Aircraft conceptual design modelling incorporating reliability and maintainability predictions

Abstract

A computer assisted conceptual aircraft design program has been developed (CACAD). It has an optimisation capability, with extensive break-down in maintenance costs. CACAD's aim is to optimise the size, and configurations of turbofan-powered transport aircraft. A methodology was developed to enhance the reliability of current aircraft systems, and was applied to avionics systems. R&M models of thermal management were developed and linked with avionics failure rate and its maintenance cost prediction methods. The impact of the environmental control system, and engine-provided bleed flow was also modelled and incorporated into CACAD. The program showed the ARINC 600 & 408A flow rates to the avionics bay, and to the deck instruments may both profitably be increased by 50%. This keeps the direct operating cost (DOC) increase at bay for long-range passenger aircraft, and offers a reduction of up to 1% in DOC for the short to medium range passenger aircraft. A methodology was developed to model all aspects of future high risk technologies, with special consideration given to reliability, maintainability, and development cost (R, M&D) predictions as applied to variable camber wings (VCW). Many aspects of VCW were modelled. These included different types of drag saving due to chord- wise, as well as span-wise camber variation. Models were also derived for mass, maintenance cost, and extra development cost increments for wing trailing edge devices, flight control, and hydraulic systems. On incorporation into CACAD, a reduction in DOC of up to 3.5% was predicted. The VCW technology were evaluated for DOC improvements, against a number of existing, future, and derivative aircraft, under different sensitivity conditions. R, M&D predictions were shown to be decisive in addressing the feasibility of a new technology. The R&M predictions of the whole study shows that, long range, low to medium capacity derivative transport aircraft are most appropriate for the VCW technology, and the short to medium range, low to medium capacity aircraft are most suitable for reliability enhancement projects of aircraft advanced systems.