22 is then directed into a u201c c u201d channel 24 installed along leading edge 32 of rotor blade 10 the u201c c u201d channel 24 is located inside rotor blade 10 further u201c c u201d channel 24 forms a tube because it is bonded or otherwise attached to the inside of leading edge 32 of rotor blade 10 therefore in some configurations heated air 22 flows from heating unit 12 along leading edge 32 of rotor blade 10 inside a contained tube 24 heated air 22 flows from root 20 of rotor blade 10 towards tip 26 when heated air 22 reaches tip 26 or a point near tip 26 its flow direction is reversed by directing the flow through a return tube 30 which forms a u201c c u201d shell of u201c c u201d channel 24 thus in some configurations the effect is effectively similar to a tube inside a tube or a shelled tube with the hottest air on the inside and the cooler return air on the outside advantageously heated air 28 from return path 30 partially insulates heated air 22 in outgoing path 24 and the return heated air 28 is re heated i e the air being heated is in a closed or nearly closed circuit in some configurations u201c c u201d channel 24 forms a tube because it is bonded to the inside surface of leading edge 32 of rotor blade 10 also as used herein a lower case u201c c u201d refers to an interior tube 24 containing the hottest heat unit 12 discharge air 22 whereas an upper case u201c c.