300-km Triangle With a Strong Headwind Return
It is 13:00 on a blue-sky cumulus day. Forecast: surface wind 250°/18 kt gusting 25, 5,000-ft wind 280°/35 kt, lift 1–2 kt, cloudbase 6,500 ft MSL, overdevelopment possible after 16:00, and isolated thunderstorms after 18:00. You are at a 1,200-ft MSL gliderport planning a 300-km triangle with two turnpoints. Your glider has a 40:1 glide ratio, no engine, and a final-glide computer. The first 40 km is downwind; the return is into wind. You have 4.5 hours of daylight. The towplane can tow to 3,000 ft AGL. A friend flying a similar glider reports 1.5-kt thermals and broken lift below 4,000 ft. A 20-km prohibited area near the second turnpoint requires a route around it.
1. Assess the launch and route decision. Would you launch as planned, modify the task, or cancel? Show the reasoning.
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Launch is reasonable only with a modified task. The first leg downwind is fast, but the return into a 35-kt wind at 5,000 ft is the governing problem. At 55 mph TAS, a 35-kt headwind leaves about 20 mph groundspeed. Effective glide becomes 40 × (20/55) ≈ 14.5:1, not 40:1. From 5,000 ft AGL, still-air range is 40 × 0.82 ≈ 33 NM; into that wind it is about 14.5 × 0.82 ≈ 12 NM. Therefore the final glide must not be planned on the computer's still-air numbers, and the return cannot depend on weak 1–2 kt thermals. I would launch but shorten the task, keep the downwind leg first, route well clear of the prohibited area, and set a hard turnback point. If lift is below 1 kt or cloudbase drops below 5,000 ft, I would abandon the triangle and land out rather than press home.
2. Define a decision point and abort criteria for the flight, including altitude and time.
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A workable decision point is the second turnpoint: by 15:30, you need enough altitude to reach the home field with a safe margin, or you divert to a known landout. Because the headwind reduces effective glide to roughly 14:1, do not accept a final glide that arrives below 1,500 ft AGL over the last 10 NM. A practical rule is to be at least 6,000 ft MSL at 40 km out, or turn toward a landout with a filed field. Abort if average climb falls below 1 kt, cloudbase drops below 4,500 ft, cumulus tops begin to flatten into overdevelopment, or surface gusts exceed 25 kt. The 16:00 overdevelopment forecast is a hard stop for the triangle; plan to be on the ground by then. The prohibited area must be avoided by at least 2 NM, not used as a shortcut.
3. What weather and human-factor risks would you brief before launch, and how do they change the go/no-go decision?
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Brief the strong low-level wind and gust spread, the 35-kt wind at 5,000 ft, the risk of overdevelopment after 16:00, and the isolated thunderstorms after 18:00. The gusty surface wind raises the risk of a bad landing and makes retrieve planning harder; the downwind first leg can create get-home-itis on the return. The weak lift means the task may become a survival flight rather than a race. Human factors: a 300-km triangle with a 4.5-hour daylight limit and a strong headwind invites pressing into deteriorating weather. Set a personal rule that the first sign of OD, dust, or a sudden wind shift ends the task. If the passenger or ground crew is waiting, do not let that pressure override the 15:30 decision point. The launch is defensible only if the task is shortened and the abort criteria are briefed aloud.