# 80 - Principles of Flight > Source: EASA ECQB-SPL (new questions not in existing set) | 52 questions --- ### Q1: Which point on the aerofoil is represented by number 4? See figure (PFA-009) Siehe Anlage 2 ^q1 - 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). ### Q2: Which point on the aerofoil is represented by number 1? See figure (PFA-009) Siehe Anlage 2 ^q2 - 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. ### Q3: Which constructive feature is shown in the figure? See figure (PFA-006) L: Lift Siehe Anlage 4 ^q3 - 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. ### Q4: "Longitudinal stability" is referred to as stability around which axis? ^q4 - 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). ### Q5: Rotation around the vertical axis is called... ^q5 - 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. ### Q6: Rotation around the lateral axis is called... ^q6 - 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. ### Q7: The elevator moves an aeroplane around the... ^q7 - 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. ### Q8: What has to be considered with regard to the center of gravity position? ^q8 - 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. ### Q9: What is the advantage of differential aileron movement? ^q9 - 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. ### Q10: The aerodynamic rudder balance... ^q10 - 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. ### Q11: What is the function of the static rudder balance? ^q11 - 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. ### Q12: The trim tab at the elevator is defelected upwards. In which position is the corresponding indicator? ^q12 - 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. ### Q13: Point number 1 in the figure indicates which flight state? See figure (PFA-008) Siehe Anlage 5 ^q13 - 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. ### Q14: In a co-ordinated turn, how is the relation between the load factor (n) and the stall speed (Vs)? ^q14 - 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. ### Q15: The pressure compensation between wind upper and lower surface results in ... ^q15 - 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. ### Q16: At stationary glide and the same mass, what is the difference when using a thick airfoild instead of a thinner airfoil? ^q16 - 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. ### Q17: What is shown by a profile polar? ^q17 - 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. ### Q18: If surrounded by airflow (v>0), any arbitrarily shaped body produces... ^q18 - 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. ### Q19: Number 3 in the drawing corresponds to the... See figure (PFA-010) Siehe Anlage 1 ^q19 - 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. ### Q20: Which design feature can compensate for adverse yaw? ^q20 - 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. ### Q21: What describes "wing loading"? ^q21 - 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. ### Q22: Point number 5 in the figure indicates which flight state? See figure (PFA-008) Siehe Anlage 5 ^q22 - 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. ### Q23: Extending airbrakes results in ... ^q23 - 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. ### Q24: The glide ratio of a sailplane can be improved by which measures? ^q24 - 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. ### Q25: What is the diffeence between spin and spiral dive? ^q25 - 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. ### Q26: Stability around which axis is mainly influenced by the center of gravity's longitudinal position? ^q26 - 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. ### Q27: What structural item provides directional stability to an airplane? ^q27 - 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. ### Q28: In straight and level flight with constant performance of the engine, the angle of attack at the wing is... ^q28 - 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. ### Q29: What is the function of the horizontal tail (among other things)? ^q29 - 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. ### Q30: Deflecting the rudder to the left causes... ^q30 - 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. ### Q31: Differential aileron deflection is used to... ^q31 - 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. ### Q32: How is the balance of forces affected during a turn? ^q32 - 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. ### Q33: What engine design at a Touring Motor Glider (TMG) results in least drag? ^q33 - 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. ### Q34: What effect is referred to as "adverse yaw"? ^q34 - 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. ### Q35: What is meant by "ground effect"? ^q35 - 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. ### Q36: Rudder deflections result in a turn of the aeroplane around the... ^q36 - 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). ### Q37: Through which factor listed below does the load factor increase during cruise flight? ^q37 - 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. ### Q38: 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? ^q38 - 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. ### Q39: What has to be considered when operating a sailplane equipped with camper flaps? ^q39 - 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. ### Q40: Which point on the aerofoil is represented by number 3? See figure (PFA-009) Siehe Anlage 2 ^q40 - 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. ### Q41: Number 2 in the drawing corresponds to the... See figure (PFA-010) Siehe Anlage 1 ^q41 - 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. ### Q42: The angle (alpha) shown in the figure is referred to as... See figure (PFA-003) DoF: direction of airflow Siehe Anlage 3 ^q42 - 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. ### Q43: The right aileron deflects upwards, the left downwards. How does the aircraft react? ^q43 - 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. ### Q44: What has to be considered when operating a sailplane with water ballast? ^q44 - 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. ### Q45: Which statement describes a situation of static stability? ^q45 - 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. ### Q46: 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? ^q46 - 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. ### Q47: Which constructive feature has the purpose to reduce stearing forces? ^q47 - 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. ### Q48: If surrounded by airflow (v > 0), any arbitrarily shaped body produces... ^q48 - 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. ### Q49: Longitudinal stability is referred to as stability around which axis? ^q49 - 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). ### Q50: What describes wing loading? ^q50 - 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. ### Q51: What effect is referred to as adverse yaw? ^q51 - 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. ### Q52: What is meant by ground effect? ^q52 - 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.