BUG: update flight simulation logic to include burn start time (#778)

* BUG: update flight simulation logic to include burn start time in conditions

* DEV: updates changelog

Author: Gui-FernandesBR

CHANGELOG.md

@@ -40,7 +40,7 @@ Attention: The newest changes should be on top -->
 
 ### Fixed
 
--
+- BUG: update flight simulation logic to include burn start time [#778](https://github.com/RocketPy-Team/RocketPy/pull/778)
 
 ## [v1.8.0] - 2025-01-20
 

rocketpy/simulation/flight.py

@@ -1451,7 +1451,7 @@ def u_dot(self, t, u, post_processing=False):  # pylint: disable=too-many-locals
         # Determine lift force and moment
         R1, R2, M1, M2, M3 = 0, 0, 0, 0, 0
         # Determine current behavior
-        if t < self.rocket.motor.burn_out_time:
+        if self.rocket.motor.burn_start_time < t < self.rocket.motor.burn_out_time:
             # Motor burning
             # Retrieve important motor quantities
             # Inertias
@@ -1788,7 +1788,7 @@ def u_dot_generalized(self, t, u, post_processing=False):  # pylint: disable=too
         speed_of_sound = self.env.speed_of_sound.get_value_opt(z)
         free_stream_mach = free_stream_speed / speed_of_sound
 
-        if t < self.rocket.motor.burn_out_time:
+        if self.rocket.motor.burn_start_time < t < self.rocket.motor.burn_out_time:
             drag_coeff = self.rocket.power_on_drag.get_value_opt(free_stream_mach)
         else:
             drag_coeff = self.rocket.power_off_drag.get_value_opt(free_stream_mach)