What type of wood is most commonly used for spars and compression members?

Softwood is predominantly used for spars and compression members in aviation applications due to several key characteristics. Softwoods, such as spruce and pine, are lightweight, have a good strength-to-weight ratio, and exhibit favorable bending and tensile properties, making them ideal for structural components like spars. These woods also tend to be more readily available and easier to work with compared to hardwoods, which are denser and can be heavier.

In contrast, hardwoods often possess greater density and may not provide the optimal strength-to-weight balance needed for aviation applications where weight is a critical factor. While bamboo and composite materials can also be used in some contexts, softwood remains the traditional and more common choice due to its combination of performance, availability, and workability in crafting essential structural members in aircraft design.