# local_stability_axes¶

Rotates the body axes onto stability axes. This rotation is equivalent to the projection of a vector in S onto B.

The stability axes are defined as:

• x_s: parallel to the free stream

• z_s: perpendicular to the free stream and part of the plane formed by the local chord and the vertical body axis z_b.

• y_s: completes the set

param dir_urel

Unit vector in the direction of the free stream velocity expressed in B frame.

type dir_urel

np.array

param dir_chord

Unit vector in the direction of the local chord expressed in B frame.

type dir_chord

np.array

returns

Rotation matrix from B to S, equivalent to the projection matrix $$C^{BS}$$ that projects a vector from S onto B.

rtype

np.array