TAILIEUCHUNG - Aircraft Design - Systhesis anh Analysis 2008 Part 8

Tham khảo tài liệu 'aircraft design - systhesis anh analysis 2008 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | ratio as is used in the definition of coefficients such as Cl and CD. Reference Lengths Various wing reference lengths are used in aerodynamic computations. One of the most important of these is the mean aerodynamic chord or . The . is the chord-weighted average chord length of the wing defined as b 2 MAC. - - J c2 dy 0 For a linearly tapered trapezoidal wing this integral is equal to . 2 3 Croot Ctip - Croot Ctip Croot Ctip For wings with chord extensions the mac may be computed by evaluating the mac of each linearly-tapered portion then taking an average weighted by the area of each portion. In many cases however the mac of the reference trapezoidal wing is used. The . is often used in the nondimensionalization of pitching moments. The . of just the exposed area is also used to compute the reference length for calculation of Reynolds number as part of the wing drag estimation. The . is chosen instead of the simpler mean geometric chord for quantities whose values are weighted more strongly by local chord that is reflected by their contribution to the area. Wing Design Parameters s wing area AR aspect ratio 4 7 s c c Ằ taper ratio tip root A sweep of c 4 line 0 wing twist angle Span Selecting the wing span is one of the most basic decisions to made in the design of a wing. The span is sometimes constrained by contest rules hangar size or ground facilities but when it is not we might decide to use the largest span consistent with structural dynamic constraints flutter . This would reduce the induced drag directly. However as the span is increased the wing structural weight also increases and at some point the weight increase offsets the induced drag savings. This point is rarely reached though for several reasons. 1. The optimum is quite flat and one must stretch the span a great deal to reach the actual optimum. 2. Concerns about wing bending as it affects stability and flutter mount as span is increased. 3. The cost of the wing .

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