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New green and quiet jet-engine test results announced

Revolutionary turbofan spun by P&W

Is there anything wrong with GTF?

Other jet-engine firms are sceptical, however.

"Is there anything wrong with GTF?" asked a Rolls Royce source at Paris yesterday, in a sardonic tone of voice.

Plenty, in Rolls' view. P&W's rival says that open rotors will offer substantially greater fuel and carbon savings right from the start - 25 per cent or more. Furthermore, according to Rolls, GTF is merely the final refinement of high-bypass turbofans, not a whole new kind of engine like open rotor. GTFs, they believe, will never offer the significant improvement over time that has happened with high-bypass turbofans - and will be seen with open rotors. While GTF stays at the 15 per cent improvement or thereabouts, open rotors will move on - perhaps cutting aviation's carbon burden in half, one day.

But GTF is here now, and it can be fitted right onto existing aircraft (open rotors are liable to require big changes, as their blade discs are a lot wider than turbofans). And while GTFs may develop maintenance issues, Saia argues that they aren't any more likely to be troublesome than open-rotors, especially open-rotors configured to deliver reverse-thrust braking after landing. This last is more or less an essential capability nowadays.

And GTF has a trump card to play: that of noise. Saia says that the PW1000G is actually quieter than normal jets - a lot quieter. The bypass fan is the main noise source, and in the case of a GTF it's spinning slower, so making less racket. Saia says that a big four-jet like the A340, equipped with GTFs, would have an 85-decibel noise footprint which fitted within a lot of airport boundaries. That means that it would be allowed to land or take off twenty-four hours a day, whereas big airliners usually have restricted hours of operation at the moment. Overall, a future GTF-equipped airline industry would be a lot quieter and more pleasant for people living near airports.

Open rotors, on the other hand, are likely to be significantly more noisy than current engines. But they potentially offer much greater fuel and carbon savings.

So which is more important? Saving the planet and/or conserving fossil fuel stocks, or cutting down on aircraft noise?

Rolls and most of the engine industry say the former, but P&W are betting on the latter - and, it has to be admitted, offering a decent fuel/carbon saving right off. Given that anti-airport protests seem to be driven as much by local residents' desire for quiet as by any fear of climate change, that could be a sound business move. ®

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