I remember as a kid hearing sonic booms and thinking it was so cool. I guess it was military planes in my area. I wonder how many people now even knows what it sounds like.
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.“
When I was a kid, my dad was a naval officer stationed on an aircraft carrier and I got to go on something called the “Dependent’s Day Cruise” where we sailed out offshore and got tours of the ship and they did a full-on airshow for us. Because we were out at sea, they could break the sound barrier with impunity, and it was mind-blowingly cool to have fighter jets flying over low enough that we could see the pilots, absolutely silently until that massive shockwave hit your chest. It’s surreal.
> would burn up to 9x more fuel per passenger per kilometer
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.
You could capture the CO2 and take a train. No matter how you get your clean fuel - burning more of it is worse for environment than burning less of it.
Okay — but there’s no harm to the environment. You’re just not improving it.
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”.
Like oil, natural gas and coal which is top 3 of our energy sources worldwide. Together in 2021 they amounted to 130 000 out of 160 000 TWh of energy produced.
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.
What's missing from all this is how stunningly impractical the route from atmospheric CO2 to aviation fuel actually is. It's multiple GJ/tonne just to reverse atmospheric entropy and get the CO2 where you want it, and that's before you have to climb backwards up combustion's enthalpy cliff to turn it back into usable fuel. But the capture cost is a rounding error, even at 1GJ/tonne.
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.
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.
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.
Thinking a bit more, there's nothing special about airplanes. The world consumes about 100 million barrels of oil per day. I guess most is transportation, but in the end it does not matter. There are about 7.5 barrels to a ton, so about 13 million tons daily, which is very nearly 5 GT per year. Each ton of oil produces about pi (3.14) tons of CO2 (of course pi is just a coincidence, but it's easy to remember). So about 15 GT of our worldwide 50 GT greenhouse gas emissions come from burning oil.
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?
The Concorde is still pretty top notch, tech wise. As far as supersonic and supercruise jet engines go, they are all military. Civilian engine development went all in improving noise levels and fuel economy. And without a viable market, no engine OEM will invest the billions needed to develop a civil supersonic engine. So it is either a huge market, or various governments foot the RnD bills. Both of which are far, far away.
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...
The 9x factor seems in the ballpark when you consider a Mach 2 jetliner will be going 2.5-3x faster than a subsonic one, and drag increases with the square of the airspeed.
At constant altitude. I believe Concorde was actually more fuel efficient per passenger mile than a 747 when flying Mach 2 up near 60,000ft where the air was very thin, but as it took half the flight’s fuel simply to get that high and that fast the overall efficiency was much lower.
I am extremely skeptical of that claim. It might be true for the original 747-100 (with GE’s first turbofan engine) in unfavorable conditions, but it certainly isn’t for any 747 made in the last 40 years with even a semi-optimal flight plan.
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.
My girlfriend and I were hanging out at a lake east of Issaquah near seattle and suddenly two Growlers came down low over the lake and we were subject to two sonic booms which was amazing. They sounded sort of like a resonant crack of thunder but much louder. They flew over a boat in the middle of the lake and I shit you not someone on it screamed "AMERICA F YEAH." It turned out this lake was one of the ones they filmed for the new Top Gun film, but it was common for Whidbey pilots to buzz it on their way back to the NAS.
My daughter lives relatively close to Cape Canaveral and hears sonic booms from the returning Spacex first stage quite frequently, as does the surrounding neighborhood.
I read some contemporary articles in a Private Eye annual from the 1960s and the problem was not really the noise but the structural damage that was (allegedly) being caused. I don't know how real that was, but in the UK concerns over structural damage to buildings was what lead to the ban.
As for this plane, what are the elements of the design that reduce sonic booms? The comically long nose?
Given that it’s 14ft tall, I’d say no, though I agree they could’ve made it clearer. It says 99’7 In, or 99 feet and 7 inches (ideally, it would be 99’7”).
Or just go straight to 30%? (Take 10% & multiply by 3)
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.)
Is there a rule / scaling relationship about the maximum passenger volume + payload of a supersonic aircraft and the fuel burn? Just wondering if by physical law, these transports are destined to be only ever extremely premium / luxury travel.
Energy argument follows: higher speed = higher drag (increases with square of speed) = higher thrust to overcome that drag = more fuel = more weight = more structure overall (larger wings etc.).
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.
I'm curious to see the fuel efficiency. Wind resistance has to be way way higher at these speeds, but it also appears to be flying at much higher elevation so they may cancel out to a certain degree.
Even if fuel economy was somehow better, it would still lead to more fuel getting burned. Because the super rich only have so much time in their lives to spend in the stratosphere or elsewhere and shorter flight times could noticeably shift their trade-off decision about the inconvenience of flying vs the inconvenience of not being where they'd like to be. Outliers in wealth aren't quite as much outliers in ecological footprint because fortunately there's only so much you can consume, but a supersonic revival would help close that gap.
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.
"Creates a sound as loud as a car door closing" -> I assume this means at ground level? I can't imagine even the propulsion being that quiet let alone the sonic boom.
Yes, the noise level is measured on the ground directly below the flight path of the plane.
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)
It’s nice when they put it like that. Now imagine you trying to relax or concentrate in your home and hearing a “car door closing”, every minute, regularly, all day. And if in the end it sounds more like the car’s tire blowing up - well… “we are looking at ways to resolve the issue”, “we are aware of the issue and working on it”, “you are the only one complaining”, “it looks you may be too sensitive to noise”, and so on. Who cares in the end. It’s just people.
Unrelated but... My brain can't tell me if 14 foot is a lot or not... I can't imagine how is it possible to do CAD design in imperial measures, it was always making me think why is not whole world moving to metric- is it not a de-facto standard now?
Too fast for it to be useful I'd guess, you're reliant on the computer anyway so why have a front window be a design constraint restricting aerodynamics, tough enough glass/plastic (a lot more force on it than the overhead/side window it does have) etc.?
But Concorde is/was for passengers, a reasonable design constraint might have been 'it needs to look like a "normal" plane for end-customer confidence'. Military etc. aircrafts of course go far faster and did well before Concorde - and it's much more normal for them to have no eyeball visibility.
One of the more unique design complexities of the Concorde was the need to swing the nose out of the way for take off and (more so) landing, specifically so that the pilots could see wtf they were doing. That's why its nose looks like it does. It absolutely did not look "normal" at the time.
> Military etc. aircrafts of course go far faster and did well before Concorde - and it's much more normal for them to have no eyeball visibility.
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?
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.“