Jet engine thrust ratios?

[BabyBear]

Can anyone tell me how thrust increases with engine speed on a typical modern aircraft? Is it straight line, or exponential?

[Intruder]

Exponential. In the simplest terms, thrust is a function of RPM**4.

Since most modern turbofans are 2-spool (or 3-spool in the case of some RR engines), the total thrust calculation will be much more complex.

[Old Smokey]

On earlier 'Straight' jets (no fan) thrust was proportional to N^3.5 (U.S. Navy).

As modern Turbofans are essentially a composite 'Straight' jet and Fan, that exponent now lies between >2.0 and 3.5, depends upon the bypass ratio.

(That portion of the thrust derived from the fan will be proportional to the spool speed squared, that portion from the jet core will be proportional to the core speed raised to the power of 3.5)

Regards,

Old Smokey

[BabyBear]

Thanks guys', it's appreciated.