The OpenConcept survey

Choosing which OpenConcept analysis to drive is the single most consequential decision in this repository: it fixes what physics is available, what can be constrained, and what the results mean. It was therefore made by reading the library rather than by picking the obvious example.

This page records that survey – 30,137 lines across 107 source files, tests excluded; 41,843 lines with them – and the conclusion it reached, which is stronger than “this example looks suitable”.

The conclusion

openconcept.examples.B738_sizing:B738SizingMissionAnalysis is the only analysis in OpenConcept that satisfies the requirement cdadt exists to meet. It is not the most convenient choice among several; it is the only one.

Three properties are needed, and exactly one example has all three:

Example	Mission profile	Closes a weight loop	Scalable engine
B738_sizing.py	FullMissionWithReserve	yes	yes
B738.py	MissionWithReserve	no	no
B738_VLM_drag.py	MissionWithReserve	no	no
B738_aerostructural.py	BasicMission	no	no
Caravan.py	FullMissionAnalysis	no	no
KingAirC90GT.py	FullMissionAnalysis	no	no
TBM850.py	FullMissionAnalysis	no	no
HybridTwin.py, HybridTwin_thermal.py	FullMissionAnalysis	no	no
HybridTwin_active_thermal.py	BasicMission	no	no
ElectricSinglewithThermal.py	FullMissionAnalysis	no	no
N3_HybridSingleAisle_Refrig.py	BasicMission	no	no
minimal.py, minimal_integrator.py	BasicMission	no	no

Established by inspection of every file in openconcept/examples/: grepping each for its mission profile, for an empty-weight buildup group, and for RubberizedTurbofan. Only B738_sizing.py matches on all three, and it is the only file in the library that imports RubberizedTurbofan at all.

Why each property is required

The mission profile must include both balanced-field takeoff and Part 25 reserves. The four profiles in openconcept/mission/profiles.py are one class with two switches:

Profile	Takeoff (BFL)	Reserves	Suitable
BasicMission	no	no	no
FullMissionAnalysis	yes	no	no
MissionWithReserve	no	yes	no
FullMissionWithReserve	yes	yes	yes

Only the last has both, and the requirement was “takeoff balanced field length and mission plus reserves”. The other three are the same class constructed with include_takeoff or include_reserve switched off.

It must close a weight loop. A fixed-weight analysis answers “how much fuel does this aeroplane burn”. A sizing analysis answers “how big must the aeroplane be”, by driving \(\mathrm{MTOW} = \mathrm{OEW}(\mathrm{MTOW}) + W_\mathrm{payload} + W_\mathrm{fuel}(\mathrm{MTOW})\) to consistency. Only B738_sizing.py does this; every other example takes weights as data. Without it, changing the wing would change the drag but not the structure, and the optimization this repository performs would be meaningless.

The engine must be scalable. RubberizedTurbofan scales thrust and fuel flow from a fixed CFM56 deck by a rated-thrust input, which is what makes engine size a design variable. The other examples use fixed decks, surrogate maps for one specific engine, or propeller/electric systems.

What is inside the chosen box

Following the imports of B738_sizing.py down, the modules that actually execute:

Module	What it contributes
mission/profiles.py	FullMissionWithReserve: the twelve phases and their linking
mission/phases.py	Ground roll, rotation, climb-angle and steady-flight phases; the implicit V1 solve
mission/mission_groups.py	Phase, integrator and trajectory group machinery
aerodynamics/drag_jet_transport.py	Component-by-component parasite drag buildup
aerodynamics/aerodynamics.py	PolarDrag: the parabolic drag polar
aerodynamics/CL_max_estimation.py	Clean and flapped maximum lift coefficients
propulsion/rubberized_turbofan.py, propulsion/cfm56.py	The scaled CFM56 thrust and fuel-flow deck
weights/weights_jet_transport.py	Structure, gear, nacelle and equipment weight correlations
stability/tail_volume_coefficient_sizing.py	Horizontal and vertical tail area from tail volume coefficient
geometry/wing_planform.py, geometry/wetted_area.py	Mean aerodynamic chord, wetted areas
atmospherics/	Standard atmosphere, true airspeed, dynamic pressure, Mach
utilities/math/integrals.py	Simpson’s rule integration of fuel burn – the reason num_nodes must be odd

What is in OpenConcept and not used

Worth recording, because it bounds what cdadt could ever be asked to do without changing the box:

• aerodynamics/openaerostruct/ (3,400 lines) – VLM and aerostructural drag polars. Higher fidelity, and a different box. Not loaded.

• thermal/ (5,100 lines) – ducts, heat exchangers, heat pipes, chillers, pumps. For electrified propulsion thermal management.

• energy_storage/ – batteries and liquid-hydrogen tanks.

• propulsion/systems/ – series hybrid, all-electric and turboprop propulsion systems; N3.py, motor.py, generator.py, propeller.py, turboshaft.py.

• weights/weights_BWB.py, weights_turboprop.py, weights_twin_hybrid.py – other aircraft classes.

• aerodynamics/drag_BWB.py – blended wing body drag.

• costs/costs_commuter.py – a commuter-aircraft cost model.

• utilities/visualization.py – OpenConcept’s own plotting helpers.

None of it is imported by cdadt, and a contract test proves that by checking sys.modules after a box is built. Any of it could become reachable by naming a different analysis in black_box.model – which is configuration, not code. See The OpenConcept black box.

How the survey was performed

Reproducible, and worth repeating whenever OpenConcept is updated:

# every source file and its size
find openconcept -name '*.py' -not -path '*/tests/*' | sort | xargs wc -l

# which mission profile each example uses
grep -oE "FullMissionWithReserve|FullMissionAnalysis|MissionWithReserve|BasicMission" \
    openconcept/examples/*.py | sort -u

# which examples close a weight loop
grep -l "EmptyWeight" openconcept/examples/*.py

# which examples can scale an engine
grep -l "RubberizedTurbofan" openconcept/examples/*.py

# what a built box actually loads
cdadt inspect cases/b738.yaml

The last command is the authoritative one: it reads the interface off the live model rather than off this page. See The interface reference.