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Home , Bristol Siddeley, Gordon Lewis (engineer), Hawker Siddeley Harrier, Michel Wibault, Ralph Hooper, Stanley Hooker

Pegasus Vectored-

Matador Harrier

Sea Harrier AV-8A

International Historic Mechanical Engineering Landmark

24 July 1993

International Air Tattoo '93 RAF Fairford

The American Society of Mechanical Engineers I MECH E I NTERNATIONAL H ISTORIC M ECHANICAL E NGINEERING L ANDMARK PEGASUS V ECTORED-THRUST T URBOFAN ENGINE 1960 T HE B RISTOL AERO- (ROLLS-R OYCE) PEGASUS ENGINE POWERED THE

WORLD'S FIRST PRACTICAL VERTICAL/SHORT--AND-LANDING JET

AIRCRAFT , THE H AWKER P. 1127 K ESTREL. USING FOUR ROTATABLE NOZZLES, ITS THRUST COULD BE DIRECTED DOWNWARD TO LIFT THE , REARWARD

FOR WINGBORNE , OR IN BETWEEN TO ENABLE TRANSITION BETWEEN THE TWO FLIGHT REGIMES. T HIS ENGINE, SERIAL NUMBER BS 916, WAS PART OF THE DEVELOPMENT PROGRAM AND IS THE EARLIEST KNOWN SURVIVOR. PEGASUS ENGINE REMAIN IN PRODUCTION FOR THE H ARRIER II AIRCRAFT.

T HE AMERICAN SOCIETY OF M ECHANICAL ENGINEERS T HE INSTITUTION OF M ECHANICAL ENGINEERS 1993 Evolution of the Pegasus Vectored-thrust Engine

Introduction cern resulted in a perceived need trol and stability problems associ- The Pegasus vectored for combat runways for takeoff and ated with the transition from hover thrust engine provides the power landing, and which could, if re- to wing-borne flight. for the first operational vertical quired, be dispersed for operation The concepts examined and short jet from unprepared and concealed and pursued to full-flight demon- aircraft. The Harrier entered ser- sites. Naval interest focused on a stration included "tail sitting" types vice with the (RAF) similar objective to enable ship- exemplified by the Convair XFY-1 in 1969, followed by the similar borne combat aircraft to operate and mounted jet engines, while oth- AV-8A with the Ma- from helicopter-size platforms and ers used jet augmentation by means rine Corps in 1971. Both services small ships, because of the high of lifting fans and ejectors. have continued to operate devel- cost and expected vulnerability of In the , ef- oped versions of the basic aircraft, large aircraft carriers. fort was concentrated on the devel- and it has been adopted by the During the 1950s, numer- opment and application of very high and the Spanish, In- ous projects and research programs thrust-to-weight lift engines fol- dian, and Italian navies. More ad- were initiated in the United States lowing the ideas put forward by Dr. vanced versions of the engine and and Western Europe to study and A. A. Griffith. This work resulted, aircraft are still under development, validate alternative means of in 1954, in the launch of the Short to extend the capability of the achieving the required short or ver- SC1, a small VTO flat-rising re- weapon system and ensure con- tical takeoff (VTO) and landing search aircraft able to take off ver- tinuing operation well into the next characteristics. The advancing tically with the thrust of four Rolls- century. technology of the of- Royce RB108 vertically mounted The engine has the special fered steadily increasing values of lift engines. The achieved engine characteristic of , engine thrust-to-weight ratio, thrust-to-weight ratio was 8:1, and enabling the thrust to be directed which encouraged the study of di- a further similar engine was in- rearward for propulsion, downward rect jet lift systems and of the con- stalled with a horizontal jet efflux for lift, and forward for braking. The concept, which has remained basically unchanged since the first prototype P.1127 flew in 1960, en- abled the goal of a single- engined VSTOL (very short takeoff and landing) jet aircraft to be realized. The aircraft deliveries pro- grammed for the present decade will ensure that the Pegasus en- gine, incorporating progressive de- velopment and refinement, will continue in service more than half a century after the first drawings were made in 1956.

Background Hawker P.1127 In the late 1940s immedi- ately following World War II, the development of ballistic and sophisticated munitions led to concern in the Western Alliance regarding the vulnerability of North Atlantic Treaty Organiza- tion (NATO) airfields. This con-

1 for propulsion. The two UK companies to become responsible for Pegasus and Harrier development were, at this time, not active in the field of VTO. The Aeroplane Company Engine Division, later to be ab- sorbed into En- gines and then into Rolls-Royce, had responded to a requirement for a light-weight engine to power a NATO strike fighter, conven- tional in configuration but able to operate from relatively unprepared Orpheus runways. This engine, the Orpheus turbojet, was selected for the Fiat G91 aircraft to meet the NATO requirement. The development program was managed and funded by the Mutual Weapons Develop- ment Program (MWDP), a United States agency with an office in having the objective of supporting projects of potential value to the NATO forces. The Fiat G91, which later entered service with the Ger- man and Italian air forces, was to be followed in a second-phase pro- gram by an aircraft with enhanced performance and in a third phase by a strike fighter with short take- Fiat G91 off and vertical-landing capability.

The Evolution of Vectored Thrust incorporated into the Pegasus en- stabilized in hovering and low- In March 1956, when gine and the Harrier airframe. The speed flight by means of air bled MWDP was turning its attention system proposed consisted of a tur- from the compressors and ejected to the third-phase NATO require- boprop engine, the Bristol BE25 from the wing tips and nose and ment, a proposal was submitted to Orion of about 8,000 horsepower, tail of the airframe. the Paris office by Michel . driving four large centrifugal com- Col. John Driscoll, at the Wibault was well known in avia- pressors, arranged like wheels at time head of the MWDP Paris of- tion in the pre-war period, the com- the sides of the fuselage. The blower fice, sent the proposal to Dr. Stanley pany of that name having been casings could be rotated to direct Hooker (later Sir Stanley) at Bristol responsible for a range of French the compressed air, and hence the Engines. It was studied by Gordon transport and . Post- thrust, through over 90 degrees. Lewis, who was responsible for new war Wibault had been working on The air was directed downwards projects. Lewis recognized the im- novel aviation projects and had for vertical takeoff and landing, portance of the thrust-vectoring produced schemes for a VSTOL obliquely for climbing or transi- principle but considered the strike fighter, which were entitled tion, and horizontally for level Wibault mechanical arrangement “Ground Attack Gyropter,” the sub- flight. The exhaust gas from the of four compressors driven by shafts ject of the March proposal. was also used for verti- and bevel gear boxes to be complex This proposal introduced cal or horizontal thrust using a gas and heavy. He proposed an alter- the concept of thrust vectoring and deviator mechanically connected native lighter and simpler arrange- described the basic principles of with the rotation of the four blower ment, substituting a two-stage axial operation that were subsequently casings. The proposed aircraft was flow fan for the four centrifugal

2 blowers and vectoring the later commercial engines. thrust through two rotating In May 1957 Sir Sydney nozzles, one on each side of Camm of con- the engine. tacted Sir to dis- This layout, desig- cuss possible VSTOL projects. The nated BE 48, retained the BE 53 schemes were presented, Orion engine and a reduc- and of Hawkers car- tion gear to drive the fan ried out a series of project designs Further weight reduction re- aiming at a VSTOL fighter with sulted from using a power real military capability. His work turbine running at the ap- contributed much to the refine- ’s Ground Attack Gyropter, propriate speed, dispensing ment of the engine design, includ- March 1956 with the reduction gear, and ing the major feature of rotating replacing the turboprop with rear nozzles, exiting on each side of the simpler and lighter the fuselage and closely integrated Orpheus turbojet. The re- with the engine. The nozzle rota- sulting design, the BE 52, tion mechanism had received much was further evolved into the attention by F. C. Marchant, in BE 53 with a three-stage fan. charge of the Bristol design office, Wibault quickly ac- and he evolved the scheme of using cepted the changes to his me- large diameter bearings to support chanical design and produced the nozzles with air motor driven a scheme of a strike fighter chains round the periphery of the using the new proposed en- bearings to affect rotation. gine. This was presented to By the autumn of 1957, the Original sketch of BE 48, August 1956 MWDP, where Col. Willis Hawker designers had prepared the Chapman, later Brigadier initial schemes of the prototype General, had replaced Col. P.1127, and the engine design, Driscoll. Chapman encour- named Pegasus, had become a com- aged Bristol to proceed with pact and light thrust vectoring en- the design, and a joint patent gine, with the thrust line passing was registered at the end of through the center of gravity in all 1956 in the names of Wibault angles of deflection. The engine and Lewis. This patent iden- configuration at the commence- tified the main feature of ro- ment of joint MWDP and company- tating nozzles, including a funded development in 1958 com- pair at the rear of the air- prised a two-stage fan, seven-stage craft to deflect the turbine compressor, and three stages of exhaust gas, and contra-ro- turbine. Wibault-Lewis patent tation of the engine spools to The program moved for- minimize the effect of gyro- ward rapidly when Hawker scopic couples on hovering launched the P.1127 prototype with stability. By this time the UK funding, and in September benefit of using a proportion 1959, the first engine ran on the of the fan delivery air to su- test bed, giving 9,000 lbs of thrust. percharge the engine com- The Hawker Chief Test Pilot, Bill pressor had been realized, Bedford, flew the P.1127 for the resulting in the necessity for first time in the hovering mode in only a single air intake. This October 1960, by which time the aspect was covered in the engine thrust had been increased patent, and the engine to 12,000 lbs. emerged as a turbofan, or John Dale, who had been bypass engine, an arrange- responsible for development of the Wibault Gyropter scheme using BE 48 ment used extensively in Orpheus engine in the Fiat G91,

3 took charge of Pegasus develop- ment engineering and led the team that progressively raised the en- gine thrust to over 21,000 lbs for the RAF’ Harriers and US Marine Corps AV-8As. In the process of thrust enhancement, the engine passed through several phases of evolu- tion to the present-day configura- tion of three fan stages, eight-stage compressor, and four stages of tur- bine with an annular combustor. Special features of the engine in- clude contra-rotation, provision for air bleed for the aircraft stabiliza- tion nozzles, and a transonic fan with no inlet guide vanes. This latter type of fan was subsequently adopted for large turbofan com- mercial engines.

Development Problems The Pegasus Harrier com- bination has been very successful, but nevertheless there have been design and development problems to be solved during its career. The Pegasus 2 early problems emerged under the following headings: Intake ducting and fan outlet system. Because the engine has to be located at the aircraft Early Hawker P.1127 configuration center of gravity, the intake duct is only about one diameter long. Con- necting the two large fuselage side intakes with the engine face re- quired short high curvature duct- ing, which introduced air flow dis- tortion at the fan inlet and led to excessive blade vibration. To keep the vibration frequencies of the blades outside the revolutions-per- minute (RPM) range of the engine, they were machined with interblade supports and made in titanium for added strength. This also solved the problem of further air distortion caused by the fan outlet ducting. The early faired ducts to the nozzles were replaced by a plenum chamber to insulate the fan from the upstream effect of the two nozzles. P.1127 first flight October 1960

4 Exhaust duct. The task of ing jet-borne flight close to the laboration has been a special fea- the exhaust duct is similar to that ground, the exhaust gases recircu- ture of the Pegasus Harrier pro- of the plenum chamber, that is, to late round the aircraft and can en- gram. split the flow of gas from the tur- ter the engine intake and produce bine into two nozzles. This in- temperature rise and flow distor- Thrust Growth duced vibration in the final-stage tion effects, which reduce engine The Hawker designers con- turbine blades, and the develop- power. These effects are caused tinually demanded increases in ment engineers introduced wire mainly by “fountains” of exhaust thrust from the engine to mature lacing as used in steam turbines to gas that form between pairs of jet the weapon-carryingcapability and restrain the blade movements. streams. The Pegasus, with four range of the aircraft. The Pegasus Later in the program, the turbine nozzles, produces two fountains, 5 was designed for the Kestrel, a was redesigned with shrouded the one nearest the intake com- development of the P.1127 for blades, also similar to steam tur- prising relatively cool air from the which a thrust of 15,500 lbs was bine practice. fan, which effectively forms a bar- required. In 1963 the United Ground erosion. With rier preventing hot exhaust gas States, United Kingdom, and West nozzles down, the jets impinge on from reaching the intake. Prob- Germany signed the Tripartite the ground and can cause erosion lems of this nature are intrinsically Agreement to fund a squadron of of the surface and throw up debris associated with a VTO system, and nine Kestrels, which carried out with damaging effects. The tech- the Pegasus configuration has been trials in 1965 to evaluate the feasi- nique of rolling takeoff, making demonstrated to have particular bility of dispersed operations and use of the thrust vectoring prin- advantages over most alternatives. establish practical procedures. To ciple, enabled this issue to be The engine and airframe compa- achieve the necessary thrust, brought under control by acceler- nies have worked closely together Bristol introduced most of the de- ating the aircraft forward before throughout the program to solve sign features that were to be incor- directing the nozzles downward. such problems associated with en- porated in the later production en- Hot gas recirculation. Dur- gine installation. This close col- gines.

5 The Pegasus Mk101 was program established the basis for the first full-production Pegasus more thrust increase, enablingfur- and entered RAF service in the ther developments of the AV-8B Harrier in April and Harrier Mk2 to be introduced 1969 with a thrust of 19,000 lbs. for ground-based and naval appli- The Pegasus Mk102 was an in- cations. The engine is now equipped terim production standard pend- with digital electronic control, re- ing introduc- placing the original hydromechani- tion of the cal system. Mk103, which powered all Operating Experience Harriers of the The deployment of RAF RAF and the Harriers to dispersed sites, the flex- corresponding ible operation of the US Marine AV-8A of the Corps AV-8A and AV-8B, and the US Marine naval operations from small air- Corps. This craft carriers have all vindicated engine was the claims made for vectored thrust also acquired VSTOL in the original Wibault pro- for the Mata- posal and detailed in the submis- dor, the name sions made for funding of the given to the P. 1127 and early Pegasus engines. aircraft pur- In 1982 in the South At- chased by the lantic and 1992 in the Persian Gulf, . these characteristics have been Thrust of the demonstrated in action. Mk103 was in- creased to Tripartite Squadron Kestrel 21,500 lbs using an increased air flow fan and improved turbine cool- ing. The later Mk104 had some changes to resist salt-water corro- sion for the Royal Navy version of the aircraft, the Sea Harrier. The McDonnell Douglas Company, which had formed a col- laboration with Hawker Siddeley to support the AV-8A program, car- ried out an extensive redesign of the aircraft to meet the require- Pegasus 11 (Mk 103) ments set for the AV-8B. This necessitated further thrust in- crease and detailed engine changes to improve reliability and engine life and modified exhaust nozzles to integrate with the aerodynamic changes that greatly increased the takeoff weight capability. Large orders were placed for the AV-8B, and parallel developments in the United Kingdom resulted in the Harrier Mk2 for the Royal Air Force. An engine demonstrator Pegasus Engine thrust progression

6 Why Vectored Thrust Succeeded tation. Since the engine spools During the 1960s and into rotate in opposite directions, there the 197Os, many extensive pro- is virtually no gyroscopic effect, grams were committed in the and control of the United States and Europe to evolve aircraft during VSTOL systems using a variety of hover and transi- concepts. These included lifting tion is not totally fans installed horizontally in the dependent on elec- wing section, ejector augmentor tronic controls and systems, multiple lift engines, and auto-stabilization. rotating engine nacelles. None of • Thrust vectoring these was developed to operational in forward flight status. can be used to in- One powerful reason why crease maneuver- the single-engine solution embod- ability in combat. ied in the Harrier was pursued was the essential simplicity of the con- The MacRobert cept. The basic principle of vec- Award tored thrust is that all the In 1969 the powerplant thrust can be orien- first MacRobert tated in any direction between hori- Award was shared zontal and vertical, so that it pro- by a team of five AV-8B vides lift as well as propulsion. persons associated Given sufficient thrust to lift off with the early design vertically, the aircraft can make a and development of smooth transition from hover to the Pegasus engine. forward flight. Vectored thrust, as This award was set represented by the Pegasus-Har- up in 1968 by the rier combination, has the following trustees of the characteristics and advantages: MacRobert Trusts,  A single engine located near the to be allocated in rec- aircraft center of gravity, with a ognition of engineer- rotating nozzle system producing a ing innovation lead- thrust resultant that can be vec- ing to the benefit of tored between horizontal and ver- the United King- tical. dom. The Council of  Engine and nozzles together form- Engineering Institu- ing a compact, self-contained power tions initiated the unit, process, and the  Rapid nozzle vectoring (over 90°/ award is now presented annually Vectored Thrust Principle sec) actuated by a powerful air mo- by the Royal Academy of Engi- tor drive system using engine-sup- neering. plied air. Leading the team was Dr.  Short takeoff, at weights substan- Stanley Hooker, in charge of engi- tially greater than those that would neeringat Bristol in the 1950s. He be possible for VTO, is effective had been responsible at Rolls- and easy, since all the thrust is Royce for the development of the available for ground acceleration, Whittle to production lift-off and transition. Also, rolling status. Sir Stanely, together with vertical takeoff and short takeoff Sir at Hawker Air- techniques minimize the impact of craft, placed his considerable repu- jets on the ground or ship’s deck. tation behind the Pegasus concept  The pilot has only one extra lever and laid the foundations for subse- in the cockpit, to affect nozzle ro- quent success.

7 sponsible for the Orpheus jet en- gine at Bristol and took charge of Pegasus development from the start of the program. He carried Pegasus engineering onward for about 20 years, earning great re- spect from operators for engineer- ing integrity and attention to flight safety. The above were nominated in 1969 as having particular in- volvement in Pegasus. However, a major engine development program requires a large team of engineers over several decades to mature and improve the product. Many of the engineers involved made signifi- Left to right: Frank Marchant, cant contributions to the design , John Dale, Sir and took part in the solution of Stanley Hooker, and Neville Quinn problems as they arose. It is not possible to do justice to all these people in this brochure. It should be emphasized Gordon M. Lewis was responsible again that the close partnership for the conceptual design of the between the engine and airframe Pegasus, emerging from the origi- engineers has always been and still nal ideas of Michael Wibault. He is a very special feature of the Pe- was originally a specialist in axial gasus Harrier program. flow compressor design and later -- Dr. G. M. Lewis, CBE, MA, F.Eng., managed major engine programs F.R.Ae.S., F.I.Mech.E. before retiring as Technical Direc- • tor Bibliography N. R. Quinn, having been • Not Much of An Engineer, Sir in charge of work at Stanley Hooker, Airlife Pub- Bristol in the piston-engine era, lishing Ltd. was heading the performance de- partment in 1956. Quinn’s percep- • Harrier and Sea Harrier, Roy tion of the merit of the Pegasus Braybrook, Osprey Publishing concept and execution of many per- Ltd. formance studies made a major con- tribution to the engine definition. • Harrier, Francis K. Mason, F. C. Marchant was in 1956 Naval Institute Press Chief Designer at Bristol Engines, and he carried out the mechanical • Harrier, Bill Gunston, Ian design of the Pegasus to achieve Allan Ltd. the high thrust-to-weight ratio needed for VSTOL. He introduced • V/STOL from the Propulsion innovative design features that Viewpoint, G. M. Lewis, Royal were later widely adopted in the Aeronautical Society, Sir aero gas-turbine industry. Sydney Camm Memorial Lec- John H. Dale had been re- ture 1983

8 The History and Heritage Program of the ASME The ASME History and Heritage Recognition Program began in September 1971. To implement and achieve its goals, ASME formed a The American Society of History and Heritage Committee, initially composed of mechanical engi- Mechanical Engineers neers, historians of technology, and curator (emeritus) of mechanical John H. Fernandes. engineering at the Smithsonian Institution. The Committee provides a President public service by examining, noting, recording, and acknowledging me- Thomas D. Pestorius, chanical engineering achievements of particular significance. The History Senior Vice President, and Heritage Committee is part of the ASME Council on Public Affairs and Council on Public Affairs Board on Public Information. For further information please contact Public Irwin Fried, Information, American Society of Mechanical Engineers, 345 East 47 Vice President, Street, , NY 10017-2392, (0101) 212-705-7740. Board on Public Information David L. Belden, Designation Executive Director’ The BS 916 Pegasus Engine is the 38th ASME International David Soukup, Historic Mechanical Engineering Landmark to be designated. Since the Director of Intl. Affairs ASME Historic Mechanical Engineering Recognition Program began in • 1971, 156 Historic Mechanical Engineering Landmarks, 6 Mechanical The ASME National Engineering Heritage Sites, and 4 Mechanical Engineering Heritage Collec- History and Heritage tions have been recognized. Each reflects its influence on society, either in Committee its immediate locale, nationwide, or throughout the world. Euan F. C. Somerscales, It is the sixth international landmark designated in conjunction Chair with IMechE: SS Great Britain in Bristol, the Newcomen Steam Atmo- Robert M. Vogel, spheric Engine in Devon, and the Steam Turbine Yacht Turbinia in Secretary Newcastle-upon-Tyne as well as the Cruquius Steam Drainage Pumping Robert B. Gaither Station in Haarlemmermeer, The Netherlands, and the Boulton and Watt Richard S. Hartenberg, PE, Rotative Steam Engine in Sydney, Australia. Emeritus A landmark represents a progressive step in the evolution of R. Michael Hunt, PE mechanical engineering. Site designations note an event or development of James L. Lee, PE clear historical importance to mechanical engineers. Collections the Joseph van Overveen, PE contributions of a number of objects with special significance to the William J. Warren, PE historical development of mechanical engineering. The ASME Historic Mechanical Engineering Recognition Program CarronGarvin-Donohue, illuminates our technological heritage and serves to encourage the preserva- Staff Liaison tion of the physical remains of historically the divergent paths of discovery. Diane Kaylor, Public Information Staff • The Institution of Mechanical Engineers Tony Denton, President Ernest Shannon, Chairman, Communications Board Geoff Humphrey, Chairman, Aerospace Industries Board E. Peter Davies, Director, International Affairs Alan Knowles, Public Affairs Manager

9 HH9302