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Would it be feasible and survivable to circumnavigate the Earth in a glider or sailplane without propulsion and without landing until the circumnavigation is completed, when you'd return to the same location you were disattached from the carrier plane or winch? What would the major obstacles be and how could one handle it? Did anyone ever attempt such endeavor?

Edit: The two-seated Perlan II sailplane once reached an altitude of more than 70,000 ft (21 km) so perhaps let's discuss more over that single plane, whether the Perlan II, assuming it reaches 70,000 ft, could cross huge areas of sea for instance. If the two pilots manage their time so that one of them navigates while the other sleeps, isn't it likely you could circumnavigate the Earth in the Perlan II?

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    $\begingroup$ The wandering albatross does this using "dynamic soaring", catching air currents that form over the top of ocean waves. They can also flap, but in practice they don't. They can travel 600 miles a day. Not an answer, because an albatross isn't legally a sailplane (FAA 21.17-2a). jeb.biologists.org/content/221/1/jeb169938 $\endgroup$
    – James K
    Mar 14 at 9:42
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    $\begingroup$ @JamesK Not just legally, it's no plane whatsoever, it's a living entity. Interesting however. Maybe if one could ride a griffin or great eagle one would wonder how long that griffin can soar without flapping and if one could circumnavigate your planet on it. $\endgroup$
    – Giovanni
    Mar 14 at 10:09
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    $\begingroup$ Humm... Does your circumnavigation have to be east-west? If you go approximately polewise, you have a lot less ocean to cross. North & South America should be fairly easy, just follow the Rockies & Andes. Then if you can get across Antarctica and the stretch of ocean to the southern tip of Africa, you could follow its east coast, across Asia Minor and then north of the Himalayas and cross Bering Strait... $\endgroup$
    – jamesqf
    Mar 15 at 5:24
  • $\begingroup$ I like where @jamesqf is going. Following the updraft from a continental divide should give a way to sail for a very long time. To be considered a circumnavigation, at least by oceangoing standards, one must cross the equator twice. One would also have to pass over a pair of antipodes, and travel a distance equal or greater than the equatorial distance. Following mountain ridges for the updraft makes two of those "easy" but not the requirement of antipodes as there's a lot of water without a ridge to ride. $\endgroup$
    – MacGuffin
    Mar 15 at 5:46
  • $\begingroup$ I like jamesqf's suggestion too. I think it qualifies for a circumnavigation because it crosses and re-crosses the equator and you return to where you began. If james posts this as an answer I'd accept that one. $\endgroup$
    – Giovanni
    Mar 15 at 6:38
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No. Both night and oceans would be major obstacles.

Night time can be survived by parking the glider in ridge lift but it requires a steady wind during the night. This is possible and has been demonstrated decades ago, but is only possible with the right weather conditions. To have those lined up between thermal-powered daytime flying is rather unlikely.

Oceans are too homogenous to create thermals. You will notice that when crossing a large body of water in a glider: Over water the air is calm while over land it is easy to find thermals. Why else would albatrosses resort to dynamic soaring if the much less stressful thermalling would be possible? Dynamic soaring works much less well for human-sized gliders because of the limited height of the wind shear layer above the ocean's surface. Besides, it is beyond normal human capability to fly intermittently at 3g over many hours without sleep.

If you start high enough, a large lake can be crossed since the lack of thermals means you also will not hit downdrafts and your glide ratio will be easy to predict. But no thermal will carry you high enough to hop between Pacific islands or from Scotland to Iceland, which is a nearly 1000 km overwater trip.

For a true circumnavigation you would need to touch the southern hemisphere and there are too many long stretches of water to plan any feasible course. Only flying across Siberia and on to Alaska, Canada and Greenland does not make it a circumnavigation. Also, I very much doubt you will find thermals over large bodies of ice and snow, too.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Jamiec
    Mar 16 at 13:56
  • $\begingroup$ Stick thermals do not depend on weather or geography, and are an extremely reliable source of lift. $\endgroup$
    – Abdullah
    Mar 20 at 17:50
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To complement Peter's answer, let me mention that the farthest a glider has ever flown is 2256km (actual distance record is just beyond 3000km, but that was not in a straight line, but going back and forth). This is 1/17 of the proposed circumnavigation distance. And these flights have been done in exceptional days, in an exceptional area (Argentinean Andes). It is not easy to find the combination of well-oriented mountains and good enough wind and atmospheric conditions. There is simply not even a remote chance of chaining reasonable enough conditions to fly accross the globe.

Thermaling could help to fly the between two good mountain areas theoretically. In practice, excellent conditions are not prevalent, and it is common for thermal days to be irregular. The idea of leaving one mountain chain and have the thermals available to reach the next mountain chain, and to arrive and find the wind blowing in the needed direction; and then repeat such feat tens of times, over days, is way beyond the reach of imagination.

Not to mention human endurance. There was a time where endurance gliding was a thing. The single seater record sits at 56 hours; twin-seater, at 71. These kind of flights are not done anymore and possible records not recognized, because it was really dangerous. To fly 40000km at 200km/h requires 200hours, so almost three times the most anybody has flown in a glider. And this is assuming a kind of speed that is only achieved in selected mountains on selected days.

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    $\begingroup$ I think your endurance claims assume there is no autopilot - the endurance record is from 1961. $\endgroup$ Mar 14 at 9:23
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    $\begingroup$ It seems to me that a hypothetical endurance glider with an autopilot would have no batteries. It would be solar powered. The pilot would operate the glider at night. The pilot could also take control when it was necessary to climb. $\endgroup$ Mar 14 at 21:03
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    $\begingroup$ @AnonymousPhysicist: do you fly gliders? To keep a glider in the air, in particular if the goal is to cover significant distance, the pilot is working and making decisions very close to 100% of the time. And, there are cloudy days, too. $\endgroup$ Mar 14 at 21:10
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    $\begingroup$ Solar cells work on cloudy days. $\endgroup$ Mar 14 at 21:13
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    $\begingroup$ Even if you had solar panels, they would need to be connected to batteries to provide power at night. But the presence or absence of batteries isn't really the issue here. Outside of occasional research projects, there aren't existent autopilots that can even try to keep a glider in the air, and certainly not any that can operate independently with the pilot asleep. $\endgroup$ Mar 14 at 23:06

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