X-59 supersonic aircraft
lockheedmartin.com
lockheedmartin.com
The article mentions commercial air flights taking half the time, but I wonder who needs that kind of speed when I see this-
“According to ICCT, supersonic flights would burn up to 9x more fuel per passenger per kilometer than their subsonic flying buddies.“
That number seems a bit hyperbolic, even for Concorde, which was 1960s technology. Modern supersonics will be far lighter, use turbofans instead of turbojets, not require (or even have) afterburners etc.
They also claim that they will be net-zero Carbon due to advances in sustainable aviation fuels, with processes like CO2-fuel direct air capture.
The truth will probably be somewhere in-between.
This fig leaf is transparent.
Somehow I think the CO2 sensor on Mauna Loa would need to be dug out from a piece of percipitated carbon.
If the fuel is made from captured CO2, then there isn’t any net CO2 from burning it after.
The grandparent claimed this was a “fig leaf”: instead, you made an ideological post about how we need to not do even environmentally neutral things — that doesn’t make carbon neutral air travel a “fig leaf”.
Producing synthetic fuel requires energy.
And yes, that’s correct:
Synthetic fuels mean that it’s carbon neutral — that’s a fact, not a fig leaf.
Wasting energy is bad. Even if we actually used synthetic fuel. Even if we actually moved to 100% renewable energy sources - we'd still have limited amount of energy. And before we do - it's just PR.
Source: https://i.imgur.com/vZkz3sf.png
People often have the wrong mental model of how energy dense aviation fuel actually is. A 747 burns 4 litres of fuel per second. Do the maths on aviation fuel energy content, and that comes out in the order of 120MW. Megawatts. With an M. 10^6. Those small modular reactors everyone's excited about? One of those. That's the thermodynamic range anything proposed has to operate in.
Ok, so divide that by the number of passengers (say 400 to make the maths easy) and it's 300KW per passenger. Multiply by 9 for our fancy new supersonic plane: 2.7MW per passenger. Concorde had 128 seats; let's say ours has 100. 270MW for the whole thing.
Now, a transatlantic flight might be 10 hours. Assume a spherical cow in a vacuum and 270MW x 10h = 2.7GWh. Say two flights per day doubles it, but they're only 5 hours each supersonic, so halve back down and that cancels out. Round to 3GWh to make the maths easy. In joules: 11TJ. With a T. 10^12.
Now, we need to fuel this thing. Which means we need to convert enough energy into enough fuel. If we completely ignore the energy cost of actually capturing the carbon, 11TJ is the absolute lower bound. It will take more than that, but in the interests of generosity let's put that to one side. 86400 seconds per day gives us 127MW.
So the good news is that the total energy requirements for this one aircraft to run on fuel made of already captured carbon are within the bounds of what we know how to build. You can, if you are a government, choose to buy these things. The bad news is that you need one per aircraft, for the eventual ability to fling 100 meatsacks across the Atlantic a bit faster.
I would suspect, looking at the costs (in terms of energy, money, space) that this is not a choice a rational actor would make.
It is sobering.
Now, leaving aside the hypothetical supersonic jet planes, we still have this problem with the existing airplanes. If we want to decarbonize aviation, then how do we go about this?
On one hand, maybe 747 is an old plane and not that fuel optimized. I checked for 787-9, and it burns only 1.5 liters per second, which translates into 55 MW. It can only carry about 300 passengers vs 520 for a 747, so overall there is an improvement by about 33%. It's not nothing, but it's not that impressive either.
Anyway, with whatever fleet of commercial airplanes the world has now, some old, some new, we consume about 100 billion gallons of fuel per year. That's about 300 million tons.
Let's say we switch to hydrogen somehow. Which has more than double the energy density of jet fuel. We would need about 150 million tons H2 per year. According to the DOE [1], a 1GW nuclear power plant can produce about 150 kT of H2 per year, so we'd need 1000 of them. The whole world produces about 400 GW from nuclear reactors, we'd need to multiply the current fleet by a factor of 2.5, just to decarbonize air travel.
[1] https://www.energy.gov/ne/articles/could-hydrogen-open-new-m...
Yep. It's better than nothing, but we'd need to find orders of magnitude from somewhere. I don't think they're there to be found, personally: keeping big lumps of metal off the ground with aerodynamic lift runs into fundamental physical constraints relatively quickly (you can do the maths on glide slope and gravitational potential energy - just by rough order of magnitude it's mindboggling that it works at all).
And you're right, we do have this problem right now. Anything that wants to keep our travel patterns as they are today needs to confront the reality that its energy requirements make any other consideration a rounding error. From my point of view the big picture is fusion or bust, but that's, uh, a bit of a long shot.
The good news is that air transport emissions are only about 2% of the total, so there are much more productive lower-hanging fruit to tackle.
How are we going to replace that?
5 billion tons per year means about 150 tons per second. At about 40 megajoules/kg, that's 6000 GW. Six thousand large (1 GW) power plants.
You say it's fusion or bust. What if we had fusion today? Commercial, economical fusion. As easy to build as natural gas power plants. How are we going to build 6000 large such power plants?
Any Co2 capture system will undoubtedly be responsible for some small amount of Co2 emissions.
Wikipedia gives the TSFC of Concorde’s Rolls-Royce 593 engines as 1.195 lb/lbf-hr and 0.6 lb/lbf-hr for a 747-400’s Rolls-Royce RB211. So that’s 45% less fuel burn per pound of thrust in favor of the 747.
Furthermore, drag increases as the cube of airspeed (which corresponds to fuel per mile scaling as speed squared). That means at constant air density, Concorde would consume (2.37)^2 = 5.6 times more fuel (not accounting for the difference in engines)
A 747 cruising very low at 30k feet would have ~4 the air density to contend with, but even that doesn’t make up for the speed difference. 747-400’s routinely cruise at over 40k feet…
Unfortunately, you can’t just wave your hands and shout “supersonic turbofan”, because high bypass ratios (what accounts for subsonic efficiency gains since the 1960’s) are incompatible with supersonic flight.
Edit, one more thing: The General Electric GEnx found on modern 747-8’s are 15% more efficient than the old 747-400’s engines!
What is true is that a Concorde flying at subsonic speeds is more efficient per passenger mile than a 747. But that’s mostly due to the very high fineness ratio and drag-reduction-above-all-else design philosophy.
All technological promises regarding civilian supersonics only exist in fancy renderings and pitch decks, there is no substance behind. Even less than there is with the various eVTOLs, at least those actually fly. Well, some of them that is...
As for this plane, what are the elements of the design that reduce sonic booms? The comically long nose?
https://www.thedrive.com/the-war-zone/44307/behold-the-x-59-...
Is metric used to actually design the plane, or does Skunkworks still use US customary measurements?
Your question did make me think of the Boom XB-1; a scaled down version of a passenger jet that I'm skeptical will ever fly commercially.
I'm guessing it should read 99ft 7in. That would put it at just over 3m, which still seems pretty small to me.
Easy mental math and much closer.
Seems easier to remember the one number than 'divide by 3 for yards then subtract 10% for meters', assuming you have no use for yards. (I use yards colloquially, but never as a measurement.)
Yep.
> That would put it at just over 3m
Nope.
Can it fly from New York’s Idlewild Airport to the Belgian Congo in 17 minutes?
Higher speed -> you reduce the angle of attack -> lower cross-section. The drag per unit of area increases, but the area decreases. Overall, you still have higher drag, but you get faster to where you need to get. It is not pre-ordained that you need to burn more fuel overall.
In fact, you can end up burning less, not more fuel.
Here's why: drag per se doesn't matter. What matters is the lift-to-drag ratio [1]. To keep the plane at a constant altitude, the lift needs to be equal to the gravitational force acting on the plane. To keep the plane at constant speed, the thrust needs to equal the drag. If the lift-to-drag ratio is 10, the thrust needs to be one tenth of the weight of the plane.
Now, the fuel consumption per second is roughly proportional to the thrust. If you double the speed and the lift-to-drag ratio gets cut in half, your overall fuel consumption is the same. But here's the thing: in supersonic regime, the lift-to-drag ratio does not get cut in half. The empirical lift-to-drag ratio is 4(v+3)/v, where v is expressed in Mach number. For example at Mach 3 you get LTD ratio = 8 and at Mach 6 you get 5.33.
Of course, things are not that rosy: on one hand the airplane needs to be sturdier, because it needs to withstand higher vibrations. On another hand, even if in cruise mode you may save fuel, it's difficult to optimize the plane in a very wide range of velocities. Concorde was horrible at low speeds, so it was burning a lot of fuel at take-off; it is quite obvious that a plane is the heaviest at take-off, so if you burn more fuel at that point, you really burn more fuel.
But design has made huge advances in 50 years. We may be able to optimize better an airplane now than we could when the fastest supercomputer was slower than the iPhone in your pocket.
Bottom line: it is not at all obvious that a supersonic plane needs to burn a lot of fuel, and it may be that it could actually burn less than a subsonic one.
A part of me sure loves the nostalgic idea of technological bigger-better-faster, but the rest is fully aware that this is not the progress we are looking for. It's bad enough when private investors put money into destructive technology like this, but if it was my tax money, I'd be shouting at them.
It's also not a place you'd want to spend too much time considering you're outside of the radiation protection of a large part of the atmosphere.
Interestingly, it’s not just the volume but also the pattern of the boom that can be altered by changing the design of the plane. There’s a great discussion of this here: https://www.elidourado.com/p/50-years-supersonic-ban (Scroll down to the images of the sound wave)
But I know I'm just over 6 foot tall, I know a foot is about the length of a ruler.
Acres are completely alien to me, same with lbs and oz's
Anything designed for an active fighting role (not just transport, observer, tanker, ...) likely has significantly better visibility than the average civilian aircaft.
Can you name an example of a fighter with visibility worse than a C172?