How do I Calculate Aircraft Range

[Mars-Bound Hokie]

Need I say more?

• More below if the answer is "yes."

 

I bet lots of you are curious about how far your planes can go from their starting point when their tanks are full. However, I doubt all of you want to waste time just taking them out for test runs - one plane at a time. This thread is to finally know, once and for all, how to calculate your planes' range?

 

In the spoiler below, you'll find SPH shots of a few of my aircraft - none of which are SSTOs. What bugs me is that the delta-V count for the engines don't really give a clue.

• If they are, then I obviously missed it. Could someone point that out, please?

Spoiler

• Supersonic plane designed to take 20 people very high and fast.

 

• Supersonic one-man jet that can take me around Kerbin's full equator (with some fuel to spare) in less than an hour
  • It's what kicked off the "Around Kerbin in 80 Minutes" challenge, which won me Thread of the Month for January 2020.

 

• Pretty impressive flight time for a small career-beginning plane.

 

All these planes are on my KerbalX

 

I also noticed that the Regional Jet Challenge had the range equation as the following. However, I don't know if it's accurate.

• Speed in this equation is the given cruising speed at the recommended altitude.

 

Is there any way to calculate the range of my aircraft without needing to download any mods? Thank you.

[bewing]

It's not nearly that simple. So the answer really is "no".

A tiny difference in how you fly your plane can make the difference in whether you can't break the sound barrier, or whether your plane will reach mach 2. If your plane is flying fast, it can fly higher. Once you are at nearly max altitude, tiny tweaks in AoA can get you hundreds more meters of altitude at a cost of a few m/s of speed. Or occasionally you can sacrifice a km of altitude to achieve an even higher top speed. Every single one of those actions will change your short-term average fuel burn rate by as much as 30% -- or even more.

Flying a KSP plane to get maximum altitude and speed out of your design will almost always get you maximum range -- but actually doing it in practice is a bit of an art form.

Max range is certainly not a simple formula. You can try plotting it out at various altitudes and speeds, and I think you will get a very interesting graph.

Edited July 20, 2020 by bewing

[Joe Kerbal]

That equation is basically correct. Point is to identify the speed (and altitude) to minimize fuel burn. You could simply decide to measure it yourself deciding a cruise altitude and speed and then sampling your fuel burn rate (checking how much fuel you spend in a minute). You can do that with half fuel load to have an average cost (it probably changes if you are fully loaded or with empty tanks)

Plus I suggest you to check how much fuel you spend to gain cruise altitude and speed and subtract that amount from the fuel you use to calculate range available. Taking off and reaching cruise altitude can be an important part of your fuel cost (expecially in short range flight)