With the exception of the earliest models which had wings and tails with wooden frames, M20s are constructed entirely of metal. All are low-wing aircraft, and the wing skin is aluminum. Slotted flaps cover 70% of the trailing edge. Earlier models use a hydraulic hand pump to extend the flaps, while later models have electrically operated flaps. The forward fuselage has a steel-tube cabin structure covered in aluminum skin; the aft portion of the fuselage is of semi-monocoque design. In many places on the skin of the airplane, flush-mounted rivets are used to reduce drag.