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/339662
EAA Experimenter 29 I consider this new electric-power industry inevitable; elec- tric motors are around 90-percent ef cient whereas gas engines are about 30-percent ef cient. In the model airplane industry, the anomaly now is the gas engine. Just about everything is electric powered. The other key attraction is that many of us don't want or need to make 4-hour trips but rather just short-duration fl ights. That's so much more ef cient to do with electric power. The concept of a four-place, all-electric airplane is a ways down the road. Maybe that will be the next boom for general aviation (GA). But for personal, af ordable fl ight, it can happen right now with af ordable, single- and two-place ultralight-type aircraft like the EMG-6. JL: What about the weight challenge of batteries? BC: First, we have to look at the weight advantage of electric motors. We're working with several, but let's consider the Plettenberg 40-hp Nova 30, for example. This motor has 20 percent more torque than a Rotax 447 standard. The 447 weighs 93 pounds. The Nova 30, including the speed controller, weighs 20 pounds. (The motor itself only weighs 11 pounds!) That leaves a dif erential of 73 pounds for batteries before we're equivalent to the zero-fuel weight of the 447. Given the current state of battery technology, that's about 20 minutes of running time. So anything that fl ies less than 20 minutes favors electric power. Anything longer still favors gas. That's where we are today. So here's our premise: We're building a glider with 20 min- utes of electric power that we can use to get up to the lift, turn of , soar as long as we are able, then still have time to return for landing, do a go-around, shoot another approach, or extend our glide for reaching the next thermal. Just adding a little power is a big boon for a glider. Otherwise a pilot has to routinely con- tend with big decisions on every fl ight. We want a clean, simple machine with some power. We're not anticipating this will be a cross-country machine just yet: It's a local machine, essentially a fi xed-wing hang glider, with electric power attached. That's our immediate goal. We're concentrating on develop- ing the platform. This is an exploding new technology. There will be powerplant packages that come and go. Many will be obsolete by the time they hit the market; the technology is evolving that quickly! It's like laptops; you get a new one, and there's already a better one out there. It is going to be the same with motors, controllers, and batteries. One approach we're considering is a modular motor mount, say, three dif erent types for three dif erent motors. We also have worked on mounting smaller, multiple motors to distrib- ute power throughout the airframe. For now our focus is on a single-engine, self-launching, 40-hp-equivalent electric powerplant. That's our end goal; right now we are fi nalizing the airframe portion. JL: Are you developing your own motors? BC: No, there are lots of really smart people working fever- ishly on motors. We'll be the fl ying test bed for several power- The aft fuselage fairing assembly installed, which incorporates the aft motor mount. The fairing attaches with one bolt and 5 screws on each side of the fairing, making it relatively simple to remove for maintenance and or inspection. It took a considerable amount of preplanning to fi gure out how to extract the nose cone's female mold from the male plug. What we ended up doing is pre- drilling holes down through the inlet ducts and inserting air fi ttings on the bottom of the male mold, which allowed us to pump air pressure in between the female fi berglass mold and the male plug. In this picture, the air hoses are hooked up to the bottom of the plug forcing air in between the two components. We were able to exert force throughout the entire component and separate the two pieces. Photography courtesy of Rainbow Aircraft E A A E X P _ J u l y 1 4 . i n d d 2 9 EAAEXP_July14.indd 29 7 / 1 / 1 4 9 : 5 7 A M 7/1/14 9:57 AM