1222. Design to Cost – The Interface Between Cost Saving and Weight Efficiency


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G P Jacobs: 1222. Design to Cost – The Interface Between Cost Saving and Weight Efficiency. 1978.



On civil transport aircraft, cost standards must be improved. To be fully effective, action must be taken from the early project phases. A disciplined procedure is necessary, as these cost activities must be kept in step with performance and timescale aims.
By considering the airline operators priorities it is shown that all contributions to ‘Life Cycle Costs’, (first cost and operating costs), must be covered, and the revenue earning potential of the aircraft enhanced where possible.
The build-up of Direct Operating Cost (D.O.C.) is studied, to determine how far we can go in the search for the ‘lowest’ cost. Cost/weight exchange rates for D.O.C. optimization are generated, their magnitude being dependent on how efficiently savings can be converted into D.O.C. improvement and/or revenue earning capability. Different combinations occur, depending on the project’s stage of development. In the earliest stages, the size of the aircraft can be reduced as a result of a weight saving and all the advantage can be taken as an operating cost improvement. The exchange rate is then about three times as great as that which subsequently applies when the geometry of the aircraft is ‘fixed’. Here the weight saving gives a smaller D.O.C. improvement but, at the same time, an increase in revenue earning potential: possible revenue improvements are quantified. If weight saving can be converted into additional passenger accommodation, aircraft D.O.C. will not reduce, but D.O.C./passenger mile will fall rapidly, and much higher exchange rates can be justified .
The increased importance of weight economy, (and the decreasing benefits of cost saving), should aviation fuel costs rise, are demonstrated. This would lead to higher exchange rates. Other factors affecting these rates are discussed.
Using typical examples, ways of effecting cost and weight improvements are considered, from changes that improve weight at the expense of cost, to those where cost savings are obtained by relaxing weight standards. The ‘best’ example saves both cost and weight, and results from design simplification, obtained through the type of function-oriented study used in Design-to-Cost activities.
Finally, a proposed ‘Project Cost Effectiveness’ rationale, incorporating D.O.C., is presented. A procedure for total cost optimization of alternatives where maintenance costs represent a significant input is outlined. It is concluded that Design-to-Cost must play a key role in raising the efficiency of the design/production/procurement matrix on future projects.


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