B737 Cg/mac?
 

Good afternoon,

I'm interested to know a bit more about CG/MAC as it is used on the B737. First off, how is the figure calculated? Does it go straight from the loadsheet into the FMC? By inputting the CG/MAC % into the FMC does it then calculate all takeoff/cruise/landing trim settings automatically or do these figures still need to be manually calculated? Last question, is CG/MAC basically the same thing? Is it still generally known as a MAC on the B737 or CG? (I know it’s stated as CRZ CG on the PERF INIT page).

Any help would be greatly appreciated!

Cheers
BAe 146

(a) CG and MAC are the same thing looked at in a slightly different way.

CG is the distance of the Centre of Mass from a datum position nominated for the measurement of fore and aft distances (arms).

(percentage of) MAC is the distance of the Centre of Mass from the leading edge of the (theoretical) MAC (mean aerodynamic chord) expressed as a percentage of the length of the MAC.

(b) if the CG (or %MAC) is entered into the sums, the FMC may be able better to optimise some calculations for which CG is relevant.