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Kerbal Experiment


Crimson_Pride14
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Well since we now have Isp\'s for engines, decided to see just how well the game models engine performance by seeing how well it can calculate Delta-V. (I know you coulda found Isp previously but I didn\'t feel like it lol) Only thing we need to know is the density of the fuel, since the tanks give it in volume. So did a test stand firing to figure out the mass of the fuel.

Screenshots of initial conditions:

screenshot16.png

screenshot17.png

Test Fire: (Patsey is a champ)

screenshot18.png

Results:

screenshot19.png

So did a little math. Note that we now know the mass flow rate as well.

KerbalStats.png

So the engine should put out about 2193 m/s of delta-V. Let\'s test that.

Orbital Firing:

screenshot20.png

screenshot22.png

screenshot23.png

So the actual delta-V from the start of firing to the end was about 2253 m/s. So the error is about 3%, and I\'m willing to chalk that up to velocity change due to carry over from the orbital path since it wasn\'t even close to circular. Even so still within 10%, so I\'ll go ahead and say that the computer model is very good at modeling theoretical performance in a vacuum. Don\'t really feel like doing it for atmospheric as well so just gonna leave it haha. Sorry if someone has already done all this, I as bored and thought it would be fun to test it. Yea, I am an aerospace engineer so I find nerdy things fun. :P

Interesting to note that the flow rate changes in a vacuum, so they must have kept thrust constant and changed flow rate as Isp changes. Opposite of what it really should do. Means burns in a vacuum will be longer than in atmosphere as well. Interesting indeed!

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Or you could just just subtract the dry mass by the full mass and you will get fuel mass?

You should be able to do all ALL rocket equations without doing a test fire.

Of course you are able to do maths without ever having seen a rocket.

The point is verifying the theoretical results with an actual flight test...

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There is a known bug in fuel usage in v0.16 that might account for the 3% difference you\'re detecting.

In any case, your maths looks sound and the final result is close to expected. Tick from me. :)

Oh yea, I forgot about that bug. Could very well be what caused the error. Would that explain the flow rate change though?

Or you could just just subtract the dry mass by the full mass and you will get fuel mass?

You should be able to do all ALL rocket equations without doing a test fire.

Yea I could have, but where is the fun in that? Always better to get real world results anyway.

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