Felix du Temple de la Croix (known almost universally as "Felix du Temple") patented his design for an aerial machine in 1857. The design featured retractable wheeled landing gear, a tractor propeller, an internal engine and a boat-shaped hull (Mons. Du Temple had been a French Naval officer). He believed that a 6 h.p. engine would suffice to lift the machine, which had an estimated weight of about one ton. To pursue his design, Felix du Temple constructed numerous bird-shaped models and deduced that a dihedral angle to the wings would assist in stability, as well as placing most of the weight to the front of the machine. He ultimately worked with his brother, Louis, to build a large-sized version of his design. Finding existing steam engines to not be lightweight and powerful enough, in 1867 the two brothers built and patented an innovative "hot air" steam engine.
By 1874 the du Temples had constructed a large finely-built monoplane, at Brest, France, with a wing span of some 40 feet and a weight (minus the operator) of only about 160 pounds. At least one attempt to actually fly the machine was made and it is generally agreed that after gaining speed down an incline, the flying machine lifted off for a short time and then returned to the ground, with both machine and operator uninjured.