Correct: C)
Explanation: The standard gravitational acceleration at the Earth's surface is 9.81 m/s² (ISA value). This value is fundamental in aeronautics: it is used to calculate weight (W = m × g), load factor, and appears in all performance equations. 1013.25 hPa is the standard pressure at sea level, and 15°C/100 m is not a correct gradient (the standard lapse rate is 0.65°C/100 m).
Correct: D)
Explanation: The permitted flap position during a sideslip is always specified in the aircraft flight manual (AFM/POH). Some gliders prohibit extended flaps in a sideslip because the combination of flaps and deflected rudder can create dangerous aerodynamic couples or exceed structural limits. Others permit certain configurations. The only correct answer is therefore to consult the AFM.
Correct: B)
Explanation: Dynamic stability describes the behaviour of an aircraft over time after a disturbance. A dynamically stable aircraft returns automatically to its original equilibrium (trim) after being disturbed — the oscillations progressively damp out. Answer A describes so-called "neutral or convergent stability towards a new equilibrium", which is different. Static stability (the immediate tendency to return) is a necessary but not sufficient condition for dynamic stability.
Correct: D)
Explanation: The manoeuvring speed VA (or turbulence penetration speed) is the maximum speed at which full control surface deflections or severe wind gusts will not cause the structural limit load to be exceeded. Below VA, the wing will stall before the structural limit load is reached, thereby protecting the structure. In severe turbulence, speed must be reduced below V_A to avoid structural damage from gust dynamic loads.
Correct: C)
Explanation: In the ICAO standard atmosphere (ISA), temperature decreases by 0.65°C for every 100 m of altitude in the troposphere (or equivalently, 2°C per 1000 ft, or 6.5°C/1000 m). Answer B (0.65°C/1000 ft) is incorrect because the unit is wrong — this would be far too small a lapse rate. Answer C is the only correct one: 0.65°C per 100 m of altitude.
Correct: A)
Explanation: Atmospheric pressure decreases with altitude in an approximately exponential manner. In the ICAO standard atmosphere, pressure is approximately half the sea-level pressure (1013.25 hPa → ~506 hPa) at an altitude of approximately 5,500 m (18,000 ft). This value is important for high-altitude physiology (oxygen requirements) and for density altitude performance calculations.
Correct: C)
Explanation: Density altitude is the altitude at which the aircraft would be in the ISA standard atmosphere if the air density were the same as in actual conditions. It is calculated from pressure altitude (altimeter set to 1013.25 hPa) corrected for the temperature deviation from ISA. A temperature higher than ISA gives a density altitude higher than pressure altitude, reducing aircraft performance. Answer A describes pressure altitude, not density altitude.
Correct: D)
Explanation: The continuity equation states that for an incompressible fluid, the volumetric flow rate Q = S × V is constant along a streamtube. If the cross-section S decreases, the velocity V must increase proportionally to keep Q constant. This principle, combined with Bernoulli's theorem, explains why air accelerates over the curved upper surface of an aerofoil, creating a low-pressure region that generates lift.
Correct: A)
Explanation: Both lift and drag are proportional to the dynamic pressure q = 0.5 × ρ × V². When air density ρ decreases (at altitude or in high temperatures), q decreases for a given speed, which reduces both lift and drag. This is why aircraft performance deteriorates at high altitude or in great heat: the aircraft must fly faster (higher TAS) to generate the same lift, while the total aerodynamic resistance decreases for a constant indicated airspeed.
Correct: D)
Explanation: The neutral point (also called the aerodynamic centre at wing level, but "neutral point" for the complete aircraft) is the point about which the pitching moment remains constant regardless of changes in angle of attack. For a stable aircraft, the centre of gravity must be forward of the neutral point — the CG-to-neutral point distance constitutes the static stability margin. Note: for an isolated aerofoil, this point corresponds to the aerodynamic centre (at approximately 25% of the chord); for the complete aircraft, the neutral point accounts for the contribution of the horizontal stabiliser.
Correct: D)
Explanation: The rigging angle (or angle of incidence) is the fixed angle, defined at construction, between the aerofoil chord line and the longitudinal axis of the fuselage. It does not vary in flight. It should not be confused with the angle of attack, which is the angle between the chord line and the direction of the relative wind (and which varies in flight according to attitude and speed). The rigging angle is chosen by the manufacturer so that the wing generates the necessary lift in cruise at an aerodynamically favourable fuselage attitude.
Correct: D)
Explanation: The transition point is precisely the location on the aerofoil where the boundary layer changes from a laminar regime (ordered flow, in parallel layers) to a turbulent regime (disordered flow, with transverse mixing). This transition is irreversible in the direction of flow: the change is from laminar to turbulent, never the reverse. The position of the transition point depends on the Reynolds number, the pressure gradient, and surface roughness — a favourable pressure gradient (acceleration) maintains laminar flow, while an adverse gradient (deceleration) triggers transition.
Correct: C)
Explanation: Wing twist (geometric or aerodynamic) varies the angle of incidence or aerodynamic characteristics along the span, so that the stall does not occur simultaneously across the entire wing. The root (higher angle of incidence) reaches the critical angle first and stalls progressively, while the outer sections remain attached. This progressive (rather than simultaneous) flow separation improves stall safety and maintains roll control via the ailerons. The effect on adverse yaw (A) is indirect and marginal.
Correct: D)
Explanation: Form drag (pressure drag) is caused by the pressure difference between the front and rear of a body, due to boundary layer separation and the formation of vortices in the wake. The more intense the vortex formation (unStreamlined body, blunt trailing edge), the higher the form drag. This is why streamlined aerofoils have much lower form drag than a flat plate or sphere — their progressively converging shape allows the flow to remain attached longer, reducing the turbulent wake.
Correct: C)
Explanation: The drag of a flat disc (non-streamlined body) is pressure drag: it depends primarily on the frontal surface area S exposed perpendicularly to the airflow, and on the dynamic pressure q = 0.5 × ρ × V². The formula is D = CD × q × S. The material strength, the disc's own density, or its weight do not influence aerodynamic drag — this is purely a function of shape, projected area, and flow conditions.
Speed Polar:
] A = tangent from the origin → best glide speed (best L/D ratio, best glide) B = tangent from a point shifted to the right on the V axis → best glide with headwind C = tangent from a point above the origin on the W axis (McCready) → optimal inter-thermal speed; touches the polar at the point of minimum sink rate D = horizontal line at the level of minimum sink rate → indicates the minimum sink speed (Vmin sink)
Correct: D)
Explanation: On the speed polar (curve showing the sink rate W as a function of horizontal speed V), the point of minimum sink rate corresponds to the lowest point of the curve (the smallest value of W in absolute terms). The tangent at this point is a horizontal tangent — this is tangent (C) on the diagram. This point corresponds to the minimum sink speed, used to maximise flight time or to exploit thermals. The tangent drawn from the origin to the polar (tangent B) gives the speed for the best L/D ratio (best glide ratio).
Correct: C)
Explanation: Induced drag is proportional to CL²: Dinduced = CL² / (π × AR × e) × q × S. By increasing the angle of attack, CL increases, and therefore CL² increases, causing induced drag to grow. In level flight at constant speed, an increase in angle of attack corresponds to a lower speed, which further increases induced drag (Dinduced ∝ 1/V²). By increasing speed (D), CL decreases in level flight and induced drag decreases. Parasite drag (A) varies independently of induced drag.
Correct: C)
Explanation: In a horizontal turn at bank angle φ, the load factor is n = 1/cos(φ). At 45° of bank, n = 1/cos(45°) = 1/0.707 ≈ 1.41. The stall speed in the turn is Vs_turn = Vs × √n = Vs × √1.41 ≈ Vs × 1.19. Therefore the minimum speed increases by approximately 19% compared to straight-and-level flight. This increase in stall speed during turns is a fundamental safety concept — tight turns at low altitude (such as on final approach) are particularly dangerous because the margin above the stall is reduced.
Correct: D)
Explanation: Adverse yaw is caused by the asymmetry of drag between the two ailerons during turn entry. The aileron that rises (on the high-wing side) increases the local angle of attack, generating more lift but also more induced drag. This additional drag on the rising side creates a yawing moment towards the rising side — i.e. in the opposite direction to the turn (hence "adverse yaw"). Differential ailerons and spoiler-airbrakes are technical solutions to mitigate this effect.
Correct: D)
Explanation: True airspeed (TAS) is obtained from indicated airspeed (IAS) by applying two successive corrections: first, position and instrument errors (yielding calibrated airspeed, CAS), then the density correction (accounting for the difference between actual air density and standard sea-level density). TAS is therefore the actual speed of the aircraft through the air mass. At high altitude, TAS is significantly higher than IAS because air density is lower.
Correct: C)
Explanation: The slotted flap speed range is indicated in the Flight Manual (AFM) and normally on the airspeed indicator (white or light green arc). It varies by glider type.
Correct: A)
Explanation: Wing tip vortices (induced vortices) come from pressure equalization from the lower surface (high pressure) to the upper surface (low pressure) at the wing tip. This phenomenon generates induced drag.
Correct: A)
Explanation: Angle of attack is the angle between the chord line and the general airflow direction (relative wind direction). It is not the angle with the horizon nor with the longitudinal axis.
Correct: D)
Explanation: The pressure in ICAO standard atmosphere at sea level is 1013.25 hPa (millibars) = 29.92 inches of mercury (inHg). 29.92 hPa is incorrect.
]
- A) The air mass flows through a larger cross-section at a higher speed
- B) The air mass flows through a smaller cross-section at a lower speed
- C) The speed of the air mass does not vary
- D) The air mass flows through a larger cross-section at a lower speed
Correct: B)
Explanation: The mean camber line is the line equidistant between the lower and upper surfaces. In the figure, it is represented by line B.
