Jetoptera VTOL aircraft design features “bladeless fans on steroids” | Hacker News Reader

Jetoptera VTOL aircraft design features “bladeless fans on steroids”

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98 pointsBerislavLopac39 comments

This thing looks really neat, and I want it to be real, but it looks awfully like the vaporware that was (is?) the Moller M200/M400 Skycar, so I’m biased deeply in suspicion. Doubly so, having idolized the Skycar as a youngster, only to see it fail to materialize over decades.

I think that particular design was plagued with efficiency problems, besides being too far ahead of its time (the software was purportedly quite advanced and likely prohibitively expensive).

Jetoptera are saying they get a 10% improvement in propulsive efficiency with 50% of the fuel consumption ... I have a lot of questions ... 10% at what ratio? across the board? on average? Does that combine with the 100% fuel efficiency increase to get 110% more thrust for the energy consumed?

Why can’t they run this device on an edf? (There is some mention of needing batteries abt 1500Wh/kg?) Those are well known for being horribly inefficient, and I’d imagine getting a 110% efficiency boost for even a model edf would be making waves all around in the modeling community.

Lastly, there are all sorts of interesting edf quadcopters; see, for example: https://m.youtube.com/watch?v=5L6FSdUmEpg It seems like it should be trivial to apply this tech to a prototype of that scale and demonstrate its effectiveness, but as the article points out, it seems most of the prototypes are for fixed wing aircraft. Why not just go right to vtol prototypes?

Efficiency claims that look way too good to be true usually are, and you have to ask how everyone else in the field somehow overlooked this apparently easy money, especially if the underlying principles are well-known and have been in use for decades, as is the case here (blown flaps and such in combat aircraft.)

I do not know whether this is the case here, but the trick to making such claims, without actually dissembling, is to first be highly specific about what it is that you are measuring and comparing, but then be quite vague about it in the press release, trusting that a journalist will cherry-pick from the claims to make his story look exciting, and quite possibly mix and match claims that cannot be satisfied together.

If this technology really could give 10% more thrust with half the power and 70% of the weight of a turbofan, then Jetoptera (or some other company) could be making real money converting at least business and commuter jets to use these devices - so why isn't this happening? The whole 737 MAX debacle started with Boeing being under intense competitive pressure to improve fuel consumption by just a few percent.

We also see that "Jetoptera is more or less agnostic about where it gets its compressed air from, although it reasons battery technology will need to reach energy density figures around 1,500 Wh/kg (current state-of-the-art batteries are around 260 Wh/kg) before it'll start making sense to fit the J-2000 with an electric compressor." That would be just a 477% improvement in a feld where 10% is a big deal! Note that current battery technology is already sufficient for conventional electric airplanes to begin to be useful.

With regard to your last paragraph, none of these technologies are trivial even in isolation, let alone combined, regardless of the number of puff-pieces like this one written by people whose enthusiasm seems to exceed their understanding.

I suspect targeting the military was not a mistake on their part.

You're dead on the money about making claims that are very precise, and then leaving the door open for the media to generalize them to make headlines.

In this case, it may well be vaporware, but it's also possible it outperforms conventional aircraft in a way that's not particularly useful to consumers (small lifting capacity, high acceleration profiles, simple landing/takeoff requirements, etc) but might be useful for drones or military applications.

I looked at some of the numbers on their website, discounting anything they did not show a photograph of. If they are actually getting 91 kg (200 lbf) static thrust with a 75 kW engine, that would be in the low-to-average range for small-airplane propellers at the same power level - quite impressive as a starting point, but such propellers are far from suitable for VTOL (small helicopters seem capable of producing ~450kg (1000 lbf) lift/thrust from that power.)

That seems so similar to the Moller that it almost has to have been inspired by it. Looking at their website, it seems like the Moller folks have finally given up. Strange that they were able to string things along for so long, though.

“edf”?

Electric Ducted Fan

TFA: "compared to small turbojets"

Yeah, turbojets are VERY inefficient on fuel, so that is a low bar.

They are putting fancy shaped obstacles in front of the engine exhaust. There is absolutely no way that it is more efficient than direct exhaust down without any obstruction.

One interesting feature about this, which you can see in the skeletal hovering demo machine, is that all the ducts are driven from a central source. Since air pressure is additive, that source could be multiple engines dumping into a single manifold before driving all the ducts equally by default. All the ducts need to do is swivel to direct the air.

Compare this to ships like the V22 which have an immensely complicated gear, shaft, and clutch arrangement to drive the props; this one also folds. Or against most multi rotors including the original Moller design where you need at least 8 engines or motors, two at each corner for safety, where you need a smart computer to balance the loads as motors fail.

Yeah, having tha actual repellers/propulsors be both lightweight and more or less arbitrary shape could enable quite some nifty designs!

Also as you just need pressurized Gass in the manifold for the thing to fly I wonder if an emergency system with a pressure bottle or even gas generator could be used to give you say 30 seconds of flight time needed for safe emergency landing if your pressure generating engine fails.

Not to mention making it easier to combine two or more independent engines to feed the manifold for redundancy without the crazy complicated and heavy gearing V22 has to achieve that, as mention above.

A single source of pressure means that the available pressure at each outlet is not independent (unless the source pressure has huge headroom). This could make control interestingly complex.

They could add an independently closable duct at each outlet.

Closing one outlet increases the pressure on the others, if the supply pressure is not ~infinity.

HVAC systems are, I'm told, an NP complete problem. Every time you increase flow in one vent the flow in all the others has to be rebalanced.

Although with only 4 ducts you might expect that problem space to be solved.

The YT channel Electric Aviation did a pretty good video on this system [0]. He goes fairly deep into the vehicle's design and efficiency, in fact all his videos are very informative. I personally cannot wait for the "Black Fly" electric aircraft to be available, the VTOL implementation is very unique [1]

[0] - https://www.youtube.com/watch?v=bPZI6XoHi10 [1] - https://www.youtube.com/watch?v=A7NVgKrrxgI

The first video shows how cherry-picked facts can be used to suggest a misleading impression of efficiency. The presenter repeats, several times, the claim that the duct moves ten times the amount of air than that delivered from the compressor. I imagine that fact came from Jetoptera, and I don't have any reason to doubt it, but that ten-times figure is irrelevant. The comparison that matters is the rate of transfer of momentum to the external airflow, compared to what can be achieved by driving a properly- or similarly-sized fan or propeller with the same motor.

Not very hopeful for the BlackFly either.. they had an 'official launch' almost three years ago, failed to go into production in 2019 as promised, then got a new CEO who left for Hyundai after barely a year at the helm.

I once met P&W military engine designer (he was an expert on heat issues with turbines) who explained to me that fancy machines like this would never work. They will not fly reliably in anything but clear air (no precip). Although he was a turbine guy, he said propellers for low-speed aircraft are simple and just work.

It's amazing how many of these ideas have already been tried in some way or another. I thought I had a couple of clever, novel ideas for aircraft design, but then I came across this book[0]. The book is about technical progress more generally, but has a long section that goes over aircraft development (mainly focusing on VTOL). All sorts of things were tried from roughly the 30s-70s, including most of the stuff that is reappearing today. Basically every clever idea I thought I'd originated had already been flown, and while some worked okay, none were better in practice than what's been settled on commercially.

[0]: https://www.amazon.com/Where-My-Flying-Car-Memoir-ebook/dp/B...

This is precisely the kind of tech I’ve always imagined to be needed for hoverboards.

Not those dumb things with WHEELS. The actual skateboard (sans wheels) hovering a couple inches off the ground.

I’ve always wanted one and at 33, looks like I’m gonna have to be the one to do research and development in this area (should my side projects come to fruition and net me the startup capital).

I'll hold your beer for you while you do that R&D! :)

Only if you point out what I should be doing next and why the quantum defribilator is preferable to the whizbang confibulator.

Imagine how loud even just a few of your skateboards would be. Much louder than jet skis.

That's a bigger problem than the propulsion.

We'll get that figured out for V2.

Do you want your neighbors to own flying cars?

A brick would generate lift if you apply enough thrust, with the right angle of attack. But it wouldn't have much of a glide ratio. And neither does this contraption.

Well, the Space shuttle had a glide ration comparable or possibly worse than a brick. ;-)

But yeah, it kinda cheated by starting the glide very very high & fast.

This should ideally reduce the tendency of VTOL aircraft to destroy landing helipads, since the vast majority of the air being pushed around is ambient temperature rather than being turbine or low bypass turbofan exhaust.

But it doesn’t solve the problem that VTOL aircraft like this are fundamentally unsafe, as they lack the ability to glide effectively and they don’t have the option to autorotate should the propulsion system fail. Helicopters are already significantly less safe than airplanes, and VTOL aircraft tend to be less safe still.

Even the Harrier, which at least could fly normally, was notoriously crash prone, with an accident rate 3x higher than the contemporary F/A-18. The V-22 is proving to be a pretty reliable marine killer in its own right, and that’s before you account for its abysmal uptime and tendency to be grounded.

Perhaps this aircraft will fix some of the issues of past VTOL aircraft, but I’d still be super wary about getting in one.

Most of the recent powered lift aircraft designs include a rocket assisted recovery parachute to use in case of power loss. However there can still be a dead zone: too high to survive a crash but too low for the parachute to be effective.

I guess with some designs they could also reduce impact via e.g. the autorotor effect that a helicopter would use if the engine dies. Obviously does not apply to this particular setup.

But most designs have at least some lift, which means there is some optimal glide ratio that minimizes vertical speed. Finally, having separate, isolated systems helps as well. This is also common with multi engine aircraft where an all engines out scenario is very rare. It's a challenge but not necessarily something that can't be addressed. Even some simple airbags could help here.

Many powered lift aircraft designs have very little aerodynamic lift and so the glide ratio is close to zero. And regardless of lift, they generally lack the articulated control surfaces necessary to establish a controlled glide.

Autorotation only works if the rotor system has significant rotational inertia and a cyclic (blade pitch) control. Most powered lift designs have multiple small, low-inertia fixed-pitch rotors. If you lose power you're going straight down and probably tumbling out of control.

Airbags can help a little in some low-altitude crash scenarios but if the aircraft is falling out of control then there's no way to guarantee that the airbag will be oriented the right way. It's just not practical to cover an entire aircraft in airbags like NASA did on the Pathfinder Mars landing: the technology doesn't scale up.

> If you lose power you're going straight down and probably tumbling out of control.

The Osprey has a really nasty habit of doing this. A number of them have crash landed upside down from relatively low altitudes, which is a very bad thing.

You're referring to a vortex ring state, which can hit helicopters flying low and slow. It has nothing to do with surviving an engine failure in a powered lift aircraft.

Vortex ring states in multi-engine VTOL aircraft have the unpleasant tendency to flip the aircraft over, which is markedly worse than being up right at least.

Most non-helicopter VTOL aircraft cannot autorotate. The V-22 cannot, for example; not enough inertia in the blades to pull that off.

How stable is the entrainment effect they plan to use in their engines under high winds, rain, changes in atmospheric pressure, etc? Accelerating air by creating a low pressure region seems like a pretty delicate setup.

Be interesting to see how far they get with this.

Previous attempts/prototypes haven’t been super successful Blown surfaces https://en.wikipedia.org/wiki/Hunting_H.126 And a whole plane with a similar system of air being ducted through the surfaces and whatnot https://en.wikipedia.org/wiki/Rockwell_XFV-12

Reminds me of slipstream 5000.

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