a few questions about the model’s flight dynamics

[xiaoweibit]

Hello, I have a few questions about the model’s flight dynamics:

1. How does the model actually generate enough force to take off against gravity?
Is the main contributor the reference trajectories used in WBPG, the fluidcoef parameters, or some other mechanism?

2. During testing, what is the correct way to compute the lift generated by wing motion?
I see that qfrc_fluid contains fluid forces for each joint degree of freedom.
Can this data be used to estimate the net lift acting on the rigid body?

Any clarification on how aerodynamic forces are modeled and how to properly extract lift from the simulation would be greatly appreciated. Thank you!

[vaxenburg]

I feel like this is really a question about how MuJoCo works, no so much the fly model per se. So maybe the MuJoCo docs is the right place to start, for example here:
https://mujoco.readthedocs.io/en/stable/computation/fluid.html

However we do have a function that can help you calculate the fluid forces on each body separately (but please note that it only considers the ellipsoid fluid model, not the inertia model):
https://github.com/TuragaLab/flybody/blob/main/flybody/ellipsoid_fluid_model.py#L16