7 ms·

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

• paulmd 11y ago
  Sonic booms are a not-insignificant problem as well. We've been pouring money and research into it for decades and we have barely made a dent in it. The only known shape which produces no sonic boom (Busemann's Biplane) also produces no lift. There is a known shape called the Sears-Haack body which produces very little turbulence - basically it's like a very long pointed football. The best we have been able to do is make airplanes resemble that shape by having short stubby wings at the widest portion of the airflow body, with an elongated snout and tail. It does reduce turbulence to a degree, but again you are hurting your lift. I think this may actually be an insoluble problem. You need to disturb the air to produce lift, i.e. create a low-pressure zone over the wing, and a high-pressure zone under the wing. My fear is that this is inextricably linked to sonic booms, as we just seem to be exploring various locations within a space defining the tradeoffs between lift and sonic booms. We may be able to do it if we get the sonic boom low enough, but this gets back to the cost tradeoff. A rocket is certainly one possible solution within this space - a no-lift body that follows a ballistic trajectory could probably be constructed not to produce a sonic boom. However any solution on this end runs right back into the cost problem that you noted. Rockets need a lot more fuel and maintenance than a fixed-wing craft, and they're a lot less safe.
  • nether 11y ago
    Reducing the boom is achieved by damping the pressure N-wave from the oblique shocks near the aircraft forebody. This is done in various ways but at this time we're exploring blunting the nose to increase the local air temperature which increases the local acoustic velocity and reduces the pressure jump across the shock, weakening (quieting) it.
    • JorgeGT 11y ago
      That's very interesting! Got any paper? =)
  • JorgeGT 11y ago
    Just a small addendum: the Sears-Haack body is the shape with the least amount of wave drag under supersonic regime, but its derivation (using the Prandtl-Glauert equation) is not valid for transonic flow, where the best approach so far seems to be maintaining the cross sectional area constant. So if we optimize for supersonic flight it won't be so good for transonic and vice-versa... I agree with you in that probably there's no way to passively eliminate sonic booms, maybe some kind of "active" solutions, but the weight problem strikes again. Also, I don't know if a rocket can be made without boom, as the transition in the nozzle is abrupt. Maybe it's time to review those aerospikes!
  • imglorp 11y ago
    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.
    • paulmd 11y ago
      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.
      • trhway 11y ago
        >You need to be pretty high before supersonic booms stop being a problem. what is the problem with sonic boom? i grew up on navy base in pretty militarized region and we had fighters frequently producing the booms (USSR, first half of 198x). It was fun, at least for us - for children :)
  • ant6n 11y ago
    What if the body deforms, with wings for take off and landing, and a more ballistic shape during cruise.
  • rwmj 11y ago
    So can't you either: Go really high (square of the distance and so on). Or: Create a shape that pushes the energy of the sonic boom out to each side rather than in a circle equal in all directions? (I'm a computer programmer, not an aero engineer, so probably both these solutions are naive)
• porsupah 11y ago
  My WAG is that won't be a huge issue, given airlines seem to have little difficulty filling existing first class and other premium tiers - but if anyone knows of actual figures, I'd be grateful. The payoff would be the substantially reduced flight time - for some business flyers, that's worth a great deal. Bear in mind, with Concorde, that at least part of its downfall lay in the sharp rise in fuel prices in the early 1970s. Had that steep increase not taken place, but something more gradual, its commercial fate could have been quite different, even if it was never going to be any mass carrier.
  • notahacker 11y ago
    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
• vegabook 11y ago
  Yet interestingly you can buy a Ferrari which goes more or less 2x as fast as, say, a VW Golf GTI and costs 10x the price, and there is burgeoning demand for the former. So if those economics apply in the air as well (speed = luxury / exclusivity), we should be able to sell cross-atlantic tickets for somewhere between 10 and 20x the price of a midrange air ticket which I would suggest is premium economy. So we're talking in the 10-20k USD range per seat. My recollection is that noise regulations and landing rights to landlocked cities in the US killed Concorde. Not seat prices.
  • anentropic 11y ago
    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
    • vegabook 11y ago
      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.