11 ms·

NASA reveals what the final X-57 all-electric X-plane will look like

244 points by prostoalex 7y ago

obmelvin 7y ago
Does anyone have enough aerospace knowledge to comment on the design? Comments on the article seem skeptical on placement of the propellers, but I have absolutely no expertise here to make any assessment myself.
- csours 7y ago
  I have no special knowledge myself, but as I understand it, the little propellers along the wing greatly reduce takeoff and landing speed and distance - they basically produce airspeed without groundspeed. Note - this is based on a video I watched one time, if I got this wrong, please educate me.
  - gnramires 7y ago
    That's correct, essentially you can apply Newton's law (F = dp/dt): the propellers over wings can produce a strong downward momentum flux (air flux) that by reaction generates lift (upward force). Without this flux being directly controllable by the wings (or steerable in other ways), you need to rely on the vehicle's airspeed to generate sufficient airflow on the wings to produce lift (so you'd expect greater takeoff speed/distance necessary). You might wonder also about efficiency. Generally the energy efficiency of an aircraft is dictated by 1) friction losses 2) outgoing airstream velocity. The lower the friction and the slower you can push an air stream the more efficient the aircraft ((2) is because the kinetic energy imparted on the air is quadratic on speed, while the momentum, and force, is only linear in speed). That's why high-bypass turbofans are now the norm (more air at slower speeds). And why you want a large propeller surface of low speed (I expect at very large propellers you get diminishing/negative returns due to additional drag), which can be few large props or many smaller props (which have the previously discussed advantages).
- starpilot 7y ago
  There's no better place to put them if your goal is redundancy with lots of small props. Puller props are generally more efficient because they're not in the wake of the wing, but it's a tradeoff and you can Google as for the pros/cons of push vs. pull props. The larger tip props are really interesting. Larger, slower rotors are more efficient. Putting them far outboard puts them in the least-disturbed flow while knocking out the tip vortices. This is only possible with lightweight electric motors vs. shrouded turbines, otherwise the wing/wing box would be quite heavy to support such a long moment arm.
- oliveshell 7y ago
  Here’s a NASA paper on the propeller arrangement: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160010105.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201600... Apparently the small propellers’ primary function is “to act as a high-lift device [1]” rather than to generate thrust. They allow the wings to have a higher aspect ratio (i.e., be ‘long and skinny’) for reduced drag. Without them, such a wing would give undesirable low-speed handling characteristics and a higher stall speed. Also, their speed can be varied independently and quickly by computer to compensate for turbulence and wind gusts. Looks like quite an interesting design that plays to the strengths of electric motors. [1]: https://en.wikipedia.org/wiki/High-lift_device https://en.wikipedia.org/wiki/High-lift_device
  - eternauta3k 7y ago
    Do you mean "lower stall speed"?
    - bathtub365 7y ago
      A higher stall speed means you need to go faster not to stall and is an undesirable property. Lower means you can go slower before stalling
    - numpad0 7y ago
      Stall speed = minimum takeoff/landing speed(without margins) Sort of the “speed you have to drive on the ramp on a highway”, you don’t want to have to merge at 250mph
- Gibbon1 7y ago
  The tip propellers reduce losses due to wing tip vortexes. From memory about half the drag from a wing comes from those. So potentially there is some savings there. The reason no ones built an conventional aircraft with tip props before is because mechanical limits, put a piston engine at the tip the wing and like a big weight on a spring. And losing an engine would mean real problems flying the aircraft. Electric motors are simple and have a higher power to weight ratio. So probably workable. And electric aircraft reducing drag is really important because of the low energy density of batteries compared to aviation fuel.
starpilot 7y ago
Really recommend watching the short video at the end of the article. It shows them fiddling with a 3d-printed prototype of the folding propeller, and some of the CFD analysis of the prop wake - wing interaction.
mfsch 7y ago
In the video they tout the X-57 as a contribution to the “urban air mobility market”, arguing that small aircraft can decrease commute times and avoid congestion. This seems very backwards to me. Cars are already very inefficient in their use of space, since they require large amounts of space around them when they are moving at speed. I expect this issue to be significantly worse for aircraft, with the speed they are moving at, the safety distances needed to avoid crashes, and the volume of air they are disturbing around them. While they can potentially make use of the vertical dimension for more space, they still have to move through the surface layer for take-off and landing and will want to stay close to the ground for short trips. And they potentially add a lot of noise to an already noisy urban environment. I’m all for ambitious research projects pushing the boundaries of electric flight, and there’s probably reasonable use cases for planes like the X-57. But a sustainable urban transport future looks much more like buses and bicycles rather than small electric aircraft.
- jacquesm 7y ago
  Facts never stood in the way of PR.
- pritovido 7y ago
  I believe they will be use for the same thing helicopters are used today: 1-Emergencies and organs transplant. No pilot means more carry load in volume and weight. 2.As a status symbol for top of the ladder executives and polititians. They will go from the top of skyscrapers to their mansions just looking down of those that waste their time in car jams. I see this being useful for short distance travel as well, but not that much in cities, but outside them.
  - pilsetnieks 7y ago
    It's still a plane, it has no VTOL capability. It cannot be used for what helicopters are used today.
    - serf 7y ago
      the parent of your comment is referring to the phrase “urban air mobility market”, which the X-57 PR video demonstrates as being small aircraft, a few of which were VTOL craft -- not the X57 itself. The PR video was basically hinting at the X57 being a technology demonstrator which will showcase techs (like electric propulsion) that the so-called “urban air mobility market” can then take off running with.
rcpt 7y ago
How different is this from what Joby is doing?
- spaceandshit 7y ago
  Joby makes the electric motors for this aircraft. https://en.wikipedia.org/wiki/Joby_Aviation https://en.wikipedia.org/wiki/Joby_Aviation (title image)
redis_mlc 7y ago
The X-plane program does fundamental research. All military and commercial aircraft have benefited from that research, in the same way WW2 German designs also influenced the world. X-57 is fundamental research, not an effort to create a final product. The closest program similar to it is the X-29, which investigated forward-swept wings, canards and augmented computer systems to control them. (Nobody wants forward-swept wings because a failure in wingtip rigidity or the computer software destroys the structure.) As a commercially-rated airplane pilot and informal aerodynamics student, I think the wingtip propellers are questionable, and the retractable inboard propellers sound like a maintenance and operations nightmare. What's weird about mounting propellers at the end of the wing is that you lose half the lift of the propeller wash over the wing, over a normal placement. What's misunderstood about wing tip vortices is that regardless of what the loss is, that flow comes from the entire wing producing lift, so is unavoidable. There are already passive techniques like winglets and fences to direct vortices that don't require daily maintenance. And we know from the Osprey that complex propeller systems fail too often. A dozen propellers means an order of magnitude more inspections, replacements, ground time (AOG), etc. At $83,000/hour to operate, a V22 Osprey is more expensive than an A380. Also, read the section on "Design Challenges": https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey Additionally, there is no "urban air mobility market" in the USA, and never will be, due to regulation and insurance requirements. In a showdown between the FAA and Uber, the FAA will always win, and the FAA reserves the perogative to change its mind later, as in drone regulation. To give you an idea, it was easier to start SpaceX than it would be to get the FAA to allow "urban air mobility." So regulation is the real challenge, not technology.
- TeMPOraL 7y ago
  > To give you an idea, it was easier to start SpaceX than it would be to get the FAA to allow "urban air mobility." So regulation is the real challenge, not technology. I though the regulatory hurdles around "urban air" come straight from the need to protect people and property from the dangers of a) falling aircraft (which would become a real concern as the use scales up), and b) excessive noise. And I'd guess c) dust clouds. We'd have to invent propulsion that's much more quiet and doesn't push air around for air taxis to make sense. So this would make the root cause of those regulatory problems be technology problems (or perhaps even physics problems).
alkibiades 7y ago
does the have anything to do with actual space travel or just a hobby project for global warming?
- kryptiskt 7y ago
  The first A in NASA stands for Aeronautics.
- TeMPOraL 7y ago
  The first A in NASA stands for Aeronautics. NASA doesn't do just space.
- redis_mlc 7y ago
  NASA did abandon aviation for space, shelving the X-plane program for about 2 decades, which was a huge loss. It's great they're back, and have been doing fantastic work in fundamental research that private companies don't get around to: hypersonic vehicles, small-airplane electronics, now electric.
- NikolaeVarius 7y ago
  > The National Aeronautics and Space Administration
sintaxi 7y ago
"spreading congestion" is not the best marketing pitch.
mlindner 7y ago
Not a fan of this design. The future for electric motors on aircraft is ducted fans, just as are used on jet engines.
- fastball 7y ago
  That sounds loud.
  - hwillis 7y ago
    For complex reasons, ducted fans are generally quieter, but less efficient if you arent going quite fast.
- mrfusion 7y ago
  Can you expand on that? I’ve wondered the same thing.
  - atrettel 7y ago
    Propeller-driven aircraft perform best at subsonic speeds (slower than the speed of sound). This is because the blade tips of the propellers approach the speed of sound at faster speeds, and this greatly increases the drag on the propeller blades, among other things. This is why after World War 2 propeller-driven fighter craft fell out of use, since they could not get much faster without major issues. Modern passenger jets operate in the transonic range (0.7 to 0.8 times the speed of sound). This range is a bit too fast for propellers and pretty much requires jet engines or something similar. Using props for passenger planes would reduce their speed as experienced by passengers today. I believe this is what the author is referring to.
mrfusion 7y ago
Meta: I haven’t seen this much negativity for an exciting new technology from HN before. It’s kind of bizarre.
- leetcrew 7y ago
  it's transportation research money that isn't being spent on bike lanes, buses, or rail.
  - rexreed 7y ago
    In our part of the US, money for bike lanes, buses, and rail comes from states and local jurisdictions, not from federal funds. The portion of money NASA is getting from this does not take away from multi-modal transportation investment at the local level.
    - leetcrew 7y ago
      sure, but it's a common thread. notice how you see similar comments on articles about electric cars. HN hates to see money spent on improving forms of transportation that are not bikes or public transit.
JoeAltmaier 7y ago
Problem in the article with the caption? It says the picture is in 'cruise mode' but when cruising at altitude, the X-57 folds the small electric motors into the wing nacelles and leaves only the two wingtip props active. Did I miss something?
- roelschroeven 7y ago
  No, the propellors fold into the motor nacelles. Not the motors into the wings.
  - JoeAltmaier 7y ago
    Thanks!
GordonS 7y ago
Aside from the pictures, the article was a bit lacking in information. According to wikipedia, it only seats 2 people, has a maximum range of only 100 miles, and a maximum flight time of only 1 hour. The batteries weigh 390kg, which sounds like a lot of weight relative to the small size of the plane. I get that electric flight is new, and it's going to take a long time before anything happens at scale, but given the limitations (and of course the fact you need an airstrip at either end of your journey) I can't help but wonder who is going to actually buy them, and what they would do with them?
- PaulRobinson 7y ago
  The X in X-Planes stands for "eXperimental". The history of them goes back within the US to 1946 and as the list [1] of vehicles shows, these aircraft are intended to test concepts and ideas, not provide a sellable solution to the market. Whilst most are betting that commercial electric in the air is going to be VTOL - and they do address the low endurance and runway issues you highlight - there are efficiency gains for longer distance in fixed wing designs, and you're going to have to think about electrification of that class of vehicle at some point. Put another way: we don't use helicopters for all passenger transport for a whole bunch of reasons, EVTOLs don't fix all those reasons, and so if you want to keep fixed wing aircraft around as a concept AND you want to use electric motors, at some point you're going to have to think about experimenting with electric passenger-carrying fixed wing aircraft. Thus: the X-57. You might wonder what the purpose of an experimental aircraft in this config is, if the eventual goal is to build airliners that can move lots of people. Well, the X-1 was no Concorde, but Concorde would not have happened without the X-1. And so it goes... It's OK then to think of the X-57 to an airliner of the future, as the X-1 was to Concorde. It's a whole set of interesting experiments that will validate some hypotheses, refute others, and we move along another step towards a better future. Seat count will get higher, endurance will improve, batteries will get lighter, and within 20 years, who knows where we'll be. [1] https://en.wikipedia.org/wiki/List_of_X-planes https://en.wikipedia.org/wiki/List_of_X-planes
  - GordonS 7y ago
    Thanks, your comment makes a lot of sense. I do understand this is experimental, but I just assumed the end goal was to do a licensing deal of some sort with a partner than would sell a commercialised variant. My assumption (yes, another one ;) was that electrification would require baby-steps towards commercialisation in order to continue to fund the kind of progress you speak of - in the same kind of way we saw with cars, where initially they were expensive, had a very short range, there was very limited infrastructure etc, but they were still an option for a small market segment.
GordonS 7y ago
With cars, we've seen a lot of companies going the hybrid route, combining multiple small electric motors with a combustion engine. I'm curious if the same could be done with aviation - perhaps a turboprop or jet engine to get to cruise altitude, then electric engines taking over. Anyone know if there are any promising hybrid planes on the horizon?
- spaceandshit 7y ago
  Only one of many competitors: https://www.rolls-royce.com/media/press-releases/2019/06-11-19-rr-announces-new-hybrid-electric-flight-demonstrator-to-be-built-with-brandenburg-partners.aspx https://www.rolls-royce.com/media/press-releases/2019/06-11-...
sergeykish 7y ago
Cruise efficiency increased from 0.7 km/kWh to 2.9 km/kWh (13 nmi/gal AuGas to equivalent 51 nmi/gal AuGas). Better than ICE car!
zelienople 7y ago
Humans need a basic amount of exercise for health. It is hard for me to understand how someone with a functioning brain would look at traffic congestion and propose this solution, particularly with the codicil, "it's already benefiting taxpayers". No, technological developments that cannot possibly be used by anyone but the wealthy few, no matter how energy-efficient, are not a sane solution to urban transportation issues. The solutions are more prosaic: (1) Reduce population, population density, and the product of population times lifestyle. We have exceeded the carrying capacity of the planet, and our science is telling us that unequivocally with a cacophony of data from coral reefs, the status of the ocean, the loss of insects, and many other sources. We must control our own numbers. There is no technological alternative to that. (2) Create spaces and routes that foster personal human-powered transportation, such as bicycling. Separate the cars from the people to stop the carnage and remove legitimate safety arguments against bicycling. (3) Make public transit extensive and free. Stop extracting a pound of flesh from the poorest for every ride that they must take to get to a job that doesn't pay a living wage. The inequity of wealth distribution in our society has passed all limits of sanity. Incentive works great in small "c" capitalism, and we need to make sure that mom and pop outfits and very small businesses have the incentive to innovate and produce, but there is no need for the unlimited capitalism that we have now. Take a few pennies out of the pockets of the uber-rich to pay for transit. (4) Stop the propaganda, herein represented by NASA's usual BS about how we all benefit from their R&D. Organ transplants my fanny. The only thing this kind of transportation is going to do is to further increase the divide between ordinary people and the ultra-rich who pay no taxes in any case. Taxpayer-funded research into new toys for the CEO. Yay. We are brainwashed into a profligately wasteful, unnecessary, insanely-self-focused lifestyle. Mass media makes us feel bad so we'll go out and spend all our money on the latest stupid thing that will break in a year or less and we'll throw out. All the while we are striving to fill some artificially-stoked hunger for more: more money, more things, more waste and more destruction. The X-57 feeds right into that brainwashing. It will be our end.
- JoeAltmaier 7y ago
  Its actually pointed at reducing the entry cost of flying. So ultimately not for ultra-rich. NASA spends peanuts, and part of those peanuts is spent on fostering innovation. When I hear "Lets just feed the poor!" I feel ill. We're not so desperate we can't do right by our people, without tearing down everything else that's good. NASA's budget isn't going to feed the poor for more than 10 minutes.

244 points by prostoalex 7y ago

Does anyone have enough aerospace knowledge to comment on the design? Comments on the article seem skeptical on placement of the propellers, but I have absolutely no expertise here to make any assessment myself.

csours 7y ago
I have no special knowledge myself, but as I understand it, the little propellers along the wing greatly reduce takeoff and landing speed and distance - they basically produce airspeed without groundspeed. Note - this is based on a video I watched one time, if I got this wrong, please educate me.
- gnramires 7y ago
  That's correct, essentially you can apply Newton's law (F = dp/dt): the propellers over wings can produce a strong downward momentum flux (air flux) that by reaction generates lift (upward force). Without this flux being directly controllable by the wings (or steerable in other ways), you need to rely on the vehicle's airspeed to generate sufficient airflow on the wings to produce lift (so you'd expect greater takeoff speed/distance necessary). You might wonder also about efficiency. Generally the energy efficiency of an aircraft is dictated by 1) friction losses 2) outgoing airstream velocity. The lower the friction and the slower you can push an air stream the more efficient the aircraft ((2) is because the kinetic energy imparted on the air is quadratic on speed, while the momentum, and force, is only linear in speed). That's why high-bypass turbofans are now the norm (more air at slower speeds). And why you want a large propeller surface of low speed (I expect at very large propellers you get diminishing/negative returns due to additional drag), which can be few large props or many smaller props (which have the previously discussed advantages).
starpilot 7y ago
There's no better place to put them if your goal is redundancy with lots of small props. Puller props are generally more efficient because they're not in the wake of the wing, but it's a tradeoff and you can Google as for the pros/cons of push vs. pull props. The larger tip props are really interesting. Larger, slower rotors are more efficient. Putting them far outboard puts them in the least-disturbed flow while knocking out the tip vortices. This is only possible with lightweight electric motors vs. shrouded turbines, otherwise the wing/wing box would be quite heavy to support such a long moment arm.
oliveshell 7y ago
Here’s a NASA paper on the propeller arrangement: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160010105.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201600... Apparently the small propellers’ primary function is “to act as a high-lift device [1]” rather than to generate thrust. They allow the wings to have a higher aspect ratio (i.e., be ‘long and skinny’) for reduced drag. Without them, such a wing would give undesirable low-speed handling characteristics and a higher stall speed. Also, their speed can be varied independently and quickly by computer to compensate for turbulence and wind gusts. Looks like quite an interesting design that plays to the strengths of electric motors. [1]: https://en.wikipedia.org/wiki/High-lift_device https://en.wikipedia.org/wiki/High-lift_device
- eternauta3k 7y ago
  Do you mean "lower stall speed"?
  - bathtub365 7y ago
    A higher stall speed means you need to go faster not to stall and is an undesirable property. Lower means you can go slower before stalling
  - numpad0 7y ago
    Stall speed = minimum takeoff/landing speed(without margins) Sort of the “speed you have to drive on the ramp on a highway”, you don’t want to have to merge at 250mph
Gibbon1 7y ago
The tip propellers reduce losses due to wing tip vortexes. From memory about half the drag from a wing comes from those. So potentially there is some savings there. The reason no ones built an conventional aircraft with tip props before is because mechanical limits, put a piston engine at the tip the wing and like a big weight on a spring. And losing an engine would mean real problems flying the aircraft. Electric motors are simple and have a higher power to weight ratio. So probably workable. And electric aircraft reducing drag is really important because of the low energy density of batteries compared to aviation fuel.

starpilot 7y ago

Really recommend watching the short video at the end of the article. It shows them fiddling with a 3d-printed prototype of the folding propeller, and some of the CFD analysis of the prop wake - wing interaction.

mfsch 7y ago

In the video they tout the X-57 as a contribution to the “urban air mobility market”, arguing that small aircraft can decrease commute times and avoid congestion. This seems very backwards to me. Cars are already very inefficient in their use of space, since they require large amounts of space around them when they are moving at speed. I expect this issue to be significantly worse for aircraft, with the speed they are moving at, the safety distances needed to avoid crashes, and the volume of air they are disturbing around them. While they can potentially make use of the vertical dimension for more space, they still have to move through the surface layer for take-off and landing and will want to stay close to the ground for short trips. And they potentially add a lot of noise to an already noisy urban environment. I’m all for ambitious research projects pushing the boundaries of electric flight, and there’s probably reasonable use cases for planes like the X-57. But a sustainable urban transport future looks much more like buses and bicycles rather than small electric aircraft.

jacquesm 7y ago
Facts never stood in the way of PR.
pritovido 7y ago
I believe they will be use for the same thing helicopters are used today: 1-Emergencies and organs transplant. No pilot means more carry load in volume and weight. 2.As a status symbol for top of the ladder executives and polititians. They will go from the top of skyscrapers to their mansions just looking down of those that waste their time in car jams. I see this being useful for short distance travel as well, but not that much in cities, but outside them.
- pilsetnieks 7y ago
  It's still a plane, it has no VTOL capability. It cannot be used for what helicopters are used today.
  - serf 7y ago
    the parent of your comment is referring to the phrase “urban air mobility market”, which the X-57 PR video demonstrates as being small aircraft, a few of which were VTOL craft -- not the X57 itself. The PR video was basically hinting at the X57 being a technology demonstrator which will showcase techs (like electric propulsion) that the so-called “urban air mobility market” can then take off running with.

rcpt 7y ago

How different is this from what Joby is doing?

spaceandshit 7y ago
Joby makes the electric motors for this aircraft. https://en.wikipedia.org/wiki/Joby_Aviation https://en.wikipedia.org/wiki/Joby_Aviation (title image)

redis_mlc 7y ago

The X-plane program does fundamental research. All military and commercial aircraft have benefited from that research, in the same way WW2 German designs also influenced the world. X-57 is fundamental research, not an effort to create a final product. The closest program similar to it is the X-29, which investigated forward-swept wings, canards and augmented computer systems to control them. (Nobody wants forward-swept wings because a failure in wingtip rigidity or the computer software destroys the structure.) As a commercially-rated airplane pilot and informal aerodynamics student, I think the wingtip propellers are questionable, and the retractable inboard propellers sound like a maintenance and operations nightmare. What's weird about mounting propellers at the end of the wing is that you lose half the lift of the propeller wash over the wing, over a normal placement. What's misunderstood about wing tip vortices is that regardless of what the loss is, that flow comes from the entire wing producing lift, so is unavoidable. There are already passive techniques like winglets and fences to direct vortices that don't require daily maintenance. And we know from the Osprey that complex propeller systems fail too often. A dozen propellers means an order of magnitude more inspections, replacements, ground time (AOG), etc. At $83,000/hour to operate, a V22 Osprey is more expensive than an A380. Also, read the section on "Design Challenges": https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey https://en.wikipedia.org/wiki/Bell_Boeing_V-22_Osprey Additionally, there is no "urban air mobility market" in the USA, and never will be, due to regulation and insurance requirements. In a showdown between the FAA and Uber, the FAA will always win, and the FAA reserves the perogative to change its mind later, as in drone regulation. To give you an idea, it was easier to start SpaceX than it would be to get the FAA to allow "urban air mobility." So regulation is the real challenge, not technology.

TeMPOraL 7y ago
> To give you an idea, it was easier to start SpaceX than it would be to get the FAA to allow "urban air mobility." So regulation is the real challenge, not technology. I though the regulatory hurdles around "urban air" come straight from the need to protect people and property from the dangers of a) falling aircraft (which would become a real concern as the use scales up), and b) excessive noise. And I'd guess c) dust clouds. We'd have to invent propulsion that's much more quiet and doesn't push air around for air taxis to make sense. So this would make the root cause of those regulatory problems be technology problems (or perhaps even physics problems).

alkibiades 7y ago

does the have anything to do with actual space travel or just a hobby project for global warming?

kryptiskt 7y ago
The first A in NASA stands for Aeronautics.
TeMPOraL 7y ago
The first A in NASA stands for Aeronautics. NASA doesn't do just space.
redis_mlc 7y ago
NASA did abandon aviation for space, shelving the X-plane program for about 2 decades, which was a huge loss. It's great they're back, and have been doing fantastic work in fundamental research that private companies don't get around to: hypersonic vehicles, small-airplane electronics, now electric.
NikolaeVarius 7y ago
> The National Aeronautics and Space Administration

sintaxi 7y ago

"spreading congestion" is not the best marketing pitch.

mlindner 7y ago

Not a fan of this design. The future for electric motors on aircraft is ducted fans, just as are used on jet engines.

fastball 7y ago
That sounds loud.
- hwillis 7y ago
  For complex reasons, ducted fans are generally quieter, but less efficient if you arent going quite fast.
mrfusion 7y ago
Can you expand on that? I’ve wondered the same thing.
- atrettel 7y ago
  Propeller-driven aircraft perform best at subsonic speeds (slower than the speed of sound). This is because the blade tips of the propellers approach the speed of sound at faster speeds, and this greatly increases the drag on the propeller blades, among other things. This is why after World War 2 propeller-driven fighter craft fell out of use, since they could not get much faster without major issues. Modern passenger jets operate in the transonic range (0.7 to 0.8 times the speed of sound). This range is a bit too fast for propellers and pretty much requires jet engines or something similar. Using props for passenger planes would reduce their speed as experienced by passengers today. I believe this is what the author is referring to.

mrfusion 7y ago

Meta: I haven’t seen this much negativity for an exciting new technology from HN before. It’s kind of bizarre.

leetcrew 7y ago
it's transportation research money that isn't being spent on bike lanes, buses, or rail.
- rexreed 7y ago
  In our part of the US, money for bike lanes, buses, and rail comes from states and local jurisdictions, not from federal funds. The portion of money NASA is getting from this does not take away from multi-modal transportation investment at the local level.
  - leetcrew 7y ago
    sure, but it's a common thread. notice how you see similar comments on articles about electric cars. HN hates to see money spent on improving forms of transportation that are not bikes or public transit.

JoeAltmaier 7y ago

Problem in the article with the caption? It says the picture is in 'cruise mode' but when cruising at altitude, the X-57 folds the small electric motors into the wing nacelles and leaves only the two wingtip props active. Did I miss something?

roelschroeven 7y ago
No, the propellors fold into the motor nacelles. Not the motors into the wings.
- JoeAltmaier 7y ago
  Thanks!

GordonS 7y ago

Aside from the pictures, the article was a bit lacking in information. According to wikipedia, it only seats 2 people, has a maximum range of only 100 miles, and a maximum flight time of only 1 hour. The batteries weigh 390kg, which sounds like a lot of weight relative to the small size of the plane. I get that electric flight is new, and it's going to take a long time before anything happens at scale, but given the limitations (and of course the fact you need an airstrip at either end of your journey) I can't help but wonder who is going to actually buy them, and what they would do with them?

PaulRobinson 7y ago
The X in X-Planes stands for "eXperimental". The history of them goes back within the US to 1946 and as the list [1] of vehicles shows, these aircraft are intended to test concepts and ideas, not provide a sellable solution to the market. Whilst most are betting that commercial electric in the air is going to be VTOL - and they do address the low endurance and runway issues you highlight - there are efficiency gains for longer distance in fixed wing designs, and you're going to have to think about electrification of that class of vehicle at some point. Put another way: we don't use helicopters for all passenger transport for a whole bunch of reasons, EVTOLs don't fix all those reasons, and so if you want to keep fixed wing aircraft around as a concept AND you want to use electric motors, at some point you're going to have to think about experimenting with electric passenger-carrying fixed wing aircraft. Thus: the X-57. You might wonder what the purpose of an experimental aircraft in this config is, if the eventual goal is to build airliners that can move lots of people. Well, the X-1 was no Concorde, but Concorde would not have happened without the X-1. And so it goes... It's OK then to think of the X-57 to an airliner of the future, as the X-1 was to Concorde. It's a whole set of interesting experiments that will validate some hypotheses, refute others, and we move along another step towards a better future. Seat count will get higher, endurance will improve, batteries will get lighter, and within 20 years, who knows where we'll be. [1] https://en.wikipedia.org/wiki/List_of_X-planes https://en.wikipedia.org/wiki/List_of_X-planes
- GordonS 7y ago
  Thanks, your comment makes a lot of sense. I do understand this is experimental, but I just assumed the end goal was to do a licensing deal of some sort with a partner than would sell a commercialised variant. My assumption (yes, another one ;) was that electrification would require baby-steps towards commercialisation in order to continue to fund the kind of progress you speak of - in the same kind of way we saw with cars, where initially they were expensive, had a very short range, there was very limited infrastructure etc, but they were still an option for a small market segment.

GordonS 7y ago

With cars, we've seen a lot of companies going the hybrid route, combining multiple small electric motors with a combustion engine. I'm curious if the same could be done with aviation - perhaps a turboprop or jet engine to get to cruise altitude, then electric engines taking over. Anyone know if there are any promising hybrid planes on the horizon?

spaceandshit 7y ago
Only one of many competitors: https://www.rolls-royce.com/media/press-releases/2019/06-11-19-rr-announces-new-hybrid-electric-flight-demonstrator-to-be-built-with-brandenburg-partners.aspx https://www.rolls-royce.com/media/press-releases/2019/06-11-...

sergeykish 7y ago

Cruise efficiency increased from 0.7 km/kWh to 2.9 km/kWh (13 nmi/gal AuGas to equivalent 51 nmi/gal AuGas). Better than ICE car!

zelienople 7y ago

Humans need a basic amount of exercise for health. It is hard for me to understand how someone with a functioning brain would look at traffic congestion and propose this solution, particularly with the codicil, "it's already benefiting taxpayers". No, technological developments that cannot possibly be used by anyone but the wealthy few, no matter how energy-efficient, are not a sane solution to urban transportation issues. The solutions are more prosaic: (1) Reduce population, population density, and the product of population times lifestyle. We have exceeded the carrying capacity of the planet, and our science is telling us that unequivocally with a cacophony of data from coral reefs, the status of the ocean, the loss of insects, and many other sources. We must control our own numbers. There is no technological alternative to that. (2) Create spaces and routes that foster personal human-powered transportation, such as bicycling. Separate the cars from the people to stop the carnage and remove legitimate safety arguments against bicycling. (3) Make public transit extensive and free. Stop extracting a pound of flesh from the poorest for every ride that they must take to get to a job that doesn't pay a living wage. The inequity of wealth distribution in our society has passed all limits of sanity. Incentive works great in small "c" capitalism, and we need to make sure that mom and pop outfits and very small businesses have the incentive to innovate and produce, but there is no need for the unlimited capitalism that we have now. Take a few pennies out of the pockets of the uber-rich to pay for transit. (4) Stop the propaganda, herein represented by NASA's usual BS about how we all benefit from their R&D. Organ transplants my fanny. The only thing this kind of transportation is going to do is to further increase the divide between ordinary people and the ultra-rich who pay no taxes in any case. Taxpayer-funded research into new toys for the CEO. Yay. We are brainwashed into a profligately wasteful, unnecessary, insanely-self-focused lifestyle. Mass media makes us feel bad so we'll go out and spend all our money on the latest stupid thing that will break in a year or less and we'll throw out. All the while we are striving to fill some artificially-stoked hunger for more: more money, more things, more waste and more destruction. The X-57 feeds right into that brainwashing. It will be our end.

JoeAltmaier 7y ago
Its actually pointed at reducing the entry cost of flying. So ultimately not for ultra-rich. NASA spends peanuts, and part of those peanuts is spent on fostering innovation. When I hear "Lets just feed the poor!" I feel ill. We're not so desperate we can't do right by our people, without tearing down everything else that's good. NASA's budget isn't going to feed the poor for more than 10 minutes.