Aircraft likeness and reference-source policy¶

Status: project policy. Applies to this repository and to every content pack published under the fighters-legacy organisation, including fl-base-pack.

This document answers four questions, and it is written before the first aircraft ships rather than after — a policy written afterwards can only ratify whatever was already done.

May I model a real aircraft type?
From what references?
With what markings?
What must I document?

1. Real aircraft types may be modelled¶

Yes. Fighters Legacy models real aircraft, names them by their real designations, and uses their real published performance. The docs already work through the F-15C, the F/A-18C and the Tu-95MS as examples, and the first bundled aircraft is a Northrop F-5E Tiger II.

What makes this defensible is not that the aircraft are fictional. It is where the data comes from, and the answer must be: the public record.

2. Public-domain and unencumbered sources only¶

This section governs both the numbers (dimensions, masses, thrust, aerodynamic values) and the pictures (visual reference for shaping geometry and authoring textures). The rule for both is the same: the source must be public-domain or unencumbered, and what ships is the derived asset, never the reference.

Permitted references — numbers:

Declassified 3-view drawings and general-arrangement diagrams.
Published Standard Aircraft Characteristics charts.
Declassified flight manuals and technical orders.
NASA and NACA technical reports (ntrs.nasa.gov).
Manufacturer marketing material for dimensions only, cross-checked against a government source.

Permitted references — visual reference for geometry and texture:

Public-domain photographs, regardless of who took them. USAF / US Navy / NASA photography (works of the US federal government) qualifies, but so does any other genuinely public-domain photograph — including manufacturer factory and assembly-line photographs of bare, unpainted airframes, which are the best panel-line reference there is and, being unmarked, raise no §4 livery question.
CC0 imagery, regardless of author. CC0 is a public-domain dedication with no attribution, no share-alike, and no downstream obligation — e.g. museum walk-around photography released CC0. fl-base-pack already carries LICENSES/CC0-1.0.txt.

Using a photograph as visual reference means informing proportions, panel lines and surface detail from it. It does not mean reproducing what is painted on the aircraft: §4 applies in full — any national insignia, unit marking, nose art, or operator livery visible in a reference photograph is not carried onto the airframe.

Not accepted — attribution / share-alike imagery (CC BY, CC BY-SA):

Freely licensed is not the same as unencumbered. CC BY requires attribution and CC BY-SA additionally requires share-alike, and both obligations propagate into any texture or mesh derived from the image — a share-alike reference would infect the derived asset and conflict with the pack's blanket CC-BY-4.0, which license-check now enforces as a required gate. Use only public-domain and CC0 imagery; the CC BY / CC BY-SA bucket is not needed and is not taken.

Forbidden, without exception:

No mesh traced from, derived from, converted out of, or "cleaned up" from another simulator, game, or commercial 3D model — regardless of how the file was obtained, what licence its uploader claimed, or how much it was modified afterwards. This restates the rule already in fl-base-pack/CONTRIBUTING.md, and makes explicit that it applies to the airframe geometry, not merely to the livery.
No mesh traced from scale plans, multi-view line drawings, or cutaway illustrations from modelling magazines, books, or partworks — including cutaways that run in Jane's and Osprey titles. These are protected creative works by identifiable artists, copyrighted regardless of where they are found and regardless of the absence of a visible licence notice; a mesh traced from one is a derivative work of the drawing. They are easy to mistake for neutral reference because they look technical rather than artistic and carry no licence tag — they are neither neutral nor free. Tracing a Jane's cutaway would breach in the content the very clean-room rule docs/developer/architecture.md already imposes on the engine.
No aerodynamic or performance values lifted from another simulator's data files. Not from DCS, not from BMS, not from a Flight Simulator add-on, not from a wiki that copied one of them.
No reference material marked export-controlled (ITAR/EAR), classified, or "distribution limited". If a document says you may not redistribute it, you may not derive from it either.

Reference imagery is not shipped. It lives outside the pack repository; only the derived asset ships. Each file used as reference is recorded — licence, author, and source URL — so the provenance is auditable (see §5).

3. Aerodynamic values are derived, not copied¶

For most aircraft — and for every trainer and light fighter — no public source publishes the stability derivatives. That is a real constraint, and the answer is not to go and find someone else's tuning file.

Derive them. Compute the moment derivatives from the geometry using USAF DATCOM methods, then calibrate the result against published performance charts: stall speed, max level Mach, rate of climb, sustained turn rate, fuel burn. fm-trim --expect exists precisely so that this calibration is a mechanical, checkable step rather than a matter of taste — the model must reproduce the aircraft's published numbers, and CI fails it when it stops doing so.

This is the same clean-room standard the engine already holds itself to with respect to Jane's Fighters Anthology: design lesson only, no code or tuning values copied (docs/developer/architecture.md). The content is held to it too.

4. Markings and liveries¶

No unit markings, squadron insignia, nose art, or operator liveries without documented clearance from the rights holder.
Default to generic, fictional, or unmarked schemes. National insignia on historical aircraft in their historical context is acceptable; a current operator's squadron badge is not.
Manufacturer logos are not reproduced on the airframe.

5. Every aircraft ships a `SOURCES.md`¶

This is a hard requirement, and it is what makes the rest of this policy auditable rather than aspirational.

Each aircraft directory contains a SOURCES.md in which every geometric dimension, mass, thrust figure and aerodynamic value is cited to a specific public document, with a URL where one exists. Values that were derived (DATCOM, curve fits, calibration against a chart) say so, and name the inputs they were derived from. Any image used as visual reference for geometry or texture is listed the same way — licence (public-domain or CC0), author, and source URL per file — even though the image itself is not committed to the repository. The pull request that adds the aircraft links the sources.

If a number cannot be cited or derived, it does not ship. If an image cannot be shown to be public-domain or CC0, it is not used as reference.

6. Trademarks¶

Aircraft type names, designations, and manufacturer names are the trademarks of their respective owners. Fighters Legacy uses them nominatively — to identify the aircraft being modelled, which is what they are for. The project claims no affiliation with, sponsorship by, or endorsement from any aircraft manufacturer or armed force, and the game's branding does not suggest otherwise.

See also the project's existing disclaimer in README.md.

7. The fallback¶

If this policy ever proves too permissive in a specific case, the fallback is not to abandon the project's realism: tools/blender_gen.py generates entirely fictional, IP-free parametric airframes, and the engine is fully content-agnostic. A pack of fictional aircraft is a supported configuration. We do not expect to need it, but the option is deliberately kept open.

Questions, or an aircraft you are unsure about? Open an issue before you start modelling. It is a cheap conversation, and it is much cheaper than a rejected pull request with a hundred hours of work in it.