Designing-in optimum life-cycle costs

Citation

(1998), "Designing-in optimum life-cycle costs", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 1. https://doi.org/10.1108/aeat.1998.12770aaf.009

Designing-in optimum life-cycle costs

Designing-in optimum life-cycle costs

The significance of the life-cycle cost of machines is becoming increasingly recognised as a cost every bit as important as the initial purchase price.

When the true cost of maintenance and downtime is considered, the purchase price becomes of less importance. This is so across a wide range of industries from the computer industry (where life-cycle cost is currently one of the hot topics) to that of the aircraft industry.

The more complex the design and the greater the length of service of the machine, the more critical is the accounting for life-cycle costs. In the aircraft industry, where expensive and long term life-cycles are the norm (cf Eurofighter, F-22, Boeing 747 and Airbus) there is a real impetus to account for and optimise these in the initial design stages. However, a design methodology that allows the various design teams to account fully for other disciplines and aspects of design is not so easy to define.

It is fairly well established that some 50-70 per cent of the life-cycle costs of an aircraft are locked-in during the conceptual and preliminary design process. After this stage even very minor alterations will have major repercussions on cost and other aspects of design.

Traditional design methods have concentrated largely on aerodynamic techniques with some allowance made for structures and systems and the properties associated with them.

Cranfield College of Aeronautics has been involved in multi-disciplinary design methods for a number of years and has developed a number of tools to optimise the effect of major life-cycle and performance cost-drivers.

A recent development has been in optimisers for the DOC (direct operating costs). These tools, which have so far been developed for a general class of four-engined long range transport aircraft similar to the A340-200, incorporate computational models of a wide range of aspects within the basic areas of aerodynamic modelling, mass modelling and maintainability, reliability and development cost modelling.

These allow the designer to make informed decisions on the effects of specific aspects of design and how they will affect the overall performance of the aircraft to the customer ­ both in terms of aerodynamic performance and commercial performance.

The kind of problems that have been modelled have been the effect of introducing a variable camber wing onto an aircraft, balancing improved performance with increased design and maintenance costs and an adverse effect on reliability. Another modelling task has been undertaken on introducing greater volumes of cooling air over avionics systems. Here, greater reliability of the electronics must be balanced against bigger cooling systems which entail greater fuel burn and hence heavier and more expensive aircraft.

The College's sophisticated optimisers, using models based on newly generated algorithms, allow designers to realise the long-term implications of particular designs with far greater precision than has previously been the case at a stage early enough to optimise overall performance and cost.

Details from Professor John Fielding, Cranfield College of Aeronautics, Cranfield University, Bedford MK43 0AL. Tel: 01234 754743; Fax: 01234 751640.