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discussed in greater detail in Chapter 5—Helicopter
Systems.
FULLY ARTICULATED ROTOR SYSTEM
A fully articulated rotor system usually consists of
three or more rotor blades. The blades are allowed to
flap, feather, and lead or lag independently of each
other. Each rotor blade is attached to the rotor hub by a
horizontal hinge, called the flapping hinge, which permits
the blades to flap up and down. Each blade can
move up and down independently of the others. The
flapping hinge may be located at varying distances
from the rotor hub, and there may be more than one.
The position is chosen by each manufacturer, primarily
with regard to stability and control.
Payload—The term used for passengers,
baggage, and cargo.
Torque—In helicopters with a single,
main rotor system, the tendency
of the helicopter to turn in
the opposite direction of the main
rotor rotation.
Blade Flap—The upward or
downward movement of the rotor
blades during rotation.
Blade Feather or Feathering—The
rotation of the blade around the
spanwise (pitch change) axis.
Blade Lead or Lag—The fore and
aft movement of the blade in the
plane of rotation. It is sometimes
called hunting or dragging.
Landing Gear
Tail Rotor

System
Main Rotor

System
Cabin
Airframe Transmission
Powerplant

 

Figure 1-2. Helicopters can have a single main rotor or a dual rotor system.
Figure 1-1. The major components of a helicopter are the
cabin, airframe, landing gear, powerplant, transmission, main
rotor system, and tail rotor system.
1-2
Each rotor blade is also attached to the hub by a vertical
hinge, called a drag or lag hinge, that permits each
blade, independently of the others, to move back and
forth in the plane of the rotor disc. Dampers are normally
incorporated in the design of this type of rotor
system to prevent excessive motion about the drag
hinge. The purpose of the drag hinge and dampers is to
absorb the acceleration and deceleration of the rotor
blades.
The blades of a fully articulated rotor can also be feathered,
or rotated about their spanwise axis. To put it
more simply, feathering means the changing of the
pitch angle of the rotor blades.
SEMIRIGID ROTOR SYSTEM
A semirigid rotor system allows for two different
movements, flapping and feathering. This system is
normally comprised of two blades, which are rigidly
attached to the rotor hub. The hub is then attached to
the rotor mast by a trunnion bearing or teetering hinge.
This allows the blades to see-saw or flap together. As
one blade flaps down, the other flaps up. Feathering is
accomplished by the feathering hinge, which changes
the pitch angle of the blade.
RIGID ROTOR SYSTEM
The rigid rotor system is mechanically simple, but
structurally complex because operating loads must be
absorbed in bending rather than through hinges. In this
system, the blades cannot flap or lead and lag, but they
can be feathered.
ANTITORQUE SYSTEMS
TAIL ROTOR
Most helicopters with a single, main rotor system
require a separate rotor to overcome torque. This is
accomplished through a variable pitch, antitorque rotor
or tail rotor. [Figure 1-3]. You will need to vary the
thrust of the antitorque system to maintain directional
control whenever the main rotor torque changes, or to
make heading changes while hovering.
FENESTRON
Another form of antitorque rotor is the fenestron or
“fan-in-tail” design. This system uses a series of rotating
blades shrouded within a vertical tail. Because the
blades are located within a circular duct, they are less
likely to come into contact with people or objects.
[Figure 1-4]
NOTAR®
The NOTAR® system is an alternative to the antitorque
rotor. The system uses low-pressure air that is forced
into the tailboom by a fan mounted within the helicopter.
The air is then fed through horizontal slots, located
on the right side of the tailboom, and to a controllable
rotating nozzle to provide antitorque and directional
control. The low-pressure air coming from the horizontal
slots, in conjunction with the downwash from the
main rotor, creates a phenomenon called “Coanda
Effect,” which produces a lifting force on the right side
of the tailboom. [Figure 1-5]
LANDING GEAR
The most common landing gear is a skid type gear,
which is suitable for landing on various types of surfaces.
Some types of skid gear are equipped with
dampers so touchdown shocks or jolts are not transmitted
　
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