Different levels of Optimization in Aircraft Design

Air transport is still one of the continuously growing industry sectors worldwide. Like all industrial sectors there is the constant request to reduce cost, improve quality and enhance security and safety. The aircraft as the central mean for transportation is under similar threats. But if we want to improve the aircraft further we have to understand the air transport system itself, identify the different actors and their role, identify each partners strengths and weaknesses and then identify the areas where further aircraft improvements will bring best value to the system. The presentation will start to quickly describe the air transport system with its main elements and partners. ACARE, the European consortium for air transport, has developed their Vision 2020 and defined two strategic research agendas to achieve the defined goals that can be used as a good basis for the next challenges. The aircraft design process can be described in four different levels. The first level is the air transport system which defines the environment and constraints in which the aircraft can be operated. In this first level, the market requirements for the aircraft have to be derived. Once the market requirements are identified, then the industrial process starts: Which aircraft in terms of size and range would best fit? What is the competitive situation? What type of aircraft, a derivative or a new design? What level of technology and risks should be taken? What propulsion system and how to secure exclusivity? Who and how many risk sharing partners/subcontractors? Here a compromise between the different aspects of marketing, engineering, finance and production has to be developed. At the third level then is the purely engineering task, handled by the chief engineer. He has to define together with his engineering teams from aerodynamics, structures, aeroelasticity, propulsion, cabin, etc., the suitable aircraft configuration which fulfils all these requirements as a compromise between the different disciplines. At this level, the aircraft performance or the DOC (direct operating cost) can be the yardstick to measure and identify the improvements compared to previous and competitors design. Today there is even a fourth level of aircraft optimisation. This is at the level of aircraft subsystems design, where another optimisation of functionalities is needed. What is the best way to control the aircraft? What is the future architecture to ensure communication within the aircraft (cable, wireless, mixed), between aircraft and ground and also for entertainment with all the new features like onboard TV, video on demand, use of mobile phones, etc. What is the optimum way of onboard power generation, distribution and economic consumption? Optimisation is needed in all of these described levels. But it is very often fairly difficult to understand and define the system boundaries, the related optimisation parameters and target functions. This chapter tries to give a global overview, but will not aim to provide all answers!