Part 1 of 3 articles researched and written by Greg Goebel of www.Airvectors.net. All images and text republished courtesy of Greg Goebel.
Prologue: The Flying Bedstead and the SC.1
* 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, the vehicle having 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, mounting twin Rolls-Royce Nene centrifugal-flow turbojet engines arranged exhaust-to-exhaust, with the 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 Nene engines only provided a total of 36.0 kN (3,675 kgp / 8,100 lbf), 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 Bedstead was moved to the Royal Aeronautical Establishment (RAE) in Bedford it crashed, killing the pilot. The second Bedstead performed its first flight in late 1957, only to crash within a week, again killing the pilot. 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, and thoroughly dangerous, 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 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 mounted vertically into a VTOL aircraft for straight-up lift, and not generally used in forward flight. It was 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 counting 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 mounted horizontally 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 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. The SC.1 was nothing resembling a production 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 displays.
Michel Wibault & the B.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 in 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 to 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 Dr. 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 by feedback from von Karman, 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 the same 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 dropping the external blowers and instead using the airflow of the engine itself, directed through swiveling exhausts. 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 swiveling exhausts immediately behind that. The memo suggested that the first two compressor stages of the big Olympus BO1.21 turbojet 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, not an aircraft — but then another lucky series of events took place. In early 1957, Hawker Aircraft’s chief designer, Sir Sydney Camm, responsible for the Hawker Hurricane, Tempest, 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 official 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
* 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.
Somewhat in Sandys’ defense, such an attitude was not unknown elsewhere, and Britain’s humiliation in ill-fated occupation of Egypt in 1956 had effectively ended British imperial ambitions for good, which implied that the aviation industry needed to be downsized. However, the consequences of the “Sandystorm”, as it would later be called, 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 no buyer was going to materialize.
* 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 in tone. 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 emerge. 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 piloted 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 speak out. 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 take notice of it.
* The first Pegasus engine began bench tests in August 1959. Obtaining the design thrust levels provided tougher than anticipated, provoking a sharp outburst from Sydney 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) lent a hand, performing 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 months’ 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 RAE 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 P.1127 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, pivoted 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 they suggested “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 outriggers as short as possible, but Camm still 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 sharp tongue — but after the visitor left, Camm 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 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.
HAWKER P.1127: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 7.42 meters 24 feet 4 inches wing area 17.2 sq_meters 185 sq_feet 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 _____________________ _________________ _______________________
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 tear and disintegrate, 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; it was written off as beyond repair.
Bill Bedford and the first prototype performed sea trials on 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.
TES / Kestrel
* 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 towards 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 liftjets engines for vertical take-off. This concept would emerge as the Mirage IIIV (read as “three-vee” for “VTOL”, not “three-five”) experimental fighter, with a conventional turbojet for forward flight and eight Rolls RB.162 liftjets. 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 farce is discussed in more detail below. 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, as it would turn out with complete sensibility, that an existing machine that worked was probably a better starting point than a supposedly far superior machine that existed only on paper. In fact, the Air Ministry had released “General Operational Requirement 345” in March 1960, defining a P.1127-based strike fighter. Unfortunately, there wasn’t any broad support for the idea, 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 financial support of the P.1127 effort — the organization was chartered to perform investigations but not 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. The Kestrels featured all the improvements that had been developed during the P.1127 test program, and were also all initially fitted with the Pegasus 5 engine. They were fitted with a new wing, a modified version of a redesigned wing fitted to the final-build P.1127 late in the evaluation 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: _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ wingspan 6.96 meters 22 feet 10 inches wing area 17.3 sq_meters 186 sq_feet 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 _____________________ _________________ _______________________
These machines originally featured the inflatable inlet lips, but they were quickly abandoned. The Kestrels had no built-in armament, though practice bombs were carried on the wing pylons on occasions, while a nose camera was fitted to help evaluate simulated attacks and to perform experimental reconnaissance flights.
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 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 claimed kills.
The TES performed 938 test flights from April 1964 through November 1965, flying the nine Kestrels plus the last P.1127, XP984, which had been fitted with the Kestrel-like wing. TES pilots performed flights from a variety of sites and performed exercises in remote deployments, defining the tactics to be used by VTOL combat aircraft and 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; that was the only aircraft lost during the test program.
* The TES then went largely idle until April 1966, when it was disbanded. 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 present 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; 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 make a true operational combat aircraft out of the Kestrel. As with everything else in the story, that decision was not made in any straightforward way.
Hawker P.1154 / Birth of the Harrier
* While Hawker and Bristol were working to get the P.1127 and then the Kestrel flying, 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)” — along the lines of afterburning, except that the augmented combustion took place 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 147 kN (15,000 kgp / 33,000 lbf) thrust.
The P.1154 concept remains appealing even today, and in fact it won the NBMR-3 competition in April 1962 — or at least “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 French Mirage IIIV proved to be a non-starter, and the program was eventually killed in 1966. The additional burden of separate lift engines, as Sydney Camm had foreseen, made the design impractical for operational 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. This joint interest turned out to be a curse in disguise, since the two services could not agree on a common configuration, seemingly determined to make sure that the single-seat “P.1154RAF” and the two-seat “P.1154RN” were as different as possible. The Royal Navy finally pulled out of the program in 1964, deciding to buy US McDonnell Phantom fighters fitted with Rolls-Royce Spey turbojets instead. Predictably, the P.1154 and the BS.100 were canceled on 2 February 1965.
The RAF was still left with an outstanding need for a new strike aircraft to replace the Hunter, and the government orders canceling 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.
Part 1 of 3 articles researched and written by Greg Goebel of wwwAirvectors.net