sloads

FAR 23 structural design loads — suite replication grown into a concept distributed-loads tool

sloads is a modern Python replication of the FAR 23 LOADS suite (Hal C. McMaster, Aero Science Software; FAA report DOT/FAA/AR-96/46) — the 22-program package that computes the structural design loads a small aircraft must sustain under 14 CFR Part 23 Subpart C — extended into an initial-concept distributed-loads tool. A concept configuration goes in; per-component and full-airframe distributed ultimate loads come out, exported as solver-ready bulk-data decks for beam-model structural sizing.

The package is pure calculation with three interchangeable front-ends: a multi-page Streamlit GUI, a command line, and the test suite. One reloadable project.json carries every input. All 22 original suite programs are ported and locked against the manual's printed worked examples to ±0.1 %.

The GUI

V-n flight envelope diagram — Balanced V-n flight envelope — maneuver and gust corners per weight/CG case and altitude.

Weight versus CG envelope chart — Weight–CG envelope of all loadings, with structural limits and required ballast.

Spanwise wing load distribution plot — Net spanwise wing loads — shear, bending and torsion per governing case.

Speed-altitude envelope chart — Speed–altitude envelope — EAS-limited below the shoulder altitude, Mach-limited above.

Aircraft three-view planform drawing — Three-view outline generated from the parametric geometry.

Balancing tail load versus CG plot — Trim & stability — balancing tail load and static margin swept across the CG range.

Scope of analysis

Mass properties: weight estimation, weight–CG envelope with ballast, 3-axis CG and mass moments of inertia.
Design airspeeds and limit maneuver load factors (23.335 / 23.337), Mach limit lines, operating-limitation placards.
The balanced V-n flight envelope with the balancing horizontal-tail load at every condition × CG case × altitude.
Critical rational flight loads for wing, horizontal tail, vertical tail and fuselage across the whole envelope.
Distributed loads: Schrenk spanwise wing air, inertia-relief and net shear / bending / torsion; chordwise tail distribution; aileron, flap and tab loads.
Engine-mount loads (torque, side, gyroscopic) and the one-engine-out vertical-tail transient.
Ground and landing loads: the full tricycle-gear FAR 23.471–23.499 condition set plus a per-leg gear free-body report.
The balanced free-free full-span airplane model — aero and inertia together, closed by a six-DOF rigid-body balance, flight and ground families in one assembled deck.

Outputs

Every deliverable load is ultimate, with the safety factor stated per case from a single governing table.
Load-case and station-distribution CSVs; a multi-sheet workbook export.
Solver bulk-data decks (GRID/FORCE/MOMENT, plus CONM2 mass decks) with global-equilibrium invariants, proven to solve in CI via a round-trip harness.
A self-contained LaTeX/PDF loads summary report written for a structural analyst who did not run the analysis.

Verification

The FAR 23 core is oracle-locked: every module is tested against the manual's printed worked example to ±0.1 %, with the page citation kept in the test. Concept-mode physics carries stated closure and invariant gates in CI with the same force. sloads is an independent open replication (MIT licence), intended as an educational and exploratory engineering tool — results are not certified for regulated structural design.