AIRPASS II
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AIRPASS was a British aircraft interception radar and
fire-control radar A fire-control radar (FCR) is a radar that is designed specifically to provide information (mainly target azimuth, elevation, range and range rate) to a fire-control system in order to direct weapons such that they hit a target. They are someti ...
system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...
developed by
Ferranti Ferranti International PLC or simply Ferranti was a UK-based electrical engineering and equipment firm that operated for over a century, from 1885 until its bankruptcy in 1993. At its peak, Ferranti was a significant player in power grid system ...
. It was the world's first airborne
monopulse radar Monopulse radar is a radar system that uses additional encoding of the radio signal to provide accurate directional information. The name refers to its ability to extract range and direction from a single signal pulse. Monopulse radar avoids prob ...
system and fed data to the world's first
head-up display A head-up display, or heads-up display, also known as a HUD () or head-up guidance system (HGS), is any transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of the name stems from a ...
. The name is an acronym for "Aircraft Interception Radar and Pilot's Attack Sight System". In the
Royal Air Force The Royal Air Force (RAF) is the Air force, air and space force of the United Kingdom, British Overseas Territories and Crown Dependencies. It was formed towards the end of the World War I, First World War on 1 April 1918, on the merger of t ...
(RAF) it was given the official name Radar, Aircraft Interception, Mark 23, normally shortened to AI.23. AIRPASS was used on the English Electric Lightning throughout its lifetime. The basic AIRPASS electronics system was later adapted as the basis for a
terrain-following radar Terrain-following radar (TFR) is a military aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude above ground level and therefore make detection by enemy radar more difficult. It is ...
for navigation and targeting for air-to-ground attacks. 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 Blackburn Buccaneer is a British aircraft carrier, carrier-capable attack aircraft designed in the 1950s for the Royal Navy (RN). Designed and initially produced by Blackburn Aircraft at Brough Aerodrome, Brough, it was later officially k ...
. 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 The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, where it was quickly adopted for many aircraft.


History

Development of the monopulse radar underlying AIRPASS began in 1951 at Ferranti's Ferry Road location in
Edinburgh Edinburgh is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. The city is located in southeast Scotland and is bounded to the north by the Firth of Forth and to the south by the Pentland Hills. Edinburgh ...
. The AIRPASS system was announced to the public in late June 1958. It was initially tested on
Douglas DC-3 The Douglas DC-3 is a propeller-driven airliner manufactured by the Douglas Aircraft Company, which had a lasting effect on the airline industry in the 1930s to 1940s and World War II. It was developed as a larger, improved 14-bed sleeper ...
TS423 (later civilian registered as G-DAKS) and later on an
English Electric Canberra The English Electric Canberra is a British first-generation, jet-powered medium bomber. It was developed by English Electric during the mid- to late 1940s in response to a 1944 Air Ministry requirement for a successor to the wartime de Havilla ...
WJ643 for higher speed trials, replacing the nose sections of these aircraft. After testing use, WJ643 was renamed T.Mk 11 and used as a trainer aircraft for the radar operators of the
Gloster Javelin The Gloster Javelin is a twin-engined all-weather interceptor aircraft designed and produced by the Gloster Aircraft Company. It was operated by the Royal Air Force from the mid-1950s until the late 1960s and was the final aircraft design to b ...
. Several further T.Mk 11 were produced, but these mounted the AI.17 from the Javelin. The first flight on the English Electric Lightning took place on airframe XG312 on 29 December 1958. It was initially linked to the de Havilland Firestreak
air-to-air missile An air-to-air missile (AAM) is a missile fired from an aircraft for the purpose of destroying another aircraft (including unmanned aircraft such as cruise missiles). AAMs are typically powered by one or more rocket motors, usually solid-fuel roc ...
. It introduced the
HOTAS HOTAS, an acronym of hands on throttle-and-stick, is the concept of placing buttons and switches on the throttle lever and flight control stick in an aircraft cockpit. By adopting such an arrangement, pilots are capable of performing all vital ...
(Hands On Throttle-And-Stick) system whereby the radar and gun sight controls were situated on the
control column A yoke, alternatively known as a control wheel or a control column, is a device used for Pilot (aeronautics), piloting some fixed-wing aircraft.Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 563. Aviation Supplies ...
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. The radar entered service with the RAF in 1960 in the English Electric Lightning interceptor. 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 The Blackburn Buccaneer is a British aircraft carrier, carrier-capable attack aircraft designed in the 1950s for the Royal Navy (RN). Designed and initially produced by Blackburn Aircraft at Brough Aerodrome, Brough, it was later officially k ...
.


Design

AIRPASS was based on a
magnetron The cavity magnetron is a high-power vacuum tube used in early radar systems and subsequently in microwave oven, microwave ovens and in linear particle accelerators. A cavity magnetron generates microwaves using the interaction of a stream of ...
source which provided pulses of about 100 kW peak. Pulses were about one microsecond in duration and sent 1000 times a second. To make the system as compact as possible, Ferranti invested in a
numerical control Computer numerical control (CNC) or CNC machining is the automated control of machine tools by a computer. It is an evolution of numerical control (NC), where machine tools are directly managed by data storage media such as punched cards or ...
system to mill the
waveguide A waveguide is a structure that guides waves by restricting the transmission of energy to one direction. Common types of waveguides include acoustic waveguides which direct sound, optical waveguides which direct light, and radio-frequency w ...
s from single blocks of aluminium. The signal was sent and received from feedhorns that were split vertically to produce two outputs, one on either side of the reflector centerline. The reflector was shaped as two partial paraboloids, so that the two signals re-combined in space in front of the aircraft. The entire assembly was mounted on a servo system that allowed the antenna assembly to be pointed in two dimensions. On reception of a pulse, the signal was sent into a
klystron A klystron is a specialized linear-beam vacuum tube, invented in 1937 by American electrical engineers Russell and Sigurd Varian,Pond, Norman H. "The Tube Guys". Russ Cochran, 2008 p.31-40 which is used as an amplifier for high radio frequenci ...
local oscillator In electronics, the term local oscillator (LO) refers to an electronic oscillator when used in conjunction with a Frequency mixer, mixer to change the frequency of a signal. This frequency conversion process, also called Heterodyne, heterodyning ...
and then into two conventional superheterodyne receivers with an
intermediate frequency In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in Transmission (telecommunications), transmission or reception. The intermediate frequency is ...
of 30 MHz. 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. This was accomplished with a highly advanced
automatic gain control Automatic gain control (AGC) is a closed-loop feedback regulating circuit in an amplifier or chain of amplifiers, the purpose of which is to maintain a suitable signal amplitude at its output, despite variation of the signal amplitude at the inpu ...
system with 100 dB range that adjusted the pulse-to-pulse outputs. To this point the system was entirely analogue, using miniaturized
vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...
s cooled by forced air. Behind the analog section was the
analog computer An analog computer or analogue computer is a type of computation machine (computer) that uses physical phenomena such as Electrical network, electrical, Mechanics, mechanical, or Hydraulics, hydraulic quantities behaving according to the math ...
portion of the system. 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. The system also read data from various aircraft systems like the
altimeter An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. Ty ...
and
air speed indicator The airspeed indicator (ASI) or airspeed gauge is a flight instrument indicating the airspeed of an aircraft in kilometres per hour (km/h), knot (unit), knots (kn or kt), miles per hour (MPH) and/or metres per second (m/s). The recommendation by In ...
and combined this into the same display. The result was the world's first
heads-up display A head-up display, or heads-up display, also known as a HUD () or head-up guidance system (HGS), is any see-through display, transparent display that presents data without requiring users to look away from their usual viewpoints. The origin of t ...
, a concept that was soon licensed by US manufacturers. AIRPASS had an average detection range against a
Tupolev Tu-95 The Tupolev Tu-95 (; NATO reporting name: "Bear") is a large, four-engine turboprop-powered strategic bomber and missile platform. Maiden flight, First flown in 1952, the Tu-95 entered service with the Soviet Long Range Aviation, Long-Range Avia ...
"Bear" bomber of about . This was more than enough to allow the Lightning to be directed into the general area of the target through ground controlled interception and then use AIRPASS to hunt it down. Some consideration was given to sending the aircraft into the right area using commands sent from the ground to the aircraft's
autopilot An autopilot is a system used to control the path of a vehicle without requiring constant manual control by a human operator. Autopilots do not replace human operators. Instead, the autopilot assists the operator's control of the vehicle, allow ...
, allowing the pilot to concentrate solely on their radar display, but this project was ultimately cancelled. Later models, the AI.23B, added additional small antennas for S-band reception of signals from ground based radars. This allowed the aircraft to seek out targets with its own radar transmitter turned off. The signal was displayed in A-scope fashion along the bottom of the radar display, which the pilot could use to seek out targets while under ground direction. When a peak of the required height appeared, the pilot would take over the approach and then turn on their own radar when the conditions appeared correct. This allowed the aircraft to make accurate approaches without signalling their presence or inviting jamming from the target. The same system was used in the E/F-band to provide home-on-jam.


AIRPASS II

In the late 1950s, Ferranti won the contract to supply radars for the
Blackburn Buccaneer The Blackburn Buccaneer is a British aircraft carrier, carrier-capable attack aircraft designed in the 1950s for the Royal Navy (RN). Designed and initially produced by Blackburn Aircraft at Brough Aerodrome, Brough, it was later officially k ...
aircraft in
Royal Navy The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
service. This version, AIRPASS II (also known by the rainbow codename ''Blue Parrot''), was modified to handle low-level scanning by eliminating the reflections from waves. Since the waves reflected away much of the signal, to make up for these losses the new version used a more powerful 250 kW transmitter and a larger
Cassegrain antenna In telecommunications and radar, a Cassegrain antenna is a parabolic antenna in which the Antenna feed, feed antenna is mounted at or behind the surface of the concave main parabolic reflector dish and is aimed at a smaller Convex mirror, convex ...
. During tests of the monopulse systems, Ferranti engineers noticed that the systems produced high quality ranging information of ground reflections. Older systems without monopulse processing made the determination of range difficult as the radar returned signals were from the entire beamwidth, meaning that it received signals that were from the ground that was closer and further from the aircraft. Monopulse processing allowed the beam to be discriminated vertically and thus range against a single feature very accurately. The ability of the radar to produce highly accurate range measurements, combined with a system that displayed the resulting data as a map, opened the possibility of producing a
terrain-following radar Terrain-following radar (TFR) is a military aerospace technology that allows a very-low-flying aircraft to automatically maintain a relatively constant altitude above ground level and therefore make detection by enemy radar more difficult. It is ...
guidance system. Ferranti developed this concept extensively through the 1960s, first with their Dakota and Canberra aircraft, and later with the Buccaneer. The idea was simple; the computer calculated a ski-ramp shaped ideal trajectory, flat directly under the aircraft and then sloping upward in a gentle curve. This pattern is rotated to follow the aircraft's velocity vector. The radar scanned in a U-shaped pattern, taking accurate measurements of the altitude and range to objects in front and slightly to either side of the aircraft. The computer compared the range and altitude of objects in the radar to the pre-calculated path, and then rotated the path so that the terrain feature would be overflown at a pre-set altitude between . This was relayed to the pilot as a dot in the heads-up display, and by following the dot the aircraft would attempt to maintain the selected altitude by continually raising or lowering the dot as the terrain moved. The ski-shaped curve was selected to ensure any required manoeuvres were half-gee, lowering loads on the crew. The concept became the basis for the ill-fated BAC TSR-2 project, which used another modified version of the AIRPASS hardware, now extensively
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
ized. As part of a proposal for the
Swiss Air Force The Swiss Air Force (; ; ; ) is the air component of the Swiss Armed Forces, established on 31 July 1914, three days after the outbreak of World War I, as a part of the Swiss Army, army and in October 1936 as an independent service. In peaceti ...
,
Saab AB Saab AB (originally , , acronym SAAB), with subsidiaries collectively known as the Saab Group (), is a Swedish aerospace and defense company, defence company primarily operating from Sweden. The company is headquartered in Stockholm, but its de ...
modified a single
Saab 35 Draken The Saab 35 Draken (; ''The Kite'', ambiguous with ''The Dragon'') is a Swedish interceptor aircraft, fighter-interceptor developed and manufactured by Saab AB, Svenska Aeroplan Aktiebolaget (Saab AB, SAAB) between 1955 and 1974. Development of ...
by replacing its relatively simple radar system with an AIRPASS II radar. This produced the Saab J35H (H for
Helvetia Helvetia () is a national personification of Switzerland, officially , the Swiss Confederation. The allegory is typically pictured in a flowing clothing, with a spear and a shield emblazoned with the Flag of Switzerland, Swiss flag, and commo ...
), but the contract was ultimately won by the Mirage III.


Structure

The radar of AIRPASS I weighed around 90 kg.


See also

*
Radar configurations and types This is a list of different types of radar. Detection and search radars Search radars scan great volumes of space with pulses of short radio waves. They typically scan the volume two to four times a minute. The radio waves are usually less than a ...
* Aircraft interception radar * Ferranti Blue Fox


References


External links

* {{usurped,
APSS
} 1960 establishments in the United Kingdom 1960 in aviation 1960 in military history Ferranti Military radars of the United Kingdom Cold War military equipment of the United Kingdom 1960 in Scotland 1960s in Edinburgh Military equipment introduced in the 1950s Military history of Edinburgh Rainbow code