Extending Jet atmCurves for thicker atmospheres

[Gordon Fecyk]

[11 SEP 2017] I started a new GitHub repository that contains the Excel sheet and Module Manager patches.

With Tellumo introduced in Galileo's planet pack, the idea of using stock jet engines to escape Tellumo's immense sea level pressures came to mind. I originally wanted to see how my Explodium Engines parts should behave with the thicker air of Eve, but Tellumo and the Advanced Jet Engines add-on let me investigate and test the idea.

At least under AJE, jet engines have considerably more thrust in thicker air at the expense of ridiculous fuel consumption. If you wanted to use AJE and GPP together, you could experience this on Tellumo right now. But what about stock jets with stock aerodynamics? This is where extending the atmCurve float curves for jets come in.

After recording stationary thrust values for the AJE versions of the stock engines all the way up to 12 kg/m³ air density, I found the stationary thrust curves for those, then extended atmCurves to match. This zip file (274 KB) contains Module Manager patches for the stock jets, an Excel sheet with graphs (no macros, promise), and hacked testing craft that suspend engines on launch clamps as high as 20 km up. Please take a look at these.

As far as I can tell, the stock jets will continue to behave normally on Kerbin, Gael or Laythe where the air doesn't exceed 1 kg/m³ by much. Maybe you'd get a slight boost since Kerbin sea level is around 1.14 and the curves are extended beyond 1.0, but flying anywhere above 300 m should be normal. Go to Tellumo or any other world with densities beyond 2 though, and see if the engines rip your craft apart Wile E Coyote style.

I'm stuck on the tangent values for the float curves though. I have no idea what these values should be in order to straighten out the curves. Some of them are OK, some of them are a little wavy. But they're not exact matches for the Excel graphs.

Edited September 12, 2017 by Gordon Fecyk
Linked to new repository

[Benjamin Kerman]

Looks pretty cool. Probaby helpful for anyone using GPP, maybe we should ping @Galileo. Like, if he wanted to include them in the next release?  

Edited September 11, 2017 by Benjamin Kerman

[Gordon Fecyk]

Something came to mind after I rested on this project. The atmCurves are supposed to be percentage of maxThrust per density according to the ModuleEngines API. But I'm wondering if I should have based my percentages on thrust at 1 kg/m³ on Tellumo and not 1 kg/m³ on Kerbin. The pressures and temperatures were different, and AJE takes these into account where the stock jets do not.

The raw data is in the Excel sheet if anyone else wants to take a look until I get home.

Also I don't believe these patches should be specific to GPP as other planet packs might have high density oxygen atmosphere worlds, but they're not really enough to be an add-on release on their own. Maybe these could go into the Module Manager patches thread? They will go into Explodium Breathing Engines though, once finalized. I'd even be OK with Squad adding them to stock, since the extensions shouldn't affect stock jet behaviour on Kerbin or Laythe.

Edited September 11, 2017 by Gordon Fecyk
Grammar

[JadeOfMaar]

Since the idea for this thread was proposed I've entertained the idea of bundling it. Your efforts would (and there may be some irony here) finally help the Tellumo Space Program to take off.  

I say that like Firespitter carried by part mods, this could be a bundle for all planet mods to carry. The ones that ideally have an oxygenated giant planet and reinvent the stock solar system.

10 hours ago, Benjamin Kerman said:

Looks pretty cool. Probaby helpful for anyone using GPP, maybe we should ping @Galileo. Like, if he wanted to include them in the next release?  

@OhioBob and I are the ones to directly address this for GPP. (But of course, the final say is Galileo's)

Edited September 11, 2017 by JadeOfMaar

[Gordon Fecyk]

All right, I replaced the spreadsheet in the zip download with an updated version. That version uses the thrust at 1.03 kg/m³ at Tellumo as a baseline to get what the thrust would be at 1.0, and then recalculates the curves based on that for each engine. The end result is a much closer match to the stock curves at Kerbin up to 1.0. I haven't yet updated the Module Manager patches; that will come later tonight. I think I can also create a GitHub repository for this and make a 'modlet' available. Assume ARR for now, but I'll likely release it under an MIT license.

All of the curves share a similar characteristic in that they remain linear and have great performance improvements from about 0.5 through 1.4, then start flattening out near 2.0. They continue linearly from there, all the way up to 12.0. The Wheesley seems to benefit the most from higher densities, where it starts to flatten out between 5 and 6. The Goliath suffers the most, flattening out at about 1.1. The Panther in wet mode isn't much better at 1.4, but makes up for it in dry mode at 2.0.

[Update] The zip file now includes the updated patches. And if you want to try playing from Tellumo, here's an experimental Tellumo Space Program configuration. (14 KB ZIP) The zip also includes a modified Kerbal X rocket that uses Goliath engines as the first stage. You can get to orbit with this, barely. Watch the fuel tank levels; stage away the Goliaths when the NCS adapters run out, then stage away the Reliants when their tanks run out. I'll leave the gravity turn as an exercise for you.

Edited September 12, 2017 by Gordon Fecyk
Added notes to new repository and updated ZIP