I have a propeller configured correctly with power absorb scalar to make the prop spin at idle at 1220 RPMs with a shaft torque force of 141 ft-lbs.. (idle), then at full thrust under ISA conditions it spins at 2000 RPM just as POH and gives the correct trust and power to take off, maintain speed, etc., all matches all works.. important to note, this is NOT using legacy tables.
However as soon as I enable PROP MODERN, the configurations goes high-wired:
prop_mod_use_absorbed_torque = 0;
This results in wrong RPMs at idle again.. it drops from 1220 RPM to almost half, is like the power absorb scalars get totally ignored in favour of something else.. nothing I could do to influence this unless you spool the engine to the wrong N1 at idle or wrong torque at idle.
So I set it as prop_mod_use_absorbed_torque = 0.. which takes me to problem 2.
prop_mod_use_absorbed_torque = 1
This keeps the correct idle torque of 141 ft-lbs, correct N1 and correct 1220 RPMs on prop, however it seems at the same time the power absorb formulas goes wrong because I end up with a propeller creating a very heavy thrust on idle (450 lbs NEW vs 180 - 200 lbs old).. causing the airplane to over taxi fairly quick!. and then at full power drops, the thrust falls too much. (losing about 300lbs of force vs non modern) making the aircraft unable to take off using the POH runway length, so clearly, the thrust goes wrong under this circumstances.
I tried altering all the PROP_MOD values to correct this issue to no availability, the only thing that helped a bit was was changing the prop_mod_aspect_ratio from 6 to 4.8 to generate more torque at the end of the curve and decrease the the prop_mod_lift_slope_cf to reduce a bit the idle thrust speed, however I could not generate more thrust at full power (969 ft-lbs as per POH), So it seems I am unable to balance the curve out with the old curve.. not matter what I tried, it seems the power absorb is calculated automatically somehow making it impossible to have the correct idle RPM vs thrust at high power.
Can we have more detail about how power absorb is calculated with the prop modern formulas and what can be used to influence it? the only solution I have so far is to reset power_propeller_absorbed_cf back to 1.0 (from 0.42 as I need it), which then returns the full power of the propeller under modern flight model, but I lose the required 1220 idle RPM speed with the required idle torque and idle N1.
Yes more, if you enable CFD + Re-inject rotors.. then the propeller lose even more thrust.. up to 200 to 250 lbs more.. why is this? how Re-inject rotors affects turbo prop performance?
I want to use Prop modern, but quiet frankly after 2 weeks of no sleep trying to tweak it, I am about to give it and leave it all legacy.. there must be something I am doing wrong, we should be able to tweak these values much easier and to control results better for sure.
I am able to tweak piston engine +prop modern fairly quick, but with TurboProps, the absorved torque is causing misbehaviour that I cannot understand or control.
Thanks in advance for the time to read this question and any insight that could be provided.