直升机飞行力学 Helicopter dynamics chapter 1
- 1. Helicopter Flight Dynamics Chapter 1: Introduction
- 2. Instructor Dr. Renliang Chen A18-204 Phone: (025)84892141 E-mail: crlae@nuaa.edu.cn
- 3. Time and Place Time: Tuesday 6:30-9:30 PM Classroom: A18-112
- 4. Prerequisites Theoretical Mechanics: Helicopter Aerodynamics Structure of Helicopter Automatic Control Theory Dynamics
- 5. Syllabus Introduction Helicopter Control Rotor Blade flapping motion Helicopter Trim in Level Flight Helicopter Stability Helicopter Response to Pilot Controls Introduction to Flying Qualities
- 6. Requirements Stressing on the physical meanings and basic concepts Understanding and gripping the analysis methods Being able to conduct the basic Calculation
- 7. Grade 50% Routine time 50% Final Exam
- 8. Textbook Bramwell, “Helicopter Dynamics”, Arnold, 2000.
- 9. Useful References Gao Zheng and Chen Renliang “Helicopter Flight Dynamics”, Science Press, 2003. Padfield, “helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling”, AIAA Education Series, 1995. R. Prouty, “Helicopter Performance, Stability and control”, PWS Publishers, 1986. Johnson, “Helicopter Theory”, Princeton University Press, 1980.
- 10. Introduction Definition of helicopter flight dynamics Characteristics of helicopter flight Scopes of helicopter flight dynamics Methodologies Objectives of helicopter flight dynamics
- 11. Definition of Helicopter Flight Dynamics The subject of studying external forces applied on helicopter as well as motions and controls External Forces: Only those changing flight path such as aerodynamic, inertial and gravity forces. Motions: Accelerations(angular acceleration), velocities and position Controls: Pilot controls from cockpit, augment stability and control Flight qualities: Specification and flight quality assessment
- 12. Characteristics of Helicopter Flight Example: from hover to forward flight Pilot Push forward Apply Long. cyclic pitch Rotor disc tilt forward Adjustment Apply Collective pitch control Paddle control Tail rotor Apply lateral Cyclic control Rotor disc tilt side
- 13. Characteristics of Helicopter Flight There are 6 freedoms of motion in space, But there are only 4 controls. Therefore the control for each freedom of motion is not independent. The response of helicopter to controls is coupled. The cross-coupling between axes is serious and needs to be removed by pilot controls or SCAS. The controls for heaving, pitch and roll motions are implemented by blade flapping motion. Thus the delay of helicopter response to pilot controls is greater than that of fixed-wing aircraft. The flight qualities of helicopter is poorer than that of fixed-wing aircraft The flight dynamics of helicopter is more complicated than fixed-wing aircraft
- 14. Scope of Helicopter Flight Dynamics Pilot Cockpit controls Aerodynamic surfaces (rotor, tail rotor) Change aerodynamic Forces and moments Gust disturbance External force disturbance SCAS Helicopter motions Flight quality specification Flight quality assessment
- 15. Methodologies Theoretical analysis Computer simulation Wind tunnel test with experimental model Flight test
- 16. Objectives Study and improve helicopter trim, stability and control. Guide helicopter design Aerodynamic and inertial distributions Primary design parameter determination (rotor, tail rotor, controls and empennage) Design of SACS and control laws
- 17. Introduction of hinges to rotor system Flap hinge Lag or drag hinge feathering Rotor Hinge System
- 18. Teetering or See-Saw Rotor
- 21. Hingeless Rotor
- 22. Coordinate System Gravity axes Body axes Wind axes Hub axes
- 23. Gravity Axes The gravity axis system O D X D Y D Z D is used to determine the flight path of helicopter in space. The origin of axes can be arbitrary point in space. The axis Y D always points in the direction of the vertical, regardless of the orientation of the helicopter. The orientation of X D and Z D axes is less important, and to some extent arbitrary. A typical choice for X D axis to point North, and the Z D axis to point East. The orientation of X D and Z D axes becomes very important in the analysis of flight test data, in piloted simulations and navigation problems
- 24. Body Axes The body axis system OXYZ is used to determine the attitude of helicopter in space. The origin of axes is at the center of mass of helicopter. The axis X points toward the nose of helicopter, the Z axis points to the right side (starboard), and the Y axis points upward . Body axes play an especially important role in flight dynamics.
- 25. Wind Axes The wind axis system OX V Y V Z V is used to determine aerodynamic loads, rotor wake and rotor flap due to wind. The origin of axes is at the center of mass of helicopter. The axis X V points toward the velocity vector of helicopter, the Y V axis lies in the plane of symmetry of the vehicle. The orientation Z V of points toward right side.
- 26. Hub Axes The hub axis system OX S Y S Z S is used to determine the rotor aerodynamic loads and rotor flap due to controls and body angular rates. The origin of axes is at the center of rotor hub. The axis Y S points upwards and aligns with the rotor shaft. The axis X S points toward the nose of helicopter and perpendicular to axis Y S . the Z S axis points to the right side..
- 27. Definition of Angles The Euler angles: The orientation of any axes relative to another can be given by three angles, which are the consecutive rotations about three axes in that order to carry one frame along with the other. This is a particular case of Euler angles . In helicopter flight dynamics, only one sets is commonly used, that for the body axes. 1. A rotation ψ about OY D , carrying the axes to OX 1 YZ 1 , is the azimuth angle. 2. A rotation υ about OZ 1 , carrying the axes to OXY 2 Z 1 , is the pitch angle. 3. A rotation γ about OX, carrying the axes to OXYZ, is the bank angle. Quatemions Z 1 X 1 Y 2
- 28. Definition of Angles The Aerodynamic angles : The linear motion V of the vehicle relative to the atmosphere can be given either by its three orthogonal components (v x ,v y ,v z ) in the body axes system, or alternatively by the magnitude V and two suitable angles. These angles, which are of fundamental importance in determining the aerodynamic forces that act on the vehicle, are defined as: Angle of attack : Sideslip angle : It will be observed that, in the sense of Euler angles, the aerodynamic angles related the bode axes and wind axes by the rotation sequence ( , ,0) which carrying the former into the latter X 1
- 29. Transformation from Gravity Axes to Body Axes A rotation of ψ: A rotation of : A rotation of γ: The complete coordinate transformation from gravity axes to body axes is: Z 1 X 1 Y 2
- 30. Transformation from Body Axes to Wind Axes A rotation of : A rotation of : The complete coordinate transformation from body axes to wind axes is: X 1
- 31. Transformation from Body Axes to Hub Axes In order to improve the flight performance and pilot Vision in cruse flight, the rotor shaft always tilts Forward as an angle . Thus: In the sense of Euler angles, the rotor shaft tilt angle related the bode axes and hub axes by the rotation sequence (0, ,0) which carrying the former into the latter
- 32. Comparison of Coordinate System in Different Country China and Russia West Country X Z O Y X Z O Y
- 33. Comparison of Definition of Parameters in Different Country O O
- 34. Comparison of Definition of Parameters in Different Country Meanings Hide force coeff. Side force coeff. Anti torque coeff. Lock Number China and Russia West country Thrust coeff.