CAA NZ CPL Aircraft Technical Knowledge key terms

The angle between the wing's chord line and the relative airflow approaching it. Increasing it raises lift up to the critical angle, after which the airflow separates and the wing stalls.

The point on an aerofoil where the total aerodynamic force acts. It moves forward as angle of attack increases, producing a pitching moment that must be balanced by the tailplane.

Drag created as a by-product of lift, caused by spanwise airflow and wingtip vortices. It increases with angle of attack and is greatest at low speed in high-lift flight.

Drag from skin friction and form resistance, independent of lift. It rises with the square of airspeed and dominates at high speed, unlike induced drag.

The ratio of total lift to the aircraft's weight, expressed in g. A level 60-degree bank gives about 2 g; exceeding the certificated limit can overstress the structure.

The tendency of an aircraft to yaw away from the turn when ailerons are applied, because the down-going aileron's extra lift and drag on the rising wing lag behind the turn.

The main spanwise structural member of a wing, carrying bending loads from root to tip. Spars are usually joined to the fuselage at a reinforced wing attachment fitting.

A chordwise structural member that shapes the aerofoil and supports the skin, transferring loads into the spars. Ribs also stiffen the wing skin against buckling.

Longitudinal stiffening members riveted to the skin and frames, running fore and aft. They carry part of the bending load and stop the thin skin from buckling.

A fuselage construction in which the stressed skin shares loads with internal frames and stringers, rather than the skin carrying everything alone as in a true monocoque.

Progressive cracking of metal under repeated cyclic loading, even at stresses below ultimate strength. Fatigue life is managed through design service goals, inspections and, where needed, component replacement.

Corrosion driven by an electrical potential difference between dissimilar metals joined in the presence of an electrolyte such as moisture. The less noble metal, for example aluminium against steel, sacrifices itself.

The sequence of induction, compression, power and exhaust strokes that a piston engine completes in two crankshaft revolutions, converting fuel energy into mechanical work at the propeller.

The ratio of cylinder volume at bottom dead centre to volume at top dead centre. Higher ratios improve efficiency but require higher-octane fuel to avoid detonation.

Explosive, uncontrolled burning of the fuel-air charge after ignition, producing a sharp pressure rise, high temperatures and possible piston damage. It is caused by over-lean mixture, high manifold pressure or low octane fuel.

Ignition of the charge before the spark plug fires, usually from a glowing hot spot such as a carbon deposit or overheated plug. It can destroy a cylinder very quickly.

A self-contained engine-driven generator producing high-voltage pulses for the spark plugs and needing no aircraft battery. Two magnetos provide independent ignition circuits so a single failure does not stop the engine.

A propeller whose blade angle is automatically adjusted by a governor to hold a selected rpm as power or airspeed changes, keeping the engine at an efficient setting.

The absolute pressure in the engine's induction system, shown on a gauge and used with rpm to set power. Falling pressure shows the throttle is being closed.

The angle between a propeller blade's chord line and its plane of rotation. Coarse angles suit high speed; fine angles let the engine rev and produce strong static thrust.

A fuel strainer, normally at the lowest point of the fuel system, that traps water and sediment before fuel reaches the carburettor or injectors and is drained during the pre-flight inspection.

An electric fuel pump used for priming, engine start and as a backup if the engine-driven pump fails, often required during takeoff and when changing tanks.

A lubrication system where oil is stored in a separate tank rather than the crankcase, then pumped through the engine and scavenged back, avoiding oil starvation in unusual attitudes.

A nitrogen-charged chamber that stores hydraulic pressure, smoothing pump demand, absorbing pressure surges and giving a limited reserve for systems such as brakes or undercarriage.

A controllable supply of heated air to the carburettor to melt or prevent ice in the venturi, at the cost of a richer mixture and some loss of power.

A device that controls alternator field current so system voltage stays within limits, protecting avionics from over-voltage or under-voltage as electrical load and engine speed vary.

A pilot- or mechanically-operated valve that stops fuel flow at the firewall, isolating the engine compartment in a fire or when the engine must be starved of fuel.

Inflatable rubber strips on the leading edges of wings and tail that expand cyclically to break off accumulated ice, giving de-icing rather than anti-icing protection.

The combined pressure sources for the airspeed indicator, altimeter and vertical speed indicator: ram air from the pitot tube and static pressure from the static ports.

The adjustable pressure setting, such as QNH, QFE or standard 1013 hPa, set in the altimeter window, which decides the datum against which indicated altitude is displayed.

The property of a spinning gyroscope that keeps its axis fixed in space, used by attitude and heading instruments to give a stable reference as the aircraft manoeuvres.

The tendency of a spinning gyroscope to respond to an applied force with movement about 90 degrees later in the direction of rotation, exploited in rate instruments.

The error in a magnetic compass caused by the aircraft's own magnetic fields, measured by a compass swing and recorded on a deviation card for each heading.

A radio beacon that replies to secondary surveillance radar interrogations with a selected code and, in Mode C or S, pressure altitude, helping ATC identify and separate aircraft.

The weight of the aircraft with unusable fuel, full oil and all standard equipment, used as the starting point for every weight and balance calculation.

The difference between maximum certificated takeoff weight and basic empty weight; it covers crew, passengers, baggage, usable fuel and any removable equipment carried.

The product of a weight and its arm measured from the datum, used to find the aircraft's centre of gravity by summing all moments and dividing by total weight.

A fixed reference point chosen by the manufacturer from which all arms are measured, often ahead of the nose or at the firewall. The datum itself has no weight significance.

The forward and aft limits within which the loaded aircraft's centre of gravity must lie, preserving controllability and preventing excessive stability or tail-heavy handling.

Pressure altitude corrected for temperature. High density altitude reduces engine power, propeller thrust and lift, lengthening takeoff and landing distances and reducing climb performance.