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Theory of Flight

Theory of Flight. 6.08 Aircraft Stability References: FTGU pages 31, 32. Review. Define load. 2. What is the difference between live load and dead load? What is the load factor in a 60 O turn? Describe the forces acting in a turn. 6.08 Aircraft Stability. MTPs: Definitions

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Theory of Flight

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  1. Theory of Flight 6.08 Aircraft Stability References: FTGU pages 31, 32

  2. Review • Define load. 2. What is the difference between live load and dead load? • What is the load factor in a 60O turn? • Describe the forces acting in a turn.

  3. 6.08 Aircraft Stability MTPs: • Definitions • Longitudinal Stability • Lateral Stability • Directional Stability

  4. Definitions Stability: How an aircraft reacts to disturbances while in flight Types of stability: • Dynamic (positive, neutral, negative) • Static • Inherent

  5. Definitions Dynamic Stability • The overalltendency of an aircraft, when disturbed, to return to its original position Positive: airplane will return to its position Negative: airplane will tend to move further away from its position Neutral: airplane will neither return to its position nor continue to change

  6. Definitions • Static Stability • Theinitialtendency of an aircraft, when disturbed, to return to its original position

  7. Definitions Inherent Stability • Built in characteristics to enable the airplane to be either stable or unstable • Stability may be built into each aircraft axis creating • Longitudinal stability • Lateral stability • Directional stability

  8. Longitudinal Stability • Stability around the lateral axis • Also known as pitch stability

  9. Longitudinal Stability • Longitudinal stability is affected by: 1. Size and position of horizontal stabilizer 2. Position of the C of G

  10. Longitudinal Stability Centre of Gravity (C of G) • C of G too far forward • Required loading on the horizontal tail surfaces to maintain angle of attack increases • Overall weight of aircraft increases • Stall speed increases

  11. Longitudinal Stability • C of G too far aft • Decreased longitudinal stability because centre of gravity is behind the centre of pressure • Violent stall characteristics • Poor stall recovery (very dangerous!) • Stall speed decreases

  12. Longitudinal Stability A - C of G too far forward STALL SPEED INCREASES B - C of G too far aft STALL SPEED DECREASES

  13. Lateral Stability • Stability around the longitudinal axis • Also known as roll stability

  14. Lateral Stability Lateral stability is created through • Dihedral • Keel effect • Sweepback wings

  15. Lateral Stability Dihedral • The angle that each wing makes with the horizontal of the aircraft • The lowered wing will produce more lift and will roll back into place • Downgoing wing • = greater angle of attack • = increased lift

  16. Lateral Stability Keel Effect • When disturbed, weight of the aircraft acts like a pendulum to swing aircraft back into position • Natural feature of high wing aircraft • Weight of the aircraft lies under the wings

  17. Lateral Stability Sweepback • Leading edge of the wing slopes backward • When one wing is dropped, the lowered wing produces more lift than the raised wing and the original position is restored

  18. Directional Stability Stability around the vertical or normal axis

  19. Directional Stability Vertical Tail Surface (fin and rudder) • Airplanes have a tendency to fly directly into the relative airflow due to the vertical tail surface • When disturbed the relative airflow will hit the side of the vertical tail surface and push it back into position

  20. Directional Stability • Sweep Back

  21. Confirmation

  22. Confirmation Match the axes with the factors affecting them Longitudinal Stability Lateral Stability Directional Stability • Keel effect • C of G • Sweepback • Vertical Stabilizer • Horizontal Stabilizer • Dihedral

  23. Confirmation What is the difference between dynamic stability and static stability? How does dihedral affect lateral stability? How does the vertical stabilizer affect directional stability?

  24. Snowbirds – CT-114

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