The A160's rotor includes blades whose stiffness and cross-section vary along their length. Their low loading and rigid, hingeless design allows for changing RPM between 140 and 350 using a two-speed transmission to optimize efficiency at different speeds and altitudes, a technique called "optimum speed rotor technology", invented by Abe Karem. It is primarily because of these features that the Hummingbird can fly with less power - and thus use less fuel - than comparable conventional helicopters, which only adjust blade pitch and keep the rotor at constant rpm.