Frequently asked questions.

Tractrix is a family of tools for simulating how aircraft and ground vehicles move on the airside: swept paths, pushback and towing, turning radii, jet blast, stand design and taxiway fillets, each checked against ICAO, FAA or EASA clearances. It is available for QGIS today, with Tractrix Cloud and add-ins for AutoCAD and Revit in preview.

Airport planners and engineers, apron and stand designers, airside operations teams, architects working on terminals and piers, and consultants who need to show that a layout works for a given aircraft or vehicle.

OpenAirside is the open-source engine; Tractrix is the product family built on it. Every Tractrix product sends the same tractrix/1 request to the same engine, so the results are identical whichever product you use. In QGIS the plugin is listed as Tractrix for QGIS (OpenAirside); its Processing provider ID and algorithm IDs (openairside:*) are unchanged.

Forward taxi and group paths with nose-gear, cockpit or custom tracking; pushback and forward towing with towbar or towbarless tugs; steady turns and 180° turns; stand entry and parking; ground vehicles with trailers. Not yet implemented: passenger boarding bridges, manufacturer-specific body-gear steering (747 and A380 aft gear), helicopter-specific manoeuvres and automatic path generation between two poses.

The library holds 388 types from the FAA Aircraft Characteristics Database and 14 ground vehicles. You can override the steering limit and the tracking distance per run. To add or correct a type permanently, edit the source data and regenerate the library with tools/build_library.py; steering limits with their citations live in tools/aircraft_overrides.json. Corrections with a source are welcome as contributions.

Against the Airbus A320 Aircraft Characteristics at six steering angles, the computed turning radii agree within 0.35 m at the nose gear, 0.45 m at the wingtip, 0.5 m at the nose and 0.2 m at the tail; the main-gear centre differs by a constant 0.7 m because Airbus places its turn centre further out. The A320 180° turn width comes out at 22.5 m against the published 22.8 m. The full results are on the validation section.

ICAO Annex 14 Volume I (Table 3-1 wingtip distances and 3.13.6 stand clearances), ICAO Doc 9157 Part 2 (Table 1-1 wheel-to-edge clearance, Appendix 1 kinematics, Table A2-1 jet blast), and FAA AC 150/5300-13B (Tables 4-1 and 4-2). EASA CS-ADR-DSN uses the ICAO values for these quantities; check them against the current issue. See the standards reference.

Tractrix produces planning aids, not certified design results. Many practitioners use swept-path results as supporting evidence; whether that is acceptable is for your authority to decide. Because the model and data are open, a reviewer can reproduce your result from the input line and aircraft type. Always check critical designs against the manufacturer's airport planning manual.

Because the main gear cannot slide sideways, it is pulled along behind the steered point and cuts the corner, tracing a tractrix. The offset between the centreline and the main-gear path is the track-in; it is what taxiway fillets are designed to accommodate. Read the explanation.

Use cockpit tracking for taxiway design: ICAO and FAA design methods assume the pilot keeps the cockpit over the centreline. Use nose-gear tracking where the nose wheel follows a marked line, such as stand lead-in lines. Use a custom distance to model judgmental oversteer. Cockpit tracking gives more track-in than nose-gear tracking.

They are indicative. The model is calibrated to ICAO Doc 9157 Table A2-1, which six types (A320, B737-8, B777-300ER, B747-8, MD-11, A380) reproduce exactly at 56 km/h. Other types use a fleet calibration accurate to about ±45 %. For design decisions, use the manufacturer's charts; they can be digitised into the jet_blast_override field.

The FAA database gives span, length, wheelbase, cockpit-to-main-gear distance and main gear width, but not the full planform. Nose and tail stations, wing and tailplane shape and engine positions are estimated from proportions, and each output lists what was estimated so you can judge whether it matters for your check. Wingtip and gear paths depend mostly on published dimensions.

Tractrix for QGIS, the OpenAirside engine and command-line tool, and the AutoCAD and Revit add-ins with the local engine are free and open source. Tractrix Cloud has a free Community tier during the preview and paid plans for teams. See plans.

Yes. The GNU General Public License (version 2 or later) places no restriction on using the software, including for paid consultancy and commercial projects. Its conditions apply when you distribute the software or modified versions of it.

Under the GPL you must make the source of your modified version available to those you distribute it to, under the same licence. Modifications used only inside your organisation are not distributed. This is a summary, not legal advice; the licence text governs.

Aircraft dimensions come from the FAA Aircraft Characteristics Database, which is in the public domain. Steering limits are re-keyed from manufacturers' published airport planning documents, and each entry cites its source. No vendor library, data file or software was used or reverse-engineered.

Report discrepancies against published charts, add steering limits with their citations, contribute test cases, or improve the code through pull requests on Downloads (account required). Run tests/run_tests.sh before submitting.

QGIS 3.34 LTR and later, including QGIS 4.x, with Qt5 or Qt6, on Windows, macOS and Linux. No additional Python packages are needed.

AutoCAD 2025 or later and Revit 2025 or later on 64-bit Windows 10 or 11; the add-ins target .NET 8. AutoCAD LT and AutoCAD for Mac do not load .NET add-ins and are not supported. The add-ins are in preview.

Yes. With the local engine the add-in runs tractrix-engine on your computer and nothing leaves it. Switch to the cloud engine in TXSETTINGS only if you want to use Tractrix Cloud.

The engine works in planar metres. In QGIS, layers in a geographic CRS such as EPSG:4326 are computed in the local UTM zone automatically. In CAD, drawing units are converted to metres; unitless drawings use the metres-per-unit setting. In Cloud, DXF units are read from the $INSUNITS header, and a DXF without units is read as metres with a warning.

Yes, in three ways: call the QGIS algorithms from Python or the graphical modeller with their openairside:* IDs; pipe JSON through tractrix-engine run from any language; or call the Tractrix Cloud API with a token. See the API reference.

During the preview, accounts are created by invitation. Tell us about your use case on GitHub Discussions or by e-mail (see early access). You will receive an invitation link valid for 14 days.

Projects, drawings and runs belong to an organisation, and only its members can see them. Viewers can see results; members can also run simulations; admins manage members and tokens; owners also manage billing and can delete the organisation. Admins can read the organisation's security audit log.

Yes. You can delete individual runs, drawings and projects, and an owner can delete the whole organisation, which deletes all of its projects, drawings and runs.

Tokens start with tx_ and are shown in full only once, when you create them. The service stores only a hash. Tokens can be given an expiry date and revoked at any time; the CAD add-ins store them encrypted for your Windows user, never in the drawing.

Drawings and results are processed to provide the service to your organisation. The details — including hosting location and retention — are in the privacy notice, which is a draft during the preview. If your drawings may not leave your network, use the desktop products with the local engine.

Prices will be published before Tractrix Cloud leaves preview. Professional will be priced per seat and billed annually. Nothing is charged during the preview.

The service refuses the new request with a message that names the limit (HTTP 402 for API clients). Nothing is deleted or blocked retroactively, and existing results stay available.

Enterprise plans are invoiced. For other arrangements, contact Tractrix.

The Community edition — the QGIS plugin, the engine and the local CAD add-ins — is free for everyone, including teaching and research. For Cloud needs in education, contact us.