Generally aircraft conceptual design is defined as the starting point for concept sketcing and evaluation, but before that work can start an even earlier stage has to be covered.
This is the stage where different scenarios are being worked through in which the aircraft as a platform is supposed to work. The scenarios will differ between civil and military use of course. but will have to fit well inside both customers and manufacturers strategic plans for the future.
In planning for the future it's vital to think and plan in broader terms, i.e. not only creating single products but rather create families of aircraft. This way of thinking and planning is usual amongst civil manufacturers. Creating a family based product line means better economics, better market coverage and of course lesser risk taking if and when the market changes. On the military side this way of thinking and planning is still quite unusual, mainly because customers are governments which usually only ask for single products.
The manufacturer from his point of view must think differently, he needs to spread his risk taking, especially as orders from the govemment are becoming scarcer. Therefore a modular product line would be of economic interest and would probably interest more customers.
The basic idea behind Saab Gripen (three roles merged into one single platform), or the US Joint Strike Fighter (JSF) idea of a modular aircraft, could be seen as the start of some kind of new family planning, but family planning on the military side could reach further than that. Probably military manufacturers can learn a lot from their civil counterparts.
Conceptual design might be a one man job in the early stages, but will very soon develop into team work. This development is only natural since the conceptual designer can't be expected to have detailed knowledge or experience which will cover every item. Conceptual design introduces a holistic viewpoint into the aircraft design process and it's vital to keep this viewpoint as long as possible. This becomes even more important over time, since the more detailed the project gets, the overall goal tends to drown into details.
Conceptual design phase offers the only occasion when design changes still can be made quite easily. Design freeze is not only a simple freeze of aircraft layout and geometry, it also sets the fmal prize tag on the aircraft. So in a way it is what you did (and what you forgot to do) in the conceptual design phase which fmally decides the faith of the end product. Hence conceptual design needs all the time it takes to be able to develop successful future products.
Generally there are two sides to conceptual design: either you develop a brand new design or make changes to an already existing one. Either way has its own needs and can't be run in the same manner, since different tools are needed in both cases. A new design needs a good conceptual design program, while in the latter case only minor parts of it might be used. A new design starts off fresh; everything is possible and nothing is sacred, but changing on an existing design means working with hands tied, you do not change things that easily.
Aircraft Conceptual Design takes long time to learn. It requires more than just being able to run a conceptual design program. Previous experience in a number of different aircraft design disciplines is a must; so is the ability to be able to humbly listen to experienced people's knowledge and advice.
This paper describes methods for aircraft conceptual design at two basic levels. At the top level there's a method described for conceptual design of civil jet transport aircraft.
On the second level different methods for conceptual design of core aircraft systems such as landing gear, environmental control and hydraulic are presented.
Linköping: Linköpings universitet , 2005. , 72 p.