ISP from different engines

[Fri3s3N]

Alright. Let me make on thing clear. I know how to calculate delta v. I have the math done and burned into my head. But I cam across a problem, how do I get the ISP, for different engines on the same stage? So say if I have a "MainSail" and a "Thud" sharing the same fuel on the same stage, how to I get the ISP to put into my formula?

[Green Baron]

http://wiki.kerbalspaceprogram.com/wiki/Cheat_sheet

Look for: Isp = ( F1 + F2 + ... ) / ( ( F1 / Isp1 ) + ( F2 / Isp2 ) + ... )

 

It's a long time since i last used the cheat sheet :-)

Edit: just saw this has allreday been answered in your thread in Gameplay-Questions ... nevermind

Edited June 13, 2016 by Green Baron

[DDE]

I guess you need to use the arithmetic average weighted by fuel consumption.