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Faster? It’s gotten slower! Significantly slower. Haven’t you noticed that modern jetliners don’t really even have swept back wings any more? The sweet spot for fuel efficiency is around 530mph for modern, very high bypass turbofan engines. In the 60’s, turbojet 707’s and DC8’s regularly flew at >600 mph. Gas was 25c a gallon.

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What modern jetliners are you referring to? the 787 has a sweep back of 32 degrees and a 707 had a sweep back of 35 degrees so not really that much difference. The 737 has a sweep back of 25 degrees and it first flew in the 1960s.

OK, but how is it that jet engines haven't become more fuel efficient since the 60s. Cars certainly have.

They have. But drag is drag and the price of fuel is the price of fuel. Drag increasing at higher speed means your fuel usage grows geometrically with speed. Slower is more efficient (to an extent, slower means higher angle-of-attack to maintain lift so your drag will start going up again if you get slow enough). No matter how efficient the engines get drag remains the same and going faster will still cost more. Engine efficiency just goes into reducing operating costs instead of travel times now.

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