Fix max_acceleration_power_off_time returning 0 when controllers are present

[Copilot]

Pull request type

• [x] Code changes (bugfix, features)

Checklist

• [x] Tests for the changes have been added (if needed)
• [ ] Docs have been reviewed and added / updated
• [x] Lint (black rocketpy/ tests/) has passed locally
• [x] All tests (pytest tests -m slow --runslow) have passed locally
• [ ] CHANGELOG.md has been updated (if relevant)

Current behavior

When a Flight has controllers (e.g., AirBrakes), max_acceleration_power_off_time always returns 0.0 and max_acceleration_power_off returns 0.0 m/s².

flight.max_acceleration_power_off_time  # Returns 0.0 (wrong)
flight.max_acceleration_power_off       # Returns 0.0 (wrong)

Root cause: np.argmax() on sliced array self.acceleration[burn_out_time_index:, 1] returns index relative to the slice, but the code uses this index directly on the full array.

New behavior

Returns correct time and acceleration values after motor burnout:

flight.max_acceleration_power_off_time  # Returns actual time (e.g., 3.9s)
flight.max_acceleration_power_off       # Returns actual acceleration

Fix in max_acceleration_power_off_time:

# Before
return self.acceleration[max_acceleration_time_index, 0]

# After  
return self.acceleration[burn_out_time_index + max_acceleration_time_index, 0]

Breaking change

• [x] No

Additional information

Fixes #803

Original prompt

---

This section details on the original issue you should resolve

<issue_title>BUG: Maximum acceleration values broken when airbrake is used</issue_title> <issue_description>Describe the bug

When running any Flight with a Rocket containing an Airbrake, the maximum acceleration and G values are broken as follows:

• "Maximum Acceleration During Motor Burn" is absurdly high (e.g. ~4000m/s²)
• "Maximum Gs During Motor Burn" is absurdly high (e.g. ~400g)
• "Maximum Acceleration After Motor Burn" is zero
• "Maximum Gs After Motor Burn" is zero

To Reproduce

Given an existing RocketPy simulation (such as given in https://docs.rocketpy.org/en/latest/user/first_simulation.html), add an airbrake to the rocket with an "empty" airbrake controller function:

# The following code assumes env is the Environment used by the simulation

def airbrake_controller_function(
    time: float,
    sampling_rate: float,
    state_raw: list,
    state_history_raw: list,
    observed_variables: list,
    air_brakes: AirBrakes,
):
    air_brakes.deployment_level = 0.0
    wind_x: float = env.wind_velocity_x(state_raw[2])
    wind_y: float = env.wind_velocity_y(state_raw[2])
    free_stream_speed = (
        (wind_x - state_raw[3]) ** 2 + (wind_y - state_raw[4] ** 2 + (state_raw[5]) ** 2
    ) ** 0.5
    mach_number = free_stream_speed / env.speed_of_sound(state_raw[2])
    return (
        time,
        air_brakes.deployment_level,
        air_brakes.drag_coefficient(air_brakes.deployment_level, mach_number),
    )
    
rocket.add_air_brakes(
    drag_coefficient_curve="airbrake_drag_curve.csv", # Note that you need to provide that file in the same folder
    controller_function=airbrake_controller_function,
    sampling_rate=10,
    clamp=True,
)

Here is an example drag curve file in .csv format (store it as "airbrake_drag_curve.csv"):

0.0, 0.1, 0.0
0.0, 0.95, 0.0
1.0, 0.1728, 0.37
1.0, 0.5, 0.37
1.0, 0.6, 0.39
1.0, 0.7, 0.53
1.0, 0.8, 0.7
1.0, 0.9, 1.08
1.0, 0.95, 1.1

After running the simulation, call flight.prints.all() and observe the output.

Expected behavior

(tested with a sounding rocket in development by BEARS e.V.) / without Airbrake added

Maximum Values

Maximum Speed: 311.570 m/s at 1.82 s
Maximum Mach Number: 0.920 Mach at 1.82 s
Maximum Reynolds Number: 2.556e+06 at 1.79 s
Maximum Dynamic Pressure: 5.721e+04 Pa at 1.79 s
Maximum Acceleration During Motor Burn: 191.146 m/s² at 0.73 s
Maximum Gs During Motor Burn: 19.491 g at 0.73 s
Maximum Acceleration After Motor Burn: 11.323 m/s² at 14.41 s
Maximum Gs After Motor Burn: 1.155 Gs at 14.41 s
Maximum Stability Margin: 3.157 c at 1.85 s
Maximum Upper Rail Button Normal Force: 0.000 N
Maximum Upper Rail Button Shear Force: 0.000 N
Maximum Lower Rail Button Normal Force: 0.000 N
Maximum Lower Rail Button Shear Force: 0.000 N

Observed behavior

(tested with a sounding rocket in development by BEARS e.V.) / with Airbrake added but zero deployment

Maximum Values

Maximum Speed: 311.663 m/s at 1.81 s
Maximum Mach Number: 0.920 Mach at 1.81 s
Maximum Reynolds Number: 2.556e+06 at 1.80 s
Maximum Dynamic Pressure: 5.723e+04 Pa at 1.80 s
Maximum Acceleration During Motor Burn: 3893.683 m/s² at 1.83 s
Maximum Gs During Motor Burn: 397.045 g at 1.83 s
Maximum Acceleration After Motor Burn: 0.000 m/s² at 0.00 s
Maximum Gs After Motor Burn: 0.000 Gs at 0.00 s
Maximum Stability Margin: 3.157 c at 1.83 s
Maximum Upper Rail Button Normal Force: 0.000 N
Maximum Upper Rail Button Shear Force: 0.000 N
Maximum Lower Rail Button Normal Force: 0.000 N
Maximum Lower Rail Button Shear Force: 0.000 N

Notice how the output maximum acceleration is absurdly high during motor burn and is zero after motor burn (despite parachutes deploying at some point etc.). The flight otherwise performs the same (apogee and everything else is identical).

Additional context

Tested in RocketPy 1.10.0.

The issue does not appear when no Airbrake is configured. </issue_description>

<agent_instructions>Please investigate, make a plan, and try to find where the BUG is</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Gui-FernandesBR @MateusStano

• Fixes RocketPy-Team/RocketPy#840

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Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 81.08%. Comparing base (9cf3dd4) to head (c87f262). :warning: Report is 25 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #898      +/-   ##
===========================================
+ Coverage    80.27%   81.08%   +0.81%     
===========================================
  Files          104      107       +3     
  Lines        12769    13814    +1045     
===========================================
+ Hits         10250    11201     +951     
- Misses        2519     2613      +94     

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