This took the outputs from the radar system, calculated the proper intercept course based on the selected weapon, and presented the results in the reflector gunsight mechanism. īehind the analog section was the analog computer portion of the system. To this point the system was entirely analogue, using miniaturized vacuum tubes cooled by forced air. This was accomplished with a highly advanced automatic gain control system with 100 dB range that adjusted the pulse-to-pulse outputs. The monopulse technique requires the signals from the two channels to be compared in strength, so the output of the amplifiers must be precisely matched. On reception of a pulse, the signal was sent into a klystron local oscillator and then into two conventional superheterodyne receivers with an intermediate frequency of 30 MHz. The entire assembly was mounted on a servo system that allowed the antenna assembly to be pointed in two dimensions. The reflector was shaped as two partial paraboloids, so that the two signals re-combined in space in front of the aircraft. The signal was sent and received from feedhorns that were split vertically to produce two outputs, one on either side of the reflector centerline. To make the system as compact as possible, Ferranti invested in a numerical control system to mill the waveguides from single blocks of aluminium. Pulses were about one microsecond in duration and sent 1000 times a second. The next version of the system was called AIRPASS II, or " Blue Parrot", and was a system optimised for use at low-level and originally developed for the cancelled BAC TSR.2 and subsequently used in the Blackburn Buccaneer.ĪIRPASS was based on a magnetron source which provided pulses of about 100 kW peak. The radar entered service with the RAF in 1960 in the English Electric Lightning interceptor. It introduced the HOTAS (Hands On Throttle-And-Stick) system whereby the radar and gun sight controls were situated on the control column and throttle lever instead of elsewhere in the cockpit, eliminating the need for the pilot to take his hands off the controls while making an interception. AIRPASS was developed by Ferranti Ltd on Ferry Road in Edinburgh. It was initially linked to the de Havilland Firestreak air-to-air missile. It entered service on interceptor aircraft from the early 1960s.
The first flight on the English Electric Lightning took place on airframe XJ312 on 29 December 1958. Several further T.Mk 11 were produced, but these mounted the AI.17 from the Javelin. After testing use, WJ643 was renamed T.Mk 11 and used as a trainer aircraft for the radar operators of the Gloster Javelin. It was initially tested on Douglas DC-3 TS423 (later civilian registered as G-DAKS) and later on an English Electric Canberra WJ643 for higher speed trials, replacing the nose sections of these aircraft.
The AIRPASS system was announced to the public in late June 1958. Elements of the AIRPASS design were used on many subsequent radars from Ferranti, while its head-up display was licensed for use in the United States where it was quickly adopted for many aircraft.ĭevelopment of the monopulse radar underlying AIRPASS began in 1951. This AIRPASS II was originally intended for the BAC TSR.2, but when that aircraft was cancelled in 1965, it was subsequently used in the Blackburn Buccaneer. The basic AIRPASS electronics system was later adapted as the basis for a terrain following radar for navigation and targeting for air-to-ground attacks. AIRPASS was used on the English Electric Lightning throughout its lifetime. In the Royal Air Force (RAF) it was given the official name Radar, Airborne Interception, Mark 23, normally shortened to AI.23. The name is an acronym for "Airborne Interception Radar and Pilot's Attack Sight System". It was the world's first airborne monopulse radar system and fed data to the world's first head-up display. The AIRPASS radar sat within the air intake of the Lightning, serving double duty as a shock cone.ĪIRPASS was a British airborne interception radar and fire-control radar system developed by Ferranti.
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