why our Defense organizations never took turbo prop engine project

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After the highly successful introduction of next generation turboprops in the mid 1980s, the continuing improvement of well known brands and the stubborn survival of two of the more popular programs – Bombardier's Q series and ATR's 42/72, more manufacturers are looking at entering the turboprop market, pinning their hopes on rising fuel costs and environmental concerns.

See related report: US regional market changes drive jet vs turboprop debate

Programs are under way in China, Russia and South Korea and both Bombardier and ATR are talking about the next generation of turboprop that, they say, could replace the regional jets that once replaced them. This is especially so given the improvements made in the last decade which puts their speed on par with regional jets with lower operating costs bringing a significant competitive advantage. It is especially significant that two legacy carriers – Alaska and American Eagle never dropped turbprops – while Continental has adopted them in the last few years as a way to grow their regional aircraft without breaking its pilot scope clause. In addition, markets that once could only sustain a 19 seater such as the Beech 1900 and Fairchild Metro are upgauging to the Bombardier Q200, once known as the de Havilland Dash 8, the Saab 340 and the Embraer Brasilia.

"Lower operating costs and the smaller ecological footprint of turboprops ensures that we are likely to see a resurgence in use of these aircraft, said AirInsight authors Erkan Pinar and Addison Schonland. Engine technology has provided enough power to operate at near jet speeds, at substantially lower fuel burn and with less pollution. Indeed a turboprop typically burns just under two thirds of the fuel needed to fly a passenger compared to a pure jet. It is generally accepted that for routes between 300 to 500 miles a turboprop is faster and more economical than a pure jet. Turboprops do not have to climb as high and therefore reach cruise faster and descend quicker."

HAL engine line page not a sing turbo prop engine Welcome to Engine Division of HAL

Review on turbo prop tech


A turboprop engine uses the same principles as a turbojet to produce energy, that is, it incorporates a compressor, combustor and turbine within the gas generator of the engine. The primary difference between the turboprop and the turbojet is that additional turbines, a power shaft and a reduction gearbox have been incorporated into the design to drive the propeller. The gearbox may be driven by the same turbines and shaft that drive the engine compressor, mechanically linking the propeller and the engine, or the turbines may be separate with the power turbine driving a concentric, mechanically isolated shaft to power the gearbox. The latter design is referred to as a "free power turbine" or, more simply, a "free turbine" engine. In either case, the turbines extract almost all of the energy from the exhaust stream using some of it to power the engine compressor and the rest to drive the propeller.

A turboprop engine is very similar to a turboshaft and many engines are available in both variants. The principal difference between the two is that the turboprop version must be designed to support the loads of the attached propeller whereas a turboshaft engine need not be as robust as it normally drives a transmission which is structurally supported by the vehicle and not by the engine itself.

THE MILLION DOLLOR QUESTION IS WHY WE NEVER TOOK THIS TECH RESEARCH SERIOUSLY WHEN THE APPLICATION POSSIBILITIES ARE ENDLESS FROM UAV'S TO TRANSPORTS TRAINING AIRCRAFT AND MORE

i would love to have productive info and discussions from members no sarcastic comments please
@Bangalorean @Kunal Biswas @pmaitra @sayareakd @Twinblade @Ray @ladder @abingdonboy @p2prada @bennedose and more sorry if i missed any

 

[Ray]

What is the difference between a turbofan and a turboprop engine?

Both engines use a turbine for power. This is where the "turbo" part of the name comes from. In a turbine engine, air is compressed and then fuel is ignited in this compressed air. The energy produced by the ignition turns the turbine. The turbine is then able to drive both the compressor at the front of the engine and also some useful load. In airplanes, it produces thrust.

The first jet engine was a turbojet. This is a simple turbine engine that produces all of its thrust from the exhaust from the turbine section. However, because all of the air is passing through the whole turbine, all of it must burn fuel. This means it is inefficient, and the solution is the turbofan.

_________________

In a turbofan, the turbine primarily drives a fan at the front of the engine. Most engines drive the fan directly from the turbine. There are usually at least two separate shafts to allow the fan to spin slower than the inner core of the engine. The fan is surrounded by a cowl which guides the air to and from the fan. Part of the air enters the turbine section of the engine, and the rest is bypassed around the engine. In high-bypass engines, most of the air only goes through the fan and bypasses the rest of the engine and providing most of the thrust.

_____________________

In a turboprop, the turbine primarily drives a propeller at the front of the engine. There is no cowl around the prop. Some air enters the turbine, the rest does not. The propeller is geared to allow it to spin slower than the turbine.

Turboprops are more efficient at lower speeds since the prop can move much more air with a smaller turbine than the fan on a turbofan engine. The cowl around the turbofan's large fan allows it to perform better than an open propeller at high speeds.

At supersonic speeds, turbojets have more of a performance benefit. They develop all of their thrust from the high velocity turbine exhaust, while turbofans supplement that with the lower velocity air from the fan. Since the air from the fan is also not compressed nearly as much as the core turbine flow, it is also harder to prevent the flow from going supersonic and causing losses.

The Concorde used turbojets because it was designed to cruise for long periods at supersonic speeds. Modern fighter jet engines are turbofans, which provide a compromise between efficiency and speed.

There are other benefits and drawbacks between turbojets, turbofans, and turboprops, but I think they are beyond the scope of this question.

Work has been done on creating a "propfan" engine, in an attempt to get the efficiency of a turboprop and the speed of a turbofan. They have yet to come up with a viable design.

Elsewhere in aviation, turbine engines are used in helicopters (as a turboshaft engine driving the rotors instead of a propeller), and in most jet aircraft and large turboprop aircraft (as an auxiliary power source, the APU).

Turbines also find use outside of aviation in power plants (to generate electricity), and even vehicles (like the Abrams tank).

Turbocharged piston engines use a turbine much differently from the examples above. Instead of being the primary power source, the turbine only assists the piston engine. A turbocharger uses a turbine to compress air sent to the engine intake. The increased compression helps the engine generate more power. The turbine of a turbocharger is driven by engine exhaust gasses, and a supercharger is similar but is directly powered by the engine. .

What is the difference between a turbofan and a turboprop engine? - Aviation Stack Exchange


This video explains the workings of a turbojet, turboprop and turbofan.





I think the emphasis was on building fighter jet and so turboprop fall by the roadside as far as HAL is concerned.

But then, that is just a conjecture.

 

[Kunal Biswas]

One has to put a requirement, As of now only various Indian Private and Government companies came together to develop aviation engines this includes UAV tubro-prop and Jet engines and next generation Kaveri ..

THE MILLION DOLLOR QUESTION IS WHY WE NEVER TOOK THIS TECH RESEARCH SERIOUSLY WHEN THE APPLICATION POSSIBILITIES ARE ENDLESS FROM UAV'S TO TRANSPORTS TRAINING AIRCRAFT AND MORE

i would love to have productive info and discussions from members no sarcastic comments please
@Bangalorean @Kunal Biswas @pmaitra @sayareakd @Twinblade @Ray @ladder @abingdonboy @p2prada @bennedose and more sorry if i missed any

 

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G-AHRF, the prototype Vickers V630 Viscount-seen here in British European Airways colors-made its maiden flight on Jul 16, 1948. Powered initially by 4 Rolls-Royce Dart 503 turboprops of 1250 shp each, 444 Viscounts of all versions were sold before production ended in 1964, making it not only the first, but one of the most successful turboprop airliners.

While the English aviation engineer Frank Whittle, who patented the concept in 1930, is generally recognized by historians as the father of the modern turbojet engine, it was a little-known Hungarian named György Jendrassik who sired the first true turboprop engine, designated the Cs1, in 1938.

With war in Europe on the horizon, the first airframe to use Jendrassik's turboprop design was slated to be the Varga RMI1 X/H reconnaissance bomber, which was planned for first flight in 1940.

Yet, unlike turboprops of today, the Cs1 was an underperformer, and though designed for an output of 1000 shaft horsepower (shp), problems with the engine limited its output to 400 shp. Although the troubles with Jendrassik's turboprop were likely surmountable, history intervened before its shortcomings could be resolved.

By late 1940, with Europe at war, Hungary signed the Tripartite Pact, reluctantly aligning itself with Nazi Germany. With the pact in place, both the Cs1 engine and the Varga reconnaissance bomber for which it was destined were shelved, and the Messerschmitt Me210-with its tried-but-true older technology-was chosen in its place.

As World War II progressed, technological innovations seemed to occur monthly, and it was the turbojet, rather than the turboprop engine, that was viewed as the quantum leap in engine technology. Heinkel Flugzeugwerke in Germany and Gloster Aircraft Company in Britain produced test bed airframes for the then-developing turbojet engine.

Late in the war, as piston-engine technology and propeller-driven aircraft were reaching their technological peak of performance, the Royal Air Force's Gloster Meteor-the first Allied jet to be operational in any numbers-soon shared the skies with the Luftwaffe's Messerschmitt Me262-the first jet fighter to actually achieve operational status.

 

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First aircraft to be flown successfully under turboprop power was a modified RAF Gloster Meteor fighter, pictured here in late 1945. Note the 2 small vertical stabilizers, added due to initial concerns of directional control under engine-out trials with the new powerplants. Fuselage markings aft of the roundels show that the aircraft is a prototype, while the "G" suffix to the RAF serial indicates that it is assigned an armed guard.

The end of the propeller age seemed near. But it was not until the end of the war that the turboprop engine surfaced again, this time perfected by the British. While the turbojet engine, when strapped to an aircraft, was a strong performer, specific fuel consumption was high, and thus range was limited.

Also, as the sound barrier had yet to be broken-at least intentionally-the limitations associated with the forward speed of high-performance propeller-driven aircraft were not seen as so important as they are today.

With gearboxes and propellers in hand, engineers at Rolls-Royce developed the RB50 Trent turboprop engine-essentially a Derwent turbojet engine fitted with a forward drive shaft, a reduction gearbox, and a 5-bladed Rotol propeller similar to those seen on later Vickers Supermarine Spitfires.

Affixed to Gloster Meteor s/n EE227, the world's first turboprop engine to power an aircraft took to the skies some 5 months after the end of WWII in the European theatre, on Oct 20, 1945.

Enter the Dart

Although the RB50 turboprop was the breakthrough engine, perfection and subsequent acceptance of technology come slowly, and it was not until 1948 that the commercial successor to the Trent-the RB53 Dart-flew on the Vickers V630 airliner, later to become the Viscount.

Eventually, in Apr 1953, the Viscount would inaugurate the world's first turboprop-powered airline service with British European Airways. Popular with passengers used to the drone of piston-engine aircraft, the pressurized Viscount was a star performer amongst its 4-engine contemporaries, and constantly set new speed records.

In the early 1950s, as the turboprop-powered Viscount was entering service, its chief competitors were all 4-engine piston airliners, many of which were outgrowths of WWII transports and all of which were of US manufacture.

The Douglas DC6 and later DC7 series were developments of the venerable DC4, which (as the C54) proved its mettle in the Berlin Airlift of 1948. The Lockheed L1649 Super Constellation, regarded by many enthusiasts as one of the most elegant-looking airliners of the day, was an outgrowth of the original L049, which entered US military service during late WWII as the C69.

Even the double-decker Boeing 377 Stratocruiser used the wings and empennage of the B50, which itself used the wings and empennage of the B29 Super_fortress, the aircraft that helped bring an end to the war.

Yet all these 4-engine, piston-powered, propeller-driven aircraft had in common a disastrous trait-one the turboprop-powered Viscount did not share-overly complex engines that were prone to fires.

To be sure, the unreliability of the Pratt & Whitney R4360-B6 Wasp-a behemoth 28-cylinder, 3500-hp radial engine-and its predisposition to fire, earned the 4-engine Boeing Stratocruiser the somewhat humorous nickname "the best 3-engined airliner of the Pacific."

Turboprop history

 

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This was a reference to the routine failures of at least one of its engines on its regular routes. In short, the 4-engine piston airliners were a dying breed, and the Rolls-Royce Dart would hasten their demise.

Rolls-Royce Dart

The propeller-driven aircraft, however, would still hold its own, especially when those propellers were affixed to the Dart. Rolls-Royce Darts proved reliable and adaptable, with growth variants ranging from 1815 shp in the Mk 520 to 3060 shp in the later Mk 542 series.

After the success of the Viscount, Darts were seen on twin-engine airframes-including the Fokker F27 Friendship, Avro 748 (later Hawker Siddeley HS748) and, later, the lesser-known Nihon YS11-as the regional market solidified under the emerging airline hub-and-spoke system.

 

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Latest version of the original 1960s-era Grumman E2, the US Navy's Northrop Grumman E2D Advanced Hawkeye (upper) is an airborne early warning and battle management aircraft. Power comes from 2 Rolls-Royce T56A-427As coupled to 8-scimitar-bladed composite NP2000 propellers. Compare with the earlier E2C (lower aircraft).

Notably, it was the Mk 529 version of the Dart that would power one of the first purpose-built business aircraft-the Grumman G159 Gulfstream, which first flew in 1958. Soon, 4-engine turbojet aircraft filled the longhaul need, and short to medium-range turboprops filled the void left by retiring piston-engine aircraft.

Although the Dart was a workhorse, and remained in production into 1987, competition in the form of even bigger, more powerful turboprops from the US and USSR would eventually outmode it.

East meets west

In 1951, when the US Air Force announced a requirement for a medium-size logistic and transport aircraft to replace a fleet of aging piston-powered transport aircraft, Lockheed responded with the C130 Hercules, now one of the most recognizable turboprops of all time.

First flown in 1954, the YC130 was powered by the new Allison-designed T56A-9 turboprop engine driving wide-chord, 3-bladed Aero Product propellers. Later, with the C130B, the 3-bladed propellers would be replaced by the now highly familiar Hartzell 4-bladed versions.

By 1957, the T56A series would show up in civilian use, on the Lockheed L188 Electra-a medium-range 4-engine turboprop airliner similar in layout and configuration to the Dart-powered Vickers Viscount.

Eventually, some 18,000 T56 turboprop powerplants would be produced, powering not only the 4-engine C130 and Electra series, but the US Navy's twin-engine Grumman C2 Greyhound and E2 Hawkeye, as well as the Electra-derived Lockheed P3 Orion.

Interestingly, production of the T56A series continues today, albeit no longer under the Allison name. In 1994, Rolls-Royce, maker of the famed Dart, announced its intention to acquire Allison Engine Company, maker of the T56A. By 1995, that acquisition was official, and Allison became a subsidiary of Rolls-Royce, again bringing Rolls to the forefront of turboprop technology.

The current iteration of the T56A-the Series IV-is capable of producing 5250 shp at only 1940 lbs of weight. In comparison, the Pratt & Whitney R4360 Double Wasp, arguably the zenith of piston-engine development at the close of WWII, could muster only 4300 hp, yet its weight was twice that of the T56.

And, while powerful by US standards, the T56A is small by comparison to Russian standards of large turboprops.

 

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Giants in the sky

At about the same time the C130 was entering the world stage and the cold war was beginning to heat up, the USSR was quietly developing a turboprop-powered intercontinental bomber of monstrous proportions-the Tupolev TU95 (NATO codename Bear).

Development of the Bear mimicked the concerns engineers in the west were facing in the 1950s. In effect, piston engines were of late WWII vintage and were simply not powerful enough, but pure turbojet engines lacked range due to high fuel consumption.

During this period, while the US flirted with the idea of supersonic intercontinental bombers, it produced the subsonic Boeing B52 Stratofortress in droves. It also began moving the 4-engine piston-powered KC97, which was based on the Boeing 377 airframe, to second-line duties, as an all-jet aerial refueling armada composed of Boeing 707-like KC135 Strato_tankers would supply the thirsty B52s.

Again it seemed that the propeller age was drawing to a close-or that, at best, propellers were to be relegated to only slow, lumbering transport aircraft. But Tupolev's TU95 was a radical turboprop design.

A long slender fuselage was attached to wings that swept back some 35 degrees. At first glance, it appeared the designers at Tupolev meant for turbojets to power the Bear. Instead, the TU95 is powered by 4 Kuznetsov NK12 turboprop engines each driving a pair of 4-bladed counter-rotating propellers.

Pilatus launched the PC12 NG next-generation version of its successful PC12 turboprop in 2006. It uses a 1200-shp P&WC PT6A-67P.

Producing some 15,000 shp, the current version of the Kuznetsov turboprop, the NK12MA remains the most powerful turboprop engine ever developed. Even in 1953, when the Bear first flew, early versions of the NK12 were producing around 12,000 shp-some 2.5 times the output of the most powerful Allison turboprop engine in production today.

While propeller-driven aircraft are typically regarded as slow by comparison to turbojet aircraft, the combination of ultra-large turboprop engines, counter-rotating propellers and a jetlike design means the TU95 is no slouch. With its maximum speed of 575 mph, or Mach 0.87, the Bear is faster than most of today's commercial jetliners.

Reported to have initially outaccelerated even afterburning western-built jet fighters, Tupolev's TU95 is easily the fastest propeller-driven aircraft in the world. And, as defense analysts have it, the Bear should remain in active service until at least 2040.

Business applications

While western and eastern militaries were experimenting with ever larger turboprops for a wide variety of aircraft, Pratt & Whitney Canada and Garrett AiResearch were working on civil and business applications for their small to midsize turboprop engines.

In 1961, the Pratt & Whitney Canada PT6A took to the skies in experimental form. By 1963, it was evident it was a winner, and the engine began a production run that continues to this day.

Eventually, the PT6A would become the most popular turboprop engine ever developed, with a notable 36,000 units delivered before its 40th anniversary in 2001. This remarkably adaptable engine, available today in models from 500-2000 shp, powers nearly the entire series of Hawker Beechcraft King Air, as well as the Cessna Caravan, Piaggio Avanti, Pilatus PC12 and Piper Cheyenne II/III.

In most applications the PT6A is mounted facing rearward-the intake side of the engine faces the rear of the aircraft and the power section and gearbox face forward, driving the propeller. Because of this design, the engine uses 2 separate shafts, making it a free (as opposed to fixed) turbine design.

Although slightly more complex than a single-shaft fixed turbine, the PT6A arrangement is a favorite among mechanics in the field as it allows ease of access to the engine's power or hot section, and it is much quieter during ground operations.

 

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No business turboprop is as well known as Hawker Beechcraft's venerable King Air series, which traces its lineage to the original piston-powered Beech 50 Twin Bonanza. Latest version of the King Air 200, the 200GT (above) is powered by 2 PT6A-52 engines of 850 shp each.

Garrett, now a division of Honeywell, also began work in the early 1960s on a turboprop engine that competed directly with Pratt & Whitney Canada's PT6A.

The Garrett TPE331, a single-shaft fixed turbine turboprop engine was soon appearing on a host of business aircraft, including the Rockwell (formerly Aero) Turbo Commander series, Cessna 441 Conquest II and Mitsubishi MU2, as well as regional aircraft such as the BAe Jetstream 31/32 and Fairchild (Swearingen) Metro.

Even the King Air, perhaps the best-known airframe using the PT6A, found itself equipped with the TPE331 for the launch of the B100 series. While used in fewer applications than the PT6A series, more than 14,000 TPE331s have been delivered since its advent in 1963.

Generally speaking, fixed-turbine turboprop engines like the TPE331 are simpler designs with fewer moving parts than a comparable free-turbine engine like the PT6A. As a result, they tend to be slightly smaller and more compact.

Yet, despite their comparative simplicity, they have their operational idiosyncrasies that are most manifest in the post-flight behavior of the crews that fly TPE331-equipped aircraft. Notably, on shutdown, pilots of these aircraft will often walk over to the propellers and spin them vigorously by hand in order to draw in additional air to cool the turbine.

The propellers on all turboprop engines are linked to the inlet or power turbines through a separate gearbox, but when the propeller stops on a fixed-turbine design so does the turbine itself. Spinning the propellers by hand also serves to expel hot air from the engine, which helps prevent shaft bow (as the TPE331 has relatively few main bearings considering its length).

This practice is also said to enhance fuel nozzle life and reduce air seal drag on the engine, which can lead to a hung start.

The Advanced Turboprop Project and the UDF

If the story of the turboprop engine ended with today's popular business applications, it would still be considered a widely successful powerplant.

But the story of the turboprop took an interesting turn in the 1970s-one that linked it forever to its fuel-efficient reputation and that resulted in the comparatively wild propeller designs found on newer turboprops.

In 1973, during the Yom Kippur war between Israel and the forces of Egypt and Syria, an oil embargo was imposed on the US, Europe and Japan, causing fuel prices to skyrocket overnight.

Six years later, as Ayatollah Khomeini ousted the Shah of Iran during the Iranian Revolution, panic struck the market. Again, oil prices soared. Volatility was the new norm, and as technology took on the task of producing more fuel-efficient engines, new life was breathed into the turboprop and its related accessory, the propeller.

Throughout the late 1970s and early 1980s, NASA engineers were working on an effort dubbed "the Advanced Turboprop Project"-a US government-funded study to examine the feasibility of developing the turboprop engine as a viable competitor to the larger, less efficient turbojet and turbofan designs found on airliners of the day.

The result of the NASA prototype and wind tunnel tests was a tractor-style turboprop design with a single row of computer-modeled scimitar-shaped blades that allowed extremely high subsonic cruise numbers without the typical drag penalties associated with propeller tips speeds as they approach supersonic.

Concurrently, and without the knowledge of NASA, engineers at General Electric were working on a similar design, but one which used 2 rows of counter-rotating blades in a pusher configuration-what would ultimately come to be known as the unducted fan (UDF). Unveiled in 1983, the GE36 UDF "propfan" was a highlight of the 1985 Paris Air Show.

By the following year, the UDF was being flown on a test bed, and Boeing announced the 7J7-a 150-seat airliner that would be powered by the UDF. Pundits and newspapers alike began to announce that the propeller was back to stay.

 

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GE36 unducted fan

 

[AVERAGE INDIAN]

General Electric's efficient GE36 unducted fan (UDF) was once seen as the future of airliner engine design. In the mid-1980s, the declining price of oil and the rise of the CFM56 engine sealed the fate of the powerplant. Its technology lives on today, largely in composite propeller designs affixed to turboprops.

The NASA team which led the Advanced Turboprop Project was awarded the Collier Trophy in 1987 for its work. Things were looking up for propeller-driven aircraft. But the story of the turboprop is inextricably linked to its fuel economy, which is revered only during times of high oil prices.

By 1987, the popular and efficient CFM56 turbofan was selling in wide numbers, and the market for the UDF evaporated as oil fell below $20 a barrel. The same collective national conscience that had once worried about fuel prices snubbed history instead, and went back to its business.

By 1989, the turboprop was again out of fashion, even as a lowly feeder aircraft-at least in North America-as Bombardier announced its Canadair Regional Jet (CRJ) program. Despite the disinterest in turboprops after the oil markets fell, the technology that came out of the Advanced Turboprop Project and the UDF lives on in today's turboprop engines and propeller systems.

Among these offspring are the Lockheed Martin C130J Hercules, which uses new Rolls-Royce AE_2100 turboprop engines coupled to all-composite, 6-bladed scimitar propellers. Similarly, EADS's 4-engine turboprop competitor to the C130J-the Airbus A400M-is equipped with all-composite 8-bladed scimitar propellers.

And even the US Navy's 1960s-era E2 Hawkeye, which still uses the trusty Allison T56A, has received a propeller update in the form of a composite 8-bladed arrangement like that on the A400M. Predictably, as oil prices peaked last summer, the propeller was again in vogue.

An Oct 24, 2008 General Electric press release entitled "GE and NASA to initiate wind-tunnel testing for open rotor jet engine systems" disclosed that GE36 UDF technology was being dusted off, albeit now under the moniker "open rotor" as opposed to "propfan." It appears that, finally, the turboprop and the propeller are here to stay.

Turboprop history

 

[AVERAGE INDIAN]

Ultra High Bypass Jet Engine Green Technology Airline Flight Test

 

[AVERAGE INDIAN]

Whatever happened to propfans?


Hailed for its fuel-saving potential when it was developed 19 years ago, the concept never quite got off the ground

In 1988 the launch of the unducted fan (UDF) was virtually a given. At the Farnborough air show, while the GE36 demonstrator engine buzzed overhead on its McDonnell Douglas MD-81 ultra-high bypass (UHB) demo testbed, GE's general manager of commercial operations at the time, Ron Welsch, told Flight International: "It's not a case of if it's a case of when."

GE chief engineer Brian Rowe was just as bullish. "There are a lot of interested people out there. We intend to sell it, and we intend the programme to go ahead in the next couple of years."

The GE36 demonstrator engine set the Farnborough air show buzzing in 1988 - and then disappeared

The UDF/UHB demonstrations in the late 1980s traced their roots to the OPEC oil embargo of 1973 and the rude awakening it gave the USA to its vulnerability to internationally controlled oil supplies. The increased price of oil affected the airline industry in particular. At the time of the crisis the USA imported 6 million barrels of oil a day, 64% of which came from OPEC.

Although US airlines began their own fuel-saving measures, reducing consumption by over a billion gallons a year, any advantages were wiped out as jet fuel prices jumped from 12¢ to more than $1 per gallon. The result was that total yearly fuel costs increased by $1 billion, or triple the earnings of the airlines. Before 1972, fuel accounted for 25% of carriers' total direct operating costs, but during the crisis it shot up to more than 50%. Today it makes up almost 40% of direct operating costs.

Political pressure turned on NASA which, in February 1975, formed the Intercenter Aircraft Fuel Conservation Technology Task Force to explore potential options. Out of this came a set of aeronautics projects including the Energy Efficient Engine (E3), which would generate advanced technology that would feature in the GE90, and the advanced turboprop (ATP). NASA believed an ATP could reduce fuel consumption by up to 30% over existing turbofan engines with comparable performance at speeds up to Mach 0.8 and altitudes up to 30,000ft (9,150m).

Despite the fuel saving predictions, public and industry perception of propellers and concerns over the technical challenges delayed the go-ahead of the ATP until 1978. NASA worked with Allison and Pratt & Whitney on a joint concept, and awarded Hamilton Standard advanced blade development contracts. In 1981 Hamilton began to design a large-scale, single-rotating, composite blade set.

In the meantime, unknown to NASA, GE was developing its own design: a gearless, counter-rotating pusher system. As GE's development was based on commercial considerations, most of its decision-making hinged on the publicity value of shifting the image away from propellers to propfans.

NASA was shown GE's UDF design in 1983 as preparations were under way to begin large-scale demonstrations of the NASA industry team ATP concept. This combined Hamilton Standard's SR-7A propfan with an Allison turboshaft and gearbox, and was tested in 1986. The complete engine, with an eight-bladed unit, flew on a modified Gulfstream II in 1987.

The P&W/Allison propfan team was also established in 1986. It spun off many of the technical and design elements from the joint NASA-industry studies. It combined an Allison 571 power section (based on an industrial and marine gas generator), a new low-pressure compressor, a new gear system and propfan module derived from the ATP work, a new nacelle and a full authority digital electronic control system derived from the PW2037.



The resulting 578-DX demonstrator included two rows of 2.95m (11.6ft) diameter blades: six in the front row (counter-clockwise rotation viewed from the rear) and six in the aft row (clockwise).

GE meanwhile flew its demonstrator in 1986 on a 727 testbed, and actively pursued potential applications on future Boeing and McDonnell Douglas projects, including the 7J7 and the MD-90 - both aft-engine configurations and the only suitable new models to which the UDF could be fitted. The demonstrator engine, based on a F404 gas generator, was also mounted on the same MD-81 that would later fly the P&W/Allison engine, and flown in mid-1987. By now backed with NASA Lewis participation, the flight tests revealed important results, including key issues such as acoustic signature and performance.

GE declared the demonstration showed that "without an acoustically attenuated duct around the fan, the community noise levels and internal cabin noise levels of such an unducted fan configuration would be acceptable and certifiable".

Performance was shown to be in the "high propulsive efficiency levels of the 1990s" and in a production version such as the planned GE36-C25 envisaged for a planned MD-92 would have been in the 0.5 (total fuel/payload lb) range versus around 0.8 for the CFM56-powered Airbus A320 and 1.3 for the JT8D-217 powered MD-80.

The P&W/Allison 578-DX tests, meanwhile, began "flawlessly" in April 1989, though by now the world had changed, and with it the prospects for propfans. Fuel prices were coming down and without the imperative of higher operating costs, neither the will nor the reasons existed for propfans to push forward.

The signs were there the year before, when Welsch admitted that at 65¢ per gallon, the fuel price was too low to justify the UDF. "If fuel were at a buck or so a gallon, they'd be clamouring," he said.

P&W is adamant that the geared turbofan will lead the next generation engine race

No business came in for either offering and, even as the P&W/Allison demonstrator prepared for take-off in the Mojave desert, the decisions that would kill any chance for a commercial production propfan (in the West at least) in the 20th century were being taken down at the coast in Long Beach.

In 1989 McDonnell Douglas admitted it was studying the International Aero Engines V2500 in place of a UHB option for the MD-90. The decision was "an either/or situation," and reflected concerns the airlines were showing "about the technology risks with the UHB", said the company at the time.

Airlines certainly appeared reluctant to gamble on the fuel efficiencies while oil prices remained low and McDonnell Douglas sounded the death knell for the UHB later that year when it confirmed selection of the V2500. Parallel efforts to launch a GE UDF-powered T-tail airliner project named the MPC-75 between Germany and China also failed around that time, leaving the various propfan concepts with nowhere to go except museums.

"If fuel were at a buck or so a gallon, they'd be clamouring." Ron Welsch, GE's former manager of commercial ops

Whatever happened to propfans? - 6/12/2007 - Flight Global

 

[AVERAGE INDIAN]

GE36

With titanium and composite advancements in the early 1980s, GE was able to produce a gas turbine engine capable of turning large diameter prop blades. The prop blades would be capable of rotating at a high RPM and sustaining supersonic tip blade speeds. The blades would be adjustable, ensuring the blades remained efficient in all speed realms. First flying in 1986, the GE36 was able to reduce the fuel consumption by 20% compared to the gas turbine engines of the day. Though the GE36 was a revolutionary idea and a valid concept, it was never widely produced and the program was canceled in 1995 ("P-9 LRAACA [Long-Range Air ASW Capable Aircraft]", 2011).

By attaining the increased fuel efficiency, the GE36 was able to utilize the hot gasses being produced from the reactive portion of the engine. Designers were able to extend the rear section of the engine while still maintaining the relatively small size of current turbofan engines (Otis & Vosbury, 2002).

Modern 9:1 high bypass ratio gas turbine engines are able to increase efficiency and reduce the fuel required for a given flight. As a result, air carriers are able increase their profit margins. With continued research in prop fans and unducted fan engines, the aircraft that we fly in the future may no longer resemble the look of current modern airliners (Otis & Vosbury, 2002).

Pros

By utilizing the hot exhaust gases that run the prop blades of an unducted fan engine, it helps to ensure that the maximum amount of energy available from the burning of the jet fuel in the combustion chamber is utilized. Modern day engines are unable to extract all of the energy from the expanding gases due to the need to reduce the length of the engine. By removing the large front fan, designers are able to reduce the number of compressor stages and subsequently, the size of the front half of the engine. Designers are then able to increase the length of the back side of the engine therefore capturing more of the energy, unlike the modern turbofan engines in use today (Otis & Vosbury, 2002).

Modern high bypass fans are designed to be efficient at certain speeds. Much like a fixed pitch prop, the efficiency decreases when the aircraft is not flying at the optimum speed. This causes a reduction in total efficiency of the engine. The unducted fan design is able to utilize a variable pitch design allowing the prop blades to be efficient at any speed. Ultimately this reduces the total fuel consumption (Otis & Vosbury, 2002).

The reduced complexity of the unducted fan will allow for decreased maintenance cost compared to modern day high bypass engines. The removal of the large main fan and the associated engineering allows designers to replace the main fan with eight to sixteen large, less complex blades. Ultimately, this decreases the lifelong cost of the engine. Unducted fan engines will reduce the cost per hour to operate the engine. Reducing the maintenance and operational cost will allow air carriers to save money from more than just fuel cost.

Being considered an ultra high bypass engine, the unducted fan GE36 is able to produce a bypass ratio much higher than current high bypass turbofan engines. By increasing the amount of air bypassing the hot section of the engine, the efficiency is increased while still maintaining the ability for the engine to operate correctly. While remaining aerodynamically efficient throughout its designed speed range, the GE36 was able to reduce fuel consumption by 20 percent (Otis & Vosbury, 2002).

Cons

Modern jet engines incorporate fan shrouding that in the case of a released fan blade, the shrouding will maintain the integrity of the engine. This allows the shrouding to keep engine parts from entering the aircraft. Designers build and test the shrouding to insure that it can withstand the impact of a fan blade when the engine is operating at max RPM. Unducted fans do not incorporate the use of the protective shrouding and could therefore increase the risk of catastrophic incident if a blade was to be released. Without the protection of the duct shrouding, aircarriers may see the risk to be too great to purchase and use aircraft equipped with current turbofan engines (Otis & Vosbury, 2002).

Jet engines utilized in the majority of aircraft being flown today have a sound level of up to 120dB. The painful noise levels for sound are from 120dB to 150dB range ("Noise"). When the GE36 was tested, the noise levels were messured to be in the 130dB to 140dB range. The increase of 10 to 20dB would cause a larger amount of noise pollution than engines in use at this time. In order for the unducted fan to be successful, the level of noise must be reduced to a less painful level. With blade tips reaching supersonic speeds, designers will be challenged to reduce the amount of noise produced by the larger blades (Otis & Vosbury, 2002).

Public perception that propellor drive aircraft are old fashion or unsafe would cause an aircraft equipped with unducted fan engines to be looked at in the same light as prop driven aircraft ("Whatever happened to propfans?", 2007). Seeing an aircraft equipped with props, or what an average passenger would perceive as props, customers will invision a step backwards in the comforts of jet travel. This would cause aircarriers to need to run an educational ad campaign to combat public perception. Without information about unducted fan engines being presented to prospective customers, air carries run the risk of potental passengers leaving to fly with other air carriers. Assuming these risks would be the decision of the airlines and the choice of the prospective passengers (Cameron & Pearson, 2012).

Conclusion

Though the GE36 could be considered a success, the implementation of such a revolutionary design was poorly executed. Reducing the fuel consumption of a jet engine in the early 1980s by some 20% was a major achievement that has yet to be fully realized (Otis & Vosbury, 2002).

With the focus of air carriers today being on fuel conservation and aircraft designers focusing on the reduction of total fuel consumption, the idea of implementing such a design as the GE36 could help the aircarriers reduce the total operational cost. Thus ultimately reduce the price of the ticket for its customers.

If desginers and air carriers can overcome the problems of high noise levels and the public perception of prop aircraft, unducted fan engines could be succesfully implemented into current fleets. Once implementation was conducted successfully, the public would view the unducted fan as truely revolutionary to air travel, just like it should be.

References

Cameron, D., & Pearson, D. (2012, July 9). Propeller Planes, Fueled By Economics, Take Off. Retrieved from The Wall Street Journal:
Propeller Planes Are More Economical - WSJ

Noise. (n.d.). Retrieved from American Speech Language Hearing Association: Noise

Otis, C. E., & Vosbury, P. A. (2002). Aircraft Gas Turboine Powerplants. Englewood, Colorado: Jeppesen Sanderson, Inc.
P-9 LRAACA [Long-Range Air ASW Capable Aircraft]. (2011, July 7). Retrieved from Globalsecurity: P-9 LRAACA [Long-Range Air ASW Capable Aircraft]

Painter, K. L. (2012, November 11). The 787 Dreamliner's fuel efficiency makes Tokyo possible for Denver. Retrieved from Denver Post: The 787 Dreamliner's fuel efficiency makes Tokyo possible for Denver - The Denver Post

Tuttle, B. (2012, September 28). Coming Soon? Airline Tickets That Cost Extra After You Purchase Them. Retrieved from Time: Airline Tickets That Cost Extra After You Purchase Them | TIME.com

Whatever happened to propfans? (2007, June 12). Retrieved from Flightglobal: Whatever happened to propfans? - 6/12/2007 - Flight Global

 

[sgarg]

The simple answer to OP's question is R&D spend in India is still too low, after significant yearly increases. So only a limited number of programs could be taken up.

The private sector was kept away from defence sector. This is also the reason.