Flight Stability and Dynamics Quiz

Study Notes

Flight stability refers to an aircraft's ability to return to a specific flight condition without pilot intervention.
An aircraft can be stable in some conditions and unstable in others (e.g., straight and level vs. inverted flight).
Stability is sometimes called inherent stability.
Stability is distinct from trim (balance) of an aircraft.
An aircraft might fly with one wing lower but still return to level flight if disturbed.
Stability is determined by the aircraft's tendency to oscillate and dampen out subsequent oscillations after an initial disturbance.

Aircraft movement is described using three axes:
- Longitudinal (x-axis): Rotation about the nose-to-tail line (rolling).
- Lateral (y-axis): Rotation about the wingtip-to-wingtip line (pitching).
- Vertical (z-axis): Rotation about the vertical line (yawing).

Parts of an aircraft: Fin, fuselage, nacelle, wing, tailplane, flap, aileron, elevator, rudder, trim tab.
Key terminology relating to aircraft components:
- Fuselage: The main body of the aircraft.
- Nacelle: Often houses the engines or other equipment.
- Wing: Generates lift.
- Tailplane: Provides stability and control.
- Flap: Increases lift at lower speeds.
- Ailerons: Control rolling.
- Elevator: Controls pitch.
- Rudder: Controls yaw.
- Trim tab: Helps maintain trim.

Static Stability: The initial tendency of an aircraft to return to equilibrium after a disturbance.
Positive static stability: The aircraft tends to return to its original attitude.
Negative static stability: The aircraft tends to move further away from its original attitude.
Neutral static stability: The aircraft doesn't return or move further from its original attitude.
Dynamic Stability: The time required for an aircraft to respond to its static stability.
Positive dynamic stability: Oscillations decrease over time.
Negative dynamic stability: Oscillations increase over time.
Neutral dynamic stability: Oscillations remain constant over time.

Dihedral Angle: Positive angle between the wing and the lateral axis. Aids lateral stability.
Anhedral Angle: Negative angle between the wing and the lateral axis. Used to counteract Dutch roll tendency.
Longitudinal Dihedral: Angle between the horizontal stabilizer and the wing chord.
Torque Effect: A tendency for an aircraft to rotate in the opposite direction to the propeller. Counteracted by washout and washin.
Ground Effect: Reduced stalling speed of the aircraft when close to the ground, due to downwash and air trapping.
Dutch Roll: Oscillatory instability involving combined rolling and yawing. It occurs with high wing loading, sweepback, and high altitude.

Modern high-speed, high-altitude aircraft are often designed to be aerodynamically unstable.
They rely on active stability control systems, which are digitally implemented, to maintain stable flight.

Directional stability is important for an aircraft to return to its original course after a sideslip or yawing disturbance.
Unsymmetrical power, like an engine failure, can create yawing moments that are balanced by controls like the rudder.