variable transmission 46 such that no more output is transferred to the rotor 18 in step 106 the landing procedure of the helicopter 8 is initiated and the auxiliary drive system 22 is set so as to introduce output again the landing procedure is initiated by the pilot by moving the rotor 18 out of the autorotation position into a landing position in which the energy stored in the rotor and transmission is used to brake the helicopter 8 this switchover can be detected by the controller 24 for example through a corresponding signal from the control system of the helicopter 8 after that the controller 24 sets the variable transmission 46 analogously to step 102 again such that the desired output is introduced into the second input 48 of the main transmission 14 in order to additionally drive the rotor 18 to enable estimation of how a flywheel mass battery and its flywheel could be dimensioned the following formulas can be used torque of a flywheel as a massive cylinder a cylindrical shell has twice the torque despite their low mass density high strength materials such as cfrp carbon fiber reinforced plastics for instance can be used as the material for the flywheel metals and metal alloys are also suitable materials by comparison lithium batteries have an energy density of 200 wh kg which corresponds to 0 72 mj kg an ec120 type helicopter has a power input of about 100 kw for 30 s this corresponds to an energy requirement of 3 mj the energy density of cfrp is 800 kj kg which yields a flywheel weight of 3 75 kg assuming a factor of 4 for.