Therefore the blades encounter an apparent frontal wind when moving {HEAD ~ downwind}, which is {TAIL ~ the resultant} of the blade speed minus the wind speed 
Therefore the blades encounter an apparent frontal wind when moving { HEAD ~ downwind } , which is { TAIL ~ the resultant } of the blade speed minus the wind speed
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH