15.3 Aviation Fundamentals

15.3 Aviation Fundamentals

Quick Answer: An aircraft in flight is acted on by four forces — lift (up), weight (down), thrust (forward) and drag (back). It rotates about three axes through the centre of gravity: pitch (lateral), roll (longitudinal) and yaw (vertical). These are controlled by the elevator, ailerons and rudder respectively.

The Four Forces of Flight

Every aircraft in flight is governed by four opposing forces:

• Lift — upward force produced mainly by the wings as air flows over the curved upper surface of the airfoil. Acts perpendicular to the relative wind.
• Weight — downward force of gravity acting through the aircraft's centre of gravity (CG).
• Thrust — forward force produced by the engine(s)/propeller or jet.
• Drag — rearward force resisting motion through the air; has two main forms, parasite drag (form, skin friction, interference) and induced drag (a by-product of lift).

In steady, unaccelerated flight, the opposing forces are in equilibrium: lift = weight and thrust = drag. Climbing requires lift greater than weight; accelerating requires thrust greater than drag.

The Three Axes of Motion

All three axes intersect at the aircraft's centre of gravity (CG) and are mutually perpendicular:

Primary Control Surfaces

The pilot controls rotation about each axis using hinged surfaces on the wing and tail (empennage):

• Elevator — on the horizontal stabiliser (tail); controls pitch (nose up/down). Pulling the stick/yoke back raises the elevator, pitching the nose up.
• Ailerons — on the rear (trailing edge) of each wing; work in opposite directions (one up, one down) to control roll. Moving the stick right raises the right aileron and lowers the left, rolling the aircraft right.
• Rudder — on the vertical stabiliser (fin); controls yaw (nose left/right) via the rudder pedals. Used mainly to keep turns coordinated by counteracting adverse yaw.

Memory aid: Pitch — Elevator; Roll — Ailerons; Yaw — Rudder.

Basic Flight Instruments

The classic "six-pack" of flight instruments centres on three that every GD Pilot candidate should recognise:

• Airspeed Indicator — shows speed through the air (in knots).
• Altimeter — shows altitude above mean sea level (MSL), using barometric pressure.
• Attitude Indicator (Artificial Horizon) — shows the aircraft's pitch and roll attitude relative to the horizon.

The other three in the basic six are the turn coordinator, heading indicator and vertical speed indicator (VSI).

Parts of an Aircraft

A fixed-wing aircraft is built from a small number of principal structural parts:

• Fuselage — the main body that houses crew, passengers and cargo.
• Wing — generates lift; carries the ailerons and usually flaps.
• Tail (Empennage) — horizontal and vertical stabilisers carrying the elevator and rudder.
• Cockpit — the forward compartment where the pilot(s) sit and operate the controls.
• Engine(s) — provide thrust; may be propeller or jet, mounted on the wing, nose or tail.
• Landing Gear — wheels/struts that support the aircraft on the ground; usually retractable on high-performance aircraft.

Why This Matters for the Test

Aviation fundamentals appear in the General Knowledge portion of the PAF GD Pilot initial test. Expect direct questions such as: "Which force opposes weight?" (Lift), "Which control surface produces roll?" (Ailerons), and "Which axis does pitch rotate about?" (Lateral). Memorise the four forces, three axes, three control surfaces, the basic instruments and the main aircraft parts.

Angle of Attack and Stalls

Two extra concepts frequently tested:

• Angle of Attack (AOA) — the angle between the wing's chord line and the oncoming relative wind. Increasing AOA increases lift — up to the critical angle of attack (typically about 15-20 degrees), beyond which the airflow separates from the upper wing surface and the wing stalls. A stall is a loss of lift caused by exceeding the critical AOA, not by low speed alone (an aircraft can stall at any speed if AOA is too high).
• Flaps — hinged surfaces on the trailing edge of the wing, extended for take-off and landing to increase both lift and drag, allowing slower approach speeds. Flaps are not primary control surfaces — they are high-lift devices.

Bernoulli and Newton

Two physical principles explain how a wing generates lift:

• Bernoulli's Principle — air moving faster over the curved upper surface has lower pressure than the slower air beneath, so the wing is pushed upward by the pressure difference.
• Newton's Third Law — the wing deflects air downward, and the reaction force pushes the wing upward.

Both descriptions are correct and complementary; exam questions may phrase lift in terms of either pressure difference or downward deflection of air.

Fixed-Wing vs Rotary-Wing

A fixed-wing aircraft (aeroplane) generates lift with rigid wings moving forward through the air. A rotary-wing aircraft (helicopter) generates lift with rotating rotor blades. The PAF operates both — fighters and transports (fixed-wing) plus helicopters for search-and-rescue, transport and training roles. For the GD Pilot branch, candidates are streamed after basic training into fighter, transport, or (less commonly for GD) rotary-wing conversion.