Balanced field take-off model.

[Kenneth-T-Moore]

Summary

This is a draft of the balanced field take-off subproblem. The example in aviary/examples/external_subsystems/balanced_field/run_balanced_field.py shows two ways to use it:

1. A more manual way where you create and add the balanced field builder to the post_mission subsystem.
2. An automated way where you just set "balanced_field" to True in the post_mission phase_info, which adds it automatically in the post_mission performance subsystem.

NOTES

1. This method works well for the Advanced Single Aisle example, but I haven't had any luck getting it to converge with a heavier aircraft.
2. Low-speed aero is still hard coded. Also, initial guesses are not yet user-tunable, and it isn't clear which ones might need to be.

IMPLEMENTATION

1. Uses Picard shooting from recent dymos. This allows the balanced field problem to be assembled and solved in dymos with a solver instead of an optimizer (using gauss-seidel).
2. The balanced field problem is a subproblem.

Related Issues

• Resolves #

Backwards incompatibilities

None

New Dependencies

None