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Comment by gorgoiler | Hacker News Reader

This product is for towing behind another aircraft, but what about winch towing?

A winched glider implements flight with renewable electricity and it does so efficiently because the power and motor never leave the ground!

A glider can climb up to 5000 feet and travel 50x that before making a landing. Wouldn’t it be glorious to see cargo being autonomously slung from site to site across the world, powered entirely by green electricity?

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The we simplify it by putting the winch on rails, and give the glider wheels, then we can chain them together and then we’ve reinvented the railroad, badly.

Yes, then we could put wheels on my grandmother and we would have invented a bicycle badly

https://youtu.be/A-RfHC91Ewc?si=uMjPf00zqbJHfSwn

We are so smart that we can take good things and modify them in stupid ways to make bad things. This is, in fact, very smart of us.

Winch launching is already a thing https://youtu.be/U3ztaJ0yfxE?si=1AjAS8F8-pCaUFZI

Building a railroad over water or through a jurisdiction full of jerks is expensive.

I can see a big winch glider being worthwhile in some very limited circumstances.

Nah. You've messing up something 4chan worked out years ago. You need a BLIMPTRAIN! Locomotive on rails towing a train of lighter than air vehicles that can detach under optimal conditions/location to deliver their cargo over the last mile.

Try loading 10 tons into some glider and shooting it up. First the winch would have to be absolutely massive, second its highly reliant on at least a bit good weather and nobody glides around during night. Pilotless doesn't remove danger of it falling onto some roof, so automation would have to be pretty much flawless.

Truck, you can load and send it much further than any glider can ever glide, any time, any day. Also throughput of highways is much bigger than airports, and you can deliver it literally to the target doors.

Not a very practical fantasy it seems.

I've done a few gliding flights. They were all towed to height by a powered aircraft and then released. Winch launch is an alternative to towing, but sounded like a fairly terrifying alternative where you were yoinked into the air by a huge winch. The terror isn't an issue if the glider is pilotless. But IIRC they used something like a 7 litre engine to winch an incredibly light glider. Presumably it would require something really powerful to launch a cargo glider.

I did once fly as a guest with a winch start, and yes it is something. The ascend is pretty steep and the acceleration is powerful. The pilot did not find good lift and we had to land shortly after. My stomach did not like his curving around looking for lift, so I wasn't too unhappy about the short flight.

I have done it. It's actually quite thrilling, feeling that initial burst of acceleration.

Can you please ELI5 winched gliding to me?

Is a glider basically joinked into the air by a large and fast winch, and then detached and the glider glides on it's own "power" back to the landing? Or is the winch at the destination, with a cable going _all_ the way across the landscape to where the launch point is, so that it can pull the glider over?

I'm a tad confused.

You nailed it: the winch pulls the glider rapidly up to altitude, lets go, and the glider floats back down to earth.

Not sure why you are being downvoted, but thanks for the response nonetheless.

Hah, it wasn't a very meaningful response. It's OK for this community to have moderated my comment appropriately, especially given drpixie's much better answer! Yes, it's just like a kite!

The winch launches the glider and gives it speed from the ground that it can then convert into enough altitude (ie time) for the pilot to find a rising air current (ideally, I guess).

Edit: so yes, your first thought is correct. :) It's somewhat similar to an aircraft carrier launch except that the glider can get a lot more altitude out of it.

Winch launches are a lot like a kid with a kite. Run fast (wind in the winch) to get speed and up it goes. At its desired altitude, the glider disconnects and goes on its way. https://youtu.be/YePIJKs5me0 gives you an idea.

On a day with a decent breeze, it is possible to "kite" a glider up to very high altitude by letting the wire out again. But this is highly frowned upon because it means there is a very long (and nearly invisible) wire dangling right through the airspace used by other aircraft!

Thanks, I tried to look exactly this up, but couldn't find anything. Looking at that video, the only thing I could think of though was that cable, presumably detaching shortly after the video ended, and the cameraman is just standing there where the cable could presumably fall. It does not look very thick and heavy, but still!

Traditionally, winch cables are single strand steel (fencing) wire - I guess because that's cheap. But they break quite often.

Cable falls can be a problem. A cable falling over power lines causes all sorts of fuss!

Cable breaks can be terrible. The cable will spring back, whip around, and is incredibly destructive - hence the cage around the winch operator. I would not have been standing anywhere nearby and certainly not next-to or behind the drum.

I'm the wrong kind of engineer to work it out, but I'd be interested to know what the implications for the strength of the cable and specifications for the winch would be for a heavy cargo glider.

Thinking on, specifying the weak links and managing failed winch launches (which happen fairly regularly) is interesting to consider. Recreational gliders are light enough to be manoeuvred by hand, although old farm tractors are used to move them more than a few dozen feet. How would all that work?

Maybe this problem is adjacent to catapult launchers on aircraft carriers.

Do you mean laying out 50 mile long cables from place to place with big engines on the ground that pull in a cable at a couple hundred miles per hour after a plane attaches to it? That wouldn't work. Not even if you skipped tow out a cable from your departure point so it could be reused.

And if you had a track for the cable to run in or a carriage holding the winch to drive travel along, then you would just make it rail freight.

No. Winch glider launches (which are not a new thing) use a ground-based winch to give the glider an initial impulse, and the glider uses that to gain altitude and then glide for a much longer distance.

https://glidingschool.com/briefing-winch-launch/

Well then it's even simpler, carrying any worthwhile amount of cargo in a winch launched glider is not going to work.

It would work fine for sending small payloads short distances but unless you're in a hurry, it would be much easier to just send more mass by truck or train. One big benefit is having a truck or train being able to return to its origin without requiring another launch facility and also being able to travel in nearly all weather. There may be some use cases where drone gliders could airdrop payloads and return to their origin. But again, this requires very specific circumstances like good weather, a lack of roads, unavailability of av gas or jet fuel, and enough cleared space to launch a glider. I do see winches as a good way to launch lightweight fixed wing drones to reduce the amount of fuel and engine size required to deliver payloads. You'd only need to account for the fuel and power required to sustain cruise if you could winch a drone into the sky. You'd get even more distance if the drone was never intended to return like a kamikaze weapon. A small clearing in a field in Ukraine could launch cheap fixed wing kamikaze drones all day long.

It wouldn't work very fine at all. Gliding at low speed a minuscule payload 50-100 miles that you have to transfer to the airport at the departure point then from the airport at the destination will almost certainly take longer and be much more expensive in terms of infrastructure and worker cost than just driving it point to point in a delivery vehicle. It's also highly weather dependent, much more so than powered aircraft.

If you're really in a hurry you need a helicopter. Then pay your indulgences to some politician's shady "carbon credit" corporation if you feel guilty about your climate sin, or use a carbon-neutral manufactured kerosene for it, and then you're even greener and still cheaper than the unpowered spruce goose idea.

How about a carrier style electromagnetic catapult to launch the glider? Except make it ski jump style so that the glider gains initial altitude.

(Now that I mention it, why don’t carriers combine both catapult and ski jump?)

Traditionalcgliders are incredibly light, I doubt anything careying sufficient cargo will be able to do a 50:1 distance to altitude ratio.

Glide ratio and weight are not related. Weight shifts the glide Polar to higher speeds and theoretically improves it slightly due to Reynolds effects.

"Weight doesn't affect glide ratio" is one of these things I learned why taking flying lessons that still feels counterintuitive every time I read it.

(Don't worry, reader, I never intended to get a pilot's license.)

So, 2 gliders with identical geometry, one standard and one made of lead will have the same glide angle? That sounds unlikely.

There is an asterisk that you have to be at the right glide velocity, but yes: they'll have the same glide angle. The leaden one will just go significantly faster. And yes, it does sound unlikely. That's why I made my previous comment.

Here are a couple of many posts on the topic:

- https://gronskiy.com/posts/glide-ratio-lift-to-drag-and-weig...

- https://skybrary.aero/articles/glide-performance

Thanks for the links. Weight may cancel out of the equations, but (being a bit pedantic) I suspect 'glide angle in independent of weight' only holds up to a point. Taking things to extremes, if the glider is heavy enough that you are going to have to go supersonic then I suspect a lot of the assumptions become invalid.

NB/ spherical cows are unable to glide in a vacuum.

I assume it is a relevant enough concept to flying an aircraft (which also happens to be the context of TFA) that you learn about it while flying.

I guess another thing worth noting is that "glide ratio" isn't the same as "gliding" in the "flying a glider" context.

The space shuttle is probably the most famous glider, and was described as "a flying brick" and getting it to the ground at the right spot was very much a matter of glide ratio. Worth noting the space shuttle's speeds started off as hypersonic.

By comparison, a typical glider's built to be able to take advantage of air currents to regain altitude, and I'm not sure how weight affects that.

Weight affects speed with minimum sink. That affects the diameter of the circle you fly. Since thermals have more lift towards the center (assuming perfectly circular thermals), you are not able to circle in the strongest lift. So you climb more slowly.

You can glide faster with the same L/D, so that might be worth it if you try to optimize for speed.

Intersting! Thanks for chiming in. :)

Make a paper airplane and drop it. It likely won't go much further than your feet. Throw it gently and it will go some distance. Throw it harder and it will go further. Glide ratio is the horizontal distance over vertical distance. The vertical distance is the product of (lift - mass)*t^2 where lift is a function of the shape of the wings and the airspeed. So given a higher mass and the same lift, the time to hit the ground will be less when the glider is dropped at 1000ft. Increase the airspeed and you'll have more lift to negate the higher mass. The increased airspeed also means your horizontal distance will be covered faster. The lead glider will travel the same path as the normal one but will be going a lot faster. The reason why gliders are built as light as possible is reduce the work required to lift them, the speed at which to release them, and the interia required to turn them. You also have the benefit of being able to land them at a lower airspeed without injury.

The same angle, but at different speeds. The speed is multiplied by the square root of the weight ratio (new/reference).

The minimum speed, at which the critical aoa is reached, increases. And therefore the take off and landing speeds.

I don't get why this got some downvotes.

It does sound unlikely, and it's not like the comment is saying "no f'ing way!!" It's about as polite a way to say "that's weird" as anything.

I don't think it's completely true. Higher weight increases the speed at which the glide ratio is optimal, and drag (parasitic drag in particular, unrelated to generating lift) increases with the square of speed. Basically, flying faster wastes more energy. That effect is going to dominate at some point, probably about 120 km/h or so with a typical glider. At 200 km/h, the glide ratio is garbage (but it's fun). I have flown gliders.

I'm not sure if simple descriptions of the phenomenon that glide ratio is independent of weight are missing an asterisk or if I'm just wrong...

A decent glider has a ratio of 1:40, an A320 1:17. Is the A320 a "bad plane" or is it optimized for higher speed with the corresponding worse glide ratio? (It also has engines that produce a lot of drag when gliding)

I don't know. On one hand there's your take.

On another hand, there are CFIs, the FAA, books, etc.

I've only found one search result that agrees with you, so far, and at least a dozen that disagree, but the one that agrees with you has no math in it, and the ones that disagree mostly seem to depend on the same source info, so that doesn't feel conclusive in either direction.

The Wikipedia page on lift-to-drag ratio also believes weight does not matter to the ratio.

As a side note, your 200km/h example also sounds like it's just not the correct angle of attack or airspeed for the aircraft, so I'm not sure if that example applies?

As a separate reply, I'll add that I think finding where/if this breaks is pretty academic.

Eg: you wouldn't build a glider out of heavy material that gives you huge speeds but also huge sink rates.

So I think the entire glide ratio conversation mostly fits in the "your plane is fully loaded" vs "your plane is empty" scenario, and the point is that your best glide ratio will be constant, but you'll be gliding at higher speeds if you have more weight.

Gliders utilize Laminar profiles, while airliners use turbulent profiles.

The Laminar profiles perform better, but only when uncontaminated (no bugs or rain). Contaminated turbulent profiles perform better than contaminated Laminar profiles. Since regulations state that you should carry fuel for the worst case scenario, it does not yet make sense to design airliners with Laminar profiles.

Naturally, manufacturers are looking for ways around this.

Traditional gliders also carry ballast for cross country flights, which increases their speed without negatively impacting their glide ratio.

Really? That seems counter intuitive.

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