6 ms·

Supersonic flights need to make a big comeback—this is just stupid.

by soheil 4y ago

philjohn 4y ago
The faster you go, the more fuel you need. You'd have to have multiple refuelling stops to go the same distance.
- cjbgkagh 4y ago
  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.
  - powderpig 4y ago
    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.
    - stametseater 4y ago
      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.
      - zbrozek 4y ago
        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?
        stametseater 4y ago
        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. Like this image depicts: https://en.wikipedia.org/wiki/Qian_Xuesen#/media/File:Tsien_Hsue-shen.jpg 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.)
        zbrozek 4y ago
        Shame; those dollars aren't going to improve my lifestyle the way that faster passenger flight would.
  - V_Terranova_Jr 4y ago
    > 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.
- PaulHoule 4y ago
  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.
  - bobthepanda 4y ago
    You still burn more energy. Even the new supersonic plane in development, Boom, has a promised range that requires a a stop for transpacific flights.
  - V_Terranova_Jr 4y ago
    > 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 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 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 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.
PaulHoule 4y ago
It's a toughie. 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 https://en.wikipedia.org/wiki/Boeing_2707 and failed but the Europeans developed a slower airliner https://en.wikipedia.org/wiki/Concorde 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-plane/ https://venturebeat.com/offbeat/nasa-sideways-supersonic-pla... to solve the takeoff problem.
- fractallyte 4y ago
  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. https://theaviationgeekclub.com/heres-why-the-sr-71-blackbird-airframe-was-designed-to-leak-fuel/ https://theaviationgeekclub.com/heres-why-the-sr-71-blackbir...
- rsync 4y ago
  "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 ? I think this only exists on aircraft carriers ?
stametseater 4y ago
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.
dehrmann 4y ago
At least for trans-atlantic flights, passengers would rather have business class than supersonic.

Supersonic flights need to make a big comeback—this is just stupid.

by soheil 4y ago

Supersonic flights need to make a big comeback—this is just stupid.

philjohn 4y ago

The faster you go, the more fuel you need. You'd have to have multiple refuelling stops to go the same distance.

cjbgkagh 4y ago
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.
- powderpig 4y ago
  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.
  - stametseater 4y ago
    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.
    - zbrozek 4y ago
      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?
      - stametseater 4y ago
        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. Like this image depicts: https://en.wikipedia.org/wiki/Qian_Xuesen#/media/File:Tsien_Hsue-shen.jpg 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.)
        zbrozek 4y ago
        Shame; those dollars aren't going to improve my lifestyle the way that faster passenger flight would.
- V_Terranova_Jr 4y ago
  > 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.
PaulHoule 4y ago
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.
- bobthepanda 4y ago
  You still burn more energy. Even the new supersonic plane in development, Boom, has a promised range that requires a a stop for transpacific flights.
- V_Terranova_Jr 4y ago
  > 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 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 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 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.

PaulHoule 4y ago

It's a toughie. 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 https://en.wikipedia.org/wiki/Boeing_2707 and failed but the Europeans developed a slower airliner https://en.wikipedia.org/wiki/Concorde 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-plane/ https://venturebeat.com/offbeat/nasa-sideways-supersonic-pla... to solve the takeoff problem.

fractallyte 4y ago
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. https://theaviationgeekclub.com/heres-why-the-sr-71-blackbird-airframe-was-designed-to-leak-fuel/ https://theaviationgeekclub.com/heres-why-the-sr-71-blackbir...
rsync 4y ago
"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 ? I think this only exists on aircraft carriers ?

stametseater 4y ago

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.

dehrmann 4y ago

At least for trans-atlantic flights, passengers would rather have business class than supersonic.