The Fly Baby was designed to be a very simple aircraft. For example, the fuel gauge is a stiff wire attached to a float poking up through the gas cap (a common application in the 1930s and 1940s, as seen on Piper and Aeronca light aircraft). The structure is of aircraft-grade spruce and plywood (Bowers did not advocate skimping on the quality of structural wood), covered with doped aircraft fabric. Aileron controls are push-tube, elevator controls are a combination of push-tube and cable, the rudder is cable-controlled.