Son of Concorde

targo writes "BBC reports that EADS is considering a new generation hypersonic commercial aircraft. "Son of Concorde" would be twice as fast, carry twice as many passengers while being much quieter than its predecessor. It would get from Tokyo to Paris in just two hours, US destinations are not mentioned. However, as Japan's failure last summer suggests, it might not happen too easily."

Comments

Two hours??

[mr.henry]

Mr. Burns' Spruce Moose can fly from New York to the Belgian Congo in 17 minutes.

Impressive

[Trioge]

2 hours to cover half the world... It almost sounds like a low-earth-orbit travel arc.

Re:Impressive

[Anonymous Coward]

9709 km / 40000 km is roughly 1/4 of the world.

An orbiting craft would do it in 1/4 * 90 min = 22 min.

Re:Impressive

[jc42]

... low-earth-orbit ...

Possibly, or a suborbital arc.

Back when the Concorde first came out, and occasionally after that, there were articles comparing supersonic flight to suborbital flight.

The main benefit of supersonic flight is that, since you're in the atmosphere, you don't need to carry your oxidizer with you. Also, you can maintain cabin pressure with a lighter shell, since the outside pressure is nonzero. But you have to push your way through all that air, so you have to be powered the whole trip.

The general benefits of the suborbital path is that you spend most of your travel time coasting above the atmosphere, not using fuel at all, and every place on Earth is at most 90 minutes away, plus the time it takes to get up and down, for a max of 2 hours. But you need to carry at least some of your oxygen (both for fuel and for breathing), and the cabin needs to be strong enough to hold pressure in a near vacuum.

The engineering calculations concluded that the crossover point in fuel consumption was at about 1500 km (1000 miles); at longer distance the suborbital flight would use less fuel than the supersonic flight.

All this was basically engineering estimates, though; nobody seems to have seen a motive for seriously developing the suborbital approach. This is probably because "space flight" is generally considered way out and unfeasible, no matter what the engineers say.

It'd be interesting to read some up-to-date calculations on this topic. I haven't seen any for a few years. Google doesn't seem to find any (or I'm not guessing the right keywords).

Anyone know of any good, recent writing on the topic?

Re:Impressive

[Anonymous Coward]

There is a big downside to "coasting above the atmosphere, not using fuel at all". That is a ballistic trajectory meaning that you will be in freefall. the name "vomit comet" mean anything to you?
passenger comfort requires "gravity", gravity requires lift, lift implies drag, and drag burns fuel.
-Rob
ps: thats not to say you wouldn't get some thrill seekers wanting to fly, but i don't think it will fly with the business crowd...

Wait a second...

[cgranade]

If we couldn't get a supersonic jet to be profitable for less than $2K/ticket, how the hell is a hypersonic jet going to be profitable. I mean, sure, it carries twice the passengers, but if its going twice as fast, can we expect it to burn more fuel, too?

Re:Wait a second...

[Lordofohio]

Yes, if everything else is equal it should burn more fuel, although I'm not sure how much more. The problem with flying faster than the speed of sound is that there is a huge increase in drag (and therefore the thrust required to overcome it) right around Mach 1. Above Mach 1 the drag doesn't increase as rapidly, but it does continue to go up.

Until very recently every plane that flew above Mach 1 had to do it while on afterburners, but I believe the new F-22 Raptor can fly at "super cruise" which is some method of breaking the sound barrier without afterburners, which saves a huge amount of fuel. Last I checked the technology behind that was still secret.

I question whether this proposed airplane will actually fly in the hypersonic region, since to an engineer that means Mach 5 or above. If it can actually make the Tokyo-Paris flight in 2 hours, you could spend a day in Tokyo, fly to Paris, get a night's sleep and live the day all over again in the land of love!

Re:Wait a second...

[The Fink]

I'm not an aeronautical engineer; just a plane nut. I may therefore have some of this wrong, and I'd welcome corrections.

Supercruise is a fairly easy-to-understand phenomenon; in effect, it requires two things:

• lots of thrust from the powerplant;
• subsonic airflow in high quantities through the engine due to the way a "conventional" turbine operates, with slightly supersonic exhaust flows.

Normally, a turbine can't attain supercruise because of the latter; the airflow needs to be slowed considerably going through the powerplant in order to stop a shock stall (where the supersonic shockwave suffocates the powerplant).

The powerplant behind the F-22 (Pratt&Whitney F119-PW-200) attains this primarily though a few good engineering tricks such as single-crystal-cast blades with a slightly shallower angle of attack than most; thus allowing the engine to operate at a higher temperature and pressure internally than is "normal". It has a lower bypass ratio (the ratio of cool air passing around the engine to that going through the engine) than most fighter-class engines; thus, it needs a smaller front fan, which in turn reduces the area causing a shock stall. It also wears out quicker, but that's another matter entirely. :)

High bypass ratios are great for fuel efficiency at subsonic speeds, but by virtue of the way these turbines work and their tendency to shock-stall when confronted with a supersonic airflow, are not much good for supersonic flight, and not for the nearly-supersonic airflows that supercruise requires.

A typical mid-to-high bypass turbine used in a fighter will have a bleed air system to reduce the airspeed running through the turbine; this has to be counteracted by dumping raw fuel into the bypass & exhaust (i.e. afterburner). Indeed, to get much over M1.0 the F22 needs to employ this same trick. A low bypass turbine can operate with input airspeeds closer to M1.0, which in turn means less air needs to be bled, while still producing a slightly supersonic exhaust out the rear end.

Re:Wait a second...

[mnemonic_]

Single-crystal titanium blades are common in high performance engines, not just the F119-PW-100 (note it's 100, not 200).

"A typical mid-to-high bypass turbine used in a fighter will have a bleed air system to reduce the airspeed running through the turbine; this has to be counteracted by dumping raw fuel into the bypass & exhaust (i.e. afterburner). Indeed, to get much over M1.0 the F22 needs to employ this same trick."

The F-22 has demonstrated supercruise at 1.53 mach, i.e. it has reached speeds significantly above 1 mach without afterburner use. Top speed in level flight, at altitude, is probably no greater than 1.9 mach due to the deletion of variable intake ramps (which the YF-22 had).

Re:Wait a second...

[Anonymous Coward]

Until very recently every plane that flew above Mach 1 had to do it while on afterburners, but I believe the new F-22 Raptor can fly at "super cruise" which is some method of breaking the sound barrier without afterburners, which saves a huge amount of fuel. Last I checked the technology behind that was still secret.

Supercruise is generally used as a term to describe an aircraft capable of maintaining supersonic speeds without the use of afterburners. Supercruise is rarely used to describe the ability to accelerate to supersonic speeds without afterburners e.g. the ability to push through the transonic region.

Supercruise as defined in the context of the F-22 is the ability to cruise M1.5 @ 50,000ft without the usage of afterburners. F-22 is unique in that it can accelerate to its supercruise speed without afterburners. However current information suggests afterburners will be used operationally in the transonic region to achieve M1.5 due to payload weightings (no publicly disclosed test has achieved M1.5 without using afterburners to attain that speed when fully laden). The only tests to attain the aircrafts supercruise speed without afterburners have been un-laden tests.

There have been plenty of aircraft capable of supercruise after using afterburners in the transonic region. SR-71 could supercruise at M1.8+, Concorde was/is capable of supercruise at M1.4+. Both aircraft would routinely supercruise at those speeds during their operational life. It might surprise you to learn that the Rolls-Royce/SNECMA Olympus 593 Mark 610 (used in concorde, designed back in the 60's) could be used to accelerate the plane through the transonic phase without afterburners, but was found to be more expensive operationally than using the afterburner from M0.95 to M1.4.
A revision of the engine was under development in the late 70's before cancellation of the concorde mrk-II project which would have made transonic acceleration economic. The intake system on the Rolls-Royce/SNECMA Olympus 593 engine is even today still a state secret and had to be removed from the planes before they could be put on public display.

As a comparison the engine specs state that:
Rolls-Royce/SNECMA Olympus 593 Mark 610
31,350 lb st dry thrust
38,050 lb st with afterburner.

F119-PW-100
35,000 lb st dry thrust
39,000 lb st with afterburner.

Failure Reborn

[Pavan_Gupta]

There are reasons why supersonic travel don't work, and especially in this kind of modern day economy. Firstly, they're damn ineffecient. They suck up fuel like it's not worth anything. Secondly, they're not economically effecient -- even holding twice as mayn people, you're only looking at carrying a relatively small amount fo people. Lastly, the price of development of a plane like this, and the price of the plane itself, is not worth it.

There is a reason why the modern concorde died, and it wasn't only because of the accidents that occured -- it had to do with the fact that there isn't a market for super high speed travel. People just want to get quickly from one place to another, they dont' want to go super fast. Moreover, people on the ground are already super angry about the sound of jet noise (especially near airforce bases -- I know first hand), and unless there is some sort of boom supression technology, these planes will not fly in the united states.

Our airline industry really needs to try and turn a profit ebfore they continue to waste time and money innovating. Sure the government will bail them out over and over -- like they do for the rail road companies, but I hate wasting my tax money on childlike business tactics by big airlines. Its about time some of these companies developed some responsiblity -- and a supersonic jet is not where it lies.

Let's make bigger planes, and try to keep them at relatively fast speeds. And there's my rant. Do with it as you must.

Re:Failure Reborn

[BiggerIsBetter]

I disagree. Flying halfway around the world is a PITA, even at the fast-ish speeds the current crop of jet-liners can fly at.

Go to any international airport and take a look at the travellers who have spent 12 hours on a flight, with 8 more ahead of them after their stopover.

Trust me on this - if they have the money, people will pay for this high-speed service. Even if it means an "economy" seat for the price of business class, it's worth it to shave 15 hours off your travel time.

Re:Failure Reborn

[BiggerIsBetter]

There is no point.

2 hours sitting on a plane vs 23 hours sitting on a plane. That's the point. That's worth a lot of money to some people, including myself

What part of that don't you understand?

Re:Failure Reborn

[Zeinfeld]

There is a reason why the modern concorde died, and it wasn't only because of the accidents that occured -- it had to do with the fact that there isn't a market for super high speed travel.

There was only one accident and in fact that had little to do with the end of service, the real issue was the Airbus consortium terminating support. The cost of maintenance would have soared. The fleet was way too small to be economic.

The real reason Concorde failed was that it carried too few passengers, used too much fuel and protectionism in the US blocked landing at the major airports until the consortium stopped manufacture.

The result was not as much of a disaster as often claimed. The development money on the first joint product went down the drain, but the collaboration led directly to airbus. With Boeing looking at a stale and aging product line and unable to get any new plane off the drawing board without a major subsidy through the pentagon, Airbus is now the dominant force in the market.

Airbus will be building a 1200 seat aircraft, which with the current glut of 600 seaters is probably the sweet spot in the market at this point.

The idea of supersonic cruisers keeps popping up and bobbing down. Eventually one will get built simply because there has to be something more interesting to build than yet another super-jumbo.

The idea that seems to crop up quite often in tendem with the superjumbo idea is the idea of lobbing satelites into space en-route. If someone could make that happen with an interesting size payload, I guess some military might sign of on the R&D.

That is probably what NASA should have built instead of the shuttle.

Re:Failure Reborn

[toxic666]

This is a European adventure, and if they want to subsidize it, have fun. Boeing tried and failed. And I'm not talking about that fuel-sucking high-subsonic Chronic Snoozer (I mean, Sonic Cruiser), they failed to pull off a viable supersonic plane before that.

But it will have a tough time getting clearance for the USA.

More annoying than jet noise are sonic booms. They are not going to be acceptable (by law) over populated areas. Therefore, any service is limited to coastal American airports (like New York City) because there just are not many airports approachable over ocean routes. Atlanta, BWI, Seattle and Orlando -- forget it (unless you want to swing way south around the FL peninsula first). LAX, NY, San Fran, New York and Boston are pretty much it, and this new aircraft would be subject to new sound analyses and intense public stakeholder scrutiny. And not many people need to fly in these planes, so they derive no benefit in having a very loud plane near their homes. It better be quiet and drop subsonic long before it approaches the coast to have a hope of landing in the USA.

As for the Air Force, I've sat on a bucolic mountaintop, enjoying the winter view and serenity, only to have a B-1 come ripping by doing low-level supersonic training. Kind of felt like a pillowfight body shot. Funny thing was, I never saw the Lancer!

Sure, a supersonic airliner would be much higher, but the sonic booms would still be unacceptable.

Re:Failure Reborn

[Drishmung]

Compare the cost of cattle class vs business class for intercontinental flight. It's not 25% more, it's not 50% more.

Since we were referring to Concorde earlier, I used the calculator at British Airways for flights London (UK) to Sydney (Australia). That's a long flight, pretty much half way around the globe.

The cheapest economy fare is GBP 511-848 (return);, Business class is GBP 1,927-2,570; 1st class is GBP 2,891-3,220. That's a huge difference, yet people are willing to pay it, just for more leg room.

You don't think those same people would pay business class rates for cattle class seating---but get there in a few hours?

Re:Failure Reborn

[mnemonic_]

"The real reason Concorde failed was that it carried too few passengers, used too much fuel and protectionism in the US blocked landing at the major airports until the consortium stopped manufacture."

Not only in the U.S., but also in Europe.

"Airbus will be building a 1200 seat aircraft, which with the current glut of 600 seaters is probably the sweet spot in the market at this point."

Whoa there! 1200 seats? The double-decker A380 currently undergoing early construction seats about 560, roughly 100 more than the 747-400 (the current largest capacity civil passenger aircraft). There are no 600 seat aircraft in service at this time, and certainly not any 1200 seaters for a while.

Re:Failure Reborn

[bigpat]

"There is a reason why the modern concorde died, and it wasn't only because of the accidents that occured -- it had to do with the fact that there isn't a market for super high speed travel."

Richard Branson disagrees and was willing to put money behind it. He wanted to add the old concordes to his Virgin Atlantic's fleet. His argument was that he had looked at the numbers and the Concorde was actually profitable on a per flight basis and that it was tremendously powerful for marketing purposes. So, if the concorde was full most every flight and they weren't losing money...

Branson's point was basically that the concorde's alleged unprofitability was just a persistent marketing campaign and that British Airways had just decided that it could just make more money shifting its customers over to it's regular fleet of bigger planes.

Now I don't know if Branson is right or wrong, but at least one person who was willing to put a lot of money on supersonic transport thought he could make money on it. I'm willing to believe that there is some combination of economics and engineering that make sense for faster air travel. Supersonic planes might not make sense for big airlines that have invested in large monolithic fleets, but what makes me think Branson might be right about the concorde's reputation being the result of negative marketing is the knee jerk reaction that you all have had to the prospect of renewed supersonic flight.

I'd like to see the real numbers on the concorde... operating costs versus revenue, development costs aside (which were paid for by European taxpayers). But just believing a large corporation when it says that nobody can successfully operate a supersonic aircraft just because they couldn't is just a bit too much blind faith in my book.

Remember the Sonic Cruiser?

[Diphthong]

This sounds like aeronautical vaporware. Boeing's attempt at a higher-speed "Sonic Cruiser" was scrapped last year when the company felt that economical flight at current speeds was the way to go (via the 7E7 project), and the Cruiser wasn't even planning to pass the sound barrier.

It's one thing for EADS to think speed is the way to go, and it's quite another to propose something as ambitious as they have. Based on the article I strongly suspect they're making token research into engine tech but aren't actually trying to design a plane at all here (no mention of fuselage design at all). It's just Fun with Public Relations.

Re:Remember the Sonic Cruiser?

[yog]

It's not clear that the Sonic Cruiser was scrapped for the right reasons. It was probably board of directors politics rather than an informed technical and business decision that killed this bird.

In general, Boeing is hurting; it's a cyclical industry and even in the best of times they have to take huge financial risks with new models.

Also, they seem to have a really antagonistic relationship with their unions, and it so happens that the mechanics and even the engineers were on strike at the time that the Sonic Cruiser had been announced. Under these circumstances, a couple of board members including John F. McDonnell, relics from the old McDonnell-Douglas corporation, were able to veto the project as "too expensive".

There's been a lot of articles about Boeing's descent from a dynamic innovator to a stodgy defense contractor, partly caused by its merger with Mc.D. See this article for example.

It's sad to see a once great company fading away.

Fast for a reason!

[AndroidCat]

It would get from Tokyo to Paris in just two hours

And because of that they dont have to server dinner. Pretty sneaky!

Re:Fast for a reason!

[mcpkaaos]

Trust me, that's more and advantage for the passengers, not the airline.

Applications for space flight

[smiff]

The biggest cost to space flight is fuel. Most fuel is spend just getting the rest of the fuel off the ground. Of the fuel, 1/8th of the mass is oxygen. It stands to reason, that if we had an air-breathing plane handle the first leg of the journey, we could dramatically reduce the fuel requirements for space flight. It would be great to see something like this used as a launching platform for spacecraft.

Re:Economics?

[Pig Hogger]

As long as air resistance scales super-linearly with velocity, getting there faster will always prove less economical than travelling at a more sedate speed.

Er, no. Concorde flew above 60,000 feet, where air resistance is much less than the customary 35,000 feet. Concorde was just as a fuel-efficient cruiser as subsonic planes; trouble is, it sucked 25% of it's fuel on take-off...

Re:Technology

[hedley]

Have you been enjoying subsonic travel lately? The latest generation of these craft utilize thousands of microprocessors and associated firmeware from FADEC's to laser ring gyro's to seat back entertainment systems. Even the lavatory flush is controlled by a microprocessor. Of course, your fear would be amplified if there was not some form of reliability in these systems and some redundancy. When you enjoy that flight on a 777, you are getting there thanks to all of those systems working nominally. When things go wrong, a microprocessor is most likely helping the crew diagnose whats going wrong. Perhaps the processor has already made a correction and has alerted the crew after the fact the problem has been controlled. Smaller crews, specialized processors to control crew workload. I am sure this aircraft will be evolutionary in that regard, an extension of where we are today wrt the glass cockpit.

Hedley

It's only tecnology research, but wise thinking

[theolein]

The BBC article states clearly that they're only doing the research on the technologies, with the aim of producing a flying hypersonic craft with noise reduction down to that of a 747. It also states that they realise full well that there is no commercial market for such a craft right now.

So why are these people researching some technology that has no current market? Obviously because they realise that the market will not always be in the slump that it now is. It's called visionary thinking. The Concorde may have not covered full costs (I don't know enough about that), but it made BA and Air France a fist full of money as tickets cost around $3000 a pop IIRC and there were definitely enough rich people willing to pay those prices for a quick pop to New York or Rio, and those same rich bastards will still be willing in the future when and if this thing ever becomes a real plane.

For the rest of us there's the double decker Airbus A380 that will be making it's maiden flight in 2005.

Re:Not half the world...

[zulux]

I think Europe to Japan is a North Pole route, so it's a lot shorter then it sounds.

Much as I love Really Fast things, the enviromental effects will be the big hurdel, not noise.

And the best thing about a Polar route? - There's none of that pesky Ozone to get in the way of your hyper-speed aero-plane.

Re:Two Hours? I dont think so.

[Anonymous Coward]

Unfortunately you have neglected what happend with the Concorde that impact your "math" quite significantly,

First of all, Concorde never flew to Tonkyo. The flights to Paya Lebar, Singapore had to stop over at Bahrain for refueling, even a quick turn around will cost you a couple of hours at best. The route flew over what was nearly all land so it had to fly at subsonic speeds on large portions of the journey (M.95), after a while even flights over the Saudi desert had to drop to subsonic speeds because of nomads whose camels reportedly stopped breeding because of the supersonic boom.

So that's why you had journey times in the 8-9h region, if they flew the journey at 2M nonstop then you would expect to half that time, so a plane going 4M nonstop could be in the region of 2h.

So much for you logic, nevermind the math.

I can't

[salesgeek]

As I read /. I am struck by the persistence of people saying:

* This can't be done!
* This can't be done economically!
* We shouldn't try because it can't be done.

I just hope the people working on making a plane that will cut down on my travel time have a different attitude. I hope they are asking how can it be done? rather than why can't it be done.

It's easy to be a nay sayer. Nothing exposes genius faster than naysayers proven wrong.

Oh Really...

[tonyr60]

Let me seee...

1 hour to get to airport,
1.5 hours check in before departure,
2 hours flight time,
30 minutes to get baggage
1 hour custums and immagration.

Yep, we need faster air travel.

Particularly this morning when my flight was delayed an hour because the pilot had not arrived and a replacement needed to be found.

Re: Son of Concorde

[Snorpus]

It appears the Beeb has confused peak speed with average speed.

According to the US Department of Agriculture, the Great Circle distance from Paris to Tokyo is 6033 miles. Let's round that to 6000 mi. The speed of sound varies with temperature, but using 750mph makes the math easy (at aircraft altitudes, the speed of sound is closer to 700mph).

If it could hold the fuel, the Concorde at Mach 2 (1500mph) could do 6000 miles in four hours. If the EADS jet achieves Mach 4 (3000mph), it could do 6000 miles in two hours. If the entire distance were covered at cruising speed.

My impression (purely from being a passenger) is that it takes half an hour or so for a typical commercial airliner on a 1000 mile flight to reach cruising speed and altitude; the plane will then be at cruising speed for about 60 minutes, and then another 30 minutes is spent in deceleration. Of the 2 hours spent in the air, only half of the time is actually spent at crusing speed.

How long would it take for the EADS-SS to reach Mach 4? And how long would it take it to slow down from that speed to the typical 150mph (+/-) landing speed that current runways are designed for? I doubt the typical passenger is prepared for Michael Schumacher / John Force g-forces on takeoff and landing.

Let's say the EADS-SS takes 45 minutes to reach Mach 4, and another 45 minutes to drop back to landing speeds. Assuming linear acceleration and deceleration, that's an hour and a half spent at an average speed of 1500mph. So 2250 miles of the trip takes 1.5 hours. Transiting the remaining 3750 miles at Mach 4 (3000mph) would take another 1.25 hours, for a total trip of 2.75 hours. [Ignoring any ground taxi times or other delays.]

I would think, fuel-wise (which is basically the only marginal cost of airplane flight), that going from Mach 2 to Mach 4 is more expensive than going from Mach 1 to Mach 2. On the other hand, Mach 1 -> 2 is done in denser air than Mach 2 -> 4, so maybe not.

This could be a great question for a final exam in Engineering Analysis and Synthesis.

Re:Technology

[Kegetys]

I think the parent means planes that have an unstable airframe, like the F-22 Raptor for example, that wont stay in the air without computers keeping it stable. Take that 777, make all the computers in it malfunction and it will still fly, glide at least. Do that to an F22 and it will drop like a rock... I'm not aware of any civilian airliners that would be like this, but maybe they are coming. I would feel less safe flying in one of those than a "traditional" airliner.

Re:Not half the world...

[mnemonic_]

Indeed. Air routes aren't determined based on the shortest path between two points, they're based on "hops" from one airport region to another (regardless of whether they actually land at the airport). Easier to keep track of the aircraft, but terribly inefficient.

Re:Economics?

[fat_bob]

Concorde didn't use its afterburners while cruising.

http://www.concordesst.com/powerplant.html

Perhaps you should think before you post?

Forget economics for a minute.

[freidog]

Just building such an aircraft would be an engineering marvel. You're talking about building a commercial aircraft that flies faster than the SR-71, and potentially higher. And instead of moving 2 guys in pressurized flight suits and some cameras with the need for refueling every ~2 hours, you want it transport a few hundred people in relative comfort half way around the world? Just getting any airfram to 4 MACH without melting is quite an accomplishment of materials and aerospace engineering.

Re:Here's a way better solution.

[mnemonic_]

In other words, designing an aircraft which performs worse would be easier. Ingenious. But to attack your points specifically...

"2. By limiting the top speed to around Mach 1.7, it also means there is less need for exotic jet engine designs, which also reduces development costs. We could, for example, develop an engine for this new SST as a derivative of the Rolls-Royce Trent engine now found on many of today's widebody airliners. That could also mean the engine will meet today's strict rules for exhaust emissions, especially oxides of nitrogen emissions."
A derivative of the Trent 900, perhaps? It would be have to be modified significantly enough (1.9 times intake air velocity complicating everything, nacelle-less configuration for essential drag reduction, etc.) that it would be necessary to design an entirely new engine.

3. [sonic boom stuff]
And who says they're not doing this? Northrop's QSP efforts reached even the mainstream-tech media, and so I find it unlikely that the British engineers are unfamiliar with it. On the other hand, are you aware of the deployable serrated flap tests on lambda wing UAV's, or the vortex generator effects analysis on the V-22's dorsal region? Or the effects of forebody LEX during high-alpha supermaneuvers?

I think you are vastly oversimplifying the design necessary for a high-supersonic airliner and, in effect, insulting the intelligence and knowledge of aerospace engineers.

bzzt. try again.

[Anonymous Coward]

not quite. I work for an airline. A positively giddy amount of work goes into flight planning. Shortest path comes into it if you're trying to be quicker, but these days fuel burn and thus cost matters a lot. Trying to maximize your tailwind, reduce headwind, avoiding restricted airspace and following airways (like an interstate in the sky) for air traffic control reasons. This might answer the "hops" you talk about. Its navigational beacons which are often at airports.

Which brings us to tracking. If you're over the open ocean you follow tracks. Its a bit like hunt for red october going through the canyons. This speed, at this altitude through these points to maintain separation. Over land, you can be spotted within a couple hundred miles by your ground-air comms. And theres a lot of those. You are almost right on the airports, depending on where you're flying, type of aircraft and and how many engines you must be within a certain flying time of a suitable airport. Its called ETOPS.

So lots of things to worry about, including weather, but it typically starts with shortest distance.

Supersonic biz-jets more realistic

[meldroc]

By going with a smaller aircraft, Learjet sized, you can reduce design and manufacturing costs. That and you can target the filthy-rich-let's-buy-a-trip-on-a-Soyuz-for-fun market instead of the save-bucks-at-all-costs airline market.

Once a few supersonic bizjets are on the market, it would be easier to scale the designs up to airliner sizes.

Unstarts and things that go bump in the night

[Latent Heat]

One characteristic of the SR-71 is the susceptability to an "unstart." The SR-71 has those movable inlet spikes to control the shock wave (the inlet shock wave not only slows the air to where the compressor can handle it, it also compresses the air, and the faster the SR-71 goes, the higher the compression ratio and more engine power, a bit like a turbojet-assisted ramjet). Of course airflow is one of those fractal-chaotic physical phenomena, and if the shock front burped, you had major loss of power on one side of the plane that slammed the pilot's head against the canopy (hence the use of crash helmets). They developed a computer control system for the inlet spikes, but I heard it wasn't perfect.

While the XB-70 Valkyrie was not quite as fast as the SR-71, it was nearly as fast (Ben Rich in "Skunk Works" tries to tell us it was only Mach 2.5, but that was only for the number 1 XB-70 because when they took it up to Mach 3, parts melted off (the brazing on the honeycomb steel panels came apart) and got ingested in the engines). They fixed that problem on the number 2 XB-70, but they crumped the number 2 XB-70 in a fatal rear-end collision doing a photo op with a bunch of "chase planes", and the XB-70 parked inside the Dayton, Ohio Air Force museum is the Mach 2.5-capable number 1 plane.

Anyway, the XB-70 also experienced the unstart problem. The XB-70 was used for aero research for the SST, and the honkin' sonic booms from the XB-70 were part of what helped discourage the SST. It was also noted that unstarts were pretty scary and would need to be remedied for the SST.

Concord/Concorde has movable inlet ramps for the shock waves -- I wonder if it ever experienced unstarts?

Also, the XB-70 was supposed to use "compression lift" -- they stuffed the six engines in this big, wide pod under the delta wing to get lift from the shock wave. This was supposed to make it much more aerodynamically efficient than the typical supersonic aircraft, allowing it to have intercontinental supersonic cruise range. I also heard that the compression lift didn't quite work up to the expectations of the wind tunnel model tests.

Is anyone considering whether compression lift (apparently there is better fluid modeling software) can result in a more fuel-efficient/longer-range SST?