Longitudinal Stability and Control – AE2111 Lecture

Vocabulary flashcards covering key terms from the AE2111 lecture on longitudinal stability, control, aerodynamic centres, static margin, and related aircraft performance concepts.

Six Degrees of Freedom

The three translational (axial, lateral, vertical) and three rotational (pitch, roll, yaw) motions an aircraft can perform.

Longitudinal Components

The pitch rotation plus axial and heave (vertical) displacements that describe motion in the aircraft’s longitudinal plane.

Lateral Components

Yaw, roll, and sideslip motions that describe movement in the aircraft’s lateral–directional plane.

Static Stability

Initial tendency of an aircraft to return toward equilibrium after a small disturbance.

Dynamic Stability

Time-history behavior of an aircraft’s motion after its initial static response; determines whether oscillations grow, decay, or stay constant.

Longitudinal Stability

Condition in which an increase in angle of attack produces a restoring (nose-down) pitching moment about the center of gravity.

Aerodynamic Centre (a.c.)

Point on an aerofoil or wing where the aerodynamic moment remains essentially constant with angle of attack.

Neutral Point

Aircraft-level equivalent of the aerodynamic centre; location along the mean aerodynamic chord where pitching moment is independent of angle of attack.

Static Margin

Non-dimensional distance (h – hn) between the aircraft center of gravity and the neutral point, expressed as a percentage of mean aerodynamic chord.

Pitch Stiffness

Slope of the CM versus angle-of-attack curve; indicates the moment required to change aircraft pitch.

Lift Curve Slope

Rate of change of lift coefficient with angle of attack; affected by wing aspect ratio and high-lift devices.

Aspect Ratio (A)

Ratio of wing span squared to wing area; higher values generally increase lift-curve slope and reduce induced drag.

Mean Aerodynamic Chord (MAC)

Characteristic chord length that represents the whole wing for aerodynamic calculations.

Center of Gravity (c.g.)

Point through which an aircraft’s weight acts; its fore-aft location strongly influences stability and control.

Aerodynamic Moment Coefficient, CM0

Pitching-moment coefficient at zero lift; must be positive for conventional tail-aft configurations.

Elevator

Hinged control surface on the horizontal tail that changes CM0 to control pitch attitude and speed.

Ailerons

Control surfaces on the wing trailing edges that produce differential lift to roll the aircraft.

Rudder

Vertical tail control surface that produces yawing moments for directional control.

Canard

Forward-mounted horizontal surface that provides pitch control; typically operates at a higher angle of attack than the main wing.

Horizontal Tail Volume Ratio (Vh)

Non-dimensional parameter St lt / (S c̄) indicating effectiveness of the horizontal tail in pitch control.

Downwash

Downward deflection of airflow behind a lifting surface that alters the effective angle of attack at the tail.

Weight-and-Balance Analysis

Process of determining aircraft c.g. location from distribution of masses to assess stability limits.

Neutral Point Aft Shift

Movement of the neutral point rearward by enlarging the horizontal tail or increasing its aspect ratio.

Pitch Trim

Adjustment of CM0 (typically via elevator) to achieve zero pitching moment and steady flight at a desired angle of attack.