Tham khảo tài liệu 'aircraft design - systhesis anh analysis 2008 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Analyses and Modeling Once we have decided on the definition of best we must find a way of relating the design variables to the goal. This process is shown schematically below. Design n Model t ctive . Variables and Constraints For aircraft design this process is often extremely complex. The number of parameters needed to completely specify a 747 is astronomical. So one uses a combination of approximation experience and statistical information on similar aircraft to reduce the number of design variables to a manageable number. This may range from 1 or 2 for back-of-the envelope feasibility studies to hundreds or even thousands of variables in the case of computer-assisted optimization studies. Even when the situation is simplified the model is usually very complicated and difficult. One generally must use a hierarchy of analysis tools ranging from the most simple to some rather detailed methods. Calculating the drag of even a simple wing is not just a matter of specifying span and area. Other parameters of importance include taper sweep Reynolds number Mach number CL or alpha twist airfoil sections load factor distribution of bugs etc. This can be programmed and available as an analysis tool but one must be very cautious. Which of these variables is included in the model What if the wing is operating at 100 000 Reynolds number Has it been compared with experiment in this regime As the design progresses more information becomes available and more refined analyses become part of the design studies. The expertise of a designer these days involves knowing what needs to be computed at what time and identifying the appropriate level of approximation in the analyses. One of the most important but least well understood parts of the design process is the conceptual design phase. This involves deciding on just what parameters will be used to describe the design. Will this be a flying wing A twin-fuselage airplane Often designers develop several competing concepts and .
