I have a question about stock cfg files and part mass

[Jesusthebird]

so I started to poke around in the cfg files just for giggles and ive notice something. 

C:\Program Files (x86)\Steam\steamapps\common\Kerbal Space Program\GameData\Squad\Parts\FuelTank\adapterTanks

im running 1.3.1, stock install. if you open up the mk3-size2 for example. note the mass. (1.79)

now open up mk3-shuttleadapter. and again note the mass. (0.7)

start ksp and compare notes.

in game -->shuttleadapter mass: 0.7

in game --> mk3-size2 mass: 14.29

this cant be the only discrepancy like this too. anyone got any ideas?

 

a quick install of KER confirms mass is 14.29kg for the size2 adapter

Edited November 27, 2017 by Jesusthebird
update

[MiffedStarfish]

I don’t think it’s just mass. I made a duplicate ion engine and upped the thrust to 40000, but it’s ended up showing in game as around 41150.

[Jesusthebird]

2 minutes ago, MiffedStarfish said:

I don’t think it’s just mass. I made a duplicate ion engine and upped the thrust to 40000, but it’s ended up showing in game as around 41150.

i also noted that when I changed propellant ratios for an engine say..the mainsail. it didnt seem to transfer over. i tried reducing the mainsails propellant requirements by half, but..nothing seemed to change

[KerikBalm]

43 minutes ago, Jesusthebird said:

im running 1.3.1, stock install. if you open up the mk3-size2 for example. note the mass. (1.79)

now open up mk3-shuttleadapter. and again note the mass. (0.7)

start ksp and compare notes.

in game -->shuttleadapter mass: 0.7

in game --> mk3-size2 mass: 14.29

this cant be the only discrepancy like this too. anyone got any ideas?

The in game mass includes the stored fuel, the mass in the .cfg file is the dry mass.

mk3-size 2: dry mass: 1.79, but also contains 1125 LF and 1375 Oxidizer. Both have a density of 0.005. So 0.005 * (1125+ 1375) = 12.5. 12.5 + 1.79 = 14.29

When all the fuel is gone this part will mass 1.79 tons, but when it is full its 14.29 tons.

Shuttle adapter: Dry mass = 0.7, but it contains no fuel, so it stays at 0.7 tons (so why is it in the fuel tank folder? who knows  )

 

Edited November 27, 2017 by KerikBalm

[Laie]

1 hour ago, Jesusthebird said:

i also noted that when I changed propellant ratios for an engine say..the mainsail. it didnt seem to transfer over. i tried reducing the mainsails propellant requirements by half, but..nothing seemed to change

You probaby touched the wrong place. The total amount of propellant/second is computed fom thrust and ISP. If you want your engine to use more or less fuel, you have to tweak either of those two.

The propellant ratios is just the mixture ratio, typically 11 units of oxidizer for 9 units of fuel. You can change that all you want, it won't affect the total propellant flow. Only the proportion of how much will be which propellant (you can make engines use three, four, N propellants if you like).

[Jesusthebird]

8 hours ago, KerikBalm said:

The in game mass includes the stored fuel, the mass in the .cfg file is the dry mass.

mk3-size 2: dry mass: 1.79, but also contains 1125 LF and 1375 Oxidizer. Both have a density of 0.005. So 0.005 * (1125+ 1375) = 12.5. 12.5 + 1.79 = 14.29

When all the fuel is gone this part will mass 1.79 tons, but when it is full its 14.29 tons.

Shuttle adapter: Dry mass = 0.7, but it contains no fuel, so it stays at 0.7 tons (so why is it in the fuel tank folder? who knows  )

 

Thank you. Exactly  i wanted to hear

 

7 hours ago, Laie said:

You probaby touched the wrong place. The total amount of propellant/second is computed fom thrust and ISP. If you want your engine to use more or less fuel, you have to tweak either of those two.

The propellant ratios is just the mixture ratio, typically 11 units of oxidizer for 9 units of fuel. You can change that all you want, it won't affect the total propellant flow. Only the proportion of how much will be which propellant (you can make engines use three, four, N propellants if you like).

I noticed that same ratio. 1.1 to .9 . I was thinking halfing those values would half the resource intake. So .9 would becomes .45 and 1.1 would become .55. But alas...what setting would  i change then? I couldn't find an isp setting. Does anyone know how  i can change it? Thx you guys!

[Corona688]

11 minutes ago, Jesusthebird said:

I couldn't find an isp setting. Does anyone know how  i can change it? Thx you guys!

I will note that I discovered recently that the mainsail is horrible for modding.  It uses an ancient config file syntax, plus bits of newer syntax which don't actually work, so its very hard to tell which parts of the config file do anything and which parts are just there.  I think they left it as-is

 

Try modding the ant engine.

Edited November 27, 2017 by Corona688
I was wrong!

[OhioBob]

23 minutes ago, Jesusthebird said:

I couldn't find an isp setting. Does anyone know how  i can change it? Thx you guys!

Isp is obtained from atmosphereCurve.  Here's and example from the Mainsail:

		atmosphereCurve
		{
			key = 0 310
			key = 1 285
			key = 9 0.001
		}

The first number is the atmospheric pressure (in atmospheres), and the second is the Isp.  So the Mainsail's vacuum Isp is 310, at 1 atm it is 285, and it goes to nearly zero at 9 atm.
 

Edited November 27, 2017 by OhioBob

[OhioBob]

6 minutes ago, Corona688 said:

The game has to compute it.  Its definition is thrust over fuel consumption.  An engine which delivers twice the thrust for the same fuel will have double the ISP, etc.

The configs files give maxThrust and atmosphereCurve.  AtmosphereCurve gives the specific impulse, and maxThrust is the thrust in a vacuum.  The fuel flow rate at the 100% throttle setting is computed from maxThrust and the vacuum Isp.  At other pressures the thrust is computed from the fuel flow rate (adjusted according to throttle setting) and the Isp obtained from atmosphereCurve.

[Corona688]

3 minutes ago, OhioBob said:

The configs files give maxThrust and atmosphereCurve.  AtmosphereCurve gives the specific impulse, and maxThrust is the thrust in a vacuum.  The fuel flow rate at the 100% throttle setting is computed from maxThrust and the vacuum Isp.  At other pressures the thrust is computed from the fuel flow rate (adjusted according to throttle setting) and the Isp obtained from atmosphereCurve.

You're too fast for me.  I edited myself when someone walked in and proved me wrong.  Sorry!

BUT

Since ISP is related to fuel consumption, that may be where you need to change that.  Change the ISP, change the fuel consumption.

Edited November 27, 2017 by Corona688

[Jesusthebird]

Thanks . very helpful!

[Ultimate Steve]

Once I gave an engine 9999999... gimbal range but it rounded up to 100000..... Probably not related, but in case it is...