Hollow wooden main wing spars were used for the first time.

The main fuselage and each wing spar is a single piece.

Structural metal fatigue was the problem in a major wing spar.

The aircraft landed too hard, breaking a wing spar and starting a fire.

Some of the forces acting on a wing spar are:

The main tubular wing spar is made of carbon fiber.

The entire plane is fabric covered with wooden wing spars and ribs.

The main wing spar crushed from race loads and required steel patches.

The only significant metal component is the wing spar, running through the middle and reinforcing the wings.