Interpolation of fuel figs
just wondering what method people use for the "interpolation" of fuel figs in flt planning.
Eg if a ac suffers a 4% penalty for every 4000ft below it optimum, and 10% penalty at 8000ft, what would the penalty be at 5200ft below???
iv been trying to factor each one in a table eg
below by / penatly
4000 ...... 4
5000 ...... 6.5
5250 ...... 6.63
5500 ...... 6.75
6000 ...... 7
8000 ...... 10
but im not getting an accurate enough answer, is this the wrong method or just poor exicution of the correct one? any help would be appreciated.