BUG: Maximum acceleration values broken when airbrake is used #840
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.