seeking equations for calculating maximum energy/fuel usage for part

[TheAlmightyOS]

I am attempting to calculate, given fuel mass, ratio, atmospheric curve and anything else that may be a factor, what the maximum fuel consumption p/sec of an engine would be. I have looked around the forum and used my best google fu, but all I could come up with is calculators for getting into space and docking and such, nothing for use in building a part from scratch.

Does anyone know where I could find these equations?

[Diazo]

Umm, fuel consumption is a flat rate calculation. According to the wiki it is ISP = ThrustInNewtons / FuelPerSec

So, for a mainsail in vacuum which has an ISP of 320 and a max thrust of 1500, at max throttle that would be 4.6875 units of fuel per second.

The issue would be what is your current ISP as you ascend? The Mainsail starts at ISP of 270 at sea level on Kerbin I believe. I'm not sure on the math to adjust for the changing ISP as you climb.

(Numbers from memory, but pretty sure the equation is right.)

D.

[TheAlmightyOS]

Thank you for the reply.

So THRUST/ISP=FPS

I suppose I am asking the wrong question then which would explain why I haven't been able to find anything. I need a way to calculate ISP. Right now I am just adjusting my part and my new resource and reloading the db over and over again to try and figure out how to make the part more balanced. Getting tired of doing that (and being I have four other engines to do this with) I want to figure out a way to calculate it. Especially atmospheric curve.

EDIT: And found. Thank you for your help. You pointed me in the right direction.

Well, no that doesn't get me what I need... so close.

To figure out the ISP, you need the Fuel Consumption, which I need to know how to calculate given the information within the cfg files. All I have is the MaxThrust, Propellant Ratio, the atmosphereCurve and the propellant density.

Edited August 25, 2014 by TheAlmightyOS

[NathanKell]

thrust / ISP / 9.82 (KSP uses that as g0, not 9.80665...) = fuel consumption in tons/sec (requestedmass)

that is apportioned as follows:

compute the mass ratio of the propellents as:

totalmass = propellant_1.density * propellant_1.ratio + propellant_2.density * propellant_2.mass +....

then find multiplier as requestedmass / totalmass

then for each propellant remove multiplier * propellant.ratio / (sum_of_all_ratios) units

The key step you're missing is the conversion between fuel flow (in tons/sec) and propellant units, and to convert you need to look at the resources' densities and at the ratios in the ModuleEngine.PROPELLANT nodes.

[TheAlmightyOS]

Thank you for the information. I am afraid I am still no closer to figuring this out despite both of you giving me very good information.

I think I am trying to edit too many things at once: the engine, generator and the resource are all being tweaked at the same time. The only constant is the max-thrust I want to achieve for this particular engine: 1000

It is compounded by the fact that the resource I am trying to use varies wildly in density depending on how it is produced. I do not know what it should be and have been experimenting. So I am trying different densities and at the same time messing with the ratio on the engine and the generator. I want to plug it all into an excel sheet but I think even that won't help. I need to just settle on a mass for the resource then edit the engine and generator around that.

Thanks for all the info. It will come in handy once I figure out my resource.