I don't agree that running fans are an obstruction. A fan that's stationary has more back pressure (to the air being forced through the grille) than one that is turning, since energy has to be expended to spin the fan and motor.
Not true. A windmilling fan blade will create FAR more drag than a stationary blade. The force created by the 'wind milling' is caused by lift created by the fan blades, and that lift creates drag. This is why propeller driven aircraft with controllable pitch propellers 'feather' the blades in the event of powerplant failure. In the radio controlled airplane world, motor controllers have built-in 'brakes' to stop the prop which helps reduce gliding drag too.
