Press Somewhat higher maximum flight airspeeds are possible with compound helicopter designs, which use auxiliary propulsion devices and/or wings to offload the rotor, i.e., to alleviate some of its propulsion or lifting requirements. However, this desirable outcome is often obtained at the expense of higher overall power requirements and fuel burn for flight than would be necessary with a fixed-wing aircraft of the same gross weight and flight airspeed.
Source: Aerodynamic Trade Study of Compound Helicopter Concepts – ERAU
