Efficiency of jet engines

[EPIRB]

If around 27% of heat energy is converted into useful work in a piston engine, can anyone tell me how much heat energy is converted into useful work in a jet engine?

[Keith.Williams.]

The conventional wisdom is that good piston engines typical achieve about 30% thermal efficiency, and jet engines achieve about 20%. These are of course generalisations. But the (UK) tax man always gets the first 85% or so if its a car that you are driving!

[Private jet]

Steam (external combustion) engines = 20%
Piston (internal combustion) engines = 30%
Gas turbine engines = 30%
Electric motors = 95% !!

These figures are of course very approximate due to the range of variables involved.

[EPIRB]

Thanks guys. And apparently the human body is 24%.