A jet engine's job is to accelerate air and turn that into thrust: mass flow rate times the difference between exhaust velocity and flight velocity. How well it does that job is overall efficiency, which splits into two multiplied factors — thermal efficiency (the Brayton cycle, set by the overall pressure ratio) turning fuel's chemical power into kinetic power in the jet, and propulsive efficiency (the Froude efficiency) turning that kinetic power into useful thrust power on the vehicle rather than wasted motion left in the exhaust. At a standstill thrust is huge but propulsive efficiency is exactly zero — the engine's oldest paradox. Raising bypass ratio trades specific thrust for a lower TSFC, the fuel-per-thrust tradeoff behind every high-bypass turbofan. Set the airflow, bypass ratio, pressure ratio, fuel flow, flight speed, and component efficiency, then watch it all play out live. It all runs on your device.
You are in the Physics lab.
Fuel power in, thermal and propulsive losses out — and how much of it survives as thrust.
What the engine schematic, the loss-split bar and the two plots are telling you — then what the model says about bypass ratio.
The schematic shows core airflow burning through the compressor, combustor and turbine while bypass airflow slips around it, both streams joining the exhaust. The gauge beside it tracks overall efficiency — how much of the fuel's chemical power actually survives as thrust power once thermal, component and propulsive losses are subtracted (the same split the loss bar shows).
The loss-split bar breaks the fuel's chemical power into three losses that never show up as a single number — thermal loss, component loss, and propulsive loss — plus what's left as delivered thrust power. Widen any slice and overall efficiency falls, since it's the product of thermal, component, and propulsive efficiency together.
The first plot ramps flight speed from a standing start up to cruise speed, tracking thrust falling and propulsive efficiency rising together — the standstill paradox made visible. The second plot draws overall efficiency and specific thrust against bypass ratio and marks where the current design sits, showing why high-bypass turbofans trade thrust density for fuel economy.
Two efficiency factors multiplied together, three losses that eat into them, and a bypass dial that trades one for the other.
Thrust is the total exhaust mass flow rate — core airflow plus bypass airflow plus the fuel burned into the stream — multiplied by the difference between exhaust velocity and flight velocity. Either pushing more air or pushing the same air faster relative to the vehicle raises thrust; a jet engine's whole job is accelerating the air passing through it.
Thermal efficiency is set by the overall pressure ratio through the Brayton-cycle relation: one minus the pressure ratio raised to the negative of gamma-minus-one over gamma. A higher pressure ratio squeezes more useful kinetic power out of the same fuel, which is why modern engines keep pushing OPR higher — component efficiency in the compressor and turbine then takes its own cut of whatever the cycle delivers.
Propulsive efficiency, the Froude efficiency, is twice the flight speed over the sum of exhaust and flight speed — it is zero at a standstill and climbs as exhaust velocity approaches flight velocity. Raising bypass ratio spreads the core's kinetic power over more total airflow, lowering exhaust velocity toward flight speed to cut TSFC and lift propulsive efficiency, but it also lowers specific thrust per unit of airflow, which is why a high-bypass turbofan needs a larger engine for the same thrust a low-bypass turbojet delivers.
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