Only radial burning enabled on hybrid class #801

The "only_radial_burning" parameter was added and set as default on the hybrid class. Also, the description of the new parameter was updated and 2 coments about derivatives set to zero were added.

Author: caioessouza

rocketpy/motors/hybrid_motor.py

@@ -203,6 +203,7 @@ def __init__(  # pylint: disable=too-many-arguments
         reshape_thrust_curve=False,
         interpolation_method="linear",
         coordinate_system_orientation="nozzle_to_combustion_chamber",
+        only_radial_burn=True,
     ):
         """Initialize Motor class, process thrust curve and geometrical
         parameters and store results.
@@ -346,6 +347,7 @@ class Function. Thrust units are Newtons.
             reshape_thrust_curve,
             interpolation_method,
             coordinate_system_orientation,
+            only_radial_burn,
         )
 
         self.positioned_tanks = self.liquid.positioned_tanks

rocketpy/motors/solid_motor.py

@@ -302,7 +302,7 @@ class Function. Thrust units are Newtons.
             "nozzle_to_combustion_chamber".
         only_radial_burn : boolean, optional
             If True, inhibits the grain from burning axially, only computing
-            radial burn. Otherwise, if False, allows the grain to also burn
+            radial burn. If False, allows the grain to also burn
             axially. May be useful for axially inhibited grains or hybrid motors.
             Default is False.
 
@@ -492,7 +492,7 @@ def geometry_dot(t, y):
                 burn_area = 2 * np.pi * (grain_inner_radius * grain_height)
 
                 grain_inner_radius_derivative = -volume_diff / burn_area
-                grain_height_derivative = 0
+                grain_height_derivative = 0  # Set to zero to disable axial burning
 
             else:
                 burn_area = (
@@ -528,6 +528,7 @@ def geometry_jacobian(t, y):
                 inner_radius_derivative_wrt_height = 0
                 height_derivative_wrt_inner_radius = 0
                 height_derivative_wrt_height = 0
+                # Height is a constant, so all the derivatives with respect to it are set to zero
 
                 return [
                     [