Rotary Wing Terminology
Lets talk a moment about
terminology. There are many terms associated with rotary
wing flight. One must become familiar with the terminology
of rotorcraft before they can expect to understand the
mechanics of rotary wing flight. Let's look at a few
definitions.
Main Rotor System
- Root: The inner end of
the blade where the rotors connect to the blade grips.
- Blade Grips: Large
attaching points where the rotor blade connects to the
hub.
- Hub: Sits atop the mast,
and connects the rotor blades to the control tubes.
- Mast: Rotating shaft
from the transmission, which connects the rotor blades
to the helicopter.
- Control Tubes: Push \
Pull tubes that change the pitch of the rotor blades.
- Pitch Change Horn: The
armature that converts control tube movement to blade
pitch.
- Pitch: Increased or
decreased angle of the rotor blades to raise, lower, or
change the direction of the rotors thrust force.
- Jesus Nut: Is the
singular nut that holds the hub onto the mast. (If it
fails, the next person you see will be Jesus).
Main Rotor Blade
 Leading
Edge: The forward facing edge of the rotor blade.
Trailing Edge: The back
facing edge of the rotor blade.
Chord: The distance from the
Leading Edge to the Trailing Edge of the rotor blade.
Controls
- Swash Plate: Turns
non-rotating control movements into rotating control
movements.
- Collective: The up and
down control. It puts a collective control input into
the rotor system, meaning that it puts either "all up",
or "all down" control inputs in at one time through the
swash plate. It is operated by the stick on the left
side of the seat, called the collective pitch control.
It is operated by the pilots left hand.
- Cyclic: The left and
right, forward and aft control. It puts in one control
input into the rotor system at a time through the swash
plate. It is also known as the "Stick". It comes out of
the center of the floor of the cockpit, and sits between
the pilots legs. It is operated by the pilots right
hand.
- Pedals: These are not
rudder pedals, although they are in the same place as
rudder pedals on an airplane. A single rotor helicopter
has no real rudder. It has instead, an anti-torque rotor
(Also known as a tail rotor), which is responsible for
directional control at a hover, and aircraft trim in
forward flight. The pedals are operated by the pilots
feet, just like airplane rudder pedals are. Tandem rotor
helicopters also have these pedals, but they operate
both main rotor systems for directional control at a
hover.
Here are some of the component
parts that make up a helicopter. While this is an example of
one specific helicopter (UH-1C), not all helicopters will
have all of the parts listed here. Some of this may be a bit
more of the same old stuff we have just discussed, but it
will show everything as it relates to everything else on the
aircraft and the location of each component.
Anatomy of a Helicopter
- Rotor Blade: The rotary
wing that provides lift for the helicopter.
- Stabilizer Bar: Dampens
control inputs to make smoother changes to the rotor
system.
- Swashplate: Transfers
non-moving control inputs into the spinning rotor
system.
- Cowling: The aerodynamic
covering for the engine.
- Mast: Connects the
transmission to the rotor system.
- Engine: Provides power
to the rotor systems.
- Transmission: Takes
power from the engine and drives both rotor systems.
- Greenhouse Window: A
tinted window above each of the pilot seats.
- Fuselage: The body of
the helicopter.
- Cabin Door: Allows
access to the cabin and cockpit.
- Skids: Landing gear that
usually have no wheels or brakes.
- Crosstube: The mounting
tubes and connection for the skids.
- Motor Mount: A flexible
way to attach the engine to the fuselage.
- Tailboom: Also known as
an "empenage" is the tail of the helicopter.
- Synchronized Elevator: A
movable wing that helps stabilize the helicopter in
flight.
- Tailrotor: Provides
anti-torque and in-flight trim for the helicopter.
- Tail Rotor Driveshaft:
Provides power to the tailrotor from the transmission.
- 45 Degree Gearbox:
Transfers power up the vertical fin to the 90 degree
gearbox.
- 90 Degree Gearbox:
Transfers power from the 45 degree gearbox to the
tailrotor.
- Vertical Fin: Holds the
tailrotor and provides lateral stabilization.
- Tail Skid: Protects the
tailboom when landing.
This picture illustrates how
the helicopter moves when using the appropriate controls. Up
and Down movements are controlled by the "Collective". Side
to Side and Forward and Back motions are controlled by the
"Cyclic". Lateral control (Also called directional control
or "Yaw") is achieved by using the "Foot Pedals".
While you are looking at the
picture of the controls (Left side of this paragraph), I
will explain how to do a normal takeoff. First, you must
make sure the throttle is all the way open (For a turbine
powered helicopter, advanced properly for a reciprocating
engine powered helicopter). Once you have established the
proper operating RPM, then you can pull up slowly on the
collective. As you increase collective pitch, you need to
push the left pedal (In American helicopters...right pedal
for non-American
models) to counteract the torque you generate by increasing
pitch. (In reciprocating engined models, you will advance
the throttle as you increase collective pitch). Keep pulling
in pitch and depressing the pedal until the aircraft gets
light on the skids. You may sense a turning motion to the
left or right, if so, you may need more or less pedal to
maintain heading. The cyclic will become sensitive and
(depending on how the aircraft leaves the ground heels or
toes of the skids last) as you continue to pull in pitch and
depress the pedal, you will put in the appropriate cyclic
input to level the aircraft as it leaves the ground. As the
aircraft eases into the air, forward cyclic will be required
to start the aircraft in a forward motion. As the aircraft
advances forward, it will gain speed until about 15 knots
and then the aircraft will shudder a little as you
transition through ETL (Effective Translational Lift...See
the unique forces page for a more in depth explanation of
ETL). As you transition through ETL, the collective will
need to be reduced, the pedal will need less pressure, and
the cyclic will need to be forced forward to counteract the
force against the front of the rotor system. Failure to push
forward will result in an abrupt nose high attitude and a
reduction in forward speed. After the shudder of ELT is
experienced, you will see a marked gain in forward airspeed,
a reduced need for pedal input and a reduced need for
collective pitch as the rotor system becomes more efficient.
The airspeed indicator will most likely jump from zero to 40
knots indicated airspeed and will smoothly advance as the
aircraft goes faster. Now you have taken off and with a
little release of foward cyclic pressure, the aircraft will
establish a climb and continue to gain airspeed. At this
point, the pedals are only used to trim the aircraft, and
most maneuvers are accomplished by using a combination of
the cyclic and collective controls. (That wasn't so
hard...was it?)
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