A drive for a helicopter, has at least one rotary member, a casing housing the rotary member and defining a compartment containing a lubricating fluid and air, and separating device for separating the lubricating fluid from the air and retaining the lubricating fluid inside the casing in the presence of airflow outwards of the casing and produced by pressure gradients between the compartment and the outside. The separating device is angularly integral with the rotary member to centrifugally separate the lubricating fluid from the air radially with respect to the axis.