MNT: net thrust addition to 3 dof in flight class (#907)

* MNT: updated flight.py 3dof for net_thrust

- MNT: added net_thrust to u_dot_generalized_3dof in flight.py

* TST: net_thrust availability test on 3 dof flight

* MNT: docstring adjustment in net_thrust test in test_flight_3dof.py

* MNT: lint check update

* DOC: changelog.md update

* DOC: bug changelog update

Author: aZira371

CHANGELOG.md

@@ -32,6 +32,7 @@ Attention: The newest changes should be on top -->
 
 ### Added
 
+- MNT: net thrust addition to 3 dof in flight class [#907] (https://github.com/RocketPy-Team/RocketPy/pull/907)
 - ENH: 3-dof lateral motion improvement [#883](https://github.com/RocketPy-Team/RocketPy/pull/883)
 - ENH: Add multi-dimensional drag coefficient support (Cd as function of M, Re, α) [#875](https://github.com/RocketPy-Team/RocketPy/pull/875)
 - ENH: Add save functionality to `_MonteCarloPlots.all` method [#848](https://github.com/RocketPy-Team/RocketPy/pull/848)
@@ -52,6 +53,7 @@ Attention: The newest changes should be on top -->
 
 ### Fixed
 
+- BUG: energy_data plot not working for 3 dof sims [[#906](https://github.com/RocketPy-Team/RocketPy/issues/906)]
 - BUG: Fix CSV column header spacing in FlightDataExporter [#864](https://github.com/RocketPy-Team/RocketPy/issues/864)
 - BUG: Fix parallel Monte Carlo simulation showing incorrect iteration count [#806](https://github.com/RocketPy-Team/RocketPy/pull/806)
 

rocketpy/simulation/flight.py

@@ -2041,11 +2041,20 @@ def u_dot_generalized_3dof(self, t, u, post_processing=False):
             R3 += fz
 
         # Thrust and weight
-        thrust = self.rocket.motor.thrust.get_value_opt(t)
+        # Calculate net thrust including pressure thrust correction if motor is burning
+        if self.rocket.motor.burn_start_time < t < self.rocket.motor.burn_out_time:
+            pressure = self.env.pressure.get_value_opt(z)
+            net_thrust = max(
+                self.rocket.motor.thrust.get_value_opt(t)
+                + self.rocket.motor.pressure_thrust(pressure),
+                0,
+            )
+        else:
+            net_thrust = 0
         gravity = self.env.gravity.get_value_opt(z)
         weight_body = Kt @ Vector([0, 0, -total_mass * gravity])
 
-        total_force = Vector([0, 0, thrust]) + weight_body + Vector([R1, R2, R3])
+        total_force = Vector([0, 0, net_thrust]) + weight_body + Vector([R1, R2, R3])
 
         # Dynamics
         v_dot = K @ (total_force / total_mass)
@@ -2133,7 +2142,7 @@ def u_dot_generalized_3dof(self, t, u, post_processing=False):
 
         if post_processing:
             self.__post_processed_variables.append(
-                [t, *v_dot, *w_dot, R1, R2, R3, 0, 0, 0]
+                [t, *v_dot, *w_dot, R1, R2, R3, 0, 0, 0, net_thrust]
             )
 
         return u_dot

tests/integration/simulation/test_flight_3dof.py

@@ -301,3 +301,26 @@ def test_weathercock_anti_aligned_uses_perp_axis_and_evolves(flight_weathercock_
     assert e_dot_magnitude > 1e-6, (
         "Quaternion derivatives should be non-zero for anti-aligned"
     )
+
+
+def test_3dof_net_thrust_available(flight_3dof):
+    """Tests that net_thrust property is available in 3 DOF mode.
+    The net_thrust property is required for energy plots and should be
+    available in both 3 DOF and 6 DOF modes.
+
+    Parameters
+    ----------
+    flight_3dof : rocketpy.simulation.flight.Flight
+        A Flight object configured for 3-DOF simulation.
+    """
+    # Check that net_thrust can be accessed
+    assert hasattr(flight_3dof, "net_thrust"), "net_thrust attribute not found"
+
+    # Check that it returns a Function object with data
+    net_thrust = flight_3dof.net_thrust
+    assert len(net_thrust) > 0, "net_thrust should have data points"
+
+    # Verify that thrust_power can be computed (uses net_thrust internally)
+    assert hasattr(flight_3dof, "thrust_power"), "thrust_power attribute not found"
+    thrust_power = flight_3dof.thrust_power
+    assert len(thrust_power) > 0, "thrust_power should have data points"