Following the flight testing of the Kestrels at Edwards AFB, the armed forces of the UK, Germany, and the USA could find no use for the Kestrel in its current form. That would have probably been the end of the line for the P.1127 project. NATO had been banking on the P.1154 Harrier supersonic VTOL combat aircraft, but this was cancelled on February 2, 1965 before anything could be built. As an alternative, a fully-militarized version of the Kestrel was suggested for the RAF's ground-attack squadrons
Only 17 days after the cancellation of the P.1154, the Ministry of Defence issued Requirement O.R. 356 for a production version of the Kestrel. The production version of the Kestrel was named Harrier, the same name that had been assigned to the abortive P.1154 project. Although it had an outward similarity to the Kestrel, the Harrier was for all practical purposes an entirely new design.
The wing was redesigned yet again, with a thickness chord ratio diminishing from 10 percent at the root to 5 percent at the tip. The sweep at quarter-chord was 34 degrees. It also featured a leading edge dogtooth and increased span, the tips now extending beyond the outrigger wheels. The area was 201 square feet. Two hardpoints were added underneath each wing, capable of accommodating 2000 pounds inboard and 650 pounds outboard. The inboard pylon was capable of accommodating a drop tank for extended range. A midair refuelling probe could be attached above the port engine air intake.
Attachment points were provided on the bottom of the fuselage for strakes or pods for a pair of 30-mm Aden cannon. The pods performed the same role as lift-enhancing strakes, although not quite as efficiently. Each pod weighed 900 pounds and carried 120 rounds of ammunition. The Harrier had an auto stabilization system to ease the pilot's workload during takeoffs and landings. Authority was initially provided only in pitch and roll, but was later provided in yaw as well. The reaction control valves were fitted with shutters that were linked to the appropriate rudder, aileron, or tailplane controls. When the controls are centralized the shutters are closed, but as the surfaces are moved, high pressure bleed air is released in proportion to the deflection. So, when the Harrier is hovering, the control surfaces will be seen to move, although they are completely ineffective at such slow speeds, the maneuvering actually being effect by the RCVs. RCVs.
The Dowty/Rotol undercarriage was beefed up to absorb much more impact by increasing the stroke of the oleo legs. The forward facing nose camera nose camera was replaced by an oblique F.95 camera aiming through an optical flat on the port side of the nose. The Harrier was equipped with a Smiths Industries heads-up display, the first British production military aircraft to be so equipped. A Ferranti navigation/attack system was provided that had an inertial platform which supplies information on position to a latitude/longitude computer that drives a moving map display.
A Martin-Baker Mk 9 zero-zero rocket-powered ejection seat was provided for the pilot. The pilot's cockpit was entirely below the keel of the upper surface of the fuselage, and hence has a poor view to the rear.
The early versions of the Harrier were powered by the Mk 101 Pegasus engine, offering a thrust of 19,000 lb.s.t. It differed from the Pegasus 5 in having an all-titanium fan, two-vane nozzles, and a water injection system. Although they are often shown attached to the engine in display photographs, the nozzles are actually a part of the aircraft and are anchored to the airframe for strength. The nozzles are rotated by dual motors, and it is arranged that if any one of them should jam, the drives to the others are immediately sheared and all four remain in the same position. Extra air for takeoff and low-speed flight is provided by a set of eight blow-in doors on each intake. A bleed-door on the cockpit side of the intake is used to remove the boundary layer, preventing it from reaching the engine. A lot of work went into designing the intake--for a while the earlier Kestrels had intake lips made of inflatable rubber which could be deflated to increase the intake area during low-speed flight.
The Harrier did not have an onboard radar. Instead, the Harrier had a Ferranti FE541 inertial navigation/attack system with a moving map display that showed the position of the aircraft. In addition, the aircraft was provided by a Specto heads-up display. Later production aircraft were fitted with a Ferranti Type 106 laser ranging and target marking system, which was later retrofitted to earlier production machines. The system could be used either autonomously or in conjunction with another designator.
The first of six pre-production Harriers flew for the first time on August 31, 1966. It was the world's first fixed-wing VTOL aircraft to achieve production status. The pre-production machines were powered initially by the Pegasus 5, and were used exclusively for service trials or were retained at the factory.
The first of an initial 60 production Harrier G.R. Mark 1s (XV738) flew on December 28, 1967. The Pegasus 10 (known to the RAF as Mk 102 and to the USMC as F402-RR-400) was introduced on the production line in 1971, the planes being designated Harrier G.R. Mk. 1A. The thrust was 20,500 lb.s.t.
Harriers were delivered to the RAF beginning in 1969. They went first to No. 1 Squadron and No. 233 OCU at Wittering and Nos 3, IV, and 20 Squadrons at Wildenrath, West Germany. Most of the RAF harriers had the ability to carry a port-facing F95 camera for reconnaissance purposes.
The US Marine Corps has an air force with a primary mission of ground support, often under conditions of very limited or nonexistent available airfields. The Marine Corps had shown interest in the Harrier since participating in the American Tri-Service Trials with the Kestrels in 1968. The Marine Corps pilots gave glowing reports of the aircraft's capabilities, and a US Navy test team was sent to Britian to carry out a preliminary evaluation of the Harrier at the 1968 Farnborough air show. Although the US Navy and the American defense establishment in general was reluctant for political reasons to order a foreign-built aircraft, the result of the trip was the placing of an initial order in 1969 for twelve aircraft to be delivered during FY 1971-72. The House of Representatives authorized procurement on September 20, 1969 and the contract for the first 12 was signed on December 23, 1969. The designation was AV-8A (Hawker factory designation was Harrier Mark 50). At the same time, Hawker concluded an agreement with McDonnell Douglas of St. Louis, Missouri for the license production of the Harrier. However, because of the American system of yearly procurement, there were never enough aircraft ordered in a given year to make the opening of a second production line economically feasible and all the USMC AV-8As were built at Kingston.
The first USMC machine (Bu No 158384, the 62nd production single-seat Harrier) was flown for the first time on November 20, 1970. The AV-8A initially had a Pegasus 10 engine, but the Mk 11 engine was introduced on the 11th aircraft and retrofitted to earlier machines. The Pegasus 11 was known by the RAF as Mark 103 (Mk 803 in the export version) and the US designation was F402-RR-402. The RR stood for Rolls Royce, which had bought the Bristol engine division in 1966. The first 59 AV-8As had the FE451 navigation attack system of the RAF version, but the simpler Smiths I/WAC attitude and heading reference system was provided. No LRMTS was fitted. The aircraft was fitted with a Stencel SIIIS-3 zero-zero ejection seat.
The AV-8A retained the Aden cannon of the RAF version. The AV-8A could carry a large number of different weapons loads, including several varieties of free fall and retarded bombs, rocket launchers, and cluster bombs. Sidewinder AAMs could be carried on the outboard underwing points. The first squadron to receive these planes was VMA-513 aboard the USS Guam. Three other squadrons were also formed--VMA-542, VMA-231, and the conversion unit VMAT-203. The accident rate was initially quite high, and the Marines quickly found that helicopter flying experience was not a good thing for a Harrier pilot to have, since it taught him some bad habits. For this reason, the Marines acquired a two-seat Harrier version designated TAV-8A.
Marine Corps pilots experimented with VIFFing (Vectoring In Forward Flight), in which the pilots rotated the nozzles to the 8 degree forward position, producing a rapid deceleration and a nose up attitude, causing a pursuing aircraft to overshoot and perhaps become subject to a missile shot from the Harrier.
47 AV-8As were upgraded to AV-8C standard between 1979 and 1984. They were given structural upgrades designed to increase the airframe lifetime. The AV-8C also received a Litton AN/ALR-45F radar warning receiver with antennae in the wingtip and tailcone. An AN/ALE-39 chaff/flare dispenser was installed in the lower fuselage. An onboard oxygen generation system was provided. New secure radios were provided. and the lift-improvement devices developed for the AV-8B were installed. The AV-8C served alongside the unmodified AV-8As until they were finally withdrawn from service in 1987. The last TAV-8As in USMC service was withdrawn in November of that year.
Serial Numbers of Hawker Siddeley AV-8A Harrier
158384/158395 Hawker Siddeley AV-8A Harrier Harrier Mk 50 purchased by Navy for USMC. C/n 712062/1-712070/9, 712088/10-712090/12. Also had RAF serials XW644/XW655. 158694/158711 Hawker Siddeley AV-8A Harrier Harrier Mk 50 purchased by Navy for USMC. C/n 712091/13-712108/30 158948/158977 Hawker Siddeley AV-8A Harrier Harrier Mk 50 purchased by Navy for USMC. c/n 712109/3-712138/60 159230/159259 Hawker Siddeley AV-8A Harrier Harrier Mk 50 purchased by Navy for USMC. c/n 712139/61-712168/90. 159366/159377 Hawker Siddeley AV-8A Harrier Harrier Mk 50 purchased by Navy for USMC. c/n 712169/91-712175/97, 712176/106, 712177/107, 712178/100, 712179/108, and 712180/102.
Specification of Hawker Siddeley AV-8A Harrier
One Bristol Siddeley Pegasus 103 vectored-thrust turbofan, 21,500 lb.s.t. Fuel capacity was 650 Imp gall in six integral tanks. Performance: Maximum speed 740 mph at sea level, Mach 0.98 at altitude. A maximum speed of Mach 1.3 could be attained in a dive. Maximum ferry range 2340 miles. Initial climb rate 22,500 feet per minute. STO distance at maximum takeoff weight was 350 yards. Service ceiling 51,200 feet. Dimensions: Wingspan 25 feet 2 inches, length 46 feet 10 inches, height 10 feet 3 inches, wing area 201 square feet. Weights: 15,535 pounds empty, maximum takeoff 25,200 pounds. Armament. Two detachable 30-mm Aden cannon pods, with 300 rounds. One centerline and four underwing store pylons. A maximum weapons load of 8000 pounds (5000 pounds in VTOL mode) could be carried .
Sources:
- Hawker Aircraft Since 1920, Francis K. Mason, Naval Institute Press, 1991.
