'Idle' curiousity
Often you see planes on the apron and the engine fans are turning slowly. I've always believed that is to prevent the turbine blades from distorting as they cool. Is that correct? But my real question is, how do the fans turn? They are not idling (as in engine running slowly), so what drives them? I can only imagine that some geared electric motor engages with the power shaft somehow, but I can't see how that would be achieved. Thanks in advance.