The BAe (Hawker) Harrier - origins
The story of the origin of the Harrier is a complicated one, involving multinational collaborations and many changes of plans. The Harrier, as it emerged from this process, was actually a compromise solution, but one that proved highly successful.
The Rolls Royce "Flying Bedstead"
Studies of "vertical takeoff or landing (VTOL)" aircraft began late in the Second World War, with German engineers coming up with a series of concepts that never got out of the paper stage. That was probably fortunate, since the postwar history of VTOL technology strongly suggested that converting such paper plans into practical flying machines was a real challenge.
Various nations began to work on flight-worthy VTOL machines after the war, though initially these aircraft were purely experimental in nature. In the UK, Rolls Royce began work on Britain's first VTOL aircraft, known by the bland name of "Thrust Measuring Rig (TMR)", apparently as a dodge to conceal the real nature of the project from those who might have thought it too far-fetched. It was designed to evaluate hovering flight using raw jet thrust, with no capability for serious horizontal flight.
The first of two TMRs was rolled out in 1953. It hardly looked like an aircraft at all, consisting only of a frame with four legs and twin Rolls Nene centrifugal-flow turbojet engines, arranged exhaust-to-exhaust with their exhausts tilted downward through the TMR's center of gravity. There were reaction jets -- "puffers" -- on arms out to each side, fed by exhaust bleed from the engines to provide maneuvering capability during a hover. The pilot sat perched on top, with little protection if the clumsy-looking thing decided to flip over. It was referred to as the "Flying Bedstead" due to its appearance; more or less the same nickname was applied to comparable VTOL evaluation rigs developed in other countries.
Initial tethered flights were performed in 1953 and 1954. The first free flight was made on 3 August 1954 with Rolls chief test pilot R.T. Shepherd at the controls. The Bedstead had an empty weight of 2,720 kilograms (6,000 pounds) and a loaded weight, with enough fuel for ten minutes of flight, of 3,400 kilograms (7,500 pounds). Since the twin Rolls Royce Nene engines only provided a total of 36.0 kN (3,675 kgp / 8,100 lbf) together and about 8% of that thrust was siphoned off for the puffers, the Bedstead had little margin of power. In addition, the throttle response of the old Nene engines was sluggish, making hovering difficult. All in all, the thing was apparently very hair-raising to fly.
After the first Flying Bedstead was moved to the Royal Aeronautical Establishment (RAE) it crashed, killing the pilot. The second Bedstead performed its first flight in late 1957, only to crash within a week. Its parts were used to repair the first Bedstead, which eventually ended up as a museum piece in the UK.
Nobody could have mistaken the ugly Bedstead for anything but a purely experimental lashup. As the Bedstead program was winding down, work was beginning on a new British VTOL machine that looked much more like a proper aircraft.
The Shorts SC.1 VTOL test aircraft
The basis for the effort was a new type of engine known as a "liftjet", the brainchild of Dr. Alan A. Griffiths, one of the pioneers of British jet technology and a major figure in the history of materials science. A liftjet was a small turbojet that was fitted vertically into a VTOL aircraft for straight-up lift, and was not generally used in forward flight. It were designed to be as compact as possible and to generate large amounts of thrust for a short time. It also had a sensitive throttle to permit fine control in hover.
Griffiths had come up with the idea in 1941, and in 1955 he had bench-tested one of the first liftjet engines, the Rolls Royce "RB.108". It weighed 122 kilograms (269 pounds) and could generate 9.0 kN (920 kgp / 2,030 lbf) thrust, not including 11% bleed to drive puffer thrusters. The British Ministry of Supply (MoS) issued a request for an experimental VTOL aircraft based on the RB.108 and several companies replied. The contract was awarded to Short Brothers of Belfast in August 1957, with funding provided for two machines, designated "SC.1".
The SC.1 was a little delta-winged aircraft with a bubble nose; fixed tricycle landing gear, all with twin wheels; and a very stubby tailfin. It had an amusing toylike appearance reminiscent of a flea or leafhopper, or something out of THUNDERBIRDS ARE GO!. It had a battery of four RB.108s mounted vertically in the center fuselage, plus one RB.108 in the tail for forward motion. The lift engines obtained airflow through a set of spring-loaded louvers directly above their intakes and a vent farther forward on the fuselage; the intake for the rear engine was at the base of the tailfin. There were puffer thrusters in the nose and wings. The SC.1 featured a sophisticated, triple-redundant autostabilization system to ensure that it remained controllable in hovering flight.
The first SC.1 performed its initial (conventional takeoff and landing) flight from Boscombe Down on 2 April 1957, with Tom Brooke-Smith at the controls; it was only fitted with the engine in the tail at the outset. The second SC.1 was the first to be fitted with the four lift engines, performing its initial (tethered) vertical flight at the Belfast factory on 26 May 1958. It performed its first untethered vertical flight on 25 October 1958.
Both prototypes performed a series of test flights into 1964. The program was regarded as a success, though one of the prototypes crashed in 1963; the pilot was killed, but the aircraft was repaired and flown again. It was nothing resembling an operational aircraft, being much too complicated and having no operational capability, but it did much to validate VTOL concepts. Both SC.1s ended up as museum pieces.
Michel Wibault & the BE.53
Even before the first flight of the SC.1, the wheels were in motion that would eventually result in an operational VTOL aircraft, though by a long and very complicated path.
In 1956, a French aircraft designer named Michel Wibault, well-known for his pre-WW II designs, proposed a VTOL aircraft named the "Gyroptere". He was interested in building a combat aircraft that would be able to operate independently of airfields, which were clearly vulnerable to immediate destruction by Soviet nuclear strikes on the event of a general European war. The Gyroptere was to be fitted with a British Bristol "BE.25 Orion" turboshaft engine, with 5,970 kW (8,000 SHP), fitted the rear fuselage to drive four blower units, arranged around the center of gravity with two blowers on each side of the aircraft. Each blower would be in a moveable snail-shaped casing that could be rotated to provide vertical or horizontal thrust.
Wibault tried to promote the Gyroptere with both the French and American air forces and got nowhere. Finally, he approached the Paris-based "Mutual Weapons Development Program (MWDP)", an American-funded NATO office that promoted technologies useful for European defense. The MWDP's chief, US Air Force Colonel John Driscoll, found the concept interesting, and passed it back to the NATO "Advisory Group For Aeronautical Research & Development (AGARD)" for comment.
AGARD's chairman was Theodore von Karman of the California Institute of Technology, one of the most prestigious figures in aerospace. Von Karman was very intrigued by the idea. Encouraged, Colonel Driscoll then passed the concept on to Bristol Aero Engines in the UK. Bristol's technical director, Sir Stanley Hooker, found Wibault's lash-up clumsy, but he liked the basic idea of using a single engine for both vertical lift and forward flight. Hooker assigned a small research team consisting of Gordon Lewis, Pierre Young, and Neville Quinn to investigate the idea.
The research team quickly concluded that Wibault's idea could be greatly improved by using the airflow of the engine itself, directed through swivelling exhausts, instead of a set of external blowers. They then gradually refined the idea:
- Their first design concept, designated the "BE.48", was described to Hooker in a memo dated 2 August 1956. The BE.48 simply extended the Orion's shaft forward to drive a large compressor turbine at the front of the engine, something like that of a modern high-bypass turbofan engine, to drive airflow through a pair of elbow-joint swivelling exhausts immediately behind that. The memo suggested that the first two compressor stages of the Olympus BO1.21 could be used for the forward fan. The turboshaft's rear exhaust remained unchanged, with the airflow straight out the back.
- This concept quickly evolved into the "BE.52", in which the Orion was replaced by a modified version of the smaller and simpler "Orpheus" turbojet engine, and the large compressor fan was more tightly integrated with the rest of the engine. The scheme provided just as much thrust, maybe even a little more, than the Orion-based concept. Versions with straight or swiveling exhausts fitted to the rear of the engine were considered.
- The next concept, the "BE.53", was similar, but the large compressor fan was changed so that it rotated in the opposite direction from the main compressor spool, eliminating gyroscopic effects that would be a nuisance in a VTOL aircraft. The BE.53 was described in the initial patent for the new type of engine, dated 12 January 1957.
Hooker took the BE.53 concept to Paris to show it to Driscoll and von Karman, who were both enthusiastic. Driscoll left the MWDP soon after Hooker's visit, but his successor, USAF Colonel Willis "Bill" Chapman, was just as enthusiastic. Hooker also hired Michel Wibault as a consultant. Wibault, far from being offended at the way the British were reworking his design concept, was delighted at their ingenuity. He and Gordon Lewis became joint patent holders for the BE.53, though sadly Wibault died just a few weeks later and never saw his idea become reality.
The Bristol work led to an engine, but not an aircraft. Then another lucky series of events took place.
In early 1957, Hawker Aircraft's chief designer, Sir Sydney Camm, responsible for the Hawker Hurricane, Typhoon, Hunter, and other famous aircraft, was attending the Paris Air Show. There, he happened to chat with the Hawker representative in France, Gerry Morel, a Frenchman who had been a member of the British Special Operations Executive during the war. Camm mentioned that he was unimpressed with most of the "lift-engine" VTOL schemes being put forward at the time, and Morel told Hooker about Bristol's tinkerings.
Camm was very worried about the future of Hawker, since the British government seemed almost indifferent to procuring new combat aircraft. Possibly, Camm reasoned, a VTOL combat aircraft might stimulate their interest. A few days later, Bristol's Hooker got a letter from Camm that read:
"Dear Hooker: What are you doing about vertical take-off engines? Yours, Sydney"
-- and a few days later Camm got back an envelope containing data on the BE.53. He passed it on to his engineering staff, and in due time got back a preliminary sketch of a VTOL aircraft. Some time later, in early March 1957, Camm then gave Hooker a call, starting out with:
"When the devil are you coming to see me?" Hooker replied: "About what?" "About this lifting engine of yours, you bloody fool! I've got an aircraft for your BE.53!"
The show was on.
Hawker embraces VTOL aircraft
Hooker and Lewis went to the Hawker establishment in Kingston the next day to inspect the aircraft design. It had been drawn up by Hawker's Ralph Hooper, with some help from his office-mate, John Fozard, who was otherwise working on another project, the Mach 2.5 "P.1121" strike fighter.
The VTOL design had the company designation "P.1127". It was a funny-looking little aircraft, and indeed nothing that resembled this initial concept would ever fly. The P.1127 featured straight wings, a BE.53 fitted under the fuselage, and three (later two) crew sitting in a bulbous canopy with its leading edge on the nose of the aircraft. In hindsight, it looked very much like one of the oddball "Luftwaffe 1946" concepts the Germans had played with near the end of World War II.
The Hawker people regarded the P.1127 as appropriate for combat liaison duties, as well as possibly for light attack. This focus was due to the fact that the British government wasn't particularly interested in new fighter or strike aircraft. Indeed, on 4 April 1957, British Defence Minister Duncan Sandys (pronounced "Sands") published his infamous "White Paper", which basically stated that Britain would have no need for new fighters and bombers. Missiles were the way of the future. The consequences of the event -- later referred to as the "Sandystorm" -- for the British aviation industry would be near-disastrous. The P.1121 strike fighter project basically died on the spot, though it lingered into late 1958 until Hawker management realized they were not going to find a buyer for it.
In the meantime, Bristol and Hawker engineers kept on tinkering with VTOL design concepts. John Fozard recalled that Hawker's first jet fighter, the Sea Hawk, had a single engine with a split exhaust, and it wasn't too much of a stretch to think that such a feature could be incorporated into the BE.53, with the twin exhausts rotating in sync the forward exhausts. Bristol engineers had also been making tweaks of their own to the BE.53 engine design, gradually raising its estimated thrust from 35.6 kN (3,630 kgp / 8,000 lbf) to 44.5 kN (4,535 kgp / 10,000 lbf). The designers began to think that they could build a true VTOL combat aircraft, and rethought the initial P.1127 design into something more realistic.
There was, unfortunately, the issue of who was going to pay. The only government project that seemed to have any potential at the time was a requirement for a Canberra replacement, and Hawker chose to collaborate with Avro to promote a P.1121 derivative, the "P.1129", in pursuit of this contract. The contract would be won by the competing BAC group with the "TSR.2", which would itself be given the axe in 1965 in another disaster of the same magnitude as the "Sandystorm".
The British government had absolutely no official interest in the P.1127 VTOL aircraft, and in fact the only official communications to Hawker and Bristol on the subject were entirely negative. Camm still felt the idea had such potential that he encouraged Hawker management to fund development of the P.1127 with company money. Building a proof-of-concept prototype didn't seem like an expensive proposition, and the payoff might be substantial.
In addition, Hawker put together a brochure describing the P.1127 concept and handed copies of it to interested parties at the Farnborough Air Show in fall of 1957. Colonel Bill Chapman of the MWDP was still very supportive, and in early 1958 Bristol management was informed that the Americans would provide support for the engine development effort. In June 1958, an agreement was reached in which the MWDP would provide 75% of the funds, while Bristol picked up the other 25%. Sir Reginald Verdon Smith of Bristol committed to the project, even though no obvious buyer could be identified.
Now the engine could move from a paper design to hardware. As the design of the P.1127 progressed, it became obvious that even 44.5 kN thrust wasn't enough. The engine design was extensively changed and refined to provide 60.0 kN (6,120 kgp / 13,500 lbf) thrust. The new incarnation was given the name "Pegasus".
While the design of the P.1127 converged towards reality, grassroots support began to spring up. In August 1958, Hawker management approved construction of the P.1127, or rather of a set of wings for testing, but it was definitely a first step that implied a second. The "fairy godmother" from the US, the MWDP, was also providing financial support, and was spreading the idea of a VTOL strike fighter to replace the Fiat G.91 around various NATO military services. The response was positive.
In fact, Hawker was getting discreet under-the-table feedback from senior British Royal Air Force (RAF) officers that they liked the notion, too, seeing the P.1127 as the seed of a VTOL strike aircraft to replace the RAF Hawker Hunter. Of course, Hawker could place no real weight on such assurances, since in the political climate a senior RAF officer who proposed a new manned aircraft might well be asked to hand in his uniform, but it seemed that if the winds changed direction, support would be forthcoming.
In early 1959 the winds did begin to shift. RAF officers opposed to the Sandys policy began to feel thick enough on the ground to be willing to stand up and have their say. In April 1959, Hawker received a draft "operational requirement" document from the British Air Ministry for a possible operational follow-on to the experimental P.1127, and in May the British MoS issued a draft requirement for the purchase of two P.1127 aircraft. The British government was finally beginning to join the parade -- or at least taking notice of it.
The Hawker P.1127 VTOL aircraft
The first Pegasus engine began bench tests in August 1959. Obtaining the design thrust levels provided trickier than anticipated, provoking a sharp outburst from Syd Camm, but it was still a major step forward.
The Americans continued their support of the program, with a stream of Yanks dropping by to see the marvelous new jet take shape; the US National Aeronautics & Space Administration (NASA) performed flight tests with a 1/7th scale model and wind-tunnel tests on a 1/8th-scale model. Part of NASA's charter was to investigate advanced aircraft concepts, and if the P.1127 didn't fit that description, nothing did. The British industry's own Aircraft Research Association at Bedford also performed wind-tunnel tests on models.
The initial Pegasus variant produced only about 39.2 kN (4,000 kgp / 9,000 lbf) thrust. It was followed five months later by the "Pegasus 2", which had 44.1 kN (4,500 kgp / 10,000 lbf) thrust. Another six month's work pushed the thrust to 49.0 kN (5,000 kgp / 11,000 lbf).
Work on putting together the first P.1127, which would be given the serial number "XP831", began in early 1960. It was stripped down of everything that wasn't essential and began ground tests on 31 August 1960, leading to its first hover flight, secured by a tether, on 21 October 1960, with Hawker chief test pilot Bill Bedford at the controls. Unfortunately, the aircraft slewed, bounced, and skidded around uncontrollably, Hooker comparing it to a "balloon on a string". There was still not enough engine power to get the machine to fly right, but the project team put their backs into it, and the first -- very cautious -- untethered hover flight was performed on 19 November 1960. The XP831 prototype was handed off to the Royal Aircraft Establishment (RAE) in Bedford in March of 1961, and was followed by the second prototype, with the serial number "XP836", soon afterward.
The two machines, flown by Bill Bedford and deputy chief test pilot Hugh Merewether, were used to characterize VTOL flight, beginning with conventional take-offs and landings; then transitions from hover to vertical flight, and the reverse; then short rolling take-offs. By September 1961, the two prototypes were being flown with confidence -- performing full vertical or short takeoffs, maneuvering as a conventional jet aircraft, and then setting down vertically.
The P.1127s was a radical new design. It was effectively built around the Pegasus engine, with large intakes on each side of the aircraft and the four rotating exhausts, which were turned by a chain-drive system, arranged around the aircraft's center of gravity. "Pen-nib" fairings were attached over the fuselage behind the rear set of exhausts to protect the fuselage from exhaust blast, though eventually they would give way to broader "spade" fairings. The engine intakes were so big that from the front the aircraft was described as having "elephant ears".
The wing had to be set high to clear the exhausts. That made putting the main landing gear in the wings impractical, and so a bicycle-type tandem arrangement was devised, with a one-wheel forward-retracting nosewheel ahead of the engine and a two-wheel backward-retracting tailwheel behind the engine. The gear had to have a narrow track to keep the tires from being blasted by the exhaust. To keep the aircraft from tipping over, outrigger landing gear was fitted on the wingtips, retracting backwards into wingtip pods. The wings were canted heavily downward to keep the length of the outriggers as short as possible, but Camm feared, fortunately wrongly, that they would snap on a hard landing. However, there were significant problems with controllability of the landing gear on conventional takeoffs at first, with the aircraft tending to snake around on the runway when it reached a speed of 64 KPH (40 MPH) or so, leaving winding patterns of skid marks on the tarmac.
During hover or low-speed flight, the P.1127 was controlled by puffer thrusters driven by engine bleed. Development of the puffer system was troublesome. The puffers drained the thrust available for vertical liftoff, and at first they were ineffectual, leading to a comprehensive redesign of the puffer system.
Although Shorts had used a complicated gyroscopic stabilization scheme for their SC.1, when a Shorts engineer insisted that such a system would be absolutely required for the P.1127, Camm heard him out, restraining his notoriously tart tongue, but after the visitor left, made a remark to the design team along the lines of: "Well, we're just ignorant buggers here, we don't understand all that stuff." The P.1127 did incorporate a stabilization system but it was a very simple one, and the aircraft flew just fine.
The tail assembly was of conventional configuration, with the tailplane in the form of an "all moving" slab surface. A ventral fin was added underneath the tail for yaw stability. The canopy opened by sliding backwards, and the cockpit was fitted with a Martin-Baker H.6 ejection seat. A pop-up "ram-air turbine (RAT)" was fitted in the top of the fuselage just forward of the vertical tailplane for emergency power in conventional flight.
The second prototype, XP836, broke Mach 1.2 in a dive in early December 1961, but it was lost a few days later, on 14 December, when one of its air intakes came loose in flight, Bill Bedford ejecting safely. Despite this setback, by this time the promise of the type was so evident that the month before, in early November, the MoS had ordered four more P.1127s, which would emerge with the serial numbers "XP972", "XP976", "XP980", and "XP984", in that order of delivery.
New versions of the Pegasus were introduced as the four new aircraft were delivered. The XP976 aircraft was the first to be fitted with the uprated "Pegasus 3" engine with 60.1 kN (6,125 kgp / 13,500 lbf) thrust, in April 1962. The last of the P.1127s, XP984, was later fitted with the "Pegasus 5", with 66.7 kN (6,800 kgp / 15,000 lbf) thrust.
|Wingspan||7.42 meters||24.34 feet|
|Wing area||17.19 sq meters||185 sq feet|
|Length||12.55 meters||41.17 feet|
|Height||3.28 meters||10.76 feet|
|Empty weight||4,630 kilograms||10,200 pounds|
|MTO weight||7,030 kilograms||15,500 pounds|
|Max speed||1,150 kmh||715 mph|
|Service ceiling||15,200 meters||49,800 feet|
|Engine type||Bristol Pegasus|
|No. of Engines||1|
The P.1127s were modified on a continuous basis. One interesting change was made to the first prototype and to a few of the other P.1127s. A flexible, inflatable black lip was built around each air intake, to be deflated at low speeds to permit large airflow and inflated at high speeds to present a sharp rim and reduce drag. The idea was clever in principle, but the lips had a tendency to rip and tear apart, and they were eventually abandoned.
One of the second batch of aircraft, XP972, was lost on 30 October 1962. Hugh Merewether took a sharp turn in the aircraft, causing the engine compressor blades to scratch the engine casing, which sparked a titanium fire. Merewether set the aircraft down as fast as he could in a hard landing, and it was written off as beyond repair.
Bill Bedford and the first prototype performed sea trials with the carrier HMS ARK ROYAL in February 1963, breaking ground for the naval use of VTOL aircraft. However, on 16 June 1963, Bedford was demonstrating XP831 to a crowd of 110,000 at the Paris Air Show when the nozzle vectoring system jammed. He put it down quickly, but his landing options were limited and he rammed into a concrete obstacle. Bedford was not hurt, but the P.1127 appeared to be totaled. In fact, although it would not fly again, it was restored to become a museum display. Of the other three P.1127 survivors, one was scrapped and the other two are now on static display.