Helicopter Dynamics and Aerodynamics

✍ Scribed by Payne P.R.

• Publisher: The Macmillan Company
• Year: 1959
• Tongue: English
• Leaves: 476
• Category: Library

✦ Synopsis

This book is an extremely valuable contribution to the advancement of the helicopter industry; it is also important and timely with reference to other types of vertically rising aircraft.
From my personal knowledge of him I know that the author is inspired by a long -standing and devoted enthusiasm for this new frontier of aeronautics. To this conviction he brings the highest scientific competence in several other fields coupled with outstanding success as a practising project engineer in VTOL aircraft development.
The increasing complexity of all branches of science spotlights one of the most enigmatic hurdles in our technology. The problem is to induce that uniquely qualified top echelon group to meet the ever-increasing demands of industrial performance while at the same time making the essential contribution to the literature which only a few of such experienced leaders can make. This text is a fine example of the type of simplification and clarification which may well be applied in other fields to link the most advanced achievements in industry with the vital educational needs of our society.
Concise and practical analytical methods are presented in several areas which were previously subject only to costly experimental solutions. Complete mastery and working familiarity with past theory and practice is evident from the fresh approach and the imaginative departure from convention when justified. Many basic concepts are presented from a new viewpoint which cannot fail to prove stimulating.
For those interested in the classical aspects of vertical flight in the dawning space age as well as for the engineer seeking more effective practical design references for industry, this book is a significant advance which should be included in every library on the subject.

✦ Table of Contents

Front Cover
Title
Copyright
Foreword
Preface
Contents
Notation
CHAPTER 1 General Aerodynamics
Symbols used in chapter 1
1.1. Introduction
1.2. Subsonic aerofoil lift
1.3. Subsonic aerofoil profile drag
1.4. Yawed aerofoils
1.5. Subsonic drag of streamline bodies
1.6. Aerodynamic pitching moment
CHAPTER 2 Induced Aerodynamics
Symbols used in chapter 2
2.1. The actuator disc
2.2. Induced velocity in vertical flight
2.3. Induced velocity in forward flight\
2.4. "Effective area" concept
2.5. Alternative non-dimensional induced velocity equations
2.6. Wake calculations
2.7. Variation of induced velocity over the disc
2.8. Induced velocity in the vicinity of a rotor
2.9. Vertical drag
2.10. Vertical drag in hovering flight
2.11. Vertical drag in vertical flight
2.12. Vertical drag in forward flight
2.13. Example of vertical drag calculations
2.14. Ground effect
2.15. Strip theory in vertical flight
2.16. Induced tip loss
2.17. Calculation of optimum twist
2.18. The application of strip theory to calculate effective disc area e in hovering
2.19 . Variation of slip stream rotation from momentum theory
2.20. Induced velocity variation due to a finite number of tip vortices
2.21. Twin-rotor interference in hovering
2.22. Twin-rotor interference in forward flight
2.23. Influence of results on tandem design
2.24 . Measurement of rotor thrust and circulation by wake survey
2.25. Ducted fan theory
2.26. General remarks on "vertical lift”
CHAPTER 3 Fundamentals of Rotor Dynamics
Symbols used in chapter 3
3.1. Rigid rotor
3.2. Freely flapping rotor with central hinges
3.3. Flapping rotor analysis
3.4. Reversed-flow region
3.5. Effect of aerodynamic compressibility on flapping
3.6. Elemental angle of attack
3.7. Approximate relationships forblade angle of attack and flight envelopes
3.8. General accelerations on a flapping-blade particle
CHAPTER 4 Dynamics of Rotors withHinge Constraint
Symbols used in chapter 4
4.1. General considerations
4.2. The stiff-hinged rotor
4.2.1. Blade flapping with respect to the shaft axis
4.2.2. Blade flapping with respect to the no-feathering orbit
4.2.3. Angle of attack distribution and retreating blade stall
4.2.4. Control advance
4.2.5. Moments in hub and blade root arms
4.2.6. Calculations for the example rotor
4.3. The high-offset flapping-pin rotor
4.4. Reversed flow effects
CHAPTER 5 Flapping Stability and Blade Movements in Gusts
5.1. Flapping stability
5.2. Blade motion in a vertical sharp-edged gust (hovering)
5.3. Blade motion in a gust in forward flight
CHAPTER 6 Performance
6.1. Simple energy equations
6.2. Variation of mean δ with tip-speed ratio
6.3. Derivation of profile torque and H-force by refined energy method
6.4. A simple performance method
6.4.1. Vertical and low-speed flight
6.4.2. Forwared flight
6.5. Comparison with flight tests and examples of application
6.6. Presentation of performance curves
6.7. Engine failure in hovering
6.8. Vertical flare-out
6.9. "Jump-Start" autogiro
6.10 . "Exact" theory of rotor performance
6.10.1. Physical explanation of induced H-force
6.10.2. Conditions at a blade element
6.10.3 Induced torque
6.10.4. Profile torque
6.10.5. Induced H-force
6.10.6. Profile drag H-Force
6.10.7. Performance computor
6.10.8. Examples of typical calculations
CHAPTER 7 Stability and Control
7.1. General control considerations
7.2. Static stability in hovering
7.3. Static stability in forward flight
7.4. Dynamic stability
7.5. Hovering stability with two degrees of freedom
7.5.1. Calculation of derivatives ∂a₁ₛ/∂q and ∂a₁ₛ/∂V and ∂á/∂a₁ in hovering
7.5.2. Period and damping of hovering oscillation
7.6. General remarks on stability calculations
7.6.1 . The downwash derivatives ∂(λᵢK)/∂μ, ∂(λᵢK)/∂λ and ∂(kλᵢ)/∂μ
7.7. Automatic servo control
7.8. Effect of control systemstiffness and damping
7.9. Control sensitivity (in pitch or roll)
7.10. Yawing stability in forward flight
CHAPTER 8 Rotor Vibration
Symbols used in chapter 8
8.1. Introduction
8.2. Vertical vibration of a balanced rotor
8.2.1. Periodic blade flexing
8.2.2. Blade stalling
8.3. In-plane vibration of a balanced rotor
8.3.1. Ground resonance
8.3.2. Coriolis forces
8.3.3. Induced forces
8.3.4. Profile drag forces
8.4. Additional causes of vibration
8.5. Transmission of blade vibration to the hub when drag hinges are fitted
8.6. Vertical vibration due to unbalance
8.7. In-plane vibration due to unbalance(in hovering)
8.7.1. Freely-flapping rotor without drag hinges
8.7.2. Fully-articulated rotor
8.7.3. Out-of-balance forces in hovering due to unequal coningangles (tip-path tracking)
CHAPTER 9 Ground Resonance and VibrationDue to Rotor Resonance
Symbols used in chapter 9
9.1. Introduction
9.2. Fuselage or hub natural frequencies
9.3. "Ground resonance” in flight
9.4. General remarks on the determination of fuselage natural frequencies
9.5. Rotor blade oscillation
9.6. Two-bladed rotor resonance
9.7. Blade Snubbers
9.8. Multi-bladed rotors
9.9. Drag hinge dampers
9.10. Coupling between fuselage and rotor oscillations (three or more blades)
9.11. Deutsch equations for critical speedand damping
9.12. Twin-rotor helicopters
9.13 . Ground resonance of two-bladed rotors
CHAPTER 10 Control Loads and Vibration
Symbols used in chapter 10
10.1. Introduction
10.2. Tail-rotor loads and vibration
10.3. Main rotor controls
10.3.1. Blade torque due to positions of blade axes
10.3.2. Torque due to aerodynamic pitching moment
10.3.3. Torque due to propeller moment
10.3.4. Inertia torque and torsion bearings
10.3.5. Torque-bar torque
10.3.6. Total torque of balanced blade
10.3.7. Additional causes of control system loads
10.4. Control vibration
CHAPTER 11 Blade Flutter and Rotor Weaving
11.1. Rotor blade flutter
11.2. Flutter of a flexible blade
11.3. Flutter tests with a model rotor
11.3.1. Effect of blade-pitch control stiffness
11.3.2. Effect of tip-speed ratio
11.3.3. Effect of flutter on blade stresses
11.4. Rotor weaving
11.4.1. The analysis of Coleman and Stempin (ref. 4.2)
11.4.2. Effect of tip jets on weaving
11.5. Loewy's theory of damping at low blade pitch angles
11.6. Advanced flutter theory
CHAPTER 12 Blade Flexing and Resonance
Symbols used in chapter 12
12.1. Introduction
12.2. Calculation of blade natural frequencies by Rayleigh energy method
12.3. Blade torsional flexure
12.3.1. Increment of Kα, due to tension
12.3.2. Effect of chordwise components of C.F.
12.3.3. Bifilar effect
12.3.4. Torque-bar effect
12.3.5. Effective southwell coefficient of torsion
APPENDIX 1 References to Literature
1. Induced Aerodynamics
2. Rotor Dynamics
3. Performance
4. Flutter and dynamic instabilities
5. Vibration
6. Stability and Control
APPENDIX 2 Trigonometric Identities
Index
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