Correct, we use the AE2100 - D3
variant. I'd be interested in learning more about the Saab2000's eng management if you have any info.
The "low prop RPM" selection would be for BETA (ground) range? & "high RPM" could be used in both; BETA & ALPHA (flight) range?
. This may take a while, I'll do my best using words.
Like Fred mentioned about the Saab2000s, we also have a similar system - normal ground idle & low speed ground idle (NGI/LSGI). We start them in LSGI which give us a prop RPM (Np) around 72%Np in BETA range.
- in BETA; pwr lever request blade angle.
- in ALPHA; pwr lever request fuel flow (horsepower).
Np - prop RPM
Ng - gas generator (compressor) RPM
BETA range (excluding reverse):
The pitch control unit - PCU, is commanded by the FADEC.
Thottle position inputs (elec signals) to the FADEC will directly control/determine the blade pitch via FADEC output signals to the PCU.
The fuel pump metering unit - FPMU, regulates fuel supply to maintain 99%Np.
There is a high pres pump/overspeed governer - HPP/OSG which has been isolated from the prop control (oil) circuit by the BETA enable valve - GBEV, within the PCU (it's switch is in the throttle quadrant).
Throttle position inputs to the FADEC now directly control/determine FPMU's fuel delivery. The prop HPP/OSG now maintains 100%Np by; regulating the air load (maintaining optimum AOA) on the prop blades.
drive coarse = more load, decrease Np.
drive fine = less load, increase Np.
Try this in a manual car to demonstrate the ALPHA range;
cruise @ a set speed, as you start going up a hill maintain speed with throttle but don't shift down gears = your fuel flow will increase (more fuel req'd to compensate extra load) with speed & eng RPM unchanged. Inverse effect for a decsend.
BETA reverse range:
same as ALPHA range with blades driving fine to increase air load.
hope this clears it up.