The four forces acting on an aircraft in steady level flight are:

Lift, buoyancy, thrust, and friction Lift, weight, thrust, and drag Pressure, gravity, momentum, and velocity Normal force, weight, engine force, and air resistance

An aerofoil's cambered (curved) upper surface generates lift primarily because:

The wing acts as a solid wall, blocking airflow and creating high pressure below Air is forced to travel farther and faster over the top surface, reducing pressure above the wing compared to below The engine creates suction on the upper surface through internal ducts Gravity pulls air downward, reducing pressure above every horizontal surface

Angle of attack (AoA) is defined as:

The angle between the aircraft's nose and the horizon The angle between the wing tip and the wing root The angle between the wing's chord line and the oncoming airflow direction The angle of the aircraft's banked turn during manoeuvring

An aircraft stalls when:

The engine stops producing thrust, and the aircraft slows to zero airspeed The angle of attack exceeds the critical angle (~15–20°), causing boundary layer separation and a sudden loss of lift The aircraft climbs too high and runs out of dense air to generate lift Ice forms on the wings, increasing weight beyond the lift capacity

Induced drag is a byproduct of lift generation. What causes it?

The engine exhaust creates turbulence behind the aircraft, slowing it down Skin friction on the wing surface increases as the aircraft generates more lift Pressure difference between the upper and lower wing surfaces causes air to curl around the wing tips, creating trailing vortices The fuselage shadow blocks airflow to the inner wing, reducing effective wing area

Gliders have very high aspect ratio wings (span²/area ≈ 30–40). What advantage does this provide?

Increased form drag, which slows the glider for safer landings Higher stall speed, giving the pilot more time to react Reduced induced drag, giving a better lift-to-drag ratio and allowing the glider to travel far for every metre of altitude lost Greater wing weight, which adds momentum and sustains flight longer

Streamlining a body with a teardrop shape primarily reduces which type of drag?

Skin friction drag, by making the surface smoother at a molecular level Induced drag, by eliminating wing tip vortices Form (pressure) drag, by delaying boundary layer separation and shrinking the turbulent wake Wave drag, by preventing sonic boom formation at subsonic speeds

All modern subsonic airliners have swept wings. The main aerodynamic reason for wing sweep is:

Swept wings generate more lift at low speed by exposing greater wing area to the airflow Sweeping the wing raises the critical Mach number, delaying shock wave formation and allowing higher cruise speeds Sweep moves the wing tips behind the engines so jet exhaust heats and thins the boundary layer Swept wings reduce span, allowing the aircraft to fit at narrower airport gates

In supersonic flight, wave drag is caused by:

The air molecules ahead of the aircraft cannot move away fast enough and collide with the fuselage High altitude reduces air density, so the wings must work harder and create more drag Shock waves that form as the aircraft compresses air faster than the speed of sound, releasing energy as pressure discontinuities The engine exhaust creates a supersonic jet that pushes back against the fuselage

A sonic boom heard on the ground is caused by:

The aircraft breaking through a physical barrier of compressed air at exactly Mach 1 The conical shock wave attached to a supersonic aircraft reaching the ground and sweeping past an observer The engine reheat (afterburner) igniting, producing a sudden blast of sound Turbulent wing tip vortices descending to the ground and impacting buildings

In wind tunnel testing, engineers use scale models because:

Scale models are easier to instrument with sensors than full-size vehicles Wind tunnels can only reach low speeds, suitable only for small models A scale model tested at the same Reynolds number as the full-size vehicle produces aerodynamically similar (correctly scaled) force results Government regulations require wind tunnel approval before manufacturing full-size aircraft

Computational Fluid Dynamics (CFD) simulations are used alongside wind tunnel tests because:

CFD is always more accurate than wind tunnels, so tunnels are only kept for historical reasons Wind tunnels cannot test aircraft at realistic speeds, so CFD fills the gap CFD can quickly explore hundreds of design variations and reveal full flow-field details that physical instrumentation cannot easily measure, while wind tunnels validate the accuracy of the CFD models Regulations require both methods to be used independently so that results cannot be cherry-picked