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Daniel Pfeffer wrote: they trade distance for height.
Just a pedantic correction: they trade height for distance and the "exchange rate" is called glide ratio[^].
Mircea
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Mircea Neacsu wrote: they trade height for distance
You're correct. I reversed the order. 
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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Greetings and Kind Regards
It occurs to me perhaps customer confidence may be an obstacle to overcome. I am not knowledgeable in such matters but it seems reasonable to me to assume a glider of carrying capacity equal to an airliner would be a technical challenge. Certainly worthy of further study. Permit me to say my own pet idea re/ Green Aviation is dirigibles. Unfortunately I can not imagine the aviation public would tolerate the lengthy flight across great distances. Perhaps it is of practical use only for freight.
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Several companies are actively creating large dirigibles for various business reasons.
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I think Dan hit all key notes as to glider economics. Just not there.
Maybe some advanced battery technology in future might tame electric power for powered flight.
Glider technology may go hand in hand.
"A little time, a little trouble, your better day"
Badfinger
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Who knows, maybe some kind of hybrid technology with batteries that are not too heavy and only used for take-off or emergency situations ...
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RickZeeland wrote: only used for take-off or emergency situations ...
If the batteries are only used in these situations, they will not be installed at all.
Takeoff power can be provided by an external source (winch, tow aircraft, etc.), so the use case simply isn't there.
In emergency situations, the pilot may need large amounts of power for a short time. Batteries that can do this are very heavy, and would be mostly parasitic weight. Technical improvements would better be invested in improving safety. There is a saying "A clever man can get out of situations that a wise man won't get into". That should apply to safety considerations.
Another reason for not having large batteries on a glider is that gliders are relatively flimsy. In an emergency, the kind of stress that a commercial aircraft can handle might snap the wings of a glider, causing the very accident that one wishes to avoid.
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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All true.
Fuel tanks get lighter with use. Not so with batteries.
Power could be solar but that's been done and it's very tricky in cloudy weather.
Interesting challenge, though.
"A little time, a little trouble, your better day"
Badfinger
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Well there are plenty of examples of gliders being launched by (electrically-powered) winch, so that could be an environmentally-friendly possibility. However gliders are even more weight-sensitive that powered aircraft, so I'm not sure people would be happy without their duty-free chocolate sales etc.
However... almost 50 years ago I worked doing research into energy savings in railway operation through coasting (i.e. power-off) when trains were running ahead of schedule, and energy savings were significant. I'm also aware of aircraft incidents where for various reasons all engine power has failed, and airliners have glided 50 miles or more[^] to their destination. Of course, as noted elsewhere, you trade height for distance and, without engines running, you severely limit your options in the case of emergency. But there might be a case, if it's technically possible to virtually guarantee an engine restart in-flight (given sufficient fuel of course), to argue that maybe aircraft could delay their powered descent and simply cut their engines at 30,000 feet and glide the final 50 miles - reducing pollution, fuel use, and noise - whilst retaining the ability to power-up in case of adverse winds, go-arounds and diversions. Aircraft engines not only provide propulsion, but also power for auxiliary services like air-con, hydraulics, comms etc so the APU (Auxiliary power unit) would need to keep running throughout.
It would certainly make for an interesting study...
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Greetings and Kind Regards
It is not re/ gliders but rather another somewhat surprising aviation technology so perhaps the YouTube video link below may be of some interest to your kind self.
Could This Change Air Travel Forever? - YouTube[^]
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Despite what the video claims the oblique wing idea has been around long enough that if it was actually useful in the market place it would have already been adopted.
The US is not the only place in the world that creates planes nor is it the only innovator. So the claims in the video about what the US market was doing would not be relevant if in fact the idea was viable.
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no. just no.
Gliders, or for us that know better, sailplanes, either slowly sink or they rise due to thermals and wind currents. It's a cute thought but nope. Sailplanes are very dependent on weather.
The fact of the matter is that you can take an aluminum cylinder, put 500 people on it and fly it around the world quite economically. It works. It's feasible. It's not killing the world (if it was, all of those very concerned stars would be paddling canoes to get to their climate change conferences and staying in tents).
Noisy, yeah I suppose so, but here in Merica, we call it the sound of freedom (long joke). THE SOUND OF FREEDOM - F15E Eagle Low Level Over My House - YouTube[^]
Charlie Gilley
“They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759
Has never been more appropriate.
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One further thought regarding passenger confidence - for any aircraft, landing is the most dangerous part of the flight, so don't forget the saying about landing a glider: Every landing is a forced landing.
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smart a$$.  truth.
I took my daughter for some sailplane piloting lessons. It was quiet, surreal and simply a wonderful experience. As in all moving objects, you have to manage your energy. It's one thing to have one or two people aboard. 150+? Nah, I'd want that throttle to fight back against reality trying to kill all of us.
All it would take is one large glider full of people to go splat because the wind changed... and we're done. Commercial aviation is hysterically safe, amazingly efficient and inexpensive. Don't let the climate change whackos tell you otherwise.
Charlie Gilley
“They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759
Has never been more appropriate.
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Looks like they will be coming next year according to the video 
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“There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss. … Clearly, it is this second part, the missing, which presents the difficulties.” -Douglas Adams, Life, The Universe, And Everything
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It's a nice thought, but you're dealing with overcoming a lot of physics that are not in your favor.
First one is weather which has many moving parts, such as windspeed, wind direction, barometric pressure gradients, and temperature. Transport requires an ability to go from point A to point B reliably. A glider will be influenced by all the weather factors that could make it impossible to get to point B.
Second one is energy. While a glider can use the weather factors to its advantage, in nominal conditions the distance it travels is based on altitude and glide slope. Something has to get the glider to the required altitude to complete the trip. It makes little difference whether it's a plane or a slingshot, it requires the same energy, more or less. Though not an exact comparison, have you ever tried to fly a kite on a still day? The only way to keep it up is to get it high enough to maybe catch some wind and if that doesn't happen, all you can do to keep the kids happy is to run back and forth with it.
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Makes sense, maybe airships are a better idea (Jacquers had a nice video about that), this seems to become reality for cargo transport next year with the "Flying Whale" from a French firm.
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We already do. Modern jets are gliders that have just enough power to do the job safely and burn as little fuel as possible doing it. I would have sold my grandmother for a 1% fuel burn improvement when I worked for the local airplane company.
Take the 787 as an example. It carries 33,384 gallons of fuel. It flies 7400 miles. That works out to .22 miles per gallon (worst case, no reserves).
The 787 carries 330 passengers in a dual class configuration so that works out to 73 passenger miles per gallon.
So, you and the spouse hop in your RAV 4 Hybrid and drive LA to NY and back, taking every side trip that interests you, and you'll use the same amount of fuel as your one way trip to Australia.
Be warned, though. If you are driving at Mach .85 (650 mph) the speeding tickets will really add up.
Also, gliders can't do go-arounds. So, no thanks.
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I could definitely see where something like spaceship one could have at least four gliders arranged in circumference, their wings folded in, of course.
If you shot that thing into the stratosphere and released them all, it'd probably be possible to get them nearly anywhere in the US, assuming a TX launch.
The problem with gliders is you can't wait around for clearance. You have to land "now", mostly. There'd be different amounts of leeway where you could trade circling off altitude, but I think you'd still mostly need or want dedicated landing strips along with some smartly located emergency ones.
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There are major airports (plural) in the US where right now there is a significant problem with over utilization.
Too many planes in too little physical space.
Unknown to me why that is even allowed. The Airlines just keep scheduling more planes. Seems like there should be a exponential fee structure in place.
Only real limit is the number of gates.
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It's literally the N-body problem, I think.
Even centralizing all of the ATC data, you just can't predict where all the blips are going to be an hour from now because all the variables are (most cases, quite literally) moving targets.
So even though you can maybe "schedule constrain" departure/arrival airport "zones", I'm going to guess the real issue creating problems is kind of the same as people getting bumped off flights.
We want to utilize our airports to at least 90% or something. Whatever max capacity it is, we don't want to permanently give up more than 10% of that capacity as emergency buffer. So when all the pool balls on the table collide just 'wrong' you end up with a bunch of the balls clustered around only two of the pockets.
That's part of why I think just having some "emergency" airports, where the whole thing is basically airport overflow parking (but for planes/gliders) is probably a pretty solid idea.
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