Sikorsky S-21 Grand

Work on the four-engine Sikorsky S-21 Grand began in August 1912, at a time when both the scale and power of the plane was unprecedented. It was originally flown with only two 100hp engines, but it had barely enough power to fly. It performed much better when tested with four engines in May 1913. In its final configuration it was renamed the Russkiy Vityaz (Russian Knight). It was damaged during testing in September 1913 after completing fifty-eight flights and proving that a large, multi-engine aeroplane was practical.