Thrust 0 kNTSFC 0 g/kN·sAir 0 kg/sT4 0 KOPR 0BPR 0N1 0 %N2 0 %loadingFPS 0

Drag to orbit, wheel or pinch to zoom. Blue = cold air, orange = hot gas (colour follows the station temperature). Casing is cut away on the near side; use Explode to separate the modules.

Turbofan Cutaway: Brayton Cycle, Bypass Ratio and TSFC

A generic civil high-bypass turbofan, station by station: set the flight condition and the cycle, read the temperatures, thrust and fuel burn, then pass five design missions.

Flight condition

Engine cycle

View

Live readouts

Stations (total conditions)

T–s diagram of the core

TSFC against bypass ratio

Design missions

Each mission fixes the flight condition and judges your current cycle settings.

Independent numerical checks

Controls

Drag / one finger: orbit; wheel / pinch: zoom; the Camera button cycles hero, front and nozzle views.
Flight sliders set altitude, Mach number and the temperature offset from the standard atmosphere; cycle sliders set bypass ratio, fan and overall pressure ratio and the turbine inlet temperature T4.
Cutaway removes the near-side casing; Explode slides the modules apart along the axis.

The science

Atmosphere and ram. ISA to 11 km (T = 288.15 − 0.0065 h, p from the hydrostatic law) with an isothermal layer above. Flight total conditions: T_t0 = T(1 + (γ−1)/2 M²), p_t0 = p (T_t0/T)^(γ/(γ−1)).

Compression. Polytropic efficiency η_p: T_out/T_in = π^((γ−1)/(γ η_p)). The overall pressure ratio OPR = p_t3/p_t2 = FPR × (booster × HPC); the booster takes 35 % of the core pressure ratio (model value).

Combustion. Fuel–air ratio from an energy balance f = (c_pH T₄ − c_pC T_t3) / (η_b LHV − c_pH T₄), LHV = 43 MJ/kg (Jet-A class), η_b = 0.995, total pressure loss 5 %.

Turbines. HPT power equals HPC power; the LPT drives the fan (whole flow) and the booster, with mechanical efficiency 0.99. Expansion uses p_out/p_in = (T_out/T_in)^(γ/((γ−1)η_t)). γ = 1.4 (c_p = 1004.5 J/kg/K) before the combustor and 1.33 (1156.7) after.

Nozzles and thrust. Choked when p_t/p₀ exceeds ((γ+1)/2)^(γ/(γ−1)): then V = √(γ R T*) and there is a pressure-thrust term (p₉ − p₀)A. F = ṁ_c(1+f)V₉ + ṁ_bV₁₉ − ṁ₀V₀ + pressure terms, TSFC = ṁ_f/F. Efficiencies: η_o = F V₀/(ṁ_f η_b LHV) = η_th η_p with η_p = 2V₀/(V₀+V_eq), V_eq = F/ṁ₀ + V₀.

Why bypass helps. Moving more air by a smaller velocity increase raises η_p at flight speed, which is why TSFC falls with BPR until the larger fan mass and drag cost more than the gain.

Simplifications. Mass flow follows a corrected-flow scaling from a reference core, no cooling air or customer bleed, no inlet or nacelle drag, no off-design compressor maps; rotor speeds N1/N2 are illustrative percentages. A civil engine only; generic, not a copy of any manufacturer's design and not affiliated with one. Models built with Blender, scene by Three.js.