Flight International - June 30, 2015 UK

TECHNOLOGY

28 | Flight International | 30 June-6 July 2015 flightglobal.com

commercial engines offer roughly double the

5.3:1 bypass ratio and the 24:1 overall pres-

sure ratio of the original CF6-6 engine.

The second-generation CF6-80C engine

benefited from the invention of full-authority

digital engine controls and from blades

designed with 3D aerodynamic shaping. In

the past decade, the GEnx engine has

replaced the CF6-80C2, with 15% better fuel

efficiency, carbonfibre fan blades and fan case

and a second-generation twin-annular pre-

swirl combustor. That will be followed, in

2020, by a GE9X engine that should be 5%

Gas turbine engines still

have decades of technical

improvement to come, but

carbon-neutral aviation

won’t happen without a

wholesale shift to biofuels

STEPHEN TRIMBLE PARIS

FUELLING CHANGE

ANA used a biofuel blend on a 787 delivery flight in 2012, working with Boeing, which hopes it will make up 1% of overall fuel usage by 2016

Boeing

“I have great confidence in

our industry – not just in GE,

but across the industry”

DAVID JOYCE

President and chief executive, GE Aviation

the engine achieved most of its thrust by

slowly accelerating a large volume of air

around the engine core, rather than rapidly

accelerating a small amount of air through the

combustion process.

The concept appeared so profound that

many of GE’s engineers sincerely believed at

the time that the CF6 had maximised the po-

tential efficiency of the turbofan engine.

“When we were done, the guys said, ‘Gee,

we’ll never do an engine this good again. This

is the greatest engine we’ve ever done.’ And

they believed it. They really did,” recalls GE

Aviation president and chief executive David

Joyce.

PLENTY OF ROOM

Forty-four years later, it’s clear that even the

breakthrough CF6 engine still left plenty of

room for improvement. In two key measures

of a turbofan engine’s fuel efficiency, modern

I

n 1971 – 34 years after the first ground test

of Frank Whittle’s prototype jet engine –

General Electric’s CF6 commercial turbo-

fan engine entered service with the Doug-

las DC-10-10, representing a historic

breakthrough in fuel efficiency.

The high bypass ratio of the CF6 meant that