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The challenges of building a hypersonic airliner

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Re: The challenges of building a hypersonic airliner

#31

Post by anentropic »

vegabook wrote: post #22
imglorp wrote: post #9

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

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 tal…

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

Re: The challenges of building a hypersonic airliner

#32

Post by ant6n »

cstross wrote: post #24

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…

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.

Re: The challenges of building a hypersonic airliner

#33

Post by vegabook »

anentropic wrote: post #31
vegabook wrote: post #22

Earlier quoted context omitted.

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 tal…

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

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.

Re: The challenges of building a hypersonic airliner

#34

Post by ant6n »

paulmd wrote: post #15
imglorp wrote: post #9

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…

What if the body deforms, with wings for take off and landing, and a more ballistic shape during cruise.

Re: The challenges of building a hypersonic airliner

#35

Post by notahacker »

porsupah wrote: post #16
imglorp wrote: post #9

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

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 earl…

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

Re: The challenges of building a hypersonic airliner

#36

Post by paulmd »

imglorp wrote: post #30
paulmd wrote: post #15

Earlier quoted context omitted.

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…

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.

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.

Re: The challenges of building a hypersonic airliner

#37

Post by douche »

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.

Re: The challenges of building a hypersonic airliner

#38

Post by mikeash »

douche wrote: post #37

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.

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.

Re: The challenges of building a hypersonic airliner

#39

Post by rconti »

douche wrote: post #37

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.

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")

Re: The challenges of building a hypersonic airliner

#40

Post by rm445 »

porsupah wrote: post #18

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

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.

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