Correct: C)
Explanation: Static (mass) balancing places counterweights ahead of the control surface hinge line, moving the surface's centre of mass forward to or ahead of the hinge axis. This prevents flutter, a potentially destructive high-frequency oscillation caused by the interaction between aerodynamic forces and the inertia of the control surface. Without proper mass balancing, flutter can develop at certain speeds and rapidly destroy the control surface or the entire tail structure. Option A (limiting stick forces) relates to aerodynamic balancing, not mass balancing. Option B (increasing forces) is not a design goal. Option D (force-free trimming) is the function of the trim system.
Correct: C)
Explanation: When the trim tab on the elevator is deflected upward, it generates a downward aerodynamic force on the trailing edge of the elevator, which pushes the elevator's leading edge up and causes the entire elevator to deflect downward. This produces a nose-down pitching moment on the aircraft, and the trim indicator accordingly shows a nose-down (forward) position. Option A (lateral trim) refers to the wrong axis entirely. Option B (neutral) would require the tab to be streamlined. Option D (nose-up) is the opposite of the effect produced by an upward trim tab deflection.
Correct: D)
Explanation: Point 1 on the polar diagram (PFA-008) is located in the region of negative lift coefficient, which corresponds to inverted (upside-down) flight where the wing generates downward force relative to the aircraft. During inverted flight, the aerofoil operates at negative angles of attack, producing negative CL values on the polar. Option A (slow flight) would appear at high positive CL near the top of the positive polar curve. Option B (best gliding angle) is at the maximum CL/CD ratio on the positive side. Option C (stall) would be at the peak CL_max point on the positive curve.
Correct: B)
Explanation: In a coordinated banked turn at constant altitude, the wing must produce enough lift to support both the aircraft's weight vertically and the centripetal force horizontally. The total required lift exceeds the weight, making the load factor n = 1/cos(bank angle) always greater than 1. Since stall speed increases with the square root of the load factor (Vs_turn = Vs x sqrt(n)), the stall speed is also higher in the turn. Option A and Option C incorrectly state n is less than 1. Option D correctly identifies n greater than 1 but incorrectly claims stall speed decreases.
Correct: D)
Explanation: At the wingtips, air flows from the high-pressure lower surface around to the low-pressure upper surface, creating trailing vortices. These vortices tilt the local relative airflow downward (downwash), effectively reducing the wing's angle of attack and tilting the lift vector rearward. The rearward component of this tilted lift vector is induced drag. Option A incorrectly labels it as profile drag, which is caused by boundary layer friction and pressure effects on the aerofoil itself. Option B is wrong because vortices create turbulent, not laminar, flow. Option C is incorrect because vortices reduce effective lift rather than generating it.
Correct: D)
Explanation: In a steady glide at equal mass, the lift must equal the weight regardless of the aerofoil shape, so lift remains the same. However, a thicker aerofoil has a larger frontal area and more pronounced adverse pressure gradients on its rear surface, which leads to greater form (pressure) drag and generally higher total profile drag compared to a thinner aerofoil. Therefore the result is more drag with the same lift. Option A and Option C incorrectly state less drag. Option B incorrectly states less lift, which is impossible in steady glide at constant mass.
Correct: D)
Explanation: A profile polar (also called a Lilienthal polar) plots the lift coefficient (cA or CL) on the vertical axis against the drag coefficient (cD or CD) on the horizontal axis for various angles of attack. Each point on the curve represents a specific angle of attack, allowing the designer or pilot to see how lift and drag relate across the entire operating range of the profile. Option A describes only one variable (CL vs alpha), not the polar relationship. Option B describes flight performance parameters, not aerofoil coefficients. Option C describes the L/D ratio, which can be derived from the polar but is not what the diagram directly plots.
Correct: C)
Explanation: Any body immersed in a moving fluid will always produce drag -- this is an unavoidable consequence of both skin friction (viscous forces) and pressure differences (form drag) acting on the body. However, not every shape produces lift; lift requires a specifically oriented asymmetric shape or angle of attack to create a pressure differential between upper and lower surfaces. An arbitrarily shaped body has no guaranteed lift-producing geometry. Option A is wrong because drag increases with the square of velocity, not remaining constant. Option B (lift without drag) violates fundamental aerodynamic principles. Option D assumes lift is always produced, which is not the case for arbitrary shapes.
Correct: C)
Explanation: In the aerofoil diagram (PFA-010), line number 3 represents the camber line (mean camber line), which is the locus of points equidistant between the upper and lower surfaces of the aerofoil at each chordwise station. The camber line defines the curvature of the profile and is a key parameter in determining its aerodynamic characteristics. Option A (chord) and Option B (chord line) both refer to the straight line from leading to trailing edge. Option D (thickness) is the perpendicular distance between the upper and lower surfaces, not a line on the diagram.
Correct: C)
Explanation: Differential aileron deflection is specifically designed to compensate for adverse yaw. In this system, the up-going aileron deflects more than the down-going aileron, which reduces the additional induced drag on the wing with the down-going aileron (the descending wing). By equalising the drag on both wings during a roll input, the undesired yawing moment opposite to the turn is minimised. Option A (wing dihedral) provides lateral (roll) stability but does not address yaw asymmetry during aileron input. Option B (full aileron deflection) would actually maximise adverse yaw rather than compensate for it. Option D repeats the question text and is not a valid answer.
Correct: D)
Explanation: Wing loading is defined as the aircraft's weight divided by the wing reference area, expressed in units such as N/m-squared or kg/m-squared. It is a fundamental parameter that influences stall speed, turning performance, gust sensitivity, and thermal circling radius. A higher wing loading means higher minimum speeds but better penetration in headwinds. Option A (drag per weight) is not a standard aerodynamic parameter. Option B (wing area per weight) is the inverse of wing loading. Option C (drag per wing area) describes a drag coefficient-related quantity, not wing loading.
Correct: D)
Explanation: Point 5 on the polar diagram (PFA-008) lies on the positive side of the polar curve at a high CL value and relatively high angle of attack, corresponding to slow flight. In slow flight, the wing operates close to but below the stall angle, with high lift coefficient and relatively high drag. Option A (best gliding angle) would be at the tangent point giving maximum CL/CD ratio. Option B (inverted flight) appears in the negative CL region of the polar. Option C (stall) would be at the very peak of the CL curve where CL_max is reached and flow separation begins.
Correct: C)
Explanation: Deploying airbrakes (spoilers or dive brakes) has a dual aerodynamic effect: they create large additional profile drag by disrupting the streamlined shape, and they partially destroy the lift on the upper wing surface by interrupting the smooth airflow. The net result is a significant increase in drag and a reduction in lift, which together steepen the glide path -- exactly the purpose for which airbrakes are designed. Option A incorrectly states lift increases. Option B incorrectly states drag decreases. Option D describes the opposite of what actually occurs.
Correct: D)
Explanation: Glide ratio (L/D) is maximised by reducing drag while maintaining optimal speed. Cleaning the wing and fuselage surfaces removes bugs and dirt that increase surface roughness and drag. Flying at the correct (best-glide) speed places the aircraft at the peak of its L/D curve. A retractable undercarriage eliminates a major source of parasite drag. Taping the wing-fuselage junction gaps reduces interference and leakage drag. Option A includes forward CG, which increases trim drag. Option B suggests higher mass, which shifts the speed polar but does not improve the maximum L/D ratio. Option C omits surface cleaning and gap taping, which are significant drag-reduction measures.
Correct: B)
Explanation: In a spin, the inner (lower) wing is deeply stalled while the outer wing may still be producing some lift, creating the autorotation. Airspeed remains approximately constant near or below stall speed throughout the spin. In a spiral dive, both wings continue to fly (neither is stalled), and the aircraft enters an ever-steepening banked descent with rapidly and continuously increasing airspeed. Option A incorrectly identifies the outer wing as stalled in the spin. Options C and D incorrectly assign rising speed to the spin and constant speed to the spiral dive, which is the opposite of reality.
Correct: C)
Explanation: The longitudinal (fore-and-aft) position of the centre of gravity directly determines pitch stability, which is stability around the lateral axis. When the CG is forward of the neutral point, the aircraft has positive static stability in pitch -- any nose-up or nose-down disturbance produces a restoring moment. Moving the CG aft reduces pitch stability and eventually makes the aircraft unstable. Option A (longitudinal axis) governs roll stability, influenced mainly by wing dihedral. Option B ("gravity axis") is not a standard axis in aircraft stability. Option D (vertical axis) governs directional (yaw) stability, influenced by the vertical tail.
Correct: C)
Explanation: A large vertical tail (fin) provides directional (yaw) stability by acting as a weathervane: when the aircraft sideslips, the fin generates an aerodynamic force that yaws the nose back toward the direction of flight, restoring equilibrium. The larger the fin, the greater the restoring moment. Option A (wing dihedral) provides lateral (roll) stability by generating a rolling moment that levels the wings during a sideslip. Option B (a large elevator) contributes to pitch (longitudinal) stability, not directional stability. Option D (differential ailerons) reduces adverse yaw during roll inputs but does not provide inherent directional stability.
Correct: D)
Explanation: At constant power, transitioning from level flight to a climb requires converting kinetic energy into potential energy, which reduces airspeed. To maintain sufficient lift at the lower climbing speed, the wing must operate at a higher angle of attack. Therefore, the angle of attack in straight-and-level flight is smaller than in a climb at the same power setting. Option A states the opposite relationship. Option B compares to take-off, which is not the comparison asked. Option C compares to descent, where the angle of attack would actually be lower (higher speed, less CL needed).
Correct: A)
Explanation: The horizontal tail (stabiliser and elevator) provides pitch stability, which is stability around the lateral axis. When the aircraft is disturbed in pitch (nose moves up or down), the horizontal tail generates a restoring aerodynamic force that returns the aircraft toward its trimmed attitude. Option B (initiating turns around the vertical axis) is the function of the rudder. Option C (stabilising around the vertical axis) is provided by the vertical fin. Option D (stabilising around the longitudinal axis) describes roll stability, which is primarily achieved through wing dihedral and sweep.
Correct: D)
Explanation: When the rudder is deflected to the left, it creates an aerodynamic force that pushes the tail to the right, which yaws the aircraft's nose to the left around the vertical axis. Yaw is rotation around the vertical axis, controlled exclusively by the rudder. Option A and Option C describe pitching motions (rotation around the lateral axis), which are controlled by the elevator, not the rudder. Option B indicates the wrong yaw direction -- a left rudder deflection produces left yaw, not right yaw.
Correct: C)
Explanation: Differential aileron deflection is specifically designed to minimise adverse yaw -- the undesired nose movement away from the intended turn direction when ailerons are applied. By deflecting the up-going aileron more than the down-going aileron, the drag difference between the two wings is reduced, thereby reducing the yawing moment that opposes the turn. Option A (increasing descent rate) is the function of airbrakes or spoilers. Option B (preventing stalls at low angles of attack) is not relevant since stalls occur at high angles of attack. Option D (reducing wake turbulence) would require winglets or similar devices.
Correct: C)
Explanation: In a banked turn, the lift vector is tilted inward, so its vertical component is less than the total lift. To maintain altitude, the total lift must be increased beyond the straight-and-level value so that the vertical component still supports the aircraft's weight while the horizontal component provides the centripetal force needed for the curved flight path. The load factor n = 1/cos(bank angle) quantifies how much additional lift is required. Option A is the opposite -- more lift, not less, is needed. Option B confuses centripetal force with centrifugal force (which is a fictitious force in the rotating reference frame). Option D describes forces but does not address the key requirement to increase lift.
Correct: C)
Explanation: A retractable engine and propeller arrangement allows the entire powerplant to be folded into the fuselage when not in use, completely eliminating the parasite drag associated with the engine cowling, propeller blades, and related protrusions. This gives the TMG pure glider-like aerodynamic performance in soaring flight. Option A (fixed nose mount), Option B (fixed fuselage mount), and Option D (fixed at the stabiliser) all leave the engine and propeller permanently exposed to the airflow, creating continuous drag even when the engine is not running.
Correct: C)
Explanation: Adverse yaw occurs when aileron deflection causes the nose to yaw away from the intended direction of turn. The down-deflected aileron (on the wing intended to rise) increases both the local lift and the induced drag on that wing. This extra drag on the rising wing pulls the nose toward it -- away from the turn direction. Option A describes the opposite effect (proverse yaw). Option B describes a rudder-induced secondary rolling effect, not adverse yaw. Option D incorrectly attributes the extra drag to the up-deflected aileron, when it is actually the down-deflected aileron that generates more drag.
Correct: A)
Explanation: Ground effect occurs when an aircraft flies within approximately one wingspan of the surface. The ground restricts the downward development of wingtip vortices, which reduces the downwash angle behind the wing. This reduction in downwash effectively increases the local angle of attack (increasing lift) and reduces the rearward tilt of the lift vector (decreasing induced drag). The result is improved aerodynamic efficiency near the ground, which is why aircraft can feel like they "float" during landing. Option B is the exact opposite. Option C incorrectly includes a lift decrease. Option D incorrectly includes an induced drag increase.
Correct: D)
Explanation: The rudder controls yaw, which is rotation around the vertical axis (also called the normal axis). When the rudder is deflected, it generates a sideways aerodynamic force on the fin and rudder assembly, creating a yawing moment that rotates the nose left or right. Option A (longitudinal axis) is the roll axis, controlled by ailerons. Option B ("rudder axis") is not a standard axis of aircraft rotation. Option C (lateral axis) is the pitch axis, controlled by the elevator.
Correct: C)
Explanation: An upward gust suddenly increases the wing's effective angle of attack, momentarily generating significantly more lift than required for level flight. This excess lift acts as an additional load on the aircraft structure, instantaneously increasing the load factor (n = L/W) above 1. The sharper the gust and the faster the aircraft is flying, the greater the load factor spike. Option A (forward CG) affects handling but does not directly increase load factor in cruise. Option B (higher weight) does not change n unless lift also changes. Option D (lower air density) actually reduces lift at the same speed, decreasing rather than increasing load factor.
Correct: C)
Explanation: The McCready ring is always set to the expected climb rate in the next thermal -- in this case 2 m/s. The pilot then reads the recommended inter-thermal cruise speed from the variometer scale at the point corresponding to the current sink rate (3 m/s). This method optimises the speed-to-fly between thermals based on the MacCready theory. Option A incorrectly sets the ring to the sink rate. Option B sets the ring to zero, which would give the minimum sink speed rather than the optimal cruise speed. Option D incorrectly sums the two values, which has no basis in MacCready theory.
Correct: C)
Explanation: During approach and landing, the camber flaps should be set to positive (increased camber) to lower the stall speed and improve low-speed handling. Changing from positive to negative camber during this critical phase would suddenly reduce the wing's maximum lift coefficient, causing an abrupt loss of lift very close to the ground -- potentially resulting in a sudden descent or stall with no altitude for recovery. Option A (full positive during winch launch) is not necessarily required and depends on the flight manual. Option B states the opposite restriction. Option D (full negative during launch) would reduce lift when maximum lift is needed.
Correct: D)
Explanation: Point 3 on the aerofoil diagram (PFA-009) represents the transition point, where the boundary layer changes from laminar to turbulent flow. This is a critical location on the aerofoil because it marks the onset of increased skin friction drag and affects the overall drag characteristics of the wing. Option A (separation point) is further downstream where the boundary layer detaches entirely from the surface. Option B (centre of pressure) is the point where the resultant aerodynamic force effectively acts. Option C (stagnation point) is at the leading edge where the airflow velocity reaches zero and total pressure equals free-stream total pressure.
