diff --git a/docs/source/user/aerodyn/coordsys.rst b/docs/source/user/aerodyn/coordsys.rst
index ca963548cb..060e480c61 100644
--- a/docs/source/user/aerodyn/coordsys.rst
+++ b/docs/source/user/aerodyn/coordsys.rst
@@ -32,23 +32,11 @@ Hub system (h)
The hub system :math:`(h)` rotates along the :math:`x_h` axis based on the shaft azimuthal position :math:`\psi` (see ElastoDyn documentation).
-Cone system (c)
----------------
-
-The cone system :math:`(c)` is not directly used by AeroDyn (see ElastoDyn documentation).
-
-
-Blade system (b)
-----------------
-
-The blade system :math:`(c)` is not directly used by AeroDyn (see ElastoDyn documentation).
-
-
Polar system (p)
----------------
The polar system :math:`(p_k)` is constructed from the hub coordinate system :math:`(h)`
-by a rotation about the :math:`x_h` axis, which corresponds to the fixed azimuthal offset :math:`psi_{0,k}` of each blade :math:`k` (the blades are distributed evenly across the azimuth).
+by rotating the :math:`x_h` axis by the azimuthal offset of each blade :math:`\psi_{0,k}` (the blades are distributed evenly across the azimuth).
For conciseness we refer to this system as the :math:`(p)` system.
If the number of blade is written :math:`n_B`, the azimuthal offset for blade :math:`k` is:
@@ -58,10 +46,29 @@ If the number of blade is written :math:`n_B`, the azimuthal offset for blade :m
\psi_{0,k} = 2 \pi \frac{k-1}{n_B}
\end{aligned}
-For blade 1, :math:`\psi_{0,1}=0`.
+For blade 1, :math:`\psi_{0,1}=0`, therefore :math:`y_{p,1}=y_h` and :math:`z_{p,1}=z_h`.
The :math:`x_{p,k}` axis is along the hub x-axis.
-The :math:`z_{p,k}` axis would correspond to the :math:`z` axis of the blade if no coning was present.
+
+
+In the absence of coning, the :math:`z_{p,k}` axis corresponds to the :math:`z_{b,k}` axis of the blade.
+
+
+Cone system (c)
+---------------
+
+The cone system :math:`(c)` is obtained from the polar system by a rotation about the :math:`y_{p,k}` axis of each blade :math:`k`.
+See ElastoDyn/FAST8 documentation for more details.
+AeroDyn uses this system to estimate the blade pitch angle (by comparing the :math:`(c)` and :math:`(b)` systems).
+
+
+
+Blade system (b)
+----------------
+
+The blade system :math:`(b)` is otbained from the cone system by a rotation (pitching) about the :math:`z_c` axis.
+It is used to define the location of the aerodynamic center, the local twist of the blade along the span of the blade.
+See :numref:`blade_data_input_file` and :numref:`ad_blade_geom`.
@@ -69,6 +76,8 @@ The :math:`z_{p,k}` axis would correspond to the :math:`z` axis of the blade if
Airfoil system (a)
------------------
+**Currently the user specifies the prebend orientation in the input file and it is used to orient the airfoil** (i.e. the axis :math:`z_a`). In the future, this orientation may be computed automatically from the AC-line.
+
The airfoil section system :math:`(a_{_{kj}})`, or :math:`(a)` for short, is the coordinate system where Blade Element Theory is applied, and where the airfoil shape and polar data are given.
The airfoil coordinate system, :math:`(a_{_{kj}})` is defined for each blade :math:`k` and each blade node :math:`j`.
@@ -78,6 +87,7 @@ The :math:`x_a` axis is normal to chord, towards the suction side (for an asymme
See :numref:`ad_cs_airfoil`.
+
.. _ad_cs_airfoil:
.. figure:: figs/FASTAirfoilSystem.svg
@@ -127,6 +137,7 @@ The :math:`t`-axis corresponds to the :math:`-y_a` axis (opposite direction).
+
Local polar system (l)
----------------------
diff --git a/docs/source/user/aerodyn/figs/FASTAirfoilSystem.svg b/docs/source/user/aerodyn/figs/FASTAirfoilSystem.svg
index f47102b313..5777caa96d 100644
--- a/docs/source/user/aerodyn/figs/FASTAirfoilSystem.svg
+++ b/docs/source/user/aerodyn/figs/FASTAirfoilSystem.svg
@@ -2,8 +2,8 @@
+ originx="56.960193"
+ originy="57.780307" />
@@ -454,7 +454,7 @@
@@ -562,7 +562,7 @@
transform="translate(-117.4793,38.49584)" />