Project 33

C5 — Static-stability model

Field	Value
Status	UNRESOLVED — An open question, conflict, or missing measurement blocks a stronger statement.
Strongest accepted evidence	MODEL ONLY
Evidence classes cited	SPECIFICATION, IMPLEMENTATION, TEST PROCEDURE, ANALYTICAL, SIMULATED
Gate reached	SOFTWARE REPRODUCTION (next: SYNTHETIC TEST)
Last review	CURRENT — snapshot recorded 2026-09-28 by tooling snapshot (no human review)

Question. Does the modeled rocket keep a static margin of 1.5-2.0 calibers through the motor burn?

Current statement. The reference Barrowman script reports 1.55-1.57 cal during a hard-coded Estes C6-5 burn. An unreviewed textbook re-derivation of the fin terms, sharing every other input, gives 0.74-0.76 cal. The two disagree about the 1.5-2.0 cal window, and the script’s motor differs from the OpenRocket model’s AeroTech G64W.

Requirements

ID	Requirement	Check	Bound	Observed	Result
R-C5-WINDOW	Static margin stays between 1.5 and 2.0 calibers through the motor burn.	machine	≥ 1.5 and ≤ 2.0 cal	1.55 – 1.57; textbook fin-term cross-check: 0.7445 – 0.7576 (NOT SATISFIED)	MODELS DISAGREE (analytical)
R-C5-FORMULATION	The static-margin formulation and its inputs are appropriate for this geometry and motor.	human review	none stated	judgement, not a value	REQUIRES HUMAN REVIEW

Predictions and measurements

ID	Quantity (condition)	Predicted	Model uncertainty	Measured	Abs. error	Rel. error	Criterion	Result
PRED-C5-DRY-CG	dry centre of gravity from nose tip (OpenRocket override masses of the body tubes only; no motor)	0.335817 m [analytical]	not quantified	NOT MEASURED	—	—	not pre-registered	NOT MEASURED

Known contradictions

• R-C5-WINDOW
• D-006

Open questions

• Which fin-term formulation is correct for this geometry (D-006)?
• Which motor should the CG history use (D-007)?

Discrepancies

• D-006 (OPEN) Reference and textbook fin-term formulations disagree about the static-margin window
• D-007 (OPEN) The static-margin script burns a different motor than the OpenRocket model
• D-008 (OPEN) Static-margin inputs omit or misread parts of the OpenRocket model
• D-009 (OPEN) Model inputs were revised until paper targets were met
• D-023 (OPEN) OpenRocket screenshots have no recorded model revision

Assumptions

• The OpenRocket file’s geometry and override masses describe the intended rocket.
• A Barrowman static margin is the quantity the 1.5-2.0 cal target refers to.

Limitations

• A static margin does not establish dynamic stability or flight readiness.
• The fin geometry was revised to meet the target; matching a target is not validation (D-009).
• Neither model has been independently reviewed.

Measurement needed to close the next gate

• Independent review of the Barrowman formulation and inputs.
• An inert balance-point measurement of the assembled airframe’s dry CG (compare to PRED-C5-DRY-CG).

Pre-registered experiments

• None.

What this claim does not establish

• Any inert physical measurement: none has been accepted for this claim.
• Physical performance of any hardware.
• Flight readiness or safety for live propulsion.

Evidence

Artifact	Class	SHA-256 (first 12)	What it is
Simulation/static_margin.py	IMPLEMENTATION	4e5749eb7ef8	Reference Barrowman static-margin script with a hard-coded motor burn.
Simulation/Folding Stabilized Rocket.ork	IMPLEMENTATION	26087d70e492	Current OpenRocket model (fins revised to 130/110/180 mm; motor G64W).
docs/EVIDENCE/C5_static_margin.csv	ANALYTICAL	11dbead6cfea	Reference model static margin during the assumed burn.
docs/EVIDENCE/C5_static_margin_inputs.json	ANALYTICAL	642c367181ca	Every input the reference calculation used, including the motor it assumed and the one the OpenRocket file specifies.
docs/EVIDENCE/C5_static_margin.png	ANALYTICAL	f25b14f130e2	Rendered reference-model margin. Values are in the CSV.
Simulation/barrowman_crosscheck.py	IMPLEMENTATION	844a03c57bed	Unreviewed textbook re-derivation of the fin terms, sharing every other input with the reference.
docs/EVIDENCE/C5_barrowman_crosscheck.json	ANALYTICAL	bbf54cd31799	Cross-check static margin. Disagrees with the reference about the 1.5-2.0 cal window.
Simulation/Stability_Graph.png	SIMULATED	899af6b7a02c	OpenRocket export. The model revision and simulation settings that produced it are not recorded.
tests/test_static_margin.py	TEST PROCEDURE	859d50abe849	Parser and regression checks; no stability window is asserted by CI.
docs/EVIDENCE/CHANGELOG.md	SPECIFICATION	ec9345c71ad5	Historical log of model inputs changed to match paper targets.

Earlier versions (failure archive)

• evidence/archive/notes-v1/C5_static_margin.md — Historical C5 note, generated by the model script.
• evidence/archive/C5_openrocket_pre_retune.ork.xml — OpenRocket model XML before the fins were revised to meet the paper’s margin target (20 mm root chord).

A change to any of these files makes the last review insufficient

• Simulation/Folding Stabilized Rocket.ork
• Simulation/Stability_Graph.png
• Simulation/barrowman_crosscheck.py
• Simulation/static_margin.py
• docs/EVIDENCE/C5_barrowman_crosscheck.json
• docs/EVIDENCE/C5_static_margin.csv
• docs/EVIDENCE/C5_static_margin.png
• docs/EVIDENCE/C5_static_margin_inputs.json
• docs/EVIDENCE/CHANGELOG.md
• tests/test_static_margin.py

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All claims · Traceability · Discrepancies · Evidence Observatory

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