Misplaced Pages

#471528

49-403: The Rolls-Royce/SNECMA M45H is an Anglo-French medium bypass ratio turbofan produced specifically for the twin-engined VFW-Fokker 614 aircraft in the early 1970s. The design was started as a collaborative effort between Bristol Siddeley and SNECMA . The VFW 614 was designed to operate over short sectors with up to a dozen flights a day. The engines were optimized for 30-minute sectors at

98-423: A bypass stream introduces extra losses which are more than made up by the improved propulsive efficiency. The turboprop at its best flight speed gives significant fuel savings over a turbojet even though an extra turbine, a gearbox and a propeller were added to the turbojet's low-loss propelling nozzle. The turbofan has additional losses from its extra turbines, fan, bypass duct and extra propelling nozzle compared to

147-480: A common output shaft, or compressed air driving a small starter adapter. The air-start method superseded the cumbersome "Buicks" when better compressed air supplies became available. Any aircraft flying at three times the speed of sound is in a severe thermal environment, both from frictional heating and stagnation ram rise. The fuel was the only heat sink available to the aircraft and after absorbing 40,000 Btu/min (700 kW), keeping everything cool enough from

196-449: A corrected speed in an area of its compressor map known as "off-design". The third problem was caused by the afterburner duct being cooled with too-hot turbine exhaust gas. U.S. patent 3,344,606 describes the changes to the engine that extended the engine's capability to Mach 3.2. They included diverting 20% of the compressor entry air after the 4th compressor stage directly to the afterburner through six external tubes. This allowed

245-435: A cruise altitude of 21,000 feet at Mach 0.65. Only a few minutes would be spent at the cruise rating and most of the flight would be at the higher climb rating or at a descent setting. The engine had a low turbine entry temperature and comparatively low rotational speed. The engine was designed to be uprated without drastic redesign. Three options were water injection (+10% thrust), improved HP turbine (+10% thrust), addition of

294-481: A requirement for an afterburning engine where the sole requirement for bypass is to provide cooling air. This sets the lower limit for BPR and these engines have been called "leaky" or continuous bleed turbojets (General Electric YJ-101 BPR 0.25) and low BPR turbojets (Pratt & Whitney PW1120). Low BPR (0.2) has also been used to provide surge margin as well as afterburner cooling for the Pratt & Whitney J58 . In

343-436: A unique compressor bleed to the afterburner that gave increased thrust at high speeds. Because of the wide speed range of the aircraft, the engine needed two modes of operation to take it from stationary on the ground to 2,000 mph (3,200 km/h) at altitude. It was a conventional afterburning turbojet for take-off and acceleration to Mach 2 and then used permanent compressor bleed to the afterburner above Mach 2. The way

392-425: A zero-bypass (turbojet) engine the high temperature and high pressure exhaust gas is accelerated by expansion through a propelling nozzle and produces all the thrust. The compressor absorbs all the mechanical power produced by the turbine. In a bypass design, extra turbines drive a ducted fan that accelerates air rearward from the front of the engine. In a high-bypass design, the ducted fan and nozzle produce most of

441-516: A zero-stage to the LP compressor (+25% thrust). The M45H-01 was to have a thrust-specific fuel consumption (TSFC) of 12.91 grams per kilonewton per second (0.456 pounds per pound-force per hour). The engine was developed at the time of the Rolls-Royce bankruptcy which resulted in delays in developing the engine. Rolls-Royce/SNECMA M45H engines are on display as part of the aero engine collection at

490-462: Is also seen with propellers and helicopter rotors by comparing disc loading and power loading. For example, the same helicopter weight can be supported by a high power engine and small diameter rotor or, for less fuel, a lower power engine and bigger rotor with lower velocity through the rotor. Bypass usually refers to transferring gas power from a gas turbine to a bypass stream of air to reduce fuel consumption and jet noise. Alternatively, there may be

539-408: Is quoted for turboprop and unducted fan installations because their high propulsive efficiency gives them the overall efficiency characteristics of very high bypass turbofans. This allows them to be shown together with turbofans on plots which show trends of reducing specific fuel consumption (SFC) with increasing BPR. BPR is also quoted for lift fan installations where the fan airflow is remote from

SECTION 10

#1732800957472

588-450: Is trading exhaust velocity for extra mass flow which still gives the required thrust but uses less fuel. Turbojet inventor Frank Whittle called it "gearing down the flow". Power is transferred from the gas generator to an extra mass of air, i.e. a larger diameter propelling jet, moving more slowly. The bypass spreads the available mechanical power across more air to reduce the velocity of the jet. The trade-off between mass flow and velocity

637-898: The Royal Air Force Museum Cosford and the Musée aéronautique et spatial Safran . Additionally, an engine, with its cowl and pylon, is displayed at the Deutsches Museum Flugwerft Schleissheim ; this museum also displays a VFW-614, which has two engines mounted. Data from Jane's All the World's Aircraft 1971-72 . Related development Comparable engines Related lists Bypass ratio Turbofan engines are usually described in terms of BPR, which together with engine pressure ratio , turbine inlet temperature and fan pressure ratio are important design parameters. In addition, BPR

686-442: The compression ratio of the system by adding to the compressor stage to increase overall system efficiency increases temperatures at the turbine face. Nevertheless, high-bypass engines have a high propulsive efficiency because even slightly increasing the velocity of a very large volume and consequently mass of air produces a very large change in momentum and thrust: thrust is the engine's mass flow (the amount of air flowing through

735-624: The Conway varied between 0.3 and 0.6 depending on the variant The growth of bypass ratios during the 1960s gave jetliners fuel efficiency that could compete with that of piston-powered planes. Today (2015), most jet engines have some bypass. Modern engines in slower aircraft, such as airliners, have bypass ratios up to 12:1; in higher-speed aircraft, such as fighters , bypass ratios are much lower, around 1.5; and craft designed for speeds up to Mach 2 and somewhat above have bypass ratios below 0.5. Turboprops have bypass ratios of 50-100, although

784-506: The NASA Stratospheric Wake Experiment, which looked at the environmental impact of using afterburning jet engines for supersonic transports. An engine was tested in an altitude chamber at a maximum condition of full afterburning at Mach 3.0 and 19.8 km altitude. Alternative solutions to combat the adverse effects of high inlet temperature on the aerodynamic performance of the compressor were rejected by

833-504: The Pratt & Whitney patentee, Robert Abernethy. One of those solutions was used in a contemporary installation. The GE YJ93/ XB-70 used a variable-stator compressor to avoid front-stage stall and rear-stage choking. Another possible solution, pre-compressor cooling, was used on the MiG-25's R-15 engines. Water/methanol was injected from a spray mast in front of the compressor to lower

882-663: The TEB tank and afterburner nozzle actuator control lines. The development of the J58 involved some of the most challenging metallurgical development problems experienced by Pratt & Whitney Aircraft so far, with components operating at unprecedented temperatures and levels of stress and durability. New manufacturing techniques as well as new alloys improved the mechanical properties, and surface coatings had to be developed to protect components. Premature cracking of turbine vanes and blades made from conventionally cast (i.e. equiaxed) Mar-M200,

931-516: The TEB tank was a perilous task; the maintenance crew wore silver fire suits. Conversely, the JP-7 fueling was so safe that some aircraft maintenance was permitted during filling. The chemical ignition was chosen instead of a conventional igniter for reliability reasons, and to reduce mechanical complexity. The TEB tank is cooled with fuel flowing around it, and contains a disk that ruptures in case of overpressure, allowing TEB and nitrogen to discharge into

980-682: The US Navy to power the planned Martin P6M jet flying boat. The P6M started out using Allison J71-A-4 engines and then switched to the Pratt & Whitney J75 , due to J58 development delays. Upon cancellation of the P6M, it was selected for the Convair Kingfish and for the Lockheed A-12 , YF-12A and SR-71 . Other sources link its origin to the USAF's requirement for a powerplant for

1029-489: The WS-110A, the future XB-70 Valkyrie . Analytical calculations of the performance of the original J58 showed three problems at Mach 2.5: "exhaust pressure was equal to the inlet pressure, the compressor was deep in surge, and there was no cool air to the afterburner liner that would therefore melt". The first problem was caused by excessive compressor delivery temperatures, which did not allow enough energy to be added in

SECTION 20

#1732800957472

1078-433: The afterburner also had a catalytic igniter that glowed in the hot turbine exhaust. Each engine carried a nitrogen-pressurized sealed tank with 600 cm (21.1 imp fl oz; 20.3 US fl oz) of TEB, sufficient for at least 16 starts, restarts, or afterburner lights; this number was one of the limiting factors of SR-71 endurance, as after each air refueling the afterburners had to be reignited. When

1127-530: The afterburner. One heat source required two-stage reduction. Before entering the fuel heat-sink system, the Environmental Control System (ECS) air leaving the engine compressor at 1,230 °F (666 °C) was so hot that ram air at 760 °F (404 °C) had to be used first. Fuel flowing from the tanks to the engines was used to cool the air conditioning systems, aircraft hydraulic fluid , engine oil , accessory drive system oil,

1176-487: The compressor and turbine aerodynamic definitions, so that it would be reliable running for prolonged periods at unprecedented temperatures, not only inside the engine but also surrounding the casings where the controls, accessories, electrical wiring and fuel and oil tubes were located. Two starting methods were used during the life of the A-12, YF-12 and SR-71 aircraft: an AG330 starter cart with two Buick V8 engines driving

1225-452: The compressor to work properly with adequate surge margin and increased airflow into the compressor. Some of the increased flow left the compressor after the 4th stage as bypass to the afterburner, and some left the last compressor stage through the previously choked area. The increased airflow gave more thrust. The inlet guide vanes were modified with trailing-edge flaps to reduce blade flutter and prevent blade fatigue failures. The afterburner

1274-437: The crew to the exhaust nozzle area indicator, it was supplied to the fuel nozzles at 600 °F (316 °C). To cope with these high temperatures, a new jet fuel with a low vapor pressure had to be developed. A chemical method for igniting the fuel, triethyl borane (TEB), was developed to match its low volatility. TEB spontaneously ignites in contact with air above −5 °C. The engine and afterburner were lit with TEB and

1323-402: The early 1950s, was an early example of a bypass engine. The configuration was similar to a 2-spool turbojet but to make it into a bypass engine it was equipped with an oversized low pressure compressor: the flow through the inner portion of the compressor blades went into the core while the outer portion of the blades blew air around the core to provide the rest of the thrust. The bypass ratio for

1372-621: The engine and doesn't physically touch the engine core. Bypass provides a lower fuel consumption for the same thrust, measured as thrust specific fuel consumption (grams/second fuel per unit of thrust in kN using SI units ). Lower fuel consumption that comes with high bypass ratios applies to turboprops , using a propeller rather than a ducted fan. High bypass designs are the dominant type for commercial passenger aircraft and both civilian and military jet transports. Business jets use medium BPR engines. Combat aircraft use engines with low bypass ratios to compromise between fuel economy and

1421-435: The engine combustor to provide any thrust from the gas generator. All the thrust-producing pressure in the jet-pipe came from ram, as with a ramjet, and none from the gas generator. Fuel for thrust could only be added in the afterburner, which became the only source of engine thrust. The speed at which the gas generator produced no thrust was raised from about Mach 2.5 to about Mach 3 by patented design changes. Beyond that speed,

1470-426: The engine with acceptable pressure loss and distortion. It had to do this in all flight conditions. The ejector, or secondary, nozzle performed the reverse function of the inlet accelerating the turbine exhaust from about Mach 1.0, as it left the primary nozzle, back up to Mach 3. Mach 3 exhaust velocity is higher than Mach 3 flight velocity due to the much-higher temperature in the exhaust. The nacelle airflow from

1519-457: The engine worked at cruise led it to be described as "acting like a turboramjet ". It has also been described as a turboramjet based on incorrect statements describing the turbomachinery as being completely bypassed. The engine performance that met the mission requirements for the CIA and USAF over many years was later enhanced slightly for NASA experimental work (carrying external payloads on

Rolls-Royce/SNECMA M45H - Misplaced Pages Continue

1568-415: The engine) multiplied by the difference between the inlet and exhaust velocities in—a linear relationship—but the kinetic energy of the exhaust is the mass flow multiplied by one-half the square of the difference in velocities. A low disc loading (thrust per disc area) increases the aircraft's energy efficiency , and this reduces the fuel use. The Rolls–Royce Conway turbofan engine, developed in

1617-433: The gas generator would become a drag item with, at Mach 3.2, a pressure ratio of 0.9. Even minimum afterburner would not balance the drag. The effect was described qualitatively by Lockheed inlet designer David Campbell "..with minimum afterburner the engine would be dragging on the engine mounts at high Mach numbers." The second problem (the compressor deep in surge) was caused by the compressor trying to operate at too-low

1666-402: The gas power is shared between a separate airstream and the gas turbine's own nozzle flow in a proportion which gives the aircraft performance required. The first jet aircraft were subsonic and the poor suitability of the propelling nozzle for these speeds due to high fuel consumption was understood, and bypass proposed, as early as 1936 (U.K. Patent 471,368). The underlying principle behind bypass

1715-443: The influence of BPR. Only the limitations of weight and materials (e.g., the strengths and melting points of materials in the turbine) reduce the efficiency at which a turbofan gas turbine converts this thermal energy into mechanical energy, for while the exhaust gases may still have available energy to be extracted, each additional stator and turbine disk retrieves progressively less mechanical energy per unit of weight, and increasing

1764-593: The intake temperature for short durations at maximum speed. Pre-compressor cooling was also proposed for a Mach 3 reconnaissance Phantom and the Mach 3+ F-106 RASCAL project. The propulsion system consisted of the intake , engine, nacelle or secondary airflow and ejector nozzle ( propelling nozzle ). The propulsive thrust distribution between these components changed with flight speed: at Mach 2.2 inlet 13% – engine 73% – ejector 14%; at Mach 3.0+ inlet 54% – engine 17.6% – ejector 28.4%. The intake had to supply air to

1813-431: The part that joins the compressor to the combustor and that contains the highest pressure in the engine. Diffuser case weld cracking led to the introduction of Inconel 718 for this part. The afterburner liner was sprayed with ceramic thermal barrier coating that, together with the cooling air from the compressor, allowed continuous use of the afterburner with flame temperatures up to 3,200 °F (1,760 °C). NASA

1862-456: The pilot moved the throttle from cut-off to idle position, fuel flowed into the engine, and shortly afterwards an approx. 50 cm (1.8 imp fl oz; 1.7 US fl oz) shot of TEB was injected into the combustion chamber, where it spontaneously ignited and lit the fuel with a green flash. In some conditions, however, the TEB flow was obstructed by coking deposits on the injector nozzle, hindering restart attempts. Refilling

1911-529: The propulsion airflow is less clearly defined for propellers than for fans and propeller airflow is slower than the airflow from turbofan nozzles. Klimov RD-33 Pratt %26 Whitney J58 The Pratt & Whitney J58 (company designation JT11D-20 ) is an American jet engine that powered the Lockheed A-12 , and subsequently the YF-12 and the SR-71 aircraft. It was an afterburning turbojet engine with

1960-434: The requirements of combat: high power-to-weight ratios , supersonic performance, and the ability to use afterburners . If all the gas power from a gas turbine is converted to kinetic energy in a propelling nozzle, the aircraft is best suited to high supersonic speeds. If it is all transferred to a separate large mass of air with low kinetic energy, the aircraft is best suited to zero speed (hovering). For speeds in between,

2009-508: The second-stage turbine blades (the life-limiting component) from 400 to 50 hours. The same thrust-enhancement studies used for this work also looked at an additional 5% thrust from additional afterburner fuel made possible with oxidizer injection ( nitrous oxide ). The nitrous oxide rate would have been limited by thermal choking of the nozzle. As of 2021 , the J58 is the only known aircraft engine designed to operate continuously at maximum afterburning at high Mach number cruise. J58 experience

Rolls-Royce/SNECMA M45H - Misplaced Pages Continue

2058-485: The strongest cast nickel-base alloy, was avoided by the development of directionally solidified parts cast in the same material. Directionally solidified Mar-M200 became the strongest cast turbine material to date and was introduced in production engines. Single-crystal turbine blades cast in Mar-M200, giving further improvement of high temperature resistance, would also be developed through testing in J58 engines. Waspaloy

2107-481: The thrust. Turbofans are closely related to turboprops in principle because both transfer some of the gas turbine's gas power, using extra machinery, to a bypass stream leaving less for the hot nozzle to convert to kinetic energy. Turbofans represent an intermediate stage between turbojets , which derive all their thrust from exhaust gases, and turbo-props which derive minimal thrust from exhaust gases (typically 10% or less). Extracting shaft power and transferring it to

2156-621: The top of the aircraft), which required more thrust to deal with higher aircraft drag. The J58, company designation JT11, had its origins in the larger JT9 (J91) engine. It was a 3/4 scale JT9 with a mass flow of 300 lb/s (140 kg/s), down from 400 lb/s (180 kg/s). The JT11 was proposed to the US Navy under their designation J58. It was also proposed for various Navy and Air Force aircraft, e.g. Convair F-106 , North American F-108 , Convair B-58C , Vought XF8U-3 Crusader III , and North American A3J Vigilante , but none of these applications followed. The J58 began development for

2205-683: The turbojet's single nozzle. To see the influence of increasing BPR alone on overall efficiency in the aircraft, i.e. SFC, a common gas generator has to be used, i.e. no change in Brayton cycle parameters or component efficiencies. Bennett shows in this case a relatively slow rise in losses transferring power to the bypass at the same time as a fast drop in exhaust losses with a significant improvement in SFC. In reality increases in BPR over time come along with rises in gas generator efficiency masking, to some extent,

2254-426: Was cooled by the bleed air that was 400 °F (220 °C) cooler than the turbine exhaust gas. Not all the oxygen in the bleed air was available for combustion, as most of the bleed air was directed into the cooling shroud before entering the afterburner cavity for reheating. The improved afterburner cooling allowed a higher flame temperature, which gave more thrust. The engine was completely redesigned, except for

2303-406: Was loaned 2 SR-71 aircraft for research work. One was modified to flight-test a Linear Aerospike rocket engine and was fitted with thrust-enhanced J58 engines. Engine thrust was increased by 5% to offset increased aircraft drag. The increased thrust came from a throttle push, or exhaust gas temperature uptrim, of 75 °F (42 °C). The increase was limited by the allowable reduction in life of

2352-460: Was the most widely used alloy in the engine, from critical high-energy rotating compressor discs to components made from sheet. Although used for turbine discs in other engines, it did not have the required properties for J58 turbine discs. Astroloy , the strongest known nickel-base superalloy in the Western world at that time, was used instead. Waspaloy was also used initially for the diffuser case,

2401-645: Was used extensively in the JTF17 engine proposal for a Mach 2.7 SST, due to significant flight time at Mach 2.7 and above. It was also used for subsequent engines developed by Pratt & Whitney, both commercial and military. The next afterburning engine, the TF30 as installed in the F-111, used an airframe-mounted secondary nozzle with free-floating flaps similar to that used on the SR-71. J58 emissions were measured as part of

#471528