aerospace engineer René Lorin patented a design for the world's first ramjet, but it was not possible to develop a working prototype as no existing airplane could achieve sufficient speed for it to operate, and thus the concept remained theoretical. Engineers in the 1930s realized that the maximum performance of piston engines was limited, as propulsive efficiency declined as blade tips approached the speed of sound. For engine performance to increase beyond this barrier, a way would have to be found to radically improve the design of the piston engine, or a wholly new type of powerplant would have to be developed. Gas turbine engines, commonly called "jet" engines, could do that. The key to a practical jet engine was the gas turbine, used to extract energy from the engine itself to drive the compressor. The gas turbine was not an idea developed in the 1930s: the patent for a stationary turbine was granted to John Barber in England in 1791. The first gas turbine to successfully run self-sustainingly was built in 1903 by Norwegian engineer Ægidius Elling. Limitations in design and practical engineering and metallurgy prevented such engines reaching manufacture. The main problems were safety, reliability, weight and, especially, sustained operation. In Hungary, Albert Fonó in 1915 devised a solution for increasing the range of artillery, comprising a gun-launched projectile which was to be united with a ramjet propulsion unit. This was to make it possible to obtain a long range with low initial muzzle velocities, allowing heavy shells to be fired from relatively lightweight guns. Fonó submitted his invention to the Austro-Hungarian Army but the proposal was rejected. In 1928 he applied for a German patent on aircraft powered by supersonic ramjets, and this was awarded in 1932.Gyorgy, Nagy Istvan, "Albert Fono: A Pioneer of Jet Propulsion", International Astronautical Congress, 1977, IAF/IAA The first patent for using a gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume. His engine was an axial-flow turbojet. In 1923, Edgar Buckingham of the US National Bureau of Standards published a report expressing scepticism that jet engines would be economically competitive with prop driven aircraft at the low altitudes and airspeeds of the period: "there does not appear to be, at present, any prospect whatever that jet propulsion of the sort here considered will ever be of practical value, even for military purposes." Instead, by the 1930s, the