Air-breathing engines, fuel consumption and Dv

[Zatnikitelman]

For my next addon, I'll be using air-breathing jet engines to assist the vehicle's initial ascent. I was wondering if there was a simple(r) way of calculating how much fuel the engines use for a given ascent say from 0-11km at a given constant speed and constant ascent rate and once at 11km how fast they can accelerate the vehicle for a given amount of fuel to determine if I should cut in the rockets at altitude, or run on the jets for a while.
I've looked over the equations in the SDK Guide and haven't been able to make the connections yet.
Any help is appreciated,
Thanks,
Zat

 

[Urwumpe]

For my next addon, I'll be using air-breathing jet engines to assist the vehicle's initial ascent. I was wondering if there was a simple(r) way of calculating how much fuel the engines use for a given ascent say from 0-11km at a given constant speed and constant ascent rate and once at 11km how fast they can accelerate the vehicle for a given amount of fuel to determine if I should cut in the rockets at altitude, or run on the jets for a while.

Did you already read the introduction from NASA?

http://www.grc.nasa.gov/WWW/K-12/airplane/bgp.html

Maybe this page especially interests you:

http://www.grc.nasa.gov/WWW/K-12/airplane/turbfan.html