Jet engines and gas turbines

Cutaway draws the chosen engine in section — turbojet, afterburning turbojet, turbofan with separate or mixed exhausts (with or without afterburner), turboprop, turboshaft or ramjet — with the standard station numbers (0 free stream, 2 compressor face, 13 fan exit, 25 HP compressor inlet, 3 compressor exit, 4 turbine inlet, 45 between turbines, 5 turbine exit, 6 mixer, 7 afterburner, 9 and 19 nozzle exits). Dots of air flow through it, coloured by the temperatures the Cycle tab works out. Click or tap a part (fan, compressor, combustor, turbines, nozzle, bypass duct, afterburner, propeller…) to read what it does and its inlet and exit conditions. The table lists every station’s total and static temperature and pressure.

Cycle is an on-design (parametric) cycle analysis. Choose Ideal (perfect components, constant gas properties) or With losses (polytropic compressor, fan and turbine efficiencies, burner and nozzle pressure losses, mechanical efficiency, separate hot-gas properties, the fuel’s mass, inlet shock losses above Mach 1, and a convergent or fully expanding nozzle). Set the flight Mach number, altitude and ISA deviation, the overall pressure ratio, turbine inlet temperature Tt4, bypass and fan pressure ratios, the afterburner temperature and the air mass flow. Out come thrust, specific thrust, TSFC, fuel flow, fuel–air ratio, thermal, propulsive and overall efficiency, compressor powers, jet velocities, and the cycle on T–s and P–v diagrams. Turboprops and turboshafts give shaft power, specific fuel consumption, propeller thrust and equivalent shaft power. A mixed turbofan’s Match the core pressure button finds the fan ratio that makes the two streams meet at equal pressure.

Trade studies sweeps one input — pressure ratio, Tt4, bypass ratio, fan pressure ratio, Mach number or altitude — and plots specific thrust, TSFC and the three efficiencies, ideal and with losses, with a note on the trend.

Compressor & turbine estimates the number of compressor and turbine stages from the pressure ratio and from blade loading; draws a compressor stage’s velocity triangles, which you change by dragging the tips of V1 and W2, giving the work, temperature rise, stage pressure ratio, reaction and de Haller number; plots an illustrative compressor map with speed lines, efficiency islands, surge and choke lines and the running line, with the surge margin at the speed you choose; and works out spool speeds from tip speed and diameter.

Real engines lists engine families with approximate public figures (thrust or power class, bypass ratio, pressure ratio), plots them, and loads any of them into the Cycle tab.

Model jets works out fuel flow, run time and the oil to add for a small turbojet such as a 66 mm KJ66-class engine, with a table of typical classes, the start-up sequence and safety notes.

On-design only: each answer is the engine designed for that point. A real engine flown off its design point (off-design or "engine deck" performance) needs component maps and matching, which this does not do — the compressor tab’s running line is the simple textbook version.

Constant specific heats (one set cold, one hot), no turbine cooling air, bleed or power offtake, and no installation losses (inlet spillage, nacelle drag). Real engines lose several per cent of thrust and TSFC to each.

The real-engine figures are approximate, rounded public numbers; turbine temperatures for them are guesses for the era. Nothing here is proprietary or suitable for engineering use.

The cutaway is schematic, not to scale, and the particle speeds are only indicative.

Model turbine figures are class averages; follow your engine maker’s manual for fuel, oil, start-up and maintenance, and your national model flying association’s turbine rules.