tailieunhanh - Aircraft Design - Systhesis anh Analysis 2008 Part 5

Tham khảo tài liệu 'aircraft design - systhesis anh analysis 2008 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | velocity increase due to t c and so we take C 0. Form Factor Calculation This calculator may be used to compute the form factor for a lifting surface. t c Mach Sweep K Default Inputs Compute Form Factor for Bodies The fineness ratio of the fuselage affects the fuselage drag by increasing the local velocities and creating a pressure drag. The increase in skin friction due to higher-than-freestream velocities can be estimated by considering the symmetric flow around a body of revolution. For bodies of revolution the increase in surface velocity due to thickness is smaller than for 2-D shapes. From potential flow theory the maximum velocity over an ellipse with thickness ratio t c is Aumax U0 t c. The maximum velocity increase on an ellipsoid of revolution is given by the potential flow solution Aumax Uo a 2-a 1-M2 where a 2 1-M2 d2 D3 tanh-1 D - D and D 1 - 1-M2 d2 and d diameter length. The actual surface velocity distribution depends strongly on the shape of the body paraboloids have about half again as much maximum perturbation velocities as ellipsoids and fuselages with constant cross-sections are quite different but the idea here is to represent the correct trend theoretically and then obtain empirical constants. If a sort of average perturbation velocity is represented by C Aumax then the form factor k for bodies may be written k 1 C Allmax U0 2 The figure below shows that a factor C leads to reasonable agreement with the purely empirical method given by .

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