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Would it be possible to use pure gliders as an eco-friendly mode of transport?

From what I have read so far, gliders can travel at a speed of 100-170 km/h. That would not be able to compete with a jet plane, but it could easily be faster than a car, and possibly even a high-speed train, since it can fly directly and doesn't have to follow train tracks.

So, would it be possible to build a glider that fills this arbitrary set of requirements that would qualify it for regular travel:

  • It needs to be able to carry at least 30 people plus luggage. Otherwise the pilots are much too expensive.
  • It needs to be able to fly regularly, only being inhibited by severe weather.
  • It needs to qualify for international, commercial passenger service in all matters (safety equipment, radio, ...)
  • It doesn't need to be able to fly around the year, pre-plannable months without service are acceptable.
  • It doesn't need to work with current infrastructure, e.g. it would be acceptable if the plane needs special runways and/or launching mechanisms.

Would it theoretically be possible to build something like this?

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    $\begingroup$ For the sake of efficiency, modern airliners are as glider-like as possible (allowing for sufficient structural strength). These gliders are boosted aloft with jets, using much less fuel in descent. Your idea is already at work. $\endgroup$ – Robert DiGiovanni Sep 8 '20 at 15:22
  • $\begingroup$ @RobertDiGiovanni I would argue that a glider that uses soaring has zero emissions, UNLIKE modern airliners. $\endgroup$ – Abdullah Sep 8 '20 at 15:48
  • $\begingroup$ Perhaps we could lift them in the air with balloons. $\endgroup$ – Robert DiGiovanni Sep 8 '20 at 15:54
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There's one thing that will forever prevent an unpowered aircraft from entering commercial passenger service: the inability to make a second attempt at a landing.

Airliners, with all their instrumentation, very experienced pilots, and such don't make go-arounds frequently -- but especially during weather, they do make go-arounds. A passenger sailplane absolutely can't make a go-around, so if it gets crossed up due to a crosswind gust low and slow, instead of advancing throttle and climbing out, all the pilot(s) can do is pick where and how hard to crash.

This complete lack of second chances, as much as any of the other objections raised in other answers, will ensure that unpowered aircraft will never see commercial service. It can also lead to "landing out" where you wind up having to retrieve your passenger glider from a farmer's field, freeway, or worse, along with its payload and crew.

The other big issue is how to launch these immense sailplanes -- with a common sport glider or competition sailplane, you're towed into the air by either another airplane, a winch, or occasionally a car or truck. The winch that could launch something the size of a 737 high enough to fly off in search of its first lift would be so big and expensive it would severely limit the number of airports that could service such craft. The airplane that could do it would be at least as big as that 737.

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  • $\begingroup$ "inability to make a second attempt at a landing": It looks like the definitive answer! Even Greta would agree. $\endgroup$ – mins Sep 19 '20 at 2:31
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Theoretically, yes. Practically, no.

  • Day to day weather is a huge factor in powered aviation. It is an even larger factor for non-powered aviation. You would not be able to satisfy the predictability and consistency needed to be a commercial scheduled carrier. At best, you may be a charter or sightseeing tour carrier.
  • No lift means no flight. Days of no or not enough vertical airmass movement would require canceling flights. Night time flights would be out of the question.
  • Faster flight and consistent lift may (I say again, may) be available in the jetstream currents. But, then you would need a pressurized cabin which adds more weight.
  • To make it commercially viable, the speed of transport would have to be significantly more than a car. Consistently faster than 100-120 miles per hour would be required to get people who already own cars to consider the added expense and hassle of air travel.
  • To make it commercially viable, after speed is considered, distance has to be factored in to get people who already own cars to consider the added expense and hassle of air travel. You would only attract people who are flying more than twice the distance of your clientele servicing diameter. For example, if it takes me 30 minutes or 30 miles to drive to the airport of departure, I would not fly to a destination that is less than 120 miles or 2 hours drive time away.
  • Competition must be considered in any commercial venture. Private land carriage like private cars would be a huge area of competition. So would public carriage like buses and trains. With increased technology reducing their ecological impact, these forms of transportation would be far more attractive than a proposed glider.
  • Most gliders efficient enough for consistent cross-country flights have interiors that are small, cramped, not climate controlled, and require the pilot and passenger to sit in an almost reclined position for the duration of the flight. Larger gliders like those used in WWII were larger, cumbersome, and required huge aircraft to lift them airborne. The military has already abandoned such projects for troop transport.
  • Trans-oceanic flights would be not at all practical if at all feasible.

This does not mean that it should not be attempted. You should know the obstacles in front of you and try to overcome them. Your failure might lead to someone else’s success.

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    $\begingroup$ Good answer. I would just add two things: it still takes fuel to get the glider to altitude, (so not clean) and the probable lack of willingness on the part of passengers to fly regularly on a craft with no go around capability. Also, too encouraging at the end! ;) $\endgroup$ – Michael Hall Sep 8 '20 at 15:44
  • $\begingroup$ @MichaelHall I would argue that 1) a glider is still cleaner 2) gliders don't explode on impact $\endgroup$ – Abdullah Sep 8 '20 at 15:52
  • $\begingroup$ @Abdullah, if you were to calculate the theoretical fuel required to tow a 30 passenger glider to altitude, and plot the range achieved in a glide against a turboprop covering the same range in the most fuel efficient manner you might find a small advantage. But likely not enough to negate my point or prove this as a viable idea. Good point about fire safety, but I’m still betting against this idea “taking off”... $\endgroup$ – Michael Hall Sep 8 '20 at 15:59
  • $\begingroup$ @MichaelHall well, soaring gliders have a chance of unlimited range.......that's what I was referring to. I mean, think about migrating seabirds. In any case, the tow plane could be an EV without compromising the range with it's heavy battery! Ah, that's one important thing. $\endgroup$ – Abdullah Sep 8 '20 at 16:01
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    $\begingroup$ “A chance” is the key word here... How many paying passengers would be willing to sit for hours as the pilot seeks out the thermals that just might allow them to reach their destination?! $\endgroup$ – Michael Hall Sep 8 '20 at 16:04
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Well new twin engines airliners are already some impressive gliders... The glide ratio (GR) of the A320 is around 17 and the new 787 GR is above 20. Those numbers are quite impresive considering the two big engines shut down adding a lot of drag. Without engines they could probably reach the lower limit of aerobatic gliders with a GR of around 25 to 30.

I could also add a safety issue to the previous answer. Every landing in a glider is mendatory. Without engines you don't have any opportunities to go around or wait in the pattern for the runway to become available. This restrict even more the weather in which you can fly, too much cross wind and it is way to dangerous to try.

Finally saying that a glider can fly directly is only partially true as it still requires to find thermal ascending current to extend it's range. In a glider you know when and where your taking off, but it's hard to say the same for the landing, not really good for commercial ops.

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