The quest for a device that a person could strap on his back, lift off from his backyard, and fly around started in the 1940s. One of the more popular ideas came from Seattle, Washington, inventor Horace Pentecost. He actually designed and built a small backpack with a coaxial rotor system powered by a 20-hp two-cylinder air-cooled engine. The assembly weighed about 90 lbs and had a 12-foot rotor diameter. An overhead cyclic control also controlled yaw with a twist grip and moved vertically to control collective pitch.
Dubbed the “Hoppi-Copter” it was plagued with several issues like getting away from the fuselage quickly in an emergency and using the pilot’s legs as landing gear (too unstable). To solve some of these problems Pentecost built a second model with a 40-hp engine and simple tripod assembly for landing gear. Even so, the tiny aircraft proved unstable and too difficult to fly. Thinking the machine also had a military appeal, he continued working on improving the design.
However, shortly into the test program a major problem arose. Early on when he had formed his company he had given 10 percent of it to his lawyer in exchange for setting up the corporation. Pentecost and his wife divorced giving her half of his 90-percent ownership. His ex-wife and lawyer soon got together and Pentecost was pushed out of the company he started. In 1956 the company was sold to a group of investors from Washington, D.C. Their idea was to raise enough capital to certify the tiny helicopter by selling 300,000 shares of the company at $1 each. Ultimately, they were unsuccessful and the original Hoppi-copter ended up at the Smithsonian National Air and Space Museum where it remains in storage or out on loan.