Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Aerocart cargo gliders

aerolane.com

Post reply on HN
Print view View original

61–70 of 112 posts

Re: Aerocart cargo gliders

#61

Post by hermitcrab »

tgsovlerkhgsel wrote: post #27
aseg wrote: post #21

Earlier quoted context omitted.

In gliding, tow upsets are pretty common and, in rare cases, can be fatal. An out-of-position glider out can _easily_ and very quickly overcome the tow planes elevator authority (ability to pitch up or down) which leads to accidents like this. This video does a good job explaining explaining the root causes and potential dangers ( https://youtu.be/5cpqFzhM9dY?si=J7GxP1dI9Xopy3xu ). Also read the comments from testimo…

> An out-of-position glider out can _easily_ and very quickly overcome the tow planes elevator authority Would this not be trivially solvable with a system that detects the situation (e.g. by measuring the forces acting on the towing plane's attachment point) and detaches the tow? If in the final concept the towed plane would be unmanned and wouldn't contain fuel, even a crash would not be particularly catastrophic.

> If in the final concept the towed plane would be unmanned and wouldn't contain fuel, even a crash would not be particularly catastrophic.

You might not say that if it hit your house or your person. It is going to have a lot of kinetic energy.

Re: Aerocart cargo gliders

#62

Post by regularfry »

usrusr wrote: post #48
chimpontherun wrote: post #33

This concept raises more questions than the site answers: * what's the point of landing in tow? The safety aspects and the failure modes are enormous * it's unclear where the 65% fuel saving comes from. Riding the wingtip vortex on the inside produces downward momentum. In order to generate positive lift from the wingtip vortex, the follower has to be outside of it (e.g., gaggles of geese in wedge formation) * taking…

Taking an "optimist's advocate" position here (I share your scepticism): 65% are almost easy to achieve, with a bit of clever accounting: you'd look at fuel per ton-mile (that much is clear and perfectly fine) and then you just pick a tow plane that's maybe a bit overpowered but doesn't have much cargo capacity. If you look at fuel saving through that lense, the sky is the limit. The contingency page in the pitch dec…

The reverse - tow plane lands separately - has some interesting challenges. If the tow plane lands first and messes up the landing, blocking the runway, the lead plane now can't land. Fine if you've planned the fuel for a round trip, and fine if there's a currently-usable second runway, but I can see a huge draw for this in being able to get interesting cargo loads into and out of smaller airfields where that won't be available.

If the tow plane lands second then it needs to loiter, gliding autonomously, for as long as it takes for the lead plane to land and get out of the way. And that sounds like a much harder problem to do safely, particularly with the lead plane's pilot having to pay attention to landing and unable to control the tow plane if it gets into a dangerous state.

Re: Aerocart cargo gliders

#63

Post by hermitcrab »

drpixie wrote: post #2

Really? Those who have had anything to do with gliders know there is plenty that can and will go wrong. Landing on-tow !?!? And what's the benefit - they might save a little in cruise, but they've got to get there (safely) first?

Landing with a towed plane behind you sounds terrifying. So much could go wrong. Also the glider is going to have very different flight characteristics from the tow plane.

Re: Aerocart cargo gliders

#64

Post by regularfry »

rkomorn wrote: post #60
regularfry wrote: post #54

Earlier quoted context omitted.

If you've got a bigger plane, you also need a bigger runway. This thing should increase the number of usable airfields. That could be interesting for avoiding more expensive routes.

If your plane+cargo glider weight is the same as your larger cargo plane weight, won't you need the same amount of runway? Your towing plane is going to have to accelerate the same mass to takeoff speed before it can get off the ground, no?

It is, but that only happens at one end of the trip. It can still drop cargo on a smaller airfield at the other because the braking can be done independently by both.

Plus there's an interesting wrinkle here: a lot of the media on the site show the tow plane as one with engines, and not a glider. I'm sure that's because those are the aircraft they could get their hands on, so that's what they made it work with, but the option is there to have the towed plane powered on takeoff. Doing that safely, with the two aircraft tethered... that sounds like a mess. But it's an option!

Re: Aerocart cargo gliders

#65

Post by rkomorn »

hermitcrab wrote: post #58
rkomorn wrote: post #47

Earlier quoted context omitted.

"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

Re: Aerocart cargo gliders

#66

Post by sysguest »

gervwyk wrote: post #41
cirrus3 wrote: post #25

Earlier quoted context omitted.

> how much does it decrease the fuel economy of the towing plane Probably a lot, but I'd assume it is by less than the fuel that 1-2x more planes would use, otherwise there wouldn't be a point to doing this.

I did a masters on design a autopilot to optimize fuel consumption in formation flight. What is interesting about the aerodynamics is that if placed in the upwash wake of the leader, you are essentially increasing the wing aspect ratio of the system, resulting in gains for both the leader and the follower aircraft. Feels very unintuitive but basically the donut spool is larger and the combined wing is bigger in the s…

could you provide a link for this? I'm interested but I'm not sure what to google for

Re: Aerocart cargo gliders

#67

Post by hermitcrab »

rkomorn wrote: post #65
hermitcrab wrote: post #58

Earlier quoted context omitted.

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.

Re: Aerocart cargo gliders

#68

Post by rkomorn »

regularfry wrote: post #64
rkomorn wrote: post #60

Earlier quoted context omitted.

If your plane+cargo glider weight is the same as your larger cargo plane weight, won't you need the same amount of runway? Your towing plane is going to have to accelerate the same mass to takeoff speed before it can get off the ground, no?

It is, but that only happens at one end of the trip. It can still drop cargo on a smaller airfield at the other because the braking can be done independently by both. Plus there's an interesting wrinkle here: a lot of the media on the site show the tow plane as one with engines, and not a glider. I'm sure that's because those are the aircraft they could get their hands on, so that's what they made it work with, but t…

> but that only happens at one end of the trip

Ah, I get what you mean.

Re: Aerocart cargo gliders

#69

Post by rkomorn »

hermitcrab wrote: post #67
rkomorn wrote: post #65

Earlier quoted context omitted.

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.

Re: Aerocart cargo gliders

#70

Post by bombcar »

gorgoiler wrote: post #35

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…

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.
Post reply on HN