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Helicopter Rotor System and Design
INDEX
SR. NO. CONTENTS PAGE NO.
1 INTRODUCTION 31.1 ANATOMY OF A HELICOPTER 32 FORCES ON HELICOPTER 63 MAIN ROTOR SYSTEM 74 CONTROLS 95 IMPORTANT PARTS 105.1 SWASH PLATE 105.2 STABILIZER BAR 126 CLASSIFICATION OF MAIN ROTOR SYSTEM 136.1 RIGID 136.2 SEMI-RIGID 136.3 FULLY ARTICULATED 146.4 ENGINEERED COMBINATION 147 THE ANTI-TORQUE EFFECT 157.1 SINGLE MAIN ROTOR 157.1.1 TAIL ROTOR 157.1.2 DUCTED FAN 167.1.3 NOTAR 167.1.4 TIP JETS 177.2 DUAL ROTORS (COUNTER ROTATING) 177.2.1 TANDEM 187.2.2 COAXIAL 197.2.3 INTERMESHING 197.2.4 TRANSVERSE 207.2.5 QUADROTOR 218 MAIN ROTOR BLADE 218.1 ROTOR BLADE DESIGN 228.1.1 AIRFOIL, LIFT AND DRAG 228.1.2 BLADE TWIST AND TAPPER 228.1.3 BLADE ROOT CUT OUT 238.1.4 TWISTING MOMENTS 238.1.5 BLADE TIP SPEED AND NOISE REDUCTION 248.2 CONSTRUCTION 249 REFERENCES 27
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Helicopter Rotor System and Design
INDEX OF FIGURE
SR NO. NAME OF FIGURE PAGE NO.
1 Anatomy of helicopter UH-1C 4
2 Helicopter assembly 5
3 Typical helicopter drive train 5
4 Forces on helicopter 6
5 Main rotor system 7
6 Rotor system drawing 8
7 Controls of helicopters 9
8 Swash plate model 10
9 Swash plate working 11
10 Tail rotor helicopter 15
11 Ducted fan helicopter 16
12 Movement of air through NOTAR 16
13 Tandam helicopter ch-47 18
14 Coaxial helicopter 19
15 HH-43 Huskie 19
16 Intermeshing rotor drawing 20
17 Transverse helicopter v-12 20
18 Quadrotor 21
19 Cross-section of rotor blade 21
20 Blade aerofoil shape 22
21 Blade twist and tapter 23
22 Blade 23
23 Force on blade 24
24 Composite design 25
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Helicopter Rotor System and Design
Helicopter Rotor System and Design
1. Introduction:
Air resistance behaves the same way as fluid resistance. When you try to swim
through water, the faster you swim, the harder it becomes. For air resistance, a surface
moving through the air will experience drag the faster it moves. What helicopter does
is use the air resistance to create a lifting force. When the leading edge of a surface is
higher and the rear edge is lower, air flow would strike the surface and be pushed
down. The air flow pushing downward is the same as the surface being pushed
upward, which creates lift. For aircraft, the slanted under surface of wing and rotor
blade allows air to create lift.
A helicopter rotor is powered by the engine, through the transmission, to the rotating
mast. The mast is a cylindrical metal shaft which extends upward from helicopter and
is driven by the transmission. At the top of the mast is the attachment point for the
rotor blades called as hub. The rotor blades are then attached to the hub.
1.1. Anatomy of a Helicopter:
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, but some of its kind.}
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Helicopter Rotor System and Design
Fig.1 Anatomy of helicopter UH-1C (helicopterpage.com)
Rotor Blade: The rotary wing that provides lift for the helicopter.
Stabilizer Bar: Dampens control inputs to make smoother changes to the
rotor system.
Swash plate: 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.
Cross tube: The mounting tubes and connection for the skids.
Motor Mount: A flexible way to attach the engine to the fuselage.
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Tail boom: Also known as an "empenage" is the tail of the helicopter.
Synchronized Elevator: A movable wing that helps stabilize the helicopter in
flight.
Tail rotor: Provides anti-torque and in-flight trim for the helicopter.
Tail Rotor Driveshaft: Provides power to the tail rotor 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 tail
rotor.
Vertical Fin: Holds the tail rotor and provides lateral stabilization.
Tail Skid: Protects the tail boom when landing.
Fig. 2 Helicopter assembly (helicopterpage.com)
Fig.3 (helicopterpage.com)
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2. Forces on helicopter:
Fig.4 Forces on helicopter (helicopterpage.com)
When the blades are spinning then the natural reaction to that is for the fuselage of the
helicopter to start spinning in the opposite direction to the rotors. If this torque isn't
controlled, the helicopter would just spin round hopelessly!
So to beat the reaction of the torque, different systems are used and is connected by
rods and gears to the main rotor so that it turns whenever the main rotor is spinning.
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3. Main Rotor System:
Fig. 5(helicopterpage.com)
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).
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Fig. 6 Rotor system drawing (helicopterpage.com)
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4.
Controls:
Fig. 7 Controls of helicopter (helicopterpage.com)
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 pilot’s 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.
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5. Important Parts:
5.1. Swash plate:
Fig. 8 Swash plate model (helicopterpage.com)
The swash plate assembly has two primary roles:
Under the direction of the collective control, the swash plate assembly can
change the angle of both blades simultaneously. Doing this increases or
decreases the lift that the main rotor supplies to the vehicle, allowing the
helicopter to gain or lose altitude.
Under the direction of the cyclic control, the swash plate assembly can change
the angle of the blades individually as they revolve. This allows the helicopter
to move in any direction around a 360-degree circle, including forward,
backward, left and right.
The swash plate assembly consists of two plates -- the fixed and the rotating swash
plates -- shown above in blue and red, respectively. The rotating swash plate rotates
with the drive shaft (green) and the rotor's blades (grey) because of the links (purple)
that connect the rotating plate to the drive shaft. The pitch control rods (orange)
allow the rotating swash plate to change the pitch of the rotor blades. The angle of the
fixed swash plate is changed by the control rods (yellow) attached to the fixed swash
plate. The fixed plate's control rods are affected by the pilot's input to the cyclic and
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Helicopter Rotor System and Design
collective controls. The fixed and rotating swash plates are connected with a set of
bearings between the two plates. These bearings allow the rotating swash plate to
spin on top of the fixed swash plate.
Fig. 9 Swash plate working (helicopterpage.com)
The pitch of main rotor blades can be varied cyclically throughout its rotation in order
to control the direction of rotor thrust vector (the part of the rotor disc where the
maximum thrust will be developed, front, rear, right side, etc.). Collective pitch is
used to vary the magnitude of rotor thrust (increasing or decreasing thrust over the
whole rotor disc at the same time). These blade pitch variations are controlled by
tilting and/or raising or lowering the swash plate with the flight controls. The vast
majority of helicopters maintain a constant rotor speed during flight, leaving only the
angle of attack of the blades as the sole means of adjusting thrust from the rotor.
The swash plate is two concentric disks or plates; one plate rotates with the mast,
connected by idle links, while the other does not rotate. The rotating plate is also
connected to the individual blades through pitch links and pitch horns. The non-
rotating plate is connected to links which are manipulated by pilot controls,
specifically, the collective and cyclic controls.
The swash plate can shift vertically and tilt. Through shifting and tilting, the non-
rotating plate controls the rotating plate, which in turn controls the individual blade