Sun Seeker- Solar Powered Ultralight Aircraft Christopher Dymond Getting a human airborne is hard, getting a human airborne using only solar energy is vastly more difficult. "If man was meant to fly God would have given him wings"É so the saying goes. Well in the case of the Sun Seeker maybe brains are what was needed, lots of tanned brains that is. The Sun Seeker was the first aircraft to traverse the continental U.S. on solar energy alone. The PV panels and battery reserves were used for lift off. The majority of the lift was found in rising warm air or thermals used just a sail plane would. Thermals are just another one of natures way of packaging solar energy. Full power was needed to lift off and was available for 10 to 15 minutes from both the batteries and PV array combined. While in flight any energy not imminently needed was stored in the batteries. Average duration time of motor use was under five minutes. The energy developed by the array took about 2.5 hours to charge the batteries. The batteries were then used either for take-off the next day or flying under power to the next thermal. To get a feel for the vast difference between flying by solar energy and flying by petroleum-fueled engines, consider the following comparisons. Keep in mind that the function of this comparison is not to draw direct analogies but rather to tickle your brain. INSERT TABLE The most striking specification of the Sun Seeker is it's weight compared to the size of its wings. At a little under 200 lbs. its another example of the incredible strength to weight ratio of advanced composites. Stall speed is 22 mph. The craft was constructed largely of graphite fiber and epoxy. Components as large as 23 feet in length required high temperature (350-degree) curing. A special monster sized oven was built for this purpose. Taking four years to complete, this aircraft was from conception designed to be pound-for-pound the most efficient aircraft possible. See "what it takes to fly with the sun" sidebar for more on the Sun Seeker specs. The PV array used on Sun Seeker ran at 160 VDC open circuit, 120 VDC under load, and produced about 2.5 Amperes of current. The 300 Watts of PV produced power was fed into FET power controller and finally to the 110 Vac synchronous motor. Insert SIDEBAR One of the biggest design concerns when building a solar power vehicle of any kind is to be able generate enough power from the exposed surface area to run the motor. In the case of the solar powered flight the amount of available area was not so much a problem as was the cells' weight and applying them to a curved surface without generating too much drag. A primary reason for the development of the Sun Seeker was to test and demonstrate the new, ultralight photovoltaic cells developed by the Sanyo Corp. These new cells were contoured to the wings of the aircraft, and used instead of heavier, rigid conventional PV cells. The new PVs are based upon a thin film cells bonded to a thin substrate called Amorton. This thermoplastic polymer has the necessary properties of being both heat resistant, flexible and transparent. PV cells are usually made on a glass substrate because, among other reasons, glass yields no contaminating off-gases during the extremely precise, high- temperature chemical process used to make the actual photovoltaic material. According to Yukinori Kuwano general manager of the Japanese company's functional materials research center in Osaka, Japan, Sanyo got technology from another Japanese firm for a polymeric substance which, like glass, poses no off-gassing problem during cell production. The layers of amorphous silicon are bonded to Amorton producing a very flexible, ultra-light PV cells about 600 times thinner than conventional cells. The cells are a mere 21 microns thick, weigh about 2 grams and are capable of being bent to a radius of only 5 mm. The power to weight ration of these cells are 10 times that of regular cells. The draw backs of these PV cell is there fairly low efficiency (approximately 4-5%). According to Sanyo this degrades by about 15% in the first year. Their efficiency continues to drop until it reaches about 70% of the initial ability at the end of 3 years. The cells then stay at this level for the remainder if their life which is estimated at 5 to 6 years total. Cost the these cells are likely to be high at first but may drop as mass production gets underway. The prospects for a material like PV cell is easily apparent. Imagine if you will having your tent or a canopy composed of electricity generating material. Or perhaps boarding an airship who's exterior is entirely composed of a flexible PV cells, the electric motors quietly propelling you along. Sure beats the heck out of train travel. What it takes to fly with the Sun Sun Seeker Specifications Class Ultralight Motor 2000 watt- 100 Vac Synchronous PV Cells 600 110 mm x 115 mm cells 100 55 mm x 115 mm cells Power available 2.5 amps @ 120 volts batteries 96 D-cell Sanyo NiCads 4.2 Amp Hours at 1.2 VDC each charge time 2.5 hrs. Mass 91 kg. (198 lbs.) Cargo 67 kg. (147 lbs.) Length 7 m. (23 ft.) Height 1.3 m. (4.3 ft.) Wing Span 17.5 m. (57.4 ft.) Fuselage Carbon fiber sandwich honeycomb and fiberglass with epoxy resin Design limits 6 g acceleration Propeller Hybrid cloth, fixed pitch weight 1.4 kg. (3.1 lbs.) length 2.4 m. (7.9 ft.) Rate of Climb 60.8 m./min. (200 ft./min.) Ceiling 14,000 m. (46,000 ft.)