin, a rolleron would be spun by airflow over its surface. A change in the missile’s axis would force this tab into the airflow, cancelling the motion. This system proved to be more effective than that used by the USAF’s competing design, the AIM-9 Falcon, which was also IR guided but proved to be unreliable in combat, and was eventually replaced by the Sidewinder.

A prototype Sidewinder mounted under the wing of an AD4 Skyraider

The new missile was known variously as Sidewinder 1, Heat-Homing Rocket, and AAM-N-7 during development, and successfully intercepted its first target during a test flight in 1953. Fifty-one more tests flights were carried out in 1954, and the USAF began its own test program the same year. In 1955, production was authorized, and by 1956 operational AAM-N-7s were being carried by USN F9F-8 Cougars and FJ-3 Furies. The first combat use of the Sidewinder came in 1958 when F-86 Sabres of the Republic of China, armed with the missiles in secret, shot down an unknown number of PRC MiG-17s during the Second Taiwan Strait Crisis. One of the Sidewinders struck its target but failed to explode, and the MiG returned to base with the missile lodged in its frame. The missile was swiftly reverse-engineered by Soviet technicians, and soon a cloned version (to the point that examples acquired by the US and allies were shown to be interchangeable with early US/NATO versions) , the !!!error: Indecipherable SUB-paragraph formatting!!! (NATO reporting name AA-2 Atoll), was being manufactured for Soviet and Warsaw Pact forces.

Two K-13 missiles mounted on a Ukrainian MiG-23

Development of the Sidewinder continued into the 1960s, with the Navy developing the AAM-N-7 Sidewinder IB (AIM-9C post-1962), which swapped out the IR seeker for a semi-active radar homing (SARH) sensor, similar to the AIM-7 Sparrow. Tested on a pair of YF-104 pre-production models bailed to the US Navy, the Sidewinder IB were intended for use by the F-8 Crusader.

The AIM-9C proved to be inferior to the AIM-7 however, and was withdrawn after a short period. The missiles were reworked into !!!error: Indecipherable SUB-paragraph formatting!!! in the 1980s however, turning them into the !!!error: Indecipherable SUB-paragraph formatting!!! ( Side winder A nti- R adiation- M issile). Though not as capable as the Standard ARM or AGM-88 HARM (the AGM-122 shared the Sidewinder’s short range and small warhead), the smaller size of the Sidearm allowed it to be carried by a wide array of aircraft, including USMC AH-1 SeaCobra helos and AV-8B Harriers and US Army AH-64s.

USMC AV-8A Harrier at China Lake carrying a training AGM-122 Sidearm

The USAF and USN continued refining the Sidewinder throughout the 1960s, improving the guidance systems to expand the engagement envelope, redesigning the forward canards to allow for more maneuverability, and upgrading the seekers with solid-state electronics to make them more reliable and robust, as well as improving their resistance to !!!error: Indecipherable SUB-paragraph formatting!!! such as flares and IR jammers.

AIM-9S were fitted to USN F-4 and F-8 fighters during the Vietnam War, and could be carried by A-4 and A-7 strike aircraft as well. The USAF’s F-4s initially carried AIM-4 Falcon missiles, but their performance was subpar, and a crash program was enacted to refit them with AIM-9s. F-105 Thunderchief strike aircraft were also able to carry AIM-9Bs for self-defense. In all, 452 Sidewinders were fired during the war, resulting in 80 kills, a !!!error: Indecipherable SUB-paragraph formatting!!! !!!error: Indecipherable SUB-paragraph formatting!!!   of 0.18.

Vietnam War-era Sidewinders. From top to bottom: AIM-9B, AIM-9D, AIM-9C

The next major advance came in the middle 1970's with the development of the “all-aspect” AIM-9L. By cooling the seeker, the ‘Lima’ model Sidewinders were able to acquire targets based on the friction-generated heat of the wings and nose, as opposed to earlier models which could only track the hot exhaust of the engine. The AIM-9L recorded their first kills in 1981, destroying two Libyan Su-22s in the !!!error: Indecipherable SUB-paragraph formatting!!! .

In the mid-1980s, the US, RAF and German Air Force planned to replace the AIM-7 and AIM-9 with newer missiles. The US committed to developing the !!!error: Indecipherable SUB-paragraph formatting!!! to replace the Sparrow, while the UK and Germany would work on the IR missile. The result, though given the identifier !!!error: Indecipherable SUB-paragraph formatting!!! , was not accepted for US service, with the AIM-9X having been developed in the interim.

The AIM-9X integrates a new !!!error: Indecipherable SUB-paragraph formatting!!! seeker and compatibility with helmet mounted displays and targeting, allowing a pilot to simply look at a target, up to 90° off-boresight, and lock-on. The missile also adds an internal cooling system, which eliminates the need for gas bottles on the launching rails, as well as thrust-vectoring controls, which allows the X model to turn tighter than its target. The AIM-9X features a carriage control configuration and has demonstrated Lock-on After Launch ability, which permits internal carriage by stealth aircraft such as the F-22 and F-35.

An AIM-9 being retracted into stowed position in an F-22

Features of the AIM-9X

facw > user314 09/23/2020 at 11:11

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The analog control systems on the original Sidewinder really seem like magic to me, it’s very cool that they were able to make that work in the 1950s. 

user314 > facw 09/23/2020 at 11:31

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The Nazis had working IR seekers during WW2, but they never were able to refine them into a working weapon. 

For Sweden > user314 09/23/2020 at 11:37

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Ah China Lake: When Edwards is not remote enough for you

RamblinRover Luxury-Yacht > user314 09/23/2020 at 12:24

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I’ve always considered the rotating mirror trick to be the essence of the kind of thing patents are for - though obviously patents weren’t a big thing in its case. A simple, elegant solution which still requires trickery to make work - but here’s the key: little enough to be easy to build and stay reliable . Something which is a huge step up on prior art and is the very definition of non-obvious.

I have no doubt the first russkie engineer that figured out what was going on in dissection had a Keanu revelation face for the ages.

Highlander-Datsuns are Forever > For Sweden 09/23/2020 at 14:46

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Edwards isn’t even remote. I mean you have the metropolis of Mojave north and Palmdale to the south.

For Sweden > Highlander-Datsuns are Forever 09/23/2020 at 14:48

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Sure, and China Lake has the cultural center of Ridgecrest

Highlander-Datsuns are Forever > For Sweden 09/23/2020 at 14:55

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I designed the wastewater evaporation lagoons and emergency overflow storage pond at Edwards. T hey built it with 30% conceptual plans, and it actually worked. The highlight of working in the area is watching F22's do circles in the sky for hours on end. 

promoted by the color red > For Sweden 09/24/2020 at 00:19

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Speaking from experience there? ;)

For Sweden > promoted by the color red 09/24/2020 at 00:26

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When you work in Aviation, you have limited duty locations, and Ridgecrest > Seattle