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Matthias Nott
6 days ago c40193824567e2d3fe01d1854382c44fadc0a636 
 SPL Exam Questions EN/30 - Flight Performance and Planning.md
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376376 
377377 #### Explanation
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-The correct answer is B because the angle of descent (glide angle) is geometrically defined as the angle between the horizontal and the flight path vector, measured in degrees.
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+The angle of descent is the angle α between the horizontal plane and the actual flight path, measured in **degrees [°]**. tan(α) = h / d, where h is the height lost and d is the horizontal distance.
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-- **A** is wrong because a "ratio expressed in degrees" is contradictory — a ratio is dimensionless or expressed as a percentage, not in degrees.
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-- **C** describes a gradient (percentage), not an angle.
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+![](figures/glide_angle_geometry.png)
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+- **A** is wrong: a "ratio expressed in degrees" is contradictory — a ratio is dimensionless or a percentage, never degrees.
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+- **C** describes a descent gradient (%), not an angle.
383385 - **D** incorrectly expresses an angle in percent.
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-- For a glider with a 1:30 glide ratio, the glide angle is approximately 1.9 degrees.
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+**Important distinction — angle of descent vs. glide angle:**
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+| | Glide angle | Angle of descent |
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+|---|---|---|
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+| Reference | Air mass | Ground |
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+| Analogy | Airspeed (TAS) | Ground speed |
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+| Wind effect | None | Headwind steepens, tailwind flattens |
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+In still air they are identical. In wind they differ because the ground speed changes while the sink rate stays the same:
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+- Airspeed 100 km/h, sink 1 m/s, **no wind** → ground speed 100 km/h → angle ≈ 2.1°
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+- Same glider, **50 km/h headwind** → ground speed 50 km/h → angle ≈ 4.1° (steeper)
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+- Same glider, **50 km/h tailwind** → ground speed 150 km/h → angle ≈ 1.4° (shallower)
385400 
386401 ### Q18: Which is the purpose of "interception lines" in visual navigation? ^t30q18
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696711 #### Explanation
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698713 The correct answer is C because glide distance equals glide ratio multiplied by height: 30 x 1,500 m = 45,000 m = 45 km. The glide ratio of 1:30 means the glider covers 30 metres horizontally for every 1 metre of height lost.
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+![](figures/glide_angle_geometry.png)
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+The diagram shows the relationship: distance d = h / tan(α), where α is the glide angle.
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700719 - **A** is wrong because 45 NM equals approximately 83 km, which would require a glide ratio of about 1:55.
701720 - **B** is wrong because 30 km would correspond to a glide ratio of only 1:20.
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16671686 The correct answer is D because a headwind reduces groundspeed while the sink rate in the airmass remains unchanged. Since the glider covers less horizontal ground distance per unit of altitude lost, the descent angle relative to the ground steepens (increases).
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+![](figures/glide_angle_geometry.png)
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+See the diagram for the geometry. Wind changes d (horizontal distance) without changing h (height loss), shifting α.
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16691692 - **A** is wrong because a tailwind decreases (flattens) the glide angle over the ground by increasing groundspeed.
16701693 - **B** is wrong because a headwind increases, not decreases, the ground glide angle.
16711694 - **C** is wrong because wind significantly affects the ground track glide angle, even though it does not affect the airmass glide angle.
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25922615 
25932616 #### Explanation
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-The correct answer is C because the Sanetsch Pass is charted at 2252 m AMSL on the Swiss gliding map. This value is directly readable from the map as the crossing altitude for planning the Alps traverse between the Fribourg Plateau and Valais.
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+The ICAO chart shows **7388 ft** next to the Sanetsch Pass. Since ICAO charts express altitudes in feet, you must convert: 7388 × 0.3048 ≈ **2252 m AMSL** (option C).
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+- **B (7385 ft)** is a near-miss distractor — close to the charted 7388 ft but not the exact value.
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+- **A (1085 m)** is too low for an Alpine pass.
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+- **D (8400 ft)** does not match any value on the chart.
25962623 
25972624 ### Q104: What category of aerodrome is Les Eplatures? ^t30q104
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27442771 The correct answer is D because the glide ratio (L/D ratio) is defined as the ratio between lift (L) and drag (D): L/D. It also directly indicates the horizontal distance covered per unit of altitude lost in unpowered gliding flight without wind. A glide ratio of 48 means the glider travels 48 m horizontally for every 1 m of descent.
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+![](figures/glide_angle_geometry.png)
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+Glide ratio = d/h from the diagram — the horizontal distance per unit of height lost.
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27462777 - **A** is wrong because lift/total weight is not the glide ratio.
27472778 - **B** is wrong because a pure glider has no thrust.
27482779 - **C** is wrong because drag/total weight gives the glide angle, not the glide ratio.
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27652796 The correct answer is D because the glide ratio directly expresses the horizontal distance covered for each unit of altitude lost. A glide ratio of 48 means: for 1 km (1000 m) of available altitude, the glider can glide 48 km in calm air without thermals. This is the operational definition of glide ratio, used directly to calculate a glider's range during flight planning.
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+![](figures/glide_angle_geometry.png)
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+A ratio of 48 means d = 48 × h, i.e. 48 m forward for every 1 m of height lost.
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27672802 ### Q113: What can cause a shift of the center of gravity? ^t30q113
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27692804 [DE](../SPL%20Exam%20Questions%20DE/30%20-%20Flugleistung%20und%20Flugplanung.md#^t30q113) · [FR](../SPL%20Exam%20Questions%20FR/30%20-%20Performances%20et%20planification%20du%20vol.md#^t30q113)