AVIONICS COOLING-RATE TRADE-OFF MODELING FOR ULTRAHIGH CAPACITY AIRCRAFT

A computer aided conceptual aircraft design methodology (CACAD) has be en developed to size ultra-high capacity jet transport aircraft. Modul es were also developed for predicting maintenance costs of each airfra me and avionics system and these were incorporated into CACAD. A metho dology was developed to enhance the reliability of avionics systems, b ased on experimentally-proven engineering design solutions. A number o f avionics cooling techniques were investigated, and reliability and m aintainability models of thermal management were developed and linked to an avionics maintenance cost module. Further models were produced t o investigate the impact of proposed changes on the environmental cont rol systems, engine-provided bleeds and power off-takes. It was found that increased flowrates above the normally recommended values for the avionics bay, and to the flight deck instruments, may increase the re liability of the avionics systems, and also increase aircraft dispatch reliability. They may not, however, greatly improve direct operating costs (DOC), due to significant fuel penalties. A separate refrigerati on unit was investigated and found to be a feasible cost-effective mea sure, even allowing for increased engine fuel consumption caused by th e effect of the engine power off-take required to drive the refrigerat ion unit.