tailieunhanh - design of wood aircraft structures phần 3

Tôi đang trên diễn đàn bé Fly và một trong các thành viên đăng một hướng dẫn lực lượng không quân để trang web của mình. Ông đã nhận nó từ một số anh chàng ở Úc. ANC-18 Bulletin. Tất cả những gì bạn có thể muốn biết về thiết kế bằng gỗ cho các cấu trúc máy bay. | fa iriVOOŨ Ốó STRA N Ó S7J 5S Figure 2-10. Three-ply plywood beam in bending. Figure 2-11. Typical plywood constructions. Arrows indicate grain direction of each ply. 43 or restrained on more than two edges. It is essential that this fundamental difference between the two groups be kept in mind during the application of the formulas 1 given here and in later sections ref. 2-25 2-43 and 2-54 . 1 The effective moduli of elasticity of plywood in tension or compression are Ea measured parallel to side a for panels sec. Et measured perpendicular to side a for panels sec. Ew measured parallel to with the face grain Ex measured perpendicular to across the face grain and are determined as 1 __ -7 s E t 2 24 where i total thickness of plywood tf thickness of 1th ply modulus of elasticity of ith ply measured in the same direction as the pertinent desired E as Ea Et Ew or Ex . The value of E. is equal to ELi EL from tables 2-6 and 2-7 or Er or Er table 2-9 as applicable. 2 The effective moduli of elasticity of plywood in bending are El measured parallel to side a for panels E2 measured perpendicular t-0 side a for panels E w measured parallel to with the face grain Efx measured perpendicular to across the face grain and are determined as J. J s E I 2 25 where El as defined under 1 1 moment of inertia of the total cross section about the centerline measured in the same dừection as the pertinent desừed E namely El E2 Ejw or Efx . 1 When computing the various moduli 0Í elasticity for plywood of balanced construction and all plies of the same species the following relationship will be found helpful Et-t-Ef X i- --E .Eu- jET Efir rE i If the veneers are quarter-sliced rather than rotary-cut the term Er should . be replaced by Er. li moment of inertia of the 7th ply about the neutral axis of the same total cross section. For symmetrically constructed plywood the neutral axis to be used in determining ĩi will be the centerline of the cross section. For

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