Gas turbine engine electrical generator

1. An aircraft gas turbine engine comprising:

a main engine shaft arranged to couple a turbine and a compressor, the main engine shaft defining an axial direction;

at least one radially extending offtake shaft coupled to the main engine shaft; and

a radially extending electric machine coupled to the radially extending offtake shaft,

wherein the electric machine comprises an axial flux electric machine in which a stator of the electric machine is axially offset relative to a rotor of the electric machine, and

wherein a nacelle is provided surrounding the gas turbine engine, and

wherein the nacelle comprises a space where an outer surface contracts inwardly before expanding outwardly downstream, the electric machine being provided at the space.

2. A gas turbine engine according to claim 1 , wherein the electric machine is directly coupled to the radially extending offtake shaft.

3. A gas turbine engine according to claim 1 , wherein the electric machine is coupled to the radially extending offtake shaft by a reduction gearbox.

4. A gas turbine engine according to claim 1 , wherein the electric machine comprises at least one of an electric motor configured to provide motive power to start the gas turbine engine in a starting mode, and a generator configured to generate electrical power when in a running mode.

5. A gas turbine engine according to claim 1 , wherein the electric machine comprises a permanent magnet electric machine.

6. A gas turbine engine according to claim 1 , wherein the gas turbine engine comprises a fan speed reduction gearbox that receives an input from the main engine shaft and outputs drive to a fan so as to drive the fan at a lower rotational speed than the main engine shaft.

7. A gas turbine engine according to claim 1 , wherein the rotor of the electric machine includes a plurality of magnets disposed along a first side of the rotor, the plurality of magnets oriented so as to face the stator of the electric machine across an air gap, and wherein a second side of the rotor opposite to the first side includes a planet carrier directly mounted to the rotor.

8. A gas turbine engine according to claim 1 , wherein the at least one radially extending offtake shaft includes a plurality of radially extending offtake shafts circumferentially arrayed around the main engine shaft.

9. A gas turbine engine according to claim 8 , wherein the radially extending electric machine comprises a plurality of radially extending electric machines, wherein each radially extending offtake shaft is directly coupled to a respective one of the plurality of radially extending electric machines.

10. A gas turbine engine according to claim 1 , further comprising a low pressure compressor or a fan coupled to a low pressure turbine by a low pressure shaft, the compressor comprising the low pressure compressor or the fan, the turbine comprising the low pressure turbine, the main engine shaft comprising the low pressure shaft.

11. A gas turbine engine according to claim 10 , wherein the gas turbine engine further comprises a high pressure compressor coupled to a high pressure turbine by a high pressure shaft.

12. A gas turbine engine according to claim 11 , wherein one or more offtake shaft is coupled to one of the low pressure shaft and the high pressure shaft.

13. A gas turbine engine according to claim 12 , wherein the one or more offtake shaft is coupled to the main engine shaft at an axial space between the high and low pressure compressors.