New aircraft rises 'like a balloon' | Hacker News Reader

New aircraft rises 'like a balloon'

bbc.com

112 pointsjdmark70 comments

Most of the mentioned use cases involve high altitudes. Higher altitudes = higher winds. The air is smooth up there but it does move. For instance, the upper level winds above my head right now are pushing 130knots. This thing will have to do more than glide gently up and down if it wants to maintain station at 10km+, airliner altitude.

I was wondering about this too. Then again, I don't know the air density difference. 130 knots at half the density (not that I know if half density is a feasible figure) would impart something like half the force, I imagine. Then again, lower density affects the ability of craft that use density for lift to operate.

> not that I know if half density is a feasible figure

1/15th - .08 kg/m^3 at 20km, 1.2 kg/m^3 at sea level. 20km is way the heck up there. And yes, it does make it difficult to build something buoyant enough, which is why the use case for this is something like a geostationary internet balloon rather than for transportation.

https://www.engineeringtoolbox.com/standard-atmosphere-d_604...

Density doesn't matter. As the density decreases the force of the wind does decrease, but the propulsive ability of propellers/wings also decreases. So the net effect is that the engines have to work equally hard.

Yup, that has been the Achille's heel of these types of vehicles. One work around is to have a bunch of vehicles and have them move to altitude, stay over the area of interest as long as possible and then change to a lower altitude without the winds to move back to the head of the line.

Apparently the craft is powered entirely by solar power, plus batteries, to work at night. A solar powered craft cannot maintain 130 knots.

Solar impulse 2 used 269.5 m2 of solar panels to produce 66 kW peak and do 75 knots.

That’s only ~1/2 the current max efficiency of solar panels. Suggesting many other improvements are at least possible and 130 knots are within reach if that’s what was being optimized for vs say cost.

The cool thing about this craft is that it’s a glider and doesn’t use solar power for direct propulsion. Instead it uses the solar power to make the ballon lighter than air. Once it reaches altitude it will start gliding by making the ballon heavier than air. While gliding it can reach very fast speeds. The question is though how many times it needs to refill the ballon during the night and if the stored power is enough.

Go higher. If you search for "high altitude wind" you'll get info from 20,000 feet, which is not at all the same as 20,000 meters. Past a point, the thinning atmosphere actually means less coupling and wind speed decreases. You'll note that tiny quote halfway through about it being difficult to get up to the required altitude of 20km. That's because the average wind speed bottoms out around 5 meters per second at an altitude between 20km and 25km [1]. Add in the thinning air reducing drag and, yeah, a solar-powered balloon can absolutely stationkeep at that altitude. Here's a wiki page with more links: https://en.wikipedia.org/wiki/Geostationary_balloon_satellit...

[1] https://www.researchgate.net/figure/Average-wind-speed-in-th...

The same method of altitude control, using a compressor and an internal "ballonet", is used on Google Loon.

With the soaring price of helium, I wonder what it costs to fill up that gas bag and how quickly it leaks out. And at what point filling it up costs more than the "almost expendable" aircraft.

In the novel/film Contact the character S.R. Hadden lives in an airliner that rarely lands. With a larger Phoenix that lifestyle could become available to somewhat less wealthy billionaires. Maybe it could eventually become an atmospheric variation of seasteading.

There are no really great lifting gases. Steam is ok but must be kept hot. H2 is dangerously explosive. Vacuum is the best (a so-called "null ship") but no known material can maintain the hull pressure under vacuum.

Excuse the silly question if it is one, but would one option be not a full vacuum but only marginally lower density of air inside the balloon, supplemented by solar-powered propellers? Could there be a material strong enough to handle a minimal density difference to provide enough lift for it to work?

No not even diamond is strong enough to allow generating a useful amount of lift that way.

To add to your Idea, could a "null ship" be carried to a greater height and then where the air is thinner have it's gas removed to take everything a little higher?

Like rocket stages but for airships.

At a greater height you need a larger airship to provide the same lift. As you move towards the vacuum of space and the differential becomes less the lift per unit volume is less.

aww :(

Yeah I had this idea also, steam vapor at 1/8 atm might be easier than a full vacuum. Havent done the math, though.

Any structure strong enough to withstand the pressure from outside the vacuum weighs too much to be lifted. At least that's what I read in some aerodynamics book. Maybe some materials scientist will come along and prove that wrong.

Can we make many small ones instead of one big one?

As volumes decrease in size, the ratio of surface to volume increases, make weight a bigger issue with smaller envelopes (given that surface thickness would not be able to decrease proportionally).

I don't think the possibility can be entirely discounted. Consider composite materials, a honeycomb. Much more difficult to analyze than a sphere of steel

> H2 is dangerously explosive.

Does it matter for an unmanned vehicle? Such a thing could be inflated at a safe distance. In some cases, being able to self destruct is a safety benefit (to prevent crashes when control is lost) and a security benefit (to prevent analysis of captured aircraft). Particularly UAVs are popular in military / spying operations.

I'd argue that hydrogen is actually among the best, with helium of course being second.

Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue.

Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas!

Prior to that accident, hydrogen had a fairly great record with airships, and it was used extensively for ballooning as well without many incidents.

Hydrogen by itself isn't flammable - you need another particular gas involved for that to be an issue. You also need a source of ignition.

The other problem with hydrogen is that it is hard to contain. Leakage and permeability of the envelope would probably end up being a bigger engineering concern than would flammability.

And yet another problem with hydrogen is that unlike helium it is reactive, including with some metals. And those metals tend to become brittle fall apart after a while: https://en.wikipedia.org/wiki/Hydrogen_embrittlement

http://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/...

See Figure 2, Gas Permeability of Mylar vs. Temperature

Helium permeates Mylar significantly faster than hydrogen over the full temperature range tested. It looks like the helium permeation rate is nearly double that of hydrogen near room temperature. Surprising! I would have guessed that lighter gases permeate faster. Note on the same figure that oxygen permeates faster than nitrogen even though it's heavier.

There is more tabular data here:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196900...

It confirms the same trend. Helium permeates Mylar faster than hydrogen.

Hydrogen is only something like 8% better for lifting than helium because they are both much lighter than air:

* https://en.wikipedia.org/wiki/Lighter_than_air#Hydrogen_and_...

Agreed that the danger of hydrogen is less than perceived. In an accident it goes up which is normally where the people are not. When it burns it doesn't create much radiant heat. Outdoors in the daytime firefighters have to use something like a broom to find hydrogen fires. Otherwise you could just walk right by one ... which is an issue if you instead walk right into the fire.

What about helium?

Helium is expensive and practically non-renewable on Earth. It forms slowly by beta decay, with most of it escaping into space (because it's molecular mass is so low, its velocity commonly exceeds Earth's escape velocity). A small amount gets trapped in deposits which we can extract.

Hydrogen will have issues supply-wise if we kick into industrial scale processes with high loss rates without some way to ensure the gas recombines with Oxygen to precipitate as water again. Which at the operating heights being suggested, would be problematic. Furthermore, what about all that waste Oxygen from Hydrolysis?

We already run into issues with water without cracking water vapor and venting hydrogen into the atmosphere at scale. I shudder at the thought of unconstrained industry being cut loose with the idea that we have an essentially limitless supply without sitting down to really figure out the numbers.

Never mind the maintenance issues. High levels of electrical generation/storage +volatile gas generator? What could possibly go wrong? Hydrogen embrittlement, high level of oxidative stress, increased radiation exposure...

Mean-time-to-failure is not giving the magic 8 ball warm fuzzies. Could be super neat for meteorological/astronomical purposes/reconnaissance purposes though.

I can see the international incidents rolling in now.

"North Korea protests American Weather Baloons"

"Russia introduces new anti-balloon laser"

"China threatens Taiwan over balloon based infrastructure"

Unfortunately, I wouldn't put it passed ad companies to utilize this "exciting new breakthrough in audience outreach" as well.

I'd really like to look at this kind of stuff how I used to as a kid again. Too much time in the tech industry has absolutely ruined my outlook however.

I'm not exactly sure what it is you're decrying. That we'll lose a significant quantity of Earth's hydrogen to space, leaving the atmosphere with too much oxygen? That we'll suffer a water shortage because we're using too much of it to make hydrogen? That nations will increasingly ignore other nations' aerospace sovereignty because balloons are filled with hydrogen instead of helium?

Hydrogen is still expensive to split from water, and the quantities required for deleterious effects to present are so high, that these are really distantly hypothetical "what ifs".

Make a vacuum onion.

1d-compressium, 1d-tensilium, and 2d-tensilium are all allotropes of obtainium, being the materials with the highest uniaxial compressive strength to mass ratio, the highest uniaxial tensile strength to mass ratio, and the highest biaxial tensile/shear strength to mass ratio. Currently, those are probably diamond struts, buckytube fiber cables, and graphene sheets.

Throw 2d-tensilium envelope around a tensegrity frame with 1d-compressium struts and 1d-tensilium cables. Pump out the interior gas until it breaches or collapses.

Start over. This time, put another frame and envelope around the first, and anchor them to each other with more 1d-tensilium cables. Pump out the interior gas of both pockets until the outer shell breaches or collapses.

Repeat, until the pressure differential on every envelope and shell is insufficient to breach the envelope or buckle the frame. Now you have a gradient from vacuum to atmospheric pressure instead of a perfect vacuum in the whole volume, but you don't have to find any unobtainium to build it.

As a bonus, you can put the envelope on the inside of the shells, and follow a similar process of breaking each one with air, to make an inflatable spacecraft hull that can hold 1 atm of breathing gas on the inside without rupturing in vacuum, using minimal mass.

Wouldn't all that inner material be too heavy to float after that?

You have to make the shell large. The bigger it is, the more slack you can get with the strength of materials and vacuum pump power.

Vacuum only gets you 7% more lifting force over hydrogen:

* https://en.wikipedia.org/wiki/Vacuum_airship#Principle

If helium gets really expensive, they could switch to hydrogen. Maybe even switch inflight, by replenishing lost helium with hydrogen. Maybe by hydrolysis. For a plane operating in remote areas at altitude, the explosion risk is not an issue.

That is an interesting idea, and I don’t know why this has been downvoted.

Sounds kind of ludicrous to propose switching from helium to hydrogen in flight to save on the cost of helium.

You’d still have to buy the helium (how else does it get off the ground?). Probably more if you intend to safely bring it back down.

The idea I got was that for long-term flights, the helium would be used for launch, and lost helium would be replaced with hydrolysed hydrogen. Doesn’t sound too unrealistic.

That makes sense, thanks. I apologize for my acerbic ignorance in the above comment.

You could switch in-flight, but you would actually increase the gas costs since you’d need 100% helium for the trip up as well as the trip down. Also, the risks would dramatically increase in exigent circumstances. What if the gas container fails, causing it to make an unexpected descent? Even for a planned descent, there has to be a way to switch back to helium.

So now you have to have at least 2 times the helium needed to attain buoyancy, plus mechanisms to generate hydrogen and vent/replace gas. And systems/procedures to handle edge cases.

It sounds like a lot of complexity and cost added. However, it might be worth it if extremely high altitude is needed. The altitude ceiling could be increased significantly (not sure how much, but <2x) for a given configuration and payload.

But for an expendible aircraft you don't need it to be buoyant on the way down. Just have a failsafe that dumps the hydrogen into the atmosphere below a certain altitude/air pressure.

That’s true. But there have to be applicable regulations around dropping expendable aircraft remains over populated areas.

> Maybe it could eventually become an atmospheric variation of seasteading.

It's like a miniature version of the Venus cloud city idea, but here on Earth.

I believe Hadden lives on a space station in both movie and book.

First a plane, then he moves up to Mir: https://scifi.stackexchange.com/questions/124894/in-movie-co...

According to the article, the Phoenix has a reversible hydrogen fuel cell on board. Just a guess, but maybe it's filled with helium on the ground (for safety purposes),then generates hydrogen (from electricity and water) once aloft to replace any lost helium?

For those curious, University of the Highlands and Islands is in Inverness, Scotland. Quite a bit north of Edinburgh and Glasgow.

That's the main campus but part of the concept is for it to be distributed over most of the Northern part of the country, including, as the name suggests, the islands:

https://www.uhi.ac.uk/en/#campuses

Just out of curiosity, do you have any relation to the Remarkable Tablet?

Nope, no connection, both independently named after the character in the Iain Banks sci-fi novel, I assume.

The solar powered blimp in the photos looks too slow to stay in one place on a somewhat windy day, which would be necessary if it's a satellite replacement.

I'm curious if it can achieve the 20km altitude. I would bet weather would be a significant factor with keeping it aloft and on course.

I remember a proposal for one of these balloon gliders by NASA. Except on an entirely different scale. Be cool to see how it works out.

I'd love a fleet of small lighter than air balloons for city coasting

This is exactly how submarines work

Submarines use a prop for forward motion and are almost never 'gliding' using their planes. The purpose of the wings on this craft are similar to the variable-buoancy underwater drones that are out there, when the craft is rising the wings are trimmed to cause forward motion and then when it is descending they are trimmed in the other direction to continue forward motion.

What decides if it's an airship or not is not whether it has wings, but whether it's lighter than air. This thing is lighter than air, thus it is an airship.

Yet more terrible writing by the BBC.

I might be misunderstanding things but it sounds like the "breathing" (compressing atmospheric air) gives it variable density? I guess it makes it a sometimes-an-airship.

"The central fuselage is filled with helium, which makes it buoyant so it can ascend like a balloon."

"And inside that there's another bag with compressors on it that brings air from outside, compresses the air, which makes the aeroplane heavier and then it descends like a glider."

It's both heavier and lighter! There's a compressor that can bring air in from the outside and make it heavier than air, and then this air can be released making it lighter again. This is explained in the article. It really is something new.

Like a hot air balloon which becomes heavier than air or lighter than air by regulating temperature in order to ascend or descend? That's fancy tech as of year 1800.

As long as we're nitpicking terminology, hot air balloons aren't airships either, they're aerostats. And they certainly don't use their variable bouyancy to propel themselves in directed flight. Saying this thing is just a hot air balloon is like saying an airplane is just a glider.

How would a more traditional airship descend, if not by becoming heavier than the air surrounding it?

It's new because it is being done in the atmosphere. I work with Autonomous Underwater Vehicles (AUV) which have employed this method of propulsion for at least a decade. For AUVs the variable buoyancy is achieved by having an expandable bladder of fluid which can be contacted to allow ballast to enter or expanded to expel ballast. Check out Slocum gliders if you are curios

Sounds like it's an air submarine. The description of the variable buoyancy sounds pretty much like what a submarine does.

This is not really accurate. Submarines maintain roughly neutral buoyancy and use a motor for propulsion. They can use lifting surfaces for buoyancy control, but they need the motor to move forward. Airships operate on essentially the same principle--- airships are closer to "air submarines" than "air ships."

This device is an air-equivalent of an underwater glider.[0]* It establishes positive buoyancy to rise through the fluid (air, in this case, rather than water) and then establishes negative buoyancy to enter a dive, after which it glides just like any other glider.

The difference between this thing and a 'normal' glider is that it uses buoyancy to rise in altitude rather than needing to be towed by a conventional airplane.

[0]https://en.wikipedia.org/wiki/Underwater_glider * An underwater glider being the water equivalent of a... glider.

Uh, cite for that? Sorry, that's ridiculous pedantry. It's very reasonable to call the thing an airship, or an aeroplane (something done in the article only once, and in the context of a sourced quote justifying the distinction no less). I'm aware of no dictionaries or professional categorizations this article violates. It's a device that spans the boundary, and the article is literally about that, as the technology is (well, sorta) interesting.

Why is lack of adherence to your personal aeronautical jargon preferences a criterion for "terrible writing"? And why is this the top comment in the topic? Come on folks.

University of the Highlands and Islands is considered a bit of a second rate institution in Scotland.

A nice bit of publicity for them none the less.

Hopefully they can develop this more and more. Scotland needs a boost to Aerospace after we got another Space port last year

https://en.wikipedia.org/wiki/Sutherland_spaceport

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