ferram4 changed the topic of #RO to: Welcome to the discussion channel for the Realism Overhaul (meta)mod for KSP! Realism Overhaul Main Thread https://goo.gl/wH7Dzb ! RO Spreadsheet http://goo.gl/Oem3g0 ! Code of Conduct http://goo.gl/wOSv2M ! | Maximal & soundnfury's RP-1 Race Into Space Signup: http://bit.ly/2DEVm2i [15:01] <soundnfury> Straight Eight Stronk (and) RP-0/1 is basically "Space Agency Spreadsheet Simulator"
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<awang>
Starwaster: Wasn't utilization defaulted to 86% or something?
<soundnfury>
awang: yep and I think the point it changed was when NK added Tank-I, Tank-II etc. The util goes up as you advance
<Starwaster>
awang I think at one point it was, yes. might not have been in the TANK nodes though but int he parent TANK_DEFINITION.... I can't remember
<Starwaster>
I'm not even sure what file(s) that was done in so I'm not sure where to check the history
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<confusedcam>
how does a 5.5 O/F ratio = 0.7454/ 0.2546? looking at the RO config for HG3.
<Starwaster>
confusedcam, 5.5 refers to a mass ratio
<Starwaster>
5.5 kg of O2 to 1 kg of H2
<Starwaster>
however, the engine configs use a volume ratio
<confusedcam>
but the 27ah
<confusedcam>
that's what i was missing.
<Starwaster>
yeah
<Starwaster>
it's a serious PITA when you're writing multiple engine configs
<Starwaster>
I use a spreadsheet to calculate that shit for me
<confusedcam>
because i have a source that says the hg3 used 5 as the mixture ratio
<Starwaster>
btw the ratios in the engien config don't have to add up to 1
<confusedcam>
why is that?
<Starwaster>
because they get normalized in the engine code
<Starwaster>
for instance, 16.10445 (H2) + 5.5 (O2) is essentially the same as .7454 - .2546
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<Starwaster>
or for methane requiring a 3.8 O/F ratio I use 1 (CH4) - 1.417456617 (O2)
<Starwaster>
it's just whatever's convenient in making the calculation... but for readability sake it's easier on other people's eyes if you normalize it yourself in the config
<confusedcam>
hmm, i think i understand, thanks
<Starwaster>
btw, you will see other sources cite 2.2 - 3.0 for methane; I used 3.8 because that's what SpaceX says they are using in the Raptor
<Starwaster>
I think the various optimized ratios actually depend on what kind of chamber pressure and temperature the engine is designed for...? Raptor should be fairly advanced so I guess they can get away with 3.8
<confusedcam>
Starwaster so i'm confused(zzz) i can't figure out how to convert it and calculate the percentage, i keep getting different answers (but not .7454) :-( thanks.
<Starwaster>
confusedcam first find the densities of the propellants involved. Take the actual resource density as defined in CRP which may differ from real life (due to being rounded)
<Starwaster>
and here's where I like to start with a ratio of 1 for the fuel (since the oxidizer has the higher mass ratio)
<Starwaster>
find the density for H2 and multiply that by 5.5 Divide the result by the mass of O2 and that is going to bhe the volume ratio for O2
<Starwaster>
if you want to normalize them, divide each one (F or O) by the sum of F + O. That's the normalized volume ratio for each one
<Starwaster>
to simplify that a bit, give the fuel a volume ratio of 1. Then give the oxidizer volume ratio of ((fuel density * mix ratio) / oxidizer density)
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