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Last Updated: Monday, 6 November 2006, 04:30 GMT
The birth of a quieter, greener plane
By Tim Bowler
Business reporter, BBC World Service

More and more of us fly every year. As we do so, the political pressure to act to curb greenhouse gas emissions from planes is rising.

Artist's impression of the SAX-40 plane in flight (Image: SAI)

Now a team of researchers in Britain and the US has come up with a revolutionary new aircraft design that could make a dramatic contribution to curbing climate change.

The SAX-40, which has been developed by the Cambridge-MIT Institute, is a radically different shape of aircraft.

Officially, it is what is known as a "blended wing". It has a tailless wedge-shaped body with two bat-wings.

The Silent Aircraft Initiative (SAI) team has succeeded in coming up with a radically quieter plane. Crucially, the SAX-40 is also 35% more fuel-efficient than any airliner currently flying.

The case for radical change is getting stronger
Prof Ann Dowling, SAI's UK team leader

Oil prices may no longer be the $78 a barrel they were a few months ago, but with high fuel costs likely to continue, fuel efficiency is a major factor in all airlines' calculations.

Yet none of this means the SAX-40 will necessarily be built. Ever since the Boeing 707 first flew in 1957 and ushered in the commercial jet age, airliners have changed very little in their basic appearance.

Airliners still consist of a tube-like fuselage, with two swept-back wings and engines slung underneath. (The world's first - but commercially unsuccessful - passenger jet aircraft, the DeHavilland Comet, had the engines integrated in its wing).

Innovation costs

There are good economic reasons why design has remained so conservative.

By making the fuselage a tube, aircraft-makers can easily build a family of larger or smaller variants, utilising many of the same parts.

And by sticking engines under the wings, it's easier to maintain them, or upgrade them halfway through an aircraft's 30-year lifespan.

Naturally, aircraft manufacturers have made considerable improvements in the past 50 years, for instance using composite materials and lighter, more efficient engines.

Airbus A380
The Airbus A380 has run into difficulties in recent months

Yet future improvements to the basic design are getting harder to make, according to Professor Ann Dowling, professor of mechanical engineering at Cambridge University and SAI team leader in the UK.

"The case for radical change is getting stronger," she says.

"It's only through such a change that one can achieve step-changes in fuel burn."

But for aircraft manufacturers like Boeing or Airbus, any design changes need to produce a quick return on their investment.

Boeing is working on developing fuel cells to power aircraft air-conditioning and electrical systems. Currently, these are run off a plane's engines, reducing their efficiency.

Bill Glover, Boeing's director of environmental performance, commercial airplanes, says using fuel cells would give significant savings.

"With fuel cells we can take conventional fuel, convert it into hydrogen and produce electricity very efficiently," he says. "The only other emission is water."

But even this is still 10 to 15 years in the future.

Radical shift?

There is a good reason for the aircraft manufacturers' caution. Building totally new planes is both costly and risky.

After Boeing launched its Boeing 747 jumbo jet in 1968, it ran into serious financial difficulties when the demand for its new plane stalled.

To survive, the company slashed its workforce from 100,000 to 38,000.

Today, Airbus is also having financial problems with its giant double-decker A380.

For manufacturers, it is much safer to develop new airframes out of what has gone before, rather than re-tool completely with a brand-new production line.

Yet with increasing concern over climate change, we could see a radical shift in aircraft design.

This would be more likely if airlines had to pay "green" taxes on their airliners' emissions of greenhouse gases.

But the skies are not going to fill with radically new aircraft shapes any time soon.

When an airline buys a new plane, it will keep it flying for decades in order to make it pay its keep.

Which means even if this design gets the thumbs-up from the manufacturers, we won't be queuing up to board planes like the SAX-40 before 2030 at the earliest.

A look at the new 'silent aircraft'

'Silent aircraft' design launched
17 Aug 05 |  Beds/Bucks/Herts
Airport joining 'silent' jet team
18 Jan 05 |  Beds/Bucks/Herts
Flying into a silent sky future
27 May 04 |  Science/Nature
Joint quest for silent air travel
20 May 04 |  Cambridgeshire

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