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Comment by yabones | Hacker News Reader

Well, the problem was never technological to start with. The problem with supersonic transports was and will always be economic. There's a reason that there were only two SSTs in the 20th century instead of the five or six that were planned, and it's because the bean counters at Boeing, McDonnel-Douglas, and Lockheed-Martin wouldn't let their companies bankrupt themselves over a vanity project.

So, you take that and couple it with 21st century VC-appeal and you have a fantastic money-losing-machine whether it works or not. Hell, it probably does work with enough R&D, but that was never the problem in the first place.

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To be technical, I'd actually argue there were four. The first Concorde reached production & was later redesigned to include an afterburner (or reheat). Why I forget, but it apparently did actually save some fuel since it was used while accelerating to supersonic then shut off.

The Tu-144 went the opposite direction. Introduce with military engines which require full time afterburner. Later it was redesigned and re-engined with a non-military engine not needing afterburner all the time.

So two airframes, but with four distinct airplanes produced as a result.

None of these were particularly economical, to your point.

Huh? The Concorde was designed with afterburners right from the start. It certainly did not enter service without them.

Yes; the Olympus engines used were derivatives of an existing military turbojet and had reheat from the beginning. It was used for takeoff and then to get through the high-drag transonic regime as quickly as possible to minimise fuel use. Once at cruising speed the engines operated 'dry'.

There was a longer-range 'Concorde B' designed, which was intended to have larger engines with no reheat at all (as well as larger wings and some other changes) but this was cancelled when it became apparent that it would never be profitable.

OK, I think I got it wrong. You're correct it always had afterburners. It could supercruise, which is flying without the afterburner at supersonic speeds. So I guess that would bring the actual number to 3.

The reheat is needed to get past the transonic region and onward to supersonic. Once you've gone supersonic the drag actually drops a lot. So you want to get through the transonic region as quickly as possible and reheat is a good way to do it. After that the Concorde just supercruised.

> Once you've gone supersonic the drag actually drops a lot.

Certainly the drag coefficient drops, does it actually drop fast enough to counter the v^2 and see total drag drop as velocity increases?

I think so, many planes are like this: the transonic regime has the highest drag. It's not as simple as v^2, you have to consider the compressibility effects (wave drag where the pressure wave moves along with the plane, like a bow wave on a ship). Flying faster also means you can fly higher in lower density air, so the indicated airspeed (proportional to density * v^2) is reduced.

> It's not as simple as v^2, you have to consider the compressibility effects (wave drag where the pressure wave moves along with the plane, like a bow wave on a ship).

I think it is that simple. Those effects are the reason the drag coefficient is changing, you don't need to account for that twice.

John Michael Greer summarized it wonderfully in the book 'Dark Age America'. Don't confuse technical capabilities with economic realities. Argued that Boeing never getting the SST off the ground was probably one of the better disasters to befall them.

Vaclav Smil was right in pointing out that passenger jets have gotten much more fuel efficient since 1967 but they travel no faster. The fuel savings were passed onto passengers and that made flight more appealing. Economics ultimately rule over what lasts long term.

Super sonic flight is a marvel of engineering but an economic nightmare. It is this lens by which a lot of technologies should be judged long term.

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