OpenPlane: parametric aircraft design in the open
A new open-source project called OpenPlane brings parametric methodology to homebuilt aircraft design. The repository contains cost tables, structural specifications and a qualification workflow intended for builders who want to document every decision from material selection to flight-test sign-off. The project is hosted on GitHub and distributed under a model that lets builders adapt the documentation to their local regulations.
Cost breakdown and regional pricing
The project provides a complete bill of materials in CSV format. Two files ship with the download: BOM.csv and HARDWARE_BY_STEP.csv. Every folded blank, each rivet driven by grip, every AN bolt installed by step, plus tube stock, bought assemblies, consumables and tools are listed with an estimated price per line. The same list powers both files so builders can filter by step or by item depending on whether they are checking hardware at a particular construction phase or looking up the cost of a specific component.
Exchange rates are fixed to 19 October 2026 closings using Pound Sterling Live. A "local-price estimate" feature takes the UK price, removes VAT, applies about 20 percent off US-made aircraft hardware, aero sheet and the engine kit when buying in the US, then adds a typical local sales tax. The result shows US prices before sales tax, plus regional rates of 21 percent for the EU, 10 percent for Japan, 10 percent GST for Australia and 13 percent HST for Canada. These figures are presented as rough guides, not quotes.
Weight, range and structural strength
The designer emphasises that weight, not fuel tank size, sets the range. A pilot fuel allowance table lists the mass the pilot can carry, the fuel quantity allowed and the resulting range for a given distance. Mass is tracked as a percentage of mean aerodynamic chord (% MAC) so the builder can see how centre-of-gravity limits are affected as the aircraft takes shape.
First-pass strength is specified as +4 / −2 g, with ultimate load at ×1.5 the allowable margin. A structural table maps each member to its ultimate load, allowable margin and the resulting safety factor. These numbers are intended as starting points the builder must verify with physical proof-loading before flight.
What's known, estimated and not yet proven
The project organises its knowledge into three categories. Exact items are those already analysed: the fold geometry, where every panel in the 3D model is produced by refolding the DXF flat pattern, and the rib-to-spar pilot holes are coordinated between parts. Estimated items have not yet been analysed: ribs, skin buckling, fittings, landing gear, tail loads, the engine mount and flutter, plus mass-balance every control surface. Not proven items have no physical part cut yet. The builder is advised to fold one rib and one spar offcut first to check the bend deduction before committing to full construction.
From DXF flat patterns to airworthiness proof
Every panel in the OpenPlane 3D model is produced by refolding the DXF flat pattern. This means the flat pattern defines the final folded shape and the rib-to-spar pilot holes are registered between parts before any material is cut. The engineering test plan is modelled on BCAR Section S practice, which is a recognised standard for homebuilt aircraft validation rather than a regulatory approval route. Costs quoted for the test plan are rough ranges for materials, hire and consumables; labour is excluded and the airframe itself is not included in the estimate. The plan lives in qualification.yaml in the repository and its pass criteria use live numbers generated during the build.
Building and flying a UK SSDR aircraft
A UK Single Seat Derived Requirement (SSDR) aircraft needs no airworthiness approval, so all responsibility rests with the builder. The recommended proof-loading procedure involves loading the wing with sandbags to +4 g and having a British Microlight Aircraft Association (BMAA) or Light Aircraft Association (LAA) inspector examine the structure before the aircraft is declared airworthy. Builders in other countries should check their national microlight rules, as approval processes vary by jurisdiction.
The project is an ongoing effort and the repository welcomes contributions from builders who want to refine the cost tables, add structural analyses or update the qualification workflow. The developer's goal is to keep the documentation practical and rooted in the realities of homebuilt construction rather than theoretical aerospace practice.