NCAA CPL Aircraft General Knowledge key terms

The angle between the wing chord line and the relative airflow. Increasing it raises lift up to the stall angle, beyond which the airflow separates and lift drops sharply.

The specific angle of attack at which airflow separates from the wing and the wing stalls. It is constant for a given wing regardless of weight, speed, or bank angle.

A condition in which the wing exceeds its critical angle of attack and lift decreases abruptly. It can occur at any airspeed and any attitude, including in level flight or a descent.

The direction of air passing the aircraft as seen from the aircraft, opposite to the flight path. Its angle to the chord line defines the angle of attack.

A straight line drawn from the leading edge to the trailing edge of an aerofoil. Angles of attack and incidence are measured relative to this reference line.

The curvature of an aerofoil, measured as the distance between the mean camber line and the chord line. More camber generally produces more lift at a given angle of attack.

The fixed angle between the wing chord line and the longitudinal axis of the aircraft. It is built into the airframe and does not change in flight.

The aerodynamic force acting perpendicular to the relative airflow that supports the aircraft. It depends on airspeed, air density, wing area, and lift coefficient.

Drag created as a by-product of lift, caused by spanwise airflow and wingtip vortices. It increases with angle of attack and decreases as airspeed rises.

Drag from form, skin friction, and interference that does not contribute to lift. It increases with the square of airspeed and is reduced by streamlining and retracting gear.

The sum of parasite and induced drag. It reaches a minimum at the speed where the two components are equal, which corresponds to best glide speed.

The airspeed giving the greatest horizontal distance per unit of altitude lost in a power-off glide. It occurs near the speed of minimum total drag.

The ratio of lift produced to the aircraft's weight, expressed in g. It rises in turns and manoeuvres, raising stall speed and structural stress on the airframe.

The minimum airspeed at which the wing can produce enough lift to support the aircraft in unaccelerated flight. It increases with weight, load factor, and altitude.

The point at which the aircraft's total weight is considered to act. Its position affects stability and control and must remain within the certified forward and aft limits.

The point on an aerofoil through which the total aerodynamic force acts. It moves forward as angle of attack increases, contributing to pitch changes near the stall.

The initial tendency of an aircraft to return to its original attitude after a disturbance. Positive static stability makes an aircraft easier to fly but less manoeuvrable.

The tendency of an aircraft, over time, to damp out oscillations after a disturbance. It depends on static stability and the damping characteristics of the airframe.

The upward angle of the wings relative to the horizontal. It provides lateral stability by creating a restoring roll when the aircraft sideslips.

A coupled oscillation in roll and yaw, often seen in swept-wing aircraft. It is countered by yaw dampers and by adequate vertical fin area.

The tendency of an aircraft to yaw away from the direction of a roll when ailerons are applied. It results from increased induced drag on the down-going aileron.

Flight in which the relative airflow is aligned with the aircraft's longitudinal axis, with no slip or skid. It is indicated by the ball of the turn coordinator.

A condition in which the aircraft moves sideways toward the inside of a turn, with the nose yawed away from the turn. It is shown by the ball displaced inward.

A condition in which the aircraft moves sideways toward the outside of a turn, with too much rudder applied. It increases load on the airframe and can lead to a spin.

An aggravated stall in which the aircraft autorotates in a descending spiral. One wing is more deeply stalled than the other, producing continuous yaw and roll.

The reduction in induced drag and increase in lift experienced when flying close to the ground, caused by interference with wingtip vortices. It can cause float during landing.

The distance between a force and the reference point about which it acts, such as the centre of gravity. It determines the magnitude of the resulting pitching or rolling moment.

The imaginary line running from the nose to the tail through the aircraft. Rotation about this axis is roll, controlled primarily by the ailerons.

The imaginary line running from wingtip to wingtip through the aircraft. Rotation about this axis is pitch, controlled primarily by the elevators.

The imaginary vertical line through the aircraft, perpendicular to the longitudinal and lateral axes. Rotation about it is yaw, controlled primarily by the rudder.

The never-exceed speed, marked by the red radial line on the airspeed indicator. Exceeding it risks structural damage or flutter and is prohibited in normal operation.

The maximum structural cruising speed, marked by the upper limit of the green arc. Above this speed, flight should be conducted only in smooth air and with caution.

A rapid, self-exciting vibration of a control surface or wing structure at high speed. It can cause structural failure within seconds and is prevented by mass balancing and speed limits.

The system that supplies ram air pressure and static pressure to the airspeed indicator, altimeter, and vertical speed indicator. Blockages cause characteristic instrument errors.

An instrument that compares pitot pressure with static pressure to display indicated airspeed. It is marked with colour-coded arcs showing operating speed ranges.

An instrument that displays altitude by measuring static pressure against a set reference pressure. Setting the correct subscale is essential for accurate altitude information.

An instrument that shows the rate of climb or descent by measuring the rate of change of static pressure. It lags briefly when the aircraft's vertical speed changes.

A device that alerts the pilot as the angle of attack approaches the critical value. It may be a reed horn, a light, or a stick shaker, and must be checked before flight.