ENH: adds new stability margin methods to flight

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- ENH: Add new stability margin properties to Flight class [#572](https://github.com/RocketPy-Team/RocketPy/pull/572)
 - ENH: adds `Function.remove_outliers` method [#554](https://github.com/RocketPy-Team/RocketPy/pull/554)
 
 ### Changed

rocketpy/simulation/flight.py

@@ -426,6 +426,10 @@ class Flight:
         Rocket's static margin during flight in calibers.
     Flight.stability_margin : Function
             Rocket's stability margin during flight, in calibers.
+    Flight.initial_stability_margin : float
+        Rocket's initial stability margin in calibers.
+    Flight.out_of_rail_stability_margin : float
+        Rocket's stability margin in calibers when it leaves the rail.
     Flight.stream_velocity_x : Function
         Freestream velocity x (East) component, in m/s, as a function of
         time. Can be called or accessed as array.
@@ -2426,6 +2430,26 @@ def min_stability_margin(self):
         """Minimum stability margin."""
         return self.stability_margin(self.min_stability_margin_time)
 
+    @property
+    def initial_stability_margin(self):
+        """Stability margin at time 0.
+
+        Returns
+        -------
+        float
+        """
+        return self.stability_margin(self.time[0])
+
+    @property
+    def out_of_rail_stability_margin(self):
+        """Stability margin at the time the rocket leaves the rail.
+
+        Returns
+        -------
+        float
+        """
+        return self.stability_margin(self.out_of_rail_time)
+
     # Reynolds Number
     @funcify_method("Time (s)", "Reynolds Number", "spline", "zero")
     def reynolds_number(self):

tests/unit/test_flight.py

@@ -258,3 +258,31 @@ def test_get_controller_observed_variables(flight_calisto_air_brakes):
     obs_vars = flight_calisto_air_brakes.get_controller_observed_variables()
     assert isinstance(obs_vars, list)
     assert len(obs_vars) == 0
+
+
+def test_initial_stability_margin(flight_calisto_custom_wind):
+    """Test the initial_stability_margin method of the Flight class.
+
+    Parameters
+    ----------
+    flight_calisto_custom_wind : rocketpy.Flight
+    """
+    res = flight_calisto_custom_wind.initial_stability_margin
+    assert isinstance(res, float)
+    assert res == flight_calisto_custom_wind.stability_margin(0)
+    assert np.isclose(res, 2.05, atol=0.1)
+
+
+def test_out_of_rail_stability_margin(flight_calisto_custom_wind):
+    """Test the out_of_rail_stability_margin method of the Flight class.
+
+    Parameters
+    ----------
+    flight_calisto_custom_wind : rocketpy.Flight
+    """
+    res = flight_calisto_custom_wind.out_of_rail_stability_margin
+    assert isinstance(res, float)
+    assert res == flight_calisto_custom_wind.stability_margin(
+        flight_calisto_custom_wind.out_of_rail_time
+    )
+    assert np.isclose(res, 2.14, atol=0.1)