theory of flight - 608 dukes · 6.08 aircraft stability mtps: •definitions ... keel effect...
TRANSCRIPT
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Theory of Flight
6.08 Aircraft Stability References:
FTGU pages 31, 32
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Review
1. Define load.
2. What is the difference between live load and dead load?
3. What is the load factor in a 60O turn?
4. Describe the forces acting in a turn.
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6.08 Aircraft Stability
MTPs:
• Definitions
• Longitudinal Stability
• Lateral Stability
• Directional Stability
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Definitions
Stability: How an aircraft reacts to
disturbances while in flight
Types of stability:
• Dynamic (positive, neutral, negative)
• Static
• Inherent
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Definitions
Dynamic Stability
– The overall tendency 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
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Definitions
• Static Stability
– The initial tendency of an aircraft, when
disturbed, to return to its original position
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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
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Longitudinal Stability
• Stability around the lateral axis
• Also known as pitch stability
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Longitudinal Stability
• Longitudinal stability is affected by:
1. Size and position of horizontal stabilizer
2. Position of the C of G
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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
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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
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Longitudinal Stability
A - C of G too far
forward
STALL SPEED
INCREASES
B - C of G too far aft
STALL SPEED
DECREASES
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Lateral Stability
• Stability around the longitudinal axis
• Also known as roll stability
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Lateral Stability
Lateral stability is created through
1. Dihedral
2. Keel effect
3. Sweepback wings
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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
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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
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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
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Directional Stability
Stability around the vertical or normal axis
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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
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Directional Stability
• Sweep Back
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Confirmation
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Confirmation
Match the axes with the factors affecting them
Longitudinal Stability
Lateral Stability
Directional Stability
1. Keel effect
2. C of G
3. Sweepback
4. Vertical Stabilizer
5. Horizontal Stabilizer
6. Dihedral
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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?
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Snowbirds – CT-114 CH146 Griffon and USCG HH-65 Dolphin