# 80 - Principles of Flight > Source: exam.quizvds.it (EASA ECQB-SPL) | 95 questions --- ### Q1: With regard to the forces acting, how can stationary gliding be described? ^q1 - A) The sum of air forces acts along the direction of air flow - B) The sum the air forces acts along with the lift force - C) The lift force compensates the drag force - D) The sum of air forces compensates the gravity force **Correct: D)** > **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. ### Q2: What is the result of extending flaps with increasing aerofoil camber? ^q2 - A) Maximum permissable speed increases - B) Minimum speed increases - C) Minimum speed decreases - D) C.G. position moves forward **Correct: C)** > **Explanation:** Extending flaps increases wing camber, which raises the maximum lift coefficient (CL_max). From the stall speed formula Vs = sqrt(2W / (rho * S * CL_max)), 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. ### Q3: Stabilization around the lateral axis during cruise is achieved by the... ^q3 - A) Wing flaps. - B) Horizontal stabilizer - C) Airlerons. - D) Vertical rudder **Correct: B)** > **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. ### Q4: All aerodynamic forces can be considered to act on a single point. This point is called... ^q4 - A) Center of gravity. - B) Lift point. - C) Transition point. - D) Center of pressure. **Correct: D)** > **Explanation:** The center of pressure (CP) is the single point on an aerofoil through which the resultant of all distributed aerodynamic pressure forces acts. It is analogous to the center of gravity for weight distribution. The CP moves with angle of attack — generally forward as AoA increases toward the critical angle. The center of gravity is where weight acts, not aerodynamic forces; the transition point is where the boundary layer changes from laminar to turbulent. ### Q5: Which point on the aerofoil is represented by number 4? See figure (PFA-009) Siehe Anlage 2 ^q5 - A) Transition point - B) Stagnation point - C) Center of pressure - D) Separation point **Correct: D)** > **Explanation:** Point 4 on the aerofoil diagram (PFA-009) represents the separation point, where the boundary layer detaches from the upper wing surface and turbulent wake forms behind it. This is not the transition point (where laminar flow becomes turbulent), the stagnation point (where airflow splits at the leading edge), or the center of pressure (the resultant aerodynamic force application point). ### Q6: Which point on the aerofoil is represented by number 1? See figure (PFA-009) Siehe Anlage 2 ^q6 - A) Center of pressure - B) Stagnation point - C) Stagnation point - D) Transition point **Correct: B)** > **Explanation:** Point 1 on the aerofoil diagram (PFA-009) is the stagnation point — located at the leading edge where incoming airflow splits, with one stream going over the upper surface and one under the lower surface; velocity here is zero and pressure is at its maximum. The transition point is where laminar flow transitions to turbulent flow, the separation point is where flow detaches from the surface, and the center of pressure is an abstract force application point. ### Q7: What pattern can be found at the stagnation point? ^q7 - A) The boundary layer starts separating on the upper surface of the profile - B) All aerodynamic forces can be considered as attacking at this single point - C) The laminar boundary layer changes into a turbulent boundary layer - D) Streamlines are divided into airflow above and below the profile **Correct: D)** > **Explanation:** The stagnation point is precisely the dividing location where incoming streamlines bifurcate — the streamline that arrives at the stagnation point splits, with air flowing around the upper and lower surfaces separately. At this point, kinetic energy is fully converted to pressure (V = 0, p = p_total). Boundary layer transition (C) occurs further aft on the upper surface; separation (A) is further aft still; aerodynamic forces are considered to act at the center of pressure, not the stagnation point. ### Q8: Which statement about lift and angle of attack is correct? ^q8 - A) Increasing the angle of attack too far may result in a loss of lift and an airflow separation - B) Increasing the angle of attack results in less lift being generated by the aerofoil - C) Decreasing the angle of attack results in more drag being generated by the aerofoil - D) Too large angles of attack can lead to an exponential increase in lift **Correct: A)** > **Explanation:** CL increases approximately linearly with AoA up to the critical angle (typically 15–18° for most aerofoils). Beyond this critical AoA, the adverse pressure gradient on the upper surface causes the boundary layer to separate, destroying the smooth flow and causing a sudden drop in lift (stall) accompanied by a large increase in drag. Lift does not increase exponentially (D), and reducing AoA generally reduces both lift and drag (not increases drag as C suggests). ### Q9: Which statement about the airflow around an aerofoil is correct if the angle of attack increases? ^q9 - A) The stagnation point moves down - B) The center of pressure moves down - C) The center of pressure moves up - D) The stagnation point moves up **Correct: A)** > **Explanation:** As angle of attack increases, the relative airflow meets the wing at a steeper upward angle. The streamline that arrives exactly at the stagnation point shifts downward (toward the lower surface of the leading edge), because more airflow is now directed over the upper surface. Simultaneously, the centre of pressure moves forward (not up or down — it moves chordwise), and the suction on the upper surface increases as flow accelerates more strongly over the curved upper side. ### Q10: Pressure compensation on an wing occurs at the... ^q10 - A) Wing tips. - B) Leading edge. - C) Trailing edge. - D) Wing roots **Correct: A)** > **Explanation:** High pressure below the wing and low pressure above create a tendency for air to flow around the wingtip from the high-pressure lower surface to the low-pressure upper surface. This spanwise flow wraps around the wingtip, creating trailing vortices (wingtip vortices). These vortices are the physical mechanism of induced drag — they impart a downward component (downwash) to the oncoming flow, effectively reducing the local angle of attack and tilting the lift vector rearward, creating an induced drag component. ### Q11: Which of the following options is likely to produce large induced drag? ^q11 - A) Large aspect ratio - B) Small aspect ratio - C) Low lift coefficients - D) Tapered wings **Correct: B)** > **Explanation:** Induced drag is proportional to CL^2 / (pi * AR * e), where AR is aspect ratio and e is Oswald efficiency factor. A small aspect ratio (short, stubby wing) produces high induced drag for a given lift coefficient because the wingtip vortices are strong relative to the span. Conversely, high aspect ratio (long, slender) wings minimise induced drag — hence gliders use very high AR wings. Low CL (option C) would reduce induced drag, not increase it. ### Q12: Pressure drag, interference drag and friction drag belong to the group of the... ^q12 - A) Parasite drag - B) Main resistance. - C) Induced drag. - D) Total drag. **Correct: A)** > **Explanation:** Total drag = parasite drag + induced drag. Parasite drag encompasses all drag not associated with lift production: skin friction drag (viscous shear on surfaces), form/pressure drag (pressure difference between leading and trailing edges due to boundary layer separation), and interference drag (junction effects). Induced drag is separately caused by the lift generation process itself (wingtip vortices and downwash). Parasite drag increases with V^2, while induced drag decreases with V^2. ### Q13: Which kinds of drag contribute to total drag? ^q13 - A) Interference drag and parasite drag - B) Induced drag and parasite drag - C) Induced drag, form drag, skin-friction drag - D) Form drag, skin-friction drag, interference drag **Correct: B)** > **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 C and D list sub-components of parasite drag but omit induced drag or incorrectly combine them. Option A omits induced drag, which is a major component especially at low speeds. ### Q14: In case of a stall it is important to... ^q14 - A) Increase the angle of attack and increase the speed. - B) Decrease the angle of attack and increase the speed. - C) Increase the angle of attack and reduce the speed. - D) Increase the bank angle and reduce the speed. **Correct: B)** > **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 (A, C) deepens the stall. Reducing speed (C, D) worsens the condition. Banking (D) increases the load factor, which raises the stall speed — exactly the wrong input. ### Q15: What types of boundary layers can be found on an aerofoil? ^q15 - A) Laminar boundary layer along the complete upper surface with non-separated airflow - B) Turbulent layer at the leading wing areas, laminar boundary layer at the trailing areas - C) Turbulent boundary layer along the complete upper surface with separated airflow - D) Laminar layer at the leading wing areas, turbulent boundary layer at the trailing areas **Correct: D)** > **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. ### Q16: Which constructive feature is shown in the figure? See figure (PFA-006) L: Lift Siehe Anlage 4 ^q16 - A) Lateral stability by wing dihedral - B) Differential aileron deflection - C) Directional stability by lift generation - D) Longitudinal stability by wing dihedral **Correct: A)** > **Explanation:** Wing dihedral — the upward V-angle of the wings relative to the horizontal — provides lateral (roll) stability. When one wing drops, the dihedral geometry increases the angle of attack and lift on the lower wing, producing a restoring roll moment. This is a geometric/structural feature, not related to differential aileron deflection or directional stability. ### Q17: "Longitudinal stability" is referred to as stability around which axis? ^q17 - A) Lateral axis - B) Propeller axis - C) Longitudinal axis - D) Vertical axis **Correct: A)** > **Explanation:** Longitudinal stability refers to the aircraft's tendency to maintain or return to its trimmed pitch attitude, which is rotation around the lateral axis (the axis running wingtip to wingtip). The propeller axis is not a standard stability axis; the longitudinal axis governs roll (lateral stability); the vertical axis governs yaw (directional stability). ### Q18: Rotation around the vertical axis is called... ^q18 - A) Slipping. - B) Pitching. - C) Yawing. - D) Rolling. **Correct: C)** > **Explanation:** Yawing is defined as rotation around the vertical (yaw) axis, producing a nose-left or nose-right movement. Pitching is rotation around the lateral axis, rolling is rotation around the longitudinal axis, and slipping is a lateral flight condition — not a rotational axis term. ### Q19: Rotation around the lateral axis is called... ^q19 - A) Yawing. - B) Pitching. - C) Rolling. - D) Stalling. **Correct: B)** > **Explanation:** Pitching is rotation around the lateral axis (wingtip to wingtip), causing the nose to move up or down. Yawing is rotation around the vertical axis, rolling is rotation around the longitudinal axis, and stalling is an aerodynamic phenomenon — not an axis of rotation. ### Q20: The elevator moves an aeroplane around the... ^q20 - A) Vertical axis. - B) Longitudinal axis. - C) Elevator axis. - D) Lateral axis. **Correct: D)** > **Explanation:** The elevator controls pitch, which is rotation around the lateral axis. By deflecting the elevator up or down, the tailplane generates a pitching moment that raises or lowers the nose. The vertical axis governs yaw (rudder), the longitudinal axis governs roll (ailerons), and an 'elevator axis' is not a standard aeronautical term. ### Q21: What has to be considered with regard to the center of gravity position? ^q21 - A) By moving the elevator trim tab, the center of gravity can be shifted into a correct position. - B) Only correct loading can assure a correct and safe center of gravity position. - C) The center of gravity's position can only be determined during flight. - D) By moving the aileron trim tab, the center of gravity can be shifted into a correct position. **Correct: B)** > **Explanation:** Only correct loading of the aircraft — placing occupants and baggage within the approved limits — can ensure the center of gravity (CG) remains within the certified forward and aft limits. Trim tabs adjust aerodynamic balance in flight but cannot physically move the CG; aileron trim tabs control roll, not pitch CG; and the CG must be verified before flight, not determined during it. ### Q22: What is the advantage of differential aileron movement? ^q22 - A) The drag of the downwards deflected aileron is lowered and the adverse yaw is smaller - B) The total lift remains constant during aileron deflection - C) The ratio of the drag coefficient to lift coefficient is increased - D) The adverse yaw is higher **Correct: A)** > **Explanation:** Differential aileron movement deflects the down-going aileron less than the up-going aileron, which reduces the additional induced drag on the descending wing. This reduces adverse yaw — the unwanted yaw opposite to the intended roll direction — making coordinated turns easier. It does not keep total lift constant during aileron deflection, and it decreases, not increases, the drag-to-lift ratio. ### Q23: The aerodynamic rudder balance... ^q23 - A) Reduces the control surfaces. - B) Delays the stall. - C) Reduces the control stick forces. - D) Improves the rudder effectiveness. **Correct: C)** > **Explanation:** An aerodynamic rudder balance (also called a horn balance or set-back hinge) places part of the control surface ahead of the hinge line, so aerodynamic forces partly assist the pilot's input, thereby reducing the stick/pedal forces required. It does not reduce the size of the control surface, delay stall, or improve rudder effectiveness per se. ### Q24: What is the function of the static rudder balance? ^q24 - A) To prevent control surface flutter - B) To trim the controls almost without any force - C) To increase the control stick forces - D) To limit the control stick forces **Correct: A)** > **Explanation:** A static (mass) balance places counterweights ahead of the hinge line to bring the control surface's center of mass to or forward of the hinge line. This prevents control surface flutter, which is a potentially destructive resonant oscillation. It is not designed to enable trimming without force, increase stick forces, or limit stick forces. ### Q25: The trim tab at the elevator is defelected upwards. In which position is the corresponding indicator? ^q25 - A) Neutral position - B) Nose-down position - C) Nose-up position - D) Laterally trimmed **Correct: B)** > **Explanation:** When the elevator trim tab is deflected upward, it generates a downward aerodynamic force on the trailing edge of the elevator, pushing the elevator leading edge up — this produces a nose-down pitching moment. The indicator therefore shows a nose-down (forward) position. Upward trim tab deflection does not result in a neutral, nose-up, or lateral trim indication. ### Q26: Point number 1 in the figure indicates which flight state? See figure (PFA-008) Siehe Anlage 5 ^q26 - A) Inverted flight - B) Slow flight - C) Stall - D) Best gliding angle **Correct: A)** > **Explanation:** Point 1 in figure PFA-008 represents inverted flight, where the lift polar shows a negative lift coefficient with the aircraft flying upside down. Slow flight, stall, and best gliding angle all correspond to positive (upright) portions of the polar curve, not the inverted segment. ### Q27: In a co-ordinated turn, how is the relation between the load factor (n) and the stall speed (Vs)? ^q27 - A) N is smaller than 1, Vs is greater than in straight and level flight. - B) N is greater than 1, Vs is smaller than in straight and level flight. - C) N is greater than 1, Vs is greater than in straight and level flight. - D) N is smaller than 1, Vs is smaller than in straight and level flight. **Correct: C)** > **Explanation:** In a coordinated (banked) turn, the lift vector must support both the vertical component (equal to weight) and provide the centripetal force for the turn, so total lift — and hence load factor n — exceeds 1. The higher effective weight means the wing must produce more lift to avoid descending, raising the stall speed Vs above its straight-and-level value. Options with n less than 1 or Vs decreasing are incorrect. ### Q28: The pressure compensation between wind upper and lower surface results in ... ^q28 - A) Induced drag by wing tip vortices - B) Laminar airflow by wing tip vortices. - C) Profile drag by wing tip vortices. - D) Lift by wing tip vortices. **Correct: A)** > **Explanation:** The higher pressure beneath the wing and lower pressure above create a pressure differential. At the wingtips, air flows from the high-pressure lower surface around to the low-pressure upper surface, forming trailing vortices. These vortices tilt the local airflow downward (downwash), effectively reducing the angle of attack and creating induced drag — not laminar flow, profile drag, or additional lift. ### Q29: At stationary glide and the same mass, what is the difference when using a thick airfoild instead of a thinner airfoil? ^q29 - A) More drag, same lift - B) Less drag, less lift - C) More drag, less lift - D) Less drag, same lift **Correct: A)** > **Explanation:** At the same mass and in steady glide, lift equals weight regardless of airfoil thickness, so lift remains the same. However, a thicker airfoil has greater form (pressure) drag due to its larger frontal area and more adverse pressure gradients, resulting in more drag with the same lift. ### Q30: What is shown by a profile polar? ^q30 - A) Ratio between minimum rate of descent and best glide - B) Ratio between total lift and drag depending on angle of attack - C) Ratio of cA and cD at different angles of attack - D) Lift coefficient cA at different angles of attack **Correct: C)** > **Explanation:** A profile polar (Lilienthal polar) plots the lift coefficient (cA) against the drag coefficient (cD) for a wing profile at various angles of attack. It directly shows the relationship between cA and cD across the operating range. It is not a polar of minimum sink versus best glide, nor does it show total aircraft lift or drag independently. ### Q31: Following a single-wing stall and pitch-down moment, how can a spin be prevented? ^q31 - A) Deflect all rudders opposite to lower wing - B) Rudder opposite lower wing, releasing elevator to build up speed - C) Pushing the elevator to build up speed to re-attach airflow on wings - D) Pulling the elevator to bring the plane back to normal attitude **Correct: B)** > **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 (D) would increase AoA and deepen the stall; pushing alone (C) without rudder does not stop the yaw. ### Q32: Flying with speeds higher than the never-exceed-speed (vNE) may result in... ^q32 - A) Reduced drag with increased control forces. - B) An increased lift-to-drag ratio and a better glide angle. - C) Too high total pressure resulting in an unusable airspeed indicator. - D) Flutter and mechanically damaging the wings. **Correct: D)** > **Explanation:** VNE is the red-line speed above which structural or aeroelastic failure becomes possible. At excessive speeds, dynamic pressure (q = 0.5 * rho * V^2) rises dramatically, and control surfaces and wing structures may enter flutter — a self-reinforcing oscillation where aerodynamic forces and structural elasticity feed each other, potentially causing rapid structural disintegration. The airspeed indicator remains usable at high speeds; glide ratio does not improve beyond the best-glide speed. ### Q33: If surrounded by airflow (v>0), any arbitrarily shaped body produces... ^q33 - A) Drag and lift. - B) Drag. - C) Lift without drag. - D) Constant drag at any speed. **Correct: B)** > **Explanation:** Any body immersed in a moving fluid (v > 0) will produce drag due to pressure and friction forces opposing the flow. Only specially shaped (lifting) bodies oriented appropriately produce lift; an arbitrarily shaped body has no guaranteed lift but always produces drag. Drag is also not constant — it increases with the square of velocity. ### Q34: Number 3 in the drawing corresponds to the... See figure (PFA-010) Siehe Anlage 1 ^q34 - A) Camber line. - B) Thickness. - C) Chord. - D) Chord line. **Correct: A)** > **Explanation:** In an aerofoil diagram (PFA-010), line 3 represents the camber line (mean camber line), which is the locus of points midway between the upper and lower surfaces. The chord is the straight line from leading to trailing edge, the chord line is the same geometric reference, and thickness is the vertical distance between upper and lower surfaces at any chordwise station. ### Q35: In which way does the position of the center of pressure move at a positively shaped profile with increasing angle of attack? ^q35 - A) It moves to the wing tips - B) It moves forward until reaching the critical angle of attack - C) It moves forward until reaching the critical angle of attack - D) It moves forward first, then backward **Correct: B)** > **Explanation:** As angle of attack increases, the suction peak on the upper surface intensifies and moves toward the leading edge, causing the center of pressure to migrate forward. This continues until the critical (stall) angle of attack is reached. Beyond the stall, the suction peak collapses as flow separates, and the center of pressure moves abruptly rearward. The forward movement of the CP with increasing AoA is important for stability analysis and contributes to the pitching moment characteristics of the aerofoil. ### Q36: Which statement about the airflow around an aerofoil is correct if the angle of attack decreases? ^q36 - A) The center of pressure moves aft - B) The center of pressure moves forward - C) The stagnation point moves down - D) The stagnation point remains constant **Correct: A)** > **Explanation:** As angle of attack decreases, the aerodynamic loading on the forward portion of the upper surface diminishes, shifting the resultant pressure force rearward — so the center of pressure moves aft (toward the trailing edge). The stagnation point also moves upward (not down) as less flow is forced over the upper surface. Understanding CP movement is important because it affects the pitching moment balance of the aircraft throughout the flight envelope. ### Q37: Which statement concerning the angle of attack is correct? ^q37 - A) Increasing the angle of attack results in decreasing lift - B) The angle of attack cannot be negative - C) A too large angle of attack may result in a loss of lift - D) The angle of attack is constant throughout the flight **Correct: C)** > **Explanation:** AoA can be negative (when the chord line points downward relative to the freestream, some aerofoils still generate positive lift due to camber, but very negative AoA produces negative lift). AoA continuously changes in flight as the pilot adjusts pitch and as airspeed changes. Within the normal range, increasing AoA increases lift — but beyond the critical angle (typically ~15°), flow separation destroys lift. Option C correctly identifies this upper limit of AoA beyond which lift collapses. ### Q38: When increasing the airflow speed by a factor of 2 while keeping all other parameters constant, how does the parasite drag change approximately? ^q38 - A) It decreases by a factor of 2 - B) It increases by a factor of 2 - C) It decreases by a factor of 4 - D) It increases by a factor of 4 **Correct: D)** > **Explanation:** Parasite drag follows the formula D_parasite = CD_p * 0.5 * rho * V^2 * S. Since dynamic pressure q = 0.5 * rho * V^2 is proportional to V^2, doubling the speed (V × 2) quadruples dynamic pressure (2^2 = 4), and thus quadruples parasite drag. This square-law relationship is fundamental: halving your speed reduces parasite drag by a factor of four, while doubling speed costs four times as much drag — which is why high-speed flight is energetically expensive. ### Q39: The drag coefficient... ^q39 - A) Is proportional to the lift coefficient - B) Increases with increasing airspeed. - C) May range from zero to an infinite positive value - D) Cannot be lower than a non-negative, minimal value. **Correct: D)** > **Explanation:** Every aerofoil has a minimum drag coefficient (CD_min) greater than zero, because skin friction and form drag exist even at the optimal low-drag AoA. The drag coefficient cannot reach zero for a real body in viscous flow — there is always some irreducible friction drag. It can increase without bound as AoA increases (especially post-stall), but has a finite positive minimum. The drag polar (CD vs CL curve) shows CD_min as the lowest point of the parabolic curve. ### Q40: Which parts of an aircraft mainly affect the generation of induced drag? ^q40 - A) The front part of the fuselage. - B) The outer part of the ailerons. - C) The lower part of the gear. - D) The wing tips. **Correct: D)** > **Explanation:** Induced drag originates from the pressure difference between the upper and lower wing surfaces causing spanwise flow that rolls up into concentrated vortices at the wingtips. The strength of these vortices — and thus the induced drag — is directly related to what happens at the wingtips. This is why winglets, raked wingtips, and elliptical planforms are used to reduce wingtip vortex strength. The fuselage, ailerons, and landing gear primarily generate parasite drag, not induced drag. ### Q41: Where is interference drag generated? ^q41 - A) At the ailerons - B) At the the gear - C) At the wing root - D) Near the wing tips **Correct: C)** > **Explanation:** Interference drag occurs where two surfaces meet and their boundary layers interact, creating turbulence and additional drag beyond what each surface would produce in isolation. The wing-fuselage junction (wing root) is the classic location: the boundary layers from the fuselage and wing interfere, creating complex flow that increases total drag. Fairings and fillets are used at wing roots to smooth this junction and reduce interference drag. The landing gear generates form drag, not interference drag specifically. ### Q42: Which of the listed wing shapes has the lowest induced drag? ^q42 - A) Rectangular shape - B) Trapezoidal shape - C) Elliptical shape - D) Double trapezoidal shape **Correct: C)** > **Explanation:** The elliptical wing planform produces the minimum possible induced drag for a given span and total lift. This is because it creates a perfectly elliptical spanwise lift distribution, which results in a uniform downwash across the span — the theoretical optimum. An elliptical distribution means no "wasteful" concentration of lift near the root or sudden drops near the tips. The Spitfire used an elliptical wing for this reason. Tapered (trapezoidal) wings approximate this and are easier to manufacture; rectangular wings have higher induced drag. ### Q43: Which design feature can compensate for adverse yaw? ^q43 - A) Which design feature can compensate for adverse yaw? - B) Differential aileron defletion - C) Full deflection of the aileron - D) Wing dihedral **Correct: B)** > **Explanation:** Adverse yaw is the tendency of the nose to yaw away from the intended turn direction when ailerons are applied. Differential aileron deflection (the down aileron moves less than the up aileron) reduces the extra drag on the descending wing, thereby reducing the adverse yaw moment. Wing dihedral addresses roll stability, not yaw; full aileron deflection would worsen adverse yaw. ### Q44: What describes "wing loading"? ^q44 - A) Wing area per weight - B) Drag per weight - C) Weight per wing area - D) Drag per wing area **Correct: C)** > **Explanation:** Wing loading is defined as the aircraft's weight (mass times gravity) divided by the wing reference area, expressed in N/m² or kg/m². It is not wing area per weight (that would be the inverse), nor is it related to drag. ### Q45: Point number 5 in the figure indicates which flight state? See figure (PFA-008) Siehe Anlage 5 ^q45 - A) Slow flight - B) Best gliding angle - C) Inverted flight - D) Stall **Correct: A)** > **Explanation:** Point 5 in figure PFA-008 corresponds to slow flight — a low speed, high angle-of-attack condition on the positive portion of the polar, before stall onset. Inverted flight would appear on the negative lift side, stall at the maximum cA point, and best gliding angle at the cA/cD maximum point. ### Q46: Extending airbrakes results in ... ^q46 - A) Less drag and more lift. - B) More drag and less lift. - C) More drag and more lift. - D) Less drag and less lift. **Correct: B)** > **Explanation:** Extending airbrakes (spoilers/dive brakes) significantly increases profile drag, which is their primary purpose for steepening the glide path. They also partially disrupt upper-surface lift, reducing the total lift generated. The other combinations (less drag, more lift, etc.) are aerodynamically incorrect for airbrake deployment. ### Q47: The glide ratio of a sailplane can be improved by which measures? ^q47 - A) Higher airplane mass, thin airfoil, taped gaps between wing and fuselage - B) Lower airplane mass, correct speed, retractable gear - C) Cleaning, correct speed, retractable gear, taped gaps between wing and fuselage - D) Forward C.G. position, correct speed, taped gaps between wing and fuselage **Correct: C)** > **Explanation:** Glide ratio (L/D) is maximized by minimizing drag and maintaining the optimum speed. Cleaning the aircraft and taping gaps reduces surface roughness and leakage drag; maintaining the correct (best-glide) speed keeps the aircraft at peak L/D; a retractable undercarriage removes a major source of parasite drag. Higher mass shifts the polar but does not change the maximum L/D ratio itself. A forward CG can actually increase trim drag. ### Q48: What is the diffeence between spin and spiral dive? ^q48 - A) Spin: stall at inner wing, speed increasing rapidly; Spiral dive: airflow at both wings, speed constant - B) Spin: stall at inner wing, speed constant; Spiral dive: airflow at both wings, speed increasing rapidly - C) Spin: stall at outer wing, speed constant; Spiral dive: airflow at both wings, speed increasing rapidly - D) Spin: stall at outer wing, speed increasing rapidly; Spiral dive: airflow at both wings, speed constant **Correct: B)** > **Explanation:** In a spin, one wing is stalled (typically the inner wing) while the other continues to fly, so the aircraft autorotates and descends at near-constant airspeed. In a spiral dive, both wings are flying (neither is stalled), and the aircraft enters an ever-steepening banked dive with rapidly increasing airspeed. Confusing the two is dangerous — recovery techniques differ fundamentally. ### Q49: The angle of attack is the angle between... ^q49 - A) The chord line and the longitudinal axis of an aeroplane. - B) The chord line and the oncoming airflow. - C) The wing and the fuselage of an aeroplane - D) The undisturbed airflow and the longitudinal axis of an aeroplane. **Correct: B)** > **Explanation:** Angle of attack (AoA, alpha) is precisely defined as the angle between the aerofoil chord line and the direction of the undisturbed (relative) freestream airflow. It is the primary determinant of lift coefficient: CL increases with AoA until the critical (stall) angle. AoA must not be confused with pitch attitude (angle between longitudinal axis and horizon) — a glider descending nose-down can still have a positive AoA if the relative airflow comes from below the chord line. ### Q50: The ratio of span and mean chord length is referred to as... ^q50 - A) Trapezium shape. - B) Tapering. - C) Aspect ratio. - D) Wing sweep. **Correct: C)** > **Explanation:** Aspect ratio (AR) = wingspan (b) / mean chord (c) = b^2 / S, where S is wing area. High aspect ratio wings (long, narrow) produce less induced drag because the wingtip vortices are proportionally weaker relative to the total span. Gliders have very high aspect ratios (typically 20–40) for this reason — minimising induced drag is essential for maximum glide ratio. Low-aspect-ratio wings produce more induced drag but are structurally lighter and more agile. ### Q51: Stability around which axis is mainly influenced by the center of gravity's longitudinal position? ^q51 - A) Longitudinal axis - B) Lateral axis - C) Gravity axis - D) Vertical axis **Correct: B)** > **Explanation:** The longitudinal position of the center of gravity directly determines the pitch stability, which is stability around the lateral axis. A CG forward of the neutral point provides positive (restoring) pitch stability; too far aft reduces or reverses it. Lateral stability is mainly influenced by wing dihedral, and directional stability by the vertical tail. ### Q52: What structural item provides directional stability to an airplane? ^q52 - A) Differential aileron deflection - B) Wing dihedral - C) Large elevator - D) Large vertical tail **Correct: D)** > **Explanation:** A large vertical tail fin acts as a weathervane, generating a restoring yawing moment whenever the aircraft sideslips, thereby providing directional (yaw) stability. Wing dihedral provides lateral (roll) stability; differential aileron deflection reduces adverse yaw; a large elevator contributes to pitch stability, not directional stability. ### Q53: The critical angle of attack... ^q53 - A) Decreases with forward center of gravity position. - B) Changes with increasing weight. - C) Is independent of the weight. - D) Increases with backward center of gravity position. **Correct: C)** > **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. ### Q54: In straight and level flight with constant performance of the engine, the angle of attack at the wing is... ^q54 - A) Smaller than in a descent. - B) Greater than in a climb. - C) Greater than at take-off. - D) Smaller than in a climb. **Correct: D)** > **Explanation:** In straight and level flight at constant engine power, the aircraft flies at a fixed speed and the wing operates at a specific angle of attack. In a climb at the same power, airspeed is lower (more energy goes into altitude gain), so the wing needs a higher angle of attack to generate sufficient lift. Therefore, the level-flight angle of attack is smaller than in a climb. ### Q55: What is the function of the horizontal tail (among other things)? ^q55 - A) To stabilise the aeroplane around the longitudinal axis - B) To stabilise the aeroplane around the lateral axis - C) To initiate a curve around the vertical axis - D) To stabilise the aeroplane around the vertical axis **Correct: B)** > **Explanation:** The horizontal tail (stabilizer and elevator) provides pitch stability — resistance to and recovery from pitch disturbances — which is stability around the lateral axis. It does not primarily provide lateral (roll) axis stability (that is the wing dihedral's role), nor does it initiate turns around the vertical axis or stabilize around the vertical axis. ### Q56: Deflecting the rudder to the left causes... ^q56 - A) Pitching of the aircraft to the left - B) Yawing of the aircraft to the left. - C) Pitching of the aircraft to the right. - D) Yawing of the aircraft to the right. **Correct: B)** > **Explanation:** The rudder deflects left, generating a leftward aerodynamic force on the tail, which yaws the nose to the left around the vertical axis. Pitching (nose up/down) is a movement around the lateral axis controlled by the elevator, not the rudder. ### Q57: Differential aileron deflection is used to... ^q57 - A) Reduce wake turbulence. - B) Avoid a stall at low angles of attack. - C) Keep the adverse yaw low. - D) Increase the rate of descent. **Correct: C)** > **Explanation:** Differential aileron deflection reduces adverse yaw — the undesired nose movement opposite to the roll direction — by giving the down-going aileron less deflection, thereby reducing the extra induced drag on the descending wing. It is not used to reduce wake turbulence, prevent stalls, or increase the rate of descent. ### Q58: How is the balance of forces affected during a turn? ^q58 - A) A lower lift force compensates for a lower net force as compared to level flight - B) Lift force must be increased to compensate for the sum of centrifugal and gravitational force - C) The horizontal component of the lift force during a turn is the centrifugal force - D) The net force results from superposition of gravity and centripetal forces **Correct: B)** > **Explanation:** In a banked turn, the lift vector is tilted sideways, so its vertical component is less than the total lift. To maintain altitude, the pilot must increase total lift above the straight-and-level value. The increased lift must balance both the weight (vertical component) and provide centripetal force (horizontal component). Load factor n = 1/cos(bank angle) and is always greater than 1 in a level turn. ### Q59: What engine design at a Touring Motor Glider (TMG) results in least drag? ^q59 - A) Engine and propeller mounted fix on the fuselage - B) Engine and propeller mounted stowable on the fuselage - C) Engine and propeller mounted fix at the aircraft's nose - D) Engine and propeller mounted fix at the horizontal stabilizer **Correct: B)** > **Explanation:** A retractable (stowable) engine and propeller arrangement on a TMG allows the powerplant to be fully folded into the fuselage when not in use, eliminating all associated parasite drag and enabling pure glider performance. Fixed nose- or tail-mounted engines and fixed fuselage mounts all produce significant drag even when the engine is off. ### Q60: What effect is referred to as "adverse yaw"? ^q60 - A) Aileron operation results in a yaw to the desired side due to less drag at the down-deflected aileron - B) Rudder operation results in a rolling moment to the opposite side due to more lift generated by the faster moving wing. - C) Aileron operation results in a yaw to the opposite side due to more drag at the up-deflected aileron - D) Aileron operation results in a yaw to the opposite side due to more drag at the down-deflected aileron **Correct: D)** > **Explanation:** Adverse yaw occurs because deflecting the ailerons asymmetrically changes the induced drag on each wing. The down-deflected aileron increases lift and — more importantly — also increases induced drag on that wing. This extra drag on the rising wing yaws the nose toward the descending wing, opposite to the intended direction of roll. Option C is incorrect because it states 'up-deflected aileron' causes more drag. ### Q61: What is meant by "ground effect"? ^q61 - A) Decrease of lift and increase of induced drag close to the ground - B) Increase of lift and decrease of induced drag close to the ground - C) Increase of lift and increase of induced drag close to the ground - D) Decrease of lift and decrease of induced drag close to the ground **Correct: B)** > **Explanation:** Close to the ground, the ground surface restricts the downward development of wing-tip vortices. This reduces the induced downwash angle, which effectively increases the local angle of attack and thus lift, while simultaneously reducing induced drag. At altitude, vortices develop freely, downwash is stronger, and induced drag is higher. ### Q62: What pressure pattern can be observed at a lift-generating wing profile at positive angle of attack? ^q62 - A) Low pressure is created above, higher pressure below the profile - B) Pressure above remains unchanged, higher pressure is created below the profile - C) High pressure is created above, lower pressure below the profile - D) Pressure below remains unchanged, lower pressure is created above the profile **Correct: A)** > **Explanation:** Lift is generated by a pressure differential: lower pressure on the upper (suction) surface and higher pressure on the lower surface. On the upper surface, flow accelerates around the curved upper side — by Bernoulli's principle, higher velocity means lower static pressure. On the lower surface, flow is slowed and compressed, increasing static pressure. The net upward pressure force integrated over the entire surface constitutes lift: L = CL * 0.5 * rho * V^2 * S. ### Q63: In order to improve the stall characteristics of an aircraft, the wing is twisted outwards (the angle of incidence varies spanwise). This is known as... ^q63 - A) Arrow shape. - B) V-form - C) Geometric washout. - D) Aerodynamic washout. **Correct: C)** > **Explanation:** Geometric washout means the wing is physically twisted so that the angle of incidence (and thus the local angle of attack) decreases from root to tip. This ensures that the wing root reaches the critical stall angle before the wingtips, so the ailerons (located outboard) remain effective even as the inboard section stalls. This gives the pilot aileron control during the approach to stall, enabling better roll control and safer stall behaviour. Aerodynamic washout (D) achieves the same effect through changing aerofoil sections rather than physical twist. ### Q64: During a stall, the lift... ^q64 - A) Decreases and drag increases. - B) Increases and drag increases. - C) Decreases and drag decreases - D) Increases and drag decreases. **Correct: A)** > **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. ### Q65: Which statement regarding a spin is correct? ^q65 - A) During recovery the ailerons should be kept neutral - B) During the spin the speed constantly increases - C) During recovery the ailerons should be crossed - D) Only very old aeroplanes have a risk of spinning **Correct: A)** > **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. ### Q66: What structural item provides lateral stability to an airplane? ^q66 - A) Wing dihedral - B) Vertical tail - C) Differential aileron deflection - D) Elevator **Correct: A)** > **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. ### Q67: Rudder deflections result in a turn of the aeroplane around the... ^q67 - A) Rudder axis. - B) Vertical axis. - C) Lateral axis - D) Longitudinal axis. **Correct: B)** > **Explanation:** The rudder is the primary yaw control, rotating the aircraft around the vertical axis. Rudder deflection generates a sideways aerodynamic force on the fin/rudder assembly, which yaws the nose left or right. The lateral axis governs pitch (elevator), and the longitudinal axis governs roll (ailerons). ### Q68: Through which factor listed below does the load factor increase during cruise flight? ^q68 - A) Lower air density - B) A forward centre of gravity - C) Higher aeroplane weight - D) An upward gust **Correct: D)** > **Explanation:** An upward gust suddenly increases the aircraft's angle of attack, momentarily generating more lift than needed for level flight — this additional lift acts as a load on the structure, increasing the load factor n above 1. Lower air density reduces lift (would decrease, not increase, load factor at the same speed); CG position and weight affect handling but not the instantaneous load factor from a gust. ### Q69: During approch to the next updraft, the vertical speed indicator reads 3 m/s descent. Within the updraft you expect a mean rate of climb of 2 m/s. According McCready, how should you adjust the speed during approach of the updraft? ^q69 - A) The McCready ring should be set to 2 m/s, the recommended speed can be read at the McCready scale next to the sum of current rate of descent at expected rate of climb (5 m/s). - B) The McCready ring should be set to 3 m/s, the recommended speed can be read at the McCready scale next to the expected rate of climb (2 m/s). - C) The McCready ring should be set to 2 m/s, the recommended speed can be read at the McCready scale next to the current rate of descent (3 m/s). - D) Outside of thermal cells, the McCready ring should be set to 0 m/s, the recommended speed can be read at the McCready scale next to the current rate of descent (3 m/s). **Correct: C)** > **Explanation:** The McCready ring is set to the expected climb rate in the next thermal (2 m/s), and the pilot reads the recommended inter-thermal cruise speed at the point on the variometer scale corresponding to the current sink rate (3 m/s). Setting the ring to the current sink rate (3 m/s) would be incorrect; the ring is always set to the anticipated thermal strength. ### Q70: What has to be considered when operating a sailplane equipped with camper flaps? ^q70 - A) During approach and landing, camber must not be changed from negative to positive. - B) During approach and landing, camber must not be changed from positive to negative. - C) During winch launch, camber must be set to full negative. - D) During winch launch, camber must be set to full positive. **Correct: B)** > **Explanation:** During approach and landing, changing the camber flap setting from positive (increased camber) to negative (reduced or reflexed camber) would dramatically reduce lift and could lead to an abrupt loss of lift very close to the ground — a potentially fatal situation. Positive camber should be maintained throughout the approach. Negative camber settings are typically used only for high-speed cruise. ### Q71: Considering longitudinal stability, which C.G. position is most dangerous with a normal gliding plane? ^q71 - A) Position beyond the front C.G. limit - B) Position too far aside permissable C.G. limits. - C) Position far back within permissable C.G. limits - D) Position beyond the rear C.G. limit **Correct: D)** > **Explanation:** Longitudinal (pitch) stability requires the centre of gravity to be ahead of the neutral point. When the C.G. moves aft beyond the rear limit, the static margin becomes negative: a pitch disturbance produces a moment that amplifies rather than corrects the disturbance, making the aircraft unstable and potentially uncontrollable. A forward C.G. (A) increases stability but requires more elevator force — it is uncomfortable but recoverable. Rearward C.G. beyond limits is the most dangerous condition because recovery from pitch divergence may be impossible. ### Q72: The static pressure of gases work... ^q72 - A) In all directions. - B) Only in flow direction. - C) Only in the direction of the total pressure. - D) Only vertical to the flow direction. **Correct: A)** > **Explanation:** Static pressure is a scalar thermodynamic quantity representing the random kinetic energy of gas molecules. Because molecular collisions occur in all directions equally, static pressure acts omnidirectionally — it presses equally on all surfaces of a container regardless of orientation. This contrasts with dynamic pressure (q = 0.5 * rho * V^2), which is directional and associated with the bulk flow velocity. Bernoulli's equation combines both: p_total = p_static + q. ### Q73: Bernoulli's equation for frictionless, incompressible gases states that... ^q73 - A) Total pressure = dynamic pressure - static pressure. - B) Total pressure = dynamic pressure + static pressure. - C) Static pressure = total pressure + dynamic pressure - D) Dynamic pressure = total pressure + static pressure. **Correct: B)** > **Explanation:** Bernoulli's theorem for an ideal (frictionless, incompressible) fluid along a streamline states that total pressure is conserved: p_total = p_static + 0.5 * rho * V^2. Total pressure is the sum of static pressure and dynamic pressure. Where air accelerates over the upper wing surface, static pressure decreases (dynamic pressure increases) while total pressure remains constant — this pressure difference generates lift. The airspeed indicator works on this principle by measuring the difference between total (pitot) and static pressure. ### Q74: The center of pressure is the theoretical point of origin of... ^q74 - A) Only the resulting total drag. - B) Gravity forces of the profile. - C) All aerodynamic forces of the profile. - D) Gravity and aerodynamic forces. **Correct: C)** > **Explanation:** The center of pressure is defined as the single point through which the entire resultant aerodynamic force — which includes both lift (perpendicular to freestream) and drag (parallel to freestream) — is considered to act. It is not a physical feature of the wing but a mathematical convenience for analysis. Gravity acts through the center of gravity, which is a completely separate point determined by the aircraft's mass distribution. ### Q75: Which point on the aerofoil is represented by number 3? See figure (PFA-009) Siehe Anlage 2 ^q75 - A) Stagnation point - B) Separation point - C) Center of pressure - D) Transition point **Correct: D)** > **Explanation:** Point 3 on the aerofoil diagram (PFA-009) represents the transition point — the location where the boundary layer changes from smooth laminar flow to turbulent flow. The stagnation point is at the leading edge (point 1), the separation point is further aft where flow detaches, and the center of pressure is the theoretical point of resultant lift application. ### Q76: Which option states a benefit of wing washout? ^q76 - A) With the washout the form drag reduces at high speeds - B) Greater hardness because the wing can withstand more torsion forces - C) At high angles of attack the effectiveness of the aileron is retained as long as possible - D) Structurally the wing is made more rigid against rotation **Correct: C)** > **Explanation:** The primary aerodynamic benefit of washout is that the wingtip (where the ailerons are) has a lower angle of incidence than the root, so it reaches its critical stall angle later. When the pilot approaches stall speed and raises the nose to a high AoA, the inboard sections stall first while the outboard/aileron sections remain unstalled and continue to generate lift and respond to aileron inputs. This gives the pilot roll control authority during the stall approach, preventing inadvertent spin entry. ### Q77: Which statement about induced drag during the horizontal cruise flight is correct? ^q77 - A) Induced drag decreases with increasing airspeed - B) Induced drag has a minimum at a certain speed and increases at higher as well as lower speeds - C) Induced drag has a maximum at a certain speed and decreases at higher as well as lower speeds - D) Induced drag increases with increasing airspeed **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. ### Q78: How do lift and drag change when approaching a stall condition? ^q78 - A) Lift decreases and drag increases - B) Lift and drag increase - C) Lift increases and drag decreases - D) Lift and drag decrease **Correct: A)** > **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. ### Q79: What leads to a decreased stall speed Vs (IAS)? ^q79 - A) Lower density - B) Decreasing weight - C) Lower altitude - D) Higher load factor **Correct: B)** > **Explanation:** From Vs = sqrt(2W / (rho * S * CL_max)): stall speed decreases when weight (W) decreases, since less lift is needed to maintain equilibrium. Lower density (A) 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 * V_TAS^2, which equals 0.5 * rho_0 * V_IAS^2). Higher load factor (D) 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. ### Q80: How does a laminar boundary layer differ from a turbulent boundary layer? ^q80 - A) The laminar boundary layer is thinner and provides more skin-friction drag - B) The turbulent boundary layer can follow the airfoil camber at higher angles of attack - C) The laminar boundary layer produces lift, the turbulent boundary layer produces drag - D) The turbulent boundary layer is thicker and provides less skin-friction drag **Correct: B)** > **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 (A 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. ### Q81: Number 2 in the drawing corresponds to the... See figure (PFA-010) Siehe Anlage 1 ^q81 - A) Profile thickness. - B) Chord line. - C) Chord line. - D) Angle of attack. **Correct: C)** > **Explanation:** Number 2 in figure PFA-010 represents the chord line — the straight reference line drawn from the leading edge to the trailing edge of the aerofoil. The profile thickness is the perpendicular distance between upper and lower surfaces, and the angle of attack is the angle between the chord line and the relative airflow direction. ### Q82: The angle (alpha) shown in the figure is referred to as... See figure (PFA-003) DoF: direction of airflow Siehe Anlage 3 ^q82 - A) Lift angle. - B) Angle of attack. - C) Angle of incidence. - D) Angle of inclination **Correct: B)** > **Explanation:** The angle of attack (alpha) is the angle between the chord line of the aerofoil and the relative direction of the oncoming airflow (free-stream velocity vector). It is not the lift angle, which is not a standard aeronautical term; the angle of incidence is the fixed geometric angle between the chord line and the aircraft's longitudinal axis. ### Q83: The right aileron deflects upwards, the left downwards. How does the aircraft react? ^q83 - A) Rolling to the left, no yawing - B) Rolling to the right, yawing to the left - C) Rolling to the left, yawing to the right - D) Rolling to the right, yawing to the right **Correct: B)** > **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 (rising) wing, yawing the nose to the left — this is adverse yaw. Rolling to the left or yawing to the right would be opposite to the aileron input described. ### Q84: What has to be considered when operating a sailplane with water ballast? ^q84 - A) Best glide angle decreases. - B) Significant CG shifts. - C) Best glide speed decreases - D) It should stay below freezing level. **Correct: D)** > **Explanation:** Water ballast must be kept above freezing level to prevent the water from freezing in the wings, which could jam ballast dump valves, shift the CG unpredictably, and damage wing structure. Water ballast increases wing loading and shifts the best-glide speed higher, but the best glide angle (L/D ratio) remains theoretically unchanged. CG shifts with water ballast are typically minor and managed within approved limits. ### Q85: The laminar boundary layer on the aerofoil is located between... ^q85 - A) The stagnation point and the center of pressure. - B) The stagnation point and the transition point. - C) The transition point and the separation point. - D) The transition point and the center of pressure. **Correct: B)** > **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. ### Q86: How do induced drag and parasite drag change with increasing airspeed during a horizontal and stable cruise flight? ^q86 - A) Parasite drag decreases and induced drag increases - B) Induced drag decreases and parasite drag increases - C) Parasite drag decreases and induced drag decreases - D) Induced drag increases and parasite drag increases **Correct: B)** > **Explanation:** In level flight, lift must equal weight, so CL decreases as speed increases (L = CL * 0.5 * rho * V^2 * S = W, thus CL = 2W / (rho * V^2 * S)). Induced drag ∝ CL^2 / V^2 ∝ 1/V^2 — it decreases with increasing speed. Parasite drag ∝ V^2 — it increases with speed. The speed where induced drag equals parasite drag is the speed of minimum total drag, which corresponds to the best lift-to-drag ratio and maximum glide range in a glider. ### Q87: Which effect does a decreasing airspeed have on the induced drag during a horizontal and stable cruise flight? ^q87 - A) The induced drag will slightly decrease - B) The induced drag will collapse - C) The induced drag will increase - D) The induced drag will remain constant **Correct: C)** > **Explanation:** As speed decreases in level flight, the angle of attack must increase to maintain sufficient lift (since CL must increase to compensate for lower dynamic pressure). Higher CL means stronger wingtip vortices and greater induced drag: D_induced ∝ CL^2 ∝ 1/V^2. This is why slow flight is dominated by induced drag — at very low speeds near stall, induced drag is very high and is the main component of total drag, while parasite drag is relatively small. ### Q88: Which statement describes a situation of static stability? ^q88 - A) An aircraft distorted by external impact will return to the original position - B) An aircraft distorted by external impact will tend to an even more deflected position - C) An aircraft distorted by external impact will maintain the deflected position - D) An aircraft distorted by external impact can return to its original position by rudder input **Correct: A)** > **Explanation:** Static stability means that when an aircraft is disturbed from its equilibrium by an external force (e.g., a gust), aerodynamic restoring forces automatically tend to return it toward the original position. An aircraft that moves further away from equilibrium has static instability; one that stays in the displaced position is neutrally stable; active rudder input is a pilot correction, not static stability. ### Q89: A sailplane is operated with additional water ballast. How do best gliding angle and speed of best glide change, when compared to flying without water ballast? ^q89 - A) Best gliding angle descreases, best glide speed decreases. - B) Best gliding angle remains unchanged, best glide speed increases. - C) Best gliding angle remains increases, best glide speed increases. - D) Best gliding angle remains unchanged, best glide speed decreases. **Correct: B)** > **Explanation:** Adding water ballast increases total aircraft weight, which requires flying faster to maintain the lift needed for level flight. The best-glide speed (minimum drag speed) therefore increases. However, the L/D ratio — and hence the best gliding angle — is a geometric property of the wing aerodynamics and remains unchanged for the same aircraft shape; water ballast does not change the aerodynamic efficiency, only the speed at which it is achieved. ### Q90: Which constructive feature has the purpose to reduce stearing forces? ^q90 - A) T-tail - B) Differential aileron deflection - C) Vortex generators - D) Aerodynamic rudder balance **Correct: D)** > **Explanation:** An aerodynamic rudder balance (horn balance or inset hinge) extends part of the control surface ahead of the hinge line. The aerodynamic pressure on this forward portion creates a moment that partially counteracts the hinge moment, reducing the force the pilot must apply to deflect the control surface. The T-tail is a configuration choice affecting downwash; vortex generators delay stall; differential aileron reduces adverse yaw. ### Q91: If surrounded by airflow (v > 0), any arbitrarily shaped body produces... ^q91 - A) Drag and lift. - B) Drag. - C) Lift without drag. - D) Constant drag at any speed. **Correct: B)** > **Explanation:** Any body placed in a moving airstream (v > 0) will experience drag, which is the component of the aerodynamic resultant force parallel to the free-stream direction. This is true regardless of shape. Only specially shaped lifting bodies produce lift; drag is not constant but varies with velocity squared; and lift without drag is physically impossible. ### Q92: Longitudinal stability is referred to as stability around which axis? ^q92 - A) Lateral axis - B) Propeller axis - C) Longitudinal axis - D) Vertical axis **Correct: A)** > **Explanation:** Longitudinal stability describes the aircraft's tendency to maintain or return to a trimmed pitch attitude — rotation around the lateral axis. The lateral axis runs from wingtip to wingtip. The propeller axis is not a stability axis; the longitudinal axis governs roll (lateral stability); the vertical axis governs yaw (directional stability). ### Q93: What describes wing loading? ^q93 - A) Wing area per weight - B) Drag per weight - C) Weight per wing area - D) Drag per wing area **Correct: C)** > **Explanation:** Wing loading = aircraft weight / wing reference area (e.g., N/m² or kg/m²). A higher wing loading means the wing must work harder to generate sufficient lift, resulting in higher stall speeds and better penetration of turbulence. 'Wing area per weight' is the inverse (specific wing area); drag per weight is the drag-to-weight ratio; drag per wing area is not a standard performance metric. ### Q94: What effect is referred to as adverse yaw? ^q94 - A) Aileron operation results in a yaw to the desired side due to less drag at the down-deflected aileron - B) Rudder operation results in a rolling moment to the opposite side due to more lift generated by the faster moving wing. - C) Aileron operation results in a yaw to the opposite side due to more drag at the up-deflected aileron - D) Aileron operation results in a yaw to the opposite side due to more drag at the down-deflected aileron **Correct: D)** > **Explanation:** Adverse yaw results from the asymmetric induced drag created by differential aileron deflection. When the pilot deflects the ailerons to roll, the down-going aileron on the rising wing creates more induced drag than the up-going aileron on the descending wing. This extra drag on the rising wing pulls the nose toward the descending wing — opposite to the intended roll direction. Option C incorrectly attributes adverse yaw to the up-deflected aileron. ### Q95: What is meant by ground effect? ^q95 - A) Decrease of lift and increase of induced drag close to the ground - B) Increase of lift and decrease of induced drag close to the ground - C) Increase of lift and increase of induced drag close to the ground - D) Decrease of lift and decrease of induced drag close to the ground **Correct: B)** > **Explanation:** In ground effect (within approximately one wingspan of the ground), the ground surface physically prevents the wing-tip vortices from fully forming and rolling downward. This reduces induced downwash, increasing the effective angle of attack and thus lift, while simultaneously reducing induced drag. Pilots experience this as a 'cushion' during flare. Options with decreased lift or increased induced drag are aerodynamically incorrect.