I'd like to open a quick discussion about the FADEC here as I strongly believe the current response is incorrect (since V1.0 even) - this also explains why many people complained that taxiing was difficult. I want to make it clear that I am NOT talking about the response SPEED of the engines, as I see no issues with that.
I did a lot of research into EPR FADEC systems and how engines with EPR as primary parameter respond. As you know, the EPR is not a linear function and you've modeled it correctly. However, where the mistake is, is that the throttle COMMAND is linear at the moment. Thus at lower N1s the response will be extremely sensitive due to EPR not changing that much, wheras at high N1 the response will be unresponsive due to EPR changing a lot - and indeed this is what happens in the TFDi 717.
Now lets look at some information:
in a classic airplane without FADEC, the response of the engine's N1 to the throttle command is fairly linear - this is good because it makes setting the power fairly easy to do, without thinking. The engine speed is fairly proportional to throttle lever. This can be observed in Flight simulator add-ons as well, I will name a few that I have experience with:
- Leonardo FlyTheMaddog, all versions from FS9 to the latest FlyTheMaddog
- Coolsky DC9/Super 80 series
- Any stock FSX/P3D aircraft
- Captain Sim 727/737/707
Now lets look at FADEC airplanes in the simulator. The throttle command "bug" does not move linearly with the throttles, but moves using the same response curve as EPR. Why? To preserve the correct throttle response, while still having the advantages of FADEC control on an engine with EPR as its primary control valve (such as these RR's). Thus, the N1 response stays linear, and the EPR throttle command moves only slightly at low positions, and more at high positions. Lets throw some examples here of again aircraft, that I have personal experience with.
- PMDG MD-11, Pratt and Whitney engines
- PMDG 747 QOTSII Pratt and Whitney or Rolls Royce engines
- FSLabs A320 - IAE V2500 engines
- Aerosoft A320 - IAE V2500 engines
- Captain Sim 757 V3 - Both engine types
In all these aircraft, FADEC is modelled, and the EPR bug/engine response moves how I describe. N1 response is linear, even though EPR is the primary control parameter. This allows fine control of engine power throughout all power levels. I've also asked a contact of mine who pilots A320 as captain aircraft a while back who confirmed this behavior is correct, to maintain control over the engines without difficulty.
In conclusion, asumming you have correctly modelled the FADEC to have the engines followed the EPR command, I believe the FADEC's EPR command should be modified to be on the same curve as the EPR indication (as its custom coded, the default P3D one is totally wrong).
I will probably making a video soon describing this behavior and demonstrating the issue exactly - I would also suggest asking your 717 pilots about this, as I would find it extremely odd if the 717 is the only airplane which had such a imprecise control system.
Please let me know if you need any further info or clarifications. I really like the 717, and I'd love for this to be solved as its one of the very last gripes I have with the aircraft.