Stanley Hiller began design of XH-44 at age 17 and saw its first successful flight at age 19. Began by buying all the books on helicopter development he could find; very few at the time. Decided to build own helicopter. Reasoned that vertical rotor robbed lifting rotors of too much engine power which could otherwise be used for direct lift. Eliminated tail rotor by using 2 coaxial blades rotating in opposite directions. Canceled out each other's torque and proved very stable. Another goal was to eliminate excessive vibration he believed existed in conventional helicopter, increasing control problem and demanding considerable pilot skill. XH-44 acclaimed first successful twin-rotor design in US, first helicopter flown successfully in western US, and first to use all-metal rotor blades. Harold Sigler, on Hiller's engineering staff, made Hiller's ideas feasible from an engineering standpoint and contributed much to furthering helicopter's design. 1945, Hiller formed United Helicopters, Inc. to continue research toward his original goal of producing a practical, low-cost, rotary-wing aircraft. From new location in Palo Alto, designed and manufactured a number of successful twin- and single-rotor helicopters.