Use Xfoil polars to calculate c_l, c_d and steering tether forces

[1-Bart-1]

In order to make the kps4_3l accurate without having to fly a real kite, the Xfoil.jl package should be used to find lift and drag coefficients for different aoa and different steering amounts.

[ufechner7]

Sounds good to me. Suggested input:

• one .dat file for the foil shape in the middle of the kite, stored in the data dir
  Generated:
• one .yaml file containing all the lift and drag coefficients for different aoa and flap angles, stored in the data dir

Format of the .dat file, describing the wing shape:
1.0000 0.0013
0.9500 0.0114
0.9000 0.0208
0.8000 0.0375
0.7000 0.0518
...
@1-Bart-1 What is the name and unit of the first and second column? And why not using a .csv file?

[1-Bart-1]

If you look here for example:
http://airfoiltools.com/airfoil/details?airfoil=naca0006-il
.dat files seem to be the standard for wing profiles. So I want to stick to the standard. Left is x coordinates, right is y coordinates. Unit does not matter: the profile is normalized so that x is between 0 and 1.

[ufechner7]

OK, just document somewhere the definition of this file format, for example by using this link: https://m-selig.ae.illinois.edu/ads.html

[ufechner7]

Additional remark: The .yaml file with the polars should NOT be in git, but added to .gitignore. It should be autogenerated when the .dat file changes. And are the polars not only valid for a curtain Raynauds number?

[1-Bart-1]

Yes, the polars depend on the Reynolds number. Paul Thedens told me they use re=18e6 for their kites at SkySails Power, and they use the following formula to calculate it:

[1-Bart-1]

I have changed to using a .csv file for the polars, because it is better suited for the tabular data.

[1-Bart-1]

Better explanation of Re formula here: https://en.wikipedia.org/wiki/Reynolds_number#Flow_around_airfoils
Another thing I am not sure about is how to take the aspect ratio of the wing into account: is this already taken into account because the Reynolds number depends on the chord length?

[1-Bart-1]

Solved with ufechner7/KiteUtils.jl#58