Dear IPACS team,
The fixed pitch prop piston engine physics have quite some flaws in AFS2. It was already the case in AFS1 and I remember Joachim wasn't totally happy with his DR400 model having a strong tendency to over-rev (fortunately enough the real Robin isn't by far as touchy).
First of all, whatever the altitude the engine seems to output the same power. I know mixture isn't implemented yet, but even with an auto-mixture it would never be the case with an atmospheric engine. Throttle must then be reduced down to some 40-45% in level flight, even when cruising at 12'000ft, while IRL you'll need almost full throttle to keep level (no talk about leaning mixture).
But the weirdest behaviour is probably at takeoff roll, with what seems to be a significant prop drag increase (and resulting RPM drop) when the aircraft starts to roll, compared to full power applied on brakes (stopped aircraft).
RPM is a figure you systematically check at takeoff to ensure power is and keeps available.
In a real DR400-140b (I've flown quite a few of them by now), when applying full throttle with this engine and propeller you'll ensure you read at least 2'300rpm (depending on density altitude). As the aircraft gains speed it slowly increases up to some 2'400 rpm.
In AFS2, I get >2'600rpm (over-rev) at full throttle on the brakes, and it suddenly drops to some 2'300rpm as the aircraft heaves into motion. It progressively rises back to some 2'400 rpm as the aircraft gains speed.
I tried adjusting some prop and engine values, I got some improvement at take-off roll, but worsened level cruise behaviour as a result.
Looking at the C172 tmd, I saw this was tweaked by setting a slightly variable pitch propeller...
Now that the Q400 is released, are there plans to improve fixed pitch propeller + piston engine behaviour?
Cheers
Antoine
EDIT : corrected claimed rpm values after repeating test with the original converted DR400 files