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Subsonic aircraft have blunt noses, while supersonic have sharp. As speed increases we want a sharp nose, but then why do spacecraft (hypersonics) have blunt noses again?
The physics of flight change when aircraft break the sound barrier.
Below the speed of sound, blunt noses have the least drag. Above the speed of sound sharp noses have the least drag because of the presence of a shock wave. A sharp nose makes it easier and cheaper to fly at supersonic speeds. However, the faster a plane goes after passing the sound barrier, the hotter it gets. That’s why many of the fastest airplanes, like the SR-71 Blackbird, are made out of titanium. Titanium won’t melt or deform at the speeds the SR-71 reaches.
If the SR-71 went as fast as a spacecraft, it would get even hotter and the titanium wouldn’t be able to stand the heat. By having a blunt nose, spacecraft make a type of shock wave called a bow shock wave. Bow shock waves actually start in front of the spacecraft and never actually touch it. That keeps the spacecraft from getting as hot as it would with a sharp nose. Using a blunt nose does require more fuel and money, so engineers only do it because they have to.
