I've always wanted one of these - they seem like an awesome way to explore the world. I once fantasized about getting a couple of them dropped in some remote location, spend a few days or weeks hiking out there, and then flying back.

Wonder what a modern variant would look like?

Something like a powered paraglider comes to mind. It has the additional benefit of being reusable.

Imagine now it could have a much larger pressurised cabin.

Why rely on an inflated wing that can be punctured or change in stiffness with temperature and altitude when fiberglass and carbon fiber rods exist?

The original use-case was supposedly spy exfiltration of a plane in a "suitcase" minus the engine.

I wonder how much it could be impoved if this project was revisited today with modern materials and manufacturing techniques.

Not sure modern safety standards would be friendly to it.

It’s 225 lbs empty so it qualifies as an ultralight aircraft like powered hand gliders. It’s a class that’s much easier to certify and has many fewer safety requirements.

They will self-certify themself and the problem disappear.

Rigid flight needs exactly this, rigidity. But we do have inflatable flight: paragliders, first flight only a few years after the inflatoplane. Inflated only by the dynamic pressure from forward movement, but they make up what they lack in pressure differential with using more bracing wires (much more). But the inflatoplane relies on bracing wires as well, so the difference could be considered surprisingly small.

I think there are lots of possibilities for inflatable vehicles which cannot be deflated.

For example, make a flimsy structure out of thin steel foil, then pressurize it to give it far more strength than it would otherwise have.

Same as the strength of a coke can.

Except with steel as the tensile material, you can probably use pressures up around 1000 psi, making the whole structure have an amazing strength to weight ratio.

> Except with steel as the tensile material, you can probably use pressures up around 1000 psi, making the whole structure have an amazing strength to weight ratio.

Congratulations, you have created a bomb.

You certainly need to think about that in the design. But by rolling a 'texture' into the sheets the structure is made from, you can make sure that any hole can't 'rip' bigger, and therefore fails slowly rather than rapidly.

You also need pressure regulator valves in case of fire.

And you might want to make the whole thing double or triple skinned so the highest pressures can be deeper inside where they are less likely to get punctured/less vulnerable to corrosion damage/crash damage.

At that point you're not dealing with a "flimsy structure out of thin steel foil" that you can inflate to hundreds of psi. You described what's basically a submarine, multiple high and low pressure hulls able to withstand hundreds of psi of pressure.

Just for some reference, 1000psi is the kind of pressure you get ~700m depth (2300ft), double what a submarine would regularly withstand. Pressure in your average propane gas tank probably peaks around 200psi in high temperature. That steel isn't flimsy, it tends to get bulky and heavy even with creative ribbing and reinforcement.

It has to make a lot of sense practically and economically to consider such an option. So it ends up being used in places where weight or cost matter less.

A CO2 fire extinguisher is about 1000 psi.

A 1000psi fire extinguisher uses ~5mm thick steel even for that relatively small diameter cylinder. A typical extinguisher is ~200ish psi with a wall probably ~1mm thick.

This highlights that high pressure and "thin steel foil" do not go well together and don't scale in your favor. Pressure makes any failure considerably more dangerous.

But when do you really need a structure that has this exceptional strength on the happy path, but would still be good enough in terms of safety when pressure is lost?

Unmanned aviation comes to mind, but the ratio between structural mass and battery+payload is already so low, even a zero-mass structure would not make a meaningful performance difference. It's all about the battery tech.

Scaling up foil boating perhaps? Carbon fiber construction would certainly appear like a good candidate for taking advantage of being pressurized, and I perhaps naively take it as a given that materials is the major limiting factor in scaling up.

> still be good enough in terms of safety when pressure is lost?

You might not design for that case. A suspension bridge can't survive a tower falling over, or a cable snapping.

The pressurized structures wouldn't be able to survive leaks over X size, and for leaks under X size, compressors would be used to maintain pressure.

Rockets are the obvious use. The structure of a rocket is far heavier than the payload, and every kilo of weight you can shave off the rocket, you can add to the payload.

Wasn’t the Centaur upper stage pressurised. I remember an incident where one collapsed under load because the tank lost pressure.

That was in fact an innovation that followed the German V2 — dropping the framework structure of the rocket in favor of relying solely on the skin of the tank under pressure to give structural integrity of the rocket.

"The tank of the Atlas consisted of stainless steel which was no thicker than a dime at any point. Generals, and later congressmen, worrying about what would happen if somebody dropped a wrench on such a tank were conducted to a test version of the "stainless steel balloon" that was stiffened by pressure and offered a choice of assorted mallets to see whether they could dent it. In each case the general or congressman grew tired before he had even succeeded in producing a mark that could be seen."

Willy Ley's "Rocket's, Missiles and Men in Space"

https://archive.org/details/rocketsmissilesm00leyw

Well, rockets are essentially bombs we try to make explode in a controlled manned. The "controlled" part is not always successful.

Fueled rockets are treated like live bombs. No one around except for people who really need to be (like astronauts).

> The "controlled" part is not always successful.

I'm assuming you're referring to the unnominal situations resulting in the unscheduled rapid disassembly procedures? I wonder how many people watch launches with similar intent as NASCAR races where they're just looking for the crashes or hockey games looking for the fights?

I must admit I tend to watch SpaceX test flights for the potential fireworks.

But for, say the JWST launch, it really wasn't with the same intent.

In the former, it is just SpaceX way of doing business, no big deal, no significant payload being destroyed and the next rocket is on the line. The latter is the result of billions of dollars, many years of work and great scientific promises that could be blown to pieces.

And of course, for manned flight, who in their right mind wants astronauts dead?

> And of course, for manned flight, who in their right mind wants astronauts dead?

Which begs the question, who wants to fly Starliner?

Or Orion’s heatshield for that matter. Orion 2 should have the attachment mechanism redesigned, most likely as arms attached to the upper side of the reentry vehicle rather than in holes in the shield itself.

Even on SpaceX launches I’m rooting for the rocket.

Yes, the Centaur upper stage was and still is using balloon tanks.

I think this is the failure you're referring to: https://www.youtube.com/watch?v=imkdz63agHY

And here's a picture from ULA/Tony Bruno showing a Centaur tank in their factory, being supported by a rig: https://twitter.com/torybruno/status/1435553806792728579

I believe that the Apollo LM also depended on pressurization for structural strength.

Atlas too. Thin aluminum shell.

Especially if Boeing is involved

It would be cool, especially with advances in plastics you could layer over the steel to protect it from corrosion like what they do with soda cans.

For reference, a steel or aluminum SCUBA tank is usually filled to 3000psi and when I fill steel tanks I can hear and sometimes see the metal start to slightly balloon. This is normal because steel is not brittle but it is very strong.

There is a lot of rules put in place for safety though. A tank has to be visually checked by a professional every year and hydro statically tested every 5. The danger is any rust/corrosion weakening the metal and causing it to rupture. More often seen in aluminum tanks, which is one reason I prefer steel.

Yes, in theory steel is not the best material for a high-pressure tank.

We use it because it's cheap and well tested. But we are probably better of with a layered combination of a few different materials. Steel may not even enter it.

Steel is the best material for certain scuba applications due more to buoyancy characteristics than strength. Firefighters typically use composite tanks for SCBA now, which are stronger but too buoyant for diving.

Layers of dissimilar materials are often problematic due to galvanic corrosion, different rates of heat expansion, and water intrusion between layers.

Also discussed in 2019: https://news.ycombinator.com/item?id=21249801

People knew how to name things back then.

Nothing will ever top shark repellent bat spray

I fly a Cessna from the time period with a Nav-O-Matic autopilot, Land-O-Matic landing gear, and an Omnivision window.

Okay, I had to look that one up, and:

> Omni-Vision – The [term for the] rear windows on some Cessna singles, starting with the 182 and 210 in 1962 and followed by the 172 and 150 in 1963 and 1964 respectively. The term was intended to make the pilot feel visibility was improved on the notably poor-visibility Cessna line. The introduction of the rear window caused in most models a loss of cruise speed due to the extra drag, while not adding any useful visibility.

That's hilarious.

Today it'd be some vague crap like "Float."

Mustard did a video on this.

Nebula (subscription required): https://nebula.tv/videos/mustard-escape-in-an-inflatable-air...

Youtube: https://www.youtube.com/watch?v=GJ-4uWwQ5HA

Can we make an aircraft with a motor and inflatable wing, such that the motor works for propulsion and also inflating the wing, and the motor's waste heat is used for heating the air in the wing?

That's how this plane worked - the inflation pressure in flight was supplied by the motor. I don't think heating the air was desired, but some heat will inevitably end up in the air as it is compressed.

You could use engine exhaust to inflate the wings.

I wonder if this is more practical nowadays. Modern “drop stitch” inflatable kayaks and paddle boards are extremely rigid, strong, light, and reliable. They also have precise 3D shapes determined by the length and position of the internal drop stitch threads. Has anyone tried using that tech to create an inflatable airplane?

Feels like an opportunity to make a very cool ultralight given the weight savings, and no pilot license is needed (though still recommended…)

DLC in a Fallout game

Google recommends the Woopy-Fly inflatable ultralight, though it's not clear whether it's actually in production

Discussions are not optimistic, but do invoke some related inflatable craft - https://www.reddit.com/r/WeirdWings/comments/n7a4k1/what_hap...

Haha, that looks incredibly dangerous. A floppy hang glider with much less lift and stability than a regular hang glider, and it needs continuous electrical power and two working fans to stay inflated.

If I've learned anything from youtube - flying is not an expensive or inaccessible hobby. But safe flying is.

My inflatable SUP is nice, and it is impressively rigid, but I wouldn't say it's light. I got the inflatable because it can be stored and transported compactly. Competition paddleboards and kayaks are fiberglass/composite foam sandwiches, and way lighter than the inflatable variants.

I think the inflatable SUPs and kayaks are as heavy as they are because of the thick layers of vinyl and nylon that prevent punctures and abrasion.

Kitesurfing kites are made of lightweight ripstop polyester, with a super-thin urethane coating, and have an inflated bladder to help hold their shape. That might be more appropriate tech for creating an airplane.

Yeah, I'd think you'd want to apply that principle, but with different materials for an aircraft. Off the top of my head I am thinking dyneema threads inside (instead of dacron/polyester) and a carbon fiber/mylar composite for the outside cloth, like is used for high end racing sails on sailboats.

I don't have experience with hard SUPs but have a cheap RetroSpec weekender 10'6" SUP at 17.5lbs - I quickly looked up the weight of similar size composite boards (e.g. Isle 2) and was seeing more like 24lbs. I googled "competition SUP" and found some at 17lbs in the same length as my inflatable, but much narrower and 100lbs lower in max weight capacity than the inflatable SUP of the same weight.

For kayaks, high end drop stitch kayaks are about half the weight of rotomolded plastic ones of the same size, and only slightly heavier than skin on frame kayaks made from exotic materials, which are the lightest kayak technology and slightly lighter overall.

I'm not 100% sure that they used drop stitch, but the company Prospective Concepts developed a few more modern designs of inflatable wings for various applications.

https://repository.tudelft.nl/islandora/object/uuid:306785d0...

https://www.prospective-concepts.ch/html/site_en.htm (click "Projects" > "Air" on the right)

Personally I think this is a technological dead-end, at least for the civil aviation use cases that I understand. The only advantage of an inflatable system is compactness / portability, but since the Inflatoplane, that's been solved in many other ways by rogallo wings, hang glider type wings, paragliders, parachutes, various types of fold-out rigid wings, etc.

And all of the other properties of inflatable wings aren't advantageous other. They're not simpler, lighter, stronger, more durable, or more reliable than the alternative best option, and they don't seem to have a particularly good mix of useful properties to win against the other best alternative for any given use case, even if you assume modern materials and modern techniques.

> The aircraft was in a descending turn when one of the control cables under the wing came off the pulley and was wedged in the pulley bracket, locking the stick. The turn tightened until one of the wings folded up over the propeller and was chopped up.

While the pulley system at the root cause of this could be improved, the failure mode of "floppy wing got chopped up by the prop" seems like there could be quite a lot of ways to get there. Dunno what you think we've done in the last 50 years to improve on this situation, but for anything other than an emergency, I wouldn't want to bet my life on a vehicle like this. Also, I'm having trouble picturing an emergency that would be resolved by an inflatable plane.

Nevermind, I've got it. A single container could hold a hundred inflatable airplanes. That'd be a helluva surprise deployment, if you don't value the lives of your pilots.

Today this would most likely have the same drawbacks as the inflatable kayaks we see for sale. Saves on space (and money?) and could be good as an entry into a hobby but at any intermediate to advanced level there are better options to choose from. With the high barrier to entry to flying I think most pilots would opt for the most reliable option from the start.

I would not want to be caught in inclement weather in an inflatable anything.

What if you are stuck in north korea and the duffel bag containing this landed just at your patio ?

I am surprised this was not pursued more aggressively, in fact.

Pretty sure NK would easily shoot this out of the sky

Is this true if you are invisible to radar ? (i assume inflatables absorb radio waves much better than metal?)

Or flying low ?

Would inflatable wings/bodies work on Mars or a similar low pressure environment?

If you searched the web, inflatable bodies have been used. The problem is Mars atmosphere is 2% and gravity is 38% that of Earth's. Gravity-corrected wing loading to reach the equivalent of say a small plane on Earth would require 20x the wing area.

A proposal demonstrator of this was suggested in a paper:

https://www.icas.org/ICAS_ARCHIVE/ICAS2014/data/papers/2014_...

wouldn’t the lower density be equivalent to a higher altitude on earth? Propellers would be not effective but some type of jet or rocket would?

Sure. It likely also means different wing geometry and it needs to move faster.

I've noodled around with something like this for a climate-controlled micromobility vehicle. Something like the Nimbus but built with ebike components (https://nimbusev.com -- godspeed to them because I really want them to succeed, in part so I can buy one).

I'm pretty sure it would be ridiculous and impractical, but we could use a way to solve the "it's only five blocks away but the weather's miserable" in a way that doesn't involve huge parking lots and otherwise terrible land use.

I know that there must be clothing that solves this, but donning a whole suit for what might be a 90-second trip is a lot of friction, especially when the alternative is feeling a little bit guilty about driving for a trip that could easily be biked/walked/etc.

Nimbus looks super cool! I’d love to try one. Top speed of 50mph suggests it’s not enough car for highway commuting, unfortunately.

I’m more excited about the Aptera. I think it’s significantly bigger and more highway-capable than the Nimbus, while still much more efficient than contemporary EVs. It’ll cost twice as much as the Nimbus as well… quite different vehicles other than the common 2-front, 1-back wheel configuration.

The Nimbus S shows 75mph

Previously discussed in 2019:

https://news.ycombinator.com/item?id=21249801 (26 comments)

I saw this in a documentary many years ago as some sort of spy aircraft to exfil from a hostile country.

While a cool concept, subsequent ultralight aircraft made this design obsolete.

Just don't get shot at or have a leak. While it could be very compact to transport, it's not very practical or robust.

Also, the service ceiling and service floor(?) could vary based on temperature. For example, if it started at sea level and very cold conditions, it's possible it could not exceed a certain altitude below the need for a pressurized cabin and below its performance coffin corner.

It says because of the airflow from the engine it could be punctured by up to 6 .30 calibre bullets and maintain pressure. Is this enough resilience? (I don't really know about aircraft combat)

So it's a flying bouncy castle or flying tube man. Makes sense. Imagine it would be extra fun if there were an inflatable Fokker Dr.I.

Neal Stephenson's novel Seveneves [1] included something like this (early in part 3), and it being inflatable wasn't even the coolest thing about it.

[1] https://en.wikipedia.org/wiki/Seveneves

Just be careful of thumbtacks in your carryon.