similar restraint of induced flow when in prox- 
imity to the ground plane. Since the induced 
rotor power required will predominate at low 
flight speeds, ground effect will produce a con- 
siderable effect on the power required at low 
speeds. During hovering and flight at low 
speeds, the elevation of the rotor above the 
ground plane will be an important factor de- 
termining the power required for flight. 
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