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> But the airline industry is still roughly as slow, and noisy, and expensive, and inefficient and dirty as it has been for the last 40 years
This is not true. Dramatic gains in fuel efficiency have been made. Such gains are the primary driver of new airliner designs. The 757, for example, had (if I recall correctly) 35% more efficient engines, and a more efficient wing. The 787 has something like another 20% less fuel burn - again, due to better engines, wing shapes and weight reduction.
You also don't see the black smoke trail anymore that was normal for the 707. The engines are much cleaner.
There is a limit to how far this can be pushed, but Boeing and the engine makers have done an amazing job in improving the situation.
I should mention that 40% of an airliner operating cost is fuel burn, if I recall correctly. That makes fuel efficiency a BFD to airlines and therefore Boeing and the engine makers. They'll spend a metric ton of money for even small improvements.
If you calculate the share of airliner operating costs - possibly. But it is smaller fraction of total ticket price. According to this video it's only 3% https://www.youtube.com/watch?v=6Oe8T3AvydU.
Noise is also reduced massively:
http://www.bdl.aero/media/filer_public/46/16/4616cefd-aa12-4...
Comparing 1960s 737 vs 1990s 737. And 787
or here: http://www.airbus.com/fileadmin/media_gallery/photogallery/b...
a380 with hushkit compared to 747-400 (first flight 1989)
You also don't see the black smoke trail anymore that was normal for the 707.
I suspect you can in part thank the DoD for that, the black smoke that the F4's engines created did not precisely increase their life expectancy over North Vietnam....
Which makes me think that the military must be very interested in electric jets, given how stealthy they could be.
you have to remember that a lot of gain come from economy of scale, making bigger planes, the gains are realized only if passenger traffic increase (hence total pollution).
The 757 was about the same size as the 727, but 35% less fuel burn. The gains I cited were for the same size aircraft. (I worked on the 757 engineering.) The gains are real, and the airliners fell all over themselves to replace the old, inefficient jets with the new ones, because the operational cost savings were immense.
Ever notice the little vertical "winglets" on the wing tips? They increase the wing efficiency. They worked so well that Boeing produced kits so older aircraft could get them, too. They're just one example. The plastic skin used on the 787 is for weight saving, another example of reduced fuel burn.
You can reduce flight count and have the same amount of passengers to have a net gain in efficiency and a reduction in pollution.
This proposal seems to ignore so much.
Like the intense friction, and heating, supersonic flight produces. Concorde's service speed was limited by heat limits place on the aluminium alloy to ensure a decent service life. They were always white as that was part of the spec - dark colours would have taken heat absorption out of limit!
Wing roots varied by >100C each flight if I remember right, and fuel was used as a heat sink. Are we going to use the batteries?
If the outer surfaces are conductors, what are we doing about icing conditions?
Concorde, or likely most SST, engines put out a lot of thrust in a very fighter-like profile (they were a continuation of a fighter engine, and had reheat). Electric fans aren't going to work efficiently in that profile and would probably be large diameter, which isn't very supersonic friendly.
How are we now handling taxiing and subsonic? Edit: To expand the last point, Concordes were horribly inefficient subsonic, and burnt something like 2t of fuel to get to the runway. Reheat was used at takeoff and going transonic. They pumped tonnes of fuel after reaching supersonic - for weight and balance and reduced drag. They were basically really big fighters.
> Like the intense friction, and heating
The heating does not come from friction. If a gas is compressed, it heats up. Moving through air compresses it in front. There's a point on the leading edge where the air is actually still. That's the point of maximum compression, and maximum heat (and minimum friction!). (Pitot tubes work on this principle, they are simply air pressure gauges calibrated to read as speed rather than PSI.)
This misattribution is one of my pet peeves. <grump>
Thanks for your on point technical replies on aircraft engineering here. Really fascinating stuff.
> They were always white as that was part of the spec - dark colours would have taken heat absorption out of limit!
Interesting. The SR-71 Blackbird was dark (almost black) in order to radiate heat efficiently [1]. Then again, the Blackbird flew much higher (at around 26 km compared to Concorde's just over 18 km) so maybe convection plays a bigger part in Concorde's thermal management.
[1] https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird (Although my primary source is the book "Skunk Works" by Ben R. Ritch and Leo Janos.)
Fascinating. Now I want to know why! Maybe at mach 3 more heat's coming from inside than being absorbed.
Concordes were specced with Anti-flash White (high reflectivity as used by US and UK nuclear bombers), and the main reason I remember is there was some publicity when France painted one Pepsi blue (not wings) for a sponsorship. It had to have speed restrictions.
Wikipedia has a little more (not much), but says the white finish reduced the skin temperature by 6 to 11 degrees Celsius.
Note that they were using titanium, and while I'm not sure what the fuel cells were made of, until they heated up it leaked quite a bit. One of the first orders of business after takeoff was getting a refuel, which included changing the type of fuel, see e.g. http://iliketowastemytime.com/facts-you-didnt-know-about-sr7...
Zing! I, too remember this from "Skunk Works". What a great book!
> They were always white as that was part of the spec - dark colours would have taken heat absorption out of limit!
Since radiant (photons) heat emission follows radiant heat absorption: Black absorbs better, but also emits it better.
Maybe they didn't care about emitting heat, they just didn't want the sun adding heat?
re: "... dark colours would have taken heat absorption out of limit!"
The SR-71 Blackbird was black because that color dissipates heat. [1] The plane was also made from titanium, not aluminum so there may be other factors but black dissipates heat as well as it absorbs it.
[1] http://www.lockheedmartin.com/us/100years/stories/blackbird....
I thought the black was paint impregnated with tiny iron oxide balls to absorb radar energy?
edit: they say that farther down the page
"...and a radar-absorbing element was added to the paint."
Does the math work out if you ditch the "supersonic" part? Supersonic is pretty niche anyway, since you can't do it anywhere near populated areas; but substantially reducing per-passenger costs for subsonic planes could change a lot.
I think the math doesn't work out with subsonic since those huge delta wings are only efficient for supersonic flight. For subsonic a conventional swept wing (like on a 747) is much more efficient.
> They were always white as that was part of the spec - dark colours would have taken heat absorption out of limit!
Wouldn't the color only matter when it comes to heating due to absorption of electromagnetic radiation?
For heat transfer by direct contact with the heat source (in this case gases that were heated when compressed by the plane's motion), wouldn't color be irrelevant?
It couldn't an electric fly way higher and avoid that friction because it has no need for oxygen?
That's the other benefit of electric planes.
This 'proposal' seems to assume that the rest of the aircraft would be almost unaffected by the change, which is very unlikely.
Existing engines are designed to compress air, combust fuel, and recover energy from the exhaust to push air (to propel the aircraft) then compress more (to keep the cycle going). Once you are no longer combusting fuel, all of that compression is simply wasted energy. An electric aircraft is much more likely to have single-stage axial fans, with a much larger diameter than jets like the Concorde (because larger and slower fans are more efficient). This difference in propulsion will probably affect various other elements of airframe design.
As an aside, Elon Musk has mentioned VTOL as a possible feature of electric aircraft, and this makes a lot of sense. If the fans can be tilted (to provide part of the 'lift' for takeoffs and landings), it means that the airplane could have very small wings, which are usually good for efficiency, but cause problems while landing conventionally.
> Once you are no longer combusting fuel, all of that compression is simply wasted energy.
Not true. Instead of burning fuel, you can use electricity (something like an arc welder) to generate heat. And the efficiency with which that heat is turned into mechanical power will be dependent on the compression ratio, regardless of whether the thermal energy is coming from electricity or burning fuel.
Thermal energy in chemical fuel and the potential energy in a battery or a raised weight have the same units, but there's actually a difference. You can turn energy in a battery or a raised weight into mechanical energy with 100% efficiency - not achieved in practice, but there's no theoretical limit.
When you turn thermal energy into mechanical energy (via Otto cycle in a car or Brayton cycle in a jet), the peak efficiency you can achieve has a theoretical limit based on how much you can compress the working fluid (air) before injecting thermal energy (burning fuel or an electric arc).
So if you've got electic energy that you can turn into mechanical energy in a fan with 100% efficiency, why would you take the thermodynamic losses of "burning" that electricity? Because we don't know how to go supersonic speeds with a fan or propeller - the only way we know how, for now, is with a jet running on the brayton cycle. And all the advances we've made in high compression fuel-burning jets would apply to electric jets just as well.
If you're okay limiting your top speed to ~Mach 0.7, then you're correct spinning a large propeller using electricity is absolutely a better way to go, and you can make that propeller a lot bigger if you're able to tilt it.
Karem Aircraft has done extremely interesting work on figuring out how to tilt rotors, and much of their research would apply to electric motors as well: http://karemaircraft.com/
> it means that the airplane could have very small wings, which are usually good for efficiency
This is all well and good under normal flight conditions, but the glide ratio in the event of motor failure would not lend itself well to commercial flight.
Short wing aircraft are fine for military use where low occupancy and ejector seats provide emergency egress. Passenger aircraft - not so much.
I had to squint to look at the images on that site. The designs may or may not be a good idea, but if we can't read them then it doesn't matter. Bit of a poor show from whoever published the article.
Looking at the accompanying text, there are some problems with his ideas. Some of that "supporting" material is also about fail-safe design and heat distribution. A copper plate running through the middle of a battery will draw the heat out nicely. These batteries are all good and well until they fail, at which point you have a huge problem. With fuel, you can dump it. What do you do with you battery wing?
One of the massive problems is energy density, but that's not the only problem. With the batteries embedded into the wings, you need you to figure out how to effectively charge them too. Planes can't afford to sit for hours on the ground between flights and swapping wings over is not going to fly with safety regulations very well.
The intentions are good but I'm not convinced there is something viable here.
> I had to squint to look at the images on that site. The designs may or may not be a good idea, but if we can't read them then it doesn't matter. Bit of a poor show from whoever published the article.
Remove the ?amp=true from the URL and you'll get the proper desktop version.
>> "...swapping wings..."
If you were going to do this, you wouldn't swap wings. Instead, you'd swap passenger compartments in and out of various airframes, probably with some kind of automated gantry. This would reduce airfield turnaround times by allowing boarding to be finished before deplaning begins and by removing baggage handling from the critical path of getting the plane back in the air. Then the batteries would be charged during maintenance on the tarmac or in a hangar. Though overall I'm a skeptic of electrical aviation.
Planes might be able to afford sitting for hours if batteries are that much cheaper than aviation fuel.
Too dangerous.
If the wing got smacked up a little and got bent, thus the positive and negative surfaces touch, you would have a massive short circuit, then heat-up and very possibly ignition of the electrolyte with a fire that is worse than a jet fuel fire.
Not a better battery, just one with slightly less packaging. That's nowhere near enough for aircraft.
"Breakthrough" articles in the battery and "nanotechnology" (usually surface chemistry) fields need to be viewed with extreme skepticism. Those two fields seem to generate a high fraction of overhyped "breakthroughs".
I can't imagine how this would deal with damage. A large amount of Tesla's safety comes from each cell having a micro-fuse connecting it to the module bus, so a failed cell simply disconnects itself. Large single battery plates might be lower-resistance, but they'd be incredibly susceptible to damage.
High performance, low maintenance and supply, fragile. Military hypersonic UAV, anyone?
This is unbelievably stupid.
(1) Supersonic airplanes get incredibly hot, just by flying. Largest battery fire the world has ever seen?
(2) It would be impossible to manufacture.
(3) It would be too heavy to fly.
Quite. Even Concorde's inner windows were hot to the touch at the end of a flight. The wings would be extremely hot. They even used the fuel as air consorting heat transfer fluid, in an interesting design choice.
I don't believe he was intending the plane to fly supersonic. Instead he was talking about using the design of the wings because they have a larger volume.
Luke Workman. Why am I not surprised to see that guy's name in this article? He took Zero Motorcycles from a battery pack that only went 40 miles to one that goes 120 miles while making the battery pack physically smaller. His work never ceases to amaze.
>He took Zero Motorcycles from a battery pack that only went 40 miles to one that goes 120 miles while making the battery pack physically smaller.
And what did he actually do? lithium ION batteries have been increasing in capacity over the years and quite considerably, 18650's are now nearly 4 times the capacity they were introduced in. I can't find anything he actually did other than hack batteries together to make "custom" packs, while this is some sort of an engineering achievement this is quite far from designing an actual battery.
Luke Workman is "some guy" who works for zero motorcycles and hack's EV's together.
"Some guy" is the best description I could come with because he isn't a scientists/researcher, he hasn't published a single paper, I can't find even a trace of his record as far as education or engineering achievements go besides soldering a couple of batteries and putting them in a motorcycle.
All records I could find of him and his company are pretty much from News Atlas (their sources and references link to their own articles) or it's affiliates.
I've met plenty of researchers and paper publishes who're full of crap. The most prolific people I know have no papers behind them. If you do science, you're a scientist; and education in its own is no more of an achievement than raising VC money is. It's just a tool.
The chicken on his shoulder is not lending much credibility either.
However, 'some guy' is perfectly fine if the idea is good. One would think that DARPA would be very interested in throwing some money at this idea, if it was a good one. While they are funding electric airplane research, it appears that they are not funding this. Ergo ...
Wings flex while in flight. Either the cells need to handle that stress or the wing needs to be super rigid. Neither is particularly easy to achieve.
Wings can't be rigid, the fluttering would shred them to pieces or worse transfer to the main body and shred it pieces (tho at 35-40K ft it doesn't really matter what breaks apart ;)).
The article mentions grid level power storage but I don't see any comments around that. What would the feasibility of creating one of these batteries as some kind of fixed structure be?
What would be the point? For land power storage you don't care about weight (or volume). Just cost.
What if the battery terminal/wing is hit by lightning?
You don't need to worry about lighting the contraction/expansion from pressure and thermal differences alone is going to be interesting to see, put a battery in a low pressure chamber and see what happens to it.
I'm also wondering how they are going to deal with the temperatures and other aspects that can affect the batteries.
Solar Impulse flew at 15,000ft, a subsonic or transonic jet would be flying at around 35,000ft, the pressure at those altitudes is about 22-23 kPa and the temperatures are around -55 to -60c, and if he's aiming for supersonic he'll have another issue which is the fact that the temperatures of the aircraft can reach several 100's degrees C from the forces of friction alone.