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MSFS Which MSFS flight_model.cfg parameters affect the sharpness of the stall (modern_fm = 1)?

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236
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unitedkingdom
Has anyone worked on the stall in the MSFS modern_fm=1 flight model? The guidelines in the SDK seem to say for modern_fm=1 your alpha/Cl curve works from zero A0A up to the stall but MSFS works out the rest from the dimensions (?).

My issue is my aircraft stall is too aggressive and loses aileron control very quickly in the stall (drops a wing) so a really positive stick-forward recovery is required. The plane is 1950's, no flaps, and stalls at ~30 knots and the real aircraft recovers quite easily unless you abuse it.

Any ideas which MSFS modern_fm=1 flight_model.cfg parameter would most affect this behaviour?
 

Lagaffe

Resource contributor
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726
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france
No idea but a very good question which interest me for a current development ;)
 
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938
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australia
aero_center_lift is very important. Changing this parameter by even a few centimetres has a big effect. Note that the wing_pos_apex_lon parameter which you might use to set the wing position is no longer used if you are using the aero_center_lift and have compute_aero_center set to zero.

lift_coef_aoa_table only works up to the stall angle so you only really need to set the stall AOA with that table.

There is a new stall debug panel in dev mode which you should need.

There's also a handful of new stall parameters which are very handy for controlling stall behaviour. But I can't find them just now. I don't think they are in the SDK docs yet. I saw them on the devsupport forum. I will keep looking.
 
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938
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australia
Here are the new stall parameters (refer to the C172 to see them in context):


Also the three presspt_fwd_Alpha parameters will adjust the aero_center_lift and thus the stall behaviour at AOA = zero, AOA = stall and AOA above stall. Use these in conjunction with the stall debug window to get a better understanding of what they do.

The add incidence and add twist stall parameters can affect how much wing drop you get. For example, a negative value for Stall_AileronAddIncidence can make incipient stalls more fun (where if you are dropping the left wing at stall adding more right aileron makes the wing drop even worse)
 
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unitedkingdom
wow thanks Anthony that information is pure gold. I've been poking around in the dark for a couple of hours and you've just switched the light on. A blending of the Cessna 172 entries and the expected SDK docs entries added here:
Code:
; =========================
; Stall properties
; =========================

presspt_fwd_Alpha0_pMAC = 0.0               ; Forward offset of pressure center of the wing at AoA 0. Ratio of local Mean Aerodynamic Chord. -ve is aft.
presspt_fwd_AlphaStall_pMAC = 0.1           ; Forward offset of pressure center of the wing at stall AoA. Ratio of local MAC. -ve is aft.
presspt_fwd_AlphaHiStall_pMAC = -0.25       ; Forward offset of pressure center of the wing high above the stall AoA (during a stall). Ratio of local MAC. -ve is aft.

StallDef_StartRatio         = 0.9           ; [0.9] Ratio of the stall AoA when the airflow will start detaching from the wing.
StallDef_EndRatio           = 1.4           ; [1.1] Ratio of the stall AoA when the airflow will be fully detached from the wing.
StallDef_CurvePower         = 1.1           ; [8.0] Power of the ratio curve controlling airflow detaching start to end.
StallDef_minTransition      = 0.025         ; [0.025] Radians. Min angle between stall AoA detach start to fully detached.
StallDef_airflowdetachspeed = 10            ; [1] ratios/sec. Speed airflow will be detaching.
StallDef_airflowattachspeed = 10            ; [1] ratios/sec. Speed airflow will be attaching.
Stall_AileronAddIncidence   = 1             ; [0] degrees. Added to the stall AoA at the ailerons.
Stall_TipAddIncidence       = 2.0           ; [2] degrees. Added to stall AoA at wingtips.
Stall_TipAddTwist           = 5             ; [2.5] degrees. Virtual added twist to reduce stall at wing root.
Stall_TipTwistScaleRatio    = 1.0           ; [0.9]. Scale of the virtual added wing twist.
 
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italy
There are few items with a big difference against default values: how they impact the stall behaviour?
 
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unitedkingdom
basically the idea with my figures (vs defaults) was to spread the stall out across a broader AoA range (0.9 to 1.4 of the stall AoA) making the stall less sudden / more gentle on a 1950's ASK7 training glider. Before these new params the plane (all planes?) defaulted to quite a sharp stall transition.
 
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