tailieunhanh - design of wood aircraft structures phần 8

Nếu bạn không muốn in nó cho mình, Essco Hướng dẫn sử dụng máy bay và cung cấp thí điểm sẽ bán cho bạn một bản sao của các ấn bản thứ hai với $ 28. Họ cũng có một bản sao của ANC-19 $ 26. | stresses to be computed without determining the principal axes of inertia or the section properties relative thereto. 3 18 L L L L L L L L L L where T-- -1 - and Mc ---------------- The values of Mb and Mc are the values of the bending moments about the X and Y axes respectively used in the section properties computations the Ỉ values are determined by the methods outlined in table 3-5 and the X and y values are the distances to the points at which the bending stresses are desired. Xf the analysis of some of the wing sections indicates that the value of ĩxv is approaching zero it is apparent that the reference axes chosen are nearly parallel to the section principal axes and the analysis of similar wing sections may be simplified by omitting the computation of the product of inertia in table 3 5. The expression for the stress at any point in this case simplifies to Mbx Mcy 4 3 19 When desired the angle of inclination of the principal axes of inertia to the XY axes is given by the following relation fig. 3-12 Tan 2ổ 2Ạy Ix-Iv 3 20 L L L L L where the values on the right side of the equation are obtained from table 3-5. The stress jf computed by the formulas applies directly only to elements having the elastic modulus selected as basic for the section and a shear lag effectiveness factor of . The actual stress for other elements is obtained by multiplying jf from the formulas by the proper effectiveness factor from table 3 5. . Secondary stresses in bending elements. a Air loads and bending deflections. Stiffeners are normally subjected to combined compression and bending. The compression results from the stiffener acting as a part of the flange material of the entire section. Two of the conditions producing bending in the stiffeners are Part of the normal airload on the skin being carried to the ribs by the stiffeners and curvature of the stiffeners due to bending deflection of the entire wing. Allowance for these bending loads may be made by using .