Integrating Aircraft Models into ROSflight

Before integrating your aircraft model into the ROSflight simulation, complete all of the required stability analyses. Go to these Xflr5 and OpenVSP sections for information on how to run a stability analysis.

After running the necessary aerodynamic and stability analyses, the next step is to add the stability and control derivatives into the required parameter file.

The file you need to change is a "dynamics.yaml" file located here: rosflight_ros_pkgs/rosflight_sim/params/anaconda_dynamics.yaml

A sample parameter file is provided below.

Sample parameter file

# Parameters for ROSflight software-in-the-loop simulation, based on RMRC Anaconda UAV.
# Authors: Ian Reid and Phil Tokumaru

# Mass and inertia parameters are defined in fixedwing.urdf.xacro.
# Mass: 4.5
# Jx: 0.24855
# Jy: 0.3784
# Jz: 0.618
# Jxz: 0.06

/**:  # Apply to any node that we load it to
ros__parameters:
    rho: 1.2682
    mass: 4.5

/fixedwing_forces_and_moments:
ros__parameters:
    wing_s: .52
    wing_b: 2.08
    wing_c: 0.2350
    wing_M: 50.0
    wing_epsilon: 0.9 # revisit -- may not need this for the calculation
    wing_alpha0: 0.05236

    D_prop : 0.381 # prop diameter in m (15 in)
    CT_0 : 0.06288743
    CT_1 : -0.02704452
    CT_2 : -0.31320732
    CQ_0 :  0.00614891
    CQ_1 : -0.0106795
    CQ_2 : -0.011779
    KV : 560.0        # Motor speed constant from datasheet in RPM/V
    KQ : 0.01705                       #((1 /(KV_rpm_per_volt)) *60) / (2 *M_PI) Back-emf constant, KV in V-s/rad, Motor torque constant, KQ in N-m/A
    V_max : 24.0                  # voltage for 6s battery at 4 volts per cell
    R_motor : 0.042              # ohms
    I_0 : 1.5                     # no-load (zero torque) current (A)

servo_tau: .01
servo_refresh_rate: 0.003
max_aileron_deflection_angle: 40. # Maximum deflection of the control surfaces in degrees.
max_rudder_deflection_angle: 40. # Maximum deflection of the control surfaces in degrees.
max_elevator_deflection_angle: 40. # Maximum deflection of the control surfaces in degrees.

# Anaconda done for C_L

C_L_O: .506
C_L_alpha: 5.61
C_L_beta: 0.0
C_L_p: 0.0
C_L_q: 7.95
C_L_r: 0.0
C_L_delta_a: 0.0
C_L_delta_e: 0.13
C_L_delta_r: 0.0

# Anaconda done for C_D

C_D_O: 0.043
C_D_alpha: 0.03
C_D_beta: 0.0
C_D_p: 0.043
C_D_q: 0.0
C_D_r: 0.0
C_D_delta_a: 0.0
C_D_delta_e: 0.0135
C_D_delta_r: 0.0

C_ell_O: 0.0
C_ell_alpha: 0.00
C_ell_beta: -0.13
C_ell_p: -0.51
C_ell_q: 0.0
C_ell_r: 0.25
C_ell_delta_a: 0.17
C_ell_delta_e: 0.0
C_ell_delta_r: 0.0024

C_m_O: 0.135
C_m_alpha: -2.74
C_m_beta: 0.0
C_m_p: 0.0
C_m_q: -38.21
C_m_r: 0.0
C_m_delta_a: 0.0
C_m_delta_e: -.99
C_m_delta_r: 0.0

C_n_O: 0.0
C_n_alpha: 0.0
C_n_beta: 0.1301
C_n_p: -0.0364
C_n_q: 0.0
C_n_r: -0.1541
C_n_delta_a: -0.011
C_n_delta_e: 0.0
C_n_delta_r: -0.069

# Anaconda done for C_Y

C_Y_O: 0.0
C_Y_alpha: 0.00
C_Y_beta: -0.98
C_Y_p: 0.0
C_Y_q: 0.0
C_Y_r: 0.0
C_Y_delta_a: 0.075
C_Y_delta_e: 0.0
C_Y_delta_r: .19

/standalone_dynamics:
ros__parameters:
    Jxx: 0.24855
    Jxy: 0.0
    Jxz: 0.06
    Jyy: 0.3784
    Jyz: 0.0
    Jzz: 0.618

The coefficients that need to be changed are the C_L, C_D, C_m, C_Y, C_n, C_ell derivatives. Replace the values for all of these stability and control derivatives with the values obtained from the stability and control analyses you ran with either Xflr5 or OpenVSP.

Note

Some of the derivatives are zero because they are "coupled" which means that they describe cross-axis effects. Usually these have a small effect on an aircraft and don't add much accuracy. See the Appendix section notation glossary to see which coefficients are coupled. Use your own best judgement when deciding whether or not to include these.

Once your parameter file is completed, save and re-name the file. You can then call this file when you launch the simulation.

Steps to add a new aircraft to the simulation environment:

1. Complete your aircraft model and complete all required aerodynamic, stability, and control analyses
2. Create new .yaml parameter file and update coefficient values (example: cessna_dynamics.yaml)
3. Save .yaml file in rosflight_ros_pkgs/rosflight_sim/params/

4. Call your aircraft model (example: cessna) when running the simulation with:

   ros2 launch rosflight_sim fixedwing_standalone.launch.py dynamics_param_file:=/path/to/param/file.yaml