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Damper
Drag Hinge
Pitch Horn
Figure 5-5. Each blade of a fully articulated rotor system can
flap, drag, and feather independently of the other blades.
5-5
The horizontal hinge, called the flapping hinge, allows
the blade to move up and down. This movement is
called flapping and is designed to compensate for dissymetry
of lift. The flapping hinge may be located at
varying distances from the rotor hub, and there may be
more than one hinge.
The vertical hinge, called the lead-lag or drag hinge,
allows the blade to move back and forth. This movement
is called lead-lag, dragging, or hunting.
Dampers are usually used to prevent excess back
and forth movement around the drag hinge. The purpose
of the drag hinge and dampers is to compensate
for the acceleration and deceleration caused by
Coriolis Effect.
Each blade can also be feathered, that is, rotated around
its spanwise axis. Feathering the blade means changing
the pitch angle of the blade. By changing the pitch
angle of the blades you can control the thrust and direction
of the main rotor disc.
SEMIRIGID ROTOR SYSTEM
A semirigid rotor system is usually composed of two
blades which are rigidly mounted to the main rotor hub.
The main rotor hub is free to tilt with respect to the
main rotor shaft on what is known as a teetering
hinge. This allows the blades to flap together as a
unit. As one blade flaps up, the other flaps down.
Since there is no vertical drag hinge, lead-lag forces
are absorbed through blade bending. [Figure 5-6]
RIGID ROTOR SYSTEM
In a rigid rotor system, the blades, hub, and mast are
rigid with respect to each other. There are no vertical or
horizontal hinges so the blades cannot flap or drag, but
they can be feathered. Flapping and lead/lag forces are
absorbed by blade bending.
COMBINATION ROTOR SYSTEMS
Modern rotor systems may use the combined principles
of the rotor systems mentioned above. Some
rotor hubs incorporate a flexible hub, which allows
for blade bending (flexing) without the need for bearings
or hinges. These systems, called flextures, are
usually constructed from composite material.
Elastomeric bearings may also be used in place of
conventional roller bearings. Elastomeric bearings are
bearings constructed from a rubber type material and
have limited movement that is perfectly suited for helicopter
applications. Flextures and elastomeric bearings
require no lubrication and, therefore, require less
maintenance. They also absorb vibration, which
means less fatigue and longer service life for the helicopter
components. [Figure 5-7]
SWASH PLATE ASSEMBLY
The purpose of the swash plate is to transmit control
inputs from the collective and cyclic controls to the main
rotor blades. It consists of two main parts: the stationary
Teetering

Hinge
Feathering Hinge
Static Stops
Pitch Horn
Figure 5-6. On a semirigid rotor system, a teetering hinge
allows the rotor hub and blades to flap as a unit. A static flapping
stop located above the hub prevents excess rocking
when the blades are stopped. As the blades begin to turn,
centrifugal force pulls the static stops out of the way.
Figure 5-7. Rotor systems, such as Eurocopter’s Starflex or
Bell’s soft-in-plane, use composite material and elastomeric
bearings to reduce complexity and maintenance and,
thereby, increase reliability.
5-6
swash plate and the rotating swash plate. [Figure 5-8]
The stationary swash plate is mounted around the main
rotor mast and connected to the cyclic and collective
controls by a series of pushrods. It is restrained from
rotating but is able to tilt in all directions and move vertically.
The rotating swash plate is mounted to the stationary
swash plate by means of a bearing and is
allowed to rotate with the main rotor mast. Both swash
plates tilt and slide up and down as one unit. The rotating
swash plate is connected to the pitch horns by the
pitch links.
FUEL SYSTEMS
The fuel system in a helicopter is made up of two
groups of components: the fuel supply system and the
engine fuel control system.
FUEL SUPPLY SYSTEM
The supply system consists of a fuel tank or tanks, fuel
quantity gauges, a shut-off valve, fuel filter, a fuel line
to the engine, and possibly a primer and fuel pumps.
[Figure 5-9]
The fuel tanks are usually mounted to the airframe as
close as possible to the center of gravity. This way, as
fuel is burned off, there is a negligible effect on the center
of gravity. A drain valve located on the bottom of
　
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