Helicopters come in many sizes and shapes, but most
share the same major components. These components
include a cabin where the payload and crew are car-
ried; an airframe, which houses the various compo-
nents, or where components are attached; a powerplant
or engine; and a transmission, which, among other
things, takes the power from the engine and transmits it
to the main rotor, which provides the aerodynamic
forces that make the helicopter fly. Then, to keep the
helicopter from turning due to torque, there must be
some type of antitorque system. Finally there is the
landing gear, which could be skids, wheels, skis, or
floats. This chapter is an introduction to these compo-
nents. [Figure 1-1]
THE MAIN ROTOR SYSTEM
The rotor system found on helicopters can consist of a
single main rotor or dual rotors. With most dual rotors,
the rotors turn in opposite directions so the torque from
one rotor is opposed by the torque of the other. This
cancels the turning tendencies. [Figure 1-2]
In general, a rotor system can be classified as either
fully articulated, semirigid, or rigid. There are varia-
tions and combinations of these systems, which will be
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 per-
mits 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 pas-
sengers, baggage, and cargo.
Torque—In helicopters with a sin-
gle, main rotor system, the ten-
dency 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.
LandinghGear
TailhRotorR
System
MainhRotorR
System
Cabin
Airframe Transmission
PowerplantR
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.
Each rotor blade is also attached to the hub by a verti-
cal 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 nor-
mally 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 feath-
ered, 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 rotat-
ing 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 helicop-
ter. 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 horizon-
tal 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 sur-
faces. Some types of skid gear are equipped with
dampers so touchdown shocks or jolts are not transmit-
ted to the main rotor system. Other types absorb the
shocks by the bending of the skid attachment arms.
Landing skids may be fitted with replaceable heavy-
duty skid shoes to protect them from excessive wear
and tear.
Helicopters can also be equipped with floats for water
operations, or skis for landing on snow or soft terrain.
Wheels are another type of landing gear. They may be
in a tricycle or four point configuration. Normally, the
TailhRotorhThrustR
tohCompensatehforhTorque
Torque
Torque
BladehRotation
Figure 1-3. The antitorque rotor produces thrust to oppose
torque and helps prevent the helicopter from turning in the
opposite direction of the main rotor.
Figure 1-4. Compared to an unprotected tail rotor, the fene-
stron antitorque system provides an improved margin of
safety during ground operations.
nose or tail gear is free to swivel as the helicopter is
taxied on the ground.
POWERPLANT
A typical small helicopter has a reciprocating engine,
which is mounted on the airframe. The engine can be
mounted horizontally or vertically with the transmis-
sion supplying the power to the vertical main rotor
shaft. [Figure 1-6]
Another engine type is the gas turbine. This engine is
used in most medium to heavy lift helicopters due to its
large horsepower output. The engine drives the main
transmission, which then transfers power directly to the
main rotor system, as well as the tail rotor.
FLIGHT CONTROLS
When you begin flying a helicopter, you will use four
basic flight controls. They are the cyclic pitch control;
the collective pitch control; the throttle, which is
usually a twist grip control located on the end of the
collective lever; and the antitorque pedals. The col-
lective and cyclic controls the pitch of the main rotor
blades. The function of these controls will be explained
in detail in Chapter 4—Flight Controls. [Figure 1-7]
Figure 1-5. While in a hover, Coanda Effect supplies approxi-
mately two-thirds of the lift necessary to maintain directional
control. The rest is created by directing the thrust from the
controllable rotating nozzle.
MainhRotorR
Wake
RotatingR
Nozzle
Downwash
AirR
Jet
Lift
AirhIntake
MainR
Rotor
MainR
Transmission
AntitorqueR
Rotor
Engine
Figure 1-6. Typically, the engine drives the main rotor through
a transmission and belt drive or centrifugal clutch system.
The antitorque rotor is driven from the transmission.
Cyclic
Throttle
Collective
AntitorqueR
Pedals
Figure 1-7. Location of flight controls.