Hiram Maxim made a fortune from his invention of the Maxim machine gun, and he used a good bit of that fortune to explore heavier-than-air flight. Maxim began his aerial experiments at Baldwyns Park, England, in the late 1880's, leading to the construction in 1893 of his enormous biplane Test-Rig, which weighed about 7,000 pounds. The machine's two steam engines each produced 180 h.p., and turned two propellers each 17-1/2 feet in diameter. Since the device was intended to be a test vehicle, it was held to a track, preventing it from rising from more than a couple of feet.