PPRuNe Forums - High-bypass turbofan

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High-bypass turbofan

Question:

On high-bypass turbofans (predominately used on all commercial jets) what is producing the majority of the thrust? Is it the thrust from the 'Bypassed' air coming from the large fan or is it the thrust from the jet blast coming out of the core of the engine?

It's the fan. Usually about 80% comes from the fan.

Turbojets are suited more to speeds in excess of Mach 1 and props become pointless at around 0.7. So going from there you could see that to optimize a passenger jet to fly at mach 0.75 - 0.8 will need more "prop" than jet. If that makes sense.

For any turbofan, have a look at the bypass ratio. That will give you a good idea of how much air gets blown through the fan compared to the jet. On the RR Trent 900 for example, the bypass ratio is 8.7:1