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Why We're Not Going To See Sub-orbital Airliners
glowend writes: Sci-fi author Charlie Stross has an article about sub-orbital flight, and why we'll never see it as a common mode of transportation. Quoting: "Yes, we can save some fuel by travelling above the atmosphere and cutting air resistance, but it's not a free lunch: you expend energy getting up to altitude and speed, and the fuel burn for going faster rises nonlinearly with speed. Concorde, flying trans-Atlantic at Mach 2.0, burned about the same amount of fuel as a Boeing 747 of similar vintage flying trans-Atlantic at Mach 0.85 ... while carrying less than a quarter as many passengers. Rockets aren't a magic technology. Neither are hybrid hypersonic air-breathing gadgets like Reaction Engines' Sabre engine. It's going to be a wee bit expensive."
Stross also makes a more general proposition that's particularly interesting to me: "One of the failure modes of extrapolative SF is to assume that just because something is technologically feasible, it will happen. ... Someone has to want it enough to pay for it—and it will be competing with other, possibly more attractive options."
Stross also makes a more general proposition that's particularly interesting to me: "One of the failure modes of extrapolative SF is to assume that just because something is technologically feasible, it will happen. ... Someone has to want it enough to pay for it—and it will be competing with other, possibly more attractive options."
So, you're not going to see it, because it doesn't save money. Except, it has the potential to be many times faster. Which is a reason to use it that isn't "it costs less." So the argument can't hope to support its thesis. If it happens or not is not based on just if "because we can." It is going to happen or not based on the actual advantages of being faster, their value, and the final cost.
We can certainly say, based on our experience with Concord, that if it is fast enough and safe enough the rich will use it, and if it as safety issues, they will abandon it quickly.
I think the thing being missed here is that people are in a hurry. If I can fly a 747 from Seattle to Japan and the flight takes 14 hours, I would pay more to be able to do it in 7. That's an easy choice. Time spent in the air is generally wasted time. Turn trans-Pacific/Atlantic into a weekend trip instead of the current 3 days of travel time and there's a market for it.
The futuristic prediction that it would be economical to take a sub-orbital flight from NY to LA is probably not going to happen, but for trans oceanic and/or China/Japan to Europe. Definitely a market there.
"Freedom in the USA is not the ability to do what you want. It is the ability to stop others from doing what THEY want"
Last time I checked all flight within the atmosphere was "sub-orbital".
Yup, this raise one of my big complaints about some SciFi stories: lack of economic plausibility.
Science Fiction is great for looking at how we might deal with various potential technologies. Readers are perfectly happy to suspend disbelief and accept whatever technology is proposed. What readers aren't willing to do is suspend disbelief and accept people behaving implausibly.
To write good science fiction, you need to accurately portray people. You can make up the technology, but you have to get humanity right. And that means you have to get the economics right.
This is exactly the problem I had with reading the Hunger Games. Everything worked, except why would a society with hover cars and other advanced technology have need of the services of the districts? Surely they didn't need coal, and yet they had a whole district dedicated to mining it. The lack of economic sense pulled me out of the book. Instead of thinking about the characters, I was thinking about why the society that was described didn't make any sense.
The other problem is lift. When you get to that kind of altitude, you either need to be at orbital speeds (not going to happen) or you need an incredible wingspan relative to mass to get lift from what little atmosphere is available. A third option is some kind of thrust to directly counteract gravity, which would be horribly fuel inefficient. Regardless, you end up with an extremely specialized, hard to fly aircraft like the U2 or SR-71 Blackbird, which has severe limitations in "normal" flight characteristics just so it can fly high and fast. Plus you're not going to be able to scale those kinds of specialized designs up from transporting just one or two people to an entire load of people to achieve the passenger volume an airline requires.
Better known as 318230.
Sure it would be the fastest transPacific transport, but who can afford it.
Some of the flight is going to be in microgravity, There goes your lunch
And of course if something goes wrong, your chances of survival are zero as well.
Similar to space tourism I guess
...will basically be executives who's time is worth the price to get them to Tokyo and back for a deal. The very nature of the beast entails a small number of seats and thus a high price per seat. The cost and logistics go up by a very large amount when you increase the size of the vehicle. There are also issues with generating supersonic booms in places that are not used to it, limiting it to mostly ocean overflights or re-entering over sparsely populated areas. It won't be a mass market item, but there may be a market for it. In the mean time, up-and-down suborbital will have a larger market than point to point.
An adjunct proposition to consider is that certain technologies will never disappear, no matter how many attractive alternatives arise.
I'll offer one example right now: paper.
Discuss.
If it weren't for deadlines, nothing would be late.
There is not one executive in the world who's time is that valuable, they over value everything they do or say.
"One of the failure modes of extrapolative SF is to assume that just because something is technologically feasible, it will happen. ... Someone has to want it enough to pay for it—and it will be competing with other, possibly more attractive options."
I'm not sure what Stross is saying here. An important part of the process of developing technology is not just to ensure it can be developed, but that it can be developed at a price that most people can afford.
So when I seen advanced technology portrayed in SF being used by fairly ordinary people, I assume that the technology has been made affordable enough that paying for it is not an issue.
Deal with reality - the world as it is - rather than ideality - the world as you would like it to be.
Give me a straight tunnel between any two points and I can get you there in 42 minutes for practically no fuel cost.
Aren't *all* airliners "sub-orbital"? "of, relating to, or denoting a trajectory that does not complete a full orbit of the earth or other celestial body."
Given fast turn around reusability with rocket engine restart capabilities claimed by SpaceX the numbers work out for high end passenger fares if you go to a lower suborbital velocity and then bleed off energy while stretching distance by passively skipping off the atmosphere. By "passive" I mean no scramjet (or other propulsive kick). If you really need distance use rocket engine restart and carry extra propellant.
Seastead this.
While Heinlein's juvenile fiction was, well, juvenile, I like that it at least played with the concepts of economics.
A fine example of moving the goalposts. He starts with the thesis:
we're not going to see sub-orbital airliners
He ends with the conclusion:
Supersonic bizjets for the rich might well be viable...Virgin Galactic's sub-orbital pleasure hops are unlikely to be problematic...But point-to-point sub-orbital passenger services are, I think, going to remain a pipe dream for the foreseeable future.
Congratulations. You've just proved yourself wrong. Maybe next time start out with a more reasonable premise like "We're not going to see point-to-point sub-orbital passenger services in the forseeable future", instead of whatever sounds dramatic.
Not to mention, his primary objection seems to be screeching about 9/11 security theatre. Maybe that's a good reason why they won't be seen in the US, but the rest of the world isn't afflicted by that particular form of paranoid dementia, and we still hold out vague hopes the US will snap out of it sometime soon.
Just because you're paranoid doesn't mean there isn't an invisible demon about to eat your face
Sci-fi is usually literate in matters of science. I'm guessing that's why they call it "Sci-fi" instead of "Econo-fi"
I've noticed those deeply moved by science and technology are a *very* different crowd than those deeply moved by economics, accounting and finance. Too many sci-fi stories cop out on the explanation of how something was funded by saying something like "we've advanced FAR beyond the need for money" as if money is merely a technology with no ties to motive, ambition, wealth, effort or culture.
As a counter-point, some sci-fi authors include economic desperation as a major motivator. My favorite was Frederik Phol in "Gateway" as part of the HeeChee Saga. Many of the dystopian-future stories focus on an overly-powerful central government working in partnership with very large corporations.
I will wait till the Eschaton teleports me to my destination with a couple of cornucopia machines.
SF also extrapolated an AI singularity and it may not be so technologically feasible.
It's pointed to in the summary and was not missed - there were not enough people in a hurry to sustain Concorde flights.
An ironic thing is the 747 was opposed within Boeing in the late 1960s because it was thought that only supersonic airliners would have a place on long hauls in the 1970s - so very few were built in the first batch. As mentioned in the summary the 747 went on to render Concorde mostly irrelevant.
The problem is not time. Obviously everybody wants to save time and would be willing to pay a premium to do so, but only to an extent.
If the cost was proportional to the time of the flight, for example 2x as fast for 2x the price, people would pay that. What they won't pay is 2x speed at 100x the price.....
And as others mentioned, rich and VIP is probably not enough of a base required to keep the infrastructure these planes would require (parts manufacturers, trained pilots licensed to fly those planes, the specializations techs will need, etc etc etc)....
+ With internet it's getting harder and harder to justify flying people to places, even CEOs
Next you're going to tell us there'll be no space elevators!
Well, no space elevators with current technology. No sub-orbital flights to Tokyo with current tech.
Less than 100 years ago we weren't even flying from New York to Chicago. But somewhere between 100 years ago and now something happened.
Are we really ruling out game changing break throughs? If so, that's really sad.
I've done some research into hypersonic technology, and it's not strictly true that hypersonic flights are necessarily less efficient per passenger mile. Sure, up to this point it has been the case, but we haven't explored in detail.
The US currently has tested a hypersonic glider that goes a heck of a long way, with a surprisingly good glide ratio, above Mach 20. Apparently it was to glide for thousands of miles, while only descending maybe 20 miles, implying a tremendously high glide ratio, over 100:1. If that's true, then you could have extremely efficient flight at Mach 20.
These "waverider" planes use radically different aerodynamics, so the old rules don't apply. They're nothing like the Concorde.
I love Mondays. On a Monday, anything is possible.
The article (well worth reading this time) argues that such a target market has left the building and is already on "bizjets" to avoid the time consuming fuss of getting onto an airliner and having to stick to a schedule. It also points out that suborbital spaceports are not going to be in the middle of cities so the time to get to and from them also has to be considered. Those factors seem to reduce the small market you suggest to zero. Expensive, fixed timetables and little or no time saved compared with "bizjets" in the same or lower price range that leave when you want and land closer to where you want to be.
Sucks, but all that extra effort to go supersonic/hypersonic prices it out of most civilian situations.
You know you have quality bullshit when the first argument out of the gate is based on an fantasy security argument. If security is going to cause such major problems for a hypersonic or suborbital vehicle, then don't do that level of security. Dubya is no longer in office, we don't need to go hardcore stupid on security any more. Then the second is convenience - conveniently ignoring that greatly shortening an air flight is convenience as well. It also ignores that most of the reason the flight was "inconvenient" was done by piling on the earlier ludicrous demands for security from argument one. Don't have those demands and you don't have so much inconvenience.
That's it. At no time did he ever mention real world constraints like fuel consumption. I can see, for suborbital flights, that the fuel costs alone could be in the many thousands of dollars per person. That's kind of expensive even for a fast ride.
Right, just attach the suborbital planes in pair with a rope to some space elevator like device and have one take off as the other land. Problem solved.
Everything I write is lies, read between the lines.
Time and Price are tradeoffs. I'd certainly pay a certain amount to go faster, or to fly in better comfort, but that is highly dependent on exactly what the added cost is. My time is certainly valuable. I'll pay a few hundred bucks for a plane ticket to fly from New York to LA rather than take a multi-day bus ride, but when we're talking about flying to Tokyo, is an extra day of travel time worth a few thousand dollars? To most travellers, probably not.
Air travel used to be a luxury that only the rich enjoyed, and there the difference was vast enough to make it worthwhile. I don't know the numbers offhand, but the time difference between taking a train coast to coast and a flight in the 1930s was probably on the order of 4 to 5 to make a wild guess. Either way, it was significant enough to be desirable, and over time the price came down to where it was so much more advantageous that now air travel is the dominant mode for long distance travel. If supersonic modes of travel can reach that time to price differential, I think we might see them come into play, but certainly not at a 1 to 1. New York to Tokyo in 3-4 hours or less, instead of 16, at twice the price? New York to London in 1-2 hours? That might be a little more tempting.
but we're just not. - Charlie Stross circa 1845. Seriously the idea that by 1918 people would be using heavier than air flying vehicles to deliver mail and engage in military action by air was absurd.
And not just because one of the most advanced technologies at the time was hot air balloons. But because a working reliable internal combustion engine wasn't going to be invented for another 40 years or more, which made airplanes possible.
So it behooves people like Stross who can easily imagine superhuman AI to also understand that technology advances in ways that are entirely unpredictable so it's always a good idea to bet that current technological problems will be overcome in time.
Try reading it again (or for the first time) and you'll find the following:
I saw a Concorde at a air show. The plane was two or three hundred meters away and facing me taxiing to the runway. The noise was amazing, I could feel it as much as I heard it. When it turned to begin the roll out to take off the sound was deafening. Brown Field is a small general aviation airport and the pilot must have had to go full throttle to get up to speed. There's a mountain to the east of the runway. From The LATimes " A business jet carrying a two-person crew and eight members of country singer Reba McEntires entourage crashed into a mountain near the U.S.-Mexico border Saturday morning, killing all 10 people on board.". I worked nearby and the crash site was visible for years. RIP.
It's likely to be like this. First you have to get to New Mexico to get on the sub-orbital flight, and it only flies on Tuesdays. Not a lot of use if you are in a hurry.
I recommend reading the full article on the website, it isn't very long and I should have read it before I wrote my single point post above. The article covers many more points including those you raised above.
If you run the numbers most of the energy in current airliners is consumed in overcoming cruise drag (potential and kinetic are much smaller) - so if you can eliminate drag (sub orbital).
Back of the envelope:
Long haul subsonic flight to 35,00 ft. 20-30 minute climb , 8 hr cruise, 20 minute idle descent. Says that the kinetic and potential energy of an aircraft at cruise is approx 20mins of overcoming cruise drag. so 9 times the potential energy -> 315 000 ft. 3 times the speed = 9x kinetic energy -> mach 2.4
Still only equals 3 hrs of current cruise time. but we've saved 5hrs of cruise time because of the higher speed. So just need to worry about the weight of lugging around the oxidiser.
The word 'never' should not be used when talking about future developments. Energy will become very cheap and abundant once zero point energy can be tapped. Then it will be trivial to power sub-orbital craft, not to mention starships, etc.
All the individual sub-arguments Stross makes are strong, but that still doesn't add up to "we're never going to see sub-orbital airliners".
First of all, never is a really long time. Really, are you comfortable saying "never"? That sounds pretty foolish to me.
Second, what exactly is the problem with selling a capability to knock half or 2/3 of the time off an intercontinental flight? This isn't a low or no-value proposition. Air travel itself was founded on essentially this value proposition. Both rail and ship traffic had to retreat and adjust dramatically as a result.
Third, his only serious negative example is Concorde. We all know the story now, a technological success and a business failure. However it doesn't take a genius to reimagine the Concorde program, updated and with different business and technical parameters. Change the dynamics and you can change the story. History is full of business examples of success and failure; you don't stop just because of the Titanic, Edsel and Concorde. If you did you'd never get the modern mega cruise ships, the Honda Accord/Toyota Corolla, or the Boeing 747.
Well, maybe Stross would. Fortunately he's not in charge of the rest of us.
Private space tourism, Moon colonies, asteroid mining. Can we forget all this juvenile 1960s naive sci-fi crap already?
I'm hoping for a bungie sling with a cannon on the end, swung from the side of the space elevator. And for landing, a net attached to a pole that rotates around the space elevator. Then you can use regenerative braking and recover some electricity during the landing.
Never? really? never? and this person calls himself an SF writer?
Here are some of the things we can do to make faster speed travel more efficient:
1. Try to capture some of the potential energy stored in an airplane at 100,000 ft over the earth
2. Reduce the duration and speed of the portion of the flight that takes place at higher atmospheric densities
3. Try to capture some of the kinetic energy of flying suborbital at Mach 3 during deceleration.
Are those easy? not at all. But that is the kind of challenge that technology is very good at solving over a few hundred years.
It's pointed to in the summary and was not missed - there were not enough people in a hurry to sustain Concorde flights
Wikipedia sites other, different reasons. Specifically, the decline of the airline industry after 9/11, combined with uncertainty because of the crash, and the withdrawal of maintenance support by the manufacturer. Sir Richard Branson was trying to pay lots of good money to buy them and continue operating, but it was that last one, lack of maintenance support, that foiled him; not any speculation about how much of a hurry people were in.
Branson would be operating them today, but for the withdrawal of maintenance support and that is just a historical fact. So there was business interest, with real cash money offers, to keep it going, and there was never any failure to sell tickets that would imply lack of interest; regardless of if interest was based on being in a hurry, or just the appeal of a premium service.
Cheap and good enough beats state of the art everytime. The reason why jets replaced prop planes was not that they were merely faster its that they could fly more passengers at a lower cost per passenger mile.
Because bicycles are so much more efficient than SUVs we'll never see people riding fast from city to city in large vehicles so there will never be suburbs or a need for interstate highways... Right... Great logic.
"Pie in the sky" old boys.
Just cannot be done in today's 'world' .
The National Academy of Sciences are correct! The people to do this at all levels of society are yet to be born!
What a damning statement of the current United States of America!
USA nor Musk can Do It!
Let Musk die trying to pay the deficits of PayPal.
How far is the foreseeable future? I'm thinking not as far as people would like to think. So the answer is "perhaps".
1) Yes economics has something to do with it.. but extrapolating concord economics to a hypersonic might be stretch.. the train is cheaper than air travel.. but you don't see near as much train travel as air travel on longer routes. It depends on the economics of the system. No you won't see a hypersonic concord, but a concord can't go hypersonic anyway. When the cost per hour (time saved) exceeds cost difference of travel.. you will see a niche. That depends on the technology and the relative cost for the energy difference. If for example you have miracle fuel where energy is cheap and the mechanicals aren't too expensive, you will see it.
Or if it fills a unique niche (time delivery or areas not easily serviced by subsonic airplanes) would also push it to execution.
2) Security.. I can imagine a number of security counter arguments.. example there is no pilot so no human error, Or the defense forces have a destruct button, or that antiballistic missile technology actually works.. for one incoming craft with a transponder. I think there are ways around the security arguments. Also the sensing arguments similar.. (infrared trackers, satellite radar, transponders, etc).
3) No, hypersonic tech isn't here, so it is rather hard to say what it would look like.. what the ground time would be for air time. But I expect if they are constructing it.. and it is economic, that the concord gives the high side of maintenance time, I would expect automatic testing, adaptive structures, advanced materials and of course engine/propulsion (and or heat/aerodynamics) would be needed to push the turn around time down. Imagine no pilot, and the craft is controlled from the ground it being so smart you mostly say go from space port A to space port B, After it lands it cycles itself through a plane service/refinish line and is ready for flight very shortly.. it might be worth while, does that make it economic.. depends on all those little details on how it does it. How well do you foresee the future?
Don't really need to recover any energy. The Earth has so much it won't miss some. Although, I suppose this would reduce the heating of the atmosphere a bit...
You know, I can imagine someone saying something similar to this to the Wright brothers. Just give the scientists, engineers and time the ability to work their magic and there's every chance someone will be able to turn it into a viable business.
....We may see a return of supersonic flight within the next 15 years.
Thanks to better understanding of how sonic booms are generated from the shape of the plane and definitely way better jet engine technology, we may be able to very soon build a business jet seating 10 passengers capable of flying at Mach 1.6 at ranges up to 6,000 nautical miles with just about no sonic boom audible on the ground even when the plane is fly at Mach 1.6.
How is this possible? First, aerodynamic research using computational fluid dynamics have identified ways to minimize the pressure wave buildup that causes the sonic boom in the first place with very careful shaping of the fuselage and wings. This makes to possible to effectively eliminate the audible sonic at speeds up to Mach 1.6. Secondly, modern engine design using variable cycle engines (GE Aero Engines successfully tested the technology on a engine intended for the Advanced Technology Fighter program that resulted in the F-22A Raptor) means high-bypass turbofan fuel efficiency at subsonic speeds but can change configuration to fly at supersonic speeds with a small amount of reheat (afterburning) to keep fuel consumption and harmful exhaust missions as low as possible. Finally, by keeping the top speed to Mach 1.6, it means less structural heating from flying at supersonic speeds and less need to run a lot of reheat (afterburning) on the engines, which means lower fuel consumption and less need for expensive high-temperature rated stainless steel or titanium structural parts like those used on the Concorde.
I've read companies that sell fractional ownership of private jets such as FlexJet or NetJets would immediately buy 50 of these supersonic business jets once approved for production. The ability to fly from New York City to London in around 4 hours as opposed to the circa 7.5 hours with current jet airliners makes it very attractive to business customers, especially since many live by the motto of "time is money."
Jets supplemented prop planes, replacing them on long haul. Prop planes still fly more flights.
Isn't there much less air resistance at suborbital elevations?
Err..
First, the Concorde cruised at Mach 2.0 without reheat. On the Concorde, reheat only added some 20% (IIRC) to the thrust was used mainly to accelerate to cruise speed.
Secondly, to design a more powerful/fuel efficient engine without reheat, you need to handle higher flows, temperatures and pressure.
Reheat is a "cheap and easy" way to work around this issue, although at the expense of fuel efficiency.
That said, using more advanced materials which can handle higher temperature and pressures to build more powerful and efficient engines is the normal business in jet engines.
Using modern materials and designs, one could surely design a high/medium bypass turbofan that is quite more efficient than Concorde's turbojets.
Right. If only someone had the vision to write (Economic) Science Fiction. . . (or maybe that's Fantasy writing right there. . . )
How about Asimov? With introduction by economist Paul Krugman https://webspace.princeton.edu/users/pkrugman/FDT%20intro.pdf
Of course some people accuse Krugman of being a a Fantasy writer...
Branson wasn't trying to pay "lots of good money" for Concorde, he massively undervalued them and their support facilities because he never wanted to operate them, it was all a PR stunt against British Airways . If British Airways had sold the Concorde and the supporting infrastructure to Branson, and the type certificate had not been withdrawn by Airbus, there would have been no more than a years worth of flights by Virgin Atlantic and then they would have been retired yet again, only this time Virgin Atlantic have some nice, cheap hangar space at Heathrow and New York that they would have otherwise had to pay through the nose for.
That was what Branson ultimately wanted.
There's another problem. Turboprops are in fact more efficient for long range and are capable of only marginally slower speeds than modern turbofan aircraft but they are comparatively very noisy. As a result, they are far less comfortable to travel in and often incur additional penalties due to noise on take off.
Evacuated tubes have much better economic dynamics than sub-orbital flight. It's high-speed rail without air friction with potentially incredibly fast speeds. You could work in New York and have a lunch at midnight in Tokyo and be back to NY for dinner. It would be amazingly expensive to build, but it could be incredibly cheap to run.
set softtabstop=4 shiftwidth=4 expandtab nocp worlddomination
Never saw one go in orbit.
'Stross also makes a more general proposition that's particularly interesting to me: "One of the failure modes of extrapolative SF is to assume that just because something is technologically feasible, it will happen. ... Someone has to want it enough to pay for it—and it will be competing with other, possibly more attractive options.'
That's also notably one of the failure modes of the technology industry for the last few decades - assuming that, just because you CAN make something, people will automatically want it enough to pay for it in quantity (e.g. 3D TV, Google Glass). For my money, "wearable computing" is the latest probable example - lots of hype, little or no obvious market call.
Private flights have gotten cheaper and have the range for transpacific destinations. Time on commercial flights is wasted. Time on private flights can be used like normal work days.
Yes, THERE is THAT much difference.
Business class isn't a substitute - and with private flights, there isn't any real slowdown at the airport. I've shown up 3 minutes before a flight, parked, they held the plane though the other 10 people were onboard already, then we started taxiing about 2 min after I boarded from a private terminal. Arrival is even easier. Private terminals have customs and immigration. Basically, no hassles at all.
Plus the smaller airport is 20 min closer than the huge international airport, no parking hassles.
14 hrs to 2 hrs WOULD make a difference. 14hrs to 7hrs really isn't enough to matter - there is still time to sleep.
Oh - and much respect to Charlie, met him last June at a conference - 3 of us where chating about nonsense, then a kid came up to get an autograph from the 3rd man. I held his coffee. Then the kid as for Charlie's autograph. I didn't know who either of these people were at the time. The guy who's coffee I held was Larry Wall. ;)
Concorde's engines WERE turbofans, the most efficient jet engines of their time in fact.
It was the use of reheat for takeoff that really killed fuel efficiency.
A Concorde successor with much lower takeoff (and landing) speed, negating the use of reheat, was easily possible at the time if the politicians hadn't been so determined to destroy the European aviation industry.
Hell, the next version of the Olympus engine didn't even have reheat. It was to output more thrust without it than the last built versions could with it.
Many of the improvements of that engine design were worked into the already built engines and the new core never went into production.
The Fallacy of the Excluded Middle to be exact. And it's right here: "and they're going to fly in and out of spaceports some distance from the destination city"
Why would that be true? The *entire article* hinges on that statement. Yet there's exactly zero explanation of why this would be so.
One might make the argument that a hypersonic would be larger than a subsonic. That's likely true, one might imagine it being twice as large. So a Cessna Citation would be the size of a G5, and a G5 would be the size of a C100. All of these operate from small to medium sized airports. Even if it's the size of a 737, it's still going to be able to land and pull up to the executive terminal at every major city on the planet.
End of argument. He's already waved away the security issues and price by defining the market to be bizjet customers, so there appears to be nothing left.
> Concorde's engines WERE turbofans
They were pure turbojets. Zero bypass. You are wrong.
> the most efficient jet engines of their time in fact.
Not even remotely close.
You are, of course, referring to the overall thermal efficiency, which was indeed quite high. This is a wonderful measure of fitness for a *heat engine*, but exactly useless for measuring the fitness of a *jet engine*, which has to use that heat to accelerate air to provide thrust. *That* is called thrust specific fuel consumption, and the Olympus was poor even for its era - the TF39 (CF6) of the same era was twice as efficient:
https://en.wikipedia.org/wiki/Thrust_specific_fuel_consumption
If you read the actual article (and perhaps some of his replies in the comments) you'll find he isn't really saying "never", he's talking about the short to medium term: the next few decades. And the main thrust of his argument depends on post-9/11 security measures rather than overall pricing. That won't last forever either ... or at least I hope not ... but it probably won't change much in that timeframe.
That word does not mean what you think it does.
While everybody loves a good Princess Bride reference, could you spell out where steelfood went wrong?
If traveling faster takes exponentially more fuel, then the cost of that fuel must drop by a similar amount - wait for it - an exponential amount, for it to be cost effective, where "cost effective" means the same overall cost as traveling at a slower speed.
That seems logically consistent.
Maybe the economic model was a bit simple; being able to travel somewhere twice as fast may well be worth paying 4x in fuel costs.
*shrug* I just thought steelfood made a valid point; I don't see why "exponential" was an incorrect choice of word.
steelfood wrote (excerpt):
The problem with high speed travel is that the higher the speed, the costlier the travel in terms of energy. The curve is exponential, so that at some point, even a small increase in speed requires a significant amount of energy to achieve. Without a source of energy exponentially cheaper than what already exists (like cold fusion), that sweet spot of price to performance is never going to move.
No, turboprops are more efficient for short range hops - at least in the airliner context. They are at their most efficient at low speed and low altitude. You're not going to need 500 knots on a 100-mile flight, nor are you going to reach over 30k ft altitude.
This is a very common misconseption. In reality, the main limiting point of turboprops is speed of sound for the propeller edges. They have slightly better performance at altitudes commonly used by modern airliners as long as speed stays at levels where its propeller edges and surrounding air flow doesn't go supersonic significantly increasing drag and reducing efficiency. That was one of the main reasons why Airbus chose turboprops instead of turbofans to power its military transporter. And if you add contra-rotating propellers, even the best modern turbofans are left in the dust at these altitudes.
Implementation of this kind of engine in civil aviation is mainly limited by extreme noise emitted by contra-rotating turboprop engine as well as the speed limitations for efficiency. Hence turbofans on all larger aircraft and a mix of turboprops and turbofans on medium sized ones.
The Concorde used a lot of fuel because it was based on a very outdated engine and it was a very heavy design. It was a design done before the 70s oil crisis, when fuel costs wasn't much of an issue. If you just replaced the mobile nose with cameras for landing + used F22 jet engines (must use an after burning jet engine, one that is capable of supersonic air intake), just that would reduce fuel consumption by a huge margin (as much as 2/3s).
People's time cost money. That doesn't apply to your average turism traveller, but I'd say over half of airline customers are willing to pay US$ 100/hr saved in travel time. That's US$ 2000 for a really long (London-Sydney, NYC-Hong Kong) trips.
BTW, the sabre powered airliner isn't quite sub orbital. It's a 80-90k feet airliner. Sub orbital is about 3x higher (above 100km or 300k ft altitude). Its still flying, just flying on thinner air.
Finally, the Sabre engine concept is also the only proposed airliner design that burns hydrogen instead of Jet fuel. Hydrogen made from natural gas still emits CO2 (on the ground, can be sequestered) but hydrogen could also be made by high temperature nuclear or hydrolysis directly from water. If the concept succeeds it might end up being mandatory for long haul flights due to the pollution argument alone.
I prefer to let Sir Branson speak to what he wanted, which he has done publicly and at length. He has a known and strong record in aerospace.
He also has a known and strong record in bullshitting in aerospace.
The big problem with the Concorde was not only was the plane very noisy on takeoff because you needed the Olympus 593 turbojets to run at full reheat on takeoff and acceleration, but you had to run a good amount of reheat (afterburner) to maintain the Mach 2.0 speed, which of course increased fuel consumption.
With a modern variable cycle jet engine, flying at below Mach 1 the engine runs like a high-bypass turbofan with its lower attendant fuel consumption, then changes mode to run at supersonic speeds (probably without reheat at speeds up to Mach 1.3; above that, some reheat operation is needed, but not as much as you needed on the Concorde flying at Mach 2.0).