I do wonder how much modern design can overcome, in materials, engines, aerodynamics, and flight controls. Less drag at higher altitudes, easier to travel further, cover more distance in less time. Should be able to eliminate refueling stops at the very least. One of the problems of fast high altitude flights is preventing stalls. Maybe computer aids and thrust vectoring would help prevent or mitigate such events.
Worth noting the use of titanium at Mach 3, Mach 3.5, is really at its limit. Any faster and you'll start to see serious problems with thermal management. This pushes you into using super nickel alloys or even ceramic matrix composites, which would be necessary for use cases at Mach 5+ for sustained flight. Acknowledging planes in the last have gone faster like the X-15 but this such plane's architecture wouldn't stop for longhaul flight distances. CMCs and super nickel alloys will be very very expensive.
The version of the X-15 that got the most impressive speed records was coated in an ablative paint designed to burn away while in flight to protect the plane.
With a rocket engine, reaction control system and ablative coating, the X-15 almost had more in common with a space ship than an airplane.
Have we gotten good enough at jet engines to be able to generate enough thrust in the upper atmosphere to turn planes into ICBMs for an ex-atmospheric inertial jaunt?
With ramjets/scramjets maybe, but developing the inverse of what you suggest is where the money is being spent. Missiles on ballistic trajectories are easier to see on radar and have less ability to maneuver, so they're easier to intercept. So instead of starting out breathing air and then pulling into a ballistic climb at the end, the idea is to start out with a rocket powered ballistic flight, reenter the atmosphere, and then glide/fly through the atmosphere, possibly with a ram/scramjet, to the target. This way the missile is much harder to detect and intercept.
> I do wonder how much modern design can overcome, in materials, engines, aerodynamics, and flight controls.
The basic physics are arrayed against you. Higher speed cruise flight already means you already fly at higher altitudes or the thermal and structural loads would be intolerable. Stall departure resistance isn't the issue. Get high enough, and you're no longer talking about cruising flight, you're talking about hypersonic glide that has been accelerated to hypervelocity by rockets (this is called point-to-point boost-glide). It has been looked at, and people are continuing to look at it. There is a whole loose industry coalition in the U.S. called "FastForward" that is interested in this topic.
No, it's exceptionally bad to fly close to Mach 1 and you do better if you fly faster up to Mach 3 or so. The "Mach 1.4 business jet" class will be terrible, the Concorde was better, something that flies at SR-71 speeds could be better still but needs SR-71 materials and relatively small wings that won't support the weight of the aircraft taking off with a full fuel and pax load.
> No, it's exceptionally bad to fly close to Mach 1 and you do better if you fly faster up to Mach 3 or so.
Where do you get this from? I suspect you are talking about the Breguet range parameter, which is (M / SFC * L / D), where M is the cruise Mach number, SFC is fuel consumption per unit thrust, and L/D is aerodynamic efficiency.
Cruise L/D drops monotonically with Mach number until it asymptotes out to hypersonic waverider type figures (the well-known Kuchemann curve fit for supersonic L/D and the asymptoting to waverider values is illustrated at: https://aerospaceweb.org/design/waverider/design.shtml ).
SFC for gas turbines is extremely sensitive to cycle parameters and internal temperature limits, but generally well-designed gas turbine propulsion systems are going to beat ramjets until they hit thermal limits. Today's gas turbine technology is far more capable than the J-58 technology of the the A-12/SR-71 era. That said, SFC is still going to increase monotonically with cruise Mach number until you asymptote out to flatter slopes of ramjet and scramjet curves. (Edit: see the Isp illustration at: https://en.wikipedia.org/wiki/Specific_impulse ; Isp is the inverse of SFC).
So you are banking on the increase in M more than offsetting the increases in SFC and decreases of L/D. This is not going to support the case for increased efficiency in high supersonic (M >= 3) cruise. You could make the argument going full-on hypersonic waverider could "make sense" since the range cost functions plateau out, but that is still going to have a strictly lower overall range parameter than a supersonic vehicle. Kuchemann addresses this topic in his well-known text, "The Aerodynamic Design of Aircraft".
A naive Breguet range parameter perspective also fails to consider airframe mass penalties associated with flying faster (roughly, aircraft acquisition costs trend with aircraft unfueled weight), or that high aerodynamic efficiency is often at extreme odds with volumetric suitability for passenger & cargo carriage. Mass penalties will come from variable geometry, thermal management, Cg management, degree of compromise in structural efficiency for aerodynamic efficiency, etc. Let's say you manage to keep Breguet range parameter really high and fuel burn per seat-mile is acceptable. All the complexity and increased airframe mass of the faster aircraft is still going to make recurring costs to operate & maintain the aircraft really high.
The above also neglects boom, which you ideally want to minimize to maximize overland flight potential for your supersonic aircraft.
As per a previous comment I made: https://news.ycombinator.com/item?id=27386119 , if you're going to go in on supersonic civil flight, you likely want to be below Mach 2. Mach 1.4 - 1.8 might be the sweet spot when you consider all factors, assuming it makes any sense at all economically.
For the majority of air travel, we would be better served by making the airport experience much more streamlined and less shitty. And I say this as one who loves and works in high-speed flight.
Circa 1960 they imagined that supersonic military aircraft would "dash" when the mission required it but otherwise fly more slowly, then they realized the fuel economy of supersonic aircraft peaks around Mach 3. Something SR-71 class has good fuel economy at speed, but has horrible problems when it comes to (1) materials, and (2) taking off. The SR-71 was of course made of Titanium and dealt with (2) by taking off with as little fuel as possible and then refueling once it was up in the air -- an answer which isn't suitable for civilian use.
Also circa 1965 it was widely thought that SSTs would make airliners like the 747 obsolete quickly because they could make more flights in a given amount of time thus being able to pay the capital cost quickly. The US aimed to develop Mach 3 class airliners
which was "successful" in terms of getting into the air but probably doomed in economics from the very beginning. The Concorde couldn't actually fly more flights per day than the 747 on the routes it flew on so it didn't get the capital cost amortization advantage that a faster plane might have gotten, and fuel economy was worse.
A more ambitious plane might require some crazy ideas like
An issue with SR-71 materials and fuel: it leaked fuel (by design) when on the ground, because the panels needed room for expansion when they heated up during flight.
"The SR-71 was of course made of Titanium and dealt with (2) by taking off with as little fuel as possible and then refueling once it was up in the air -- an answer which isn't suitable for civilian use."
Couldn't we, in theory, slingshot the planes into the air to achieve the same relative fuel burn rates ?
> Couldn't we, in theory, slingshot the planes into the air to achieve the same relative fuel burn rates ?
The required release velocity would need to be so high that drag from air resistance (which increases with the square of velocity) would slow down the vehicle such that there would be no benefit.
Carrier catapults violently accelerate aircraft to the point they are going fast enough to lift their own weight, within the takeoff length on the deck.
You could likely lessen fuel burn of a supersonic aircraft taking off (as you could with a subsonic aircraft) by accelerating it via a catapult of sorts, but you have to do so at acceleration levels tolerable to all passengers, which would make for a long, unwieldy catapult. Release speed is also obviously going to be very subsonic.
The fuel needed to get to take-off speed is a tiny fraction of the fuel needed to get from take-off to altitude. In practice, the benefit is for runway length only.
> then they realized the fuel economy of supersonic aircraft peaks around Mach 3
As I noted in a below comment, there isn't a way for this statement to be accurate without a lot more qualifications. For "equivalent technology level", Mach 2 cruise will beat Mach 3 cruise in passenger seat-miles per unit fuel burn, and below Mach 2 will be better still.
The extremely questionable economics of supersonic commercial flight were realized by technical people far before the 1960s US programs were terminated. Two excellent sources on this topic are by aviation historian Richard K. Smith,
20 hours to travel to the other side of the planet should be more than fast enough for anybody. Supersonic passenger flight isn't coming back, and your sense of entitlement is the stupid part. If you don't want to be on one airplane for 20 hours, then split your trip in two with a layover.
Thats true - I have flown Delhi-Newark in United Polaris business class a few times after the outbreak of the Ukraine war. What used to be a 14 hour flight is now over 15 hours due to the avoidance of Russian airspace. Even in business class with comfortable flat-bed seats, its becomes a bit of struggle towards the end of such long flights.
If you're not already hitting the melatonin, now's the time to try it.
The struggle is real on those long flights when there's little respite from turbulence, though, to the degree that the service is constantly interrupted (or abbreviated), passengers can't get up to use the facilities, and everyone's too nauseous to sleep. I've been on a few where the seat belt light was lit up almost the entire ride.
I had two back to back 10 hour flights on the same plane a few years ago. When we stopped we were not allowed to deplane or stand in the aisle because the crew had to clean. We had to stay in our row. It wasn’t totally miserable but it was not easy.
Airports suck less than being on an airplane. Usually.
I can walk around, find something to eat or read, people watch. Plug in a laptop and sit at a table that's reasonably comfortable to work on. Relocate somewhere quieter, or more interesting. See if I can find bathrooms that aren't slammed. Get my steps in / some exercise.
How would skipping a stop have a negative influence on emissions? It must be the weight of the extra fuel, but I'm somewhat surprised it adds such a substantial overhead when you're so high up in the sky most of the time.
You're putting much less passengers in the same plane - the extra fuel takes up the space where ~100 passengers would sit if it was done as two flights with a refueling stop.
I recall flying LA to London on New Years Eve once - there was about 10 of us on the whole plane, and someone got a cricket game going down the fuselage. When we landed in the early hours, I set my watch to UK time and it was only a day or two later I realised I'd skipped NYE as a result :)
New Zealand started selling the sky couch which is just an entire row of economy or poor mans business class. I guess the idea is if you are flying with one other person you can buy the middle seat as well. They also are adding some beds that you can rent for a few hours in economy kind of like an extended crew rest. Seems like that is the only way to do 20 hours in economy.
The only time I used sky couch the plane was half empty so they put out all the ones they had and many people had their own bed. We had paid for it anyway but we got 2 beds between our family instead of 1.
I support when people react poorly in the context of airlines. I want as many unruly passengers as possible to strike fear into airlines and a government that seems hell bent on making flying as painful and frustrating as possible. I miss the COVID era rebelliousness among airline passengers. When one freaks out, remember that at least some of the docile faces and people around them are rooting for them to continue.
Ultra low tier services like spirit airlines shouldn't exist for flights longer than 4 hours. Ultra Economy seats for more than 10 hours might as well qualify as torture in some nations.
If no one flied them, they wouldn't exist, and regular economy airlines would be cheaper. To be clear, I am saying that spirit airlines tier ultra low cost airlines are bad for everyone because it means that the economics of scale don't kick in as well for the economy tier airlines right above the bottom as offered by say, delta or Alaska (which is the first level at which flying isn't torture)
Consumers are wrong and actively bad for being willing to buy ultra low cost tickets on long flights. These people are wrong and regulations should exist to prevent their lunacy. We do this in many other industries where there would be a race to the bottom of regulations didn't exist. Water, transportation, electricity, why not airlines?
There is no race to the bottom every airliner has to follow the same safety regulations. And people have the freedom to decide for themselves what they consider torture. I remember when I was young I used to spend the last 24 hours of a vacation without sleep in order to cut hotel costs.
I used to take a 17hr nonstop from NYC to Bangkok on Thai Airways. There’s not much that can make a flight like that easy, but it was by far preferred to the >28hr trips that had connections.
If people need to travel long haul, this is the way to go.
My dream (ha!) is for medical science to advance enough for routine, safe, "deep sedation" for travel.
I arrive at the station/terminal/depot, get put to sleep and loaded into a pod, then wake up at my destination. No fuss, no mess!
All the inconveniences go away and transport efficiency skyrockets.
Though I do worry that I may wake in the wrong place, given how airlines tend to lose baggage today - once we start treating passengers as cargo then we have to worry about all the cargo issues...
The folks at the airport bars sell a wonderful concoction called a "Long Island Iced Tea"
Don't let the name fool you; if you drink one 30 minutes before departure (and make it to the plane), you'll open your eyes just as the plane touches down :)
Or just take it a bit further, put on VR suit and arrive in destination within seconds without taking any drugs. For real life live images with rented personal drone at location to live stream reality.
The future of air travel should be airplanes with higher pressure and humidity (e.g. 787 Dreamliner is much better than any other Boeing plane), more ergonomic seats, and a government-issued obligation to have enough legroom on flights which are longer than, say, 8 hours.
My flight was 24 hours with a 3 hour stop in dubai to fuel.
I would have preferred 20 hour flight without stop.
Ok there was barey anyone on the plane, so getting up to toilet was easy and service was great. I mostly slept in my seat with my belt on, instead of some people sleeping on a row of chairs.
Didn't feel like shit when I arrived.
Is it the airlines problem that people with problems book long haul flights?
Even a 3 hour flight feels like torture. I can't imagine suffering for 20 hours on a plane. They should offer the same level of comfort as sleeper trains if the flight is that long.
But sleeper trains offer beds to everyone not just the first class. And 20 hours is two times longer than a typical trip on a sleeper train. Even the cheapest bunk bed is way better than an airplane seat.
What is the health effect to the pilots and crew? Are they not people and passengers, too? Without a stop there is no chance to change them for fresh employees. Sounds like a safety concern.
Long flights are required to carry enough staff that pilots and stewards can meet the rest requirements and still have everything covered. They also need to meet the crew requirements for the plane's size. I understand there is some variance in regulatory rules between countries and regions.
I traveled 30+ hours journeys on train or bus, both usually non AC, bus even without toilet and I would take AC airplane with toilets anytime over these. You can walk in plane as much as in train, same narrow aisle, though with trains there is usually sleeper option for reasonable price (compared to plane) and leg space is usually a bit better even with seat vs seat.
But still 20 hours ain't really that much, not even a full day.
74 comments
[ 3.2 ms ] story [ 139 ms ] threadWith a rocket engine, reaction control system and ablative coating, the X-15 almost had more in common with a space ship than an airplane.
Like this image depicts: https://en.wikipedia.org/wiki/Qian_Xuesen#/media/File:Tsien_... (This sort of missile flight is sometimes called a Qian Xuesen trajectory, after the man who first came up with the idea.)
The basic physics are arrayed against you. Higher speed cruise flight already means you already fly at higher altitudes or the thermal and structural loads would be intolerable. Stall departure resistance isn't the issue. Get high enough, and you're no longer talking about cruising flight, you're talking about hypersonic glide that has been accelerated to hypervelocity by rockets (this is called point-to-point boost-glide). It has been looked at, and people are continuing to look at it. There is a whole loose industry coalition in the U.S. called "FastForward" that is interested in this topic.
Even the new supersonic plane in development, Boom, has a promised range that requires a a stop for transpacific flights.
Where do you get this from? I suspect you are talking about the Breguet range parameter, which is (M / SFC * L / D), where M is the cruise Mach number, SFC is fuel consumption per unit thrust, and L/D is aerodynamic efficiency.
Cruise L/D drops monotonically with Mach number until it asymptotes out to hypersonic waverider type figures (the well-known Kuchemann curve fit for supersonic L/D and the asymptoting to waverider values is illustrated at: https://aerospaceweb.org/design/waverider/design.shtml ).
SFC for gas turbines is extremely sensitive to cycle parameters and internal temperature limits, but generally well-designed gas turbine propulsion systems are going to beat ramjets until they hit thermal limits. Today's gas turbine technology is far more capable than the J-58 technology of the the A-12/SR-71 era. That said, SFC is still going to increase monotonically with cruise Mach number until you asymptote out to flatter slopes of ramjet and scramjet curves. (Edit: see the Isp illustration at: https://en.wikipedia.org/wiki/Specific_impulse ; Isp is the inverse of SFC).
So you are banking on the increase in M more than offsetting the increases in SFC and decreases of L/D. This is not going to support the case for increased efficiency in high supersonic (M >= 3) cruise. You could make the argument going full-on hypersonic waverider could "make sense" since the range cost functions plateau out, but that is still going to have a strictly lower overall range parameter than a supersonic vehicle. Kuchemann addresses this topic in his well-known text, "The Aerodynamic Design of Aircraft".
A naive Breguet range parameter perspective also fails to consider airframe mass penalties associated with flying faster (roughly, aircraft acquisition costs trend with aircraft unfueled weight), or that high aerodynamic efficiency is often at extreme odds with volumetric suitability for passenger & cargo carriage. Mass penalties will come from variable geometry, thermal management, Cg management, degree of compromise in structural efficiency for aerodynamic efficiency, etc. Let's say you manage to keep Breguet range parameter really high and fuel burn per seat-mile is acceptable. All the complexity and increased airframe mass of the faster aircraft is still going to make recurring costs to operate & maintain the aircraft really high.
The above also neglects boom, which you ideally want to minimize to maximize overland flight potential for your supersonic aircraft.
As per a previous comment I made: https://news.ycombinator.com/item?id=27386119 , if you're going to go in on supersonic civil flight, you likely want to be below Mach 2. Mach 1.4 - 1.8 might be the sweet spot when you consider all factors, assuming it makes any sense at all economically.
For the majority of air travel, we would be better served by making the airport experience much more streamlined and less shitty. And I say this as one who loves and works in high-speed flight.
Circa 1960 they imagined that supersonic military aircraft would "dash" when the mission required it but otherwise fly more slowly, then they realized the fuel economy of supersonic aircraft peaks around Mach 3. Something SR-71 class has good fuel economy at speed, but has horrible problems when it comes to (1) materials, and (2) taking off. The SR-71 was of course made of Titanium and dealt with (2) by taking off with as little fuel as possible and then refueling once it was up in the air -- an answer which isn't suitable for civilian use.
Also circa 1965 it was widely thought that SSTs would make airliners like the 747 obsolete quickly because they could make more flights in a given amount of time thus being able to pay the capital cost quickly. The US aimed to develop Mach 3 class airliners
https://en.wikipedia.org/wiki/Boeing_2707
and failed but the Europeans developed a slower airliner
https://en.wikipedia.org/wiki/Concorde
which was "successful" in terms of getting into the air but probably doomed in economics from the very beginning. The Concorde couldn't actually fly more flights per day than the 747 on the routes it flew on so it didn't get the capital cost amortization advantage that a faster plane might have gotten, and fuel economy was worse.
A more ambitious plane might require some crazy ideas like
https://venturebeat.com/offbeat/nasa-sideways-supersonic-pla...
to solve the takeoff problem.
https://theaviationgeekclub.com/heres-why-the-sr-71-blackbir...
Couldn't we, in theory, slingshot the planes into the air to achieve the same relative fuel burn rates ?
I think this only exists on aircraft carriers ?
The required release velocity would need to be so high that drag from air resistance (which increases with the square of velocity) would slow down the vehicle such that there would be no benefit.
See: https://en.wikipedia.org/wiki/Max_q
However, it then raises the question: What are they doing on aircraft carriers and how is that different ?
https://en.wikipedia.org/wiki/Aircraft_catapult
... I assumed those had some fuel-use benefit, but perhaps their only benefit is shortening the runway ?
You could likely lessen fuel burn of a supersonic aircraft taking off (as you could with a subsonic aircraft) by accelerating it via a catapult of sorts, but you have to do so at acceleration levels tolerable to all passengers, which would make for a long, unwieldy catapult. Release speed is also obviously going to be very subsonic.
As I noted in a below comment, there isn't a way for this statement to be accurate without a lot more qualifications. For "equivalent technology level", Mach 2 cruise will beat Mach 3 cruise in passenger seat-miles per unit fuel burn, and below Mach 2 will be better still.
The extremely questionable economics of supersonic commercial flight were realized by technical people far before the 1960s US programs were terminated. Two excellent sources on this topic are by aviation historian Richard K. Smith,
https://www.jstor.org/stable/26802349 , with text freely available at: https://www.thefreelibrary.com/THE+SUPERSONIC+AIRLINER+FIASC...
and the book "High Speed Dreams" which also covers the 1990s HSCT era: https://press.jhu.edu/books/title/8516/high-speed-dreams
There's significantly more to the problem than just managing heat and "solving" takeoff.
The struggle is real on those long flights when there's little respite from turbulence, though, to the degree that the service is constantly interrupted (or abbreviated), passengers can't get up to use the facilities, and everyone's too nauseous to sleep. I've been on a few where the seat belt light was lit up almost the entire ride.
or, you know, beer.
I can walk around, find something to eat or read, people watch. Plug in a laptop and sit at a table that's reasonably comfortable to work on. Relocate somewhere quieter, or more interesting. See if I can find bathrooms that aren't slammed. Get my steps in / some exercise.
Ultra low tier services like spirit airlines shouldn't exist for flights longer than 4 hours. Ultra Economy seats for more than 10 hours might as well qualify as torture in some nations.
They don’t if you don’t fly them.
Consumers are wrong and actively bad for being willing to buy ultra low cost tickets on long flights. These people are wrong and regulations should exist to prevent their lunacy. We do this in many other industries where there would be a race to the bottom of regulations didn't exist. Water, transportation, electricity, why not airlines?
And others are rooting for security to remove them as quickly as possible so that they can get to where they’re going without additional delays.
If people need to travel long haul, this is the way to go.
I arrive at the station/terminal/depot, get put to sleep and loaded into a pod, then wake up at my destination. No fuss, no mess!
All the inconveniences go away and transport efficiency skyrockets.
Though I do worry that I may wake in the wrong place, given how airlines tend to lose baggage today - once we start treating passengers as cargo then we have to worry about all the cargo issues...
https://www.washingtonpost.com/travel/2022/08/16/craft-beer-...
But not a lot of options if I need to get to Indonesia or the Bahamas.
Or they lose track of your pod and find you a dried husk in a warehouse a few years later.
The folks at the airport bars sell a wonderful concoction called a "Long Island Iced Tea"
Don't let the name fool you; if you drink one 30 minutes before departure (and make it to the plane), you'll open your eyes just as the plane touches down :)
Is it the airlines problem that people with problems book long haul flights?
But still 20 hours ain't really that much, not even a full day.