Content:

1. Static and Dynamic Stability

2. Three Axes of Flights

3. Longitudinal Stability

4. Lateral Stability

5. Directional Stability

6. Stalls

7. Spins

1. Static and Dynamic Stability

• Stability: the airplane's tendency to return to equilibrium, or steady flight, when disturbed by control inputs or external factors

• Maneuverability: the ability to move the airplane away from equilibrium and withstand the stress resulting from the maneuver

• Controllability: how well the airplane responds to control inputs

• Static vs. Dynamic Stability:

• Static stability: An airplane's initial response after a disturbance distrupts its quilibrium

• Dynamic stability: How an airplane responds over time after a disturbance

2. Three Axes of Flights

• Longitudinal Axis (Roll)

• Ailerons: Control rotation around the longitudinal axis

• Lateral Stability:?The airplane's ability to resist rolling?motion

• Lateral stability depends on:

• Weight distribution

• Improve lateral stability through proper weight distribution

• Dihedral

• Upward angle that each wing makes when viewed from the front

• The dihedral produces roll that returns an airplane to a laterall balanced flight condition when a sideslip occurs due to a disturbance

• Sweepback

• The backward angle of the wings from the roots to the wingtips

• Sweepback improves lateral stability

• During an unintentional roll, the low wing moves forward into the relative wind, and the lift on the low wing increases until the airplane rolls to its original flight attitude

• Keel Effect????

• Provides lateral stability through vertical fin and side area of fuselage above the CG

• As the aircraft encounters the side force of the air, keel effect rolls the aircraft back toward a wings-level attitude

• Lateral Axis (Pitch)

• Elevator: Controls rotation around the lateral axis

• Longitudinal Stability: The airplane's ability to resist pitching motion

• Longitudinal stability depends on:

• Location of the center of lift

• Manufacturers achieve longitudinal stability in most of their airplanes by positioning the center of gravity slightly ahead of the center of lift. This creates a slight nose-heavy tendency

• CG position

• CG range: airplanes' forward and aft limits for the position of the CG

• Tail-down force created by horizontal stabilizer

• On most single engine propeller-driven airplanes, downwash from the propeller and wings exerts forces on horizontal tail surfaces

• Downwash strength is affected by angle of attack, speed, and power setting

• Power effects / thrust

• Reducing power during flight reduces the downwash on the elevator. This creates a nose-down pitching tendency

• Increasing power has the opposite effect. It increases downwash on the horizontal stabilizer, causing the nose of the airplane to pitch up

• Vertical Axis (Yaw)

• Rudder: Controls rotation around the vertical axis

• Directional Stability: An airplane's ability to resist yaw

• The tendency of the airplane to "weathervane" into the relative wind is due to the greater side area behind the center of gravity, plus the force created by the vertical tail

• If the airplane yaws from its original attitude, the airflow strikes the vertical tail surface from the side and tends to return it to its original flight path

6. Stalls

• Factors affecting stalls (when the airfoil exceeds its critical angle of attack, also known as the stalling angle of attack):

• Lower airspeeds: At lower airspeeds, less air flows over the wing, so to maintain altitude, increase the angle of attack

• Aircraft weight: More weight requires more lift

• Weight distribution: A forward CG requires more tail-down force to balance the airplane, which adds to the weight the wings must support, increasing the stall speed

• Turbulence: Turbulance can cause a stall at a higher airspeed than in smooth conditions

• Snow, ice, or frost: they increase stall speed by disrupting airflow over the the wing

• An airplane always stalls?when the?critical angle of attack is exceeded regardless of airspeed, flight attitude, or weight

• To avoid stalls:

• Don't fly with ice on the wings

• Load airplane within the approved CG limits

• Don't overload the airplane

• Maintain coordinated flight

• Typical indications of a stall:

• A mushy feeling in the flight controls

• A stall warning alert

• Reduction in the sound of air flowing along the fuselage

• Buffeting, pitching, or vibration

• Kinesthetic sense

• Stall recovery:

• Decrease the angle of attack

• Level the wings

• Smoothly apply maximum allowable power to increase airspeed and minimize altitude loss

7. Spins

• A spin is a complex flight maneuver that can be described as an aggravated stall resulting in rotation

• Spins begin when one wing stalls more than the other one

• During a spin:

• The wing remain unequally stalled

• The angle of attack remains greater than the stalling angle of attack

• High drag combines with the large upward component of the relative wind

• Rotation continues as the unequal lift on each wing combines with the unequal drag

• To avoid spins:

• Prevent stalls by keeping the wing below the critical angle of attack

• Prevent yaw during a stall by maintaining coordinated flight

• Keep the CG within approved limits

• Spin Recovery (always recover from an inadvertent spin as soon as possible):

• Reduce the power to idle

• Position the ailerons to neutral

• Apply full opposite rudder against the rotation

• Apply a positive and brisk, straight, forward movement of the elevator control forward of neutral to break the stall

• After rotation stops:

• Neutralize the rudder

• Begin applying back-elevator pressure to raise the nose to level flight