Wing area in non-clean configuration

[TheAviationDoctor]

Hi @junzis,

Note: this was previously part two of another question, which I decided to split.

I have a question related to the drag polar script, please.

The drag polar calculations in drag.py make extensive use of the wing area S (as one would expect). Furthermore, as I understand, the values provided in the aircraft data files for S are for a clean configuration (i.e., flaps/slats retracted).

Therefore, I assume that when calculating e.g. delta_cd_gear a takeoff or landing configuration, I would need to add the flaps/slats area to S using the Sf / S ratio. Is that a reasonable assumption?

On that note, I found that, for the B737 family, the flap area is 29-30% of the wing area (source) - mentioning it just in case you would like to consider updating Sf / S accordingly for this type.

Thank you in advance, @junzis.

[junzis]

So, are you suggesting the equation should be Sf / (S+Sf)?
I think in McCormick's book, S represents the reference area, which should be a constant value.