I think it might be a bit more complicated than that. On my plane (not a hawker) we burn 50lbs/h more for an increase in temp over ISA of 10 degrees (and 50lbs/h less when its ISA -10). So you would think that the most fuel efficient for us at the same mach is when its ISA minus a lot. But thats for the same MACH number and TAS obviously varies with temp so there's a bit of swings and roundabouts going on. I don't think ISA makes a busting lot of difference to our specific fuel burn (ie the amount of fuel we burn per nautical mile). You get more power when its cold because there's a bit more air (so you climb better) and you therefore get to a height where you have a lower fuel burn more quickly.
there are many variables. I think its a difficult equation.
Last edited by tommoutrie; 23rd Jan 2013 at 18:49.
Reason: I'm thick and can't write grammatically correct sentences