CL-alpha troubles

[MSFS 2020] Questions & Community Discussions
1

The current FM allows to define a CL-alpha curve consisting of (according to the documentation) of no less than 47 points. However, most devs agree that the CL-alpha curve is built from only 2-3 values.

This is an issue, because now there is no way to define the curvature between AOA=0 and AOA=max. Some CL-alpha lines are practically straight in real-life, but still curved in MSFS. The CLmax achieved is often substantially different from the values entered (stall debug window). The subsequent appearance of the Stalldef parameters allows some tweaking at the upper end. Unfortunately, this is a mathematical approach rather than a physical. The parameter such as StallDef_CurvePower and StallDef_EndRatio are not commonly understood. Not to mention the clcd_normalization_aoa_deg_high thing.

Once a more-or-less suitable CL-alpha curve is finally achieved, matters get worse when setting flaps. In particular the ‘incidence’ parameter in its own right can totally disrupt the achieved CL-alpha curves. In some cases the CLmax with flaps down ends up LOWER than without flaps, just to match the incidence value!! Which it hardly ever does BTW.

So now we have around 10 parameters, that we don’t fully understand and an endless trial-and-error and no good final result.

Asobo can we PLEASE PLEASE PLEASE have CL-alpha tables for each individual flap and slat setting?

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2

I second that. A great option would be a set of 2d lift carpet (Cl-aoa-mach) for each slats config.
Flaps would be a geometric transform of these curves (offset in CL, AOA and scalar)

3

I agree with the issues… My request would be for a bit more explicit documentation of what the stall and flap parameters do to both the lift and drag properties, particularly with respect to speed and/or AoA.

I spend a huge amount of time tweaking those parameters for glider flaps (i.e. WEEKS) where it’s essential to accurately control the lift AND the drag lift/drag equates to the glide ratio which is the dominant aerodynamic property required in gliders. In gliders setting flaps to operate accurately for both lift and drag requires an additional layer of real-time flight model adjustment via coding (you can tune overall drag in real time by moving the spoilers 0…3% and hiding that in the instruments/animations). This is mostly a non-issue for power planes unless you turn the engines off on the approach, and simple plates stuck out into the atmosphere seem ‘good enough’ - the new flap parameters improve things but the impact isn’t entirely clear.

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4

Same request on ground effect in Cl. It turns out it takes the max value and apply some undocumented function to decrease it with height/span ratio