7 ms·

The challenges of building a hypersonic airliner

26 points by williamhpark 11y ago

podgib 11y ago
"This thoroughbred airliner could fly from London to Sydney in 17 hours, three minutes and 45 seconds; compared to around 22 hours on a Boeing 747." This sounds wrong - the concorde's cruising speed was more than double that of a 747. Unless they're taking the refueling time into account (Concorde would need more refueling stops)
- Mtinie 11y ago
  From what I've been able to find the route was a one-off chartered flight in February, 1985[1]. There were a few delays and because they were attempting for a world-record time, a bit longer because certain conditions had to be met. [1] https://news.google.com/newspapers?nid=1301&dat=19850215&id=N8BWAAAAIBAJ&sjid=PegDAAAAIBAJ&pg=2081,21154&hl=en https://news.google.com/newspapers?nid=1301&dat=19850215&id=...
- notahacker 11y ago
  That's apparently the record time it achieved, as a charter flight. I'm sure there were multiple stopovers built in, and another major factor is likely to have been speed restrictions when flying overland. On the grounds of comfort I'd have preferred the even longer journey in the 747...
  - scrumper 11y ago
    Yes that would have been a fairly miserable trip. Concorde was pretty noisy, cramped and, near the end of the flight as the fuel (which was also a coolant) got used up, really quite hot. I did once fly on her from London to New York and it was a pretty amazing trip, but for any flight much longer than that I'd rather take first class on a 747 any day.
- bengali3 11y ago
  Also there were over land speed limits applied. Apparently while at BOS you could hear the boom as the JFK-LHR flights accellerated once far enough off the coast
  - vegabook 11y ago
    A far better measure is the London-NY time record comparison. 777-200 did it in 5.27 hours on Jan 15 (http://www.telegraph.co.uk/news/worldnews/northamerica/usa/11337617/Jet-stream-blasts-BA-plane-across-Atlantic-in-record-time.html http://www.telegraph.co.uk/news/worldnews/northamerica/usa/1...). Concorde record was 2.88 hours (2h 53 minutes). Ratio = 1.83:1. Much higher than the confusing Sydney comparison (1.25:1) with its stopovers.
- cstross 11y ago
  Concorde had to stop for ground refuelling something like 4 times on the London-Sydney trip. Each time it took about an hour and a half to come down from cruising altitude and land, slurp up a hundred tons of jet fuel, and take off again. Short legs.
  - logfromblammo 11y ago
    In-flight refueling is a solved problem for military aircraft. It has never worked out for commercial airlines, though.
gopalv 11y ago
"the heat that accumulated at Mach 8 was up to 30% less than at Mach 5." while the original paper says "Actually the thermal flux during Mach 8 flight is shown to be only 25 to 35% higher than at Mach 5. On top of this, the reduced flight times at Mach 8 yields a 20 to 25% reduction of the overall integrated heat load to the fuselage with respect to the Mach 5 cruise." The combined effect seems to be that the shorter the flight (& faster), the lower the impact of the heating for people inside.
- Gravityloss 11y ago
  Active cooling: If you put the extra heat into fuel, you have a higher fuel flow per second at the faster speed so you can indeed cope with the higher heat flux and enjoy the lower total heat quantity. Passive cooling: If you have to radiate the heat away , then the surfaces will reach a steady state relatively quickly and you have to deal with the flux. If you burn up in two minutes it doesn't help you that the flight would only last two hours. You can't carry heavy heat sinks in an aircraft.
matthewmcg 11y ago
This article is somewhere between "needs significant copyediting" and "probably generated by a bot." It's almost unreadable.
- bengali3 11y ago
  > (caption) The Soviet Tu-144 was the only only airliner to take passengers faster than the speed of sound I would agree with your bot assessment.
  - notahacker 11y ago
    I'm going with drunk/nonexistent copyeditor, but the Beeb did publish this recently: http://www.bbc.co.uk/news/technology-34204052 http://www.bbc.co.uk/news/technology-34204052
euroclydon 11y ago
If the engine has no moving parts, how do you get a ramjet off the ground?
- paulmd 11y ago
  It needs to be assisted up to something like Mach 0.5 by a conventional engine or a first-stage.
- aidenn0 11y ago
  Turbofan or rocket.
imglorp 11y ago
The biggest challenge will the same thing that killed Concorde: finding customers to pay super prices for super speed.
- paulmd 11y ago
  Sonic booms are a not-insignificant problem as well. We've been pouring money and research into it for decades and we have barely made a dent in it. The only known shape which produces no sonic boom (Busemann's Biplane) also produces no lift. There is a known shape called the Sears-Haack body which produces very little turbulence - basically it's like a very long pointed football. The best we have been able to do is make airplanes resemble that shape by having short stubby wings at the widest portion of the airflow body, with an elongated snout and tail. It does reduce turbulence to a degree, but again you are hurting your lift. I think this may actually be an insoluble problem. You need to disturb the air to produce lift, i.e. create a low-pressure zone over the wing, and a high-pressure zone under the wing. My fear is that this is inextricably linked to sonic booms, as we just seem to be exploring various locations within a space defining the tradeoffs between lift and sonic booms. We may be able to do it if we get the sonic boom low enough, but this gets back to the cost tradeoff. A rocket is certainly one possible solution within this space - a no-lift body that follows a ballistic trajectory could probably be constructed not to produce a sonic boom. However any solution on this end runs right back into the cost problem that you noted. Rockets need a lot more fuel and maintenance than a fixed-wing craft, and they're a lot less safe.
  - nether 11y ago
    Reducing the boom is achieved by damping the pressure N-wave from the oblique shocks near the aircraft forebody. This is done in various ways but at this time we're exploring blunting the nose to increase the local air temperature which increases the local acoustic velocity and reduces the pressure jump across the shock, weakening (quieting) it.
    - JorgeGT 11y ago
      That's very interesting! Got any paper? =)
phkahler 11y ago
How does water vapor last longer at 25km than at 33km? From 33km it has to pass through the lower altitude which would mean more time than vapor that started at 25.
- paulmd 11y ago
  It probably precipitates more rapidly due to temperature or having more nuclei to form droplets around. Once it's precipitated, it's no longer vapor, so it doesn't spend any time at 25km. Not sure which, or what particles there would be more of at 33km than 25km, but that's my immediate guess.
- Someone 11y ago
  1. It may have significant vertical speed by the time it hits 25 km. 2. It may be of a different constitution by the time it hits 25 km (larger droplets drop faster; extreme example: hail), giving it a higher terminal velocity. (I don't know whether any of these is true)
porsupah 11y ago
I admit, I was a little disappointed to find no mention of Skylon, even if it's at an earlier stage of development than some of these other contenders. The SABRE engine appears to be coming along well, with one of the largest challenges - cooling the incoming air extremely rapidly - seemingly overcome. http://www.reactionengines.co.uk/sabre_howworks.html http://www.reactionengines.co.uk/sabre_howworks.html
- rst 11y ago
  Lapcat is a project from the same company that's doing Skylon (Reaction Engines, Ltd.); it's a different application of similar propulsion technology, with an airframe redesigned to suit.
- rm445 11y ago
  That's a fascinating project and it would be wonderful if it succeeds... but it has been rumbling on for over 25 years. Even with a reserve of goodwill for the project, reasonable people might choose not to take too much notice until further results are demonstrated.
- deleted 11y ago
  [deleted]
cstross 11y ago
Last time I flew trans-Atlantic -- last month -- in-flight wifi with mid-ocean coverage was available for $30. And we've got Facebook, SpaceX, et al promising us all clusters of satellites delivering broadband everywhere on the planet within 5-10 years. As the energy cost of high speed travel goes up with the square of the velocity, it'd be a whole lot cheaper to stick to subsonic travel in business class -- lie-flat beds, in-flight showers, and broadband. How many people are willing to pay $10,000+ to save 10-15 hours on the flight time from LHR-SYD or LAX-Tokyo? Especially when the accommodation during hypersonic flight is going to be cramped and spartan due to weight constraints (and it's still going to involve security theater at the gate and waiting hours for a scheduled departure time to roll round)? I can believe in Aerion's supersonic Mach 1.5 bizjet -- the core market is CEOs wanting to bounce over to the opposite coast of the USA and back for a meeting within the same working day -- but I just don't believe there's going to be a mass market for hypersonic antipodeal travel on a commercial scheduled service.
- Retric 11y ago
  Energy costs don't necessarily increase as the square of velocity, at higher speeds you can travel though less dense atmosphere which dramatically reduces drag. Another major issue is afterburners are not efficient and have been used for a wide range of high Mach aircraft. On a positive note, a faster aircraft can do more trips per day which reduces depreciation and crew costs.
- ant6n 11y ago
  Additionally, they should consider that the easiest way to reduce overall travel time of a journey is to make the slowest sections faster, not the fastest sections.
- rconti 11y ago
  I like to bitch about this every chance I get, but I just don't understand why nobody puts money into making travel pleasant. I'm not talking about a few inches more legroom, I'm talking about my own armrest (and, okay, maybe a few inches more legroom). I flew first class on a Virgin American domestic leg lately, and the legroom was absurd-- I couldn't even reach the seat in front of my with my legs outstretched. I don't need that much room, and in fact it makes it difficult to reach my underseat bag. (although it means I can escape to the aisle without disturbing my seatmate). If a narrowbody jet went from a 3+3 coach config to a 2+2 that's 50% more cost per passenger. Throw in a couple more inches of legroom. Call it 100% more cost to be generous. How are there not plenty of folks like myself who would be happy to pay it, but can't even fathom the idea of paying 5x as much for today's business class? Yes, I realize today's first and business class fares subsidize coach to some extent, but .. I just don't understand how a premium service can't catch on in this day and age. Talk about customer loyalty.
douche 11y ago
Why not go the other direction? Build a large, slow moving blimp/dirigible, and offer overnight service with relatively comfortable accommodations? If I could take off in Boston or New York in the evening, sleep through the night, and wake up in London or Paris or Berlin, I think that would be an improvement over the transatlantic flights that I have taken.
- mikeash 11y ago
  It isn't going to be overnight. It's going to take days. If "overnight" is 12 hours, then you're only moving about half as fast as an airliner moves. That makes for something like a 300MPH cruising speed, which would be challenging to achieve in an airship. The Hindenburg (I know, great example) could cruise at about 76MPH. NYC-London is about 3500 miles, so that's about two days, assuming the wind neither helps nor hinders.
- rconti 11y ago
  With a 7.5h flight time from JFK to LHR, plus a 5 hour time difference, that's a 12.5h of effective travel time. So, you already DO take off at, say, 19:30 from JFK and land at 08:00 in Heathrow. From SFO this is a 19.5h journey when you factor in the time difference, which means to "wake up" at 08:00 at LHR, you leave at 12:30 from SFO. In both cases, making the journey longer isn't going to make it particularly more pleasant, even if the dirigible was more comfortable. And anyway, how fast do you envision this craft flying? A 200mph dirigible sounds like a feat, and it still would take AGES (with time difference, basically 24h from JFK to LHR). (yes, I'm aware we don't typically factor time change into these travel time calculations, but I'm doing it for the sake of "go to sleep in X and arrive rested and refreshed in Y")
Nemant 11y ago
Want shorter travel time? No need for faster planes, just get rid of the useless TSA and create efficient check-in systems. Most travel time would decrease by about 15%-25%.

26 points by williamhpark 11y ago

"This thoroughbred airliner could fly from London to Sydney in 17 hours, three minutes and 45 seconds; compared to around 22 hours on a Boeing 747." This sounds wrong - the concorde's cruising speed was more than double that of a 747. Unless they're taking the refueling time into account (Concorde would need more refueling stops)

Mtinie 11y ago
From what I've been able to find the route was a one-off chartered flight in February, 1985[1]. There were a few delays and because they were attempting for a world-record time, a bit longer because certain conditions had to be met. [1] https://news.google.com/newspapers?nid=1301&dat=19850215&id=N8BWAAAAIBAJ&sjid=PegDAAAAIBAJ&pg=2081,21154&hl=en https://news.google.com/newspapers?nid=1301&dat=19850215&id=...
notahacker 11y ago
That's apparently the record time it achieved, as a charter flight. I'm sure there were multiple stopovers built in, and another major factor is likely to have been speed restrictions when flying overland. On the grounds of comfort I'd have preferred the even longer journey in the 747...
- scrumper 11y ago
  Yes that would have been a fairly miserable trip. Concorde was pretty noisy, cramped and, near the end of the flight as the fuel (which was also a coolant) got used up, really quite hot. I did once fly on her from London to New York and it was a pretty amazing trip, but for any flight much longer than that I'd rather take first class on a 747 any day.
bengali3 11y ago
Also there were over land speed limits applied. Apparently while at BOS you could hear the boom as the JFK-LHR flights accellerated once far enough off the coast
- vegabook 11y ago
  A far better measure is the London-NY time record comparison. 777-200 did it in 5.27 hours on Jan 15 (http://www.telegraph.co.uk/news/worldnews/northamerica/usa/11337617/Jet-stream-blasts-BA-plane-across-Atlantic-in-record-time.html http://www.telegraph.co.uk/news/worldnews/northamerica/usa/1...). Concorde record was 2.88 hours (2h 53 minutes). Ratio = 1.83:1. Much higher than the confusing Sydney comparison (1.25:1) with its stopovers.
cstross 11y ago
Concorde had to stop for ground refuelling something like 4 times on the London-Sydney trip. Each time it took about an hour and a half to come down from cruising altitude and land, slurp up a hundred tons of jet fuel, and take off again. Short legs.
- logfromblammo 11y ago
  In-flight refueling is a solved problem for military aircraft. It has never worked out for commercial airlines, though.

gopalv 11y ago

"the heat that accumulated at Mach 8 was up to 30% less than at Mach 5." while the original paper says "Actually the thermal flux during Mach 8 flight is shown to be only 25 to 35% higher than at Mach 5. On top of this, the reduced flight times at Mach 8 yields a 20 to 25% reduction of the overall integrated heat load to the fuselage with respect to the Mach 5 cruise." The combined effect seems to be that the shorter the flight (& faster), the lower the impact of the heating for people inside.

Gravityloss 11y ago
Active cooling: If you put the extra heat into fuel, you have a higher fuel flow per second at the faster speed so you can indeed cope with the higher heat flux and enjoy the lower total heat quantity. Passive cooling: If you have to radiate the heat away , then the surfaces will reach a steady state relatively quickly and you have to deal with the flux. If you burn up in two minutes it doesn't help you that the flight would only last two hours. You can't carry heavy heat sinks in an aircraft.

matthewmcg 11y ago

This article is somewhere between "needs significant copyediting" and "probably generated by a bot." It's almost unreadable.

bengali3 11y ago
> (caption) The Soviet Tu-144 was the only only airliner to take passengers faster than the speed of sound I would agree with your bot assessment.
- notahacker 11y ago
  I'm going with drunk/nonexistent copyeditor, but the Beeb did publish this recently: http://www.bbc.co.uk/news/technology-34204052 http://www.bbc.co.uk/news/technology-34204052

euroclydon 11y ago

If the engine has no moving parts, how do you get a ramjet off the ground?

paulmd 11y ago
It needs to be assisted up to something like Mach 0.5 by a conventional engine or a first-stage.
aidenn0 11y ago
Turbofan or rocket.

imglorp 11y ago

The biggest challenge will the same thing that killed Concorde: finding customers to pay super prices for super speed.

paulmd 11y ago
Sonic booms are a not-insignificant problem as well. We've been pouring money and research into it for decades and we have barely made a dent in it. The only known shape which produces no sonic boom (Busemann's Biplane) also produces no lift. There is a known shape called the Sears-Haack body which produces very little turbulence - basically it's like a very long pointed football. The best we have been able to do is make airplanes resemble that shape by having short stubby wings at the widest portion of the airflow body, with an elongated snout and tail. It does reduce turbulence to a degree, but again you are hurting your lift. I think this may actually be an insoluble problem. You need to disturb the air to produce lift, i.e. create a low-pressure zone over the wing, and a high-pressure zone under the wing. My fear is that this is inextricably linked to sonic booms, as we just seem to be exploring various locations within a space defining the tradeoffs between lift and sonic booms. We may be able to do it if we get the sonic boom low enough, but this gets back to the cost tradeoff. A rocket is certainly one possible solution within this space - a no-lift body that follows a ballistic trajectory could probably be constructed not to produce a sonic boom. However any solution on this end runs right back into the cost problem that you noted. Rockets need a lot more fuel and maintenance than a fixed-wing craft, and they're a lot less safe.
- nether 11y ago
  Reducing the boom is achieved by damping the pressure N-wave from the oblique shocks near the aircraft forebody. This is done in various ways but at this time we're exploring blunting the nose to increase the local air temperature which increases the local acoustic velocity and reduces the pressure jump across the shock, weakening (quieting) it.
  - JorgeGT 11y ago
    That's very interesting! Got any paper? =)

phkahler 11y ago

How does water vapor last longer at 25km than at 33km? From 33km it has to pass through the lower altitude which would mean more time than vapor that started at 25.

paulmd 11y ago
It probably precipitates more rapidly due to temperature or having more nuclei to form droplets around. Once it's precipitated, it's no longer vapor, so it doesn't spend any time at 25km. Not sure which, or what particles there would be more of at 33km than 25km, but that's my immediate guess.
Someone 11y ago
1. It may have significant vertical speed by the time it hits 25 km. 2. It may be of a different constitution by the time it hits 25 km (larger droplets drop faster; extreme example: hail), giving it a higher terminal velocity. (I don't know whether any of these is true)

porsupah 11y ago

I admit, I was a little disappointed to find no mention of Skylon, even if it's at an earlier stage of development than some of these other contenders. The SABRE engine appears to be coming along well, with one of the largest challenges - cooling the incoming air extremely rapidly - seemingly overcome. http://www.reactionengines.co.uk/sabre_howworks.html http://www.reactionengines.co.uk/sabre_howworks.html

rst 11y ago
Lapcat is a project from the same company that's doing Skylon (Reaction Engines, Ltd.); it's a different application of similar propulsion technology, with an airframe redesigned to suit.
rm445 11y ago
That's a fascinating project and it would be wonderful if it succeeds... but it has been rumbling on for over 25 years. Even with a reserve of goodwill for the project, reasonable people might choose not to take too much notice until further results are demonstrated.
deleted 11y ago
[deleted]

cstross 11y ago

Last time I flew trans-Atlantic -- last month -- in-flight wifi with mid-ocean coverage was available for $30. And we've got Facebook, SpaceX, et al promising us all clusters of satellites delivering broadband everywhere on the planet within 5-10 years. As the energy cost of high speed travel goes up with the square of the velocity, it'd be a whole lot cheaper to stick to subsonic travel in business class -- lie-flat beds, in-flight showers, and broadband. How many people are willing to pay $10,000+ to save 10-15 hours on the flight time from LHR-SYD or LAX-Tokyo? Especially when the accommodation during hypersonic flight is going to be cramped and spartan due to weight constraints (and it's still going to involve security theater at the gate and waiting hours for a scheduled departure time to roll round)? I can believe in Aerion's supersonic Mach 1.5 bizjet -- the core market is CEOs wanting to bounce over to the opposite coast of the USA and back for a meeting within the same working day -- but I just don't believe there's going to be a mass market for hypersonic antipodeal travel on a commercial scheduled service.

Retric 11y ago
Energy costs don't necessarily increase as the square of velocity, at higher speeds you can travel though less dense atmosphere which dramatically reduces drag. Another major issue is afterburners are not efficient and have been used for a wide range of high Mach aircraft. On a positive note, a faster aircraft can do more trips per day which reduces depreciation and crew costs.
ant6n 11y ago
Additionally, they should consider that the easiest way to reduce overall travel time of a journey is to make the slowest sections faster, not the fastest sections.
rconti 11y ago
I like to bitch about this every chance I get, but I just don't understand why nobody puts money into making travel pleasant. I'm not talking about a few inches more legroom, I'm talking about my own armrest (and, okay, maybe a few inches more legroom). I flew first class on a Virgin American domestic leg lately, and the legroom was absurd-- I couldn't even reach the seat in front of my with my legs outstretched. I don't need that much room, and in fact it makes it difficult to reach my underseat bag. (although it means I can escape to the aisle without disturbing my seatmate). If a narrowbody jet went from a 3+3 coach config to a 2+2 that's 50% more cost per passenger. Throw in a couple more inches of legroom. Call it 100% more cost to be generous. How are there not plenty of folks like myself who would be happy to pay it, but can't even fathom the idea of paying 5x as much for today's business class? Yes, I realize today's first and business class fares subsidize coach to some extent, but .. I just don't understand how a premium service can't catch on in this day and age. Talk about customer loyalty.

douche 11y ago

Why not go the other direction? Build a large, slow moving blimp/dirigible, and offer overnight service with relatively comfortable accommodations? If I could take off in Boston or New York in the evening, sleep through the night, and wake up in London or Paris or Berlin, I think that would be an improvement over the transatlantic flights that I have taken.

mikeash 11y ago
It isn't going to be overnight. It's going to take days. If "overnight" is 12 hours, then you're only moving about half as fast as an airliner moves. That makes for something like a 300MPH cruising speed, which would be challenging to achieve in an airship. The Hindenburg (I know, great example) could cruise at about 76MPH. NYC-London is about 3500 miles, so that's about two days, assuming the wind neither helps nor hinders.
rconti 11y ago
With a 7.5h flight time from JFK to LHR, plus a 5 hour time difference, that's a 12.5h of effective travel time. So, you already DO take off at, say, 19:30 from JFK and land at 08:00 in Heathrow. From SFO this is a 19.5h journey when you factor in the time difference, which means to "wake up" at 08:00 at LHR, you leave at 12:30 from SFO. In both cases, making the journey longer isn't going to make it particularly more pleasant, even if the dirigible was more comfortable. And anyway, how fast do you envision this craft flying? A 200mph dirigible sounds like a feat, and it still would take AGES (with time difference, basically 24h from JFK to LHR). (yes, I'm aware we don't typically factor time change into these travel time calculations, but I'm doing it for the sake of "go to sleep in X and arrive rested and refreshed in Y")

Nemant 11y ago

Want shorter travel time? No need for faster planes, just get rid of the useless TSA and create efficient check-in systems. Most travel time would decrease by about 15%-25%.