Principles of Helicopter Flight

Foreword     xiPreface     xiiPhysics     1Newton's Laws     1Newton's First Law     1Newton's Second Law     2Newton's Third Law     3Conclusion     3Mathematical Terms     3Velocity     3Acceleration     3Equilibrium     4Gravitational Forces     4Centripetal Force     5Vector Quantities     5Moments and Couples     6Moments     6Couples     6Energy     6Pressure Energy     6Dynamic (Kinetic) Energy     7Units of Measurement     7Graphs     8Review 1     10The Atmosphere     11Atmospheric Pressure     11Air Temperature     11Combined Effects     12Moisture Content     12The Standard Atmosphere (ISA)     12Pressure Altitude     13Density Altitude     13Summary     13Operational Considerations     14Review 2     14Lift     15Definitions     15The Lift Formula     18Dynamic Energy     20Summary     20Indicated Airspeed and True Airspeed     21Center of Pressure     22Aerodynamic Center     24Review 3     26Drag     27Types of Drag     28Parasite Drag     28Profile Drag     29Form Drag     29Skin Friction     30Induced Drag     31Tip Vortices     33Effect of Airspeed on Induced Drag     34Effect of Aspect Ratio     34Methods to Reduce Induced Drag     35Wash-out     35Tip Design     35Total Drag Curve     36Conclusion     37Review 4     38Lift/Drag Ratio     39Best (or Maximum) L/D Ratio     40Other Factors Influencing L/D Ratio     41Conclusion     41Review 5     42Aerodynamic Forces     43Definitions     43Rotor Systems     45Introduction      45Rotational Airflow (Vr)     46Blade Angle of Attack     46Induced Flow     47Airflow Caused by Aircraft Velocity     48The Forces     48Total Rotor Thrust     49Rotor Drag (Torque)     49Angle of Attack and the Rotor Thrust/Rotor Drag Ratio     50Induced Flow and the Rotor Thrust/Rotor Drag Ratio     50Inflow Angle     51The Force Opposing Weight     52Factors Influencing Rotor Thrust     53Air Density     53Rotor rpm     54Blade Angle     54Disc Area     54Significant Aspects of High Inertia Blades     55Conclusion     55Review 6     56Rotor Blade Airfoils     57Drag Factors     57Stress Factors     58Effect of Local Air Velocity on Blade Design     59Blade Tip Speeds     59Development in Blade Design     60Review 7     60Rotor Drag (Torque)     61Disc Loading Changes     61Changes in Gross Weight     62Changes in Altitude      62Changes in Configuration     62Ground Effect     62Translational Lift     64Summary     65Review 8     66The Anti-Torque Rotor     67Anti-Torque Functions     67Mechanical Considerations     68Anti-Torque and Demand for Power     68Effect of the Wind     69Translating Tendency (Tail Rotor Drift)     70Rolling Tendency     71Tail Rotor Flapping     71Shrouded Tail Rotors     72Tail Rotor Design     72Other Methods of Anti-Torque Control     72Strakes and Anti-Torque     73Tail Rotor Failure     74Review 9     76Controls and Their Effects     77Collective Control     77Cyclic Control     78Effect of Controls on Blade Lead-Lag Behavior     78Mean Lag Position     78The Four Main Causes of Movement about the Lead/Lag Hinge     78Conservation of Angular Momentum (Coriolis Effect)     78Hookes Joint Effect     79Periodic Drag Changes     80Random Changes      80Review 10     80The Hover     81Hover Our-of Ground Effect (OGE) and In-Ground Effect (IGE)     81Factors Affecting Ground Effect     82Helicopter Height Above Ground Level     82Density Altitude and Gross Weight     82Gross Weight and Power Required     83Nature of the Surface     83Slope     83Wind Effect     84Confined Areas - Recirculation     84Factors Determining the Degree of Recirculation     84Over-Pitching     85Review 11     86Forward Flight     87Three Basic Aspects of Horizontal Flight     89Tilting the Disc with Cyclic     89An Alternate Explanation of Cyclic Action     91Dissymmetry of Lift     91Eliminating Dissymmetry of Lift     92Blow-Back (Flap Back)     94Blow-back (Flap-Back) When Using Collective     95Summary     96Designs that Reduce Flapping Amplitude     96Delta-3 Hinges     96Offset Pitch Horns     97Reverse Flow     98Translational Lift     99Transverse Flow Effect     101Review 12     102Power, Range and Endurance     103Power     103Ancillary Power     103Profile Power     103Induced Power     104Parasite Power     104The Total Horsepower Required Curve (the HPR)     105Attitude     106Weight     107Slingload and Parasite Drag Items     107Flying the Helicopter for Range     108Effect of the Wind     109Engine Considerations     110Range Summary     110Flying the Helicopter for Endurance     111Endurance Summary     111Review 13     112Climbing and Descending     113Climbing     113The Horsepower Available Curve (The HPA)     114Factors Affecting the Horsepower Available Curve     114Altitude     114Density Altitude     115Leaning the Mixture     115Collective Setting     115Rate of Climb     115Angle of Climb     116Effect of Lowering Horsepower Available Curve     116Summary      117Effect of the Wind     117Climb Performance Summary     118Descending     118Angle of Descent     119Effect of the Wind on Descents     120Descent Performance Summary     121Review 14     122Maneuvers     123Turning     123Rate of Turn     124Radius of Turn     125Rate and Radius Interaction     125The Steep Turn     125Power Requirement     126The Climbing Turn     127The Descending Turn     127Effect of Altitude on Rate of Turn and Radius of Turn     127Effect of Changes in Gross Weight on Rate and Radius     128Effect of the Wind on Rate and Radius     128Effect of the Wind on Indicated Airspeed and Translational Lift     129Effect of Slingloads     130Effect of Slipping and Skidding     131Pull-Out from a Descent     131Review 15     132The Flare     133Initial Action     133Flare Effects     133Thrust Reversal     134Increasing Total Rotor Thrust      134Increasing Rotor rpm     134Management of Collective     135Review 16     136Retreating Blade Stall     137Effect of Increasing Airspeed on Stall Angle     137Factors Affecting the Advancing Blade     138Symptoms of Retreating Blade Stall     138Recovery     139Factors Influencing V[subscript ne]     140Conclusion     141Review 17     142Autorotation     143Initial Aircraft Reaction     143The Lift/Drag Ratio and Forces Involved     143The Stalled Region     144The Driven (Propeller) Region     145The Driving (Autorotative) Region     145Combined Effects of All Regions     146Autorotation and Airspeed     148Combined Effect     149Effect of Forward Speed on the Three Regions     150Effect of Airspeed Changes on Rotor rpm     150Autorotation Range and Endurance     150Effect of Altitude on Range and Endurance     151Effect of Gross Weight on Range and Endurance     151Effect of Parasite Drag and Slingloads on Range and Endurance     152Touchdown      152Loss of Power at Low Heights     153Factors Influencing Rotor rpm Decay When the Engine Fails     153Combination of Airspeed and Height Best Avoided     153Review 18     156Hazardous Flight Conditions     157Vortex Ring State     157Effect on the Root Section of the Blade     158Effect on the Tip Section of the Blade     158Flight Conditions Likely to Lead to Vortex Ring State     160Symptoms of Vortex Ring State     160Recovery from Vortex Ring State     161Tail Rotor Vortex Ring State     161Ground Resonance     162Causes of Ground Resonance     162Factors that May Cause Ground Resonance     163Rotor Head Vibrations     163Fuselage Factors     163Ground Resonance Recovery Action     164Blade Sailing     164Dynamic Rollover     165Factors Influencing the Critical Angle     165Cyclic Limitations     166Mast Bumping     167Avoiding Mast Bumping     169Recovery from Low and Zero g     169Mast Bumping Summary     169Exceeding Rotor rpm Limits     169Reasons for High Rotor rpm Limits     169Engine Considerations     169Blade Attachment Stress     169Sonic Problems     170Reasons for Low Rotor rpm Limits     170Insufficient Centrifugal Force     170Reduced Tail Rotor Thrust     170Rotor Stalls     170Recovery from Low Rotor rpm     171Review 19     172Helicopter Design and Components     173Transmission     173Main Rotor Gear Box     173Freewheeling Unit     174Drive Shafts     174Tail Rotor Gear Box     174Rotor Brake     174Clutch     174Chip Detectors     175Governors     175Swashplate (Control Orbit)     176Phase Lag     177Advance Angle     177Rotor Blades     179Chordwise Blade Balancing     180Spanwise Blade Balancing     180Trim Controls     180Bias Control     180Electronic Servo Systems     180Tail Rotors     181Tail Rotor Flapping      181Tail Rotor Rotation     181Helicopter Vibrations     181Types of Vibrations     182Vertical Vibrations     182Lateral Vibrations     183Combined Vertical and Lateral Vibrations     183High Frequency Vibrations     183Engine Vibrations     184Remedial Action by the Pilot     184Control Functions     184Collective     184Twist Grip Throttle     184Engine Cooling     185Carburetor Icing     185Dual Tachometer Instruments     186Rotor Stabilizing Design Systems     187The Bell Stabilizing Bar     187The Hiller System     187The Underslung Rotor System     188Rotorless Anti-Torque System     189Advantages of the Notar System     189Components     189Air Intake     190Engine-driven Fan     190Slots     190Direct Jet Thruster     191Vertical Stabilizers     191Undercarriages     192Skids     192Wheels     192Oleo (Shock) Struts     193Review 20     195Stability     195Static Stability     195Dynamic Stability     195Stability in the Three Planes of Movement     196Longitudinal Stability     197Longitudinal Stability Aids     197Lateral Stability     198Directional Stability     199Directional Stability Aids     200Cross Coupling with Lateral Stability     200Offset Flapping Hinges     200Review 21     202Special Helicopter Techniques     203Crosswind Factors     203Lateral Blow-back (Flap-back)     203Weathervane Action     203Effect on tail Rotor Thrust     203Different Types of Takeoffs and Landings     204Downwind Takeoffs and Landings     204Running Takeoff     204Cushion-Creep Takeoff     205Confined Area Takeoff (Towering Takeoff)     205Maximum Performance Takeoff     206Running Landing     206The Zero-Speed Landing     207Operations on Sloping Surfaces     207Sling Operations      208The Equipment     208The Sling     210Ground Handling     211Flying Techniques     212Snagging of Cable or Strap on the Undercarriage before Liftoff     212Never-Exceed Speed (V[subscript ne])     213Preflight Rigging     213Length of Cable or Strap     213Number and Type of Slings     213Nets     213Pallets     214Load Center of Gravity     214Pilot Action in Case of Helicopter Oscillation     214The Approach     215Types of Slingload     215Horizontal Loads     215Unusual Loads     216Conclusion     219Review 22     220Mountain Flying     221Updrafts and Downdrafts     221Thermal Currents     223Katabatic and Anabatic Winds     224Mechanical Turbulence     224Wind Strength     225Size and Shape of Mountains     226Stability or Instability of Air     226Wind Direction Relative to Mountain Orientation     227Summary     227Valley Flying      227Ridgeline Flying     228The "Standard" Mountain Approach     228General Coinments on Mountain Approaches     230High Attitude Approach Considerations     230Transition     232Ground Effect Considerations on Mountain Sites     232Determining Wind Change during Critical Phases     233Landing Site Selection     233Surface of Sites     233Flight in Areas Covered in Snow and Ice     234Survival Equipment     235Review 23     236Helicopter Icing     237Ice Accretion     237Influence of Temperature and Drop Size     237Water Content of Air     238Kinetic Heating     238Shape of Airfoils and Other Aircraft Components     238Mechanical Flexion and Vibration     239Ice Formation on Blades at Different Temperatures     239Electrical Anti-Icing     240Consequences of Ice Accretion     240Engine Intake Icing     241Review 24     242Helicopter Performance     243Helicopter Performance Factors     243Altitude     243Pressure Altitude      244Density Altitude     246Combined Effect of Pressure and Density Altitude     247Moisture Content of Air     248Aircraft Gross Weight     248External Stores     248The Wind     249Power Check     249Performance Graphs     250Units of Measurement     251Hover Ceiling Graph     252Takeoff Distance over a 50-Foot Obstacle     254Turbine Engine Power Check     256Maximum Gross Weight for Hovering     258Climb Performance     260Range     261Endurance     262Review 25     263Weight and Balance     265Definitions     265Weight     267Balance     267Beyond the Center of Gravity Limits     268Excessive Forward Center of Gravity     268Excessive Aft Center of Gravity     269Summary     269Calculating the Center of Gravity Position     269To Calculate the Longitudinal Center of Gravity Position     271To Calculate the Lateral Takeoff Center of Gravity Position     271Summary      273Effect of External Loads on Center of Gravity Position     273Conclusion     274Review 26     274Sample Examination     277Temperature Conversion     287Altimeter Setting Conversion     289Review and Examination Answers     291Glossary     295Index     299