TABLE OF CONTENTS Whereas the airplane was developed by young men not previously known as inventors the fortunes of the helicopter have been more in the hands of those with reputation previously acquired elsewhere.
E.P. Warner [323], 1922
This chapter introduces the direct-lift vehicles, e.g. vehicles that generate lift by the action of one or more rotors. This category includes helicopters, autogiros and convertiplanes. The chapters that follow are a survey of performance calculation methods that make use of simplified models (one-dimensional axial flow). However, most of the discussion is limited to the conventional helicopter.
The flight conditions of a conventional helicopter include hover, axial climb and descent, forward (inclined) climb and descent, level forward flight, sideways, backward and yawed flight, turning and maneuvering, autorotation, and flight conversion. The flight condition between hover and level flight at moderate speeds is called flight transition. Besides these conditions, we must consider off-design flight operations, such as the vortex ring state, autorotation and cornering flight. Therefore, the number of possible flight conditions of a rotary-wing aircraft exceeds that of a fixed-wing aircraft.
A full performance analysis, aimed at selecting or designing a helicopter, planning a mission, or upgrading a vehicle, must include at least range, endurance, hover in- and out-of-ground, climb rates at full power and OEI, fuel consumption, and performance in non-standard atmosphere...
