Wood and Wood Structures

Wood

Wood has been the main construction material for man for thousands of years and, hence when aircraft were invented (about 100 years ago), it was used for airframe construction.

Compared with metal, it has many advantages that are stated below.

• Generally, wood possess light weight and its density of wood may vary. Some can be so dense that they are over 1000kg/m3 and will not float on water. The density of spruce (used for the construction of main spares and other structural members) is between 300 and 600kg/m3, whereas Aluminium is 2800kg/m3.
• Readily available and a renewable resource.
• Easily machined, drilled, filed, screwed, planed and sanded.
• Easily joined using wood-screws, nuts and bolts, nails/panel pins, adhesives, staples etc.
• Good thermal insulation.
• They are as strong as aluminium. But some aluminium alloys can be over 10 times stronger than wood and steel can be over 60 times stronger.

Disadvantages include:

• Quality of the wood is not consistent, even within the same type of wood from a different tree of the same species. Depending on where the tree was grown and the rate of growth in any one year, the wood quality can vary.
• Quality within a single plank of wood can vary due to knots, grain inclination, defects, insect attack etc.
• The mechanical properties of wood are said to be anisotropic, i.e. the strength and elastic properties are different when measured along the grain or across the grain. Wood is much stronger in tension and compression along the grain than across it and stronger across the grain in shear.
• Wood can shrink and warp, is liable to rot, can deteriorate with age and is subject to pest attack.