Theory of Flight 2

1. CI Norwood Theory of Flight 2 PO 402 References: FTGU Pages 9-50, Pilot’s Handbook of Aeronautical Knowledge Chapters 1-3

2. Review • What are the main parts of the aircraft? • How does a wing create lift? • What is a slot and what does it do?

3. Topics to be covered • Aircraft controls • Stability • Aircraft performance • Stalls, spins, spiral dives and load factor • Aircraft instruments

4. Aircraft controls • Aircraft can move around or in three axis • In order to move, some type of control mechanism must be in place • Three main control surfaces:Ailerons (roll)Elevator (pitch)Rudder (yaw)

5. Ailerons • Control surfaces attached to the outboard trailing edge of the wing • Move in opposite directions • When the control column is moved to the right, the left aileron goes down (increasing lift) and the right aileron goes up (decreasing lift), this causes the plane to roll to the right Source: Pilot’s Handbook of Aeronautical Knowledge

6. Elevators • Hinged to the trailing edge of the horizontal stabilizer • Move up or down when the pilot pulls the column back or pushes forward • Controls the pitching motion of the airplane Source: Pilot’s Handbook of Aeronautical Knowledge

7. Rudder • Attached to the vertical stabilizer and moves the aircraft left and right through a motion called yaw • Controlled by the rudder pedals at the pilots feet • Causes the rudder to deflect and a force is created at the tail Source: Pilot’s Handbook of Aeronautical Knowledge

8. Trim Tab • Helps eliminate excess force on the controls by the pilot • Acts as an small elevator on the control surface which creates a force to keep it in a constant position • Moves in the opposite direction of the surface Source: Pilot’s Handbook of Aeronautical Knowledge

9. Review • What are the three main control surfaces and where are they located? • How do ailerons roll the aircraft? • If we wanted to hold a nose high attitude, which direction would we want to the trim tab to move?

10. Axis of the Aircraft Source: Pilot’s Handbook of Aeronautical Knowledge

11. Adverse Yaw • In a turn, the outside wing creates more lift (and therefore more drag) than the inside wing • This creates an imbalance that causes the nose to swing to the outside of the turn and is called adverse yaw • This can be correct through rudder inputs and reduced by modifying the ailerons Source: Pilot’s Handbook of Aeronautical Knowledge

12. Balanced Controls Mass Balance Static Balance • A mass (or weight) is placed in front of a hinge or control surface • This gives the surface better stability in flight • The centre of gravity of a control is placed so that the surface is balanced without any airflow

13. Balanced controls Dynamic Balance • When part of the control surface is placed ahead of the hinge • This places it into the airflow and aids the pilots in moving the control surface Source: From the Ground Up

14. Review • What are the axis of the aircraft? • What is adverse yaw? • What are the three types of balanced controls?

15. Stability • Tendency of an aircraft to return to its original position once disturbed without intervention by the pilot • Two main types of stability:StaticDynamic • Inherent stability: stability characteristics built into the design of the aircraft

16. Static Stability Static stability is the initial tendency for an aircraft to return to its original position once disturbed Source: Pilot’s Handbook of Aeronautical Knowledge

17. Dynamic Stability Dynamic stability is the overall tendency of the aircraft to return to its original position through a series of damped oscillations Source: Pilot’s Handbook of Aeronautical Knowledge

18. Positive Stability: • Will create forces or moments which will eventually return to its original position • Neutral Stability: • Stabilizing forces are absent. Aircraft will not return to its original position but will not depart further away either • Negative Stability: (Instability) • Will generate forces or moments which will displace it further away

19. Longitudinal Stability • Known as pitch stability • Around the lateral axis • Affected by 3 factors:Location of the C .G.Location of the wingSize and location of the horizontal stabilizer Source: Pilot’s Handbook of Aeronautical Knowledge

20. Lateral Stability • Stability around the longitudinal axis and is known as roll stability • Affected by factors:DihedralKeel effectSweepbackDistribution of weight

21. Dihedral • Dihedral angle is the angle that the wings make with the horizontal • If a wing is displaced, the down going wing creates a higher angle of attack and lifts the wing Source: Pilot’s Handbook of Aeronautical Knowledge

22. Keel Effect • In aircraft that have a low center of gravity, a pendulum effect is created • When the aircraft is rolled, the weight pulls it back to the centre Source: Pilot’s Handbook of Aeronautical Knowledge

23. Sweepback • In faster aircraft, the wing is sweptback for aerodynamic efficiency • This also increases roll stability • When a wing drops and the aircraft swings towards the outside wing, the leading edge of the dropped wing meets the airflow head on and creates lift Source: Pilot’s Handbook of Aeronautical Knowledge

24. Distribution of Weight • Proper distribution of weight will aid in keeping the aircraft level • If too much weight is on one side, the aircraft may not have enough aileron authority to maintain level flight

25. Directional Stability Source: Pilot’s Handbook of Aeronautical Knowledge Around the vertical or normal axis, known as yaw stability Affected by the size and location of the fin

26. Review • What are static and dynamic stability? • What is dihedral and what does it do? • What factors affect longitudinal stability?

27. Aircraft Performance

28. Left Turning Tendencies Torque • In North America, propellers turn clockwise when viewed from the pilot seat • The reaction from this spinning causes the plane to roll counter-clockwise (to the left) Source: Pilot’s Handbook of Aeronautical Knowledge

29. Left Turning Tendencies Asymmetric Thrust (P-Factor) • At high angles of attack, the down going blade meets the air at a higher angle of attack than the up going blade • This creates an imbalance of force and the aircraft yaws to the left Source: Pilot’s Handbook of Aeronautical Knowledge

30. Left Turning Tendencies Slipstream • As air is pushed back from the propeller, it flows back in a corkscrew pattern Source: Pilot’s Handbook of Aeronautical Knowledge

31. Left Turning Tendencies Precession • When the propeller is spinning, it acts like a big gyroscope • When a force is applied to a gyroscope, it acts 90 degrees in the direction of rotation Source: Pilot’s Handbook of Aeronautical Knowledge

32. Climbing • The ability for an aircraft to climb is dependant on the ability to create excess thrust • There are three types of climbs that we use:Best rate of climbBest angle of climbNormal climb

33. Best angle vs. best rate Source: Pilot’s Handbook of Aeronautical Knowledge

34. Gliding • When in a glide, there is no power from an engine to produce thrust and gravity pulls the aircraft down • In order to maintain equilibrium, lift must act slightly forward to pull the aircraft through the air • Best glide speed for range: Speed at which the most distance will be covered for a given loss of height • Best glide speed for endurance: Speed at which the most time aloft will be given for a given loss of height

35. Review • What are the four left turning tendencies? • What is the difference between the best rate and angle of climb? • If you were gliding and wanted to stay aloft for a long period of time, what speed would you fly?

36. Forces in a Turn • Lift acts 90 degrees to the wing • When the plane banks the lift vector is tilted • Vertical lift force: Acts straight up and maintains altitude • Horizontal lift force: Acts to the inside and pulls the aircraft into the turn, known as centripetal force • An apparent force is felt by the pilot that pulls them to the outside of the turn, this is called centrifugal force and is a product of inertia

37. Forces in a Turn Source: Pilot’s Handbook of Aeronautical Knowledge

38. Effect of Bank Angle in a Turn • If Bank angle is increased in a turn, the following occurs: • Higher rate of turn • Smaller radius of turn • Higher loading on the wings • Higher stall speed Source: Pilot’s Handbook of Aeronautical Knowledge

39. Effect of Airspeed in a Turn • When airspeed is increased in a turn the following occurs • Slower rate of turn • Larger radius of turn Source: Pilot’s Handbook of Aeronautical Knowledge

40. Climbing and Descending Turns Descending Turn Climbing Turn • The lower wing meets the airflow at a higher angle of attack creating more lift • Upper wing moves faster and also creates more lift • Two forces compensate one another so angle of bank remains the same • Lower wing meets the relative airflow at a smaller angle of attack and creates less lift • Upper wing moves faster and creates more lift • Two forces act to cause angle to increase

41. Review • Which force pulls the aircraft into the turn? • If you are in a turn and increase your angle of bank, what will happen to your turn radius and turn rate? • If you are in a turn and decrease your airspeed, what will happen to your turn radius and turn rate?

42. Stalls, Spins and Spiral Dives

43. Stall • A stall occurs when the wing cannot produce sufficient lift to maintain flight • In order to produce enough lift, the airflow over the wing must be smooth • When the angle of attack increases to a certain point, the airflow becomes turbulent and separates from the wing • This angle is known as the critical angle of attack

44. Stall Source: Pilot’s Handbook of Aeronautical Knowledge

45. Factors Affecting the Stall • Weight: As weight increases, stalling speed increases • C of G location: The further forward the C of G is, the higher the stall speed • Turbulence: Vertical gust can cause the critical angle of attack to be exceeded • Turns: Increasing the angle of bank increases loading and stall speed • Flaps: Deploying flaps will decrease stall speed • Contaminants: If the wing is dirty or has ice on it, it will disrupt airflow and increase stall speed

46. Load Factor • Dead load: The weight of the aircraft • Live load: The change in apparent weight of the aircraft due to acceleration and turns (the amount of force acting on the wings) • Load factor: Live load over dead load and is expressed in G’s • Example: In a 60 degree turn, the wings must produce twice the amount of lift to support the weight of the aircraft, therefore the load factor is 2

47. Load Factor and Stall Speed • As load factor increases, stall speed increases • Formula to determine stall speed: • Where: VS Turn is the stall speed in the turn VS is the stall speed in level flight n is the load factor

48. Load Factor and Stall Speed • Referring to the table below, we can calculate the stall speed of a Cessna 172 in a 30 degree turn:

49. Additional Notes on Stalls • An aircraft will stall if the critical angle of attack is exceeded, regardless of airspeed or attitude • An aircraft will stall at the same indicated airspeed regardless of altitude

50. Review • When will an aircraft stall? (Hint...angle) • What factors affect stall speed? • What is the formula used to determine stall speed?