Hypersonic Flight?

[Orbital_Decay]

Is it possible to obtain hypersonic flight in KSP? The highest airspeed I've achieved with an airplane yet was somewhere around Mach 4, but can you go any higher?

Edited June 28, 2020 by Orbital_Decay

[Streetwind]

The problem with hypersonic flight in KSP is that Mach 6.5 is orbital velocity on Kerbin.

On Earth, orbital velocity is roughly Mach 25. So it makes sense to think "what if we could fly at Mach 6". But in KSP, it doesn't. If you try, you just end up in orbit.

[jimmymcgoochie]

It’s very hard to fly that fast in a plane in KSP for a few reasons: you’re getting close to orbital velocity (hence why SSTO spaceplanes are feasible) so the plane will naturally want to climb into the upper atmosphere where its engines will run out of air and flame out; most engines and almost all air intakes can’t operate effectively at such high speeds and the few that can (Whiplash and Rapier) aren’t very fuel efficient; you run a significant risk of overheating at lower altitudes; and flying higher to get thinner air means the engines don’t get nearly as much thrust so while cruising at high speed is possible and indeed very fuel efficient, it’s much harder to accelerate than when you’re at lower altitude.
Rather than trying to push towards Mach 5, it’s easier to build a plane that is very stable and can cruise efficiently at around Mach 3 (1km/s or so) and just use physics warp at x2-x4 to get where you’re going sooner.

The fastest sustained flight I’ve done recently was 1400m/s, but that required a couple of mod parts and was on the verge of overheating for a lot of its flight time.