[gamegoblin]

I recently had a pie-in-the-sky business idea and I would love for someone who knows more about the industry why it will definitely fail. I assume it's unworkable for a lot of reasons, but it is just plausible enough to be a fun idea for a sci-fi novel.

Get a fleet of 2-4 seater unpowered glider planes [1]

Get a bunch of rural properties spaced ~100km apart.

Put little glider landing and launch strips on each property. Use a powerful electric winch to launch the gliders.

Develop software that can fly the planes autonomously from strip to strip (I assume this is the really hard part, but I am under the impression that autonomous flying is a much easier problem than autonomous driving?).

You now have the ability to shuttle passengers around your network of airstrips at ~200kph for the cost of electricity used by your winches and maintenance of the glider fleet.

My thought is that the electricity of the winches is pretty minimal and could be served with some locally installed solar panels and batteries, and the maintenance is super low since the gliders don't have many moving parts onboard.

The main use-case would be city-to-city short hops that are currently poorly served by rail. It's far easier to build a string of small airstrips than a whole rail corridor.

This idea came to me when thinking about SpaceX's recent plans to catch their Starship boosters out of the air instead of having landing gear on them. The reasoning is that you can have essentially unlimited mass for ground support equipment, but mass on the booster is precious. So you offload the landing gear from the booster to the ground support equipment, even if it's big and complicated. This idea is like electric aircraft, but you've offloaded the propulsion and batteries to the ground support equipment.

[1] https://en.wikipedia.org/wiki/Glider_(sailplane)

[rsp1984]

Here's a simple test I use on startup ideas. I call it the reversion test.

Let's suppose for a moment that air travel today worked the way you described it, with gliders, 60 mile range, electric winches etc.).

Then someone comes along and invents the motorized plane and now all of a sudden you can start and land a plane pretty much anywhere you want, you're no longer dependent on weather and, in addition, you multiply your range by a factor of 5x to 10x.

To me that sounds more disruptive than the other way around, so your idea would unfortunately fail the reversion test.

[Leherenn]

A winch gets you maybe about 1/3 of the cable length (and thus strip length) at best. A typical cable length is between 1 to 2km long. Let's say you can gain 500 m height. A glide ratio around 50 is probably on the higher end of what's achievable, so you're looking at 25 km of range. That's before you account for wind, that the world is not flat or the fact that you don't start your landing at 0 m, but more like 200/300 m from the ground.

Honestly, for short ranges, you're much better served by electric planes, or gliders with a self-launch motor. Small strips and winches don't go together.

[TheOtherHobbes]

You can get almost infinite range on hot days by riding thermals.

This assumes thermals are available in the area (some days are better than others, as are some locations), and the s/w knows how to ride them.

But that is a much harder problem than just launching and gliding.

Also, gliders that could carry even a handful of passengers + baggage would be huge, and likely far too heavy for a simple winch lift.

As for the automation - airliner flight is more or less a solved problem, for flights in good weather that don't suffer any emergencies.

It hasn't been taken further because most passengers don't want to fly without a human in charge. And also because the edge cases - unexpected turbulence, difficult weather, mechanical failures, unruly passengers, software failure - happen often enough to be a problem, and they need someone trained on board to take over.

Otherwise people die. And that's very bad.

[CPLX]

For context I have a pilots license and have tooled around in a glider a few times as well.

Some problems with this scheme come to mind quickly but these are the first few:

1) Weather. It exists and basically makes this plan totally unworkable on any practical level.

2) Physics. An unpowered glider would have at best 1/100th the potential energy to fly distances like the ones you describe assuming perfect weather. Remember there are hard limits on altitude (due to oxygen) and speed (need to not rip the wings off) and those plus weight are the variables in your equation that tell you how far your glider can get unless it’s able to exploit unpredictable thermals.

3) Refundancy, or lack of it. The failure mode for the slightest miscalculation is certain death for your passengers and maybe a few on the ground. Unpowered flight leaves essentially no margin for error which makes it a non-starter.

[zamadatix]

Not familiar but like the spirit of the idea. At first glance from just the material you provided it'd have to be a lot closer than 100km apart, 30:1-40:1 seem to be typical ratios with 70:1 being cutting edge and winch launch height seems to top out at 3000 ft (less than 1km). Not to mention for a lot of travel the ground isn't flat which can be problematic even in the direction there is an average decrease in ground height.

Flying in good conditions may be an easier problem to solve than driving in good conditions but the issues seem to move towards what happens in the bad conditions. It's not like you can just hit the brake or park on the side of the road and continue later when the system detects a current or upcoming problem. Even if you get it so 99.99% of flights are in favorable weather and wind without piloting issue a 1 in 10,000 chance your glider is going to make an emergency landing or worse is not good enough odds, especially if it's multiple flights each way. And that ignores the problem of the service being unavailable if certain weather conditions aren't met, so the backup transportation option is still needed at a moments notice in full force anyways.

Then, much like self driving, there are the regulation issues https://www.ssa.org/glider-pilot-ratings/ which would be their own challenge to change and require you solve them before the business can even get it's chance to get going.

That being said I like the concept, just not sure it's really any easier. Perhaps we should just build the missing rail instead :).

[gregmac]

> Develop software that can fly the planes autonomously from strip to strip (I assume this is the really hard part, but I am under the impression that autonomous flying is a much easier problem than autonomous driving?).

As a software developer, this part is what I don't like.

We're still quite a ways from fully autonomous driving cars (as in: don't rely on a human taking over for backup). A bad bug in an autonomous car could drive you at high speed into a wall, but there can at least be an "emergency stop" button that disables the main processor and jams on the brakes.

Planes have no such ability to just "stop". At best, they could deploy a parachute, but even then landing safely is by no means guaranteed.

I think we need a decade or so of fully autonomous cars being accepted into daily life before this can be attempted with anything that flies.

[holycrapwhodat]

As both a software developer and a pilot...

We're (much?) closer to Fully-Self-Flying planes than FSD cars because the problem space is - perhaps counterintuitively - MUCH smaller to tackle. And we have a lot more experience tackling it.

Additionally there could easily be remote pilots as backup in case of catastrophe (See remote piloted military and border patrol UAVs)

And pulling a parachute at 1000'+ altitude actually has quite a bit of precedent (See https://en.wikipedia.org/wiki/Cirrus_Airframe_Parachute_Syst...)

Now... There's probably a lot of cultural and regulatory reasons why the "string of automated glider ports" idea will never come to fruition.

But... As far as technical hurdles go, there's not much new technology that would need to be invented here.

[theYipster]

As an industry leader on this specific subject matter... I agree: the problem space is much smaller, in theory.

However, certification requirements and safety assurance needs will drive both cost and time into realizing fully autonomous aircraft. They will be here, but we are 10-15 years away.

The problem is in how to certify machine learning code. Today, you can't. Existing AMCs (accepted means of compliance) are incompatible with the nature of ML. (The breakdown is specifically with assurance architectures focused on code traceability and coverage.) A new architecture for demonstrating safety assurance with AI/ML is needed, and is being built, but is still 1.5-2 years away from being released, and then it will take another year or two before a CAA (civil aviation authority, like the FAA or EASA) will certify a component with ML code--and that will not be an autonomous pilot. That will come in time, but the industry is conservative--especially on safety-critical matters--and it will take years to develop trust in both technology, human factors, and methodology to work up to autonomously flown passenger aircraft.

From the regulator perspective, EASA has taken poll position in thought leadership. Google their AI Roadmap or their Concept Paper for Level 1 Machine Learning Applications.

[silvestrov]

> string of automated glider ports

There is a small precedent here: the space shuttle flew almost 100% by computers.

There was a small involvement of the pilots when landing and some change of software due to small RAM size in the computers.

I could imagine "Fully-Self-Flying planes" would start out with cargo planes between areas with low population.

[topspin]

Point of information; certified autoland systems appeared on airliners in 1968. Yes, we're a ways off from the level of automation for a fully pilotless system as proposed here, but I think it a matter of a few years, perhaps a decade.

[jonfw]

You know what they say- the last 20% of the problem is 80% of the effort. I think that these percentages probably understate things, but the point is that getting something to be mostly functional in ideal circumstances really isn't much of an achievement.

[topspin]

"mostly functional in ideal circumstances"

Autoland was developed for and is usually used in poor conditions.

[azalemeth]

A few points:

-- I don't know of any glider mass-produced after WW2 that seats more than two individuals, ± a water/sand ballast tank, ± a range-extender or self-launching engine.

-- Have you ever experienced a winch launch? Try it. It's about 3g of acceleration, sometimes more. I quite like them. Most normal people probably wouldn't.

-- At the top of the winch launch, you pretty much need to immediately find a thermal and gain some height before flying off cross country. You've got about a minute or two to do so, before entering the circuit and needing to re-launch and try again.

-- Replace "200 kph" with "about 80 kt IAS". Remember that gliders fly beneath the weather 99.9% of the time and the winds in clouds are strong -- although the only youtube videos I've seen of an aircraft landing "backwards" on a runway are of a Russian high-wing aircraft, it's entirely plausible that you could end up getting a negative tack speed in a cloud.

-- Cloud flying, or flying in inclement weather is insanely dangerous for a glider. They're relatively light, have large aspect ratio wings, and don't usually have a whole lot of instrument navigation equipment on board. If the wings are wet, their coefficient of lift goes down...which would have very bad consequences for your business model. There's a reason that cross-country glider pilots have a friend with a land rover and a trailer, and train to land in fields, after all.

-- You have absolutely no opportunity to make a go-around in a glider landing. Zilch. Nada. Screw it up and Plan-B is a well placed field. This is less likely to be acceptable commercially.

[carabiner]

The problem is rural areas are not cities by definition. So you'll drive out 30 minutes to a rural airstrip, fly out to another rural area in a 30 minute flight, then presumably rent a car in the rural area (build an Avis there I suppose), and drive 30 minutes to the other city. Including time for transitions, checking in, and paperwork, it's maybe 2-2.5 hours for 100 km of travel. You could maybe take rideshare, but if this is truly "rural" that might not be an option. Have you ever tried getting an Uber to take you 30 minutes outside of a city? I regularly drive such distances on the weekend in 1 hour. The overall idea of travel between cities is what air taxis were for: https://en.wikipedia.org/wiki/Air_taxi but it was for distances of 200-500 miles.

The energy would probably be better spent on a bus, with even a gas-powered bus being more efficient per passenger-mile than a 4 pax aircraft. It could also go city to city and skip the rural areas altogether.

[ericpauley]

This has a lot of physical issues, not least of which is air resistance (drag). Simply launching a plane off the ground does not impart enough energy to make the full trip at high speed, and airplanes must continually burn fuel to counteract drag and gravity.

Gliders are able to bypass this limitation in certain scenarios (such as updrafts) but this only works in specific cases. It also usually takes more than a launch to bring them to sustainable altitude, and they are slow.

[amirhirsch]

Electric aircraft (not necessarily gliders) could use a tethered assisted take-off and ascent as a way to save on the initial power draw. You probably would want to use another assistant plane (not a ground station) to pull the passenger plane to altitude and speed and then return to a runway while the other continues on it's longer flight.

[thehappypm]

Gliders don't launch by winch. They are towed up to launch height by powered planes.

Also, gliders are not really able to handle emergencies that well since they are unpowered -- if there's a need to divert or something, they're completely at the mercy of their own gravitational energy. Gliders are usually very safe to fly in because they're very light and maneuverable, and crash-landings are usually OK. That safety net completely evaporates with thousands of pounds of human cargo.

[decadancer]

>Develop software that can fly the planes autonomously from strip to strip (I assume this is the really hard part, but I am under the impression that autonomous flying is a much easier problem than autonomous driving?).

I guess it could be easier in some ways, still the idea of passenger UAV(?) seems insane for some reason

[maximus-decimus]

This me reminds me of Canada's joke political party : the Rhinoceros Party.

They proposed stuff like putting steroids in water supplies to make Canadians stronger. One of their propositions was to build an inclined bike road across Canada so you could "coast from coast to coast."

[skanga]

1. Use it for CARGO only. Air freight is a huge business. 2. Do NOT fly in poor weather. Use it ONLY when conditions are favorable.

[Izikiel43]

Wouldn't landing be the hardest part?

[gamegoblin]

Totally possible, though I was under the impression that the UAVs used by the military already land autonomously. But I agree that the autonomous flight part is almost certainly the hardest part here.

I am mainly curious if the general physics and economics of the idea are remotely feasible, assuming the software is solvable.

[jonfw]

UAVs are under constant supervision... when they say unmanned, they really mean that they're not lugging around the human who is manning them.

[TrainedMonkey]

I would expect handling all of the edge cases is the hardest part. For example, there is an emergency of board and you have to land immediately, what do you do?

[kaba0]

Other than the already mentioned parts, wouldn’t the acceleration be too great for your average passenger?

[gamegoblin]

On a 1km runway you could get up to 700kph with 3g of acceleration over 10 seconds. I think some rollercoasters pull higher G's than that.

[squeaky-clean]

Rollercoasters generally warn the elderly and those with heart conditions not to ride them. Commercial aircraft pull about 1.3 G maximum.

[kaba0]

Oh, I imagined a much smaller runway — of course longer ones could be more than good from this aspect.