09 Sep. 1992|
Aircraft wood types,garden furniture plans pdf,diy backyard swing set plans,fine woodworking shop design - How to DIY
If a solid spar must normally cope with compression stresses along the upper edge, tension stresses along the lower edge and shear stresses in between, then the solid wood in the shear area need not be so massive.
The wood-plywood beams (box-, I-, double I-, and C-) are generally more efficient load-carrying members than the plain wood types (plain rectangular and routed). The C-beam affords one flush face for the flush type of rib attachment but it is unstable under shear loading. Plain rectangular beams are generally used where the saving in weight of the wood-plywood types is not great enough to justify the accompanying increase in manufacturing trouble and cost. Routed beams are somewhat lighter than the plain rectangular type for the same strength but not so light as wood-plywood types.
In determining the relative efficiency of any beam type, reduction in allowable modulus of rupture due to form factors must be considered.
Since the tension strength of a wood member is more adversely affected by any type of defect than is any other strength property, it is recommended that all tension flanges be laminated in order to minimize the effect of small defects and to avoid the possibility of objectionable defects remaining hidden within a solid member of large cross section. A discussion of the relative merits of these various beam types is presented in succeeding paragraphs. This type allows a given flange area to be concentrated farther from the neutral axis than other types. Actually the cantilever spars for each wing join through the fuselage and can be regarded as a single unit supporting the weight of the aircraft at its centre. All aircraft wing spars are solid, I-beam or box-beam variants and their flanges tend to be called spar caps. Most of the document deals with the strength of wood and plywood elements and methods of structural analysis.
The types of beams shown [below] have been used frequently as wing spars, control surface spars, floor beams and wing ribs.
A detailed discussion of methods of laminating beams and beam flanges is in section 2.4 of ANC Bulletin 19, Wood Aircraft Inspection and Fabrication (ref.