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by jandrese
2175 days ago
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Air pressure difference between FL350 (traditional airliners) and FL600 (Concorde) is about 1/2. But the speed difference was about 2.5x, so overall you would expect Concorde to need to expend about 3.125 times as much energy per flight hour. Even with the flight time divided by 2.5 you're burning more fuel for the trip. Interesting to consider a Concorde like design today using a slightly scaled up version of the P&W F135 supercruise capable turbofans. But you'd still be competing with highly efficient turbofans like the GEnx series in a cost dominated aviation market. Also you still have issues like not being able to fly over land in the US that seriously limit the potential market. |
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This is false. First, drag is proportional to air density, not pressure, with density at FL600 being 30% of FL350. Drag is increased by 1.728 times[1], which means thrust required is increased by 1.728 times, but energy required is not linearly proportional to thrust required. As a jet engine moves at higher speeds and through less dense air, it's efficiency increases and therefore the power required to produce a unit of thrust decreases. So even though you need 1.728 times the thrust, you need less that 1.728 times the power. Even if it were the same amount of power, at 2.44 times the speed you are only expending that power for 41% of the time, and thus the energy consumption would be 73%.
There are plenty of very valid concerns with regards to the concorde and supersonic transport in general. For starters, you can't simply slap a modern turbofan on there and call it a day, you'd have to sacrifice decades of lessons learned to make high bypass turbofans of the necessary size, so they're still going to be inferior to more refined engines on subsonic aircraft. But the belief that the laws of physics force SSTs to be ridiculous gas guzzlers and no amount of technological refinement can overcome it is misguided at best.
[1] This is actually an oversimplification. Drag does not scale perfectly with qV^2 through the transonic and low supersonic regimes. Wave drag dramatically increases drag close to Mach 1 (which as an aside is the source of the term sound barrier). Wave drag becomes less significant past Mach 1.4 though and by the time you get to supercruise qV^2 is once again a good approximation.