Winglets Flag in flight_model.cfg

[MSFS 2020] Bug Reports
1

Version: *1.36.2.0

Frequency: Consistently

Severity: Low

Context: SDK description incorrect

Bug description: The SDK says that the wing_winglets_flag parameter in the [Airplane Geometry] section of the flight_model.cfg file is a legacy FSX parameter not used in the modern flight model. However, as shown in the attached screenshots, this is incorrect. The only difference in the flight_model.cfg file used in the attached screenshots is whether the wing_winglets_flag is set equal to zero or one.

As can be seen in the drag debug window, there is a term in the “target cd” equation for “wingledcd.” I assume this is supposed to be “wingletcd.” Note that it’s value is zero when the wing_winglet-flag is set to zero, and it is non-zero when the wing_winglet_flag is set to 1.

Also, note that the total drag is actually lower for the non-winglet case than for the winglet case, which is a bit paradoxical.

Repro steps: Establish a steady-state unaccelerated, level, straight flight cruise condition. For the same conditions (weight, speed, altitude, cg, atmospheric parameters, etc.) compare the drag with the wing_winglets_flag set to zero to the drag with the wing_winglets_flag set to 1.

Attachments:

Winglet flag issue
Winglet flag issue1920Ă—1561 294 KB

1 Like
2

Hello @AwarePlot117729

That’s a good point.
Although this parameter is no longer used to specify the wing geometry directly, it is still used to determine if the winglet drag is to be accounted for in the target drag value used in the normalization process.

We will change the documentation accordingly.
Thank you for pointing this out.

Regards,
Sylvain

1 Like
3

Thanks for the response and updating of the documentation. However, your response and the updated documentation confuses me. Your explanation and the updated documentation as well as my findings documented above seem to indicate that adding winglets increases drag. If that were so, winglets would never be used on real airplanes. The purpose of using winglets is to reduce drag by reducing induced drag.

In any case, what is the algorithm or equation that is being used by MSFS to determine the winglet cd increment?