Fuel tank capacity and mass for volume?

[Panel]

Hey

I'm making a part pack with a few 1.875 meter parts, including fuel tanks. However, I can't find anything on how much fuel to add for the volume. Is there a specific set of rules for this, or should I just go with what I feel is balanced? Same with mass. I'm sure there must be some rules for this.

[stupid_chris]

2 hours ago, Panel said:

Hey

I'm making a part pack with a few 1.875 meter parts, including fuel tanks. However, I can't find anything on how much fuel to add for the volume. Is there a specific set of rules for this, or should I just go with what I feel is balanced? Same with mass. I'm sure there must be some rules for this.

you usually set it so that the capacity/mass ratio is always constant. So just set whatever capacity you feel makes sense, then adjust the mass accordingly.

[AndyMt]

Volume is pretty easy, you can calculate this based on dimensions. I would just substract 10-20% for structural things like bulkhead domes etc. But then you have to translate this into "Units" and there I don't recall the factors for LF and Ox. But I have an Excel sheet at home I used to do these calculations. I'll try to remember to post it this evening...

As for the Mass: that's a bit more difficult. You can't just calculate this linear or quad or whatever. It depends on the construction of a tank IRL. But for the stock tanks that is not always the case, so dry mass sometimes is good and sometimes really bad compared to real life...

In my Excel sheet I did some assumptions that resulted in similar figures if you enter the stock 1.25m tanks dimensions, but not for the 2.5m parts.

[Jso]

On 5/8/2016 at 10:38 PM, Panel said:

Hey

I'm making a part pack with a few 1.875 meter parts, including fuel tanks. However, I can't find anything on how much fuel to add for the volume. Is there a specific set of rules for this, or should I just go with what I feel is balanced? Same with mass. I'm sure there must be some rules for this.

BDB uses 87% utilization by volume, 5 liters per fuel unit, and dry mass 1/8 of fuel mass. That balances well with stock.

Calculate the volume of your tank in cubic meters. Take 87% of that and multiply by 1000 for liters. Divide that by 5 for total fuel units. Simplified it's Fuel Units = volume * 0.87 * 1000 / 5 = volume * 174.

Round the fuel units down to the nearest 20, or nearest 100 in bigger tanks to get round numbers when you do the 0.9/1.1 LF/OX split.

Liquid Fuel is Fuel Units / 2 * 0.9

Oxidizer is Fuel Units / 2 * 1.1

Liquid fuel and oxidizer both weigh 0.005 tons per unit, so the fuel mass is Fuel Units * 0.005. Set the mass of the tank to 1/8 of that.

The cost of the tank should include the cost of the fuel. $0.80 per unit for Liquid fuel and $0.18 for Oxidizer. Plus a base cost of around $1000 per dry ton will put you in the right neighborhood.

[AndyMt]

@JSO: thanks a lot ! I'll update my Excel sheet accordingly.