Critical to NATO planning is the need to control what is known as the Greenland-Iceland-UK gap-the area of sea through which the surface warships, submarines and maritime patrol aircraft of the Soviet Navy's Northern Fleet must pass in order to reach the North Atlantic. The forces which monitor this vital area are receiving a new boost in capability with the entry into RAF service of the Tornado F.2, the finest interceptor in the world.
Also referred to as the Tornado ADV (Air Defence Variant), it is not an agile dogfighter, but a high-endurance interceptor able to patrol 500nm or more (over 800km) north of the UK, capable of dealing with mass enemy raids at low level in the worst conditions which darkness, bad weather or jamming can create.
Air Staff Target 395, issued in 1971, specified the performance required from the RAF's replacement for the Phantom and Lightning. The most obvious candidate for the task was a new version of the Panavia Tornado IDS strike aircraft. The original operational requirement for the Tornado, drawn up in 1968, contained many parameters which would be useful in an interceptor-good acceleration, climbing performance and specific excess power. As a result, the RAF was able to specify a minimal-change version of the Panavia aircraft. Almost inevitably, the original minimal-change design did not stand the test of time, but the fighter now being delivered to the RAF still has sufficient commonality with the existing IDS version to allow it to be built using the same trinational production facilities.
The new role required a different radar designed for air-interception. This had to be larger than the Texas Instruments set carried by Tornado IDS, and operated at different frequencies. To cope with these changes, the nose of the aircraft had to be I stretched, and a new radome matched to the revised frequencies. When the latter component was designed, engineers replaced the relatively blunt shape used on the IDS with a more elongated design.
The first studies for the Tornado ADV assumed that the Sky Flash missiles could be carried on underwing pylons, but it I soon became obvious that the drag imposed by such a scheme would cut the performance of the new fighter to below that of the Phantoms it was to replace. The obvious solution was to use the semi-flush method of carriage featured by the AIM-7 I Sparrow armament of the Phantom, but; the fuselage of Tornado was too short to accommodate four rounds beneath the 1 belly. To overcome this problem, a further lengthening of the forward fuselage was needed. A new fuselage section was inserted just aft of the cockpit, a move which allowed the aircraft's internal fuel capacity to be increased by fully 10 per cent.
Before giving the go-ahead for development to begin, the MoD looked at alternative US designs. The F-14 probably came closest to what the RAF wanted; the F-15 offered attractive flight performance, but it was felt that its radar and single-seat cockpit were not able to meet the requirements of all-weather combat in the face of heavy ECM.
Three prototypes were built, with the first flying in October 1979. Flight trials went smoothly, and the first production aircraft were handed over to the RAF in the spring of 1984. An eventual fleet of 165 is planned, some of which will be dual-control trainers.
The stretching of the fuselage by a total of 4ft 5in (1.36m) to create space for the new radar and semi-flush-mounted missile armament forced other minor structural modifications. Since the aircraft's centre of gravity had been moved forward, the centre of pressure had to be moved to compensate. The sweep angle on the wing inboard fixed section was therefore increased, and the Kruger flap installed in this location on the IDS was deleted.
Wing sweep and flap/slat position are varied automatically by the flight-control system to match the aircraft's angle of attack. Four basic angles of wing sweep are normally used: 25deg at speeds of up to Mach 0.73, 45deg up to Mach 0.88, 58deg to Mach 0.9 and 67deg at higher speed. Flaps and slats are available only at 25deg, slats alone at 45deg. At all greater angles, slats and flaps are retracted.
The ADV will rely on tanker support to extend its range and endurance, but cannot afford the drag penalty of the bolt-on flight refuelling probe used on the IDS. A neat retractable probe was devised, and fitted in the port side of the forward fuselage.
When the Tornado was designed, no off-the-shelf European powerplant was available. Buying American powerplants was rejected, so the three nations were forced to mate a new engine with a new airframe-often a recipe for problems.
Early production aircraft are being delivered with the RB.199 Mk 103 turbofan fitted to the Tornado IDS, but the interceptor role requires more thrust, particularly at altitude. Turbo-Union has devised an uprated Mk 104 version of the engine. This has an afterburner extended by around 14in (36cm), giving up to 7 per cent more thrust than Mk 103 but having a slightly improved specific fuel consumption in afterburner.
Another feature of the Mk 104 is a digital engine control unit (DECU). A replacement for the current analogue mechanical system, this will give better control over the engine, be more reliable, and incorporate built-in test equipment. The new engine will be introduced on the production line in 1985, and will probably be retrofitted to earlier examples, while a further-developed RB.199 variant is already under study. Demonstration engines offering a 35 per cent increase in thrust have already been run, and some of this technology could find its way into a future ADV powerplant.
The RB199 is in the same thrust class as the US 179 turbojet and its F404 turbofan replacement. The veteran J79 is 208in (530cm) long and weighs 3,847lb (1,745kg). The use of modern technology on the later F404 brought the length of that engine down to 159in (403cm) and the weight to around 2,000lb (908kg). The Turbo-Union design team produced an even more compact engine only 127in (323cm) long, and managed to shave the weight down to l,980lb (900kg). The initial service model was the Mk 101, which developed around 8,000lb (3,630kg) of dry thrust and more than 15,800lb (7,167kg) with afterburner.
The engine's compact lines are largely a result of the use of three shafts, each of which is free to rotate at the speed best suited to the section of the engine mounted on it. The outer shaft carries the three-stage LP fan and is driven by a two-stage turbine, while the intermediate shaft rotates in the opposite direction and carries a three-stage compressor and single-stage turbine.
The inner shaft rotates in the same direction as the outer, and has a six-stage compressor whose final stages are made from heat-resistant alloy rather than the titanium used for the earlier stages and the blades of the IP compressor and LP fan. The HP shaft is driven by a single-stage turbine able to withstand the 1,327 deg С gas from the annular combustion chamber.
The afterburner is very compact, having no section in which core gas and bypass air may mix-the two are burned concurrently. At the aft end are located the variable-area nozzle and twin-bucket thrust reverser.
Items of avionics not required for the air-defence mission were removed from the aircraft, while other units were either modified for the new role or replaced by new equipment. The Texas Instruments terrain following/ground mapping set was replaced by the Marconi Avionics AI.24, often referred to as Foxhunter. This is a coherent pulse-Doppler set using frequency-modulated interrupted continuous-wave (FMICW) modulation. A high PRF is available for use against head-on targets; a low-PRF for tail-chase interceptions, short-range combat and navigational ground mapping. Maximum detection range .is around lOOnm (185km), and track-while-scan facilities are provided for an unspecified number of targets, reported to be between 12 and 20.
Much attention had been given to maximising resistance to ECM. The radar antenna is of conventional inverse-Casse-grain type rather than the currently-fashionable planar array. The older technology gives more consistent performance over a wide range of frequencies, and has lower sidelobes (unwanted secondary "beams" which may be exploited by a hostile ECM system). Digital signal processing techniques were used to create a fast frequency analyser and correlator able to prepare spectra of all received signals, filtering out wanted target returns from natural interference such as clutter and man-made interference resulting from jamming.
AI.24 is an active radar system, but on occasions when the Tornado may not want to emit tell-tale radar transmissions which might alert its victim, or if the target is emitting a powerful jamming signal which makes radar-guided attacks difficult, the crew may rely on data from the Marconi Space and Defence Systems Hermes radar homing and warning receiver.
Other new items of equipment include a new HUD, Cossor IFF interrogator, Singer Kearfott secure data link, a second Ferran-ti FIN 1010 inertial platform, and a Smiths Industries/Computing Devices missile-management system. In the longer term the aircraft will be fitted with the planned NATO Identification System being developed to replace the current IFF system.
Additional avionics mean additional heat to be dissipated, so the ADV is fitted with an extra heat-exchanger to cope with the thermal load imposed by the radar.
Existing equipment modified for use on the ADV includes the autopilot, triplex command stability augmentation system, and computer (increased from 32K of memory to 64K, with 128K planned for the long-term). One planned item of avionics which has been shelved for the moment is a long-range electro-optical viewing system for target identification. This was to have been installed in a retractable mounting just ahead of the canopy. The RAF still has a requirement for this equipment, and the main reason for its elimination was probably a need to trim costs.
Tornado IDS carries a pair of 27mm Mauser cannon, but studies of likely ADV operations suggested that a single cannon would be acceptable for the new role. One of the Mausers was duly deleted, freeing internal space for other systems.
For short-range combat the ADV carries AIM-9L Sidewinders. The original armament scheme called for these to be carried on the outboard pylons, but one change introduced during development was the addition of an extra pair of AIM-9s on the inboard wing pylons. AIM-9L will eventually be replaced by the planned ASRAAM.
The current long-range weapon is the BAeD Sky Flash originally fielded on the RAF's Spey-powered Phantoms and now being further developed for use on Tornado ADV. The missile is currently powered by a Sparrow-style rocket motor, and coasts to the target after an initial boost.
An improved motor incorporates a sus-tainer section which will improve performance against high-flying targets. A thermal battery will replace the current built-in generator, reducing pre-launch warm-up time.
Sky Flash is carried on a new pattern of launcher developed by Frazer-Nash. This is the first launcher able to fire missiles at any point in the launch aircraft flight envelope, a feat made possible by pyro-technically actuated rams which apply a force of up to 4 tons to the round, forcing it away from the fuselage and through the airflow around the aircraft.
In the late 1980s the Tornado ADV will be retrofitted with the Hughes AIM-120 AMRAAM "fire-and-forget" missile. This modification will involve the installation of new missile launchers-also being developed by Frazer-Nash-and the addition of a US-style 1553 digital data bus to the avionics suite of the aircraft.
Tornado F.2 shares most of the fine flying qualities of the IDS version, but adds one or two extra features of its own. Thanks to the use of a system known as SPILS (Spin Prevention and Incidence Limiting System), the pilot is free to demand maximum deflection of the aircraft's control surfaces without the risk of spinning or stalling. The only limit on manoeuvring then becomes the g limits on the aircraft and its crew.
The aircraft has already been flown to Mach 2.16 at height and 800kt (l,480km/h) indicated airspeed. Given a normal weapon and fuel load, it can get airborne in only 2,500ft (760m), while the touchdown speed of only 115kt (213km/h) allows the aircraft to land with a roll of just over 1,200ft (370m).
A typical combat air patrol might involve a two-hour loiter on station 300 to 400nm (550 to 750km) from base, with sufficient fuel for 10 minutes of combat. The capacity of the underwing drop tanks was increased from 396 to 660 US gall (1,500 to 2,500 litres) during development, in order to extend range and endurance.
Performance will be significantly increased when the Mk 104 engine enters service. The SEP of the aircraft will be improved by 15 per cent, time-to-intercept will be cut by 10 per cent, and sustained turn rate will icrease.
Most results of F.2 flight testing are still under security wraps, but early in 1984 Flight International pilot Joey Gough (a former Lightning 'driver') was allowed to fly the second prototype and tell the story. He found the aircraft easy to fly and was entranced by it's manoeuvrability-"the most exciting thing about the F.2 is that its manoeuvrability can be fully utilised without any heart-stopping moments. It out-accelerates the Lightning. I am told it out-scissors a Hunter. If the combat simulator is anything to go by, its ability to defeat the F-4 is as predictable as everything else about the Tornado F.2."
At one point in the flight, BAe F.2 project test pilot Peter Gordon-Johnson flew the aircraft in a 4g 360deg turn directly over the airfield, a manoeuvre which barely exceeded the field boundaries. The ADV may not have the agility of the dedicated "dogfighters", but it clearly has the ability to outmanoeuvre virtually everything else.