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Electric Power

Conceptualization of an electric powerplant project actually pre-dates the 1997 founding of Sonex Aircraft. In 1994, John Monnett and Pete Buck devised the concept to design, build, and fly a small electric powered and manned aircraft that would be capable of a short duration flight in order to set or establish speed records for this new class of aircraft. Pete Buck prepared a detailed feasibility study for the project dubbed "Flash Flight". Buck, who works full time as an engineer at Lockheed Advanced Development Company "Skunk Works" and is Sonex Aircraft's Chief Engineer, also spent 2 semesters of his engineering degree analyzing and building the battery/power system for a Hybrid Electric Vehicle (HEV) sponsored by Ford Motor Company.

Buck’s study concluded that Flash Flight was feasible using many “off the shelf” components at relatively little risk. The aircraft would fulfill it’s record-attempt mission, however, it would only have an endurance of approximately 10 minutes. Other tasks associated with the founding of Sonex Aircraft, LLC took priority, and Flash Flight never came to fruition.

Since 1994 and Flash Flight’s feasibility study, the popularity of radio controlled electric powered toy vehicles, gas-electric hybrid cars, and the boom in wireless electronic devices such as cell phones and PDA’s have pushed the state-of-the-art in battery, electric motor and controller technology. Brushless DC cobalt motors are now lighter and more efficient. Advances in microprocessors have allowed motor controllers to be smaller, lighter and more efficient. Lithium Ion and Lithium Polymer battery technology has pushed the endurance, efficiency and power output of electronic devices, while shrinking in physical size and weight. The Sonex R&D team concluded that the time for this endeavor had arrived.
 

A New Mission
 
The contemporary e-Flight electric project will benefit greatly by the maturation of technology since our initial studies. Using a purpose-built AeroConversions brushless DC cobalt motor, controller, and highly efficient battery and charging system, the e-Flight electric systems will be able to power a larger aircraft to higher top speeds with greatly increased endurance. e-Flight’s proof-of-concept prototype will use the flight proven Waiex airframe so that the emphasis can be placed solely on powerplant research and development. Initial top speeds will reach approximately 130 mph, and endurance is expected to range between 25-45 minutes or longer, depending upon power usage on each individual flight.

The initial emphasis for the e-Flight proof-of concept aircraft has been shifted away from immediate pursuit of FAI speed records, although the possibility remains that those records could be obtained in short-order after successful first flight. With the advanced state of the technologies concerned, the goal of the project is to develop and prove the application of the technology and pave the way for near-term electric powerplant Sonex and AeroConversions products for sale to the sport aviation marketplace and beyond.

The current state and growing popularity of electric powered model RC aircraft leads the layman to assume that an electric powered aircraft of this type is simply a matter of hooking a bigger battery to a bigger motor, charging it up in an hour or two and taking-off. While that is essentially true in raw principle, the reality of this project is that scaling-up these technologies in a viable manner presents significant challenges.
 

AeroConversions Electric Motor
 
Brushless DC cobalt motor technology has advanced significantly since 1994’s Flash Flight study, allowing the design team to now consider their use, however, just like before, a suitable brushless DC cobalt motor of this level of power output with an acceptable size and weight does not exist and can not be built and provided by a third party vendor without incurring unacceptable costs. As a result, the design team is designing and building a completely-new AeroConversions motor.

This motor is the most powerful, lightest-weight, and efficient unit of this type ever produced. It is a 3 phase, 270 volt, 200 amp motor that will be over 90 percent efficient. It uses elegantly designed CNC machined anodized aluminum and nickel-plated steel parts in combination with “off the shelf” bearings, races, snap rings, magnets, etc.

The prototype AeroConversions motor is slightly larger than a 35 ounce coffee can and weighs approximately 50 pounds. The motor will be a modular, scalable unit. The motor core’s design will have modular sections that can be reduced to a lower-output, smaller motor (shortened in length), or added upon to make a larger motor with a higher power output.
 

AeroConversions Electronic Motor Controller
 
Electronic motor controllers for brushless electric motors are quite commonplace today, mostly used in the electric RC market. A suitable controller for a 270 volt, 200 amp motor does not exist. Running such high current requires much larger components. Although there are a handful of third party vendors who could design and build the appropriate controller for this project, it would take 6-7 months lead time and cost 20-50 Thousand Dollars. The time and cost associated with acquiring such a controller was deemed unacceptable and the research and development team, in cooperation with a key electronics expert, began designing a proprietary AeroConversions electronic motor controller.

The controller can commutate the motor in two different ways: using Hall effect sensors to determine the magnet core’s position in relation to the coils, or using the motor’s back-EMF to sense rotor position, eliminating the need for Hall sensors. The AeroConversions controller will initially employ a Hall effect sensor-equipped motor, but back-EMF controlling will also be explored to potentially further simplify the AeroConversions motor design. The AeroConversions controller will also provide in-cockpit monitoring of battery power levels to the pilot.
 

AeroConversions Battery System
 
Most contemporary electric powerplants for gas-electric and pure electric cars and previous generations of RC electric vehicles utilize Lithium Ion battery technology. While much improved in power density and discharge rate over lead-acid and NiCad batteries, Li-Ion batteries still do not offer enough power discharge-to-weight ratio to support an electric powerplant for an aircraft that is based on battery power alone and has a market-viable endurance. Newer RC electric vehicles, cell phone, laptop computers and other mobile devices have been moving toward Lithium Polymer cells. Li-Poly battery cells can safely discharge at a rate of 25 times their capacity, or “25c.”

With all the extra energy of a Li-Poly cell, however, comes extra volatility. The potential volatility of Li-Ion batteries has been documented in the well-publicized exploding laptop computer and other similar incidents and the risks with Li-Poly batteries are even more significant.

Future generations of safer, more powerful Li-Poly batteries show the near-term possibility of further extended flight duration while personal electronics and transportation will undoubtedly continue to push improvement of the technology in years to come.

 


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