Tham khảo tài liệu 'aircraft structures 3e episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 386 Stress analysis of aircraft components Choosing GREF 27 600N mm2 then from Eq. - 14 0 -122 -07 Similarly t 3 24 mm Í35 46 Í56 mm Hence Sly f j 1542 J12 Similarly 250 24 725 Ỗ34 233 Ớ35 546 736 556 368 Substituting the appropriate values of 6 in Eq. for each cell in turn gives the following. For cell I 2 7 0007 -M1542 250 - 25 M w az I 20o U0ƯƠREP For cell II d -250 250 725 233 725 - 233i7ni u az 2 X J00 UUUƠREF For cell III Ĩ6ĩĩ Õ0 7 - 233 7 rf36 233 736 368 ni az 2 X tot UUUƠREP In addition from Eq. X 106 2 258 000ft 355 000ft 161 OOOftii iv Solving Eqs i to iv simultaneously gives ft mm fti mm ftn mm The shear stress in any wall is obtained by dividing the shear flow by the actual wall thickness. Hence the shear stress distribution is as shown in Fig. . Fig. Shear stress N mm2 distribution in wing sertion of Example . Wings 387 Shear Initially we shall consider the general case of an TV-cell wing section comprising booms and skin panels the latter being capable of resisting both direct and shear stresses. The wing section is subjected to shear loads sx and Sy whose lines of action do not necessarily pass through the shear centre s see Fig. the resulting shear flow distribution is therefore due to the combined effects of shear and torsion. The method for determining the shear flow distribution and the rate of twist is based on a simple extension of the analysis of a single cell beam subjected to shear loads Sections and . Such a beam is statically indeterminate the single redundancy being selected as the value of shear flow at an arbitrarily positioned cut . Thus the TV-cell wing section of Fig. may be made statically determinate by cutting a skin panel in each cell as shown. While the actual position of these cuts is theoretically immaterial there are advantages to be gained from a numerical point of view if the cuts are made near the centre of the top or .
