Rotary Wing Aerodynamics And Development

1. Rotary Wing Aerodynamics And Development Regan J. Patrick

2. Learning Outcomes • Evaluate basic aerodynamics of rotary-wing flight • Become familiar with basic helicopter components • Become familiar with basic helicopter aerodynamic phenomenon

3. Helicopter Aerodynamics LIFT THRUST DRAG WEIGHT

4. Relevant Aerodynamic Principles/Laws • Bernoulli’s Principle • Newton’s Laws • Inertia, Acceleration, Action • Coriolis Effect

5. AIRFLOW Bernoulli’s Principle • The relationship between internal fluid pressure and fluid velocity High Pressure High Velocity Low Pressure Low Velocity

6. Sir Isaac Newton 1642-1727 Newton’s Laws of Motion • 1st - Law of Inertia • 2nd - Law of Acceleration • 3rd - Law of Action

7. The Law of Inertia • A body at rest remains at rest and a body in motion remains in motion at the same speed and direction until affected by some external force • An object’s resistance to motion is determined by its mass • Appliczation: It takes greater force to start an object moving than to sustain the motion (hover to forward flight)

8. The Law of Acceleration • The force required to produce a change in motion of a body is directly proportional to its mass and the rate of change in its velocity • Force = Mass x Acceleration • Application: Heavy helicopters will not accelerate as fast as lighter helicopters

9. The Law of Action • For every action there is an equal, but opposite reaction • If an interaction occurs between two bodies, equal forces in opposite directions will be imparted to each body • Application: Torque Effect

10. Action to a Sailboat

11. Gustave Gaspard de Coriolis 1792 to 1843 Coriolis Effect • Conservation of Angular Momentum • As the Rotor Blades flap up, the center of mass of each blade moves closer to the axis of rotation • As this occurs, the speed of rotation will increase • “Spinning Skater”

12. Helicopter 101 • Essential Components • Systems and Controls • Basic Operation

13. The Basic Helicopter The “Sikorsky Standard” Tail Rotor Rotor System Engine Flight Controls Transmission/ Gearbox Landing Gear

14. Engine and Transmission • Engine Types • Piston • Turbine • Turboshaft • Transmission • Transfer angle/speed of drive

15. Rotor System (or How We Overcome Newton’s Law of Action) • Numerous Configurations • Anti-torque (common) • Dual • Tilt • Number of Blades • Blade Shapes / Types • Flexibility

16. Anti-Torque Solutions • “Standard” Configuration • Dual Rotor • Coaxial • Synchropter • Tilt Rotor

18. Anti-torque Tail Rotors • Conventional • Fenestron • NOTAR

20. Main Rotor Hub • Swashplate • Pitch Control Rods • Main Drive Shaft / Hub • Main Rotor Blades

21. Swashplate • Common to all Rotary Wing aircraft • Transmits control inputs from the collective/ cyclic flight controls to the rotor system • Non-rotating inputs to rotating rotor assembly (blades) • Stationary and rotating plates • Rotating plate connected to pitch change links

22. Pitch Change Links • Connects swashplate to main rotor blades • Makes all pitch change inputs to the rotor system Pitch Change Links Swash Plate

23. Swashplate Pitch Change Links

24. Main Rotor Blades • Number (pluses and minuses) • Composition • Shapes/Types • Compressibility • Twist • Rotor Blade Inertia

26. FEATHER Rotor Blade Movement FLAP LEAD LAG FLAP

27. Blade Twist • Helicopter blades are designed with a twist to offset differential lift caused by blade speed • Twisted blades generate more lift near the root and less lift at the tip than untwisted blades

28. Main Rotor Systems • Three Main Types • Rigid • Semi-Rigid • Fully Articulated

29. Rigid Rotor System • Mechanically Simple, Structurally Complex • Smaller, Simpler Helicopters • Minimal Blade Movement • Blades absorb most movement • Feather only (pitch) • Eurocopter Bo 105

30. Bo-105

31. Semi-Rigid Rotor System • Normally Two Bladed Systems • “See-Saw” or Underslung • Blades Move in Two Directions • Feather • Flap • Bell UH-1 Huey

32. Semi-Rigid Rotor System

33. UH-1 Huey

34. Fully Articulated Rotor System • 3 or more blades • Blades travel independently of each other through full range of motion • Anti-flap bushings • Dampers • Sikorsky H-60

35. MH-60K

37. Skids Wheels Skis Floats Landing Gear

38. Flight Controls Cyclic Anti-Torque Pedals Throttle Collective

39. Basic Helicopter Flight Controls Cyclic • Cyclic Control Stick • Located in front of pilot’s seat • Controls the tilt of the main rotor disk • Changes pitch angle of blades independently

40. Basic Helicopter Flight Controls Collective • Collective Control Stick • Located on left side of pilot’s seat • Changes pitch angle of all MRB simultaneously

41. Basic Helicopter Flight Controls Pedals and Throttle • Tail Rotor Pedals • Located on the floor in front of the pilot’s seat • Controls the pitch of the tail rotor blades • Throttle(s) • Regulates Engine RPM • Located on Collective (twist grip) or Overhead Panel (PCL)

42. Basic Aerodynamics for Helicopters • Lift • Hovering Flight • Forward Flight • Sideward/Rearward/Turning Flight

43. Hovering Flight • Translating Tendencies • Blade Coning • Ground Effect (In/Out) • Gyroscopic Precession

44. No Wind Hover Downwash Pattern Equidistant 360°

45. Translating Tendencies • Aircraft will translate (drift) in the direction of tail rotor thrust • Main Rotor Disk is rigged to compensate

46. Lift C Effect Blade Coning • Centrifugal force causes the rotor blades to “pull” from the center of the rotor hub • Provides strength to support helo • Lift generated from blade AoA • Coriolis Effect Hover Flat Pitch (On the Ground) Center of Mass

47. Ground Effect • Less than 1 Rotor Disk diameter hover height • Induced flow reduced by surface friction, lift increases • Lower blade AoA for same lift • Restricts generation of blade tip vortices

48. In Ground Effect

49. Out of Ground Effect • Induced flow no longer restricted • Blade tip vortices increase with decreased outward airflow • Drag increases • More power required

50. Out of Ground Effect