Correct: C)
Explanation: In steady (stationary) gliding flight, there is no thrust, so only two forces act: gravity (weight) and the total aerodynamic force (the vector sum of lift and drag). For the glider to be in equilibrium, these two must be equal and opposite — meaning the resultant air force exactly compensates gravity. Lift and drag are merely components of this single aerodynamic resultant; neither lift alone nor drag alone balances weight.
Correct: C)
Explanation: Extending flaps increases wing camber, which raises the maximum lift coefficient (CLmax). From the stall speed formula Vs = sqrt(2W / (rho * S * CLmax)), a higher CL_max directly lowers the minimum flying speed Vs. This allows the aircraft to fly slower without stalling, which is why flaps are used during approach and landing. The maximum permissible speed typically decreases with flaps extended (not increases), because flap structures are not designed for high dynamic pressure.
Correct: D)
Explanation: An incipient spin begins when one wing stalls before the other — the stalled wing drops, creating a yawing and rolling moment. The correct response is to apply rudder opposite the direction of yaw/lower wing to stop the rotation, and simultaneously release elevator back-pressure (or push forward) to reduce the angle of attack below the critical value, allowing airflow to re-attach and lift to be restored. Pulling the elevator (A) would increase AoA and deepen the stall; pushing alone (C) without rudder does not stop the yaw.
Correct: D)
Explanation: The lateral axis is the pitch axis (nose up/down). The horizontal stabilizer provides longitudinal (pitch) stability: it generates a restoring moment whenever the nose pitches up or down from trim, because its lift force changes with AoA at the tail. Ailerons control roll (longitudinal axis), the vertical rudder controls yaw (vertical axis), and flaps are high-lift devices, not stability surfaces.
Correct: A)
Explanation: Exceeding VNE risks aeroelastic flutter — a self-reinforcing oscillation of the control surfaces or wings that can destroy the structure within seconds. Flutter onset speed is close to VNE. Structural failure of spars, attachments, or control surfaces may follow. The other options describe effects that do not occur at excessive speed: glide angle does not improve, drag does not decrease, and the ASI is designed to function at all normal and abnormal speeds.
Correct: B)
Explanation: A rearward CG reduces the restoring moment arm between the CG and the horizontal stabiliser, diminishing longitudinal (pitch) stability. In extreme cases the aircraft can become unstable in pitch — the pilot may be unable to prevent a nose-up divergence, especially during winch launch or in turbulence. The forward CG limit ensures adequate pitch stability; the aft limit ensures adequate controllability. A rearward CG does not increase stall speed or roll effectiveness, and it makes the aircraft less, not more, stable.
Correct: D)
Explanation: The vertical tail fin (fin + rudder) provides yaw stability and yaw control. The fixed fin acts as a weathervane that generates a restoring yaw moment if the aircraft sideslips. The movable rudder allows the pilot to command deliberate yaw inputs for coordination, crosswind correction, or spin recovery. The horizontal stabiliser handles pitch; wing dihedral handles roll stability; the vertical tail does not generate lift in the conventional sense.
Correct: C)
Explanation: In a level coordinated turn, the load factor n = 1/cos(bank angle). At 60° bank, n = 1/cos(60°) = 1/0.5 = 2.0. This means the effective weight the wings must support doubles. Stall speed increases by a factor of √n = √2 ≈ 1.41, i.e. a 41% increase. This is why steep turns at low altitude are dangerous for gliders — the stall margin shrinks dramatically.
Correct: C)
Explanation: Induced drag is inversely proportional to aspect ratio (AR): D_induced ∝ CL² / (π × AR × e). A longer, narrower wing (high AR) produces the same lift with weaker wingtip vortices and therefore less induced drag. This is why gliders have very high aspect ratios — it is the primary design feature that maximises the lift-to-drag ratio and glide performance.
Correct: A)
Explanation: A downward-deflected trim tab produces an upward aerodynamic force on the trailing edge of the elevator, pushing the elevator's trailing edge up and its leading edge down — this effectively deflects the elevator downward, creating a nose-up pitching moment. Trim tabs work by aerodynamic force to relieve the pilot of sustained stick forces; their deflection is opposite to the desired elevator deflection.
Correct: B)
Explanation: The glider's speed polar plots the vertical sink rate (Vz, typically in m/s) against the horizontal airspeed (Vh). It is the fundamental performance diagram for a glider: it reveals the minimum sink speed (the lowest point on the curve), the best glide speed (given by the tangent from the origin), and inter-thermal cruise speeds (McCready tangents). All cross-country speed-to-fly decisions are based on this curve.
Correct: C)
Explanation: In level flight, lift must equal weight (L = W). Since L = CL × 0.5 × ρ × V² × S, when speed V increases the lift coefficient CL must decrease to keep lift constant. A lower CL corresponds to a lower angle of attack. Therefore, faster flight requires a smaller angle of attack, and slower flight (toward the stall) requires a progressively larger angle of attack.
Correct: C)
Explanation: Wing fences are thin vertical plates on the upper surface of a swept or tapered wing that prevent the boundary layer from flowing spanwise (outward toward the tips). Without fences, the boundary layer migrates outward due to the pressure gradient, thickening at the tips and promoting tip stall. Fences confine the boundary layer to its local region, improving tip stall characteristics and aileron effectiveness at high angles of attack.
Correct: C)
Explanation: The best glide ratio (maximum L/D) occurs at the speed where total drag is minimum. At this point, induced drag exactly equals parasite drag — any faster increases parasite drag more than induced drag decreases, and any slower increases induced drag more than parasite drag decreases. For a glider, this speed gives the flattest glide angle and the greatest distance per unit of altitude lost in still air.
Correct: C)
Explanation: Wing dihedral — the upward V-angle of the wings — is the primary design feature providing lateral (roll) stability. When a gust or disturbance causes one wing to drop, the dihedral geometry increases the angle of attack on the lower wing, generating more lift and creating a restoring roll moment toward wings-level. The vertical fin provides directional stability; the horizontal stabiliser provides pitch stability; and elevator trim sets a pitch reference, not a roll reference.
Correct: C)
Explanation: IAS is based on dynamic pressure (q = 0.5 × ρ × V²). At higher altitude, air density ρ is lower, so a given IAS corresponds to a higher TAS. The relationship is TAS = IAS × √(ρ₀/ρ), where ρ₀ is sea-level density. For glider pilots, this means that at altitude, the ground speed for the same indicated approach speed is higher, and the landing roll will be longer.
Correct: B)
Explanation: Load factor (n) is defined as the ratio of the lift generated by the wings to the aircraft's weight: n = L/W. In straight and level flight, n = 1. In a turn, n > 1 because extra lift is needed for the centripetal force. In a vertical pullup, n can exceed the design limits. The structural design of the glider is rated for specific load factor limits (typically +5.3g / -2.65g for utility category).
Correct: C)
Explanation: The best L/D ratio is determined by the aerodynamic shape of the aircraft and is independent of weight. Increasing weight shifts the speed polar downward and to the right — the best glide speed increases (must fly faster) but the maximum L/D ratio stays the same. This is why adding water ballast in gliders improves inter-thermal cruise speed without changing the glide angle — only the speed at which that angle is achieved changes.
Correct: C)
Explanation: The minimum sink rate speed is the speed at the lowest point of the speed polar. Any speed change — faster or slower — from this point increases the sink rate. Accelerating beyond minimum sink speed increases parasite drag faster than induced drag decreases, resulting in a higher total drag and therefore a greater rate of descent. This is the trade-off in cross-country flying: flying faster covers more ground but at the cost of increased sink rate.
Correct: C)
Explanation: Airbrakes (spoilers) disrupt the smooth airflow over the wing surface, reducing the pressure differential and therefore reducing lift. Simultaneously, the raised spoiler panels create a large increase in drag. This combined effect steepens the glide path dramatically, which is precisely their purpose — to allow the pilot to control the approach angle and land precisely. Without airbrakes, gliders would float long distances due to their excellent L/D ratio.
Correct: C)
Explanation: Induced drag is proportional to CL², and CL is highest in slow flight at high angle of attack (where the wing must generate maximum lift per unit of dynamic pressure). In a dive or at high speed, CL is low and induced drag is minimal — parasite drag dominates instead. At best glide speed, induced drag equals parasite drag but is not at its maximum. The slow-flight regime is where induced drag dominates total drag.
Correct: A)
Explanation: The elevator trim tab allows the pilot to reduce or eliminate the stick force needed to hold a given pitch attitude in steady flight. By deflecting the trim tab, an aerodynamic force is applied to the elevator that counters the natural hinge moment, allowing hands-off or reduced-force flight at the trimmed speed. This reduces pilot fatigue on long flights and allows the pilot to concentrate on navigation and thermal exploitation.
Correct: C)
Explanation: In a turn, the load factor n = 1/cos(bank angle) exceeds 1, meaning the wings must generate more lift than in straight flight. The stall speed increases by the factor √n. At 45° bank, stall speed increases by 19%; at 60° bank by 41%. This is a critical safety consideration when thermalling near the ground — the steeper the bank, the closer the pilot is to the elevated stall speed.
Correct: C)
Explanation: The centre of pressure (CP) is the point on the chord line where the resultant aerodynamic force (sum of all pressure and friction forces) can be considered to act. Unlike the aerodynamic centre, the CP moves with changing angle of attack — it moves forward as AoA increases and rearward as AoA decreases. This movement is one reason why the CG position must remain within limits: if the CP moves too far from the CG, pitch control may be compromised.
Correct: D)
Explanation: Parasite drag is proportional to V² (dynamic pressure). The faster the aircraft flies, the greater the parasite drag. At VNE — the maximum speed — parasite drag reaches its peak within the normal flight envelope. At slow speeds near the stall, parasite drag is minimal while induced drag dominates. Parasite drag includes form drag, skin friction drag, and interference drag — all of which grow with the square of the airspeed.
Correct: B)
Explanation: Bernoulli's principle states that in a steady, incompressible flow, an increase in flow velocity is accompanied by a decrease in static pressure, and vice versa. Applied to an aerofoil, the air accelerates over the curved upper surface, creating a region of lower pressure compared to the lower surface. This pressure differential generates lift. While Newton's third law (downwash) also contributes to lift, the Bernoulli pressure distribution is the primary mechanism for conventional subsonic flight.
Correct: B)
Explanation: Adverse yaw occurs because the down-going aileron (on the wing that rises) increases both lift and induced drag on that wing. The extra drag on the rising wing pulls the nose toward the descending wing — opposite to the intended turn direction. This is why coordinated use of rudder with aileron is essential, and why differential aileron deflection was developed as a design solution.
Correct: B)
Explanation: Ground effect becomes significant when the aircraft is within approximately one wingspan of the surface. The ground physically restricts the development of wingtip vortices and reduces the induced downwash angle, which effectively increases lift and reduces induced drag. Pilots experience this as a floating sensation during the landing flare — the glider wants to keep flying in ground effect, which can cause overshooting the intended touchdown point if not anticipated.
Correct: B)
Explanation: Washout is a deliberate design feature in which the wing's angle of incidence decreases progressively from root to tip (geometric washout) or the aerofoil section changes to produce less lift at the tip (aerodynamic washout). This ensures that the wing root stalls before the tip, preserving aileron effectiveness during a stall and making the stall behaviour more benign and recoverable. Washout is particularly important in gliders with their long, high-aspect-ratio wings.
Correct: B)
Explanation: In the pre-stall regime, the lift coefficient CL increases approximately linearly with angle of attack (AoA). The slope of this line is the lift curve slope (typically about 2π per radian for a thin aerofoil). This linear relationship continues until the critical angle of attack is reached, at which point flow separation causes CL to peak (CL_max) and then drop sharply — the stall. The linearity of the CL vs. AoA relationship is one of the foundational results of aerodynamic theory.
Correct: C)
Explanation: Extending flaps increases the wing's maximum lift coefficient (CLmax) by adding camber and, in some designs, wing area. From the stall speed formula Vs = sqrt(2W / (ρ × S × CLmax)), a higher CL_max yields a lower stall speed. This allows approach and landing at slower speeds with a shorter ground roll. Retracting flaps removes this benefit and returns stall speed to the higher clean-configuration value.
Correct: C)
Explanation: Laminar-flow aerofoils are designed with their maximum thickness further aft than conventional profiles, creating a favourable pressure gradient that keeps the boundary layer laminar over a larger portion of the chord. Since laminar boundary layers produce far less skin friction drag than turbulent ones, the overall profile drag is significantly reduced. Gliders exploit this extensively — clean laminar-flow wings are the reason modern gliders achieve glide ratios exceeding 50:1.
Correct: C)
Explanation: Air density decreases with altitude because atmospheric pressure drops and air expands. In the standard atmosphere, density at 5,500 m is roughly half the sea-level value. Reduced density means reduced dynamic pressure at a given TAS, which is why aircraft performance (lift and drag per unit TAS) degrades at altitude — the aircraft must fly faster in TAS to maintain the same IAS and lift.
Correct: B)
Explanation: Static stability describes the aircraft's immediate response to a disturbance — whether restoring forces act to push it back toward the original equilibrium. Dynamic stability describes what happens over time: if the resulting oscillations decrease in amplitude and the aircraft eventually returns to its trimmed state, it is dynamically stable. An aircraft can be statically stable but dynamically unstable (oscillations grow), which is a dangerous condition.
Correct: C)
Explanation: Vortex generators are small tabs that protrude from the wing surface and create tiny vortices that mix high-energy air from outside the boundary layer into the slower boundary layer flow near the surface. This energised boundary layer can resist adverse pressure gradients more effectively, delaying flow separation and improving control effectiveness at high angles of attack. They trade a small increase in skin friction for a significant delay in stall onset and better aileron authority near the stall.
Correct: C)
Explanation: The pilot can directly change airspeed V (by adjusting pitch attitude) and indirectly change the lift coefficient CL (by changing the angle of attack, or by extending/retracting flaps). Air density ρ changes with altitude and temperature but is not directly controlled. Wing area S is fixed (except in rare variable-geometry designs or Fowler flap configurations). Airspeed and angle of attack are the pilot's primary tools for managing lift.
Correct: C)
Explanation: As angle of attack increases in the pre-stall range, the pressure distribution shifts such that the centre of pressure moves forward along the chord. This forward CP movement produces a nose-up pitching moment that must be counteracted by the tail — one of the main reasons aircraft require a horizontal stabiliser. At very low (or negative) angles of attack, the CP moves rearward. This CP migration is why the aerodynamic centre concept is useful: the moment about the aerodynamic centre stays constant regardless of AoA.
Correct: D)
Explanation: The critical angle of attack is an inherent property of the aerofoil's geometric shape — it is the angle at which the flow can no longer remain attached to the upper surface and separates, causing the stall. It does not change with weight, altitude, or airspeed. What changes with those factors is the stall speed — the speed at which the wing reaches the critical angle of attack in level flight. The aerofoil geometry (camber, thickness, leading edge radius) determines how well the flow follows the upper surface at high angles.
Correct: A)
Explanation: Induced drag decreases monotonically with increasing airspeed in level flight: D_induced = 2W^2 / (rho * V^2 * S^2 * pi * AR * e). As V increases, induced drag continuously falls — there is no minimum/maximum within the normal flight envelope. Parasite drag (not induced drag) has the U-shaped curve described in B/C. Total drag has a minimum at the speed where induced drag equals parasite drag; induced drag itself simply decreases with speed.
Correct: D)
Explanation: The standard aerodynamic breakdown of total drag is: Total drag = Induced drag + Parasite drag. Induced drag arises from lift generation (wingtip vortices). Parasite drag is the collective term for all non-lift-related drag: form/pressure drag, skin friction drag, and interference drag. Options A and C list sub-components of parasite drag but omit induced drag or incorrectly combine them. Option B omits induced drag, which is a major component especially at low speeds.
Correct: C)
Explanation: As the critical angle of attack is reached, flow begins to separate from the upper surface, starting at the trailing edge and progressing forward. Once past the critical AoA, the clean attached flow that generated lift breaks down — CL drops sharply. Simultaneously, the separated flow creates a large turbulent wake with very high pressure drag, so CD rises dramatically. The drag polar shows this clearly: the nose of the polar curves sharply as the stall condition is approached, with CL falling and CD rising.
Correct: C)
Explanation: Stall recovery requires reducing angle of attack below the critical value so that airflow can re-attach to the upper surface and lift can be restored. The pilot must push forward on the elevator control to lower AoA, which also allows the aircraft to accelerate (or the pilot applies power if available). Increasing AoA (B, D) deepens the stall. Reducing speed (D, A) worsens the condition. Banking (A) increases the load factor, which raises the stall speed — exactly the wrong input.
Correct: D)
Explanation: This is the definitive stall characteristic: lift collapses because boundary layer separation destroys the pressure differential that generates it, while drag rises dramatically due to the large turbulent separated wake. The CL vs. AoA curve shows CL_max at the critical angle, then a steep drop — this is the stall. The CD vs. AoA curve rises steeply through and beyond the stall. This combination (less lift, more drag) is why the stall is critical — the aircraft loses lift while simultaneously experiencing high drag that would further reduce speed.
Correct: B)
Explanation: The critical (stall) angle of attack is a fixed aerodynamic property of the aerofoil shape — it is the AoA at which flow separation occurs regardless of airspeed, weight, or altitude. What changes with weight is the stall speed (Vs = sqrt(2W / (rho * S * CL_max))), not the stall AoA. A heavier aircraft must fly faster to generate the same lift, but it still stalls at the same critical AoA. C.G. position affects pitch stability and control effectiveness but does not change the aerofoil's critical angle.
Correct: C)
Explanation: From Vs = sqrt(2W / (rho * S * CLmax)): stall speed decreases when weight (W) decreases, since less lift is needed to maintain equilibrium. Lower density (B) increases true airspeed (TAS) stall speed but the IAS stall speed remains approximately constant (since IAS is based on dynamic pressure q = 0.5 * rho * VTAS^2, which equals 0.5 * rho0 * VIAS^2). Higher load factor (A) effectively increases apparent weight (n*W), raising stall speed. Lower altitude means higher density, which slightly lowers TAS stall speed but does not significantly change IAS stall speed.
Correct: B)
Explanation: Spin recovery technique (PARE: Power off, Ailerons neutral, Rudder opposite to spin direction, Elevator forward) requires keeping ailerons neutral because using ailerons during a spin can worsen the rotation — applying aileron into the spin raises the inner wing's AoA (which may already be stalled) and can deepen the spin. Rudder opposite to spin direction stops the autorotation; forward elevator then reduces AoA to unstall both wings. Speed does not constantly increase in a spin — the aircraft reaches a stabilised spin with relatively constant speed and rotation rate.
Correct: D)
Explanation: The boundary layer development follows a specific sequence: flow is divided at the stagnation point, a laminar boundary layer develops from the stagnation point rearward, then at the transition point the laminar layer converts to turbulent, and finally at the separation point the turbulent layer detaches from the surface. The laminar boundary layer therefore occupies the region from the stagnation point to the transition point. Laminar flow aerofoils are designed to push the transition point as far aft as possible to minimise friction drag.
Correct: C)
Explanation: The natural sequence of boundary layer development on an aerofoil runs from laminar (near the leading edge, where the flow is orderly and Reynolds number is low) to turbulent (further aft, after transition). The reverse sequence (turbulent first, then laminar) does not occur naturally. This forward laminar / aft turbulent arrangement is why designers place the maximum thickness of laminar-flow aerofoils further back — to extend the favourable pressure gradient that maintains laminar flow as far as possible before transition.
Correct: D)
Explanation: The turbulent boundary layer, despite having higher skin friction drag than the laminar layer, has more energetic mixing that allows it to remain attached to the surface against an adverse pressure gradient at higher angles of attack. This is its critical advantage: it resists flow separation better. The laminar boundary layer is indeed thinner (C is partly correct about thickness) and has lower friction drag — but it separates more easily. This is why turbulators are sometimes used on gliders: deliberately triggering transition to turbulent flow to prevent laminar separation bubbles.
Correct: B)
Explanation: Lateral (roll) stability — the tendency to return to wings-level after a roll disturbance — is primarily provided by wing dihedral (the upward angle of the wings from horizontal). When a gust rolls the aircraft, the lower wing descends and its angle of attack increases (it meets more airflow), generating more lift and creating a restoring moment back to level. The vertical tail provides directional (yaw) stability; ailerons are roll control surfaces (not stability), and the elevator controls pitch. High-wing aircraft achieve similar lateral stability through the pendulum effect of the fuselage hanging below the wings.
