Hybrid propulsion system with controllers (5, 7, 11) and a drive shaft of a helicopter with a main rotor which is connected to a gear box and is configured to keep a stable flight attitude set by a pilot, comprising: a pilot controller, a combustion engine and an electric motor, both of which act directly on the drive shaft, wherein the VM is connected to a VM controller which is configured to adjust a fuel supply from a fuel tank to the VM in order to provide a desired propulsive power at the drive shaft; and wherein the EM is connected to an EM controller, which is configured to operate the EM by discharging a battery or charge the battery by applying mechanical power on the EM, whereby the drive shaft would either be accelerated or decelerated respectively, wherein one or more torque sensors and tachometers are each arranged on the drive shaft, and both the VM controller and the EM controller are configured to each receive values of the current speed and the current torque during operation, and wherein predetermined values of the speed and the torque, in which the VM is configured to attain its optimum efficiency, are stored and can be called up for the EM controller, wherein the former can also be called up for the VM controller, and in that the VM controller, by adapting the output of the VM, is autonomously capable at any time of achieving the predetermined speed at the drive shaft and keeping it constant in order to maintain stable any flight attitude set by the pilot controller, wherein the EM controller is configured to additionally accelerate or decelerate the drive shaft by engaging the EM, whereby the VM controller is configured to automatically adapt the output at the VM on the basis of the current rotational speed in order to achieve or maintain the predetermined rotational speed at the drive shaft, characterized in that a first directive is stored in the EM controller to continuously exert such an accelerating or decelerating force from the EM on the drive shaft, thereby causing the VM, when it has reached or is maintaining an optimum speed at the drive shaft, to automatically generate the torque on the drive shaft at which it reaches an optimum engine output. a pilot controller, a combustion engine and an electric motor, both of which act directly on the drive shaft, wherein the VM is connected to a VM controller which is configured to adjust a fuel supply from a fuel tank to the VM in order to provide a desired propulsive power at the drive shaft; and wherein the EM is connected to an EM controller, which is configured to operate the EM by discharging a battery or charge the battery by applying mechanical power on the EM, whereby the drive shaft would either be accelerated or decelerated respectively, wherein one or more torque sensors and tachometers are each arranged on the drive shaft, and both the VM controller and the EM controller are configured to each receive values of the current speed and the current torque during operation, and wherein predetermined values of the speed and the torque, in which the VM is configured to attain its optimum efficiency, are stored and can be called up for the EM controller, wherein the former can also be called up for the VM controller, and in that the VM controller, by adapting the output of the VM, is autonomously capable at any time of achieving the predetermined speed at the drive shaft and keeping it constant in order to maintain stable any flight attitude set by the pilot controller, wherein the EM controller is configured to additionally accelerate or decelerate the drive shaft by engaging the EM, whereby the VM controller is configured to automatically adapt the output at the VM on the basis of the current rotational speed in order to achieve or maintain the predetermined rotational speed at the drive shaft, characterized in that a first directive is stored in the EM controller to continuously exert such an accelerating or decelerating force from the EM on the drive shaft, thereby causing the VM, when it has reached or is maintaining an optimum speed at the drive shaft, to automatically generate the torque on the drive shaft at which it reaches an optimum engine output.