[SEE]

Controls menu - Aircraft - 'Toggle Selected Engine(s)'

Assign a Keyboard command or Press the switch on your Stick to assign it to that command.

You will still need to set the fuel Cock first before starting the engine.


Alternatively, all aircraft start procedures can be done automatically by selecting AI pilot - AI control of ac is in the difficulty level settings (I think the default is A) - press A and the plane starts/TO/flies untill you press A again to give you control - If you only want to start - press A and then press A again when started.