Proposed Lapcat II Hypersonic Airliner: Brussels to Sydney in Less Than 3 Hours

New submitter AG_2011 writes: Could an airliner that flies anywhere in under 3 hours be in service by 2030? One estimate puts the cost one way at €5,000 (£3,700) per seat for a Brussels to Sydney trip. The Lapcat-II project's Mach 8 airliner will be capable of 8,500 km/h (5,280 mph) and could take passengers on this trip in 2 hours and 55 minutes. The race is on...

Comments

For future reference,

[Beck_Neard]

So that everyone can have an informed opinion about this, the laws of physics of high-speed travel are quite simple. The lower the lift-drag ratio of your craft (at cruise speed at level flight), the more fuel you have to consume per mile. The problem with supersonic travel is that at supersonic speeds, high lift-drag ratios become virtually impossible. A 747 has a L/D ratio of over 25; the Concorde had a L/D of about 7 at Mach 2 (and it was a pretty efficient, low-drag design). The best supersonic designs I'm aware of achieve a L/D of around 9 at L/D at Mach 1.5. These are incredibly optimized designs that have been fine-tuned with supercomputers and would be quite unfeasible for a passenger aircraft (weird shapes, no windows, etc.) As a result the Concorde consumed about 3x more fuel PER MILE than a comparable subsonic jet. So half the mass of the Concorde was fuel (!), it winded up being very heavy, and it carried only 100 passengers. And its maximum range was limited to 4500 miles.

And if you look at a craft like the SR-71 blackbird, it fits the same pattern. It had a L/D of about 6 at cruise speed (Mach 3.2), 60% of its mass was fuel, and it could only go about 3000 miles before requiring refuelling.

At hypersonic speeds, it's even worse, as various laws start catching up with you and limiting your theoretical L/D to about 4 or 5. If you're running on typical jet fuel, forget London to Sydney. Such a craft could barely make it from London to Athens. So because of that, they're suggesting hydrogen. Which is both hilarious and also firmly puts this idea in the realm of 'things that are never going to happen.'

Re:For future reference,

[Anonymous Coward]

Concorde suffered from being small - with limited volume and so poor number of passengers for overall weight (about 1passenger per dry tonne, versus about 2 for a large airliner) A larger SST could get to similar 2 passengers per tonne figures with more internal volume available.

Concorde B (minor wing and engine changes, never built due to halt in production) would have lifted range about 10-20% from Concorde. L/D about 7.5. Modern jets are not 25, more like 21-22, so yeah about 3x, though a new Mach 2 SST might get L/D up to 8 or 9

But cost of travel is about 1/3 fuel, 1/3 capital and 1/3 staff. Travel 2.5 times as fast (concorde) and capital costs are reduced by about half as are staff costs. Optimised Mach 2 engines are also far higher efficiency than subsonic engines due to higher efficiency of inlet air compression so fuel costs are only about 2.5x and overall cost about 1.2-1.3x. That is affordable. You are also only in the air for 3-4 hours at a time, so don't need to provide for high staff headcounts and sleeping spaces or meals as on long-haul flights.

Change to LNG as a fuel and you can lower fuel costs and increase range by 20-30% and might be even cheaper than conventional jets.

Also we now have a raft of improvements since 1970's - like building from lighter stiffer stronger carbon fiber, improved higher temp engines, better control systems, no need for droop noses, cheap fast cfd and fea optimisations, and even ability to do laminar flow wings that can all hook together to greatly reduce weight of aircraft and increase efficiency compared to old Concorde.

The boom remains the big problem, but the economics could otherwise probably work, and there is a market for international flight over oceans, that dropping flight times would increase further. With passenger volumes increased by an order of magnitude since the 70's the time for supersonic airliners might be returning - Boom Nimbys are the big uncertainty/roadblock. And of course corporate risk aversion.

Maybe the chinese govt will do it - it is the kind of thing that would appeal to them and would let them break into civilian aerospace doing an end-run around the Boeing Airbus duopoly.

Re:For future reference,

[joe_frisch]

Agreed. Its also very difficult to make efficient scramjets which makes the problem even worse. The best scram jets so far have barely been able to maintain steady flight at a single mach number and in a short range test vehicle.

I think there is a good chance that you want to jump from supersonic all the way to mostly ballistic sub-orbital. It also completely avoids the noise footprints except (and its a BIG except) at the launch and landing points.

As several people have also said, I'll take hyper-sonic travel seriously only after we have supersonic commercial flight again. Existing airliner speeds haven't changed significantly in 60 years. (!!!). (the same time it took to go from the Wright brothers to near mach-1 travel).

Re:For future reference,

[Beck_Neard]

The dependence between L/D ratio and range is independent of height or air density. Assuming fixed speed, in less dense air, you have less drag, but you also produce less lift.