The challenges of building a hypersonic airliner
bbc.com
bbc.com
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.
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.
I would agree with your bot assessment.
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.
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.
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)
[1] https://news.google.com/newspapers?nid=1301&dat=19850215&id=...
On the grounds of comfort I'd have preferred the even longer journey in the 747...
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.
Short legs.
The SABRE engine appears to be coming along well, with one of the largest challenges - cooling the incoming air extremely rapidly - seemingly overcome.
Even with a reserve of goodwill for the project, reasonable people might choose not to take too much notice until further results are demonstrated.
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 "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.
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")
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.
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!
Also, at what altitudes does a boom become irrelevant? This thing will be very high so cross-continental might not be an issue either.
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.
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 :)
(I'm a computer programmer, not an aero engineer, so probably both these solutions are naive)
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.
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
My recollection is that noise regulations and landing rights to landlocked cities in the US killed Concorde. Not seat prices.
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
Not sure which, or what particles there would be more of at 33km than 25km, but that's my immediate guess.
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)