Theory of Flight: Aerodynamics, Stability, and High-Speed Flight

Comprehensive vocabulary flashcards covering ground effect, static and dynamic stability, flight control axes, high-speed flight regimes, wing planforms, and aerodynamic vortex phenomena.

Ground Effect

The positive influence on the lifting characteristics of the horizontal surfaces of an aircraft wing when close to the ground, caused by the distortion of airflow below the wing due to surface proximity.

Aerodynamic Influence of Ground Effect

The restriction of airflow upwash and downwash by the runway surface, which generates additional lift, impedes the formation of wingtip and line vortices, reduces drag, and enhances the lift-to-drag ($L/D$) ratio.

In-Ground-Effect Hover

A helicopter operational state where the downward and outward airflow pattern restricts vortex generation, improving outboard rotor blade efficiency and reducing system turbulence from vortex ingestion and recirculation.

Stability

The inherent aircraft design quality that corrects for conditions disturbing equilibrium, enabling the aircraft to return to or continue along its original flight path.

Static Stability

The initial tendency or directional movement of an aircraft back toward equilibrium immediately following an attitude disturbance.

Positive Static Stability

The initial tendency of an aircraft to return to its original state of equilibrium after being disturbed.

Neutral Static Stability

The initial tendency of an aircraft to remain in a new condition without returning or moving further away after its equilibrium is disturbed.

Negative Static Stability

The initial tendency of an aircraft to continue moving farther away from its original state of equilibrium after being disturbed.

Dynamic Stability

The aircraft property governing the amount of time taken to react to static stability forces and the behavior of resulting oscillations over time.

Positive Dynamic Stability

A condition in which pitch or attitude oscillations dampen out over time, returning the aircraft to its trimmed, undisturbed state.

Neutral Dynamic Stability

A condition in which displacement oscillations neither decrease nor amplify over time, continuing indefinitely at constant amplitude.

Negative Dynamic Stability

A condition in which displacement oscillations become progressively larger and amplify over time.

Lateral Stability

Stability around the longitudinal axis that governs roll movement, influenced by fuel weight distribution, wing dihedral, and fuselage/vertical stabilizer keel effect.

Wing Dihedral

The upward angle of an airplane's wings with respect to the horizontal plane, designed to promote lateral stability.

Longitudinal Stability

Stability around the lateral axis that governs pitching movement, primarily determined by the center of gravity ($CG$) position and horizontal stabilizer effectiveness.

Directional Stability

Stability around the vertical axis that governs yawing movement, provided primarily by the vertical stabilizer and the fuselage.

Primary Flight Controls and Axes of Rotation

The flight control configuration where ailerons control roll about the longitudinal axis (lateral stability), elevators/stabilators control pitch about the lateral axis (longitudinal stability), and rudders control yaw about the vertical axis (directional stability).

Speed of Sound

The propagation rate of acoustic pressure waves through the air, measuring $761\,\text{mph}$ at a standard day sea-level temperature of $59\,^\circ\text{F}$.

Mach Number

The ratio of the true airspeed of an aircraft to the local speed of sound in the surrounding atmospheric conditions.

Ernst Mach

The physicist whose contributions to fluid dynamics and supersonic flight provided the namesake for the ratio of flight speed to local acoustic velocity.

Subsonic Regime

The flight speed regime characterized by Mach numbers strictly below $0.75$.

Transonic Regime

The flight speed regime characterized by Mach numbers spanning from $0.75$ to $1.20$.

Supersonic Regime

The flight speed regime characterized by Mach numbers ranging from $1.20$ to $5.00$.

Hypersonic Regime

The flight speed regime characterized by Mach numbers exceeding $5.00$.

Critical Mach Number ($M_{\text{crit}}$/Mach Crit)

The flight speed at which airflow over any individual part of the aircraft structure first reaches, but does not exceed, Mach $1.0$.

Wing Aspect Ratio ($AR$)

A measurement of wing span-to-chord slenderness calculated as the square of wingspan divided by wing area ($AR = \frac{b^2}{A}$), where higher values reduce induced drag and yield slight lift gains.

Elliptical Wing

A wing planform that is aerodynamically optimal for slow-speed flight, though it exhibits less favorable stall progression than a rectangular wing.

Rectangular Wing

A wing planform that has lower aerodynamic efficiency than an elliptical wing but delivers superior, more forgiving stall characteristics.

Tapered Wing

A wing planform designed to decrease drag and increase lift efficiently at high speeds while providing favorable stall behavior.

Sweptback and Delta Wings

Wing planforms designed specifically to delay compressibility shockwave onset and remain aerodynamically efficient at high cruise and supersonic speeds.

Wing Tip Vortices

Whirlpools of swirling air caused by higher-pressure air beneath the wing escaping outward around the tips toward the low-pressure zone above; circulating counterclockwise around the right tip and clockwise around the left tip when viewed from behind.

Airbus Air Data Instrumentation

A system of external flight sensors comprising Multi-Functional Probes (MFP for Pitot, AoA, and TAT), Integrated Static Ports (ISP), StandBy Static Ports (SBSP), Side Slip Angle sensors (SSA), and Ice Detectors (ICE).