P&W touts geared turbofan version of Airbus A320

P&W touts geared turbofan version of Airbus A320 as early as 2011 to gain two year advantage over potential new Boeing narrowbody

Re-engined version of Airbus narrowbody could begin flight testing in 2010 and enter service a year later

Pratt & Whitney and Airbus are studying a modified version of the A320 powered by the geared turbofan (GTF) for service entry as early as 2011, offering Airbus a potential market advantage of up to two years over any competing new single-aisle design from Boeing.

Industry sources say the proposed A320 development is being studied - a move which, if confirmed, could force Boeing to accelerate its 737 replacement studies currently aimed at the 2013 timeframe. It could also provide Airbus with a quicker solution than any all-new designs being considered under its Next Generation Single-Aisle (NGSA) A320 successor studies.

The venture also raises questions about the continuing solidarity of the International Aero Engines consortium, in which P&W is a leading partner with Rolls-Royce. While both companies publicly continue to support their commitment to IAE, P&W has not ruled out going forward with a revised partnership if the GTF concept goes ahead.

P&W declines to comment on the specific potential for an early Airbus application, but confirms that its "current technology development plans support engine certification in 2011. We have been executing rig tests and technology proving demonstrations since late 2005, and we're scheduled to conduct the first ground test of the GTF demonstrator engine in mid-November 2007."

Airbus says that "no decision has been, or is about to be, taken on a new aircraft in this category", adding that it is "examining all possible technologies for the future".

The plan under discussion is believed to involve installation and flight tests on an A320 in early 2010, with engine-airframe certification following by mid-2011. Industry sources say that, although the installed GTF is expected to weigh considerably more than the CFM International CFM56 or International Aero Engines V2500, the specific fuel consumption advantage could be as much as 6% over existing engines. P&W previously said the advantage would be up to 12% in an all-new design.

The A320 wing would also require extensive modification to take the GTF, which is expected to be configured with a 1.95m (77in)-diameter fan - roughly the maximum size the existing A320 design can take without significant landing gear and other knock-on structural and configuration changes. Estimated wing change costs are believed to be in the $0.5-1.0 billion range, although this would increase if Airbus opted for an all-composite structure such as that planned for the A350.

"We plan to begin our GTF flight test programme in the middle of 2008, which would complete the required technology maturation for a programme launch that year. A programme launch in late 2008 would support FAR33 engine certification near the end of 2011," adds P&W. Flight tests were originally due to take place using P&W's 747, but testing on board Airbus's A340 flying testbed is believed to be under consideration.

I'm no expert, but I believe its basically a jet design were only some of the air sucked in by the main fan is actually compressed and added to fuel to burn.. much of the air intake is simply directed around the combustion and right out the back of the jet like prop thrust.

IE, instead of burning fuel to provide the bulk of the thrust, the fuel is bruned to primarily spin the fan, as the bypass pushed air the fan moves provides most of the thrust, not the combustion.

I guess you could call it a jet/prop hybrid, as a pure jet, pushes all the air through combustion and burns fuel to provide great thrust.. and a prop burns fuel in more traditional piston design to spin a propeller...

This design uses a smaller jet to turn a much larger fan (sort of a prop concept on steroids) to generate the thrust. Burns less fuel than a pure jet, produces greater thrust than traditional prop.

Again, I don't remotely claim to be knowlegable on this, just how my tiny little mind understands it... I'm sure someone else here will point out anything I've said that's wrong.

The article you linked to describes it pretty well. Some clarifying comments:

ALL recent commercial turbofan engines (from JT3D to GEn-x) have a high speed rotor (with a compressor and turbine) and a low-speed rotor (with a compressor and turbine). The fuel is burned in the combustor located between the high speed compressor and high speed turbine. Rolls-Royce engines usually have three rotors, the third having an intermediate rotor speed. Up to now, the fan has rotated at the same speed of the low speed compressor.

The GEn-x and Trent 900 engines on the 787 have an engine bypass ratio (ratio of fan air to core air) of about 9, which is near the practical limit without the added gearbox.

The innovation here is that the added gearbox permits the fan to rotate at a lower speed than the low-speed compressor and turbine. The added gearbox permits higher bypass ratios, lower fan noise and thereby lower fuel consumption.

As you pointed out, the weight, cost and reliability of the gearbox are the technical issues that need to be overcome.

My former company is working with P&W on the nacelle, the pod that goes around the engine. There are other design innvoations that will improve fuel burn and decrease noise.

"I'm no expert, but I believe its basically a jet design were only some of the air sucked in by the main fan is actually compressed and added to fuel to burn ... much of the air intake is simply directed around the combustion and right out the back of the jet like prop thrust."

You are correct. This is how turbofans operate. There is a good history here, and more info here.

The limit on the diameter of a turbofan is driven by the the outer edges of the fan approaching the speed of sound. A larger fan is possible, but it must rotate more slowly. But if it rotates more slowly, it must be even bigger.

A geared turbofan will allows bigger fans and even higher bypass ratios.

Basic question

I'm not a propulsion engineer, and I don't even play one on TV. But I am a retired aircraft engineer, and I occasionally find myself reassuring passengers on the whys and wherefores of flight. I explain to them that if they were in a boat and they had a large rock and they stood up and shoved that rock behind them into the water behind boat, they would expect that the boat would move forward in a reaction. And that is the only reason a jet engine pushes an aircraft forward - it does so by hurling masses of air backward, and the reaction propels the plane forward.
Similarly, the reason the plane flies is that when it's going forward the wings knock a large quantity of air downward - and the reaction lifts the plane up.
But the issue of turbofans is the issue of how much horsepower it takes to generate how much thrust. The thrust developed by the engine is proportional to the mass of air that's thrown backward per second and to the change in velocity of that air. The power required to throw air back, OTOH, is proportional to the mass of air thrown back per second and to the difference in the square of the velocity of the air.
And that just means that the greater mass of air you throw back, the more thrust you get for the same horsepower, and thus for the same fuel consumption rate. There is an obvious trade-off between how much air you assay to move, and the size and complexity of the mechanism for moving the air.

the simplest mechanism for throwing air backward is the simple turbojet, which has a compressor and a turbine to drive the compressor - and only the air compressed and then expanded through that machine is thrown backward. It is thrown backward at very high speed, but the quantity of air involved is low, and the horsepower and fuel required for a given thrust level is high.

the opposite extreme is the helicopter rotor: a huge propeller which must operate at very low RPM compared to gas turbine which provides the horsepower. And which therefore requires an expensive, heavy, and potentially trouble-prone gear reduction box to allow a turbine to turn such a low-RPM device. The penalties in reliability, weight, and cost are worth it in the helicopter because the helicopter's thrust requirement is so high that any simpler mechanism simply is impractical for getting the thing off the ground and keeping it aloft. Harrier jets do hover without big rotors, but they hover only briefly because of the fuel consumption rate involved.

The turboprop is intermediate between the turbojet and the helicopter rotor, in that the blades spin slower than the turbine does but much faster than the helicopter rotor does.

the turbofan engine is an intermediate stage between the pure turbojet engine and the turboprop. It has a fan which throws a larger quantity of air that the turbine alone pumps, but for simplicity and reliability it is driven at the same speed as the turbine.

and the geared turbofan is apparently an intermediate stage between the turbofan and the turboprop engine - the fan is larger than is suitable for operation at turbine speeds, but smaller than a turboprop and undoubtedly designed to turn faster than a turboprop propeller does.

Note: noise and efficiency limits the RPM of a fan blade because you would like the blade tip to not exceed the speed of sound.

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