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Briefing: Some Facts About Aviation

September 1, 2004 12:00 AM
By Paul Burall in Challenge
Diagram showing average fuel use for flights of varying length. Per passenger kilometre, average fuel use is highest for short-haul flights - due to high consumption on take-off - and for very long flights - due to the extra weight of fuel carried a

Diagram showing average fuel use for flights of varying length. Per passenger kilometre, average fuel use is highest for short-haul flights - due to high consumption on take-off - and for very long flights - due to the extra weight of fuel carried at take-off.

In brief

Bent Wing Aircraft (Source: NASA)

Bent Wing Aircraft

How fuel efficient can aircraft be?

For new aircraft, from concept to end-of-life usually covers a period of 50 years. The aircraft being developed now will therefore still be contributing to climate change in 2050. So how much more fuel efficient will be the aircraft now on the designers' computer screens?

Boeing's Sonic Cruiser - now being designed - is expected to carry 200 to 250 passengers, have a range of 6-9,000 miles, and fly 15 to 20 per cent faster than current passenger aircraft, cutting an hour off the time for every 3,000 miles travelled. But it will be no more fuel efficient than current aircraft.

Even the revolutionary BWB (Bent Wing Aircraft - see picture) proposed by NASA specifically to be fuel efficient will, compared with today's aircraft, cut fuel consumption by only 20 per cent.

Alternative fuels

In the medium-term, one of the most likely routes to more sustainable ground transport is the use of liquid hydrogen manufactured using renewable energy.

However, one of the major benefits of using hydrogen for road transport is that it would replace the combustion engine with the far more efficient fuel cell/electric power system; this advantage would be lost in aircraft, as the hydrogen would have to be used in a conventional combustion jet engine. Hydrogen would also produce more than twice the water vapour which, at high altitudes, itself adds to global warming. In total, the radiative impact of a hydrogen-fuelled aircraft would probably be at least 10 times greater than for kerosene.

Bio-ethanol has been suggested as a possible aviation fuel. However it has a lower energy density than kerosene, requiring aircraft to carry more fuel; it too would increase water vapour emissions.

So fossil fuel-based kerosene is likely to remain the fuel for aircraft for the foreseeable future.

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