In late October 1958, the plane was officially and formally named "Lightning". in a British aircraft.
Production
The first operational Lightning, designated Lightning F.1, was designed as an interceptor to defend the V Force airfields in conjunction with the "last ditch" Bristol Bloodhound missiles located either at the bomber airfield, e.g. at RAF Marham, or at dedicated missile sites near to the airfield, e.g. at RAF Woodhall Spa near the 3-squadron Vulcan station RAF Coningsby. The bomber airfields along with the dispersal airfields, would be the highest priority targets in the UK for enemy nuclear weapons. To best perform this intercept mission, emphasis was placed on rate-of-climb, acceleration, and speed, rather than range – originally a radius of operation of from the V bomber airfields was specified – and endurance. It was equipped with two 30 mm ADEN cannon in front of the cockpit windscreen and an interchangeable fuselage weapons pack containing either an additional two ADEN cannon, 48 unguided air-to-air rockets, or two de Havilland Firestreak air-to-air missiles. The Ferranti AI.23 onboard radar provided missile guidance and ranging, as well as search and track functions. The A.I.23B radar and Red Top missile offered a forward hemisphere attack capability and deletion of the nose cannon. The new engines and fin made the F.3 the highest performance Lightning yet, but with an even higher fuel consumption and resulting shorter range. The next variant, the Lightning F.6, was already in development, but there was a need for an interim solution to partially address the F.3's shortcomings, the Interim F.Mk6.
thumb|left|Lightning F.3 in flight, 1983
The Interim F.Mk6 introduced two improvements: a new, non-jettisonable, ventral fuel tank, and a new, kinked, conically cambered wing leading edge, incorporating a slightly larger leading edge fuel tank, raising the total usable internal fuel by . The conically cambered wing improved manoeuvrability, especially at higher altitudes, and the ventral tank nearly doubled available fuel. The increased fuel was welcome, but the lack of cannon armament was felt to be a deficiency. It was thought that cannon would be useful in a peacetime interception for firing warning shots to encourage an aircraft to change course or to land.
The Lightning F.6 was originally nearly identical to the F.3A with the exception that it could carry two ferry tanks on pylons over the wings. These tanks were jettisonable in an emergency, and gave the F.6 a substantially improved deployment capability. There remained one glaring shortcoming: the lack of cannon. This was finally rectified in the form of a modified ventral tank with two ADEN cannon mounted in the front. The addition of the cannon and their ammunition decreased the tank's fuel capacity from . Although the F.2A lacked the thrust of the later Lightnings, it had the longest tactical range of all Lightning variants, and was used for low-altitude interception over West Germany.
Export and further developments
The Lightning F.53, otherwise known as the Export Lightning, was developed as a private venture by BAC. While the Lightning had originated as an interception aircraft, this version was to have a multirole capability for quickly interchanging between interception, reconnaissance, and ground-attack duties. The F.53 was based on the F.6 airframe and avionics, including the large ventral fuel tank, cambered wing and overwing pylons for drop tanks of the F.6, but incorporated an additional pair of hardpoints under the outer wing. These hardpoints could be fitted with pylons for air-to-ground weaponry, including two bombs or four SNEB rocket pods each carrying eighteen 68 mm rockets. A gun pack carrying two ADEN cannons and 120 rounds each could replace the forward part of the ventral fuel tank. Alternative, interchangeable packs in the forward fuselage carried two Firestreak missiles, two Red Top missiles, twin retractable launchers for 44× rockets, or a reconnaissance pod fitted with five 70 mm Type 360 Vinten cameras.
BAC also proposed clearing the overwing hardpoints for carriage of weapons as well as drop tanks, with additional Matra JL-100 combined rocket and fuel pods (each containing 18 SNEB rockets and of fuel) or bombs being possible options. This could give a maximum ground attack weapons load for a developed export Lightning of six bombs or 44 × rockets and 144 × 68 mm rockets. The Lightning T.55 was the export two-seat variant; unlike the RAF two-seaters, the T.55 was equipped for combat duties. The T.55 had a very similar fuselage to the T.5, while also using the wing and large ventral tank of the F.6.
In 1963, BAC Warton was working on the preliminary design of a two-seat Lightning development with a variable-geometry wing, based on the Lightning T.5. In addition to the variable-sweep wing, which was to sweepback between 25 degrees and 60 degrees, the proposed design featured an extended ventral pack for greater fuel capacity, an enlarged dorsal fin fairing, an arrestor hook, and a revised inward-retracting undercarriage. The aircraft was designed to be compatible with the Royal Navy's existing aircraft carriers' carrier-based aircraft, the VG Lightning concept was revised into a land-based interceptor intended for the RAF the following year. Various alternative engines to the Avon were suggested, such as the newer Rolls-Royce Spey engine. It is likely that the VG Lightning would have adopted a solid nose (by moving the air inlet to the sides or to upper fuselage) to install a larger, more capable radar. The engines were fed by a single nose inlet (with inlet cone), with the flow split vertically aft of the cockpit, and the nozzles tightly stacked, effectively tucking one engine behind the cockpit. The result was a low frontal area, an efficient inlet, and excellent single-engine handling with no problems of asymmetrical thrust. Because the engines were close together, an uncontained failure of one engine was likely to damage the other. If desired, an engine could be shut down in flight and the remaining engine run at a more efficient power setting which increased range or endurance; although this was rarely done operationally because there would be no hydraulic power if the remaining engine failed.
thumb|left|Lightning F.6 XS904 after a high-speed taxi run at 2012 Cold War Jets Day, Bruntingthorpe
Production aircraft were powered by various models of the Avon engine. This power-plant was initially rated as capable of generating of dry thrust, but when employing the four-stage afterburner this increased to a maximum thrust of . Later models of the Avon featured, in addition to increased thrust, a full-variable reheat arrangement. A special heat-reflecting paint containing gold was used to protect the aircraft's structure from the hot engine casing which could reach temperatures of . Under optimum conditions, a well-equipped maintenance facility took four hours to perform an engine change so specialised ground test rigs were developed to speed up maintenance and remove the need to perform a full ground run of the engine after some maintenance tasks. The stacked engine configuration complicated maintenance work, and the leakage of fluid from the upper engine was a recurring fire hazard. The fire risk was reduced, but not eliminated, following remedial work during development. For removal, the lower No.1 engine was removed from below the aircraft, after removal of the ventral tank and lower fuselage access panels, by lowering the engine down, while the upper No.2 engine was lifted out from above via removable sections in the fuselage top.
The fuselage was tightly packed, leaving no room for fuel tankage or main landing gear. While the notched delta wing lacked the volume of a standard delta wing, each wing contained a fairly conventional three-section main fuel tank and leading-edge tank, holding ; the wing flaps also each contained a fuel tank and an additional was contained in a fuel recuperator, bringing the aircraft's total internal fuel capacity to . The main landing gear was sandwiched outboard of the main tanks and aft of the leading edge tanks, with the flap fuel tanks behind. The long main gear legs retracted toward the wingtip, necessitating an exceptionally thin main tyre inflated to the high pressure of . On landing the No. 1 engine was usually shut down when taxiing to save brake wear, as keeping both engines running at idle power was still sufficient to propel the Lightning to 80 mph if brakes were not used. Dunlop Maxaret anti-lock brakes were fitted.
The Lightning fuel capacity was increased with a conformal ventral fuel tank. A rocket engine pack containing a Napier Double Scorpion engine and of high-test peroxide (HTP) to drive the rocket turbopump, and act as an oxidiser, was planned to be located in place of the ventral tank and would boost performance if non-afterburning engines were fitted. Fuel for the rocket would come from the aircraft fuel supply. The rocket engine option was cancelled in 1958 when it was established that performance with afterburning Avon engines was acceptable. The ventral store was routinely used as an extra fuel tank, holding of usable fuel.
Avionics and systems
thumb|Underside of a Lightning F.3 with undercarriage deployed, 23 June 1979
Early versions of the Lightning were equipped with the Ferranti-developed AI.23 monopulse radar, which was contained right at the front of the fuselage within an inlet cone at the centre of the engine intake. Radar information was displayed on an early head-up display and managed by onboard computers. The AI.23 supported several operational modes, which included autonomous search, automatic target tracking, and ranging for all weapons; the pilot attack sight provided gyroscopically-derived lead angle and backup stadiametric ranging for gun firing.
thumb|left|upright|F.6 cockpit
The cockpit of the Lightning was designed to meet the RAF's OR946 specification for tactical air navigation technology, and thus featured an integrated flight instrument display arrangement, an Elliott Bros (London) Ltd auto-pilot, a master reference gyroscopic reader, an auto-attack system, and an instrument landing system. Despite initial scepticism of the aircraft's centralised detection and warning system, the system proved its merits during the development program and was redeveloped for greater reliability. Communications included UHF and VHF radios and a datalink. Unlike the previous generation of aircraft which used gaseous oxygen for lifesupport, the Lightning employed liquid oxygen-based apparatus for the pilot; cockpit pressurisation and conditioning was maintained through tappings from the engine compressors.
Electricity was provided via a bleed air-driven turbine housed in the rear fuselage, which drove an AC alternator and DC generator. This approach was unusual, since most aircraft used driveshaft-driven generators/alternators for electrical energy. A 28V DC battery provided emergency backup power. Aviation author Kev Darling stated of the Lightning: "Never before had a fighter been so dependent upon electronics". Each engine was equipped with a pair of hydraulic pumps, one of which powered the flight-control systems and the other power for the undercarriage, flaps, and airbrakes. Switchable hydraulic circuits were used for redundancy in the event of a leak or other failure. A combination of Dunlop Maxaret braking parachute slowed the aircraft during landing. A tailhook was also fitted. Accumulators on the wheel brakes performed as backups to the hydraulics, providing minimal braking. Above a certain airspeed a stopped engine would 'windmill', that is, continue to be rotated by air flowing through it in a similar manner to a ram air turbine, sufficient to generate adequate hydraulic power for the powered controls during flight. Plans were mooted to supplement or replace the obsolete Red Top and Firestreak missiles with modern AIM-9L Sidewinder missiles to help rectify some of the obsolescence, but these ambitions were not realised due to lack of funding. An alternative to the modernisation of existing aircraft would have been the development of more advanced variants; a proposed variable-sweep wing Lightning would have likely involved the adoption of a new powerplant and radar and was believed by BAC to significantly increase performance, but ultimately was not pursued.</blockquote>
The Lightning possessed a remarkable climb rate. It was famous for its ability to rapidly rotate from takeoff to climb almost vertically from the runway, though this did not yield the best time-to-altitude. The Lightning's trademark tail-stand manoeuvre exchanged airspeed for altitude; it could slow to near-stall speeds before commencing level flight. The Lightning's optimum climb profile required the use of afterburners during takeoff. Immediately after takeoff, the nose would be lowered for rapid acceleration to IAS before initiating a climb, stabilising at . This would yield a constant climb rate of approximately . Climb techniques and flight profiles were developed to put the Lightning into a suitable attack position. To avoid risking the U-2, the Lightning was not permitted any closer than and could not fly in front of the U-2. For the intercepts, four Lightning F1As conducted 18 solo sorties. The sorties proved that, under GCI, successful intercepts could be made at up to . Due to sensitivity, details of these flights were deliberately avoided in the pilot log books.
In 1984, during a NATO exercise, Flight Lieutenant Mike Hale intercepted a U-2 at a height which they had previously considered safe (thought to be ). Records show that Hale also climbed to in his Lightning F.3 XR749. This was not sustained level flight but a ballistic climb, in which the pilot takes the aircraft to top speed and then puts the aircraft into a climb, exchanging speed for altitude. Hale also participated in time-to-height and acceleration trials against Lockheed F-104 Starfighters from Aalborg. He reports that the Lightnings won all races easily with the exception of the low-level supersonic acceleration, which was a "dead heat". Lightning pilot and Chief Examiner Brian Carroll reported taking a Lightning F.53 up to over Saudi Arabia at which level "Earth curvature was visible and the sky was quite dark", noting that the engines were "touchy" in terms of staying lit in the thin air, and "getting down to a more reasonable and sane altitude needed delicate handling."
Carroll compared the Lightning and the McDonnell Douglas F-15C Eagle, having flown both aircraft, stating that: "Acceleration in both was impressive, you have all seen the Lightning leap away once brakes are released, the Eagle was almost as good, and climb speed was rapidly achieved. Takeoff roll is between , depending upon military or maximum afterburner-powered takeoff. The Lightning was quicker off the ground, reaching height in a horizontal distance of ". Chief test pilot for the Lightning Roland Beamont, who also flew most of the "Century Series" US aircraft, stated his opinion that nothing at that time had the inherent stability, control, and docile handling characteristics of the Lightning throughout the full flight envelope. The turn performance and buffet boundaries of the Lightning were well in advance of anything known to him.
Aircraft performance
The Lightning was a fully aerobatic aircraft.
Early Lightning models, the F.1, F.1A, and F.2, had a maximum speed of at in an ICAO standard atmosphere, and IAS at lower altitudes. Later models, the F.2A, F.3, F.3A, F.6, and F.53, had a maximum speed of at , and speeds up to indicated air speed for "operational necessity only". A Lightning fitted with Avon 200-series engines, a ventral tank, and two Firestreak missiles had a maximum speed of on a standard day; while a Lightning powered by the Avon 300-series engines, a ventral tank and two Red Top missiles had a maximum speed of Mach 2.0. Imposed Mach limits during missile launches ensured adequate directional stability;