The Art of the Helicopter John Watkinson - Karatunov.net

10 The Art of the Helicopter
The pure helicopter obtains the great majority of its lift in all modes of flight from a
power driven rotor or rotors, and any lift due to airflow around the hull is incidental.
The majority of today’s rotary wing machines are pure helicopters. The thrust from a
rotor is closely aligned with a line drawn perpendicular to the tip path, and the pure
helicopter propels itself by tilting the rotor forward to obtain a component of rotor
thrust which balances the drag, as shown in Figure 1.10(a).
The gyroplane (also known by de la Cierva’s trade name of autogyro) obtains lift
from an undriven rotor that must be tilted away from the direction of flight to make
air flow up through it. The rearward rotor-thrust component, along with the drag, is
balanced by the forward thrust of a conventional airscrew as shown in Figure 1.10(b).
As the rotor needs to be pulled through the air to maintain height, the autogyro cannot
hover in still air, although it can give the illusion of hovering by flying into wind.
Simple autogyros must taxi to spin up the rotor, but later machines could spin the
rotors with engine power on the ground, and use the stored energy to perform a jump
take-off.
Between the pure helicopter and the gyroplane is the gyrodyne, which obtains lift
from a power driven rotor. Unlike the pure helicopter, the gyrodyne maintains the
rotor disc parallel to the direction of flight, as in Figure 1.10(c) and propels itself with a
conventional airscrew. The Fairey Gyrodyne (Figure 1.11) replaced the tail rotor with
a side-mounted airscrew to cancel torque reaction when hovering, but also to provide
thrust for forward flight. More recently the Lockheed Cheyenne (Figure 1.12) had both
anti-torque and pusher rotors at the tail. The gyrodyne offers high speed potential, with
the penalties of raised complexity, weight and difficulty of control. Some gyrodynes
have wings in addition to the rotor.
Fig. 1.11 The Fairey Gyrodyne had a side-mounted anti-torque rotor that became a tractor propeller in
forward flight.(AugustaWestland)