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EVOLVING AEROSPACE DESIGN

EVOLVING AEROSPACE DESIGN – TAKING INSPIRATION FROM NASA TO THE MASS MARKET

Nigel Pready, Senior Consultant in the Structures team at leading engineering consultancy Frazer-Nash, looks at the cutting edge of aerospace design, and how new simulation methods can be used to help bridge the gap between ‘blue skies’ concepts and the mass market.

Innovation is and always has been at the heart of the aerospace industry. Today’s major innovation drivers include reducing fuel burn, lower operating costs and environmental impact, as well as increased production rates, to meet the increasing demand for aircraft, particularly in the emerging markets of Asia, South America and Africa. According to the Airbus Aircraft Global Market Forecast 2013-2031 it is anticipated that air traffic will grow at 4.7 per cent, requiring over 29,000 new passenger and freight aircraft over the next 30 years.

The aerospace industry has led the way in improved efficiency, with modern aircraft offering a fuel burn per seat as much as 70% lower than those being flown in the 1960s. However, the limits of conventional aircraft designs are now being reached, and to make a further step change improvement will require significant enhancements in aerodynamic efficiency. Whilst this challenge is primarily faced by civil aircraft manufacturers, similar issues are faced in the defence sector when designing large aircraft, such as airlifters and tankers, where the weight of the aircraft including its fuel impacts on the operational capacity.

Various ‘blue skies’ concepts have been proposed, including blended wing bodies, such as those developed by NASA. A major challenge to the adoption of radical designs, is that current structural design methods are not sufficiently flexible to be able to analyse these novel aircraft architectures. Furthermore, the aerodynamic improvement needs to be coupled with a level manufacturability to support a significant increase in production rates. So how do we bridge the gap between ‘blue skies’ design and the mass market?

Current aircraft structural analysis approach

Aerospace structural analysis methods and tools have been developed over decades. The standard stressing approach uses a component level model to determine the loads distribution. These loads are then used as inputs to tools which calculate the reserve factors of the local structure against potential failures. With advances in computing it has been possible to augment stressing tools based on classical analytical methods with more complex tools, which are able to provide solutions to problems with non-linear geometric and material behaviour.

An ever increasing volume of test data has increased confidence in failure prediction, and this has allowed a more flexible approach to aircraft design, leading to weight savings. However, the local stressing tools on which this approach relies need to be able to treat the aircraft structure as a series of similar features with idealised boundaries. For example, wing and fuselage skins are typically idealised as orthogonal stiffened panels.

To apply this approach to a design which is not consistent with this structural idealisation would require new stress tools to be defined, created, and validated. Not only would this be a very slow and expensive process, it would still be inflexible as the new tools would need to be based on a fixed structural idealisation based around a new concept.

Requirements of structural analysis approach for the future

New aircraft concepts which could deliver significant aerodynamic enhancements have been proposed by NASA, Boeing, Airbus and others. These ideas range from those which look like modified variants of today’s aircraft, to radical blended wing body designs. To be able to select the concept which will provide the optimal performance requires an assessment to be made of various parameters including aerodynamic efficiency, weight and operational factors. To be able to as

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