Adding the option to *not* use the local WingXSec frame

[willjrh]

Hi Peter,

I have found myself defining wings where using the local frame (think Wing._compute_frame_of_WingXSec) causes undesired effects when visualizing a wing with the Wing.draw method. When looking at things like blended wing bodies, I have found it can be challenging to use a local reference frame.

Just wondered if you have any advice, perhaps this is just a poor definition on my part.

I can stop this happening if I add something like this to enforce using a 'global' frame, with some use_global_frame bool:

if self.use_global_frame:
            xg_local = np.array([1,0,0])
            yg_local = np.array([0,1,0])
            zg_local = np.array([0,0,1])

within the Wing._compute_frame_of_WingXSec method (and still rotating with the twist angle):

# Twist the reference frame by the WingXSec twist angle
        rot = np.rotation_matrix_3D(self.xsecs[index].twist * pi / 180, yg_local)
        xg_local = rot @ xg_local
        zg_local = rot @ zg_local

Interested to hear your thoughts/implications of using a modification such as above.

Thanks!
Will