I understand the SR-71 had to deal with a lot of issues in order to keep its speed (special fuel which leaked on the runway, titanium fuselage and probably other stuff). But wouldn’t the same type of engine be able to power a relatively slower fighter jet capable of easily cruise at match 2-2.5, so it doesn’t have to deal with so much friction as the SR-71 at match 3.
But while the engines exist since the 1960s, relatively few fighters go faster than match 2 and it took all the way to the 21st century to have fighters capable of supercruise (and still below match 2). So I guess there has to be a reason for that.
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If you look up the top speed of 1st, 2nd, 3rd, 4th and 5th gen fighters you’ll notice a trend. Let’s say for example, for each respective generation:
F-86, F-104, F-14, F-16 and F-35 for the USA
MiG-15, MiG-21, MiG-29, Su-27, Su-57 for the USSR/Russia
You’ll notice that as the years progress, fighters got faster, but somewhere in the 80s to 90s this trend reversed. We’re seeing a slight decrease in the top speed of fighter jets now. This is because missile technology had evolved so far that speed and altitude no longer guarantee immunity. With the relatively slow and short range missiles of the 60s it was feasible for an aircraft to deplete their energy enough to outrun them, using only sheer speed. Though not a fighter, this is what the SR-71 was built for. It flew too high and too fast for soviet missiles of the time. However, the missiles of today are capable of shooting down satellites, and have ranges in the hundreds of kilometers. The new defense against them is stealth, not speed. That’s what we’re seeing with 5th gen. It’s just no longer advantageous to build big, heavy and expensive engines for Mach 3 and above.
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