5 ms·

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

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 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?

mannykannot 5y ago
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.
- horsawlarway 5y ago
  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.
  - mannykannot 5y ago
    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.)
jsight 5y ago
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.
kps 5y ago
“edf”?
- na85 5y ago
  Electric Ducted Fan
dmitrygr 5y ago
TFA: "compared to small turbojets" Yeah, turbojets are VERY inefficient on fuel, so that is a low bar.
dvh 5y ago
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.

mannykannot 5y ago

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.

horsawlarway 5y ago
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.
- mannykannot 5y ago
  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.)

jsight 5y ago

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.

kps 5y ago

“edf”?

na85 5y ago
Electric Ducted Fan

dmitrygr 5y ago

TFA: "compared to small turbojets" Yeah, turbojets are VERY inefficient on fuel, so that is a low bar.

dvh 5y ago

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.