Air University Review, September-October 1982
If aircraft possess a lineage like racehorses, then the British Aerospace Harrier is a thoroughbred. To those attuned to such things, the fine hand of Sir Sydney Camm, chief designer of the Hawker Hurricane of Battle of Britain fame, is apparent in the Harrier’s every line. Nor should this be a surprise: a distinct family resemblance is evident in the long line of famous Camm-inspired Hawker fighter designs, extending through the graceful Hunter, the Tempest, Typhoon, and Hurricane of World War II, all the way back to the elegant Fury of the 1930s, the fastest operational biplane fighter ever built.
But 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 recently acquiring stepparent status for the coproduced American AV-8B derivative. The Harrier and its immediate predecessors, the P-1127 and Kestrel, have been known by no less than six 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 Kestrel also received the United States military designation XV-6A. 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 formal tracing of names, however, may obscure the main point: the P-1127/Kestrel/Harrier series, as the first operationally viable fighter aircraft capable of hovering flight, represented a clean break with past operational tradition; but that break was made within an engineering tradition which was in many important ways surprisingly traditional, even conservative.
The Harrier first took form in the mid-1950s in Camm’s creative brain as he, in common with other aircraft designers, sought ways to come to grips with the turbojet revolution. Turbojets offered the prospect of previously unattainable speeds, but they also presented designers with a basic problem: the design characteristics called for by high speeds, notably small, thin wings, tended to be incompatible with good control at low airspeeds. There were solutions, but they were not free. Camm was keenly aware of weight and performance penalties exacted by the structural and aerodynamic compromises needed to slow a high-performance aircraft down to reasonable approach and landing speeds. He was also sensitive to the vulnerability of runways and parking areas to air attack.
He combined these concerns with an awareness of the potential inherent in the steadily growing thrusts and power-to-weight ratios of turbofan engines and achieved a conceptual breakthrough. He perceived that the problem could be finessed by vectoring the thrust of a fighter’s engine downward to permit vertical, or near-vertical, landings and takeoffs. This, if it could be done, would solve both problems at once. A fighter that could slow down and land on vectored engine thrust would have little need for flaps and other high-lift devices, and wing design could be optimized for high-speed flight. The operational advantage of being able to operate into and out of restricted areas spoke eloquently for itself.
Camm was not the only designer to see the operational advantages of V/STOL fighters; but he was the first—and arguably the only one—to combine his perception with a practical engineering solution that would make the idea work. The worth of his solution was not readily apparent to many. The idea of directing the efflux of a jet engine through a series of angled pipes and rotating louvers seemed mechanically complex and aerodynamically inefficient. This was perhaps true in theory, but the practical disadvantages of the competing solutions proved far more serious. Both "tail sitters" and configurations with swiveling, wingtip-mounted engines created serious problems with high downwash velocities, and the former were forbiddingly difficult to fly. The value of separate, downward-pointing lift engines embedded in the fuselage is still a matter of debate, the argument hinging on the equivocal success of the Soviet Yak-36 Forger deployed on Soviet Minsk and Kiev class antisubmarine carriers.
But for all the striking originality of Camm’s initial conception, he turned it into reality in a remarkably and typically disciplined, conservative manner. First of all, close consultation with power plant engineers produced support for his ideas about the direct lift potential of turbofan engines, and his faith in the developmental promise of Bristol Siddeley’s BS-53, later to become the Pegasus, was richly rewarded: During the life span of the P-1127/Kestrel/Harrier series, its available thrust has increased by a factor of nearly one and three-fourths, from 12,500 pounds to 21,500 pounds.
Having staked all on the lift capacity of the Pegasus, Camm’s design team approached the problem of hover control with a system of reaction jets, or puff pipes," ejecting compressor bleed air from orifices in the wingtips, nose, and tail to control roll, pitch, and yaw. The reaction jets were controlled by an orthodox stick and rudder, and aside from a small lever to control the angle of the vectored thrust louvers the cockpit layout was completely conventional. This proved remarkably successful.
But having begun with two highly innovative—even daring—concepts, vectored thrust and reaction jet hover controls, Camm’s team approached their project in measured, incremental fashion. The initial plan had been to vector only cool air from the precompressor fan stage of the turbofan engine for lift, but experience with the Sea Hawk carrier attack aircraft had shown that a jet engine’s exhaust could be routed through two right angle bends with remarkably little loss of thrust. This gave the P-1127 its second set of thrust louvers, establishing the basic configuration for the series. Not surprisingly, there is a strong family resemblance between the Sea Hawk and its V/STOL descendants, particularly in the empennage area.
The design phase of the P-1127 was complete by the fall of 1957, and prototype construction began shortly thereafter. It remained a private Hawker project until June of 1960 when official Air Ministry backing was received. Initial tethered hovering tests began on 21 October 1960, and development proceeded thereafter at a measured pace with six P-1127s ultimately being built. A contract was let for nine advanced P-1127 derivatives, Kestrels, in May of 1962; between the fall of 1964 and the fall of 1965, these Kestrels underwent extensive testing by a tripartite test group with members from the RAF, Royal Navy, USAF, U.S. Army, U.S. Navy, and the Luftwaffe.
The Royal Air Force requirement under which the Harrier was procured was issued in mid-1966, and the first Harrier flew in August of that year. The first Harrier unit, Number 1 Squadron, RAF, became operational in July of 1969.
Carrier landing tests were conducted with the P-1127 and Kestrel at an early stage, and Royal Navy interest, sharpened by the pending decommissioning of the last two British attack carriers, led to the first Sea Harrier order in May of 1975. Deliveries commenced in 1978.
In the meantime, U.S. Marine Corps interest in the Harrier had led to extensive operational tests, followed by procurement of the AV-8A with deliveries to operational Marine squadrons starting in early 1971. The McDonnell Douglas AV-8B stems from a 1973 proposal and features a modified wing of increased size making extensive use of new carbon fiber material. It represents the most advanced development of the series to date.
The incremental design changes, which began almost as soon as the first prototype P-1127 flew, have had powerful cumulative effect: Wings were progressively swept back and reduced in size on the Kestrel and Harrier, only to be increased again on the AV-8B. Engine inlet contours have been refined, and total airframe length has increased by about four feet. But maximum gross weights—perhaps the best single measure of increased capacity—have grown by nearly 2½ times.
As an example of successful innovation combined with continuity of engineering practice, Camm’s series of fighter and fighter bomber designs has few rivals. Among individual aircraft designers, Camm, who died in 1966 at the age of 73, has only a handful of peers in terms of success, versatility, and longevity: Igor Sikorsky, Geoffrey de Havilland, and Lockheed’s Clarence "Kelly" Johnson. Sikorsky’s career ranged from the world’s first four-engined bomber in 1913, through highly successful amphibian transports in the 1930s, to the world’s first operationally capable helicopters in the 1940s, and on to their eminently effective turbine-engined derivatives in the 1950s and 1960s. De Havilland reached prominence with a series of successful fighters and light bombers during World War I, featured a wide array of light transports, trainers, and racing aircraft during the interwar period, reached his apogee with the phenomenally successful Mosquito bomber and fighter of World War II, and extended on into the turbojet age with the Venom and Vampire fighters and the Comet, the world’s first jet airliner. Johnson was responsible for, among other projects, the P-38, C-121, F-104, U-2, and SR-71 . Though the achievements of all of these men are remarkable by any standard, it is worth noting that of the four, only Camm and Sikorsky made the transition from conventional aircraft to vertical flight.
The Harrier’s thoroughbred lineage fares well even when matched against the progeny of entire companies and design bureaus. Of all other first-line fighters in service today, only Grumman’s F-14 can trace its ancestry, directly and without a break in engineering tradition, to a biplane antecedent, the tubby little F-3F of the mid-1930s.
J.F.G.
Disclaimer
The conclusions and opinions expressed in this document are those of the author cultivated in the freedom of expression, academic environment of Air University. They do not reflect the official position of the U.S. Government, Department of Defense, the United States Air Force or the Air University.Air & Space Power Home Page | Feedback? Email the Editor