February 2013

Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.

Issue link: https://experimenter.epubxp.com/i/108002

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Page 19 of 44

R e d d y K il o w a t t M e e t s t h e Ul t r a li g h t great; it's very stable," said Fishman. "If you can fly a Cessna 150, you can fly this. It feels a bit like a sailplane but needs less rudder." The ULS has twin tail booms (and two rudders) along with mild dihedral, which helps it track well. He said, "I initially wanted a single tail boom, but the airframe designer preferred two. I've grown to like the hard points it adds for the landing gear, which is a light weight, trailing link suspension, which avoids the need for a heavy spring gear." Two-thirds-span flaperons and spoilers give it serious soaring chops. Spoilers help degrade glide angle during landings. Without spoilers you're in for long, challenging final approaches. A bit more about electric "fuel": Current research promises manyfold increases in energy density battery capacity—the energy output per pound of weight—in the future. For now, lithium polymer (LiPo) and lithium iron phosphate (LiFePO4) are the name of the game. Fishman designs his own powerpacks with reliable, well-tested LiPo cells. He has tested cells from many different producers since 2006 and is happy with the quality from his current supplier. The ULS sports a stainless-steel battery box in each wing root for protection in case of fire: LiPo cells, if badly mistreated, can catch fire. (Of course, so can gasoline.) Each steel wing box measures 21 inches wide, 17 inches across, and 3 inches deep. The ULS comes with two battery packages: the "half" pack provides 3.35 kWh (kWh = kilowatt hours) total. The "full" pack serves up nearly 2 hours of flight per charge. To help understand what the ultralight's full-pack capacity of 6.7 kWh actually means, let's use a real-world example. Say you use 0.75 kWh of energy to climb to 2,000 feet by running the motor at its maximum 15-kilowatt power setting for three minutes. Te ElectraFlyer ULS in fight. Then you throttle back—way back to perhaps 20 percent—to a 3-kilowatt power setting for sustained cruise. Fly around for an hour at that setting, and you've drained a little more 3 kWh—kilowatt hours, remember?—from the batteries. That leaves your battery "tank" about half full. The meter says you have around 3 kWh left: enough for another half hour of cruise, with maybe a half hour (1.5 kWh) of reserve. Capiche? Descent is done at 0 or low discharge rate. Thirty years ago FAA worded the FAR 103 rule to allow ultralights "a maximum fuel capacity of five U.S. gallons." That meant single-seat ultralights could weigh 284 pounds with full fuel. Since no one was addressing electric flight for ultralights 30 years ago, the topic needs re-examination. How to translate 5 gallons of gas into battery weight? As 5 gallons in equivalent volume for the batteries? Or 5 gallons in gas weight, which is 30 pounds? At that crossroads lies the potential for design freedom…or imprisonment. Testing and adjusting all the components of the electric motor system. 20 Vol.2 No.2 / February 2 013 "It's still up in the air," said Fishman, although he's optimistic the volume interpretation will eventually carry

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