Photos: A century of helicopters

This cheery fellow is Frank Piasecki, waving from his single-rotor PV-2 design in a demonstration flight in October 1943. According to the Smithsonian Institution's National Air and Space Museum, it "flew with an unprecedented smoothness and stability." Engineers and dreamers alike at the time envisioned creating a new class of personal vehicles that would let ordinary people fly as conveniently as they drove their cars. (The NASM entry says the PV-2 starred in a newsreel called An Air Flivver in Every Garage.)

The PV-2, which didn't progress past the prototype stage, featured a 90-horsepower Franklin engine, and the transmission was built mostly of junked auto parts, according to the NASM. The real innovations were in the rotors, especially in the way they were balanced.