Correct: C)
Explanation: Number 2 in figure PFA-010 represents the chord line — the straight reference line connecting the leading edge to the trailing edge of the aerofoil. It is the baseline from which the angle of attack and camber are measured. Option A (angle of attack) is an angular measurement, not a line on the diagram. Option B (profile thickness) is the perpendicular distance between the upper and lower surfaces, not a straight reference line.
Correct: C)
Explanation: The angle alpha between the chord line and the direction of the oncoming airflow is the angle of attack, the primary aerodynamic variable determining lift coefficient and stall behaviour. Option A (angle of inclination) is not a standard aeronautical term. Option B (angle of incidence) is the fixed structural angle between the chord line and the aircraft's longitudinal axis, set during manufacturing. Option D (lift angle) is not a recognized aviation term.
Correct: A)
Explanation: When the right aileron deflects upward (reducing lift on the right wing) and the left aileron deflects downward (increasing lift on the left wing), the aircraft rolls to the right. Simultaneously, the down-deflected left aileron creates more induced drag on the left wing, producing adverse yaw — the nose swings to the left, opposite the intended roll direction. Options C and D incorrectly identify a leftward roll. Option B states yaw to the right, but adverse yaw always opposes the roll direction.
Correct: D)
Explanation: Water ballast must be kept above freezing (i.e., the aircraft should stay below the freezing level) to prevent the water from freezing in the wing tanks, which could jam dump valves, cause unpredictable CG shifts, and damage wing structure. Option A is wrong because the best glide angle (L/D ratio) is theoretically unchanged with ballast. Option B is incorrect — best glide speed increases with additional weight. Option C is misleading because water ballast tanks are designed to minimise CG shifts, keeping them within approved limits.
Correct: D)
Explanation: Static stability means that when an aircraft is displaced from equilibrium by an external force, inherent aerodynamic forces automatically tend to return it toward its original state without pilot input. Option A describes active pilot correction, not inherent stability. Option B describes neutral stability, where the aircraft stays wherever it is displaced. Option C describes static instability, where the aircraft diverges further from equilibrium.
Correct: A)
Explanation: Water ballast increases total aircraft weight. The best L/D ratio (and therefore the best gliding angle) is an aerodynamic property of the aircraft's shape and does not change with weight. However, the speed at which this optimum L/D occurs increases because more dynamic pressure is needed to generate the extra lift required by the heavier aircraft. Option B wrongly claims the angle changes. Options C and D incorrectly state that best glide speed decreases.
Correct: C)
Explanation: An aerodynamic rudder balance (horn balance or set-back hinge) extends part of the control surface ahead of the hinge line, so aerodynamic pressure partially assists the pilot's deflection effort, directly reducing the force required. Option A (T-tail) is a configuration choice affecting downwash and deep-stall characteristics. Option B (vortex generators) energise the boundary layer to delay flow separation. Option D (differential aileron deflection) reduces adverse yaw, not control forces.
Correct: A)
Explanation: Any body immersed in a moving airstream (v > 0) always produces drag, because viscous friction and pressure differences are unavoidable in real fluid flow. Lift requires specific shaping or angle of attack and is not guaranteed. Option B is wrong because lift is not always produced. Option C is incorrect because drag increases with V² — it is not constant. Option D is physically impossible — drag-free flight does not exist in a real fluid.
Correct: D)
Explanation: Despite the potentially confusing name, longitudinal stability describes pitch stability, which is rotation around the lateral axis (wingtip to wingtip). It is the tendency to maintain or return to a trimmed pitch attitude. Option A (vertical axis) governs directional/yaw stability. Option B (propeller axis) is not a standard stability axis. Option C (longitudinal axis) governs roll/lateral stability.
Correct: B)
Explanation: Wing loading is the aircraft's total weight divided by the wing reference area (e.g., N/m² or kg/m²). Higher wing loading means higher stall speeds but better penetration in turbulence. Option A (drag per wing area) is not a standard metric. Option C (drag per weight) describes a drag-to-weight ratio. Option D (wing area per weight) is the mathematical inverse of wing loading.
Correct: D)
Explanation: Adverse yaw occurs because the down-deflected aileron, which increases local lift on the rising wing, also increases induced drag on that wing. This extra drag pulls the nose toward the rising wing — away from the intended turn direction. Option A describes the opposite phenomenon. Option B describes a secondary rudder-roll coupling, not the primary adverse yaw effect. Option C incorrectly attributes the drag increase to the up-deflected aileron; in reality, it is the down-deflected aileron that creates more drag.
Correct: D)
Explanation: In ground effect (within approximately one wingspan of the surface), the ground physically constrains wingtip vortex development, reducing downwash. This increases the effective angle of attack (raising lift) while simultaneously reducing induced drag. Pilots notice this as a floating sensation during the landing flare. Options A, B, and C all incorrectly describe the lift-drag relationship — the correct combination is increased lift with decreased induced drag.
