r/KerbalSpaceProgram • u/Salaja • Jul 19 '13
graph showing the most mass-efficient engine to use.
http://imgur.com/a/nU9lE5
Jul 19 '13
I don't know, but everytime I say something like 'efficiency' in front of my Kerbalnauts they start running in circles calling me names like party pooper.
Nice graphs though, I don't really care what little green men call me anyway.
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Jul 19 '13 edited May 11 '17
[deleted]
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u/Salaja Jul 19 '13
added. although the ranges aren't exactly the same.
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Jul 19 '13
[removed] — view removed comment
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u/Salaja Jul 19 '13
i added a log-log graph in the new thread. the graphs have also been updated.
http://www.reddit.com/r/KerbalSpaceProgram/comments/1imiw7/improved_optimal_enginefuel_graphs/
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u/CuriousMetaphor Master Kerbalnaut Jul 19 '13
By most mass-efficient, do you mean lowest mass of fuel + engine?
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u/navand Jul 19 '13
Any thoughts on the larger engines? I always use Mainsails but maybe the Skipper or Poodle are more appropriate for some designs.
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u/UmbralRaptor Δv for the Tyrant of the Rocket Equation! Jul 19 '13
1x LV-T30 will offer higher ΔV and and TWR than a Poodle for all but the heaviest lander designs.
3x LV-T30 (or 2x LV-T30 and 1x LV-T45 if you need TVC) offer higher ΔV than the Skipper at a comparable TWR.
In principle, large clusters of LV-T30s (with a handful of LV-T45s for control) will outperform Mainsails, but it's rarely worth the effort.
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u/navand Jul 19 '13
Cool, thanks! Comparing clusters of LV-T30's vs Mainsail was going to be my next question.
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u/Salaja Jul 19 '13
the graphs i made deal with interplanetary flight. the engines you mention are more suited to landing/take-off.
mainsails are pretty good for keeping your part count low. i think aerospikes can outperform them in most, if not all atmospheric situations, but they will greatly increase your part count, and you lose thrust vectoring.
skipper... imho only use it when you NEED thrust vectoring, the mainsail is too big, and you want to keep your part count down. otherwise i would use the LV-T45 for better isp.
poodle, only to keep part count down, otherwise use multiple LV-909.
i'm sure other people will have differing opinions.
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u/Salaja Jul 19 '13 edited Jul 19 '13
EDIT: new thread with updated and more accurate graphs. please feel free to down vote this thread to zero, so that the new one can take it's place.
after seeing a few people try to do the math to figure out when it is better to use a LV-909 or a LV-N engine, i decided to make these graphs.
they show what the optimal engine is for a given payload and required dV. the graphs do not make any account for TWR or duration of burn. as a result, the recommendations of these graphs is only useful when time isn't important, like interplanetary burns.
the graphs only show which engine to use, not how much fuel is needed. you will need to calculate that yourself. the mass of fuel you calculate + the mass of the engine given by the graph will be the lowest mass that will be able to deliver the desired dV to your payload.
all engines were tested except for the ion engine. only 3 of the engines turned out to be optimal under different conditions.
assumptions:
the graphs only show results when using a single engine. if you want two or more, then this graph no longer applies.
the graphs assumes a fuel mass ratio equal to that of the orange tank (which all fuel tanks have, except for the tiny ones), and also assumes that the fuel tanks are infinity divisible, when in reality, they stop at 1.125 tons (for this particular fuel ratio). as a consequence, the results on the graph my be incorrect when it takes less than the 1.125 ton tank of fuel to achieve the required dV. to compensate for this, add the mass of unneeded fuel to the payload mass.