Aircraft need design ‘step change’

Pulse detonation engines, blended wing bodies, fuel cells and multiple mini-engines are the future of aerospace engineering technology outlined by Dr. Mike Howse in the 2004 Whittle Lecture last Tuesday.

Dr. Howse, director of engineering and technology at Rolls-Royce, told an audience at the Royal Aeronautical Society that plans to halve CO2 emissions by 2020 will be the main driver for new aerospace technologies in the civil market. He said a ‘step change’ would be required in airframe and engine design to bring forward novel concepts such as the blended wing body, advanced gas turbine architectures and perhaps radical integrated power systems derived from fuel cells.

Dr. Howse also raised the possibility of a system of mini-engines where high-efficiency cores power multiple fans, as pioneered by NASA. ‘This uses gas turbines to provide a number of propulsive jets through ducts, which are particularly efficient aerodynamically because they increase lift and fill the aircraft trailing edge wake.

‘Another version of this idea, which Rolls-Royce particularly likes, being in the gas turbine business, involves 20 or more gas turbines along the trailing edge of the aircraft.’

While an advanced cycle gas turbine or fuel cell remain possibilities in the long term, major advances in ceramic materials and miniaturisation would be necessary, however, to make the solid oxide fuel cell suitable for aircraft.

Dr. Howse said great benefit is envisaged through the application of ‘more electric’ technologies across both the defence and civil sectors. This might include projects such as oil-less active magnetic bearings and generators on fan shafts to power airframe systems and flight-control actuators. This would demand advances in electrical and magnetic materials, he said.

‘Super-conducting motors and switching devices may eventually be developed to open new applications of electric technologies to aerospace. These are currently being addressed through the extensive Rolls-Royce research base.’

One example of a radical approach is the constant volume combustion (CVC) engine. This combines wave rotor technology with pulse detonation engine technology. CVC, he said, could offer improvements in fuel consumption, and an advantage for long-haul, high-bypass fan engines and potential low-cost, high-Mach engines.

However, more advances in gas modelling are required among other things, and high-pressure experiments to develop a method of initiating the required combustion detonations, said Howse.

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