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Rolls-Royce/Snecma Olympus 593

From Alfawiki
Rolls-Royce/Snecma Olympus 593
Company typeJoint venture
IndustryAerospace
PredecessorBristol Siddeley Olympus 22R
Founded1960s
FounderBristol Siddeley Engines Limited and Snecma
FateIntegrated into Rolls-Royce after acquisition of Bristol Siddeley in 1966
Headquarters
United Kingdom and France
,
UK, France
ProductsTurbojet engines
ParentRolls-Royce (after 1966)

The Rolls-Royce/Snecma Olympus 593 was a turbojet engine equipped with afterburner technology, developed through an Anglo-French partnership to power the supersonic airliner Concorde. Originally a collaborative effort between Bristol Siddeley Engines Limited (BSEL) and Snecma, it evolved from the Bristol Siddeley Olympus 22R model. Following Rolls-Royce's acquisition of BSEL in 1966, the latter was integrated as the Bristol Engine Division within Rolls-Royce.

Up until Concorde ceased commercial operations in October 2003, the Olympus 593 remained distinctive as the sole turbojet engine featuring reheat used in commercial aviation.

During supersonic cruise (supercruise), its overall efficiency reached approximately 43%, marking the highest efficiency recorded for any conventional thermodynamic engine of its era.

Development

The engine’s origins trace back to a civil adaptation of the Olympus 22R, initially labeled as the 591, intended to sustain flight at Mach 2.2 on the BAC TSR-2. It was subsequently redesigned into the 593, with final specifications established on 1 January 1964. Development responsibilities were split between Bristol Siddeley in the UK and Snecma in France; Snecma also contributed to the unrelated M45H turbofan project.

Initial evaluations weighed turbojet versus turbofan configurations, ultimately favoring turbojets due to their reduced frontal area, which was crucial for aerodynamic performance. Notably, the rival Russian Tu-144 began with a turbofan engine incorporating reheat but later transitioned to a non-afterburning turbojet to enhance performance.

Bristol Siddeley concentrated on the engine core and accessory systems, while BAC took charge of variable intake design and installation aspects. Snecma was responsible for developing the exhaust nozzle assembly, which integrated thrust reversers, noise suppression features, and afterburner capabilities. The division of production mirrored aircraft manufacturing allocations: Britain assumed greater responsibility for engine fabrication, whereas France handled more of the fuselage construction. Ground testing operations were coordinated between facilities in both countries.

As the aircraft’s weight increased during design iterations, thrust requirements rose by roughly 20%, prompting Snecma to develop a partial reheat system to meet these demands.

In July 1964, two prototype engines designated 593D confirmed key design elements such as turbine cooling and operation at elevated temperatures. These trials indicated a need for an enlarged version, leading to the creation of the 593B. The Olympus 593B first ran in November 1965 as an upgraded variant of the smaller 593D originally intended for an earlier Concorde model; this designation was eventually discontinued.

By June 1966, a complete Olympus 593 engine coupled with a variable geometry exhaust system was tested at Melun-Villaroche. Flight evaluations employed an RAF Avro Vulcan bomber modified as a test platform but limited to Mach 0.98 due to aerodynamic constraints. The engine surpassed thrust expectations by delivering up to 35,190 lbf (157 kN).

By early 1966, thrust output with afterburner reached approximately 37,000 lbf. In April 1967, testing continued within a high-altitude chamber at Saclay; by January 1968, Vulcan flight trials accumulated over 100 hours and clearance was granted for use on Concorde prototypes.

Concorde prototype 001 made its maiden flight on 2 March 1969 from Toulouse under pilot André Turcat. Utilizing afterburner power, it achieved takeoff speed at 205 knots following a ground roll of about 4,700 feet.

A proposed Mk 622 variant aimed to deliver higher thrust without afterburner to reduce noise emissions and improve fuel efficiency for extended routes such as trans-Pacific and transcontinental flights. However, disappointing sales of Concorde resulted in this ‘Concorde B’ development being discontinued.

Engine

The Olympus 593 was a two-shaft turbojet engine featuring afterburning capabilities. Both the low-pressure (LP) and high-pressure (HP) compressors comprised seven stages, each powered by a single-stage turbine. Due to the elevated inlet air temperatures encountered during Mach 2 cruise—surpassing —the compressor drums and blades were constructed from titanium, except for the final four HP stages, which utilized Nimonic 90 nickel alloy. Although nickel alloys are commonly reserved for hotter turbine sections, their use here was necessitated by the supersonic compressor temperatures. Cooling was applied to the HP turbine stator and rotor blades as well as the LP turbine rotor blades.

The partial reheat system provided a thrust increase of approximately 20%, allowing Concorde to operate from existing airfields and accelerate from Mach 0.95 up to Mach 1.7; beyond this speed, the aircraft maintained supersonic flight without reheat. During cruise, the engine itself generated about 8% of the total thrust directly, with the remainder derived indirectly—63% originated from intake pressure recovery and 28% from exhaust nozzle pressure.

Key components of the Olympus 593 were engineered for a service life of 25,000 hours, while compressor and turbine blades were rated at 10,000 hours. Engine swaps on Concorde could be completed in under two hours.

Intake

The Concorde’s variable-geometry intake, developed by BAC, played a vital role in supplying high-pressure, low-distortion airflow to the engine compressor. Inefficient pressure recovery reduces intake compression effectiveness, while excessive flow distortion can cause engine surging. For Concorde’s turbojet with afterburning, the intake also provided cooling air for the hot reheat duct and nozzle. Achieving these performance goals throughout the entire flight envelope was critical for commercial success and was accomplished through a variable geometry intake coupled with a control system that optimized both engine and aircraft operation.

Supersonic pressure recovery relied on generating multiple shock waves within the intake; increasing the number of shocks enhanced pressure recovery by compressing supersonic airflow via directional changes. Concorde’s forward ramps produced oblique external shock waves and isentropic compression, differing from the TSR-2’s half-cone translating centre-body design. Subsonic pressure recovery was improved by removing boundary layer air at the ramp bleed slot and through careful shaping of the subsonic diffuser. At Mach 2 cruise, Concorde’s intake achieved an impressive pressure ratio of 7.3:1.

Shock waves caused boundary layer thickening on the front ramp, which was managed by diverting this airflow through the ramp bleed slot to bypass both the subsonic diffuser and engine, thus preventing duct losses and flow distortion. The bleed slot’s position downstream of shocks allowed changes in engine airflow without modifying the external shock pattern. During engine throttling or shutdown, dump doors opened; these remained closed during cruise to avoid thrust penalties caused by air leakage.

Because the intake area was optimized primarily for cruise conditions, an auxiliary inlet provided additional airflow during take-off phases. This auxiliary door was accompanied by an aerodynamic cascade designed to minimize distortion at the engine face.

Internal airflow dynamics generated rearward drag in the initial converging section due to supersonic deceleration and forward thrust in the diverging duct as airflow slowed subsonically. As a result, at cruise speed, approximately 63% of total thrust was contributed by intake forces.

To precisely regulate ramp and spill positions, BAC implemented a digital signal processor within the Air Intake Control Units around 1972 at Filton. This innovation ensured fuel-efficient transatlantic operations and accurately controlled engine speeds to maintain surge margins under all conditions.

Concorde’s Air Intake Control System also introduced digital data highways—multiplexed serial data buses—that connected aerodynamic sensors located at the nose with control units near the intakes via roughly of lightweight twisted pair cables. This approach significantly reduced wiring weight compared to traditional analog systems.

This sophisticated control architecture guaranteed optimal propulsion system performance regardless of pilot commands or environmental variations.

At Mach 2 cruise and , Concorde achieved an overall pressure ratio near 82:1—comprised of 7.3:1 from the intake and 11.3:1 across two engine compressors—far surpassing subsonic contemporaries and delivering an overall thermal efficiency close to 43%.

Secondary nozzle

The exhaust system initiates with the engine's variable primary nozzle. Exhaust gases from the engine, combined with secondary air drawn from the nacelle intake, are directed into the airframe-integrated combined modulating secondary nozzle and thrust reverser, engineered by SNECMA. This secondary nozzle incorporates two movable "eyelids" that adjust their position depending on the flight phase; when fully closed, they function as thrust reversers to assist in slowing the aircraft during landing and taxi operations.

When positioned fully open during cruise, these eyelids, along with the engine nozzle, create an ejector nozzle that manages the expansion of exhaust gases. The eyelids form a divergent pathway while the engine's exhaust flow induces secondary airflow from the intake ramp bleed slot. This expanding mixture generates a forward-directed thrust force on the exhaust nozzle assembly, accounting for 29% of the total propulsive thrust during cruise conditions.

At a cruising speed of Mach 2.02, each Olympus 593 engine delivers approximately of thrust, corresponding to per unit.

The primary exhaust nozzle and jet pipe have a certified operational lifespan of 30,000 hours; meanwhile, the Thrust Reverser Aft (TRA) component is rated for 40,000 hours of service.


Variants

  • 593 – Initial model designed for Concorde
    • Thrust output: 20,000 lbf (89 kN) dry / 30,610 lbf (136 kN) with afterburner
  • 593-22R – Prototype variant featuring improved performance aligned with modifications in aircraft requirements
    • Thrust output: 34,650 lbf (154 kN) dry / 37,180 lbf (165 kN) with afterburner
  • 593-610-14-28 – Final production iteration for Concorde
    • Thrust output: 32,000 lbf (142 kN) dry / 38,050 lbf (169 kN) with afterburner

Engines on display

Several Rolls-Royce/Snecma Olympus 593 engines have been preserved and are displayed at:

Additional exhibits include:


References

External links

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