tailieunhanh - Thiết kế kỹ thuật máy bay chiến đấu Episode 1 Part 6

Tham khảo tài liệu 'thiết kế kỹ thuật máy bay chiến đấu episode 1 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | THE NATURE OF AIR 95 versions with the same aerofoil sections. Fig. shoỵys the differences in lift and drag coefficients that occur with Reynolds number with the same aerofoil section. Thus a narrow chord can cause a peaky lift curve with a sudden hard stall but increase the chord and the stall characteristics are softened. Furthermore at a given angle of attack a broader chord can generate a higher lift drag bringing with it better cruise efficiency. Fig. General effect of Reynolds number upon lift and drag characteristics of the same aerofoil surface. The disadvantages of narrow chords can be alleviated somewhat by the introduction of controlled turbulence and vortices. Fig. la and c show vortex generators at a flap knuckle to delay separation and a vibrating rubber band in front of the leading edge of the wing of a model sailplane to generate turbulence so improving the flow. Roughened surfaces are used in Nature to improve flying qualities. The barn owl for example has feathers with vortex-generating spiked vanes forming a serrated leading edge. The wing trailing edges are soft downy surfaces. The combination enables the owl to fly silently by delaying transition noise in the boundary layer a thing quite impossible when the wings are lacquered. The noise is caused by fluctuating changes of pressure as the flow oscillates between laminar and turbulent at the point of transition on the wing chord. Q. Vortex get erc Gors or kvsuaULles cck to JeJexy control Sorf-txae s e. xr ex. t- i Ot A oftevA. IcxcQe d oct-ed uúLaC sp Q c cUiev ed L31 V- Some forms of turbulence and vortex generators all of which make flows stick longer to lifting surfaces than would be the case without them. Wilkout r oJiSi i xg Ì t e esicj CK i êíci Ểre êk . c cTooíy lacàiaaÌ C-S op La Co rd e. by f pby y .cxr . THE DESIGN OF THE AEROPLANE THE NATURE OF AIR 97 Bats and many insects have thin membrane wings that are not efficient devices in themselves. But such