The aeroplane, as we now see it, has changed very little in the past 60 years - the same basic designs have been gradually refined and optimised, but the concepts would be recognisable to an aero engineer from the 1950s.
But last week, the industry took a look at some of the technologies of the at the second New Aircraft Concepts Research (NACRE) conference in London, an event that is partially funded by the European Commission.
Fuel costs are driving short-term demand, but ecological concerns are playing a part too. Dr Askin Isikveren from the University of Bristol says: “It’s like the oil crisis of the ‘80s. All that money was invested into unducted fan (UDF) technology, but when the oil price fell it was left to gather dust. We can’t let that happen again. It needs a politician to stand up and say the environment comes first.”
However, NACRE is working on aircraft of the future in accordance with the ACARE goals. The environmental goals are to reduce emissions of CO2 by 50%, NOx by 80% and perceived noise by 50%.
NACRE is specifically aiming for a reduction of 15% in aircraft economics; a -10dB noise reduction; 25% less fuel burn in kg/seat/km and 15-20% volume improvement per passenger at the same aircraft efficiency and enhanced services. João Frota, Airbus employee and NACRE project Coordinator, says: “NACRE is working to break the barriers that prevent efficient design of novel aircraft configurations to provide quantum steps in air travel affordability and in an environmentally friendly way,”
Fundamentally NACRE has chosen three types of aircraft to investigate from three direct goals. First is the ‘proactive green’ aircraft that is aimed to give the minimum environmental impact; second is the ‘passenger-friendly’ aircraft which has been designed inside out and focuses on creating the largest internal space and comfort. The third option is the ‘simple flying bus’, similar to today’s aircraft but with an emphasis placed on the return on investment over the aircraft’s life.
But what about the technology covered by the research? A key, and recurring, theme for making aircraft more efficient is using laminar flow, when the boundary layer of air passing over an airfoil is kept smooth with minimal turbulence. Laminar flow requires a smooth surface, and when looking at wings, it means the leading edges cannot have any high lift devices such as slats.
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So how can an aircraft that is optimised for laminar flow characteristics make use of high lift devices? One such technology, that while still at least ten years from usability, is morphing. In effect the leading edge can bend up or down in any way to provide the aerodynamics that are required, while maintaining laminar flow.
Kevin Nicholls of Airbus UK and leader of work package 2 – novel lifting surfaces says: “We have begun structural investigations of a morphing aerofoil. At first it will be a morphing leading edge, and then over the wing box until only the rear spar and elevator are left untouched.”
Wing designs are a key element of NACRE’s work – even the conventional swept wing is being turned upside down. NACRE has been looking at advanced wings and is investigating the concept of high aspect ratio, low-sweep (HARLS), thinner wings with a shorter chord. “One of the problems this creates is systems integration,” says Nicholls. “Do we have to go to radical structural layouts to accommodate that?”
Forward swept wings would allow better laminar flow. “But then you cannot have slats as these upset natural laminar flow. We also had to look at divergence and flutter issues that such a configuration gives you,” he adds.
From ten forward-swept designs that have been studied, the team is taking the design simply known as PW-A forward to the detailed design phase. Nicholls says PW-A is free from divergence and flutter.
For the ‘simple flying bus’ wing, the main design focus is on bringing down the cost of manufacturing. “For that we mainly focused at the concept level. How we join it together, rather than any detailed design - because it already looks like a wing,” says Nicholls.
Blended wing bodies, (BWB) are also being explored for the passenger-optimised aircraft. But another concept is that of the ‘flying cruiseliner’, which is almost shaped like a boat, with an aerodynamic structure built around the ‘cruiseliner’ section.
Airbus vice president R&T strategy and plans Peter Chivers summarises the main levers of design: “Advanced materials continue to be an area of interest and development. And the evolution of aerodynamics over time, what is the game-changing technology?
“We’re looking at laminar flow and see it as a major player.We have looked at a whole range of concepts, what are the opportunities. We have already achieved 70% NOx reduction with the same basic configuration,” he says.
But the conference also raised the issue of what the airlines want. EasyJet’s Hal Calamkovis says: “There is a key difference between what people want, and what they need. In short-haul operations they need a clean, comfortable seat, get to where they are going when they expect to – and with luggage.
“What happens if you turn that on its head and ask the airline? We need 50% less fuel burn, 50% less sticker price, 100% availability, new aircraft that will not affect the residual value of my current aircraft. Oh, and I don’t want you to sell it to my competitors!” he says.
He highlighted the risk of going to an airline and asking them what they want by remembering a famous project of the 1960s. “Just look at the VickersVC10. It was built to serve BOAC’s ‘medium-range Empire’ routes,” Calamkovis says.
“Will airlines fund some of the R&D? That becomes difficult. Then we own it - and we won’t want to sell it to Ryanair!” he adds.
Source: Flight International
