Lift-independent drag coefficient attributable to flaps

[TheAviationDoctor]

Hi @junzis,

Note: this post initially contained two questions, until I decided to move the second question to its own post.

OpenAP is amazing work. I have a question related to the drag polar script, please.

Table 3 and equations 24-25 of Sun et al. (2020) refer to δf as the flap deflection in degrees. The drag.py script also calls for the flap_angle argument to be passed in degrees.

However, the script then converts degrees to radians in the last line of the delta_cd_flap calculation:

delta_cd_flap = (
            lambda_f
            * (cfc) ** 1.38
            * (SfS)
            * self.np.sin(flap_angle * self.np.pi / 180) ** 2
        )

I just wanted to confirm that this is intentional, since equations 24-25 do not reflect the conversion to radian ( δf * π / 180). Assuming a flap deflection angle of 10°, and using Cf/C and Sf/S values for the A320neo (and using a λf of .9 for slotted flaps), I get a value of .0004 if converting δf to radians, which looks small for the drag generated by 10° flaps, and an order of magnitude smaller than if I leave δf in degrees (.004).

Thank you in advance, @junzis.

[junzis]

@TheAviationDoctor, thanks for the comment.
That's correct. For scientific notation, the angles are usually written in degrees for the better understanding. For computers, it always takes the radians as input.