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Principles of Flight

Q1: Regarding the forces at play, how is steady-state gliding flight best characterised? ^t80q1

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Answer

C)

Explanation

In steady (stationary) gliding flight, there is no thrust, so only two forces act: gravity (weight) and the total aerodynamic force (the vector sum of lift and drag). For the glider to be in equilibrium, these two must be equal and opposite — meaning the resultant air force exactly compensates gravity. Lift and drag are merely components of this single aerodynamic resultant; neither lift alone nor drag alone balances weight.

Q2: What happens to the minimum flying speed when flaps are extended, thereby increasing wing camber? ^t80q2

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Answer

C)

Explanation

Extending flaps increases wing camber, which raises the maximum lift coefficient (CLmax). From the stall speed formula Vs = sqrt(2W / (rho * S * CLmax)), a higher CL_max directly lowers the minimum flying speed Vs. This allows the aircraft to fly slower without stalling, which is why flaps are used during approach and landing. The maximum permissible speed typically decreases with flaps extended (not increases), because flap structures are not designed for high dynamic pressure.

Key Terms

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Answer

D)

Explanation

An incipient spin begins when one wing stalls before the other — the stalled wing drops, creating a yawing and rolling moment. The correct response is to apply rudder opposite the direction of yaw/lower wing to stop the rotation, and simultaneously release elevator back-pressure (or push forward) to reduce the angle of attack below the critical value, allowing airflow to re-attach and lift to be restored. Pulling the elevator *(A)* would increase AoA and deepen the stall; pushing alone *(C)* without rudder does not stop the yaw.

Key Terms

AoA = Angle of Attack ### Q4: Which component is responsible for pitch stabilisation during cruise? ^t80q4

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![](figures/AnatomysailplaneEN.png)

Answer

D)

Explanation

The lateral axis is the pitch axis (nose up/down). The horizontal stabilizer provides longitudinal (pitch) stability: it generates a restoring moment whenever the nose pitches up or down from trim, because its lift force changes with AoA at the tail. Ailerons control roll (longitudinal axis), the vertical rudder controls yaw (vertical axis), and flaps are high-lift devices, not stability surfaces.

Key Terms

AoA = Angle of Attack ### Q5: What can happen when the never-exceed speed (VNE) is surpassed in flight? ^t80q5

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Answer

A)

Explanation

Exceeding VNE risks aeroelastic flutter — a self-reinforcing oscillation of the control surfaces or wings that can destroy the structure within seconds. Flutter onset speed is close to VNE. Structural failure of spars, attachments, or control surfaces may follow. The other options describe effects that do not occur at excessive speed: glide angle does not improve, drag does not decrease, and the ASI is designed to function at all normal and abnormal speeds.

Key Terms

VNE = Never Exceed Speed ### Q6: What effect does a rearward centre of gravity position have on a glider's handling? ^t80q6

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Answer

B)

Explanation

A rearward CG reduces the restoring moment arm between the CG and the horizontal stabiliser, diminishing longitudinal (pitch) stability. In extreme cases the aircraft can become unstable in pitch — the pilot may be unable to prevent a nose-up divergence, especially during winch launch or in turbulence. The forward CG limit ensures adequate pitch stability; the aft limit ensures adequate controllability. A rearward CG does not increase stall speed or roll effectiveness, and it makes the aircraft less, not more, stable.

Key Terms

CG = Centre of Gravity ### Q7: What purpose does the vertical tail fin (rudder assembly) serve? ^t80q7

![](figures/AnatomysailplaneEN.png)

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Answer

D)

Explanation

The vertical tail fin (fin + rudder) provides yaw stability and yaw control. The fixed fin acts as a weathervane that generates a restoring yaw moment if the aircraft sideslips. The movable rudder allows the pilot to command deliberate yaw inputs for coordination, crosswind correction, or spin recovery. The horizontal stabiliser handles pitch; wing dihedral handles roll stability; the vertical tail does not generate lift in the conventional sense.

Q8: In a coordinated level turn at 60 degrees of bank, the load factor is approximately ^t80q8

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Answer

C)

Explanation

In a level coordinated turn, the load factor n = 1/cos(bank angle). At 60° bank, n = 1/cos(60°) = 1/0.5 = 2.0. This means the effective weight the wings must support doubles. Stall speed increases by a factor of √n = √2 ≈ 1.41, i.e. a 41% increase. This is why steep turns at low altitude are dangerous for gliders — the stall margin shrinks dramatically.

Key Terms

n — Load Factor (ratio of lift to weight: n = L/W) ### Q9: What is the relationship between aspect ratio and induced drag? ^t80q9

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Answer

C)

Explanation

Induced drag is inversely proportional to aspect ratio (AR): D_induced ∝ CL² / (π × AR × e). A longer, narrower wing (high AR) produces the same lift with weaker wingtip vortices and therefore less induced drag. This is why gliders have very high aspect ratios — it is the primary design feature that maximises the lift-to-drag ratio and glide performance.

Key Terms

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Answer

A)

Explanation

A downward-deflected trim tab produces an upward aerodynamic force on the trailing edge of the elevator, pushing the elevator's trailing edge up and its leading edge down — this effectively deflects the elevator downward, creating a nose-up pitching moment. Trim tabs work by aerodynamic force to relieve the pilot of sustained stick forces; their deflection is opposite to the desired elevator deflection.

Q11: What does the polar curve of a glider depict? ^t80q11

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Answer

B)

Explanation

The glider's speed polar plots the vertical sink rate (Vz, typically in m/s) against the horizontal airspeed (Vh). It is the fundamental performance diagram for a glider: it reveals the minimum sink speed (the lowest point on the curve), the best glide speed (given by the tangent from the origin), and inter-thermal cruise speeds (McCready tangents). All cross-country speed-to-fly decisions are based on this curve.

Key Terms

m — mass of the aircraft ### Q12: In straight and level flight, what happens to the required angle of attack as speed increases? ^t80q12

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Answer

C)

Explanation

In level flight, lift must equal weight (L = W). Since L = CL × 0.5 × ρ × V² × S, when speed V increases the lift coefficient CL must decrease to keep lift constant. A lower CL corresponds to a lower angle of attack. Therefore, faster flight requires a smaller angle of attack, and slower flight (toward the stall) requires a progressively larger angle of attack.

Key Terms

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Answer

C)

Explanation

Wing fences are thin vertical plates on the upper surface of a swept or tapered wing that prevent the boundary layer from flowing spanwise (outward toward the tips). Without fences, the boundary layer migrates outward due to the pressure gradient, thickening at the tips and promoting tip stall. Fences confine the boundary layer to its local region, improving tip stall characteristics and aileron effectiveness at high angles of attack.

Q14: What happens to total drag at the speed for best glide ratio? ^t80q14

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Answer

C)

Explanation

The best glide ratio (maximum L/D) occurs at the speed where total drag is minimum. At this point, induced drag exactly equals parasite drag — any faster increases parasite drag more than induced drag decreases, and any slower increases induced drag more than parasite drag decreases. For a glider, this speed gives the flattest glide angle and the greatest distance per unit of altitude lost in still air.

Q15: What structural feature contributes to lateral (roll) stability in a glider? ^t80q15

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Answer

C)

Explanation

Wing dihedral — the upward V-angle of the wings — is the primary design feature providing lateral (roll) stability. When a gust or disturbance causes one wing to drop, the dihedral geometry increases the angle of attack on the lower wing, generating more lift and creating a restoring roll moment toward wings-level. The vertical fin provides directional stability; the horizontal stabiliser provides pitch stability; and elevator trim sets a pitch reference, not a roll reference.

Q16: How does increasing altitude affect true airspeed (TAS) for a given indicated airspeed (IAS)? ^t80q16

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Answer

C)

Explanation

IAS is based on dynamic pressure (q = 0.5 × ρ × V²). At higher altitude, air density ρ is lower, so a given IAS corresponds to a higher TAS. The relationship is TAS = IAS × √(ρ₀/ρ), where ρ₀ is sea-level density. For glider pilots, this means that at altitude, the ground speed for the same indicated approach speed is higher, and the landing roll will be longer.

Key Terms

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Answer

B)

Explanation

Load factor (n) is defined as the ratio of the lift generated by the wings to the aircraft's weight: n = L/W. In straight and level flight, n = 1. In a turn, n > 1 because extra lift is needed for the centripetal force. In a vertical pullup, n can exceed the design limits. The structural design of the glider is rated for specific load factor limits (typically +5.3g / -2.65g for utility category).

Key Terms

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Answer

C)

Explanation

The best L/D ratio is determined by the aerodynamic shape of the aircraft and is independent of weight. Increasing weight shifts the speed polar downward and to the right — the best glide speed increases (must fly faster) but the maximum L/D ratio stays the same. This is why adding water ballast in gliders improves inter-thermal cruise speed without changing the glide angle — only the speed at which that angle is achieved changes.

Q19: A glider is flying at the speed for minimum sink rate. If the pilot accelerates, what happens to the sink rate? ^t80q19

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Answer

C)

Explanation

The minimum sink rate speed is the speed at the lowest point of the speed polar. Any speed change — faster or slower — from this point increases the sink rate. Accelerating beyond minimum sink speed increases parasite drag faster than induced drag decreases, resulting in a higher total drag and therefore a greater rate of descent. This is the trade-off in cross-country flying: flying faster covers more ground but at the cost of increased sink rate.

Q20: What is the effect of extending airbrakes (spoilers) on a glider? ^t80q20

![](figures/AnatomysailplaneEN.png)

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Answer

C)

Explanation

Airbrakes (spoilers) disrupt the smooth airflow over the wing surface, reducing the pressure differential and therefore reducing lift. Simultaneously, the raised spoiler panels create a large increase in drag. This combined effect steepens the glide path dramatically, which is precisely their purpose — to allow the pilot to control the approach angle and land precisely. Without airbrakes, gliders would float long distances due to their excellent L/D ratio.

Q21: In which flight condition is induced drag greatest? ^t80q21

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Answer

C)

Explanation

Induced drag is proportional to CL², and CL is highest in slow flight at high angle of attack (where the wing must generate maximum lift per unit of dynamic pressure). In a dive or at high speed, CL is low and induced drag is minimal — parasite drag dominates instead. At best glide speed, induced drag equals parasite drag but is not at its maximum. The slow-flight regime is where induced drag dominates total drag.

Key Terms

CL — Lift Coefficient — dimensionless measure of aerodynamic lift ### Q22: What is the primary function of an elevator trim tab? ^t80q22

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Answer

A)

Explanation

The elevator trim tab allows the pilot to reduce or eliminate the stick force needed to hold a given pitch attitude in steady flight. By deflecting the trim tab, an aerodynamic force is applied to the elevator that counters the natural hinge moment, allowing hands-off or reduced-force flight at the trimmed speed. This reduces pilot fatigue on long flights and allows the pilot to concentrate on navigation and thermal exploitation.

Q23: What happens to stall speed in a turn compared to straight-and-level flight? ^t80q23

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Answer

C)

Explanation

In a turn, the load factor n = 1/cos(bank angle) exceeds 1, meaning the wings must generate more lift than in straight flight. The stall speed increases by the factor √n. At 45° bank, stall speed increases by 19%; at 60° bank by 41%. This is a critical safety consideration when thermalling near the ground — the steeper the bank, the closer the pilot is to the elevated stall speed.

Key Terms

n — Load Factor (ratio of lift to weight: n = L/W)

Q24: What is the centre of pressure of an aerofoil? ^t80q24

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Answer

C)

Explanation

The centre of pressure (CP) is the point on the chord line where the resultant aerodynamic force (sum of all pressure and friction forces) can be considered to act. Unlike the aerodynamic centre, the CP moves with changing angle of attack — it moves forward as AoA increases and rearward as AoA decreases. This movement is one reason why the CG position must remain within limits: if the CP moves too far from the CG, pitch control may be compromised.

Key Terms

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Answer

D)

Explanation

Parasite drag is proportional to V² (dynamic pressure). The faster the aircraft flies, the greater the parasite drag. At VNE — the maximum speed — parasite drag reaches its peak within the normal flight envelope. At slow speeds near the stall, parasite drag is minimal while induced drag dominates. Parasite drag includes form drag, skin friction drag, and interference drag — all of which grow with the square of the airspeed.

Key Terms

VNE — Never Exceed Speed ### Q26: What is the Bernoulli principle as applied to an aerofoil? ^t80q26

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Answer

B)

Explanation

Bernoulli's principle states that in a steady, incompressible flow, an increase in flow velocity is accompanied by a decrease in static pressure, and vice versa. Applied to an aerofoil, the air accelerates over the curved upper surface, creating a region of lower pressure compared to the lower surface. This pressure differential generates lift. While Newton's third law (downwash) also contributes to lift, the Bernoulli pressure distribution is the primary mechanism for conventional subsonic flight.

Q27: What is adverse yaw? ^t80q27

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Answer

B)

Explanation

Adverse yaw occurs because the down-going aileron (on the wing that rises) increases both lift and induced drag on that wing. The extra drag on the rising wing pulls the nose toward the descending wing — opposite to the intended turn direction. This is why coordinated use of rudder with aileron is essential, and why differential aileron deflection was developed as a design solution.

Q28: When does ground effect become significant? ^t80q28

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Answer

B)

Explanation

Ground effect becomes significant when the aircraft is within approximately one wingspan of the surface. The ground physically restricts the development of wingtip vortices and reduces the induced downwash angle, which effectively increases lift and reduces induced drag. Pilots experience this as a floating sensation during the landing flare — the glider wants to keep flying in ground effect, which can cause overshooting the intended touchdown point if not anticipated.

Key Terms

AGL = Above Ground Level ### Q29: What does the term "washout" refer to in wing design? ^t80q29

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Answer

B)

Explanation

Washout is a deliberate design feature in which the wing's angle of incidence decreases progressively from root to tip (geometric washout) or the aerofoil section changes to produce less lift at the tip (aerodynamic washout). This ensures that the wing root stalls before the tip, preserving aileron effectiveness during a stall and making the stall behaviour more benign and recoverable. Washout is particularly important in gliders with their long, high-aspect-ratio wings.

Q30: What is the relationship between the angle of attack and the lift coefficient up to the stall? ^t80q30

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Answer

B)

Explanation

The lift formula is:

L = CL x ½ρv² x S

where CL is the lift coefficient, ρ is air density, v is airspeed, and S is wing area. In the pre-stall regime, CL increases approximately linearly with angle of attack (AoA):

CL ≈ CL₀ + a x α

where a is the lift curve slope (typically about 2π per radian ≈ 0.11 per degree for a thin aerofoil), CL₀ is CL at zero AoA, and α is the angle of attack. This linear relationship continues until the critical angle of attack is reached, at which point flow separation causes CL to peak (CL_max) and then drop sharply — the stall.

Key Terms

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Answer

C)

Explanation

Extending flaps increases the wing's maximum lift coefficient (CLmax) by adding camber and, in some designs, wing area. From the stall speed formula Vs = sqrt(2W / (ρ × S × CLmax)), a higher CL_max yields a lower stall speed. This allows approach and landing at slower speeds with a shorter ground roll. Retracting flaps removes this benefit and returns stall speed to the higher clean-configuration value.

Key Terms

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Answer

C)

Explanation

Laminar-flow aerofoils are designed with their maximum thickness further aft than conventional profiles, creating a favourable pressure gradient that keeps the boundary layer laminar over a larger portion of the chord. Since laminar boundary layers produce far less skin friction drag than turbulent ones, the overall profile drag is significantly reduced. Gliders exploit this extensively — clean laminar-flow wings are the reason modern gliders achieve glide ratios exceeding 50:1.

Q33: How does air density change with increasing altitude? ^t80q33

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Answer

C)

Explanation

Air density decreases with altitude because atmospheric pressure drops and air expands. In the standard atmosphere, density at 5,500 m is roughly half the sea-level value. Reduced density means reduced dynamic pressure at a given TAS, which is why aircraft performance (lift and drag per unit TAS) degrades at altitude — the aircraft must fly faster in TAS to maintain the same IAS and lift.

Key Terms

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Answer

B)

Explanation

Static stability describes the aircraft's immediate response to a disturbance — whether restoring forces act to push it back toward the original equilibrium. Dynamic stability describes what happens over time: if the resulting oscillations decrease in amplitude and the aircraft eventually returns to its trimmed state, it is dynamically stable. An aircraft can be statically stable but dynamically unstable (oscillations grow), which is a dangerous condition.

Q35: What is the purpose of vortex generators on a wing? ^t80q35

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Answer

C)

Explanation

Vortex generators are small tabs that protrude from the wing surface and create tiny vortices that mix high-energy air from outside the boundary layer into the slower boundary layer flow near the surface. This energised boundary layer can resist adverse pressure gradients more effectively, delaying flow separation and improving control effectiveness at high angles of attack. They trade a small increase in skin friction for a significant delay in stall onset and better aileron authority near the stall.

Q36: Which of the following factors does a pilot directly control that affects lift? ^t80q36

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Answer

C)

Explanation

The pilot can directly change airspeed V (by adjusting pitch attitude) and indirectly change the lift coefficient CL (by changing the angle of attack, or by extending/retracting flaps). Air density ρ changes with altitude and temperature but is not directly controlled. Wing area S is fixed (except in rare variable-geometry designs or Fowler flap configurations). Airspeed and angle of attack are the pilot's primary tools for managing lift.

Key Terms

CL = Lift Coefficient ### Q37: In which direction does the centre of pressure move as the angle of attack increases (pre-stall)? ^t80q37

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Answer

C)

Explanation

As angle of attack increases in the pre-stall range, the pressure distribution shifts such that the centre of pressure moves forward along the chord. This forward CP movement produces a nose-up pitching moment that must be counteracted by the tail — one of the main reasons aircraft require a horizontal stabiliser. At very low (or negative) angles of attack, the CP moves rearward. This CP migration is why the aerodynamic centre concept is useful: the moment about the aerodynamic centre stays constant regardless of AoA.

Key Terms

AoA = Angle of Attack ### Q38: What determines the critical angle of attack at which a wing stalls? ^t80q38

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Answer

D)

Explanation

The critical angle of attack is an inherent property of the aerofoil's geometric shape — it is the angle at which the flow can no longer remain attached to the upper surface and separates, causing the stall. It does not change with weight, altitude, or airspeed. What changes with those factors is the stall speed — the speed at which the wing reaches the critical angle of attack in level flight. The aerofoil geometry (camber, thickness, leading edge radius) determines how well the flow follows the upper surface at high angles.

Q39: How does induced drag behave with increasing airspeed in level flight? ^t80q39

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Answer

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 options B and C. Total drag has a minimum at the speed where induced drag equals parasite drag; induced drag itself simply decreases with speed.

Key Terms

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Answer

D)

Explanation

The standard aerodynamic breakdown of total drag is: Total drag = Induced drag + Parasite drag. Induced drag arises from lift generation (wingtip vortices). Parasite drag is the collective term for all non-lift-related drag: form/pressure drag, skin friction drag, and interference drag.

Q41: How do lift and drag change when a stall is approached? ^t80q41

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Answer

C)

Explanation

As the critical angle of attack is reached, flow begins to separate from the upper surface, starting at the trailing edge and progressing forward. Once past the critical AoA, the clean attached flow that generated lift breaks down — CL drops sharply. Simultaneously, the separated flow creates a large turbulent wake with very high pressure drag, so CD rises dramatically. The drag polar shows this clearly: the nose of the polar curves sharply as the stall condition is approached, with CL falling and CD rising.

Key Terms

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Answer

C)

Explanation

Stall recovery requires reducing angle of attack below the critical value so that airflow can re-attach to the upper surface and lift can be restored. The pilot must push forward on the elevator control to lower AoA, which also allows the aircraft to accelerate (or the pilot applies power if available). Increasing AoA (B, D) deepens the stall. Reducing speed (D, A) worsens the condition. Banking *(A)* increases the load factor, which raises the stall speed — exactly the wrong input.

Key Terms

AoA = Angle of Attack ### Q43: During a stall, how do lift and drag behave? ^t80q43

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Answer

D)

Explanation

This is the definitive stall characteristic: lift collapses because boundary layer separation destroys the pressure differential that generates it, while drag rises dramatically due to the large turbulent separated wake.

The lift and drag formulas show why:

L = CL x ½ρv² x S (Lift = Lift Coefficient x dynamic pressure x wing area)

D = CD x ½ρv² x S (Drag = Drag Coefficient x dynamic pressure x wing area)

At the stall, CL drops sharply (past CL_max on the CL vs. AoA curve), so lift falls. At the same time, CD rises steeply due to the massive flow separation, so drag increases. This combination (less lift, more drag) is why the stall is critical — the aircraft loses lift while simultaneously experiencing high drag that further reduces speed.

Key Terms

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Answer

B)

Explanation

The critical (stall) angle of attack is a fixed aerodynamic property of the aerofoil shape — it is the AoA at which flow separation occurs regardless of airspeed, weight, or altitude. What changes with weight is the stall speed (Vs = sqrt(2W / (rho * S * CL_max))), not the stall AoA. A heavier aircraft must fly faster to generate the same lift, but it still stalls at the same critical AoA. C.G. position affects pitch stability and control effectiveness but does not change the aerofoil's critical angle.

Key Terms

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Answer

C)

Explanation

From Vs = sqrt(2W / (rho * S * CLmax)): stall speed decreases when weight (W) decreases, since less lift is needed to maintain equilibrium. Lower density ****(B)**** increases true airspeed (TAS) stall speed but the IAS stall speed remains approximately constant (since IAS is based on dynamic pressure q = 0.5 * rho * VTAS^2, which equals 0.5 * rho0 * VIAS^2). Higher load factor *(A)* effectively increases apparent weight (n*W), raising stall speed. Lower altitude means higher density, which slightly lowers TAS stall speed but does not significantly change IAS stall speed.

Key Terms

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Answer

B)

Explanation

Spin recovery technique (PARE: Power off, Ailerons neutral, Rudder opposite to spin direction, Elevator forward) requires keeping ailerons neutral because using ailerons during a spin can worsen the rotation — applying aileron into the spin raises the inner wing's AoA (which may already be stalled) and can deepen the spin. Rudder opposite to spin direction stops the autorotation; forward elevator then reduces AoA to unstall both wings. Speed does not constantly increase in a spin — the aircraft reaches a stabilised spin with relatively constant speed and rotation rate.

Key Terms

AoA = Angle of Attack ### Q47: The laminar boundary layer on the aerofoil lies between ^t80q47

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![](figures/BoundarylayerEN.svg)

Answer

D)

Explanation

The boundary layer development follows a specific sequence: flow is divided at the stagnation point, a laminar boundary layer develops from the stagnation point rearward, then at the transition point the laminar layer converts to turbulent, and finally at the separation point the turbulent layer detaches from the surface. The laminar boundary layer therefore occupies the region from the stagnation point to the transition point. Laminar flow aerofoils are designed to push the transition point as far aft as possible to minimise friction drag.

Q48: What types of boundary layers are found on an aerofoil? ^t80q48

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![](figures/BoundarylayerEN.svg)

Answer

C)

Explanation

The natural sequence of boundary layer development on an aerofoil runs from laminar (near the leading edge, where the flow is orderly and Reynolds number is low) to turbulent (further aft, after transition). The reverse sequence (turbulent first, then laminar) does not occur naturally. This forward laminar / aft turbulent arrangement is why designers place the maximum thickness of laminar-flow aerofoils further back — to extend the favourable pressure gradient that maintains laminar flow as far as possible before transition.

Q49: How does a laminar boundary layer differ from a turbulent one? ^t80q49

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Answer

D)

Explanation

The turbulent boundary layer, despite having higher skin friction drag than the laminar layer, has more energetic mixing that allows it to remain attached to the surface against an adverse pressure gradient at higher angles of attack. This is its critical advantage: it resists flow separation better. The laminar boundary layer is indeed thinner (C is partly correct about thickness) and has lower friction drag — but it separates more easily. This is why turbulators are sometimes used on gliders: deliberately triggering transition to turbulent flow to prevent laminar separation bubbles.

Q50: Which structural element provides lateral (roll) stability? ^t80q50

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![](figures/AnatomysailplaneEN.png)

Answer

B)

Explanation

Lateral (roll) stability — the tendency to return to wings-level after a roll disturbance — is primarily provided by wing dihedral (the upward angle of the wings from horizontal). When a gust rolls the aircraft, the lower wing descends and its angle of attack increases (it meets more airflow), generating more lift and creating a restoring moment back to level. The vertical tail provides directional (yaw) stability; ailerons are roll control surfaces (not stability), and the elevator controls pitch. High-wing aircraft achieve similar lateral stability through the pendulum effect of the fuselage hanging below the wings.

Q51: What is the mean value of gravitational acceleration at the Earth's surface? ^t80q51

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Answer

C)

Explanation

The standard gravitational acceleration at the Earth's surface is 9.81 m/s² (ISA value). This value is fundamental in aeronautics: it is used to calculate weight (W = m × g), load factor, and appears in all performance equations. 1013.25 hPa is the standard pressure at sea level, and 15°C/100 m is not a correct gradient (the standard lapse rate is 0.65°C/100 m).

Key Terms

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Answer

D)

Explanation

The permitted flap position during a sideslip is always specified in the aircraft flight manual (AFM/POH). Some gliders prohibit extended flaps in a sideslip because the combination of flaps and deflected rudder can create dangerous aerodynamic couples or exceed structural limits. Others permit certain configurations. The only correct answer is therefore to consult the AFM.

Q53: An aircraft is said to have dynamic stability when ^t80q53

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Answer

B)

Explanation

Dynamic stability describes the behaviour of an aircraft over time after a disturbance. A dynamically stable aircraft returns automatically to its original equilibrium (trim) after being disturbed — the oscillations progressively damp out. Answer A describes so-called "neutral or convergent stability towards a new equilibrium", which is different. Static stability (the immediate tendency to return) is a necessary but not sufficient condition for dynamic stability.

Q54: In severe turbulence, airspeed must be reduced ^t80q54

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Answer

D)

Explanation

The manoeuvring speed VA (or turbulence penetration speed) is the maximum speed at which full control surface deflections or severe wind gusts will not cause the structural limit load to be exceeded. Below VA, the wing will stall before the structural limit load is reached, thereby protecting the structure. In severe turbulence, speed must be reduced below V_A to avoid structural damage from gust dynamic loads.

Q55: In the ICAO standard atmosphere, the temperature lapse rate in the troposphere is ^t80q55

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Answer

C)

Explanation

In the ICAO standard atmosphere (ISA), temperature decreases by 0.65°C for every 100 m of altitude in the troposphere (or equivalently, 2°C per 1000 ft, or 6.5°C/1000 m). Answer B (0.65°C/1000 ft) is incorrect because the unit is wrong — this would be far too small a lapse rate. Answer C is the only correct one: 0.65°C per 100 m of altitude.

Key Terms

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Answer

A)

Explanation

Atmospheric pressure decreases with altitude in an approximately exponential manner. In the ICAO standard atmosphere, pressure is approximately half the sea-level pressure (1013.25 hPa → ~506 hPa) at an altitude of approximately 5,500 m (18,000 ft). This value is important for high-altitude physiology (oxygen requirements) and for density altitude performance calculations.

Key Terms

ICAO = International Civil Aviation Organization ### Q57: Density altitude always corresponds to ^t80q57

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Answer

C)

Explanation

Density altitude is the altitude at which the aircraft would be in the ISA standard atmosphere if the air density were the same as in actual conditions. It is calculated from pressure altitude (altimeter set to 1013.25 hPa) corrected for the temperature deviation from ISA. A temperature higher than ISA gives a density altitude higher than pressure altitude, reducing aircraft performance. Answer A describes pressure altitude, not density altitude.

Key Terms

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Answer

D)

Explanation

The continuity equation states that for an incompressible fluid, the volumetric flow rate Q = S × V is constant along a streamtube. If the cross-section S decreases, the velocity V must increase proportionally to keep Q constant. This principle, combined with Bernoulli's theorem, explains why air accelerates over the curved upper surface of an aerofoil, creating a low-pressure region that generates lift.

Key Terms

Q59: The aerodynamic resultant (drag and lift) depends on air density. When air density decreases ^t80q59

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Answer

A)

Explanation

Both lift and drag are proportional to the dynamic pressure q = 0.5 × ρ × V². When air density ρ decreases (at altitude or in high temperatures), q decreases for a given speed, which reduces both lift and drag. This is why aircraft performance deteriorates at high altitude or in great heat: the aircraft must fly faster (higher TAS) to generate the same lift, while the total aerodynamic resistance decreases for a constant indicated airspeed.

Key Terms

DE · FR

Answer

D)

Explanation

The neutral point (also called the aerodynamic centre at wing level, but "neutral point" for the complete aircraft) is the point about which the pitching moment remains constant regardless of changes in angle of attack. For a stable aircraft, the centre of gravity must be forward of the neutral point — the CG-to-neutral point distance constitutes the static stability margin. Note: for an isolated aerofoil, this point corresponds to the aerodynamic centre (at approximately 25% of the chord); for the complete aircraft, the neutral point accounts for the contribution of the horizontal stabiliser.

Key Terms

CG — Centre of Gravity ### Q61: The angle between the aerofoil chord line and the aircraft's longitudinal axis is called ^t80q61

DE · FR

Answer

D)

Explanation

The rigging angle (or angle of incidence) is the fixed angle, defined at construction, between the aerofoil chord line and the longitudinal axis of the fuselage. It does not vary in flight. It should not be confused with the angle of attack, which is the angle between the chord line and the direction of the relative wind (and which varies in flight according to attitude and speed). The rigging angle is chosen by the manufacturer so that the wing generates the necessary lift in cruise at an aerodynamically favourable fuselage attitude.

Q62: What does the transition point correspond to? ^t80q62

DE · FR

Answer

D)

Explanation

The transition point is precisely the location on the aerofoil where the boundary layer changes from a laminar regime (ordered flow, in parallel layers) to a turbulent regime (disordered flow, with transverse mixing). This transition is irreversible in the direction of flow: the change is from laminar to turbulent, never the reverse. The position of the transition point depends on the Reynolds number, the pressure gradient, and surface roughness — a favourable pressure gradient (acceleration) maintains laminar flow, while an adverse gradient (deceleration) triggers transition.

Q63: Geometric or aerodynamic wing twist results in ^t80q63

DE · FR

Answer

C)

Explanation

Wing twist (geometric or aerodynamic) varies the angle of incidence or aerodynamic characteristics along the span, so that the stall does not occur simultaneously across the entire wing. The root (higher angle of incidence) reaches the critical angle first and stalls progressively, while the outer sections remain attached. This progressive (rather than simultaneous) flow separation improves stall safety and maintains roll control via the ailerons. The effect on adverse yaw *(A)* is indirect and marginal.

Q64: The profile drag (form drag) of a body is primarily influenced by ^t80q64

DE · FR

Answer

D)

Explanation

Form drag (pressure drag) is caused by the pressure difference between the front and rear of a body, due to boundary layer separation and the formation of vortices in the wake. The more intense the vortex formation (unStreamlined body, blunt trailing edge), the higher the form drag. This is why streamlined aerofoils have much lower form drag than a flat plate or sphere — their progressively converging shape allows the flow to remain attached longer, reducing the turbulent wake.

Q65: The aerodynamic drag of a flat disc in an airflow depends notably on ^t80q65

DE · FR

Answer

C)

Explanation

The drag of a flat disc (non-streamlined body) is pressure drag: it depends primarily on the frontal surface area S exposed perpendicularly to the airflow, and on the dynamic pressure q = 0.5 × ρ × V². The formula is D = CD × q × S. The material strength, the disc's own density, or its weight do not influence aerodynamic drag — this is purely a function of shape, projected area, and flow conditions.

Key Terms

DE · FR

Speed Polar:

![](figures/t80_q66.png)

A = tangent from a point above the origin on the W axis (McCready) → optimal inter-thermal cruise speed B = tangent from the origin → best glide speed (best L/D ratio) C = tangent from a point shifted to the right on the V axis → best glide with headwind D = horizontal tangent at the top of the polar → minimum sink rate speed (Vmin sink)

Answer

C)

Explanation

On the speed polar (sink rate W vs. airspeed V), the minimum sink rate is at the highest point of the curve (least negative W). At that point the tangent to the curve is horizontal — this is tangent (D) on the diagram. Flying at this speed maximises flight time and is used when circling in thermals.

The other tangents: (B) from the origin gives best L/D (best glide angle). (C) from a right-shifted point on V compensates for headwind. (A) from a point above the origin on the W axis is the McCready tangent for optimal inter-thermal cruise speed.

Q67: Induced drag increases ^t80q67

DE · FR

Answer

C)

Explanation

Induced drag is proportional to CL²: D_induced = CL² / (π × AR × e) × q × S. By increasing the angle of attack, CL increases, and therefore CL² increases, causing induced drag to grow. - In level flight at constant speed, an increase in angle of attack corresponds to a lower speed, which further increases induced drag (D_induced ∝ 1/V²). By increasing speed (D), CL decreases in level flight and induced drag decreases. - Parasite drag (A) varies independently of induced drag.

Key Terms

DE · FR

Answer

C)

Explanation

In a horizontal turn at bank angle φ, the load factor is n = 1/cos(φ). At 45° of bank, n = 1/cos(45°) = 1/0.707 ≈ 1.41. The stall speed in the turn is Vs_turn = Vs × √n = Vs × √1.41 ≈ Vs × 1.19. Therefore the minimum speed increases by approximately 19% compared to straight-and-level flight. This increase in stall speed during turns is a fundamental safety concept — tight turns at low altitude (such as on final approach) are particularly dangerous because the margin above the stall is reduced.

Key Terms

DE · FR

Answer

D)

Explanation

Adverse yaw is caused by the asymmetry of drag between the two ailerons during turn entry. The aileron that rises (on the high-wing side) increases the local angle of attack, generating more lift but also more induced drag. This additional drag on the rising side creates a yawing moment towards the rising side — i.e. in the opposite direction to the turn (hence "adverse yaw"). Differential ailerons and spoiler-airbrakes are technical solutions to mitigate this effect.

Q70: True Airspeed (TAS) is the speed shown by the ASI ^t80q70

DE · FR

Answer

D)

Explanation

True airspeed (TAS) is obtained from indicated airspeed (IAS) by applying two successive corrections: first, position and instrument errors (yielding calibrated airspeed, CAS), then the density correction (accounting for the difference between actual air density and standard sea-level density). TAS is therefore the actual speed of the aircraft through the air mass. At high altitude, TAS is significantly higher than IAS because air density is lower.

Key Terms

DE · FR

Answer

C)

Explanation

The slotted flap speed range is indicated in the Flight Manual (AFM) and normally on the airspeed indicator (white or light green arc). It varies by glider type.

Key Terms

VA = Manoeuvring Speed ### Q72: Wing tip vortices are caused by pressure equalisation from: ^t80q72

DE · FR

Answer

A)

Explanation

Wing tip vortices (induced vortices) come from pressure equalization from the lower surface (high pressure) to the upper surface (low pressure) at the wing tip. This phenomenon generates induced drag.

Q73: The angle of attack of an aerofoil is always the angle between: ^t80q73

DE · FR

Answer

A)

Explanation

Angle of attack is the angle between the chord line and the general airflow direction (relative wind direction). It is not the angle with the horizon nor with the longitudinal axis.

Q74: In the standard atmosphere, the values of temperature and atmospheric pressure at sea level are: ^t80q74

DE · FR

Answer

A)

Explanation

The ICAO Standard Atmosphere sea-level values are: - Temperature: 15 °C (= 288.15 K = 59 °F) - Pressure: 1013.25 hPa (= 1013.25 mbar = 29.92 inHg = 760 mmHg)

Option A matches both.

Key Terms

DE · FR

![](figures/t80_q75.png)

Answer

B)

Explanation

The mean camber line is the line equidistant between the lower and upper surfaces. In the figure, it is represented by line B.

Q76: In a correctly executed turn without altitude loss, why is slight back-pressure on the elevator necessary? ^t80q76

DE · FR

Answer

A)

Explanation

In a coordinated turn without altitude loss, back pressure is needed to increase lift and balance centrifugal force (load factor > 1). Lift must compensate for both gravity and centrifugal force.

Q77: When the frontal area of a disc in an airflow is tripled, drag increases by: ^t80q77

![](figures/t80_q77.png)

DE · FR

Answer

C)

Explanation

The drag equation is D = ½ × rho × V² × Cd × A, where A is the frontal (reference) area. Drag is directly proportional to frontal area: if A triples, drag triples.

Key Terms

Q78: Aerodynamic wing twist (washout) is a modification of: ^t80q78

![](figures/t80_q78.png)

DE · FR

Answer

B)

Explanation

There are two types of wing twist (washout):

The question specifically asks about "aerodynamic wing twist," which is the aerofoil profile change (B). Both types aim to make the wing root stall before the tip, preserving aileron effectiveness during stall.

Key Terms

Q79: What is the average value of gravitational acceleration at the Earth's surface? ^t80q79

DE · FR

Answer

C)

Explanation

Standard gravitational acceleration at Earth's surface is 9.81 m/s². This is the ISA value used in all performance calculations.

Key Terms

ISA = International Standard Atmosphere ### Q80: The speed displayed on the airspeed indicator (ASI) is a measurement of: ^t80q80

DE · FR

Answer

B)

Explanation

Airspeed indicator reading is based on the difference between static pressure and total pressure (dynamic pressure). The ASI measures this difference via the Pitot tube and static port.

Q81: The horizontal and vertical stabilisers serve in particular to: ^t80q81

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

C)

Explanation

The horizontal and vertical stabilizers serve primarily to stabilize the aircraft in flight (longitudinal and directional stability). Without them, the aircraft would be unstable.

Q82: When slotted flaps are extended, airflow separation: ^t80q82

DE · FR

Answer

D)

Explanation

When extending slotted flaps, airflow separation occurs at a lower speed, because flaps increase the maximum lift coefficient (CL max). Stall speed decreases.

Key Terms

CL = Lift Coefficient ### Q83: The aerodynamic centre of an aerofoil in an airflow is the point of application of: ^t80q83

DE · FR

Answer

B)

Explanation

The aerodynamic centre (or centre of pressure) is the point where the resultant of all aerodynamic pressure forces (lift + drag) acts on the aerofoil. It lies on the chord line, typically near the quarter-chord point (~25% of chord from the leading edge).

Q84: Pressures are expressed in: ^t80q84

DE · FR

Answer

C)

Explanation

Pressures are expressed in bar, psi (pounds per square inch) and Pa (Pascal). g is an acceleration, not a pressure. Alpha (a) is not a pressure unit.

Q85: TAS (True Air Speed) is the speed of: ^t80q85

DE · FR

Answer

B)

Explanation

TAS (True Air Speed) is the aircraft's speed relative to the surrounding air mass. It is the actual speed through the air, corrected for atmospheric density.

Key Terms

TAS = True Airspeed ### Q86: Yaw stability of an aircraft is provided by: ^t80q86

DE · FR

Answer

C)

Explanation

Yaw stability is provided by the fin (vertical stabilizer/rudder). Wing sweep contributes to roll stability, not yaw.

Q87: The trailing edge flap shown below is a: ^t80q87

DE · FR

![](figures/t80_q87.png)

Answer

C)

Explanation

The flap shown, extending from the wing with a slot, is a Slotted Flap. The slot channels air from the lower to upper surface, delaying separation.

Q88: The risk of airflow separation on the wing occurs mainly: ^t80q88

DE · FR

Answer

C)

Explanation

The risk of stall/separation appears mainly during an abrupt pull-out after a dive, as the angle of attack increases very rapidly and can exceed the critical angle before the pilot can react.

Q89: The drag of a body in an airflow depends notably on: ^t80q89

DE · FR

Answer

C)

Explanation

Aerodynamic drag depends notably on air density (ρ), since F_D = Cd × 0.5 × ρ × v² × A. The body's own density, chemical composition, and mass do not directly affect aerodynamic drag.

Key Terms

Q90: In the drawing below, the aerofoil chord is represented by: ^t80q90

DE · FR

![](figures/t80_q90.png)

Answer

C)

Explanation

The chord line is the straight line connecting the leading edge to the trailing edge. In the figure, it is represented by H.

Q91: The angle of attack of an aerofoil is always measured between: ^t80q91

DE · FR

Answer

A)

Explanation

The angle of attack (AoA) is defined as the angle between the chord line and the direction of the undisturbed relative airflow, making A correct.

Key Terms

AoA = Angle of Attack ### Q92: Given equal frontal area and equal airflow speed, what determines the drag of a body? ^t80q92

DE · FR

Answer

C)

Explanation

When frontal area and airspeed are held constant, the remaining variable in the drag equation D = CD × 0.5 × rho × V² × S is the drag coefficient CD, which is determined entirely by the body's shape. A streamlined shape produces far less drag than a blunt one.

Key Terms

DE · FR

Answer

C)

Explanation

Induced drag originates from the pressure difference between the lower (high pressure) and upper (low pressure) wing surfaces. At the wingtips, air flows from the high-pressure lower surface around to the low-pressure upper surface, forming trailing vortices that tilt the lift vector rearward, creating induced drag.

Q94: What is the sea-level pressure in the ICAO standard atmosphere? ^t80q94

DE · FR

Answer

C)

Explanation

The ICAO International Standard Atmosphere defines sea-level pressure as exactly 1013.25 hPa (hectopascals).

Key Terms

DE · FR

![](figures/t80_q95.png)

Answer

B)

Explanation

The mean camber line is the locus of points equidistant between the upper and lower surfaces of the aerofoil, representing the profile's curvature. In this diagram, line B corresponds to this curved reference line.

Q96: In a level turn without sideslip or altitude loss, why is back pressure on the elevator necessary? ^t80q96

DE · FR

Answer

D)

Explanation

In a banked turn at constant altitude, the load factor exceeds 1 because lift must counterbalance both the aircraft's weight and provide the centripetal force for the curved flight path. Back pressure on the elevator increases the angle of attack and thus total lift to meet this requirement.

Q97: A wing stall occurs: ^t80q97

DE · FR

Answer

B)

Explanation

A stall occurs when the wing's angle of attack exceeds the critical value (typically around 15-18 degrees), causing flow separation from the upper surface and a sudden loss of lift. This is a fundamental aerodynamic principle independent of airspeed or attitude.

Key Terms

DE · FR

Answer

D)

Explanation

Airflow separation occurs when the angle of attack reaches the critical stall angle, which is a fixed aerodynamic property of the aerofoil shape.

Key Terms

AoA = Angle of Attack ### Q99: What is the mean gravitational acceleration at the surface of the Earth? ^t80q99

DE · FR

Answer

A)

Explanation

The standard gravitational acceleration at sea level is 9.81 m/s², used throughout aviation for weight, load factor, and performance calculations.

Key Terms

ISA = International Standard Atmosphere ### Q100: True Airspeed (TAS) is obtained from the airspeed indicator (ASI) reading by: ^t80q100

DE · FR

Answer

C)

Explanation

TAS is derived from the ASI reading (IAS) through two successive corrections: first, position and instrument errors are removed to obtain calibrated airspeed (CAS), then a density correction accounts for the difference between actual air density and ISA sea-level density.

Key Terms

DE · FR

Answer

B)

Explanation

The centre of gravity (CG) is determined by the distribution of mass within the aircraft, so only physically moving mass — such as shifting ballast, passengers, or baggage — changes it.

Key Terms

CG = Centre of Gravity ### Q102: The high-lift device shown in the diagram is a: ^t80q102

DE · FR

![](figures/t80_q102.png)

Answer

D)

Explanation

A Fowler flap moves rearward and downward, simultaneously increasing both wing area and camber, making it the most effective type of trailing-edge flap. The diagram shows this characteristic rearward extension. - A plain flap (A) simply hinges downward without moving aft. - A split flap (B) deflects only the lower surface panel. - A slotted flap (C) opens a gap but does not significantly increase wing area like the Fowler design.

Q103: The resultant of all aerodynamic forces on a wing profile acts through the: ^t80q103

DE · FR

Answer

C)

Explanation

The aerodynamic centre is the point on the aerofoil through which the resultant of all aerodynamic pressure forces (lift and drag combined) is considered to act, and about which the pitching moment coefficient remains approximately constant with changes in angle of attack, located near the quarter-chord point.

Q104: At approximately what altitude is the air density half of its sea-level value? ^t80q104

DE · FR

Answer

D)

Explanation

In the ICAO standard atmosphere, air density decreases approximately exponentially with altitude and reaches half its sea-level value at roughly 6,600 m (about 21,600 ft).

Key Terms

ICAO = International Civil Aviation Organization ### Q105: The airspeed indicator (ASI) reading is based on a measurement of: ^t80q105

DE · FR

Answer

B)

Explanation

The ASI measures dynamic pressure, which is the difference between total (pitot) pressure and static pressure: q = ptotal - pstatic = 0.5 × rho × V². This differential measurement directly indicates airspeed.

Key Terms

DE · FR

Answer

D)

Explanation

Roll (lateral) stability — the tendency to return to wings-level after a disturbance — is primarily provided by wing dihedral and wing sweep, both of which create restoring roll moments when the aircraft sideslips after a bank disturbance.

Q107: The speed range for operating slotted flaps: ^t80q107

DE · FR

Answer

C)

Explanation

The permitted speed range for flap operation varies between aircraft types and is always specified in the Aircraft Flight Manual (AFM), typically also indicated on the ASI as a white arc.

Key Terms

DE · FR

Answer

C)

Explanation

Geometric twist (washout) is a physical twist built into the wing so that the angle of incidence progressively decreases from root to tip. This ensures the root stalls first, preserving aileron effectiveness near the tips.

Key Terms

D — Drag ### Q109: Barometric pressure in the Earth's atmosphere has the characteristic of: ^t80q109

DE · FR

Answer

D)

Explanation

Atmospheric pressure follows an approximately exponential decay with altitude, as described by the barometric formula. Each equal altitude increment reduces pressure by the same percentage, not the same absolute amount.

Q110: The simplified continuity equation says the same mass of air passes through different cross-sections at the same instant. Therefore: ^t80q110

DE · FR

Answer

B)

Explanation

The continuity equation for incompressible flow states A1 × V1 = A2 × V2 (area times velocity is constant). If the cross-section increases, velocity must decrease proportionally to maintain the same mass flow rate.

Q111: On the aerofoil diagram, what does point number 4 represent? ^t80q111

DE · FR

![](figures/t80_q111.png)

Answer

B)

Explanation

Point 4 on the boundary layer diagram marks the separation point, where the boundary layer detaches from the upper wing surface due to an adverse pressure gradient, forming a turbulent wake behind it.

Q112: On the aerofoil diagram, what does point number 1 represent? ^t80q112

DE · FR

![](figures/t80_q112.png)

Answer

C)

Explanation

Point 1 on the boundary layer diagram is the stagnation point at the leading edge, where the incoming airflow divides into upper and lower streams, velocity is zero, and static pressure reaches its maximum.

Q113: What constructive feature is depicted in the figure? ^t80q113

DE · FR

![](figures/t80_q113.png)

Answer

C)

Explanation

The figure shows wing dihedral — the upward V-angle of the wings relative to the horizontal plane — which provides lateral (roll) stability. When one wing drops in a sideslip, the lower wing experiences a higher effective angle of attack, generating more lift and producing a restoring roll moment.

Q114: "Longitudinal stability" refers to stability around which axis? ^t80q114

DE · FR

Answer

C)

Explanation

Despite its potentially confusing name, longitudinal stability refers to pitch stability, which is rotation around the lateral axis (the axis running from wingtip to wingtip). It describes the aircraft's tendency to return to a trimmed pitch attitude.

Q115: Rotation about the vertical axis is termed ^t80q115

DE · FR

Answer

B)

Explanation

Yawing is the rotation of the aircraft around the vertical (normal) axis, causing the nose to swing left or right. It is controlled primarily by the rudder.

Q116: Rotation about the lateral axis is termed ^t80q116

DE · FR

Answer

D)

Explanation

Pitching is the rotation of the aircraft around the lateral axis (wingtip to wingtip), resulting in nose-up or nose-down movement, controlled by the elevator.

Q117: The elevator causes the aircraft to rotate around the ^t80q117

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

B)

Explanation

The elevator controls pitch, which is rotation around the lateral axis (running from wingtip to wingtip). By deflecting the elevator, the pilot changes the aerodynamic force on the tail, creating a pitching moment that raises or lowers the nose.

Q118: What must be considered regarding the centre of gravity position? ^t80q118

DE · FR

Answer

C)

Explanation

The centre of gravity position is determined solely by how mass is distributed within the aircraft — only correct loading of occupants, baggage, and ballast within approved limits ensures a safe CG.

Key Terms

CG = Centre of Gravity ### Q119: What benefit does differential aileron deflection provide? ^t80q119

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

D)

Explanation

Differential aileron deflection means the down-going aileron deflects less than the up-going aileron, which reduces the extra induced drag on the descending wing and thus minimises adverse yaw — the unwanted yawing opposite to the intended roll direction.

Q120: What does the aerodynamic rudder balance accomplish? ^t80q120

DE · FR

Answer

B)

Explanation

An aerodynamic rudder balance (such as a horn balance or set-back hinge) positions part of the control surface ahead of the hinge line, so that aerodynamic pressure partially assists the pilot's input, reducing the force needed to deflect the control.

Q121: What purpose does static rudder (mass) balancing serve? ^t80q121

DE · FR

Answer

C)

Explanation

Static (mass) balancing places counterweights ahead of the hinge line to move the control surface's centre of mass to or forward of the hinge. This prevents flutter — a dangerous self-exciting aeroelastic oscillation that can destroy the control surface and airframe at speed.

Q122: When the elevator trim tab is deflected upwards, what does the trim indicator show? ^t80q122

DE · FR

Answer

C)

Explanation

An upward-deflected trim tab generates a downward aerodynamic force on the trailing edge of the elevator, which pushes the elevator's leading edge upward, creating a nose-down pitching moment. The trim indicator therefore shows a nose-down position.

Q123: On the polar diagram, what flight condition does point number 1 indicate? ^t80q123

DE · FR

![](figures/t80_q123.png)

Answer

D)

Explanation

Point 1 on the polar diagram lies in the region of negative lift coefficient, representing inverted flight where the aircraft flies upside down and the wing produces downward lift relative to its normal orientation.

Key Terms

DE · FR

Answer

B)

Explanation

In a coordinated banked turn, the lift vector must support both the weight and provide centripetal force, so the load factor n = 1/cos(bank angle) is always greater than 1. The stall speed increases by the factor sqrt(n), because more lift is needed and thus a higher speed is required to avoid the stall.

Key Terms

DE · FR

Answer

D)

Explanation

The pressure difference between the lower (high pressure) and upper (low pressure) wing surfaces causes air to flow around the wingtips, forming trailing vortices. These vortices create downwash that tilts the lift vector rearward, producing induced drag.

Q126: In steady glide at equal mass, how does using a thicker aerofoil compare to a thinner one? ^t80q126

DE · FR

Answer

D)

Explanation

In a steady glide at the same mass, lift must equal weight regardless of the aerofoil thickness, so lift remains the same. However, a thicker aerofoil generates greater form (pressure) drag due to its larger cross-section and more severe adverse pressure gradients.

Q127: What does a profile polar diagram display? ^t80q127

DE · FR

Answer

D)

Explanation

A profile polar (Lilienthal polar) plots the lift coefficient (cA or CL) against the drag coefficient (cD or CD) at various angles of attack, showing how aerodynamic efficiency changes across the operating range.

Key Terms

DE · FR

Answer

C)

Explanation

Any body in a moving airflow always experiences drag due to viscous friction and pressure forces opposing the motion — this is unavoidable in a real fluid. Lift, however, requires specific aerodynamic shaping or orientation.

Q129: In the diagram, what does number 3 represent? ^t80q129

DE · FR

![](figures/t80_q129.png)

Answer

C)

Explanation

In the aerofoil diagram, number 3 represents the camber line (mean camber line), which is the curved line equidistant between the upper and lower surfaces of the aerofoil.

Q130: Which design feature can compensate for adverse yaw? ^t80q130

DE · FR

Answer

C)

Explanation

Differential aileron deflection reduces adverse yaw by deflecting the down-going aileron less than the up-going aileron, thereby reducing the extra induced drag on the descending wing that causes the nose to yaw opposite to the intended turn.

Q131: What does "wing loading" describe? ^t80q131

DE · FR

Answer

D)

Explanation

Wing loading is defined as total aircraft weight divided by wing reference area, expressed in units such as N/m² or kg/m². It determines stall speed, gust sensitivity, and overall handling characteristics.

Q132: On the polar diagram, what flight state does point number 5 represent? ^t80q132

DE · FR

![](figures/t80_q132.png)

Answer

D)

Explanation

Point 5 on the polar diagram corresponds to slow flight — a high angle of attack, low speed condition on the positive portion of the polar before reaching the stall point.

Key Terms

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

C)

Explanation

Airbrakes (spoilers/dive brakes) serve to steepen the glide path by significantly increasing drag while simultaneously disrupting upper-surface airflow, which reduces lift.

Q134: Which combination of measures can improve the glide ratio of a sailplane? ^t80q134

DE · FR

Answer

D)

Explanation

Glide ratio (L/D) is maximised by minimising total drag while flying at the optimal speed. Cleaning surfaces reduces skin friction, taping gaps prevents leakage drag, retractable gear eliminates a major source of parasite drag, and maintaining best-glide speed keeps the aircraft at peak L/D.

Key Terms

CG = Centre of Gravity ### Q135: What distinguishes a spin from a spiral dive? ^t80q135

DE · FR

Answer

B)

Explanation

In a spin, the inner (lower) wing is deeply stalled while the outer wing may still be producing some lift, creating autorotation at a near-constant, relatively low airspeed. In a spiral dive, neither wing is stalled, and the aircraft descends in a tightening bank with rapidly increasing airspeed.

Q136: The longitudinal position of the centre of gravity primarily affects stability around which axis? ^t80q136

DE · FR

Answer

C)

Explanation

The longitudinal (fore-aft) position of the CG directly determines pitch stability, which is stability around the lateral axis. The CG must be forward of the neutral point for positive pitch stability; the further forward, the more statically stable but the heavier the elevator forces.

Key Terms

CG = Centre of Gravity ### Q137: Which structural element provides directional stability? ^t80q137

DE · FR

Answer

C)

Explanation

The vertical tail fin acts as a weathervane, producing a restoring yawing moment whenever the aircraft sideslips, thereby providing directional (yaw) stability around the vertical axis. A larger fin provides greater stability.

Q138: In straight-and-level flight at constant engine power, how does the wing's angle of attack compare to that in a climb? ^t80q138

DE · FR

Answer

D)

Explanation

In a climb at the same engine power, the aircraft flies slower because more energy goes into gaining altitude, requiring a higher angle of attack to maintain sufficient lift. Therefore, the level-flight angle of attack is smaller than in a climb.

Key Terms

AoA = Angle of Attack ### Q139: What is one function of the horizontal tail? ^t80q139

DE · FR

Answer

A)

Explanation

The horizontal tail (stabiliser and elevator) provides longitudinal (pitch) stability, which is stability around the lateral axis. It generates restoring moments when the aircraft's pitch attitude is disturbed.

Q140: What happens when the rudder is deflected to the left? ^t80q140

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

D)

Explanation

When the rudder is deflected to the left, it produces a sideways aerodynamic force on the tail that pushes the tail to the right, yawing the nose to the left around the vertical axis.

Q141: Differential aileron deflection is employed to ^t80q141

DE · FR

Answer

C)

Explanation

Differential aileron deflection gives the down-going aileron less deflection than the up-going aileron, reducing the drag asymmetry between the two wings during a roll input and thereby minimising adverse yaw.

Key Terms

AoA = Angle of Attack ### Q142: How is the force balance affected during a banked turn? ^t80q142

DE · FR

Answer

C)

Explanation

In a banked turn at constant altitude, the tilted lift vector must be large enough that its vertical component still equals weight while its horizontal component provides the centripetal force for the curved path. This means total lift must exceed the straight-and-level value, with the load factor n = 1/cos(bank angle).

Key Terms

DE · FR

Answer

C)

Explanation

A retractable engine and propeller can be fully stowed inside the fuselage when not in use, completely eliminating the parasite drag from the powerplant and propeller during soaring flight.

Key Terms

TMG = Touring Motor Glider ### Q144: What effect is known as "adverse yaw"? ^t80q144

DE · FR

Answer

C)

Explanation

Adverse yaw occurs because the down-deflected aileron increases both lift and induced drag on its wing. This extra drag on the rising wing yaws the nose toward it — away from the intended direction of turn.

Q145: What is the "ground effect"? ^t80q145

DE · FR

Answer

A)

Explanation

When flying within approximately one wingspan of the ground, the ground surface restricts the full development of wingtip vortices, reducing downwash. This effectively increases the local angle of attack (more lift) and reduces induced drag simultaneously.

Q146: Rudder deflections rotate the aircraft around the ^t80q146

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

D)

Explanation

The rudder controls yaw, which is rotation around the vertical axis, causing the nose to swing left or right.

Q147: Which of the following factors causes the load factor to increase during cruise flight? ^t80q147

DE · FR

Answer

C)

Explanation

An upward gust suddenly increases the wing's angle of attack, temporarily generating lift in excess of the aircraft's weight. This additional lift translates into a load factor greater than 1, stressing the structure.

Key Terms

CG = Centre of Gravity ### Q148: While approaching the next updraft, the variometer shows 3 m/s descent. You expect a mean climb rate of 2 m/s in the thermal. How should you set the McCready ring? ^t80q148

DE · FR

Answer

C)

Explanation

The McCready ring is always set to the expected climb rate in the next thermal (2 m/s in this case), and the recommended inter-thermal cruise speed is then read at the variometer needle position showing the current sink rate (3 m/s).

Q149: What must be considered when flying a sailplane equipped with camber flaps? ^t80q149

DE · FR

Answer

C)

Explanation

During approach and landing, switching the camber flap from positive (increased camber, higher lift) to negative (reduced or reflexed camber) would cause a sudden and dramatic drop in lift close to the ground, potentially leading to a dangerous sink or ground contact.

Key Terms

D — Drag ### Q150: On the aerofoil diagram, what does point number 3 represent? ^t80q150

DE · FR

![](figures/t80_q150.png)

Answer

D)

Explanation

Point 3 on the boundary layer diagram is the transition point, where the boundary layer changes from smooth laminar flow to turbulent flow. The position of this transition depends on Reynolds number, surface roughness, and pressure gradient.

Q151: In the diagram, what does number 2 correspond to? ^t80q151

DE · FR

![](figures/t80_q151.png)

Answer

C)

Explanation

Number 2 in figure represents the chord line — the straight reference line connecting the leading edge to the trailing edge of the aerofoil. It is the baseline from which the angle of attack and camber are measured.

Q152: In the figure, the angle (alpha) is referred to as ^t80q152

DE · FR

![](figures/t80_q152.png)

Answer

C)

Explanation

The angle alpha between the chord line and the direction of the oncoming airflow is the angle of attack, the primary aerodynamic variable determining lift coefficient and stall behaviour.

Q153: If the right aileron deflects upward and the left aileron deflects downward, how does the aircraft react? ^t80q153

![](figures/AnatomysailplaneEN.png)

DE · FR

Answer

A)

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 wing, producing adverse yaw — the nose swings to the left, opposite the intended roll direction.

Q154: What must be taken into account when flying a sailplane with water ballast? ^t80q154

DE · FR

Answer

D)

Explanation

Water ballast must be kept above freezing (i.e., the aircraft should stay below the freezing level) to prevent the water from freezing in the wing tanks, which could jam dump valves, cause unpredictable CG shifts, and damage wing structure.

Key Terms

CG = Centre of Gravity ### Q155: Which description characterises static stability? ^t80q155

DE · FR

Answer

D)

Explanation

Static stability means that when an aircraft is displaced from equilibrium by an external force, inherent aerodynamic forces automatically tend to return it toward its original state without pilot input.

Q156: How do the best gliding angle and best glide speed change when a sailplane carries water ballast compared to flying without it? ^t80q156

DE · FR

Answer

A)

Explanation

Water ballast increases total aircraft weight. The best L/D ratio (and therefore the best gliding angle) is an aerodynamic property of the aircraft's shape and does not change with weight. However, the speed at which this optimum L/D occurs increases because more dynamic pressure is needed to generate the extra lift required by the heavier aircraft.

Q157: Which constructive feature is designed to reduce control forces? ^t80q157

DE · FR

Answer

C)

Explanation

An aerodynamic rudder balance (horn balance or set-back hinge) extends part of the control surface ahead of the hinge line, so aerodynamic pressure partially assists the pilot's deflection effort, directly reducing the force required.

Q158: When any body of arbitrary shape is surrounded by airflow (v > 0), it always produces ^t80q158

DE · FR

Answer

A)

Explanation

Any body immersed in a moving airstream (v > 0) always produces drag, because viscous friction and pressure differences are unavoidable in real fluid flow. Lift requires specific shaping or angle of attack and is not guaranteed.

Key Terms

D — Drag ### Q159: "Longitudinal stability" refers to stability around which axis? ^t80q159

DE · FR

Answer

D)

Explanation

Despite the potentially confusing name, longitudinal stability describes pitch stability, which is rotation around the lateral axis (wingtip to wingtip). It is the tendency to maintain or return to a trimmed pitch attitude.

Q160: What does "wing loading" mean? ^t80q160

DE · FR

Answer

B)

Explanation

Wing loading is the aircraft's total weight divided by the wing reference area (e.g., N/m² or kg/m²). Higher wing loading means higher stall speeds but better penetration in turbulence.

Key Terms

D — Drag ### Q161: What phenomenon is known as adverse yaw? ^t80q161

DE · FR

Answer

D)

Explanation

Adverse yaw occurs because the down-deflected aileron, which increases local lift on the rising wing, also increases induced drag on that wing. This extra drag pulls the nose toward the rising wing — away from the intended turn direction.

Q162: What is the "ground effect"? ^t80q162

DE · FR

Answer

D)

Explanation

In ground effect (within approximately one wingspan of the surface), the ground physically constrains wingtip vortex development, reducing downwash. This increases the effective angle of attack (raising lift) while simultaneously reducing induced drag. Pilots notice this as a floating sensation during the landing flare.

Q163: Does air density affect the minimum speed (IAS) of a glider? ^t80q163

DE · FR

Answer

C)

Explanation

Stall occurs when the wing reaches its critical angle of attack. The stall speed in IAS is Vs = sqrt(2W / (rho0 x S x CLmax)), where rho0 is the reference density used by the airspeed indicator. The ASI measures dynamic pressure (q = 0.5 x rho x TAS^2) and displays it as IAS. Since lift L = CL x q x S, the stall always occurs at the same CLmax regardless of density. Therefore the indicated stall speed (IAS) remains constant at any altitude or density - this is why all reference speeds in procedures are given as IAS.

Key terms

Q164: In which speed range can vibrations and flutter occur? ^t80q164

DE · FR

Answer

C)

Explanation

Aeroelastic flutter is a self-sustaining, divergent oscillation of control surfaces or lifting surfaces. Its onset speed is deliberately set above Vne. In normal flight below Vne, properly mass-balanced controls and a sufficiently rigid structure prevent flutter. By exceeding Vne, the aircraft enters a regime where flutter becomes a real risk and can lead to structural destruction within seconds.

Key terms

Q165: Vibrations can occur when ^t80q165

DE · FR

Answer

A)

Explanation

Excessive play in the mechanical linkages of control surfaces or flaps creates conditions favourable to vibration by reducing structural damping. The play allows surfaces to move freely under aerodynamic forces, potentially generating oscillations. This is one reason why control system play is strictly limited and checked during maintenance inspections. Large amounts of play can lower the flutter onset speed to below Vne.

Q166: Vibrations can also occur under which conditions? ^t80q166

DE · FR

Answer

C)

Explanation

Ice on control surfaces alters their mass distribution and thus their mass balance. Mass balancing is designed to position the control surface's centre of mass at or ahead of the hinge axis, preventing flutter. Ice, depositing mainly on leading edges and outer surfaces, can shift the centre of mass behind the hinge and lower the critical flutter speed well below Vne. Flying at high speed with ice-contaminated, unbalanced control surfaces is particularly dangerous.

Q167: In which speed range can the maximum load factor be exceeded, leading to structural overload? ^t80q167

DE · FR

Answer

B)

Explanation

Below Va, full control deflection causes the wing to stall before the structural limit load is reached - the stall protects the structure. Above Va, the wing can generate enough lift to exceed the limit load factor before stalling. It is in the Va-Vne range that abrupt manoeuvres or severe gusts can subject the structure to excessive loads. Above Vne, the flutter risk is added to the overload risk.

Key terms

Q168: Above which speed can abrupt or full control deflections damage the glider's structure? ^t80q168

DE · FR

Answer

A)

Explanation

Manoeuvring speed Va is precisely the speed above which abrupt or full control deflections can produce aerodynamic loads exceeding the aircraft's structural limits. Below Va, the wing stalls before these loads are reached. Above Va, a full deflection can generate enough lift or control surface force to damage spars, wing attachments or the tailplane. Va is therefore the practical limit for energetic manoeuvres and turbulence penetration.

Q169: When the maximum load factor is exceeded, what is the primary risk? ^t80q169

DE · FR

Answer

D)

Explanation

The maximum (limit) load factor is the highest load the glider's structure can withstand repeatedly without permanent deformation. Beyond the ultimate factor (typically 1.5 times the limit), structural failure can occur. Exceeding the limit load factor during abrupt manoeuvres or in turbulence can cause deformation or rupture of wing spars, fuselage attachments or control surfaces. Stall and spin are aerodynamic phenomena, not structural ones, and occur at insufficient load factors, not excessive ones.

Q170: The mass balance (mass balancing) of an aileron has lost lead weights. What can be the consequence? ^t80q170

DE · FR

Answer

B)

Explanation

Mass balancing places lead counterweights ahead of the hinge axis to bring the control surface's centre of mass to or ahead of that axis. If these counterweights fall off, the centre of mass shifts aft of the hinge. The control surface then becomes susceptible to flutter - a self-amplifying aeroelastic oscillation in which inertial and aerodynamic forces reinforce each other. This flutter can quickly become divergent and destroy the control surface and airframe. That is why any damage to control surface counterweights requires inspection before the next flight.

Q171: What is the danger of flying at minimum speed in turbulent air? ^t80q171

DE · FR

Answer

C)

Explanation

At minimum speed (stall speed), the wing operates at its maximum lift coefficient CL_max with virtually no margin before stall. In turbulent air, upward gusts can suddenly increase the angle of attack beyond the critical angle, causing an instantaneous stall. In addition, speed fluctuations induced by turbulence can momentarily reduce airspeed below Vs. This is why it is particularly dangerous to fly at minimum speed in rough air, especially on final approach during landing.

Q172: How does air density change when temperature increases? ^t80q172

DE · FR

Answer

A)

Explanation

According to the ideal gas law (P = rho x R x T), at constant pressure, an increase in temperature T causes a decrease in density rho. Warmer air is less dense. For a glider, this means performance degrades in hot conditions (density altitude higher than actual altitude): lift and drag are reduced for a given indicated airspeed, and the true airspeed (TAS) at stall is higher. This is the density altitude effect on aircraft performance.

Key terms

Q173: In what proportion does drag change with airspeed? ^t80q173

DE · FR

Answer

C)

Explanation

Parasite drag is proportional to dynamic pressure q = 0.5 x rho x V^2. If speed doubles, q quadruples and therefore parasite drag quadruples as well. This quadratic (square) relationship means a small speed increase produces a large drag increase. This is why gliders flying at high speed lose much more altitude per unit of distance - drag grows far faster than any additional lift available.

Key terms

Q174: What is understood by static pressure? ^t80q174

DE · FR

Answer

C)

Explanation

Static pressure is the pressure exerted by the surrounding atmosphere on an object at rest relative to the air. It is measured by static ports (flush orifices on the fuselage, away from airflow disturbance). It decreases with altitude according to the standard atmosphere model. In the Pitot-static system, static pressure is subtracted from total pressure (Pitot) to obtain dynamic pressure, which is proportional to the square of true airspeed - this is the operating principle of the airspeed indicator.

Q175: How does the maximum permissible speed Vne of a glider in IAS behave as altitude increases? ^t80q175

DE · FR

Answer

C)

Explanation

Vne is a structural limit tied to true airspeed (TAS), since aerodynamic forces and flutter risk depend on TAS. The airspeed indicator measures IAS (based on dynamic pressure). At altitude, density decreases, so the same IAS corresponds to a higher TAS. To keep the TAS limit constant, the IAS limit must be reduced. Thus the Vne in IAS as shown on the airspeed indicator decreases with altitude. Some AFMs give Vne as TAS (constant) and specify the IAS reduction per altitude band.

Key terms

Q176: In what proportion does lift change when airspeed increases? ^t80q176

DE · FR

Answer

B)

Explanation

Lift L = CL x 0.5 x rho x V^2 x S. At constant angle of attack and density, lift is proportional to V^2. If speed doubles, lift quadruples. This property allows flight at high speed with a lower angle of attack - the lift generated scales with the square of speed. It also explains why stall speeds increase with the square root of the load factor: in a turn, more lift is required, demanding a higher speed to avoid stalling.

Q177: Which statement is FALSE regarding the relationship between lift/drag and airspeed? ^t80q177

DE · FR

Answer

C)

Explanation

The FALSE statement is C. Neither lift nor drag varies linearly with speed - both vary as the square of speed (proportionally to dynamic pressure q = 0.5 x rho x V^2). Doubling speed quadruples both lift AND drag (at constant angle of attack). Statements A, B and D are correct: lift does increase with speed, drag does vary with speed, and lift does depend on angle of attack via the lift coefficient CL.

Q178: What is understood by total pressure? ^t80q178

DE · FR

Answer

C)

Explanation

Total pressure (or stagnation pressure) is the pressure measured when the airflow is brought to rest isentropically. It equals the sum of static pressure (ambient atmospheric pressure) and dynamic pressure (0.5 x rho x V^2). The Pitot tube measures total pressure by stagnating the airflow at its inlet. By subtracting static pressure (measured by the static port) from total pressure (measured by the Pitot), one obtains dynamic pressure, which allows calculation of indicated airspeed.

Key terms