v2.0.1 / 1 of 3 / 01 may 02 / greg goebel / public domain
* 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.
* Experiments, some of them crazy, with VTOL aircraft took place through the 1950s and into the early 1960s. Results were generally discouraging, but one line of investigation did in fact lead to an operational VTOL combat aircraft.
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 8,000 horsepower, fitted the rear fuselage to drive four blower units, two on each side of the aircraft and arranged around the center of gravity. 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, and 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 back in the UK.
Bristol's technical director, Sir Stanley Hooker, found Wibault's lash-up clumsy and inefficient, but he liked the basic idea of using a single engine for both vertical lift and forward flight. Other VTOL experiments at the time had separate sets of engines for the two purposes. 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 using the airflow of the engine itself, directed through swivelling exhausts, instead of a set of external blowers. They then gradually refined the idea:
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.
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 many 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 was demonstrating almost absolute indifference 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
"When the devil are you coming to see me?" Camm said.
"About what?" Hooker replied.
"About this lifting engine of yours, you bloody fool! I've got an aircraft for your BE.53!" The show was on.
* 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 BE.53 was fitted under the fuselage, the three (later two) crew sat in a bulbous canopy with its leading edge on the nose of the aircraft, and straight wings. 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 liason duties, as well as possibly 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, which was 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 3,630 kilograms (8,000 pounds) to 4,535 kilograms (10,000 pounds). Gradually, 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 for the work on the thing. 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".
There was absolutely no official interest in the P.1127 VTOL aircraft from the British government, and in fact the only official communications to Hawker and Bristol on the subject were entirely negative. Camm nonetheless 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 such an expensive proposition, anyway.
In addition, Hawker put together a brochure describing the P.1127 concept, and handed copies of it out to interested parties at the Farnborough Air Show in fall of 1957. Colonel Bill Chapman of the MWDP was still very enthusiastic, 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 an actual machine. As the design of the P.1127 progressed, it became obvious that even 4,535 kilograms (10,000 pounds) thrust wasn't enough. The engine design was extensively changed and refined to provide 6,120 kilograms (13,500 pounds) 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 "good fairy" 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 enthusiastic.
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 RAF Hawker Hunters. 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 was likely to 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 enough strength in numbers 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 Ministry of Supply (MoS) issued a draft requirement for the purchase of two P.1127 aircraft. The government was beginning to join the parade.
* The first Pegasus engine began bench tests in August 1959. Obtaining the design thrust levels provided trickier than anticipated, provoking an angry outburst from Syd Camm, but it was nonetheless a major step forward.
There was still no official British government interest. However, the Americans continued their assistance, with a stream of Yanks dropping by to see the marvelous new jet take shape, and 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 generated only about 4,000 kilograms (9,000 pounds) thrust. It was followed five months later by the "Pegasus 2", which had 4,500 kilograms (10,000 pounds) thrust. Another six month's work pushed the thrust to 5,000 kilograms (11,000 pounds).
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. 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 hovering 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 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 two P.1127s were a radical new design. They were basically 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 engine 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 provided at 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 reaction thrusters ("puffers") 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" experimental VTOL aircraft, when a Shorts engineer insisted that such a system would be absolutely required for the P.1127, Camm heard him out, restraining his notorious sharp 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 horizontal 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" 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 6,125 kilograms (13,500 pounds) thrust, in April
1962. The last of the P.1127s, XP984, was later fitted with the "Pegasus 5",
with 6,800 kilograms (15,000 pounds) thrust.
HAWKER P.1127:
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spec metric english
_____________________ _________________ _______________________
wingspan 7.42 meters 24 feet 4 inches
length 12.55 meters 41 feet 2 inches
height 3.28 meters 10 feet 9 inches
empty weight 4,625 kilograms 10,200 pounds
loaded weight 7,030 kilograms 15,500 pounds
max speed at altitude 1,150 KPH 715 MPH / 620 KT
service ceiling 15,200 meters 49,800 feet
_____________________ _________________ _______________________
* 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 and sparking 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 static display at the RAF Museum, and is now at the Science Museum in London. Of the other three P.1127 survivors, one was scrapped and the other two are now on static display.
* Despite the good results of the trials, at the time there was little prospect of fielding the P.1127. Along with the British government's muddled attitude about about new aircraft, the P.1127 also had competition.
Even as the Hawker VTOL aircraft was taking shape, Rolls-Royce and Dassault had been internationally promoting a VTOL version of the Dassault Mirage III fighter, using Rolls-Royce auxiliary "lift engines" for vertical take-off. This concept would emerge as the Mirage IIIV (read "three-vee" for "VTOL" and not "three-five") experimental fighter, with a conventional turbojet for forward flight and eight small lift engines.
The result of all this activity was the evolution of the "NATO Basic Military Requirement 3 (NBMR-3)" in 1959 and 1960 for a Mach 2 VTOL fighter, with a number of different manufacturers developing proposals. The whole NBMR-3 charade is discussed in more detail in the next section.
One of its implications, however, was that the firmly subsonic P.1127 began to look like a dead end. There were those in the RAF and the British Air Ministry who tried to promote the P.1127 as the basis for a combat aircraft, reasoning that an existing machine that worked was probably a better starting point than a far superior machine that existed only on paper, and in fact had released "General Operational Requirement 345" in March 1960, defining a P.1127-based strike fighter. However, they were a minority, and military aviation in the UK was in a state of complete chaos at the time.
At that point, the MWDP came to the rescue once more. The British Minister of Aviation, Peter Thorneycroft, had discussions with the Germans on cooperative development of a combat aircraft based on the P.1127, and on 14 January 1961 announced such a joint program. The MWDP had been scaling back their financial support of the P.1127 effort, since the organization was only really chartered to support prototype development, but the idea of a multinational investigation of the possibilities of VTOL combat aircraft appealed to some MWDP and senior US military officers.
One of the MWDP civilian staff, a very wealthy American named Larry Levy, lobbied hard to interest the British, West German, and American governments into funding a joint effort to investigate the military potential of the P.1127. The result was the "Tripartite Evaluation Squadron (TES)".
Hawker was given an "Instruction to Proceed" on the construction of new aircraft for the TES on 22 May 1962, but the company asked for a delay, since their current round of testing was suggesting new features that would result in a much better aircraft.
The "Tripartite Agreement" that formally created the TES was signed on 16 January 1963, with manufacture of the new aircraft beginning that summer. Although 18 aircraft were originally planned, the British had the total cut down to nine. The aircraft were originally named the "P.1127-Evaluation", but in September 1964 they were redesignated the "Kestrel F(GA) Mark 1", where "F(GA)" stood for "Fighter (Ground Attack)".
The first had already flown on 7 March 1964. They featured all the
improvements that had been devised during the P.1127 test program, and were
also all initially fitted with the Pegasus 5 engine. They featured a new
wing that had been fitted to some P.1127s late in the test program; a short
fuselage stretch; twin strakes fitted to the belly of the aircraft; a stores
pylon under each wing for a drop tank; and a rear landing-gear door stressed
for use as an airbrake.
HAWKER SIDDELEY KESTREL F(GA).1:
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spec metric english
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wingspan 6.96 meters 22 feet 10 inches
length 12.8 meters 42 feet
height 3.28 meters 10 feet 9 inches
operating weight 4,990 kilograms 11,000 pounds
loaded weight 8,620 kilograms 19,000 pounds
max speed at altitude 1,210 KPH 750 MPH / 650 KT
service ceiling 13,700 meters 45,000 feet
range 2,000 kilometers 1,245 MI / 1,080 NMI
_____________________ _________________ _______________________
The TES was formally set up on 15 October 1964 in the UK, under the command of Wing Commander D. McL. Scrimgeour, with pilots from the RAF, Luftwaffe, USAF, US Navy, and US Army performing flight tests. The US Marines were interested, but did not participate. The Kestrels sported a "TES" insignia that combined USAF and Luftwaffe insignia with the RAF roundel like a pie with three big slices.
Wing Commander Scrimgeour was assisted by two deputies, one from the US Navy and the other from the West German Luftwaffe. The deputy from the Luftwaffe was Oberst Gerhardt Barkhorn, one of Germany's top aces, with 301 kills to his credit.
The TES performed 938 test flights from April 1964 through November 1965, flying the nine Kestrels plus the last P.1127, XP984, which alone among the six P.1127s had a Kestrel-like wing. They performed flights from a variety of sites and performed exercises in remote deployments, identifying not only the tactics to be used by VTOL combat aircraft but the logistical procedures needed to support them. One of the Kestrels was written off after a nasty ground loop when a US pilot tried to perform a rolling takeoff with the parking brake on, but the pilot escaped with little injury, and none of the other aircraft were lost during the test program.
* The TES then went largely idle until April 1966, when it was broken up. Two the Kestrels stayed in Britain, while the other six survivors, including the West German aircraft, were purchased outright by the Americans at a pre-arranged "used" price and shipped across the Atlantic.
In US service, the six Kestrels were originally designated "VZ-12", but this designation was quickly changed to "XV-6A". They were used for extensive tri-service flight trials, in competition with two other VTOL aircraft prototypes, the Lockheed "XV-4 Hummingbird" and the "Ryan XV-6 Vertifan".
After the trials, the US military services decided they had no need for such an aircraft, though that wasn't the end of the story by any means. NASA conducted extended trials with two of the Kestrels after the service trials, and one of the NASA Kestrels later ended up in the hands of the Smithsonian Air & Space Museum in Washington DC.
* By the time the TES was disbanded, the British government had already decided to take the next step and create a true operational combat aircraft out of the Kestrel. As with everything else in the story, they did not come to this decision by any straightforward path.
* While Hawker and Bristol were working to get the P.1127 and then the Kestrel into the air, they were also playing with concepts for an operational VTOL combat aircraft.
One interesting early concept put forward in the summer of 1958, the Hawker "P.1132", looked something like a bigger P.1127 / Kestrel with a wider wing. The outriggers were mounted in mid-wing, with the wings folding up beyond that point, presumably for carrier stowage. Given the limited thrust expectations for the Pegasus at the time, the P.1132 had twin side-by-side engines, one with two rotating exhausts on the right, the other with two rotating exhausts on the left.
With the emergence of the NATO NBMR-3 requirement for a Mach 2 VTOL fighter, Hawker came forward with a new concept, the "P.1150", which looked like a stretched version of the P.1127. The P.1150 was an elegant machine with the sleek lines of a dolphin, like a jet fighter from Atlantis. It was to be powered by an advanced Pegasus variant with "plenum chamber burning (PCB)", similar to afterburning, except that the augmented combustion took place just after the front fan, allowing enhanced thrust to be generated in the front nozzle pair.
NBMR-3 was finalized in March 1961, and Hawker submitted an improved concept, the "P.1154", which looked much like the P.1150 concept externally but had an entirely new engine, the Bristol-Siddeley "BS-100", with PCB and 15,000 kilograms (33,000 pounds) thrust.
The P.1154 concept remains appealing even today, and in fact it won the the NBMR-3 competition in April 1962, or possibly it might be more accurate to say it "sort of" won the competition. The reality was that the French refused to accept the British aircraft, preferring their own Mirage-IIIV, and so the international collaboration for a supersonic VTOL fighter gradually bogged down and died.
The Mirage-IIIV proved to be a non-starter, and the program was eventually killed in 1966. The additional burden of separate lift engines, as Syd Camm had forseen, made the design impractical for actual use, though the IIIV was one of the few supersonic VTOL aircraft flown in the 20th century.
For a time, however, the P.1154 remained alive and seemingly healthy. Both the RAF and the British Royal Navy (RN) found the concept very attractive. However, this joint interest turned out to be a curse in disguise, as the two services could not agree on a common configuration. They seemed determined to make sure that the "P.1154RAF" and the "P.1154RN" were as different as possible.
The Royal Navy finally pulled out of the program in 1964, electing to buy US McDonnell Phantom fighters fitted with Rolls-Royce Spey turbojets instead. Predictably, the P.1154 and the BS.100 were cancelled on 2 February 1965. However, the RAF still had an outstanding need for a new strike aircraft to replace the Hunter, and the government orders cancelling the P.1154 also included instructions for the development of a combat-capable version of the Kestrel, to be extensively redesigned and fitted with P.1154 avionics.
The result was the "P.1127RAF", which would become the "Harrier GR (Ground Attack / Reconnaissance) Mark 1", the first operational VTOL combat aircraft. A contract for six pre-series machines was issued on 17 February 1965, a little more than two weeks after the cancellation of the P.1154.