Module 12-02 Helicopter Aerodynamics, Structures and Systems

181 Pages·2017·5.05 MB·English

AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

Mo d u l e 1 2 - 0 2
He l i c o p t e r Ae ro d y n a m i c s , St ru c t u r e s a n d Sy s t e m s

F l i gh t Co nt ro l Syst e ms

12 - 02- 1
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

T a b l e o f c o n t e n t s

I. INTRODUCTION ........................................................................................................................................................................................................................ 6
1. AXIS: ....................................................................................................................................................................................................................................... 6
1.1. Plane of rotation: ............................................................................................................................................................................................................... 7
1.2. Axis of rotation: ................................................................................................................................................................................................................. 7
1.3. Flight control components: ................................................................................................................................................................................................ 8
2. PROPERTIES: ...................................................................................................................................................................................................................... 11
3. MAIN PILOT COMMANDS: .................................................................................................................................................................................................. 11
4. OTHER PILOT COMMANDS: ............................................................................................................................................................................................... 12
II. CYCLIC CONTROL ................................................................................................................................................................................................................. 14
1. GENERAL: ............................................................................................................................................................................................................................ 14
1.1. Tip path plane - TPP: ...................................................................................................................................................................................................... 15
1.2. Swashplates principle: .................................................................................................................................................................................................... 16
2. FUNCTIONS OF CYCLIC CONTROL: ................................................................................................................................................................................. 17
2.1. Main functions of cyclic control: ...................................................................................................................................................................................... 17
2.2. Additional functions: ........................................................................................................................................................................................................ 22
III. COLLECTIVE CONTROL ........................................................................................................................................................................................................ 23
1. COLLECTIVE CONTROL AND PITCH ANGLE: ................................................................................................................................................................. 24
2. THROTTLE CONTROL: ....................................................................................................................................................................................................... 24
3. GOVERNOR AND CORRELATORS: ................................................................................................................................................................................... 25
IV. SWASHPLATE ........................................................................................................................................................................................................................ 29
1. SWASHPLATE ASSEMBLY: ............................................................................................................................................................................................... 29
1.1. Swashplate components: ................................................................................................................................................................................................ 31
1.2. Swashplate description: .................................................................................................................................................................................................. 31
2. SWASHPLATE OPERATION: .............................................................................................................................................................................................. 35
2.1. Collective input operation: ............................................................................................................................................................................................... 35
2.2. Cyclic operation: ............................................................................................................................................................................................................. 36
3. SPIDER CONTROL MECHANISM: ...................................................................................................................................................................................... 37
V. YAW CONTROL ...................................................................................................................................................................................................................... 38
1. ANTI-TORQUE CONTROL: .................................................................................................................................................................................................. 38
2. TAIL ROTOR: ........................................................................................................................................................................................................................ 39
2.1. Heading control: .............................................................................................................................................................................................................. 39
2.2. Tail rotor commands: ...................................................................................................................................................................................................... 41
12 - 02- 2
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

2.3. Fenestron tail rotor systems:........................................................................................................................................................................................... 43
2.4. Tail rotor control systems: ............................................................................................................................................................................................... 45
3. TWIN NON-COAXIAL ROTORS: ......................................................................................................................................................................................... 46
3.1. Tandem rotors: ................................................................................................................................................................................................................ 46
3.2. Side-by-side rotors: ......................................................................................................................................................................................................... 47
3.3. Twin intermeshing rotors: ................................................................................................................................................................................................ 48
3.4. Twin coaxial rotors: ......................................................................................................................................................................................................... 50
4. BLEED AIR – NOTAR HELICOPTERS:............................................................................................................................................................................... 53
4.1. NOTAR® concept: .......................................................................................................................................................................................................... 53
4.2. NOTAR® system operation: ........................................................................................................................................................................................... 54
VI. MAIN ROTOR HEAD – DESIGN AND OPERATION FEATURES ......................................................................................................................................... 57
1. INTRODUCTION: .................................................................................................................................................................................................................. 57
2. COMPARISON OF MAIN ROTOR TYPES: ......................................................................................................................................................................... 57
2.1. Rigid rotor systems: ........................................................................................................................................................................................................ 58
2.2. Semirigid rotor systems: ................................................................................................................................................................................................. 63
2.3. Fully articulated rotor system: ......................................................................................................................................................................................... 66
2.4. Combination rotor system: .............................................................................................................................................................................................. 73
2.5. Bearingless Main Rotors (BMR technology): .................................................................................................................................................................. 75
VII. BLADE DAMPERS: FUNCTION AND CONSTRUCTION ................................................................................................................................................... 78
1. ROTOR VIBRATIONS: ......................................................................................................................................................................................................... 78
1.1. Low frequency vibrations: ............................................................................................................................................................................................... 78
1.2. Medium and high frequency vibrations: .......................................................................................................................................................................... 78
2. HELICOPTER GROUND AND AIR RESONANCE: ............................................................................................................................................................. 78
2.1. Ground resonance phenomenon: ................................................................................................................................................................................... 80
2.2. Air resonance phenomenon: ........................................................................................................................................................................................... 80
2.3. Ground (and air) resonance solutions: ........................................................................................................................................................................... 80
2. DAMPER FUNCTION: .......................................................................................................................................................................................................... 81
2.1. Hydraulic dampers: ......................................................................................................................................................................................................... 81
2.2. Elastomeric dampers: ..................................................................................................................................................................................................... 82
2.3. Variable dampers: ........................................................................................................................................................................................................... 85
2.4. Fluid filled dampers: ........................................................................................................................................................................................................ 86
3. DAMPER CONTRUCTION: .................................................................................................................................................................................................. 87
3.1. Hydraulic dampers: ......................................................................................................................................................................................................... 87
3.2. Elastomeric inertial dampers:.......................................................................................................................................................................................... 88
3.3. Embedded inertial dampers: ........................................................................................................................................................................................... 89
VIII. ROTOR BLADES: MAIN AND TAIL ROTOR BLADE CONSTRUCTION AND ATTACHMENT ....................................................................................... 91
1. GENERAL: ............................................................................................................................................................................................................................ 91
12 - 02- 3
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

2. BLADE DESIGNS: ................................................................................................................................................................................................................ 91
3. BLADE STRUCTURES AND MATERIALS: ........................................................................................................................................................................ 94
3.1. Forces acting on blades: ................................................................................................................................................................................................. 94
3.2. Types of blades: .............................................................................................................................................................................................................. 95
3.3. Wood blades: .................................................................................................................................................................................................................. 96
3.4. Metal blades: ................................................................................................................................................................................................................... 96
3.5. Composite blades: .......................................................................................................................................................................................................... 98
3.6. NACA design airfoils: ...................................................................................................................................................................................................... 99
3.7. ONERA design airfoils: ................................................................................................................................................................................................. 100
4. ROTOR TRANSMISSION: .................................................................................................................................................................................................. 104
5.1. Main purposes: ............................................................................................................................................................................................................. 104
5.2. Clutch: ........................................................................................................................................................................................................................... 105
5.3. Belt drive clutch: ............................................................................................................................................................................................................ 107
5.4. Centrifugal clutch: ......................................................................................................................................................................................................... 107
5. MAIN ROTOR HEADS: ....................................................................................................................................................................................................... 108
5.1. Hooke joint teetering head: ........................................................................................................................................................................................... 108
5.2. Bell 206 teetering head: ................................................................................................................................................................................................ 109
5.3. Tri-hinge head: .............................................................................................................................................................................................................. 109
5.4. Door-hinge hub: ............................................................................................................................................................................................................ 110
5.5. Semi-teetering head with elastomeric element: ............................................................................................................................................................ 111
6. MAIN ROTOR CONSTRUCTION AND ATTACHMENT: ................................................................................................................................................... 111
6.1. Rotor head of the BO-105: ............................................................................................................................................................................................ 112
6.2. Rotor head of Lockheed AH-56 Cheyenne: .................................................................................................................................................................. 114
6.3. Rotor head of Westland Lynx:....................................................................................................................................................................................... 115
6.4. Rotor head of Bell-412: ................................................................................................................................................................................................. 116
6.5. Rotor head of EC-725: .................................................................................................................................................................................................. 119
6.6. Sikorsky S-64 Skycrane example: ................................................................................................................................................................................ 122
6. TAIL ROTOR CONSTRUCTION AND ATTACHEMENT: .................................................................................................................................................. 135
6.1. Antitorque systems: ...................................................................................................................................................................................................... 136
6.2. Antitorque fenestron systems: ...................................................................................................................................................................................... 137
6.3. Robinson R22 antitorque example: .............................................................................................................................................................................. 138
IX. TRIM CONTROL, FIXED AND ADJUSTABLE STABILIZERS ............................................................................................................................................ 139
1. TRIM CONTROL: ................................................................................................................................................................................................................ 139
1.1. Introduction: .................................................................................................................................................................................................................. 139
1.2. Magnetic brakes: ........................................................................................................................................................................................................... 141
1.3. Electrical trim actuators: ................................................................................................................................................................................................ 142
2. FIXED AND ADJUSTABLE STABILIZERS: ...................................................................................................................................................................... 145
12 - 02- 4
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

2.1. Fixed stabilizers: ........................................................................................................................................................................................................... 145
2.2. Adjustable stabilizers: ................................................................................................................................................................................................... 147
X. SYSTEM OPERATION: MANUAL, HYDRAULIC, ELECTRICAL AND FLY-BY-WIRE ...................................................................................................... 150
1. MANUAL SYSTEM OPERATION: ...................................................................................................................................................................................... 150
1.1. Introduction: .................................................................................................................................................................................................................. 150
1.2. Screw jacks (or jackscrews): ......................................................................................................................................................................................... 150
1.3. Cables, pulleys, chains and push rods: ........................................................................................................................................................................ 152
2. HYDRAULIC SYSTEM OPERATION: ................................................................................................................................................................................ 152
2.1. Hydro-mechanical: ........................................................................................................................................................................................................ 152
3. ELECTRO-MECANICALSYSTEM OPERATION (FLY-BY-WIRE): ................................................................................................................................... 158
XI. ARTIFICIAL FEEL ............................................................................................................................................................................................................... 163
1. ARTIFICIAL FEEL SYSTEMS: ........................................................................................................................................................................................... 163
1.1. A simple spring feel units: ............................................................................................................................................................................................. 163
1.2. Q feel units: ................................................................................................................................................................................................................... 164
2. MAIN ROTOR CONTROL SYSTEM FEEL – GRADIENT UNITS: .................................................................................................................................... 167
3. TAIL ROTOR CONTROL SYSTEM FEEL – YAW PEDAL DAMPERS: ............................................................................................................................ 170
4. FEEL INTEGRATION WITH AUTOFLIGHT SYSTEMS:.................................................................................................................................................... 173
XII. BALANCING AND RIGGING .............................................................................................................................................................................................. 175
1. MAIN ROTOR BLADE ALIGNMENT: ................................................................................................................................................................................ 175
2. UNBALANCED SEMIRIGID ROTOR SYSTEMS: .............................................................................................................................................................. 175
2.1. Lateral: .......................................................................................................................................................................................................................... 175
2.2. Chordwise: .................................................................................................................................................................................................................... 176
2.2. Spanwise:...................................................................................................................................................................................................................... 176
2.3. Combined: ..................................................................................................................................................................................................................... 177
3. VERTICAL VIBRATIONS: .................................................................................................................................................................................................. 177
3.1. Extreme low frequency vibrations: ................................................................................................................................................................................ 178
3.2. Low frequency vibrations: ............................................................................................................................................................................................. 178
3.3. Medium frequency vibrations: ....................................................................................................................................................................................... 178
3.4. High frequency vibrations: ............................................................................................................................................................................................ 179
4. MAIN ROTOR BLADE TRACKING: ................................................................................................................................................................................... 179
4.1. Electronic blade tracker: ............................................................................................................................................................................................... 179
4.2. Reflector tracking: ......................................................................................................................................................................................................... 180
4.3. Strobe light: ................................................................................................................................................................................................................... 180
12 - 02- 5
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

I. INTRODUCTION

1. AXIS:
The flight control systems allow the operation on the three axis device:
 Roll control (longitudinal axis),
 Pitch control (lateral axis), and
 Yaw control or direction (vertical axis).

12 - 02- 6
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

1.1. Plane of rotation:
A plane formed by the average tip path of the blades is known as the plane of rotation. The plane of rotation is at a right angle to the axis of rotation.

1.2. Axis of rotation:
An imaginary line that passes through a point on which a body rotates is called the axis of rotation. Its rotation is at a right angle to the plane of
rotation.

 Disc area (A):
The span length of one blade is used as the radius. The area of the hub in the disc area is not included since it doesn't make any lift
(but is negligible).
The disc area is the total space in the area of the circle formed by the rotating rotor blades.
The following formula is used to figure disc area:
12 - 02- 7
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

2
A = πR

where:
A: disc area,
π = 3.1416,
R: radius.

1.3. Flight control components:
Flight control on helicopters is obtained by changing the configuration of the main and tail rotors. The lift force is generated by the blades of the main
rotor that are usually in a number between two and six.
To manoeuvre a helicopter three controls are used; a collective pitch lever, cyclic pitch stick and yaw pedals.
12 - 02- 8
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

 Collective pitch lever:
Movement of the collective pitch lever will increase or decrease the pitch angle of all main rotor blades, by the same amount and at the same
time. Increasing the pitch on all main rotor blades will increase the total rotor thrust, and decreasing it will have the opposite effect.
 Cyclic pitch lever:
The cyclic pitch stick is used to tilt the main rotor disc, forwards, backwards and to the left or the right, or some combination of these.
This will provide a thrust in the direction in which the disc is tilted, and will cause the helicopter to move in that direction.
The tilting of the main rotor disc is achieved by independently adjusting the pitch on individual rotor blades causing them to move upwards or
downwards. When cyclic pitch inputs are made the main rotor blades will be subject to an increase or decrease in their pitch angle as they
rotate, and so the disc remains tilted in the direction selected by the pilot.
 Governor/FADEC controls:
It is normal for modern helicopter engines to remain at a fixed flight idle speed, which is controlled by a fuel governor or computer controlled
FADEC (Full Authority Digital Engine Control system), although some older helicopters, and some of those below the 5700 Kg MTOM weight
category, provide a hand throttle twist grip on the collective pitch lever.
In governed or FADEC systems an increase or decrease in the power required is automatically achieved, in systems using a hand throttle it
is necessary for the pilot to make adjustments to the engine RPM in response to control inputs, obviously the governed or FADEC systems
are more accurate and relieve the pilot of the additional workload imposed by the need to maintain engine, and therefore rotor RPM.
 Yaw pedals:
The yaw pedals increase the pitch angle of the tail rotor blades, collectively only, as tail rotors do not require cyclic pitch inputs. The tail rotor
is used to cancel out the torque reaction caused by the main rotor. An increase in main rotor collective pitch will produce more torque, and
will therefore require more thrust from the tail rotor to oppose the resultant torque reaction.
In addition to allowing the pilot to counteract torque reaction, the yaw pedals provide a means by which the helicopter can yaw; the nose
moves to left or right.
To yaw the helicopter against the torque reaction more thrust will be required, therefore more pitch is applied to the tail rotor blades,
producing the necessary thrust.
To yaw the aircraft in the same direction as the torque reaction, it will merely be necessary to reduce the tail rotor pitch and allow the
helicopter to be rotated by the torque reaction force.
From this it can be seen that the helicopter controls are very interactive, for example in the hover an increase in main rotor collective pitch
will cause an increase in torque, and therefore torque reaction and additional thrust will be required from the tail rotor to oppose any
tendency for the torque reaction to yaw the helicopter.
12 - 02- 9
AeroGATES: PART-66 courseware 12 – Helicopter aerodynamics, structures and systems
Category  A  B1  B2  B3 02 – Flight control systems
Level  1  2  3

 Electronic systems:
Many helicopters, other than the most basic types, will incorporate electronic systems within the basic control systems to provide automatic
stabilising and, in larger type’s automatic pilot.
 Autostab:
Automatic stabilising systems, sometimes referred to as “autostab”, are used to ensure that the helicopter remains at a fixed height,
heading and speed, regardless of any disturbing influences, such as wind gusts. These systems ensure that the helicopter remains
stable, without the need for continuous inputs from the pilot, thereby reducing pilot workload and fatigue.
 Autopilot:
Many of the larger helicopters have a full autopilot system, where a pre-selected flight plan can be flown with a minimum of inputs from
the pilot, thereby further reducing cockpit workload.

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