The challenges of building a hypersonic airliner(bbc.com)
bbc.com
The challenges of building a hypersonic airliner
http://www.bbc.com/future/story/20150914-the-challenges-of-building-a-hypersonic-airliner
10 comments
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.
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.
This article is somewhere between "needs significant copyediting" and "probably generated by a bot." It's almost unreadable.
> (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.
I would agree with your bot assessment.
I'm going with drunk/nonexistent copyeditor, but the Beeb did publish this recently: http://www.bbc.co.uk/news/technology-34204052
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.
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.
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.
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.
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.
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.
"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)
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)
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=...
[1] https://news.google.com/newspapers?nid=1301&dat=19850215&id=...
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...
On the grounds of comfort I'd have preferred the even longer journey in the 747...
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.
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.
Short legs.
In-flight refueling is a solved problem for military aircraft. It has never worked out for commercial airlines, though.
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
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/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.
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.
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
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
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.
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.
Even with a reserve of goodwill for the project, reasonable people might choose not to take too much notice until further results are demonstrated.
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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.
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.
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")
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")
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.
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.
The biggest challenge will the same thing that killed Concorde: finding customers to pay super prices for super speed.
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.
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.
Just a small addendum: the Sears-Haack body is the shape with the least amount of wave drag under supersonic regime, but its derivation (using the Prandtl-Glauert equation) is not valid for transonic flow, where the best approach so far seems to be maintaining the cross sectional area constant.
So if we optimize for supersonic flight it won't be so good for transonic and vice-versa... I agree with you in that probably there's no way to passively eliminate sonic booms, maybe some kind of "active" solutions, but the weight problem strikes again.
Also, I don't know if a rocket can be made without boom, as the transition in the nozzle is abrupt. Maybe it's time to review those aerospikes!
So if we optimize for supersonic flight it won't be so good for transonic and vice-versa... I agree with you in that probably there's no way to passively eliminate sonic booms, maybe some kind of "active" solutions, but the weight problem strikes again.
Also, I don't know if a rocket can be made without boom, as the transition in the nozzle is abrupt. Maybe it's time to review those aerospikes!
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.
That's very interesting! Got any paper? =)
So can't you either: Go really high (square of the distance and so on). Or: Create a shape that pushes the energy of the sonic boom out to each side rather than in a circle equal in all directions?
(I'm a computer programmer, not an aero engineer, so probably both these solutions are naive)
(I'm a computer programmer, not an aero engineer, so probably both these solutions are naive)
What if the body deforms, with wings for take off and landing, and a more ballistic shape during cruise.
I never understood why this was an issue for crossing oceans from coastal airports. Is it a huge hassle to slow to 600kt as they get close to land?
Also, at what altitudes does a boom become irrelevant? This thing will be very high so cross-continental might not be an issue either.
Also, at what altitudes does a boom become irrelevant? This thing will be very high so cross-continental might not be an issue either.
Most popular air corridors aren't over oceans. There's a reason that the only route the Concorde regularly ran was from JFK to London or Paris. Anything in South-East Asia is pretty close to land. The great-circle distance means that the shortest path runs over Canada or Greenland for many routes, and so on. And in the abstract it's more desirable to be over land because you have a place to ditch if something goes wrong.
Typical pattern traffic is much slower than 600kt. It's a hazard to have aircraft at 600kt zooming around 747s approaching at 200kt and so on. You can come up with protocols to minimize the risks (eg running patterns at different flight levels and on different runways) but there's only so far you can take it, and there's still an increase in risk, particularly in emergency situations.
When trans-sonic aircraft are operating at low speeds they're operating inefficiently. The longer and slower you're running them, the higher the fuel burn. That translates into higher operating cost and longer flight times. In an ideal world you would want them supersonic as soon as they can possibly get to cruising speed.
You need to be pretty high before supersonic booms stop being a problem. The Concorde could do up to 60k altitude and was still a nuisance. So maybe 75k or 100k feet? Even that might not be enough - booms can travel as far as 100 miles and the difference in air density isn't significant enough to fully dampen this. You might be able to get away with flying lower with an aircraft that was designed to reduce booming.
Typical pattern traffic is much slower than 600kt. It's a hazard to have aircraft at 600kt zooming around 747s approaching at 200kt and so on. You can come up with protocols to minimize the risks (eg running patterns at different flight levels and on different runways) but there's only so far you can take it, and there's still an increase in risk, particularly in emergency situations.
When trans-sonic aircraft are operating at low speeds they're operating inefficiently. The longer and slower you're running them, the higher the fuel burn. That translates into higher operating cost and longer flight times. In an ideal world you would want them supersonic as soon as they can possibly get to cruising speed.
You need to be pretty high before supersonic booms stop being a problem. The Concorde could do up to 60k altitude and was still a nuisance. So maybe 75k or 100k feet? Even that might not be enough - booms can travel as far as 100 miles and the difference in air density isn't significant enough to fully dampen this. You might be able to get away with flying lower with an aircraft that was designed to reduce booming.
>You need to be pretty high before supersonic booms stop being a problem.
what is the problem with sonic boom? i grew up on navy base in pretty militarized region and we had fighters frequently producing the booms (USSR, first half of 198x). It was fun, at least for us - for children :)
what is the problem with sonic boom? i grew up on navy base in pretty militarized region and we had fighters frequently producing the booms (USSR, first half of 198x). It was fun, at least for us - for children :)
Yet interestingly you can buy a Ferrari which goes more or less 2x as fast as, say, a VW Golf GTI and costs 10x the price, and there is burgeoning demand for the former. So if those economics apply in the air as well (speed = luxury / exclusivity), we should be able to sell cross-atlantic tickets for somewhere between 10 and 20x the price of a midrange air ticket which I would suggest is premium economy. So we're talking in the 10-20k USD range per seat.
My recollection is that noise regulations and landing rights to landlocked cities in the US killed Concorde. Not seat prices.
My recollection is that noise regulations and landing rights to landlocked cities in the US killed Concorde. Not seat prices.
and the Ferrari doesn't even go 2x as fast in practice, because roads
OTOH a Ferrari is a conspicuous sign of wealth and bad taste... the hypersonic flight, while significantly time-saving and maybe good for a couple of selfies on instagram, probably doesn't function so well in that regard
OTOH a Ferrari is a conspicuous sign of wealth and bad taste... the hypersonic flight, while significantly time-saving and maybe good for a couple of selfies on instagram, probably doesn't function so well in that regard
I was working at a bank in the late 90s where for a year all VPs (there were 4000 of them) were allowed to upgrade business class automatically to Concorde if seats were available. Most of them didn't shut up about this, constantly telling people what it was like. It was definitely right up there with neon-lit conspicuous consumption. I think a Ferrari is maybe even marginally less irritating than that.
My WAG is that won't be a huge issue, given airlines seem to have little difficulty filling existing first class and other premium tiers - but if anyone knows of actual figures, I'd be grateful. The payoff would be the substantially reduced flight time - for some business flyers, that's worth a great deal.
Bear in mind, with Concorde, that at least part of its downfall lay in the sharp rise in fuel prices in the early 1970s. Had that steep increase not taken place, but something more gradual, its commercial fate could have been quite different, even if it was never going to be any mass carrier.
Bear in mind, with Concorde, that at least part of its downfall lay in the sharp rise in fuel prices in the early 1970s. Had that steep increase not taken place, but something more gradual, its commercial fate could have been quite different, even if it was never going to be any mass carrier.
The problem isn't finding people to buy tickets. The problem is finding enough people that want super-expensive transport to repay the costs of an unusually complex airframe and engine development program with virtually no commonality with anything that's been built before. You haven't got an economy class when the premium seats aren't selling with these either, unlike every other airline operation that's ever run a profit, and you've got the risk that if one of these fails due to unanticipated technical issues, the entire programme probably gets junked. Even the time savings don't look that impressive if there's only 1 flight per day, and you can work pretty well in first class on an internet and voice connected modern jumbo.
So far the efforts seem to be mostly government subsidised, which mitigates the commercial viability issues a little. I did a back of an envelope calculation once that suggested the UK government underwrote Concorde's development to the tune of $2000 per passenger per flight in today's dollars, and that was an aircraft with a relatively high degree of overlap with existing technology
So far the efforts seem to be mostly government subsidised, which mitigates the commercial viability issues a little. I did a back of an envelope calculation once that suggested the UK government underwrote Concorde's development to the tune of $2000 per passenger per flight in today's dollars, and that was an aircraft with a relatively high degree of overlap with existing technology
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.
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.
Not sure which, or what particles there would be more of at 33km than 25km, but that's my immediate guess.
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)
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)
If the engine has no moving parts, how do you get a ramjet off the ground?
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%.
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.