Everyone knows the analogy of the whistling train rushing through a station to illustrate the Doppler effect, the apparent shift of frequency of a wave motion if the source is moving with respect to the observer. Doppler naturally applies to radar. If a fighter detects another aircraft coming head-on, the received signals from the target will have a frequency higher than the true frequency of the fighter’s radar; similarly, the frequency will be reduced if the two aircraft are moving apart. This shift in frequency can be used to separate a target return from a background of clutter. In most traditional-type interceptions there is little clutter, except that caused by chaff or heavy rain, but today non-stealth attacking aircraft would invariably penetrate hostile territory at treetop height to try to get under the defending radar coverage. A fighter would therefore see them from above, against the Earth’s surface. Except in stark mountain or desert areas, the Earth’s surface is moving: sea waves, trees and even grass are constantly in motion, causing clutter that shows as interference on the radar display. The fighter’s radar is itself moving with respect to the Earth.
With a PD (pulse Doppler) radar the received RF signal is processed by mixers and bandpass filters that cleverly eliminate everything except targets of real interest. (The reader will note that targets may be flying in such a way that the radial distance from the fighter is constant, i.e. they seem to have no relative speed; they too can be distinguished, but it needs radars with very small ‘sidelobes’ and other advanced features.) The returns from these real targets are converted into streams of digital pulses which are fed to a computer and thence to the pilot’s display. On the latter, nothing appears except real targets and inserted information. Instead of being a mere CRT, the modern display is a synthetic picture made up of target spots and pictures, sightlines, impact points, velocity vectors, markers, range scales and a host of alphanumeric information.
Some of the most challenging radar problems of all are met with ‘overland downlook radar’ of this type, especially those having power to search beyond the visual horizon out to a radius of about 245 miles. Such a radar is fitted to the AWACS (Airborne Warning And Control System), the aircraft platform being the Boeing E-3 Sentry. This can pick out hedgehopping aircraft coming head-on, trying to protect themselves with every hostile ruse, even though the signal pulses have to travel for scores of miles right along the surface of the Earth. Only a few years ago this would have been quite impossible. AWACS and the Russian Il-78 are airborne stations which, among other things, serve as the main GCI directors for all modern fighters in the same airspace. Of course, there is no need to talk, because all data and even radar pictures are transmitted from computer to computer across perhaps 150 miles of airspace by high-speed digital links. Thus, today’s fighter may well know precisely what is coming long before any target gets within the range of its own radar.
As for software control, this simply means the control by digital computer I have been describing. The computer has to be digital, small, fast and completely reliable. As in many fields, the compact digital computer has revolutionized airborne radar (we no longer talk about ‘AI’).
To a considerable degree today’s radar is designed as a collection of standard modules, each equipped with automatic fault diagnosis, and capable of being pulled from its racking and replaced in about two minutes by a man at an Arctic base wearing fur mitts. The actual collection of modules assembled into the fighter depends on what the customer wants and can pay for. Even then the characteristics can be grossly changed, either with a screwdriver or on pilot command, by the software programmed into the computer. The computer can change the p.r.f. (pulse-repetition frequency) or the wavelength; it can change the characteristics of the signal or the pulses; it can change basic parameters according to flight-test results or different kinds of expected targets; it can change the radar ‘signature’ (how the radar’s emissions look to an enemy) between peace and war, or even hour by hour, to defeat hostile intelligence (electronic intelligence, or Elint) or countermeasures.
Countermeasures is a gigantic subject today, but it still embraces passive jammers such as chaff (which is now automatically cut to length on board the ECM aircraft or fighter by a system that listens to the hostile radars and sizes the chaff to match it) and plain noise jammers which blot out the hostile radar frequencies. One obvious way of making the noise-jammer’s life more difficult is to work your own fighter radar on changing frequencies. Modern magnetrons and TWTs (travelling-wave tubes, another potent source of microwaves) can operate over a frequency spread of more than 1 GHz, instead of being tuned exactly to a central frequency. It is possible in modern software-controlled radars, if they are switched out of the PD mode, to make their operating frequency vary rapidly and seemingly randomly all over the available range. Thus a hostile jammer has to jam on all these frequencies, so instead of using a small transmitter he needs something coupled to the National Grid. All fighters, of course, carry simple dispensers for chaff, flares or active RF-jammer payloads, and most also have passive warning receivers on the fin and many other ECM systems.
Typical of the best Western practice of the 1970 period is the F-15 Eagle. This big twin-engined aircraft was designed by a team at St Louis which still thought of itself as McDonnell, creator of the Phantom, but which in 1966 had become McDonnell Douglas. Most of them were shocked to find themselves in August 1997 part of Boeing; thus, today it is the Boeing F-15. When it was being planned, a popular slogan in USAF corridors of power was ‘Not a pound for air-to-ground!’. This meant that the F-15 was to be absolutely uncompromised as an air-combat fighter, with no thought of carrying bombs or similar uncouth stores. Of course, the winds of fashion often reverse direction, and before long the F-15E was in production, with a maximum bomb load of 24,500 lb!
From the outset, the F-15’s avionics were ‘state of the art’. The original radar was the Hughes APG-63, with a flat-plate mechanically driven scanner (such scanners are discussed later). The basic ECM system, the Loral ALR-56, was based on low-band and high-band tuners fed by a blade aerial and by small spiral receiver aerials on the tips of the wings and vertical tails to give all-round coverage. It served several functions, the most crucial being to warn the pilot if his aircraft was being illuminated by a hostile radar. It also provided steering directions for the ALQ-135 internal jamming system. ‘Internal’ does not mean the system jams the fighter’s own systems, but that the equipment is an integral part of the aircraft, not contained in an external pod.
This was typical of the EW (electronic-warfare) suites fitted to fighters of the 1970s. At least, such equipment was fitted to the fighters of most countries. In Britain the purse-strings were clamped so tightly by the Treasury that most British warplanes were worse equipped than they had been back in the Second World War. When, in April 1982, a task force had to be assembled to retake the Falkland Islands from the Argentine invaders, the last Fleet carrier had been withdrawn and there was no seagoing airpower except for Harriers and helicopters. With no sense of urgency, British Aerospace was delivering Sea Harriers, which had some air-combat capability. Suddenly, these aircraft were seen as absolutely crucial. It was then discovered that no money had been voted to equip them with any electronic-warfare system. Harriers and Sea Harriers went into action with bundles of chaff jammed under the airbrake; thus, to release chaff, the pilot had to open the airbrake just at the time when he wanted maximum performance! Frantic orders for chaff and flare cartridge dispensers were placed with the American Tracor company, to bring the Harriers and Sea Harriers almost half-way to the standard of fighters in other countries.
In the 1950s the Moscow-based Central Aero and Hydrodynamics Institute (CAHI, often rendered as TsAGI) had refined a configuration for Mach-2 aircraft with a triangular delta wing and swept tailplanes. This shape was used by Mikoyan for the MiG-21 family, and by Sukhoi for the significantly larger Su-9 all-weather interceptor. By 1962 this had been developed into the Su-11, with a more powerful radar and better missiles. By this time the Sukhoi bureau was working on a much more powerful twin-engined design, the T-58, which matured as the Su-15. Production aircraft followed the Yak-28P at Novosibirsk, the final batches being of the Su-15TM version with R13-300 engines, later radar and additional weapon options including externally hung UPK-23-250 gun pods. Called ‘Flagon’ by NATO, these attractive aircraft had a wing extended in span to just over 30 feet, but a fuselage no less than 69 feet long. They achieved the rare distinction of shooting down unidentified targets that turned out to be civil airliners that had strayed far from their authorised track: a 707 on 20 April 1978 and a 747 on 1 September 1983, both of Korean Air Lines.
In 1966 PVO regiments began receiving the biggest fighter in history. The sheer size of the Soviet Union made it almost impossible to defend against the multiple threats from USAF Strategic Air Command, partnered by US Navy carriers on which were A-3 Skywarriors carrying nuclear weapons. Thus, defence had to be provided even along the 15,000 km northern frontier. The job called for big aircraft with big radar and big missiles. For a start, in January 1958 work began on Kompleks K-80, which included the RLS Smerch (waterspout) radar and PR-S-80 sighting system. Biesnovat worked on the K-80S missiles, which in production became the R-4. Cutting a long story short, the aircraft part of the system was the Tupolev Tu-128. Prototypes puzzled the West, which called them ‘Fiddler’. Powered by two AL-7F engines, the mighty interceptor could reach over 1,200 mph, Mach 1.96, even though it was almost 100 feet long (the upgraded Tu-128M just exceeded 100 ft) and carried four giant missiles externally. Factory 18 at Voronezh delivered 189 of the initial version, plus eleven trainers with stepped cockpits.
The threats from Strategic Air Command continued to escalate. According to legend, Artyom Mikoyan, who had previously concentrated on quite small fighters, was instantly impressed by the (secret) intelligence on the North American project which became the A-5 Vigilante. He liked the broad box-like fuselage with sharp supersonic inlets to the two engines, high-mounted thin wing with sweep replaced by leading-edge taper, and (an innovation) twin vertical tails. In late 1959 he authorized project design of a similar aircraft, with the range of the Tu-128 but greater speed and altitude. He calculated that two R-15B engines would give a speed of 3,000 km/h (Mach 3, 1,864 mph) and a sustained ceiling of 26 km (85,300 ft).
While Britain was regretting that the primitive Lightning had already reached a stage where it would be difficult to cancel, but certainly was not going to be permitted a steerable nosewheel, the Soviet Aviation Ministry urged development of a series of Ye-155 prototypes, which began flight-testing from 6 March 1964. The first to fly was actually the Ye-155R-1, to lead to a reconnaissance aircraft, the MiG-25R. The Ye-155P-1 first flew on 9 September 1964, leading to production of the MiG-25P interceptor. These amazing aircraft were to sustain the biggest development programme in history, leading to forty-nine versions, of which thirty-three flew and more than twenty entered service. Production of the two basic subfamilies, the MiG-25P and the MiG-25R reconnaissance aircraft, amounted to 1,186, all from the enormous Factory 21 at Gorkiy (today called Nizhni-Novgorod).
Apart from the SR-71 ‘Blackbird’, a specialized unarmed reconnaissance aircraft, no other country had aircraft with anything even approaching the speed/altitude/range capability of the MiG-25. The United States decided against offering a bribe to the first MiG-25 pilot to defect, so it was with astonished delight that a team of US experts arrived at Hakodate airbase in Japan to examine a MiG-25P which had been flown there (undetected by Japanese defences) by a defecting PVO pilot on 6 September 1976. This event spurred development on the next generation, which had been launched in 1968 when the Council of Ministers ordered Mikoyan to build the Ye-155M.
The Mikoyan experimental factory built two prototypes, called Izdeliye (product) 83. Aircraft 831 began flight testing on 16 September 1975, and the fully equipped 832 followed in May 1976. These led to the production at the Gorkiy factory of 500 MiG-31s. At first glance a MiG-31 might be mistaken for a MiG-25, but in fact in order to find common parts one has to come down to the level of rivets and pipe-joints. It would be inappropriate here to list all the equipment carried by even the original MiG-31, prior to ongoing upgrades, but in my book on MiG aircraft I list thirty-three different items of fire-control and navigation electronics. The biggest item is the SBI-16 Zaslon (barrier) multimode radar, which has electronic scanning and can track ten targets simultaneously while guiding four R-33 missiles against those posing the greatest threat. On-board computers and secure data transmitters can link a finger-four formation to defend a front 900 km (560 miles) wide, the outer members of the formation being 600 km (373 miles) apart. In 1990 the MiG-31 was replaced in production by the MiG-31B, with improved avionics and R-33S missiles, but the largely redesigned MiG-31M came after the collapse of the Soviet Union and was never funded.
To round off the former Soviet scene, in the late 1960s design began on two engines for a future generation of fighters. As before, MiG was (at this stage only verbally) tasked with a smaller aircraft and Sukhoi with a larger edition. By 1974 both the new engines were on test. The Klimov RD-33 and Lyul’ka AL-31 are turbofans with large afterburners and advanced variable nozzles. Each of the new fighters was planned around two of the new engines mounted wide apart in a broad fuselage that merged imperceptibly into a broad wing tapered on the leading edge. A vertical tail was mounted above each engine, while a snake-like forward fuselage projected ahead from between the engine inlets. In partnership with the Central Aero and Hydrodynamics Institute, this shape was refined until it was perfect.
As in the 1950s, Sukhoi was assigned the bigger aircraft. The T-10-1 prototype flew before the first MiG, on 20 May 1977. Powered by AL-21F-3 engines, almost identical to those of later Tu-128s, it was impressive, but as testing of later T-10s progressed they ran into severe and sometimes fatal problems. Some redesign was necessary, and General Designer Simonov told the author, ‘In the end, we managed to retain the main wheels and ejection seat’ (he was not really joking). What followed, starting with the T-10S, became the Su-27, perhaps the most beautiful, and certainly most impressive, fighter ever built. When it appeared, Western analysts predictably wrote things like, ‘A cross between the F-15 and F/A-18’. Simonov said, ‘You can’t win if you just copy.’ Once Western pilots were allowed to fly the Su-27 one heard comments like ‘What an airplane! If only I could afford to buy one.’ Most production versions have the outstanding AL-31F engine, which among other things can tolerate having its inlet rotate nose-up through up to 135° in what is called the Cobra manoeuvre (which no Western fighter has yet been able to do). Later Su-27 versions, including the Su-30, 33, 35 and 37 (note, not the S-37), have later engine versions, some of which have a fully vectoring engine nozzle, and in many cases canard foreplanes. Virtually all production today is for export, though small numbers of naval and land-based bomber versions have been delivered, and advanced variants are being produced under licence in China and India.
In terms of numbers, the smaller rival MiG has done ever better. First flown as the ‘901’ on 6 October 1977, virtually no redesign was needed and production aircraft were delivered from 1982. The initial production version, called Izdellye (product) 9-12 for the Soviet Union, 9-12A for the Warsaw Pact countries and 9-12B for export, is much better known as the MiG-29. For some reason NATO gives it an extra name, ‘Fulcrum’. There have since been almost twenty versions, all similar externally apart from some later variants having canards, like certain Su-27 derivatives. Crippling lack of money meant that the Russian Air Force could no longer buy fighters after the 1980s, and production of MiG-29s tapered off in the early 1990s with a large number of aircraft not quite finished. Fortunately for what is now the MiG Aviation Scientific/Industrial Complex, many air forces (thirty at the most recent count) have enabled these aircraft to be completed, and have also bought used MiG-29s. This brought the number of completions by 1997 to 1,257. Since then the only immediate prospect of new construction has rested on Indian Navy adoption of the MiG-29K carrier-based version.
Income from these sales enabled MiG to design and build a single example of a supposed next-generation aircraft, the impressive 1.44, also known as the MFI. This big aircraft, with both foreplanes and tailplanes and with a huge chin inlet feeding two of Viktor Chepkin’s superb AL-41 engines, made two flights in early 2000. Slightly less strapped for cash, Sukhoi conducted an extended test programme with the even more astonishing black-painted Su-47 (originally, confusingly designated S-37) Berkut (eagle), which has a forward-swept wing and two D-30F6M engines almost identical to those of the MiG-31. An extended test programme with this aircraft has helped underpin the only funded programme for a new Russian fighter, the Sukhoi LFS (light frontal aeroplane). Possibly to fly in 2005, this will be powered by two AL-41F engines, and have a predictably outstanding suite of electronics.
Turning now to the USA, in April 1972 the US Air Force picked General Dynamics and Northrop to build prototypes, respectively called YF-16 and YF-17, of an LWF, standing for Lightweight Fighter. Restyled ACF, for Air Combat Fighter, the F-16 was selected. At a USAF briefing, the author was told, ‘It’s an exercise in seeing what can be done using one F100 engine instead of two. We expect our allies will buy it, but there’s no question of it becoming an important type in the Air Force inventory – why buy a Volkswagen when you can have a Cadillac [the speaker meant the F-15]?’ Allies did indeed buy it, starting with 306 aircraft for Belgium, Denmark, the Netherlands and Norway. By the end of the twentieth century they had been joined by sixteen other countries, but what the 1975 spokesman would have found amazing is that, of the current total of 4,347 F-16s, no fewer than 2,230 are for the USAF, plus another twenty-six for the Navy!
The loser in the ACF competition was the Northrop YF-17, which differed in having two engines. In a unique about-face, this was metamorphosed into the F/A-18 Hornet for the US Navy, a McDonnell Douglas aeroplane with Northrop reduced to the role of mere forty-per cent associate contractor. Compared with the F-17, the F/A-18 was marginally bigger, and had a stronger and heavier airframe suitable for carrier operation. Unlike the F-16, the Hornet had a large multimode radar, the Hughes APG-65, and thus could be armed with big medium-range missiles such as Sparrow and later the AIM-120 Amraam. While McDonnell Douglas got on with the US Navy order, Northrop tried to sell a simpler version, 2,600 lb lighter, and with significantly higher performance and anything up to double the payload/range. To its astonishment, all the export customers (who had to go to McDonnell Douglas, not Northrop) chose to buy the heavier and supposedly inferior carrier-based version, even though they were going to operate from airfields. The situation led to an unprecedented lawsuit between the two partners. This led to the F/A-18 becoming an all-McDonnell Douglas product. By 1996 the original F/A-18 versions had been developed into the F/A-18E/F Super Hornet, which is more of an upgrade than it looks. But Boeing had the last laugh; in 1997 it bought McDonnell Douglas.
By the 1970s the technology of what was officially called LO (low observables), but became better known as ‘stealth’, appeared likely to revolutionize the whole of warfare. Few commentators recalled that in 1936 Watson-Watt had pointed out how important it would be in future for all weapons, even small ones, to be designed to minimize their signature on hostile radars. Certainly nobody cared to offer an explanation of why this advice had been ignored, and then regarded as if it were something new. Cutting a long story short, the LO technology was first put to use in a dedicated attack aircraft, the F-117 Nighthawk. Astonishingly, the even more stealthy Navy counterpart, the A-12A Avenger II, was cancelled in 1991, so in the twenty-first century the Navy/Marines still fly the venerable A-6.