Having imported a 2020 glider into 2024 with an unchanged flight_model.cfg the stall behaviour is very different.
In 2020 the main wing stalls first, loses lift, and the glider pitches forwards, as intended.
In 2024 the Aircraft / Sim Forces look similar in the stall (pic below) but the plane seems stable in the stalled condition and descends surprisingly slowly (like a parachute) with no aileron / elevator authority at all until hitting the ground at a speed I think I’d have walked away from. I’m assuming the new flight model is looking at the vertical airflow passing the control surfaces and deciding they’re not working, but I don’t understand why the aircraft is now stable in the stall condition as opposed to the nose dropping as in MSFS2020.
TBH I don’t know how to interpret the lines on the Aircraft / Sim Forces diagram (any docs for that tool?) but it should be suggesting the glider would pitch down.
Is there a flight_model.cfg setting to ‘force’ the 2020 flight model simulation? That would be the most expedient fix.
Or is there a good explanation of why 2024 is behaving this way but 2020 doesn’t so I might have a better shot at changing the flight_model.cfg for 2024 ?
On a positive note, other 2020 gliders I’ve tested with their 2020 flight models are behaving more-or-less as expected in 2024, so there’s probably something about this wood-and-fabric glider that’s pushing it closer to the edge between the two sims.
The thing that stands out immediately in your screenshot is that the force lines for the tail section do not match the position represented by the 3D model. The geometry parameters appear to be too low and forward from where they should be.
This could have an effect with the new flight model if the more detailed airflow model is having a different effect on these flight surfaces.
The other detail I notice is that the force lines from the fuselage also do not line up with the 3D model, specifically the angle which appears to be moving downward as it approaches aft. This would indicate that the pitch attitude of the 3D model is misaligned.
Perhaps this is intentional but it does complicate the debugging of forces. Correcting the aero geometry would certainly have a large effect on the flight model requiring re-tuning. But this may be a worthwhile effort.
There is definitely something going on in MSFS2024 which is making the stall behaviour slightly different than that in 2020.
If I try I can tiptoe my glider into a wings-level straight-ahead stall (this is kinda normal but is easier in 2024 than 2020) and in MSFS2024 (never MSFS2020) it can end up in a kind of semi-stable flat vertical fall descending relatively slowly, but with none of the controls being able to get it out of the stall. AoA in this stall condition is understandably off the charts at 37 degrees, but stable around there. The correct behaviour is for the plane to relatively sharply drop a wing and you recover from there, this reliably happens in 2020.
I’m assuming the red lines on the forces diagram simply mean the AoA is above the stall value as in the pic below taken with the plane in this flat stall. Someone pls correct me if I’m wrong.
Any idea what is different in MSFS2024 that will provide clues?
I think I’ll be able to change the flight model (so for 2020 & 2024) which will push the performance outside this behaviour in 2024, but my key question is to try and understand what’s different in 2024 - I thought the 2020 package flight model would be the same in 2024.
