While cruising at supersonic speeds the engines were actually the most efficient machines of their time achieving 43% thermal efficiency [0]. Despite being very efficient they still had high fuel consumption rates as the total amount of energy required to sustain those speeds is a lot higher than subsonic.
Modern jet are in the 50%s thermally efficient [1] but despite airframe improvements there has been no way to improve fundamental aerodynamics so that supersonic energy costs aren't high.
The Concorde did use reheat to take off and break the supersonic barrier which is very fuel inefficient.
Using a modern airframes and engines that also don't need reheat will reduce fuel consumption but not to a level anywhere similar to a modern jetliner.
[0] https://en.wikipedia.org/wiki/Rolls-Royce/Snecma_Olympus_593
I think the industry was thinking of having electric tugs or motors built into the plane to move passenger jets around on the ground to save the fuel used getting from the stand to the start of the runway.
"For a heat engine, thermal efficiency is the fraction of the energy added by heat (primary energy) that is converted to net work output (secondary energy)."
Does thermal efficiency = actual efficiency in the case of jet engines? I find that difficult to believe.
Propulsive efficiency is how good the engine is a converting this energy into thrust. The Concorde's engines were a type where all the propulsion was from the fast gasses exiting at the back, i.e. a turbojet. Efficiency is less than 100% as energy is taken from the gasses to power the engine and not all the gasses exiting the rear usefully push the aircraft forwards.
I don't have the exact number for the Concorde to hand but looking at [1] from my previous post, we can see it was typically around 60% in 1970, but these numbers are likely for (low bypass) turbo fans. These work in a slightly different way where they have more energy in the rotation of the shaft and less in the gasses going out the back. The energy in the shaft drives the big fan at the front which pushes a large volume of air more slowly out of the back. This is to address the problem of the gasses which exit the back but don't usefully push the aircraft forward.
To get the total efficiency of the jet you have to multiply the thermal efficiency by the propulsive efficiency.
edit: changed division to multiplication
Also need to consider combustion efficiency (i.e., the percentage of fuel turned into heat as an input to the heat engine), though for gas turbines this is typically ~99.9%.
Multiply surely? Otherwise reducing the propulsive efficiency would increase overall efficiency
Boom uses turbofan engines to reach supersonic speeds which are much, much more efficient. In fact, many airliners could theoretically go past mach 1. The reason they don't is that the airframe itself doesn't have the correct shape to deal with transonic and supersonic speeds.
I'd expect fuel consumption to be higher than a typical passenger jet but nowhere near concorde levels. Fuel consumption would also depend on the climb profiles of the plane, ideal cruise altitudes, etc. Since the more time you spend in subsonic flight and at lower altitudes the more fuel you burn (more friction and the aerodynamics and engines will be optimized for supersonic flight).
Concorde didn't use afterburners "at speed". The afterburners were used for takeoff, and to go through the mach wall.
Concorde burned insane amounts of fuel on the ground because turbojets are very inefficient at low-speed. Not unlike the SR-71's really (though the SR-71 also had such extreme high-speed bypass it was basically using ramjets at speed).
It's not only that. It's because they didn't have alloys which would handle the thermal constraints without significant expansion, so they had to design for that expansion. And in the same way rail tracks handle expansion by leaving gaps, that's what they did.
Furthermore, due to limited room and systems able to handle the temperature gradients, the fuel acted not just as fuel but also coolant, heat sink and even hydraulic fluid for some propulsion components (e.g. the afterburner nozzles and inlet guide vanes used JP7 as hydraulic fluid).
Either way, it’s fairly obscene.
1: https://www.iata.org/contentassets/ebdba50e57194019930d72722...
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To put things in perspective, Concorde was using two Olympus engines designed originally in the 50s.
It was already a marvel that they can run for such a range at Mach 2.0 when designed 70 years ago.
A lot of things improved since. Most fighter jets can supercruise at supersonic speed without afterburners nowadays.
You can do that in a conventional jet at latitudes far from the equator. You can walk faster than the earth rotates if you're very close to a pole (very very close).
Eh, within 15 miles or so. 4MPH * 24h = 96 mile circumference circle, 96 miles / 2pi ~= 15 miles.
Even so, supersonic flight is less efficient than getting there a bit slower. Unfortunately, air resistance is nonlinear like that.
To be clear, that's wrong, because of other factors; when you go faster in a given airplane, you can be more efficient at higher altitudes - mindful that wing size is dictated more by landing speeds than just how fast you want to go - if anything, you want smaller wings for weight, cost, and other considerations, but landing speed gets in the way. So, if you took the time to solve that equation for an airplane at, say, 30k feet, and for say 50k feet altitude, would you still get efficiencies over say, one of the modern , slower jumbo jets?
[1] https://web.mit.edu/16.unified/www/SPRING/systems/Lab_Notes/... (edited for line spacing)
The same physics applies to fast trains and other modes of transit. Fast electric trains have the advantage of not having to lug their fuel along with them at speed.
> consider that energy is a function of both power and time applied; if you double the speed to fly from say London to NY, would you cut the time to fly to less than 1/8th what it would otherwise be?
I think I understand what you’re trying to say, but note that by definition going twice as fast will get you there in half the time. Work and Energy are in alignment here because of the various efficiency losses you’re talking about.
The Concorde did have some reprieve in that it flew 20k feet higher than the usual cruising altitude.
https://aviation.stackexchange.com/questions/21881/at-what-a...
Ultimately high speed transport is not about conservation of energy. It’s about conservation of human time. Weighing that against the environment and other factors are important but few people weigh their total use of energy in a given day.
There are some military planes flying on biofuel, so ideally we’re not that far off.
HSR has its own unsolved problems. Like not being able to work over deep ocean... and insane infrastructure costs.
It’s bad, but not that bad. If you double the speed, you need 8 times the power, but only half as long for a given distance, so energy use is ‘only’ 4 times what you had.
(Of course, were talking about a very rough approximation that likely is so inexact that 8 might even be a better estimate)
Concorde didn't get to move beyond its first model. This boom jet is leveraging decades and decades of post-concorde engineering.
That's ignoring the trillions it would cost. The US does not have the population density to make HSR viable.
I would actually pay a premium. This actually is reality today. Acela on the Northeast corridor is more expensive than comparable air fares and it's not even that good.
I do like the idea of the 3/4 day trip as part of a holiday
Because of air resistance planes are more fuel efficient as well for those longer trips (don't forget about energy lost to brakes when the train needs to stop)
https://en.wikipedia.org/wiki/Regenerative_brake#Electric_ra...
I'd do 18 hours on a NY to LA if I could walk around, eat, talk, sleep, etc over a 5 hour misery ride in an airplane any day.
All that said, of course, figuring out how to lower costs safely would be a great thing.
That's frankly an insane figure, and depends vastly on what you're building and where. For something that's largely running through rural landscape, you really should expect no more than half that for the total construction cost. Maybe US construction is that expensive, but… wow.
In France the average cost is €15m/km, and that's for extremely high standards / constraints (350km/h or 220mph nominal speed, incl. barriers & bridges for wildlife)
What really made the difference for me is that the 4-5 hour train ride is done after 4 to 5 hours. My 1 hour flight starts 3 to 3.5h before the flight to get to the airport and through security and at the destination, after de-boarding, I'll spend another hour for security and to get from the airport to my actual destination.
I recall one of the senior marketing guys where I worked did London to Edinburgh on the overnight sleeper didn't get much sleep and was uncomfortable.
Traditionally there has been a large jolt at Crewe where carriages and/or the locomotive gets changed on the train. This will wake you up. But if you are properly tired from working hard then sleep is no problem.
They changed the trains recently. They were with stupidly small 'bedrooms' with absolutely nowhere to put your stuff. Plus sharing a 'bedroom' with a random stranger in the other bunk is slightly weird when they snore and take up all of the available space.
The end carriage used to be a gambling den with an all-night bar. It wasn't supposed to be a gambling den but the large round table and movable chairs made it perfect for betting on card games. The crowd was a regular one for this, working on oil rigs in the North Sea. I liked this illicit activity not that I was involved.
I also did the plane option a few times, but this was not optimal if you were trying to get work done.
Rather than just take the tube across town to Euston for the sleeper train there would be a fraught journey out to the airport - Heathrow. So you would have to do this during working hours hoping not to get caught up in rush hour. At the other end you would need to get a taxi from the airport plus you would need to book a hotel room. There would be no working maximum hours at both destinations, any money saved by the plane would be wasted on taxi and hotel bills and it would also be a mad rush rather than sensibly paced. The 'bump in the night' at Crewe and the guy in the lower bunk snoring was a small price to pay.
Most plane flights are for leisure rather than business. What makes sense for work doesn't make sense for leisure, the cheap flight wins every time when it is you that is paying for it.
Regionally it would make a ton of sense over absurdly short flights.
Most people are not flying LA to NYC so that is a minority use case anyways.
This is true, but it is however one of the busiest aviation routes in the US. Certainly you can almost certainly go after some of the busiest routes (New York/Chicago, LA/SF), but where you go after that is less clear.
The Democrats, after they take the Senate and Presidency, should launch a $1-$1.5 trillion regional HSR development project, partnering with Japan.
Here are the regional routes, generally speaking, that make tremendous sense and should be built this decade:
Oklahoma City, Dallas Ft Worth, San Antonio, Austin, Houston
San Diego, Los Angeles, Phoenix, Las Vegas, Bay Area, Sacramento
Milwaukee, Chicago, St Louis, Indianapolis, Detroit, Cleveland, Louisville, Cincinnati, Columbus, Pittsburgh, Philadelphia, Washington DC, Baltimore, New York City, Boston
Arguments can be made for linking up New Orleans initially; then later using that to link into Florida and Atlanta. Later on you'd link Atlanta to Nashville, and then Nashville to Louisville, completing the Texas to NYC connection. You'd later take Dallas or San Antonio out to El Paso, and then to Tucson & Phoenix, and then to Los Angeles, completing Texas to California. You could also debate Atlanta to Charlotte to Richmond to DC, completing Texas to DC & NYC by another path and creating an easy link from NYC to Miami. No idea what to do about Portland, Seattle, Denver and a few others.
If you build the three major regional HSR sections, you get a de facto national trivially with just a few more connections.
Ideally we would work with Canada and they'd simultaneously fund HSR using the same tech from Japan for max compatibility, and we'd link across the border to Toronto (and they'd link Toronto, Ottawa, Montreal, Quebec City.
This can be done. All it requires is the Democrats to have the gumption to steamroll the zoning / regulatory / environmental bullshit out of the way using executive orders and being abusive with federal power as necessary to the loads of idiots that will inevitably try to get in the way. Knock them down, push them out of the way, build the fucking rail. We might get one good shot at doing it before we drown in debt and it's too late (ie we might as well drop another trillion dollars plus in debt into the never-to-be-repaid ocean).
The older east coast cities make some sense at least since they tend to have some trains and density due to historical past but they mostly already have rail lines you can take (albeit not high speed).
Also, as European who has traveled a lot in train, they are not always so super comfortable over night.
Also, lets be honest, 90% of the discomfort of plane, has to do with boarding, and not plane rides themselves. Those things can be expressed relativity easily.
Building incredible expensive high speed trains across a territory as large as the USA is insane in scope and expense, and minimal in benefit. Specially with electronic planes, cars and autonomy happening.
There is also the reality that there are already huge amounts of airport infrastructure that could be activated with electric planes.
Building a high speed train network is a 30 year project, that in 30 years would be mostly pointless and unused.
https://www.sciencemag.org/news/2019/07/former-playwright-ai...
Whether you can fly JFK-CDG in 8 hours or 4 hours, when you factor in how irritating airports are, parking, security line ups, waiting for baggage, etc, it still takes all day to make the trip.
Might as well save several thousand dollars and take a longer flight. I believe they would have to cut the flight time down to about an hour to justify Concorde pricing.
It ran profitably for 27 years. [0]
It failed because it crashed and killed 109 people 3 years before they threw in the towel. [1]
[0] https://en.wikipedia.org/wiki/Concorde#Operating_economics
The airlines might have profited, but the R&D and manufacturing programs were a more or less write offs.
[1] https://simpleflying.com/british-airways-1-pound-concorde/
You can read about the supersonic experiments over Oaklahoma City in the 1960's to learn about the effects of sonic booms, and why people don't like them.
For reference, the Space Shuttle generated annoying sonic booms over west Los Angeles when landing at Edwards Airforce Base. The approach path to Edwards is more than 30 miles from west LA. So, for any supersonic airway, you'd need to set aside a roughly 60-70 mile wide swath of land. That's a lot of people voting to shut down your SST operation (or suing you).
Several European states without commercial airframers introduced supersonic overflight bans too and the Anti Concorde Project started in the UK so I don't think the argument it was all protectionism stands up anyway.
And realistically it also failed because while flying west makes sense as you could land "before" you took off, going east didn't work like that. Sure you're losing less time either way compared to a regular flight but flying east, you might as well take a slow flight to get some shuteye.
This problem still hasn't been solved.
1. Communication was not as instantaneous as today and more things required face to face meetings.
2. You could basically walk onto an air plane with minimal security interference.
My dad said he flew the Concorde several times from Europe to NYC for business in the late 70s and early 80's and he said it was worth it in that context.
I should ask him how comfortable it was next time I see him. I've been inside of a Concorde that was turned into a museum piece and it is a pretty cramped airframe. I dunno how modern 2020 people would feel about the compactness.
Security lines weren't a thing until 2001. The Concorde operated from 1976 to 2003. The retirement was due to low passenger count due to a crash in 2000 and 9/11 in 2001.
Slowing down in general is an easy way to bring down energy usage, but it's often a hard sell.
Why do you think Boom is environmentally unsustainable? Boom is working with fellow YCombinator startup Prometheus to use synthetically produced fuels that are net zero emissions.
I believe the Concorde is a marvel. You could travel faster than the rotation of the earth in it! However I don’t think we need more environmentally unsustainable travel.