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# Chapter 2 Principles Of Flight

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• Relative windDirection of airflow with respect to the bladeOpposite the flight path of the blade
• Pitch angleAcute angle between blade chord and plane of rotationVaried by collective and cyclicNot to be confused with angle of attack
• Acute angle between chord line and relative wind.Not always the same as pitch angle
• LiftForce produced at right angle to the relative windOpposes gravityBased on Bernoulli’s principleIncreased velocity, decreases pressureDragResists airfoils movement through the airParallel to relative windPerpendicular to liftSlows rotor when angle of attack is increasedVaries with the square of velocity
• Imaginary point where the result of aerodynamic forces are considered to be concentratedCan move as forces changeMoves great distances on unsymmetrical airfoilsMoves very little on symmetrical airfoils
• Helicopter use both symmetrical and unsymmetrical airfoils
• Streamlined airflow separates and reverse flow occursResults in loss of lift
• Rotor DroopBlades droop due to gravity when at rest – Static rotor droopNot to be confused with dynamic rotor droopOvercome by centrifugal forceLift react perpendicular to centrifugal forceNew position is referred to as coningDepends on lift and weight of helicopterTip path plane. – Circular path that tip pass throughOut of track – Causes vibrations
• Feathering axis required to change angle of attack of each blade as they pass along the disc.Note: pause and discuss collective and cyclic before next slide
• Movement occurs 90 deg. from the force applied in the direction of rotationTo do this a swashplate is used
• For every action there is an opposite and equal reactionFuselage moves in opposite direction of M/RSeveral designs to eliminateCoaxialIntermeshingTandemRamjet at the rotor tipsSingle Main with tail rotorTail rotor uses a great deal of engine powerDifferent methods used to reduce tail rotor power requirementsVertical fin that is offset keeps the fuselage straight in fwd flight
• Velocity of airfoil section increases farther out from mastTwist is incorporated to increase to angle of attack for slower moving airfoil sectionsThis increase overall lift of the rotor system
• Lift on retreating half less than advancing halfEarly inventors could not achieve fwd flightJuan De Cierva incorporated flapping hinge
• Flapping hingeAllows advancing blade to move upThis reduces it’s liftRetreating blade moves downIncreases lift on retreating sideSeesawTwo bladed systemBlades are connected so if one moves up the other moves down
• Coriolis EffectRotors with flapping hinge are subjected to it more than seesaw systemsChange in velocity to compensate for the change in distance in the centre of mass of the blades from the axis of rotation.As the blade flaps up it acceleratesAs the blade flaps down(retreating) it slows downLike a figure skaterCauses geometric imbalance.
• Underslung RotorUsed with seesaw systemMounted below the top of the mastKeeps the distance from the C of G of the blades to the axis of rotation, smallLong masts, mounted with flexibility to absorb any geometric imbalance
• Rigid headUses feathering axis onlyUnable to correct for dissymmetry of liftFibreglass blades allow for flappingHighly manoeuvrableBO 105 can perform a barrel roll and a loop
• Simplified construction.Not dependant on the centrifugal force for rigidity.More subject to wind gustsBending forces are applied to the blade rootSemirigid rotors require underslinging of the rotor.Some are gimbaled for movement about the chordwise axisOthers use swashplate correction factors to compensate for coriolis effect.
• The rotor disc may tilt without tilting the mast because of the flapping hinge.Flapping hinges relieve bending forces at the root of the blade, allowing coning of the rotor.The flapping hinge reduces gust sensitivity due to the individual blade flap.Flapping hinge bearing areas are subject to heavy centrifugal loads.The flapping hinge introduces geometric imbalance.This geometric imbalance requires an additional drag hinge.The drag hinge relieves bending stresses during acceleration of the rotor.Drag hinge bearings are subject to high centrifugal loads.The lead-lag hinge allows the main rotor blades to self align. Therefore, there is no need to statically align a fully articulated main rotor head assembly
• Cyclic controls are sometimes used to offset translating tendency (tail rotor drift)
• within half of rotor diameter to the groundDownward flowing air can’t escapeAir density increasesForms a ground cushionAt hover speeds. Lost above 3 to 5 mph
• Correlation box changes engine power with collective movement
• ### Transcript

1. Principles of Flight<br />
2. M/R & T/R Blade Terminology<br /><ul><li>Root
3. Span
4. Tip
5. Chord
6. Trailing edge
7. Leading edge</li></li></ul><li>Fig. 2-1 Nomenclature of the blade<br />Fig. 2-2 Nomenclature of the cross section of an airfoil.<br />
8. Wing Design<br />Camber - the characteristic curve of the airfoil’s upper<br /> and lower surfaces.<br />Chord line - an imaginary straight line<br />drawn through the airfoil <br /> from the leading edge to <br /> the trailing edge.<br />Angle of Attack - the angle between the chord line of the <br /> airfoil and the direction of the relative wind.<br />
9. Wing Design<br />Upwash-the deflection of the oncoming airstream <br /> upward and over the wing <br />Trailing Edge - the portion of the <br /> airfoil where the <br /> airflow over the <br /> upper surface <br /> rejoins the lower <br /> surface airflow.<br />Leading Edge - the part of the airfoil <br /> which meets the airflow first<br />Downwash - the downward deflection of the <br /> airstream as it passes over the <br /> wing and past the trailing edge.<br />As an airfoil moves through the air, it alters the air pressure around its surface. A typical subsonic airfoil has <br />a rounded nose, or leading edge, a maximum thickness about one-third of the way back, and a smooth taper<br /> into a relatively sharp point at the rear or trailing edge.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
10. Definitions of Aerodynamic Principles<br /><ul><li>Relative Wind
11. Pitch Angle
12. Angle of Attack
13. Lift
14. Drag
15. Center of Pressure
16. Blade Stall</li></li></ul><li>FLIGHT PATH<br />RELATIVE WIND<br />FLIGHT PATH<br />FLIGHT PATH<br />RELATIVE WIND<br />RELATIVE WIND<br />FLIGHT PATH<br />RELATIVE WIND<br />Fig. 2-5 The relationship of the rotor blade and the relative wind.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
17. Fig 2-6: The relationship of the pitch angle to the plane of rotation.<br />Pitch Angle<br />
18. Angle of Attack<br />Fig 2-7: The angle of attack in relation to the relative wind.<br />
19. Fig 2-8: Lift versus drag<br />
20. Fig 5-57: Typical alignment point on a rotor blade.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
21. Centre of Pressure<br />
22. Asymmetrical = High speed airfoil, High lift airfoil<br />Symmetrical = General purpose airfoil<br />Fig. 2-9 Symmetrical and unsymmetrical airfoils.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
23. Fig. 2-10 The stall angle of the airfoil.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
24. Effects<br />On<br />Lift<br />Fig. 2-11 Lift, thrust, weight, and drag components in relationship to the helicopter.<br />
25. Fig 2-12: Rotor droop occurs when the rotor is at rest.<br />Fig 2-13: A rotating rotor system.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
26. Fig 2-14: A loaded rotating system.<br />Fig 2-15: Coning is affected by the weight of the helicopter.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
27. Fig 2-16: The rotor disc or tip path plane.<br />Fig 2-17: In track and out of track condition.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
28. Coning<br />
29. Fig. 2-18 Aerodynamic force vectors applied during modes of flight.<br />
30. Hovering<br />
31. Thrust<br /> Thrust gives helicopter directional movement.<br /> Obtained by the movement of the tip path plane of the rotor or rotor disc.<br />
32. FEATHERING AXIS<br />Fig. 2-19 The feathering axis or pitch axis of the rotor.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
33. Gyroscopic Precession<br />
34. Gyroscopic Forces<br />Fig 2-21: Basic principles of the swashplate.<br />
35. Fig 2-22: The results of gyroscopic precession as applied to the main rotor system.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
36. Torque<br />Newton’s Third Law<br />
37. Torque<br />Newton’s Third Law<br />ROTATION OF THE ROTOR<br />COUNTER ROTATION <br />OF THE FUSELAGE<br />TAIL ROTOR<br />Fig. 2-23 Anti-torque is applied by the tail rotor.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
38. Blade Twist<br />Fig 2-24: The rotor speed increases from the root of the blade outward.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
39. A<br />B<br />C<br />Mast<br />C<br />A<br />B<br />A-A<br />ROOT<br />B-B<br />CENTRE<br />C-C<br />TIP<br />Fig. 2-25 More twist at the root of the blade increases the lift.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
41. Dissymmetry of Lift<br /> Flapping hinge<br /> Seesaw system<br /> Coriolis effect<br /> Drag or lead-lag hinge<br /> Underslung rotor<br />
42. Dissymmetry of Lift<br />
43. Fig 2-26: Forward speed increases the difference in speed between the advancing and retreating blades.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
44. Fig. 2-27 The flapping hinge is used to control dissymmetry of lift.<br />Fig. 2-28 This seesaw action is used on semirigid rotors.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
45. Coriolis Effect (Hook’s Joint Effect)<br />
46. BLADE MOVEMENT<br />LEAD LAG<br />HINGE<br />ROTOR HUB<br />Fig. 2-29 Lead-lag action is required on systems using the flapping design.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />BCIT Aerospace www.bcit.ca/transportation/aerospace<br />
47. Underslung Feathering Axis<br />
48. Underslung Feathering Axis<br />
49. Rotor Heads<br /> Rigid rotor<br /> Semirigid<br /> Fully articulated<br />
51. BO 105<br />
52. Fig. 2-31 The head shown in the top view has <br />movement on two axes while the bottom head <br />has movement on only one axis only.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
53. Semirigid<br />
54. Main Rotor Head Fully Articulated<br />
55. Aerodynamic Characteristics<br /><ul><li>Translating tendency
56. Ground Effect
57. Transitional Lift</li></li></ul><li>Translating Tendency<br /> This is a tendency for the whole helicopter to drift in the direction of the tail rotor thrust.<br />
58. Sometimes the mast is offset to correct for this.<br />Fig 2-32: Mast tilt is sometimes used to cancel translating tendency.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
59. Ground Effect<br />
60. Effective Translational Lift<br />
61. Fig 2-33: The variation in downward airflow causing the transverse flow effect.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
62. Blade Tip Stall<br /><ul><li>Insufficient airspeed
63. Too great an angle of attack
64. Heavy wing loading</li></li></ul><li>Fig 2-34: Forward speed is a major factor in retreating blade stall.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
65. Fig 2-35: Stall occurs first on the retreating half of the disc.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
66. Autorotation<br />
67. Fig. 2-36 The autorotative region changes in forward flight.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
68. AutorotativeForce<br />
69. Fig 2-37: Autorotation is not safe at low altitude and low airspeed.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
70. Fig 5-121: Autorotation chart used on Hughes 500.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
71. Ground Resonance<br /> Is a self-exciting vibration which occurs on the ground.<br /> Aerodynamic phenomenon associated with fully articulated rotor systems.<br /> Blades move out of phase with each other.<br />
72. Ground Resonance<br />
73. Causes<br /> Soft Oleo<br /> Improper tire pressure<br /> Uneven ground <br /> Soft ground<br /> Improperly rigged flight controls<br />
74. Stability<br /><ul><li> Static stability
75. Dynamic stability</li></li></ul><li>Stability<br /> 1. Tendency to return to it’s original position.<br /> 2. Dynamic stability is related to all objects that possess static stability.<br /> 3. Bell uses a stab bar and some manufacturers use an offset flapping hinge.<br />
76. DISTURBING FORCE ORIGINAL<br />FORCE APPLIED RELEASED POSITION<br />POSITIVE STATIC STABILITY<br />Fig. 2-38 All aircraft must be able to demonstrate stability.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
77. FORCE APPLIED CONE FALLS CONE FAILS TO <br /> RETURN TO ORIGINAL<br /> POSITION<br />Fig. 2-39 Negative stability will result in problems of controllability.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
78. DISTURBANCE<br />Fig. 2-40 The helicopter is usually considered statically stable<br />and dynamically unstable.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
79. The Bell method<br />Fig. 2-41 The stabilizer bar is the most common <br />method used to obtain dynamic<br />stability on semirigid rotors.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
80. OFFSET FLAPPING<br />HINGE<br />Fig. 2-42 Two methods used with fully articulated heads are shown here.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
81. Primary Flight Control Terminology<br /> Collective<br /> Anti-torque pedals<br /> Cyclic control<br />
82. EXAMPLE OF ALL THREE FLIGHT CONTROLS<br />CYCLIC<br />ANTI-TORQUE PEDALS<br />COLLECTIVE<br />
83. CYCLIC<br />COLLECTIVE<br />PEDALS<br />Fig. 2-43 Controls used to maintain flight.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
84. Collective Pitch<br /><ul><li> Location: Left hand side of pilot seat.
85. Moves blades up and down equally.
86. Also known as “power lever”.</li></li></ul><li>Fig. 2-44 Raising of the collective requires more engine power.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
87. Anti-Torque Pedals<br /><ul><li> Primary function is to counteract Newton’s 3rd law.
88. Secondary function is directional control.
89. Anti-torque pedals are sometimes known as tail rotor pedals.</li></li></ul><li>TAIL MOVES<br />NEGATIVE OR LOW POSTIVE PITCH<br />Fig. 2-45 The movement<br />of the anti-torque pedals <br />is directly related to the <br />amount of main rotor <br />pitch.<br />MEDIUM POSITIVE PITCH<br />HIGH POSITVE PITCH<br />TAIL MOVES<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
90. Cyclic Controls<br /> Used to tilt main rotor disk in desired direction of flight<br />
91. DIRECTION OF ROTATION<br />DECREASED PITCH<br />SWASH PLATE TILTED FORWARD<br />INCREASED PITCH<br />Fig. 2-20 Cyclic pitch change through the swashplate.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
92. Fig. 2-48 The cyclic control is used to obtain directional control of the helicopter.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
93. Fig 2-49: A typical movable horizontal stabilizer.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
94. Fig 2-50: A typical fixed position horizontal stabilizer.<br />Reproduced with permission of Jeppesen Sanderson, Inc. NOT FOR NAVIGATIONAL USE. Copyright Jeppesen Sanderson, Inc. 2007<br />
95. ATA System Format<br /> ATA Code Differences between Fixed & Rotary Winged Aircraft.<br /> Helicopters use ATA Chapter 67 for Flight Controls verses Chapter 27 for Airplanes.<br /> Helicopters also use Chapters 62 thru 66 specifically.<br />
96. Gyroscopic Precession Blade Flapping<br />