[HELP!] Calculate ATM ISP and ATM Thrust?

[Xyphos]

I got an engine part via

PartLoader.LoadedPartsList

now I know how to get the thrust and ISP info, but I want to know how do I compute the atmospheric ISP and atmospheric thrust.

 

I assume I use the atmCurve node and use the key that has an index of 1, then use the second number as a multiplier?

what's the third and fourth numbers for?

[HebaruSan]

Check how KER does it:

• https://github.com/CYBUTEK/KerbalEngineer/blob/master/KerbalEngineer/VesselSimulator/EngineSim.cs#L125-L127

They get the atmospheric Isp from the atmosphereCurve, using the pressure in units of Earth atmospheres (so 0 is space and 1 is sea level):

• https://github.com/CYBUTEK/KerbalEngineer/blob/master/KerbalEngineer/VesselSimulator/SimManager.cs#L370

The Isp times 9.81 m/s/s gives you the exhaust velocity, and you can multiply that by the "flow rate" at which the exhaust leaves the engine to get the thrust:

• https://github.com/CYBUTEK/KerbalEngineer/blob/master/KerbalEngineer/VesselSimulator/EngineSim.cs#L292-L295
• https://github.com/CYBUTEK/KerbalEngineer/blob/master/KerbalEngineer/VesselSimulator/EngineSim.cs#L259-L280

I have not bothered to look up what Mathf.Lerp does yet.

[Xyphos]

This man is a legend. ---^

five for five. thanks.

[HebaruSan]

10 minutes ago, Xyphos said:

This man is a legend. ---^

five for five. thanks.

I have to admit I'm curious what you're working on! Something to do with part cost and atmospheric thrust/Isp, which has a toolbar button and is localized. This is like playing a programming version of Twenty Questions.

[Xyphos]

13 minutes ago, HebaruSan said:

I have to admit I'm curious what you're working on! Something to do with part cost and atmospheric thrust/Isp, which has a toolbar button and is localized. This is like playing a programming version of Twenty Questions.

I'm attempting to convert Gary Court's optimal rocket calculator to an in-game version.
Gary's json/javascript code has all the data embedded, but only for stock parts. I wanna go beyond that and have every part, stock and mod included without needing external configs.

also, I forgot KER had a part simulator, so now I have to scrap my current test version and start over using parts of KER code.

[Xyphos]

but my next question will be GUI related; all those part options surely will need a scrolling window pane. while I'm confidant in my C# skills, I've very little experience in developing KSP plugins, and KSP's API is huge and fairly cryptic.

[Aelfhe1m]

1 hour ago, Xyphos said:

but my next question will be GUI related

 

[HebaruSan]

2 hours ago, Xyphos said:

I'm attempting to convert Gary Court's optimal rocket calculator to an in-game version.

Cool! If I may make a suggestion, both that tool and KER commit what I consider a design error by making the atmospheric flag all-or-nothing for all stages in a craft, whereas the atmospheric values are important for the first 3 km/s or so, and vacuum thereafter. Especially if you're going to try to auto-generate whole craft, it would be good to be able to place vacuum engines on upper stages but not lower. I tried to address this in SmartTank by making the atmosphere flag toggleable per-stage, but that may not work for you if your mod is also generating all the stages.

[Xyphos]

3 minutes ago, HebaruSan said:

Cool! If I may make a suggestion, both that tool and KER commit what I consider a design error by making the atmospheric flag all-or-nothing for all stages in a craft, whereas the atmospheric values are important for the first 3 km/s or so, and vacuum thereafter. Especially if you're going to try to auto-generate whole craft, it would be good to be able to place vacuum engines on upper stages but not lower. I tried to address this in SmartTank by making the atmosphere flag toggleable per-stage, but that may not work for you if your mod is also generating all the stages.

great ideas. I'll try to incorporate them, but I'm still working out the details.
edit: with some math work, it could be possible to simulate the atmosphere pressure at each stage.... but first, I am gonna make the all-or-nothing as the basis for the mod, then further develop it to full feature

Edited July 12, 2017 by Xyphos

[Starwaster]

23 hours ago, Xyphos said:

what's the third and fourth numbers for?

Although not relevant to your current situation (which you seem to have under control) the third and fourth numbers are used ONLY to control the shape of the curve and can make transitions from one point to another more abrupt or more curvier. You only need to mess with them when creating a new curve. They're optional parameters but not using them can result in undesired behavior. Read more about them here:

http://forum.kerbalspaceprogram.com/index.php?/topic/84201-info-ksp-floatcurves-and-you-the-magic-of-tangents/

Handy curve editor here:

http://forum.kerbalspaceprogram.com/threads/83246

[Xyphos]

Thanks for the clarification, @Starwaster - it's appreciated.

23 hours ago, HebaruSan said:

I have not bothered to look up what Mathf.Lerp does yet.

Lerp performs Linear Interpolation. I checked.