Could this mean for more fuel efficient supersonic commercial cruising?
If so in what ways would it need to be modified and how possible is this?
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3$\begingroup$ There is a lot more to supersonic cruising than just the engine... $\endgroup$– Ron BeyerCommented Mar 2, 2017 at 3:30
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$\begingroup$ I know but it is a part of it and the question stands @ron beyer $\endgroup$– SRawesCommented Mar 2, 2017 at 19:27
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2 Answers
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According to Wikipedia the J58 is comparable to the Rolls-Royce/Snecma Olympus 593 that powered the Concorde, so yes it's possible.
Will it be efficient? The Olympus 593 was as efficient as can be, even by today's standards:
The Concorde cruised at Mach 2.05 with its engines giving a SFC of 1.195 lb/(lbf·h); this is equivalent to a SFC of 0.51 lb/(lbf·h) for an aircraft flying at Mach 0.85, which would be better than even modern engines; the Olympus 593 was the world's most efficient jet engine. However, Concorde ultimately has a heavier airframe and, due to being supersonic, is less aerodynamically efficient, i.e., the lift to drag ratio is far lower. In general the total fuel burn of a complete aircraft is of far more importance to the customer.
It's not just the engine that makes an aircraft efficient, as the paragraph above highlights. The amount of fuel the Concorde burnt for 100 passengers is the same for 700 passengers on two Jumbo Jets.
As I highlighted here, even if fuel is cheap, or the ticket price covers the fuel cost, propulsive efficiency isn't the whole story. The Concorde wasn't retired because of fuel. I'm mentioning the Concorde because of its very efficient engines and supersonic regime.
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$\begingroup$ This was an interesting read. $\endgroup$– user9394Commented Mar 8, 2017 at 15:13
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I would like to complement @ymb1's answer by adding that a major part of the aerodynamic drag, in the case of the Concorde, was due to the generation of its massive shock wave. Hence, the relative inefficiency despite having highly efficient engines.
Commercial operation usually calls for larger aircraft in order to benefit from economies of scale. But larger aircraft also generate powerful shock waves that we have yet to deal with.
I would recommend reading the following paper for addition information on the subject
History and economics of, and prospect for, commercial supersonic transport
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$\begingroup$ "Commercial operation usually calls for larger aircraft in order to benefit from economies of scale." That's an over-simplification. Sales of the A380 are super-sluggish, for example. $\endgroup$ Commented Mar 8, 2017 at 13:52
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$\begingroup$ And the scaling laws mean it's not actually true. Larger aircraft have more absolute drag, but the drag-to-payload ratio (which is what actually matters) might easily be better. $\endgroup$ Commented Mar 9, 2017 at 19:23