wuzak
Captain
Flyboy is right about longevity. It takes a lot longer for aluminium to corrode than for wood to rot/go bad.
Do you think that WW2 aircraft were designed for longevity? I wouldn't have thought so.
Corrosion isn't the only factor - there is also fatigue.
A number of aircraft have used steel spars. Steel is much heavier than aluminium. BUT if the loads you expect to have to deal with are large enough, and since steel IS stronger than aluminium ( in general, there are a lot of alloys of both) a steel part MAY provide more strength than an EQUIVALENT WEIGHT aluminium part. Same for wood depending on the loads involved, the size of the parts, and the type of wood.
Depending on grades, steel and aluminium hav much the same tensile strength to weight ratio. That means that for pure tensile loading steel and aluminium members that take a certain load will weight the same. But the aluminium section will be bigger than the steel one.