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    1. Project Sunrise

    2. Los Angeles California 1974

    3. Flight of the Worlds First Solar Powered Aircraft

    4. by

    5. Roland Boucher


Structure


Early structural tests using a whiffle tree showed that while balsa wood could be used for tension loads, it would fail completely in shear at the wing attachment points on a 22 pound plane. The final design of the wing spars used spruce spar caps with maple doublers at all attachment points with dual 3/32 balsa shear webs attached to 1/8 x 3/8 hard balsa strips mounted to the upper and lower wing spars. The ribs were 3/32 balsa. This was in effect a balsa box with tapered spruce caps. The leading edge was covered with 1/32 balsa to form a D spar at the leading edge. The trailing edge was formed by two two-inch wide 1/32 sheets forming a triangle with 1/8 x 3/8 vertical spar sections between the ribs. The covering was 1/2 mil Mylar obtained from FAI Model Supply. The result was 32 foot wing which weighed 5 pounds and could handle loads up to 100 pounds.


Aerodynamics


The aerodynamic design of this plane was primarily that of a sailplane. The tail volume coefficient was over 100 percent ensuring a stable climb attitude even when out of sight of ground control. The principal point of concern by the Lockheed team was the reliability of the German model data used in selecting the Eppler 387 airfoil. The plan was to build a 1/4 scale model of Sunrise and measure its sink rate in calm air. Through the influence of DARPA, one of the giant blimp hangars in Tustin California was set aside for the glide test. The model was hand-launched from a catwalk at the 100 foot level and guided in a circular flight path down to floor level. This was a complete success. A sink rate less than one foot per second was achieved with the 1/4 scale model. This test duplicated the Reynolds number at the expected peak altitude of 78,000 feet. Later, when the 32 foot plane was tested at Bicycle Lake using battery power, both the aerodynamic and propeller performance were confirmed.


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