FAA-H-8083-21B
Helicopter Flying Handbook
Helicopter Flying Handbook
U.S. Department of Transportation
FEDERAL AVIATION ADMINISTRATION
Flight Standards Service
2019
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The Helicopter Flying Handbook is designed as a technical manual for applicants who are preparing for their private,
commercial, or flight instructor pilot certificates with a helicopter class rating. Certificated flight instructors may find
this handbook a valuable training aid, since detailed coverage of aerodynamics, flight controls, systems, performance,
flight maneuvers, emergencies, and aeronautical decision-making is included. Topics such as weather, navigation, radio
navigation and communications, use of flight information publications, and regulations are available in other Federal
Aviation Administration (FAA) publications.
This handbook conforms to pilot training and certification concepts established by the FAA. There are different ways of
teaching, as well as performing, flight procedures and maneuvers, and many variations in the explanations of aerodynamic
theories and principles. This handbook adopts a selective method and concept to flying helicopters. The discussion and
explanations reflect the most commonly used practices and principles. Occasionally the word “must” or similar language
is used where the desired action is deemed critical. The use of such language is not intended to add to, interpret, or relieve
a duty imposed by Title 14 of the Code of Federal Regulations (14 CFR). Persons working towards a helicopter rating are
advised to review the references from the applicable practical test standards (FAA-S-8081-3 for recreational applicants,
FAA-S-8081-15 for private applicants, and FAA-S-8081-16 for commercial applicants). Resources for study include
FAA-H-8083-25, Pilot’s Handbook of Aeronautical Knowledge, and FAA-H-8083-1, Weight and Balance Handbook, as
these documents contain basic material not duplicated herein. All beginning applicants should refer to FAA-H-8083-25,
Pilot’s Handbook of Aeronautical Knowledge, for study and basic library reference.
It is essential for persons using this handbook to become familiar with and apply the pertinent parts of 14 CFR and the
Aeronautical Information Manual (AIM). The AIM is available online at www.faa.gov. The current Flight Standards
Service airman training and testing material and learning statements for all airman certificates and ratings can be obtained
from www.faa.gov.
This handbook supersedes FAA-H-8083-21A, Helicopter Flying Handbook, dated 2012. Gyroplane information can be
found in the FAA-H-8083-20, Gyroplane Flying Handbook.
This handbook is available for download, in PDF format, from www.faa.gov.
This handbook is published by the United States Department of Transportation, Federal Aviation Administration, Airman
Testing Branch, P.O. Box 25082, Oklahoma City, OK 73125.
Comments regarding this publication should be emailed to [email protected].
Preface
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The Helicopter Flying Handbook was produced by the Federal Aviation Administration (FAA) with the assistance of Safety
Research Corporation of America (SRCA). The FAA wishes to acknowledge the following contributors:
Federation of American Scientists (www.fas.org) for rotor system content used in Chapter 5
Kaman Aerospace, Helicopters Division for image of Kaman used in Chapter 5
Burkhard Domke (www.b-domke.de) for images of rotor systems (Chapters 1 and 4)
New Zealand Civil Aviation Authority for image of safety procedures for approaching a helicopter (Chapter 9)
Shawn Coyle of Eagle Eye Solutions, LLC for images and content used in Chapter 10
Dr. Pat Veillette for information used on decision-making (Chapter 13)
Additional appreciation is extended to the Helicopter Association International (HAI), United States Helicopter Safety Team
(USHST), Leonardo Helicopters, Aircraft Owners and Pilots Association (AOPA), and the AOPA Air Safety Foundation
for their technical support and input.
Acknowledgments
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Table of Contents
Preface.....................................................................v
Acknowledgments ................................................vii
Chapter 1
Introduction to the Helicopter ............................1-1
Introduction ....................................................................1-1
Turbine Age ...................................................................1-2
Uses ................................................................................1-3
Rotor System ..................................................................1-3
Rotor Configurations ..................................................1-4
Tandem Rotor ........................................................1-4
Coaxial Rotors .......................................................1-4
Intermeshing Rotors ................................................1-4
Tail Rotor ...................................................................1-5
Controlling Flight...........................................................1-5
Cyclic ........................................................................1-5
Collective ...................................................................1-5
Antitorque Pedals .......................................................1-6
Throttle ......................................................................1-6
Flight Conditions ...........................................................1-6
Chapter Summary ..........................................................1-7
Chapter 2
Aerodynamics of Flight .......................................2-1
Introduction ....................................................................2-1
Forces Acting on the Aircraft ........................................2-2
Lift ..............................................................................2-3
Bernoulli’s Principle ...............................................2-3
Venturi Flow ...........................................................2-4
Newton’s Third Law of Motion ..............................2-5
Weight ........................................................................2-5
Thrust .........................................................................2-6
Drag ............................................................................2-6
Profile Drag ............................................................2-6
Induced Drag ..........................................................2-7
Parasite Drag ...........................................................2-7
Total Drag ...............................................................2-7
Airfoil ............................................................................2-7
Airfoil Terminology and Definitions .........................2-7
Airfoil Types ..............................................................2-8
Symmetrical Airfoil ................................................2-8
Nonsymmetrical Airfoil (Cambered) ......................2-8
Blade Twist ...............................................................2-9
Rotor Blade and Hub Definitions ...........................2-9
Airflow and Reactions in the Rotor Disk .......................2-9
Relative Wind .............................................................2-9
Rotational Relative Wind (Tip-Path Plane)................2-9
Resultant Relative Wind ...........................................2-11
Induced Flow (Downwash) ..................................2-11
Rotor Blade Angles ..................................................2-12
Angle of Incidence ................................................2-12
Angle of Attack .....................................................2-13
Powered Flight .............................................................2-14
Hovering Flight ............................................................2-14
Translating Tendency (Drift)....................................2-15
Pendular Action ........................................................2-15
Coning ......................................................................2-16
Coriolis Effect (Law of Conservation of Angular
Momentum) .............................................................2-16
Gyroscopic Precession .............................................2-17
Vertical Flight ..............................................................2-17
Forward Flight .............................................................2-17
Airflow in Forward Flight .......................................2-19
Advancing Blade .................................................2-19
Retreating Blade ..................................................2-19
Dissymmetry of Lift .............................................2-20
Translational Lift ......................................................2-21
Effective Translational Lift (ETL) ........................2-22
Translational Thrust ..............................................2-22
Induced Flow ............................................................2-23
Transverse Flow Effect ............................................2-23
Sideward Flight ............................................................2-23
Rearward Flight ...........................................................2-24
Turning Flight ..............................................................2-24
Autorotation .................................................................2-25
Vertical Autorotation ................................................2-25
Autorotation (Forward Flight) ..................................2-26
Chapter Summary ........................................................2-26
Chapter 3
Helicopter Flight Controls ..................................3-1
Introduction ....................................................................3-1
Collective Pitch Control .................................................3-2
Throttle Control .............................................................3-2
Governor/Correlator ......................................................3-2
Cyclic Pitch Control .......................................................3-3
Antitorque Pedals ...........................................................3-4
Heading Control .........................................................3-4
Chapter Summary ..........................................................3-5
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Chapter 4
Helicopter Components, Sections,
and Systems ........................................................4-1
Introduction ....................................................................4-1
Airframe .........................................................................4-1
Fuselage .........................................................................4-2
Main Rotor System ........................................................4-2
Semirigid Rotor System .............................................4-2
Rigid Rotor System ....................................................4-3
Fully Articulated Rotor System ..................................4-4
Tandem Rotor .............................................................4-6
Coaxial Rotors ............................................................4-6
Intermeshing Rotors ...................................................4-6
Swash Plate Assembly ...................................................4-6
Freewheeling Unit ..........................................................4-7
Antitorque System .........................................................4-7
Fenestron ....................................................................4-8
NOTAR® ....................................................................................................4-8
Antitorque Drive Systems ..............................................4-8
Engines ...........................................................................4-8
Reciprocating Engines ................................................4-8
Turbine Engines .........................................................4-8
Compressor ...........................................................4-10
Combustion Chamber ...........................................4-10
Turbine ..................................................................4-10
Accessory Gearbox ...............................................4-10
Transmission System ...................................................4-10
Main Rotor Transmission .........................................4-11
Dual Tachometers .................................................4-11
Structural Design ..................................................4-12
Clutch .......................................................................4-12
Belt Drive Clutch ..................................................4-12
Centrifugal Clutch ................................................4-13
Fuel Systems ................................................................4-13
Fuel Supply System ..................................................4-13
Engine Fuel Control System ....................................4-14
Carburetor Ice ...........................................................4-14
Fuel Injection ............................................................4-15
Electrical Systems ........................................................4-16
Hydraulics ....................................................................4-16
Stability Augmentations Systems ................................4-17
Force Trim ................................................................4-17
Active Augmentation Systems ................................4-17
Autopilot ...................................................................4-18
Environmental Systems ...............................................4-18
Anti-Icing Systems .......................................................4-19
Engine Anti-Ice ........................................................4-19
Airframe Anti-Ice .....................................................4-19
Deicing ....................................................................4-19
Chapter Summary ........................................................4-19
Chapter 5
Rotorcraft Flight Manual .....................................5-1
Introduction ....................................................................5-1
Preliminary Pages ..........................................................5-2
General Information (Section 1) ....................................5-2
Operating Limitations (Section 2) .................................5-2
Instrument Markings ..................................................5-2
Airspeed Limitations ..................................................5-2
Altitude Limitations ...................................................5-3
Rotor Limitations .......................................................5-3
Powerplant Limitations ..............................................5-3
Weight and Loading Distribution ...............................5-4
Flight Limitations .......................................................5-4
Placards ......................................................................5-4
Emergency Procedures (Section 3) ................................5-4
Normal Procedures (Section 4) ......................................5-5
Performance (Section 5) ................................................5-5
Weight and Balance (Section 6) ....................................5-5
Aircraft and Systems Description (Section 7) ...............5-5
Handling, Servicing, and Maintenance (Section 8) .......5-5
Supplements (Section 9) ................................................5-6
Safety and Operational Tips (Section 10) ......................5-6
Chapter Summary ..........................................................5-6
Chapter 6
Weight and Balance ............................................6-1
Introduction ....................................................................6-1
Weight ............................................................................6-2
Basic Empty Weight ...................................................6-2
Maximum Gross Weight ............................................6-2
Weight Limitations .....................................................6-2
Balance ...........................................................................6-2
Center of Gravity ........................................................6-2
CG Forward of Forward Limit ...................................6-3
CG Aft of Aft Limit ...................................................6-3
Lateral Balance ...........................................................6-3
Weight and Balance Calculations ..................................6-4
Reference Datum ........................................................6-4
Chapter Summary ..........................................................6-4
Chapter 7
Helicopter Performance ......................................7-1
Introduction ....................................................................7-1
Factors Affecting Performance ......................................7-2
Moisture (Humidity) ..................................................7-2
Weight ........................................................................7-2
Winds .........................................................................7-2
Performance Charts ........................................................7-2
Height/Velocity Diagram ...........................................7-2
The Effect of Weight Versus Density Altitude .......7-3
Autorotational Performance .......................................7-4
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Hovering Performance ...............................................7-4
Sample Hover Problem 1 ........................................7-5
Sample Hover Problem 2 ........................................7-5
Sample Hover Problem 3 ........................................7-6
Climb Performance.....................................................7-6
Sample Cruise or Level Flight Problem .................7-8
Sample Climb Problem ...........................................7-8
Chapter Summary ..........................................................7-9
Chapter 8
Ground Procedures and Flight
Preparations.........................................................8-1
Introduction ....................................................................8-1
Preflight ..........................................................................8-2
Minimum Equipment Lists (MELs) and
Operations with Inoperative Equipment.....................8-2
Engine Start and Rotor Engagement ..............................8-3
Rotor Safety Considerations .......................................8-3
Aircraft Servicing .......................................................8-4
Safety in and Around Helicopters ..................................8-4
Ramp Attendants and Aircraft Servicing
Personnel ....................................................................8-4
Passengers ..................................................................8-4
Pilot at the Flight Controls .........................................8-6
After Landing and Securing .......................................8-6
Chapter Summary ..........................................................8-6
Chapter 9
Basic Flight Maneuvers ......................................9-1
Introduction ....................................................................9-1
The Four Fundamentals .................................................9-2
Guidelines ..................................................................9-2
Straight-and-Level Flight ...............................................9-3
Technique ...................................................................9-3
Common Errors ..........................................................9-3
Turns ..............................................................................9-3
Technique ...................................................................9-3
Slips ............................................................................9-4
Skids ...........................................................................9-4
Normal Climb ................................................................9-5
Technique ...................................................................9-5
Common Errors ..........................................................9-5
Normal Descent .............................................................9-5
Technique ...................................................................9-5
Common Errors ..........................................................9-6
Vertical Takeoff to a Hover ...........................................9-6
Technique ...................................................................9-6
Common Errors ..........................................................9-6
Hovering ........................................................................9-7
Technique ...................................................................9-7
Common Errors ..........................................................9-7
Hovering Turn ................................................................9-7
Technique ...................................................................9-7
Common Errors ..........................................................9-9
Hovering—Forward Flight ............................................9-9
Technique ...................................................................9-9
Common Errors ..........................................................9-9
Hovering—Sideward Flight ...........................................9-9
Technique ...................................................................9-9
Common Errors ........................................................9-10
Hovering—Rearward Flight ........................................9-10
Technique .................................................................9-10
Common Errors ........................................................9-10
Taxiing .........................................................................9-10
Hover Taxi ................................................................9-10
Air Taxi ....................................................................9-10
Technique .............................................................9-11
Common Errors ....................................................9-11
Surface Taxi .............................................................9-11
Technique .............................................................9-11
Common Errors ....................................................9-11
Normal Takeoff from a Hover .....................................9-12
Technique .................................................................9-12
Common Errors ........................................................9-12
Normal Takeoff from the Surface ................................9-13
Technique .................................................................9-13
Common Errors ........................................................9-13
Crosswind Considerations During Takeoffs ................9-13
Ground Reference Maneuvers .....................................9-13
Rectangular Course ..................................................9-14
Technique .............................................................9-14
Common Errors ....................................................9-15
S-Turns .....................................................................9-15
Technique .............................................................9-15
Common Errors ....................................................9-16
Turns Around a Point ...............................................9-16
Technique .............................................................9-16
Common Errors ...................................................9-17
Traffic Patterns .............................................................9-17
Approaches ..................................................................9-18
Normal Approach to a Hover ...................................9-19
Technique .............................................................9-19
Common Errors ....................................................9-19
Normal Approach to the Surface ..............................9-20
Technique .............................................................9-20
Common Errors ....................................................9-20
Crosswind During Approaches ................................9-20
Go-Around ...................................................................9-20
Chapter Summary ........................................................9-20
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Chapter 10
Advanced Flight Maneuvers .............................10-1
Introduction ..................................................................10-1
Reconnaissance Procedures .........................................10-2
High Reconnaissance ...............................................10-2
Low Reconnaissance ................................................10-2
Ground Reconnaissance ...........................................10-2
Maximum Performance Takeoff ..................................10-2
Technique .................................................................10-3
Common Errors ........................................................10-3
Running/Rolling Takeoff .............................................10-3
Technique .................................................................10-4
Common Errors ........................................................10-4
Rapid Deceleration or Quick Stop ..............................10-4
Technique .................................................................10-4
Common Errors ........................................................10-5
Steep Approach ............................................................10-5
Technique .................................................................10-6
Common Errors ........................................................10-6
Shallow Approach and Running/Roll-On Landing ......10-6
Technique .................................................................10-7
Common Errors ........................................................10-7
Slope Operations ..........................................................10-7
Slope Landing ..........................................................10-8
Technique .............................................................10-8
Common Errors ....................................................10-8
Slope Takeoff ...........................................................10-8
Technique .............................................................10-9
Common Errors ....................................................10-9
Confined Area Operations ...........................................10-9
Approach ................................................................10-10
Takeoff ..................................................................10-10
Common Errors ......................................................10-10
Pinnacle and Ridgeline Operations ............................10-11
Approach and Landing ...........................................10-11
Takeoff ...................................................................10-11
Common Errors ......................................................10-12
Chapter Summary ......................................................10-12
Chapter 11
Helicopter Emergencies and Hazards .............11-1
Introduction ..................................................................11-1
Autorotation .................................................................11-2
RPM Control ............................................................11-3
Risk Management during Autorotation Training ....11-3
Straight-In Autorotation ...........................................11-4
Technique (How to Practice) ................................11-4
Common Errors ....................................................11-5
Autorotation with Turns ...........................................11-6
Common Errors ....................................................11-7
Practice Autorotation with a Power Recovery ........11-7
Technique (How to Practice) ................................11-7
Common Errors ....................................................11-8
Practicing Power Failure in a Hover ........................11-8
Technique (How to Practice) ................................11-8
Common Errors ....................................................11-9
Vortex Ring State ........................................................11-9
Common Errors—Traditional Recovery ................11-10
Common Errors—Vuichard Recovery ...................11-10
Retreating Blade Stall ................................................11-10
Common Errors ......................................................11-11
Ground Resonance .....................................................11-11
Dynamic Rollover ......................................................11-11
Critical Conditions .................................................11-12
Cyclic Trim.............................................................11-12
Normal Takeoffs and Landings ..............................11-13
Slope Takeoffs and Landings .................................11-13
Use of Collective ....................................................11-13
Precautions .............................................................11-13
Low-G Conditions and Mast Bumping ......................11-14
Low Rotor RPM and Rotor Stall ...............................11-15
System Malfunctions .................................................11-16
Antitorque System Failure......................................11-16
Landing—Stuck Left Pedal ....................................11-17
Landing—Stuck Neutral or Right Pedal ...............11-17
Loss of Tail Rotor Effectiveness (LTE) .................11-18
Main Rotor Disk Interference (285–315°) ..........11-20
Weathercock Stability (120–240°) .....................11-20
Tail Rotor Vortex Ring State (210–330°) ...........11-21
LTE at Altitude ...................................................11-21
Reducing the Onset of LTE ................................11-21
Recovery Technique (Uncontrolled
Right Yaw) ..........................................................11-21
Main Drive Shaft or Clutch Failure ........................11-21
Hydraulic Failure ....................................................11-22
Governor or Fuel Control Failure ...........................11-22
Abnormal Vibration ...............................................11-22
Low-Frequency Vibrations .................................11-22
Medium- and High-Frequency Vibrations ..........11-23
Tracking and Balance .........................................11-23
Multiengine Emergency Operations ..........................11-23
Single-Engine Failure ............................................11-23
Dual-Engine Failure ..............................................11-23
Lost Procedures ..........................................................11-23
VFR Flight into Instrument Meteorological
Conditions ..................................................................11-24
Emergency Equipment and Survival Gear .................11-27
Chapter Summary ......................................................11-27
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Chapter 12
Night Operations ...............................................12-1
Introduction ..................................................................12-1
Visual Deficiencies ......................................................12-2
Night Myopia ...........................................................12-2
Hyperopia .................................................................12-2
Astigmatism .............................................................12-2
Presbyopia ................................................................12-2
Vision in Flight ............................................................12-2
Visual Acuity ............................................................12-3
The Eye.....................................................................12-4
Cones ........................................................................12-4
Rods ..........................................................................12-4
Night Vision .................................................................12-4
Night Scanning .........................................................12-4
Obstruction Detection...............................................12-5
Aircraft Lighting.......................................................12-6
Visual Illusions .........................................................12-6
Relative-Motion Illusion ..........................................12-6
Confusion with Ground Lights .................................12-6
Reversible Perspective Illusion ................................12-6
Flicker Vertigo .........................................................12-7
Night Flight ..................................................................12-7
Preflight ....................................................................12-7
Cockpit Lights ..........................................................12-8
Engine Starting and Rotor Engagement ...................12-8
Taxi Technique .........................................................12-8
Night Traffic Patterns ...............................................12-8
Takeoff .....................................................................12-8
En Route Procedures ................................................12-9
Collision Avoidance at Night ...................................12-9
Approach and Landing .............................................12-9
Illusions Leading to Landing Errors .........................12-9
Featureless Terrain Illusion ................................12-10
Atmospheric Illusions .........................................12-10
Ground Lighting Illusions ...................................12-10
Helicopter Night VFR Operations .............................12-10
Chapter Summary ......................................................12-10
Chapter 13
Effective Aeronautical Decision-Making .........13-1
Introduction ..................................................................13-1
Aeronautical Decision-Making (ADM) .......................13-2
Scenario ....................................................................13-2
Trescott Tips .............................................................13-3
The Decision-Making Process..................................13-4
Defining the Problem ............................................13-4
Choosing a Course of Action ................................13-4
Implementing the Decision and Evaluating the
Outcome ................................................................13-4
Decision-Making Models .........................................13-5
Pilot Self-Assessment ..................................................13-6
Curiosity: Healthy or Harmful? ................................13-6
The PAVE Checklist ................................................13-6
Single-Pilot Resource Management .............................13-7
Risk Management ........................................................13-9
Four Risk Elements ..................................................13-9
Assessing Risk ........................................................13-10
Using the 3P Model to Form Good Safety
Habits .....................................................................13-11
Workload or Task Management .................................13-12
Situational Awareness ................................................13-13
Obstacles to Maintaining Situational
Awareness .............................................................13-13
Operational Pitfalls .................................................13-15
Controlled Flight Into Terrain (CFIT)
Awareness ..................................................................13-15
Automation Management ...........................................13-18
Chapter Summary ......................................................13-18
Glossary ..............................................................G-1
Index ......................................................................I-1
xiv
1-1
Chapter 1
Introduction to the Helicopter
Introduction
A helicopter is an aircraft that is lifted and propelled by one
or more horizontal rotors, each rotor consisting of two or
more rotor blades. Helicopters are classified as rotorcraft
or rotary-wing aircraft to distinguish them from fixed-wing
aircraft, because the helicopter derives its source of lift from
the rotor blades rotating around a mast. The word “helicopter”
is adapted from the French hélicoptère, coined by Gustave de
Ponton d’Amécourt in 1861. It is linked to the Greek words
helix/helikos (“spiral” or “turning”) and pteron (“wing”).
1-2
Figure 1-1. Search and rescue helicopter conducting a pinnacle
approach.
Figure 1-2. Search and rescue helicopter landing in a confined area.
As an aircraft, the primary advantages of the helicopter are
due to the rotor blades that revolve through the air, providing
lift without requiring the aircraft to move forward. This lift
allows the helicopter to hover in one area and to take off
and land vertically without the need for runways. For this
reason, helicopters are often used in congested or isolated
areas where fixed-wing aircraft are not able to take off or
land. [Figures 1-1 and 1-2]
Piloting a helicopter requires adequate, focused and safety-
orientated training. It also requires continuous attention
to the machine and the operating environment. The pilot
must work in three dimensions and use both arms and
both legs constantly to keep the helicopter in a desired
state. Coordination, timing and control touch are all used
simultaneously when flying a helicopter.
Although helicopters were developed and built during the
first half-century of flight, some even reaching limited
production; it was not until 1942 that a helicopter designed by
Igor Sikorsky reached full-scale production, with 131 aircraft
built. Even though most previous designs used more than one
main rotor, it was the single main rotor with an antitorque
tail rotor configuration that would come to be recognized
worldwide as the helicopter.
Turbine Age
In 1951, at the urging of his contacts at the Department of
the Navy, Charles H. Kaman modified his K-225 helicopter
with a new kind of engine, the turbo-shaft engine. This
adaptation of the turbine engine provided a large amount of
horsepower to the helicopter with a lower weight penalty
than piston engines, heavy engine blocks, and auxiliary
components. On December 11, 1951, the K-225 became
the first turbine-powered helicopter in the world. Two years
later, on March 26, 1954, a modified Navy HTK-1, another
Kaman helicopter, became the first twin-turbine helicopter
to fly. However, it was the Sud Aviation Alouette II that
would become the first helicopter to be produced with a
turbine engine.
Reliable helicopters capable of stable hover flight were
developed decades after fixed-wing aircraft. This is largely
due to higher engine power density requirements than
fixed-wing aircraft. Improvements in fuels and engines
during the first half of the 20th century were critical factors
in helicopter development. The availability of lightweight
turbo-shaft engines in the second half of the 20th century led
to the development of larger, faster, and higher-performance
helicopters. While smaller and less expensive helicopters
still use piston engines, turboshaft engines are the preferred
powerplant for helicopters today.
The turbine engine has the following advantages over a
reciprocating engine:
• Less vibration
• Increased aircraft performance
• Reliability
• Ease of operation
1-3
Figure 1-3. The many uses for a helicopter include search and rescue
(top), firefighting (middle), and construction (bottom).
Hub
Mast Rotor blades
Figure 1-4. Basic components of the rotor system.
Uses
Due to the unique operating characteristics of the helicopter—
its ability to take off and land vertically, to hover for extended
periods of time, and the aircraft’s handling properties under
low airspeed conditions—it has been chosen to conduct tasks
that were previously not possible with other aircraft or were
too time- or work-intensive to accomplish on the ground.
Today, helicopters are used for transportation, construction,
firefighting, search and rescue, and a variety of other jobs
that require its special capabilities. [Figure 1-3]
Rotor System
The helicopter rotor system is the rotating part of a
helicopter that generates lift. A rotor system may be mounted
horizontally, as main rotors are, providing lift vertically; and
it may be mounted vertically, such as a tail rotor, to provide
lift horizontally as thrust to counteract torque effect. In the
case of tilt rotors, the rotor is mounted on a nacelle that
rotates at the edge of the wing to transition the rotor from a
horizontal mounted position, providing lift horizontally as
thrust, to a vertical mounted position providing lift exactly
as a helicopter.
The rotor consists of a mast, hub, and rotor blades. [Figure 1-4]
The mast is a hollow cylindrical metal shaft which extends
upwards from and is driven by the transmission. At the top
of the mast is the attachment point for the rotor blades called
the hub. The rotor blades are then attached to the hub by
several different methods. Main rotor systems are classified
according to how the main rotor blades are attached and
move relative to the main rotor hub. There are three basic
classifications: semirigid, rigid, or fully articulated, although
some modern rotor systems use an engineered combination
of these types. All three rotor systems are discussed with
greater detail in Chapter 4, Helicopter Components, Sections,
and Systems.
With a single main rotor helicopter, a torque effect is created
as the engine turns the rotor. This torque causes the body of
the helicopter to turn in the opposite direction of the rotor
(Newton’s Third Law: Every action has an equal and opposite
reaction, as explained in Chapter 2, Aerodynamics of Flight).
To eliminate this effect, some sort of antitorque control must
be used with a sufficient margin of power available to allow
the helicopter to maintain its heading and prevent the aircraft
from moving unsteadily. The three most common controls
used today are the traditional tail rotor, Fenestron (also called
a fantail), and the NOTAR®. All three antitorque designs will
be discussed in Chapter 4, Helicopter Components, Sections,
and Systems.
1-4
Figure 1-7. Coaxial rotors.
Figure 1-5. Igor Sikorsky designed the VS-300 helicopter
incorporating the tail rotor into the design.
Figure 1-6. Tandem rotor helicopters.
Rotor Configurations
Most helicopters have a single, main rotor but require a
separate rotor to overcome torque which is a turning or
twisting force. This is accomplished through a variable
pitch, antitorque rotor or tail rotor. This is the design that
Igor Sikorsky settled on for his VS-300 helicopter shown
in Figure 1-5. It has become the recognized convention for
helicopter design, although designs do vary. Helicopter main
rotor designs from different manufacturers rotate in one of
two different directions (clockwise or counter-clockwise
when viewed from above). This can make it confusing when
discussing aerodynamic effects on the main rotor between
different designs, since the effects may manifest on opposite
sides of each aircraft. For clarity, throughout this handbook,
all examples use a counter-clockwise rotating main rotor
system when viewed from above.
For clarity, throughout this handbook, all examples use a
counter-clockwise rotating main rotor system when viewed
from above.
Tandem Rotor
Tandem rotor (sometimes referred to as dual rotor) helicopters
have two large horizontal rotor assemblies, instead of one
main assembly and a smaller tail rotor. [Figure 1-6] Single
rotor helicopters need a tail rotor to neutralize the twisting
momentum produced by the single large rotor. Tandem
rotor helicopters, however, use counter-rotating rotors, each
canceling out the other’s torque. Counter-rotating rotor
blades will not collide with and destroy each other if they
flex into the other rotor’s pathway. This configuration has
the advantage of being able to hold more weight with shorter
blades, since there are two blade sets. Also, all the power
from the engines can be used for lift, whereas a single rotor
helicopter must use some power to counter main rotor torque.
Because of this, tandem helicopters make up some of the
most powerful and fastest rotor system aircraft.
Coaxial Rotors
Coaxial rotors are a pair of rotors turning in opposite
directions, but mounted on a mast, with the same axis of
rotation, one above the other. This configuration is a noted
feature of helicopters produced by the Russian Kamov
helicopter design bureau. [Figure 1-7]
Intermeshing Rotors
Intermeshing rotors on a helicopter are a set of two rotors
turning in opposite directions, with each rotor mast mounted
on the helicopter with a slight angle to the other so that
the blades intermesh without colliding. [Figure 1-8] This
arrangement allows the helicopter to function without the
need for a tail rotor. It has high stability and powerful lifting
capability. This configuration is sometimes referred to as a
synchropter. The arrangement was developed in Germany
1-5
Tail rotor driveshaft
located inside
of tail body
Tail rotor shaft
Tail rotor
Pitch change links
Cross Head
Figure 1-8. HH-43 Huskie with intermeshing rotors.
Figure 1-9. Basic tail rotor components.
for a small anti-submarine warfare helicopter, the Flettner
Fl 282 Kolibri. During the Cold War the American Kaman
Aircraft company produced the HH-43 Huskie, for USAF
firefighting purposes. The latest Kaman K-MAX model is
a dedicated sky crane design used for construction work.
Tail Rotor
The tail rotor is a smaller rotor mounted vertically or near-
vertically on the tail of a traditional single-rotor helicopter.
The tail rotor either pushes or pulls against the tail to counter
the torque. The tail rotor drive system consists of a drive shaft
powered from the main transmission and a gearbox mounted
at the end of the tail boom. [Figure 1-9] The drive shaft may
consist of one long shaft or a series of shorter shafts connected
at both ends with flexible couplings. The flexible couplings
allow the drive shaft to flex with the tail boom.
The gearbox at the end of the tail boom provides an angled
drive for the tail rotor and may also include gearing to adjust
the output to the optimum rotational speed typically measured
in revolutions per minute (rpm) for the tail rotor. On some
larger helicopters, intermediate gearboxes are used to angle
the tail rotor drive shaft from along the tail boom or tailcone
to the top of the tail rotor pylon, which also serves as a vertical
stabilizing airfoil to alleviate the power requirement for the
tail rotor in forward flight. The pylon (or vertical fin) may
also provide limited antitorque within certain airspeed ranges
if the tail rotor or the tail rotor flight controls fail.
Controlling Flight
A helicopter has four primary flight controls:
• Cyclic
• Collective
• Antitorque pedals
• Throttle
Cyclic
The cyclic control is usually located between the pilot’s legs
and is commonly called the “cyclic stick” or simply “cyclic.”
On most helicopters, the cyclic is similar to a joystick;
however, Robinson helicopters have unique T-bar cyclic
control systems. A few helicopters have cyclic controls that
descend into the cockpit from overhead while others use side
cyclic controls.
The control is called the cyclic because it can vary the pitch
of the rotor blades throughout each revolution of the main
rotor system (i.e., through each cycle of rotation) to develop
unequal lift (thrust). The result is to tilt the rotor disk in a
particular direction, resulting in the helicopter moving in that
direction. If the pilot pushes the cyclic forward, the rotor disk
tilts forward, and the rotor produces a thrust in the forward
direction. If the pilot pushes the cyclic to the side, the rotor
disk tilts to that side and produces thrust in that direction,
causing the helicopter to hover sideways. [Figure 1-10]
Collective
The collective pitch control, or collective, is located on the
left side of the pilot’s seat with a pilot-selected variable
friction control to prevent inadvertent movement. The
collective changes the pitch angle of all the main rotor blades
1-6
Horizontal stabilizer
70
5
30
85
50
15
100
70
5
30
85
50
15
100
Twist grip throttle
Collective control
Throttle cable
Throttle linkage
Fuel control or carburetor
Figure 1-11. The throttle control mounted at the end of the collective
control.
Figure 1-12. The horizontal stabilizer helps level the helicopter to
minimize drag during flight.
Swash plate
Figure 1-10. Cyclic controls changing the pitch of the rotor blades.
collectively (i.e., all at the same time) and independently of
their positions. Therefore, if a collective input is made, all
the blades change equally, increasing or decreasing total
lift or thrust, with the result of the helicopter increasing or
decreasing in altitude or airspeed.
Antitorque Pedals
The antitorque pedals are located in the same position as the
rudder pedals in a fixed-wing aircraft and serve a similar
purpose, namely to control the direction in which the nose
of the aircraft is pointed. Application of the pedal in a given
direction changes the pitch of the tail rotor blades, increasing
or reducing the thrust produced by the tail rotor, causing the
nose to yaw in the direction of the applied pedal. The pedals
mechanically change the pitch of the tail rotor, altering the
amount of thrust produced.
Throttle
Helicopter rotors are designed to operate at a specific rpm.
The throttle controls the power produced by the engine, which
is connected to the rotor by a transmission. The purpose of
the throttle is to maintain enough engine power to keep the
rotor rpm within allowable limits to produce enough lift for
flight. In single-engine helicopters, if so equipped, the throttle
control is typically a twist grip mounted on the collective
control, but it can also be a lever mechanism in fully
governed systems. Multi-engine helicopters generally have
a power lever or mode switch for each engine. [Figure 1-11]
Helicopter flight controls are discussed in greater detail
throughout Chapter 4, Helicopter Components, Sections
and Systems.
Flight Conditions
There are two basic flight conditions for a helicopter: hover
and forward flight. Hovering is the most challenging part of
flying a helicopter. This is because a helicopter generates
its own gusty air while in a hover, which acts against the
fuselage and flight control surfaces. The end result is the
need for constant control inputs and corrections by the pilot
to keep the helicopter where it is required to be. Despite
the complexity of the task, the control inputs in a hover are
simple. The cyclic is used to eliminate drift in the horizontal
direction that is to control forward and back, right and left.
The collective is used to maintain altitude. The pedals are
used to control nose direction or heading. It is the interaction
of these controls that makes hovering so difficult, since an
adjustment in any one control requires an adjustment of the
other two, creating a cycle of constant correction.
Displacing the cyclic forward initially causes the nose to
pitch down, with a resultant increase in airspeed and loss
of altitude. Aft cyclic initially causes the nose to pitch up,
slowing the helicopter and causing it to climb; however, as
the helicopter reaches a state of equilibrium, the horizontal
stabilizer helps level the helicopter to minimize drag, unlike
1-7
an airplane. [Figure 1-12] Therefore, the helicopter has
very little pitch deflection up or down when the helicopter
is stable in a flight mode. The variation from absolutely
level depends on the particular helicopter and the horizontal
stabilizer function.
Increasing collective (power) while maintaining a constant
airspeed induces a climb while decreasing collective causes
a descent. Coordinating these two inputs, down collective
plus aft cyclic or up collective plus forward cyclic, results
in airspeed changes while maintaining a constant altitude.
The pedals serve the same function in both a helicopter
and a fixed-wing aircraft, to maintain balanced flight. This
is done by applying pedal input in whichever direction is
necessary to center the ball in the turn and bank indicator.
Flight maneuvers are discussed in greater detail throughout
Chapter 9, Basic Flight Maneuvers.
Chapter Summary
This chapter gives the reader an overview of the history
of the helicopter, its many uses, and how it has developed
throughout the years. The chapter also introduces basic terms
and explanations of the helicopter components, sections, and
the theory behind how the helicopter flies.
1-8
2-1
Introduction
This chapter presents aerodynamic fundamentals and
principles as they apply to helicopters. The content relates
to flight operations and performance of normal flight tasks.
It covers theory and application of aerodynamics for the
pilot, whether in flight training or general flight operations.
Aerodynamics of Flight
Chapter 2
2-2
Rotor thrustLift component of rotor thrust
Propulsive force
component of
rotor thrust
Drag
WeightResultant of drag and weight
Figure 2-3. Four forces acting on a helicopter in forward flight.
Figure 2-2. Profile of an airfoil.
20´
5´
Figure 2-1. Area of a blade.
Gravity acting on the mass (the amount of matter) of an object
creates a force called weight. The rotor blade below weighs
100 lbs. It is 20 feet long (span) and is 1 foot wide (chord).
Accordingly, its surface area is 20 square feet. [Figure 2-1]
The blade is perfectly balanced on a pinpoint stand, as you
can see in Figure 2-2 from looking at it from the end (the
airfoil view). The goal is for the blade to defy gravity and
stay exactly where it is when we remove the stand. If we do
nothing before removing the stand, the blade will simply fall
to the ground. Can we exert a force (a push or pull) opposite
gravity that equals the 100 lb. weight of the blade? Yes, for
example, electromagnetic force could be used. In helicopters,
however, we use aerodynamic force to oppose weight and
to maneuver.
Every object in the atmosphere is surrounded by a gas that
exerts a static force of 2,116 lb per square foot (a force
times a unit area, called pressure) at sea level. However, that
pressure is exerted equally all over the blade (top and bottom)
and therefore does not create any useful force on the blade.
We need only create a difference of a single pound of static
pressure differential per square foot of blade surface to have a
force equal to the blade’s weight (100 lb of upward pressure
opposite 100 lb downward weight).
Total pressure consists of static pressure and, if the air is
moving, dynamic pressure (a pressure in the direction of the
air movement). As shown in Figure 2-3, if dynamic pressure
is increased the static pressure will decrease. Due to the
design of the airfoil, the velocity of the air passing over the
upper surface will be greater than that of the lower surface,
leading to higher dynamic pressure on the upper surface than
on the lower surface. The higher dynamic pressure on the
upper surface lowers the static pressure on the upper surface.
The static pressure on the bottom will now be greater than
the static pressure on the top. The blade will experience an
upward force. With just the right amount of air passing over
the blade the upward force will equal one pound per square
foot. This upward force is equal to, and acts opposite the
blade’s weight of 100 lb. So, if we now remove the stand, the
blade will defy gravity and remain in its position (ignoring
rearward drag for the moment).
The force created by air moving over an object (or moving
an object through the air) is called aerodynamic force. Aero
means air. Dynamic means moving or motion. Accordingly,
by moving the air over an airfoil we can change the static
pressures on the top and bottom thereby generating a useful
force (an aerodynamic force). The portion of the aerodynamic
force that is usually measured perpendicular to the air flowing
around the airfoil is called lift and is used to oppose weight.
Drag is the portion of aerodynamic force that is measured
as the resistance created by an object passing through the air
(or having the air passed over it). Drag acts in a streamwise
direction with the wind passing over the airfoil and retards
forward movement.
Forces Acting on the Aircraft
Once a helicopter leaves the ground, it is acted upon by
four aerodynamic forces; thrust, drag, lift, and weight.
Understanding how these forces work and knowing how to
control them with the use of power and flight controls are
essential to flight. [Figure 2-3] They are defined as follows:
2-3
Increased air
pressure underneath
Reduced air pressure Upper camber helps
to deflect air down
Mass of air deflected down
Figure 2-4. Production of lift.
• Lift—opposes the downward force of weight, is
produced by the dynamic effect of the air acting on the
airfoil and acts perpendicular to the flightpath through
the center of lift.
• Weight—the combined load of the aircraft itself, the
crew, the fuel, and the cargo or baggage. Weight pulls
the aircraft downward because of the force of gravity.
It opposes lift and acts vertically downward through
the aircraft’s center of gravity (CG).
• Thrust—the force produced by the power plant/
propeller or rotor. It opposes or overcomes the force
of drag. As a general rule, it acts parallel to the
longitudinal axis. However, this is not always the case,
as explained later.
• Drag—a rearward, retarding force caused by
disruption of airflow by the wing, rotor, fuselage, and
other protruding objects. Drag opposes thrust and acts
rearward parallel to the relative wind.
For a more in-depth explanation of general aerodynamics,
refer to the Pilot’s Handbook of Aeronautical Knowledge.
Lift
Lift is generated when an object changes the direction of
flow of a fluid or when the fluid is forced to move by the
object passing through it. When the object and fluid move
relative to each other and the object turns the fluid flow in
a direction perpendicular to that flow, the force required to
do this work creates an equal and opposite force that is lift.
The object may be moving through a stationary fluid, or the
fluid may be flowing past a stationary object—these two are
effectively identical as, in principle, it is only the frame of
reference of the viewer which differs. The lift generated by
an airfoil depends on such factors as:
• Speed of the airflow
• Density of the air
• Total area of the segment or airfoil
• Angle of attack (AOA) between the air and the airfoil
The AOA is the angle at which the airfoil meets the oncoming
airflow (or vice versa). In the case of a helicopter, the object
is the rotor blade (airfoil) and the fluid is the air. Lift is
produced when a mass of air is deflected, and it always acts
perpendicular to the resultant relative wind. A symmetric
airfoil must have a positive AOA to generate positive lift. At
a zero AOA, no lift is generated. At a negative AOA, negative
lift is generated. A cambered or nonsymmetrical airfoil may
produce positive lift at zero, or even small negative AOA.
The basic concept of lift is simple. However, the details of how
the relative movement of air and airfoil interact to produce
the turning action that generates lift are complex. In any case
causing lift, an angled flat plate, revolving cylinder, airfoil,
etc., the flow meeting the leading edge of the object is forced to
split over and under the object. The sudden change in direction
over the object causes an area of low pressure to form behind
the leading edge on the upper surface of the object. In turn,
due to this pressure gradient and the viscosity of the fluid,
the flow over the object is accelerated down along the upper
surface of the object. At the same time, the flow forced under
the object is rapidly slowed or stagnated causing an area of
high pressure. This also causes the flow to accelerate along
the upper surface of the object. The two sections of the fluid
each leave the trailing edge of the object with a downward
component of momentum, producing lift. [Figure 2-4]
Bernoulli’s Principle
Bernoulli’s principle describes the relationship between
internal fluid pressure and fluid velocity. It is a statement
of the law of conservation of energy and helps explain why
an airfoil develops an aerodynamic force. The concept of
conservation of energy states energy cannot be created or
destroyed and the amount of energy entering a system must
also exit. Specifically, in this case the “energy” referred
to is the dynamic pressure (the kinetic energy of the air—
more velocity, more kinetic energy) and static air pressure
(potential energy). These will change among themselves, but
the total pressure energy remains constant inside the tube.
A simple tube with a constricted portion near the center of its
length illustrates this principle. An example is running water
through a garden hose. The mass of flow per unit area (cross-
sectional area of tube) is the mass flow rate. In Figure 2-5,
the flow into the tube is constant, neither accelerating nor
decelerating; thus, the mass flow rate through the tube must
be the same at stations 1, 2, and 3. If the cross-sectional area
at any one of these stations—or any given point—in the
tube is reduced, the fluid velocity must increase to maintain
a constant mass flow rate to move the same amount of fluid
through a smaller area. The continuity of mass flow causes
the air to move faster through the venturi. In other words,
fluid speeds up in direct proportion to the reduction in area.
2-4
WATER INPUT WATER OUTPUT
Station 1
Station 2
Station 3
Velocity increased
Static pressure decreased
(compared to original)
Same mass of air
Mass of air Cross-section of cylinder
PTotal = PDynamic + PStatic
34 PSF PD 41 PSF PD
2116 PSF PS
2109 PSF PS
Point 1 Point 2
PT = 2150 PSF
PD = 34 PSF
PS = 2116 PSF
V = 100 KTS
Point 1
PT = 2150 PSF
PD = 41 PSF
PS = 2109 PSF
V = 120 KTS
Point 2
Figure 2-5. Water flow through a tube.
Figure 2-6. Venturi effect.
Bernoulli (Ptotal = Pdynamic + Pstatic) states that the increase
in velocity will increase the streamwise dynamic pressure.
Since the total pressure in the tube must remain constant,
the static pressure on the sides of the venturi will decrease.
Venturi effect is the term used to describe this phenomenon.
Figure 2-6 illustrates plates of one square foot in the dynamic
flow and on the sides of the tube indicating static pressure,
with corresponding pressure. At point 2, it is easier to
visualize the static pressure reduction on the top of the airfoil
as compared to the bottom of the airfoil, which is depicted as
outside of the tube and therefore at ambient static pressure.
Keep in mind with actual blades it is not a simple as this
example because the bottom static pressure is influenced by
blade design and blade angle, among other things. However,
the basic idea is that it is the static pressure differential
between the top and bottom multiplied by the surface area
of the blade that generates the aerodynamic force.
Venturi Flow
While the amount of total energy within a closed system (the
tube) does not change, the form of the energy may be altered.
Pressure of flowing air may be compared to energy in that the
total pressure of flowing air always remains constant unless
energy is added or removed. Fluid flow pressure has two
components—static and dynamic pressure. Static pressure
is the pressure component measured in the flow but not
moving with the flow as pressure is measured. Static pressure
is also known as the force per unit area acting on a surface.
Dynamic pressure of flow is that component existing as a
result of movement of the air. The sum of these two pressures
is total pressure. As air flows through the constriction, static
pressure decreases as velocity increases. This increases
dynamic pressure. Figure 2-7 depicts the bottom half of the
constricted area of the tube, which resembles the top half of
an airfoil. Even with the top half of the tube removed, the air