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[0.21.1] StretchyTanks v0.2.2 (updated 8-26-13)

AncientGammoner

By AncientGammoner
in KSP1 Mod Releases

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Jahulath

Jahulath

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Textures. You can definitely make working high poly stretchy tanks but the textures are collected and applied by the plugin not the .MU so whatever you make is only going to look horrible unless you overwrite the originals (Nathan, I haven't read through your amendments but I suspect you just appended extra textures yeah?) and even then you have to copy the same 2 texture layout as the original. It's a bit of a shame really but I have no idea where to start in C - is there even a "contains" function one could apply to an array of possible textures rather than the if equals it uses now? It is so tempting to experiment with just removing that whole section just to see how the .mu copes with foraging it's own textures up...

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Starwaster

Starwaster

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Oh, right. It expects a certain transform hierarchy, sorry. Well, if it scaled at the model node, rather than the actual mesh, that might help?

Can't get it to work no matter where I try applying the scaling. The part looks normal in the parts list in the editor in that the module displays stretchy tank usage (under the description) but once placed, it displays no information when moused over and cannot be scaled. If MFT is also present, the tank can't be edited either. Guessing that error in the log is more serious than I thought. Have to look at it later.

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Jahulath

Jahulath

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One of my plans is to change it so all texture info is read from a cfg, to avoid just that.

Yeah, just remove the whole section and models will use the textures they were designed for.

Well that could be interesting... I'm pretty useless at C# (or any programming language really) but I can read through and generally know what is going on so I'll have a play and see what I come up with - and then not release it because it's AG's gig and we can't be jumping about on his toes like this, it feels rude :P .

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Herra Tohtori

Herra Tohtori

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I was trying to make an Apollo style CSM spacecraft with internal structure and separate fuel and oxidizer tanks (I'll leave to your imagination what I could do with such a spacecraft - for example, if I were to hide some decouplers under one of the oxygen tanks...), but I couldn't get enough fuel and oxidizer to physically fit. After a bit of confusion I realized that using separate LF and oxidizer tanks makes the tanks much less dense for some reason, so no wonder I was having tank volume problems. Combined LF/OX tanks are about three times heavier than a liquid fuel or oxidizer tank of same dimensions.

I read through the thread and noticed that it is apparently a feature by design, rather than a bug. And I can sort of understand doing it to avoid making aircraft even more fuel-efficient than they already are.

However this doesn't really make much sense, to be honest. There's only one fuel type in the game and it's most likely some equivalent of kerosene; Jet A and RP-1 are not fundamentally that much different in physical or energy density. Even more strangely, oxidizer seems to be also affected by this seemingly arbitrary compression, but not nearly as much as the Liquid Fuel tanks...

Even worse still, the independent LF and oxidizer tanks actually have a worse fuel fraction than the combined tank, which means if you wanted to have your fuel and oxidizer in different tanks, you're taking ridiculous weight penalty. That means there's strong incentive to never use the Oxidizer tanks at all, since you would only need them if you have separate Liquid Fuel tanks.

Pictured below is the extent of how much this is not making sense:

l3o0.png

Both fuel tank arrangements have about the same amount of LF and oxidizer.

However the separate tanks require almost three times the space, and the combination of the two tank types ends up having about 78% more dry mass than the integrated LF/OX tank.

If this mod gets updated at some point, I would request the author to consider making the amount of fuel or oxidizer more directly related to the volume of the container.

If there actually was more fuel types supported (in stock game) it would make sense to have LH2 tanks have different properties than RP-1 tanks - they would be much more voluminous due to low density of hydrogen.

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Starwaster

Starwaster

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I was trying to make an Apollo style CSM spacecraft with internal structure and separate fuel and oxidizer tanks (I'll leave to your imagination what I could do with such a spacecraft - for example, if I were to hide some decouplers under one of the oxygen tanks...), but I couldn't get enough fuel and oxidizer to physically fit. After a bit of confusion I realized that using separate LF and oxidizer tanks makes the tanks much less dense for some reason, so no wonder I was having tank volume problems. Combined LF/OX tanks are about three times heavier than a liquid fuel or oxidizer tank of same dimensions.

I read through the thread and noticed that it is apparently a feature by design, rather than a bug. And I can sort of understand doing it to avoid making aircraft even more fuel-efficient than they already are.

However this doesn't really make much sense, to be honest. There's only one fuel type in the game and it's most likely some equivalent of kerosene; Jet A and RP-1 are not fundamentally that much different in physical or energy density. Even more strangely, oxidizer seems to be also affected by this seemingly arbitrary compression, but not nearly as much as the Liquid Fuel tanks...

Even worse still, the independent LF and oxidizer tanks actually have a worse fuel fraction than the combined tank, which means if you wanted to have your fuel and oxidizer in different tanks, you're taking ridiculous weight penalty. That means there's strong incentive to never use the Oxidizer tanks at all, since you would only need them if you have separate Liquid Fuel tanks.

Pictured below is the extent of how much this is not making sense:

Both fuel tank arrangements have about the same amount of LF and oxidizer.

However the separate tanks require almost three times the space, and the combination of the two tank types ends up having about 78% more dry mass than the integrated LF/OX tank.

If this mod gets updated at some point, I would request the author to consider making the amount of fuel or oxidizer more directly related to the volume of the container.

If there actually was more fuel types supported (in stock game) it would make sense to have LH2 tanks have different properties than RP-1 tanks - they would be much more voluminous due to low density of hydrogen.

It's not likely to change either, certainly not in the official release.

I suggest that you get ModularFuelTanks. StretchyTanks has compatibility files zipped up somewhere in the StretchyTanks folder. If you do, also get my mass fix from my signature and you should also get my StretchyTank patch or NathanKell's. (his not only incorporates my fix but has other enhancements as well). (actually the mass fix file might not be necessary anymore. I know it's not in the new version of MFT)

If you do that you'll be able to configure separate LF / OX tanks though frankly, MFT is designed to let you configure a singular tank with multiple tank types, but that's apparently not your intent :)

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Starwaster

Starwaster

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It would be nice to have an optional lighter dry mass version to go with http://forum.kerbalspaceprogram.com/threads/52882-0-22-Kerbal-Isp-Difficulty-Scaler-v1-2. I don't know the specific numbers but maybe someone else can find them.

I could be wrong but I think the problem described there is less to do with tank mass than it is to do with the engines. Also, when I was working on an alternate set of Real Fuels configs for Modular Fuels, I did some serious number crunching using the Space Shuttle's main fuel tank as a baseline and the tank masses seem reasonably close enough to me. As it turns out I was only unnecessarily duplicating the efforts of others who had gone before me.

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Starwaster

Starwaster

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Huh, I'd like to see those figures--everything I've found points to needing to reduce tank mass to 1/3 what it is.

Actually we should probably dispense with them since the Shuttle's external tank was a lot more sophisticated than just a couple of fuel tanks inside a metal skin.

The numbers work more or less for Modular Fuels cryogenic tank especially since the H2 tank is getting a mass discount.

They don't work for the default tank.

The page he linked to specifically mentioned the Saturn V first stage so I just got done hunting down some numbers for that.

This is what I have for the S-1C FUEL TANK ONLY! (this is metric. I had to do the conversion myself since all the documents are in pounds. but I think they're correct)

RP-1 mass: 622.43559 tons

tank dry mass: 10.90 tons

This is a stock stretchy which uses KSPs default mass values. LiquidFuel (this is basically RP-1 for anyone else paying attention)

wet mass: 82.463 tons

dry mass: 10.91801

So dry mass is pretty close to where I want it to be.

Fuel mass is off by quite a bit. But it's even more off than my worst case scenario.

That's a mass ratio (tank only keep in mind) of 0.0175 for the Saturn V first stage

In KSP that's about 0.1324

Nathan, would you mind double checking my fuel mass? That's 203,000 gallons of RP-1. I gotta run now.

One caveat though is that there's additional overhead for the tank base mass that I didn't take into account. If we get rid of the basemass then it improves a bit to 0.106 which is still off by a factor of 10

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NathanKell

NathanKell

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Haven't checked those figures (they sound right) but I did some basic guesstimates when considering that KSP tanks are not actually tanks, they're stages with tanks inside.

So, let's talk about the Titan I (the kerolox version) and its first stage.

I figure as one of the first missiles, and not a tank-is-skin job like the Atlas (that to this day has one of the best dry:wet ratios ever), it's a good minimum baseline. In addition, it's nice because it has not much in the way of thrust plates or heavy interstages or guidance, and it's easy to see on a cutaway that the fuel tanks take up most of the internal volume of the stage.

I come up with:


		Diam	Height	Mass	Fmass	Ehgt	Emass	Enum	Vol	Dry Mass Mass/KSPVol	Mratio (dry:dry+fuel)
Titan I-1	3.05	16	4	72.2	3.13	0.84	2	86.7	2.32	0.000133757	0.030446194
Fake TI-1	1.95	10.24	1.13	22.16	2.00	0.28	2	21.7	0.57	0.000132367	0.024607888

The fake Titan I uses the 64% rescales (real:KSP), and a rescale of 1/3 on engine mass (close to .64^3). Its dry mass is slightly lower to account for a 0.4t decoupler.

Note that the volume ratio is about 1/4.7 stock (stock is 0.000625, or 1/1600), and the mass ratio is about 1/4.5 stock (stock is 0.11111, or 1/9).

If the tanks were just tanks, as you say, rather than 2 tanks + outer skin + misc structural mass, then it does seem reasonable the ratios would be off by a factor of 10, not ~5.

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Starwaster

Starwaster

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Yes. And shortly I'll release an update of my patch that works better with MFS and finally only sends message to MFS, it doesn't store anything itself, as AG wished.

That being the case I'll take mine down or replace it with a link to yours.

Been meaning to do that for a while anyway.

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Starwaster

Starwaster

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What do I need to do? Just edit the config files for career mode?

Ah I forgot about Career mode. (haven't had a chance to even really play with it myself)

It works fine in Sandbox and yeah you'll have to edit the parts to add them to career mode. Strange, for some reason I thought someone might have posted some config files for them but I guess not.

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NathanKell

NathanKell

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So, I haven't tested it on linux, and I haven't played career mode yet (anyone want to suggest some nodes?)

But here is my updated StretchySRB patch. If you want to use it with Modular Fuels, you need v3 of MFSC or above (posting simultaneously), and you need to have the Modular Fuels patch cfg from the original ST extracted, so the modules are applied.

MAKE SURE that if you still have a StretchyTanks_modularFuelTanks.cfg file hanging around ANYWHERE, that you delete it BEFORE applying this patch!

https://www.dropbox.com/s/q6c7qdk7fnkihyn/StretchySRB.zip

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