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: http://experimenter.epubxp.com/i/108002

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Page 20 of 44

Tis view shows the standard fxed two-blade prop that comes on the ULS, as well as the twin rudders. Fishman discusses his ElectraFlyer ULS in this video. the day. "But a full 5 gallons of volume would be about 110 pounds of batteries." Fishman expects the issue to come down on the side of time in flight, so let's revisit the concept of energy density. Current battery technology supplies perhaps 1/72 the energy density of gasoline. If we consider the greater efficiency of electric propulsion, the ratio narrows to 1/20. Restricting battery capacity to the gas equivalent weight of 30 pounds (5 gallons x 6 pounds/ gallon) will allow for only about 30 minutes of power due to the higher discharge rate. Fishman isn't worried. "I'm working on this with EAA," he said. "We're asking FAA to set an energy equivalent to a specific volume of gas, say one gallon." One gallon of gas produces the equivalent of 36.6 kWh of energy, but gas engines are much less efficient than electric motors. So perhaps a 7- to 10-kWh equivalent storage capacity would be a reasonable battery capacity for ultralights. In LiPo cells that's about 100 pounds, very close to Fishman's 90-pound "full packs" for the ULS. And the aircraft still conforms to the sport flying spirit of the ultralight rule, with decent endurance and a traditional safety reserve. Photography by James Lawrence and Bill Leavens The limitations of batteries are why motorglider designs still dominate electric flight: Small motors, reasonable weights of batteries, and efficient aerodynamics equate to sips rather than gulps of electric "fuel." Fishman projects the life of his 2-hour packs at 800 recharge cycles, 1,600 hours of flight time. For the average pilot who flies 100 hours per year, that's around 15 years! If ultralight-style electric motorgliding isn't quite your cup of electric tea, ElectraFlyer is working on an allcomposite, two-place experimental kit plane. Fishman will be overhauling his website, www.ElectraFlyer.com, soon, so check there for updates. Let's be clear: The ULS is an impressive step forward, but these are still the early days of electric flight. Within 5 years, we may well have two- and four-seat electric aircraft that cruise beyond 100 knots for 2 hours and more. Meanwhile, with the ULS, Randall Fishman proves yet again that the electric future is already here. Yes, we are still living in the pioneer days…but how completely cool is that? Every major effort requires a first step. James Lawrence is a frequent contributor to a variety of aviation magazines. EAA Experimenter 21

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