A NACA duct is simply a duct designed to draw air into itself without creating a load of turbulence behind the duct. I does this because the divergent part of the duct creates a lower pressure zone into which the surrounding air is drawn. NACA ducts are used on all sorts of aircraft for all sorts of reasons. You can even see them on light aircraft to draw air into the cockpit for ventilation.
go to extreme lengths to maximise thrust and minimise fuel burn which is why GE
use NACA ducts and other companies such as Rolls Royce simply hang the sensors out in the breeze.
The EEC (electronic engine control) uses T12 temperature and P25 pressure sensors to work out the MASS of air entering the engine. It uses air mass to calculate how much fuel the fuel control unit sprays into the combustion chamber. The fuel control unit is called a HMU on a CF6-80C2 (hydro mechanical unit) Note. T12 and P25 are not the only sensors that the EEC uses.
Incidentally, It's called a T12 sensor because it is fitted in staion (location) 1.2
Station 1.2 is fwd of the LP
compressor, station 2.5 is between the LP
is measured at the compressor discharge, T4
.9 (EGT) is measured between the HP
The generator is cooled primarily by a fuel/oil cooler which heats the fuel going to the HMU but it has a air/oil cooler which provides additional cooling at low power settings (low fuel flow). The air/oil cooler takes its air from the bypass duct aft of the fan. Some engines do use air to cool the EEC but I don't recall it being cooled on the CF6-80C2. It is on the RB211