AV-8B Harrier History

However clean the Harrier's lines may be, the tracing of its lineage is a remarkably complex business. During its life span, the Harrier's parent company has changed names from Hawker to Hawker-Siddeley to British Aerospace, with McDonnell Douglas acquiring stepparent status for the coproduced American AV-8B derivative, a responsibility later passed on to Boeing with that company's acquition of McDonnell Douglas.

The Harrier and its immediate predecessors, the P-1127 and Kestrel, have been known by no less than eight names: The concept that led to the Harrier was initially assigned the Hawker project designation P-1127, under which it flew as a prototype and concept demonstration vehicle. The Kestrel, the ensuing service test version, was named for a species of small European falcon noted for its habit of turning into the wind and hovering over a fixed spot while looking for its prey.

The designation XV-6A was applied to nine Hawker Siddeley (P.1127), Kestrels (FY-Serial: 64-18262 - 64-18270), (RAF Serial: XS688 - XS696), only 7 of which were delivered. Following completion of the operational evaluation in the United Kingdom, six of the Kestrels were shipped to the United States in 1966, designated XV-6As. The designation VZ-12 was applied to a pair of Hawker Siddeley P.1127 (FY-Serial: 62-4507 - 62-4508), which were never delivered.

An improved version, known as the Harrier, became the world's first operational V/STOL fighter when it entered Royal Air Force service in 1969. The definitive Royal Air Force production derivative was named Harrier after a genus of highly maneuverable, low-flying hawks that build their nests on the ground. Sea Harrier was subsequently-and logically-applied to the navalized version. The initial Marine Corps variant was assigned the colorless AV-8A designation.

The Harrier today is one of the truly unique and most widely known of military aircraft. It is unique as the only fixed wing V/STOL aircraft in the free world. It also is unusual in the international nature of its development, which brought the design from the first British P.1127 prototype to the AV-8B Harrier II of today. When the Harrier II was first flown in the fall of 1981, 21 years had elapsed since the original Hawker P.1127 first hovered in untethered flight. This basic design, only one of many promising concepts of the time, has weathered its growing up period and reached maturity in the AV-8B.

Initial US involvement with the Harrier began in 1957 when Hawker's revolutionary design was met with disinterest by the British government and a lack of government funding to proceed into development. By that time, the US had conducted extensive research on numerous competitive concepts for V/STOL flight, including aircraft-tilting (tail sitters), thrust-tilting (tilt rotors), thrust-deflection (deflected slipstream), and dual-propulsion (lift-cruise engines) concepts. The simplicity and elegance of the rotatable nozzle vectored-thrust concept of the P.1127 so impressed NASA Langley management and researchers that a formal agreement for cooperative testing was initiated with Hawker under the Mutual Weapons Development Program of NATO.

Following completion of the operational evaluation in the United Kingdom, six of these Kestrels were shipped to the United States in 1966, designated XV-6As. Here they underwent national trials, including shipboard tests and additional testing of V/STOL fighter techniques. Two subsequently served in a research role with NASA. Within the United States it was a tri-service venture (Army, Navy, Air Force) with the Army functioning as the lead service. However, the final interservice agreement later transferred responsibility for this category of aircraft to the Air Force.

The Hawker-Siddeley Kestrel (XV-6A) was a single-place, prototype, vectored-thrust, V/STOL strikereconnaissance aircraft. A single Rolls Royce Pegasus Mark 5 engine powers the Kestrel. The Pegasus is an axial-flow vectored-thrust turbofan engine with an uninstalled sea-level static thrust rating of 69 000 newtons (15 500 Ib). Thrust is vectored through two pairs of controllable engine exhaust nozzles and is equally distributed between the forward nozzles which exhaust cool air from the fan and the aft nozzles which exhaust turbine air. The nozzles are mechanically interconnected and can be rotated, at rates up to 90°/sec, to any position from fully aft (O: = 0°) to 5° forward of vertically downward (9* = 95° Y Nozzle angle is controlled by a single lever located inboard on the throttle quadrant which is the only additional control required for thrust vectoring in the Kestrel.

Control moments during nonvectored flight are provided by conventional aerodynamic surfaces. The ailerons and tail plane are powered by tandem hydraulic systems; the rudder is unpowered. Lateral control forces are provided by a nonlinear spring unit and longitudinal forces by a q-feel unit supplemented with a feel spring. A bobweight in the control run increases longitudinal maneuvering forces by 8.9 N/g (2 Ib/g), and 4.9 N/rad/sec2 (1.1 Ib/rad/sec2) for pitch acceleration.

During vectored flight, reaction control moments are added to those produced by the normal aerodynamic surfaces. Reaction control shutter valves, located at the nose, tail, and wing tips, are mechanically connected to their corresponding aerodynamic control surface and receive high-pressure engine bleed air as a function of engine nozzle angle. Full reaction control is provided at engine nozzle angles greater than 300. No stability augmentation system (SAS) is provided. However, during flight at low dynamic pressures where the pilot does not get feedback to the control stick from forces on the control surfaces, an artificial-feel system is provided. Lateral feel is provided by a nonlinear spring unit and longitudinal forces are provided by a g-feel unit supplemented with a feel spring.

Analytical and simulator studies of the flight and handling qualities of aircraft require that accurate estimates of the aerodynamic parameters be used if the results are to be valid. One of the more accurate methods of obtaining aerodynamic parameters is from data obtained during flight tests. To provide aerodynamics for analytical and simulator studies, and also to provide numerical values for comparison with wind-tunnel data and theoretical estimates, parameters have been extracted from flight data for many years. Flight-test data were used to extract the longitudinal aerodynamic parameters of the Kestrel aircraft. The aircraft configurations included thrust-jet angles of 0°, 15°, and 30°, and Mach numbers of 0.43, 0.62, and 0.82. The results show that deflecting the thrust past 15° has an effect on the pitching-moment derivatives. Deflecting the thrust downward decreases the longitudinal static stability parameter -Cm and generally decreases the damping-in-pitch parameter -(Cm + Cm .\ for trim normal-force coefficient -Cz 0 values greater than 0.2. The trend toward reduction in the longitudinal stability parameter also had been noted by the pilots during flights of the Kestrel.

While the Kestrel operation trials were being completed and the six aircraft were headed for the United States, the RAF ordered an updated version, the P.1127 (RAF), subsequently given the designation Harrier GR 1. Retaining its basic concept, Hawker-Siddley extensively redesigned the P.1127 for production.

In 1969 the concept was developed of using thrust vectoring on P.1127-type aircraft to enhance the maneuverability of fighters in air combat. Although the application of vectoring in forward flight (VIFF) was fundamentally attractive, considerable engineering concern existed over potential control requirements, stability characteristics, and the physical well being of the engine in such maneuvers. A joint VIFF program between NASA and the Royal Aircraft Establishment was initiated in 1972, and flying in the United Kingdom continued through 1976. Results obtained in flight evaluations against a variety of high-performance adversary aircraft and analyses of evasive maneuvers provided by VIFF against enemy ground-to-air and air-to-air missiles resulted in overwhelming support for VIFF as a valuable tool for the AV-8 pilot.

By the mid-1960s, naval gunfire was increasingly hard to obtain for Marine Corps amphibious landings. The Navy began employing missile-equipped ships and naval air support had decreased as they fielded fewer aircraft with smaller bomb loads. In 1968, during the height of the Vietnam War, Colonels "Tom" Miller and Bud Baker went to England to attend the Farnborough Air Show. While there, they flew the Hawker Siddeley Harrier and returned to the States convinced that they had the answer to the fire support problem. After successfully briefing the Commandant, Colonel Miller became the key man in a campaign to get the aircraft for the Marines. With a mixture of political skill, hard work, and sheer enthusiasm, he overcame the odds and convinced the Navy, the aircraft industry, and Congress that the Harrier was a "must" for the Corps.