Turbojet Concept Design Deliverables

You are not buying a report. You are buying the material for three decisions: is this design point real, does it fit the mission, and can I defend spending the next tranche of money. A serious concept-design package is the set of artefacts that lets you make those decisions without taking the seller's word for anything. Anything less is a brochure with equations.

This guide walks the package artefact by artefact, in the order you should ask for them. The running example is the Orion reference release, because it is ours and every figure in it is public, which is itself one of the points.

The closed design point, with its thresholds

The core artefact is one design point closed against thresholds that were declared before the run: thrust, specific fuel consumption, pressure ratio, turbine inlet temperature, mass flow, dry mass: each with a measured value and the requirement it was held against.

This is what a go or no-go decision on the design point rests on, and it only rests on evidence if the thresholds are in the document. If the thresholds are not in the document, the closure cannot be checked, and you are back to adjectives. The discipline is explained in what "nineteen checks, nineteen passes" actually means; the short version is that a pass with a hidden requirement proves only that someone wrote the word "pass."

The cycle-selection trail

A serious package shows the points that lost. Pressure ratio and turbine temperature trade against each other in ways that are well understood; if the first configuration tried is also the one delivered, either the trade space was not searched or the search was not reported.

The trail tells you whether the designer searched the space or scripted a path through it. Orion's trail is three lines long and the middle line is the valuable one: a prescribed screening point at 8.5:1 pressure ratio that closed at 13.25 kN and a TSFC of 105.0, missed the fuel target, and stayed on the record. The selected cycle, 11.0:1 at 99.3, means more because the miss is visible next to it.

The off-design deck

Engines are designed at a point and flown across an envelope. The package should contain operating points away from the design condition (altitude and Mach corners that matter to your mission), each solved, not interpolated from a chart.

Off-design lines are where you find out whether the mission is flown by this engine or merely survived by it. Orion publishes three points: 13.34 kN at sea-level static, 7.93 kN at 5 km and Mach 0.40, 5.01 kN at 10 km and Mach 0.70, with TSFC degrading from 99.3 to 123.7 kg/(kN·h) across them. If your critical mission corner is at altitude, those off-design lines (not the headline) are what you are buying.

The gas path, station by station

Under the operating points should sit per-station tables: total temperature, total pressure, Mach and mass flow at each engine station, for each solved condition. This is the thermodynamic working, shown.

Paired with the declared model basis and component assumptions, the station tables let your own propulsion engineer audit the internal consistency of the solution and trace each headline number back to the gas path that produced it. The tables alone do not let anyone re-derive the results (they sit on the model's assumptions, not outside them), so a package with them still asks you to trust the model. What it does not ask you to trust is the summary arithmetic. Also check that the installation data your airframe team needs (compressor-face conditions, nozzle throat area) exists in a usable form.

A mass model with declared bases

Not a number, a budget. Look for a component-level breakdown where every row carries a declared material basis, where subsystem allowances are explicit rather than dissolved into optimism, and where the method is stated. Orion's mass model partitions the geometry by volume, density and a design-realization factor, floors it with a declared subsystem allowance, and publishes both constructions: 165.2 kg in advanced materials against a 209.0 kg conventional all-metal fallback.

Read this for where the weight risk lives, and how much growth your aircraft can absorb. The gap between the advanced and conventional figures is a quantified risk statement, not a marketing spread.

Geometry you can open

The package should include the geometry itself: a watertight release mesh with topology validation and CAD exchange files (STEP) that your airframe team can import today. Two things matter about provenance. The geometry should be generated from the closed cycle (the shape is the solution, not an illustration of it) and the mesh should be machine-checked: Orion's release mesh is 5,252,496 triangles with zero boundary and zero non-manifold edges, verified by a validator independent of the generator.

This is the fit question. Clearance checks, duct routing and bay packaging can start in your CAD the day the package arrives, not after a data-conversion project.

The check matrix and the seal

Finally, the audit layer: an automated check matrix in which every published figure appears against its declared threshold, both numbers shown, and a sealed release that re-executes deterministically, reproducing the checks and, in Orion's case, a byte-identical mesh with a published SHA-256. Replay is the hardest thing in the package to fake, because it either works or it does not.

This decides whether you can verify the work from your desk, without a site visit, a clearance or a phone call. That question matters more than any single number in the package.

What a serious package does not contain

No hardware. No qualification data. No certification claim. A concept-design package is decision-grade evidence about an engine that does not yet exist as hardware, and any seller who lets the vocabulary drift past that ("flight-proven design," "certification-ready") is selling across a line. The boundary between concept design, detailed design, qualification and certification is worth understanding precisely; it is mapped in the companion boundary guide.

Red flags

• Headline thrust with no declared flight condition attached.
• A TSFC figure with no units, no basis and no statement of where in the envelope it was measured.
• No rejected alternatives anywhere in the package.
• Dry mass as a single number with no breakdown, no material bases and no fallback construction.
• Renders where geometry should be; screenshots where tables should be.
• "Validated" or "verified" with no thresholds published.
• Nothing that re-runs: no package, no replay, no way to check the work yourself.

One or two of these might be commercial modesty. A pattern of them is a product that does not survive audit.

The fee-and-scope shape of packages like this (what a closed cycle alone costs versus cycle plus geometry) is on the packages page. If you are earlier in the process and still assembling your side of the table, start with the design-brief checklist; the quality of what comes back is bounded by the quality of what you freeze.

Next step: open the Orion engine page and treat it as a reference package: every artefact above is on it, public, with the thresholds shown.