Last week we finished the construction of all eight rotor blades! This represents the completion of the single largest task, and obviously one of the most important components of the helicopter. Each rotor weighs only 5 lbs, with the majority of the weight (3.5 lbs) in the carbon fibre spar. The rotors will be the largest ever built for a quad-rotor helicopter, and will make less than 20 rotations during the length of the 1-minute Sikorsky Prize flight!
As you can see from the photo, the construction style is very minimalist. There are ways of making aerodynamically cleaner airfoils by extending the foam on the leading edge, adding extra ribs, and putting in a more rigid trailing edge, however, design optimizations showed that the savings in profile drag would not offset the additional weight of the structure. In that sense the wing of the Atlas is very much like that of the Gossamer Albatros (shown below left), rather than the heavier, but aerodynamically smoother wings of the Daedalus or the Snowbird Human-Powered Ornithopter (shown below right).
