Electric sports plane the highlight of the e-flight initiative

Electric Power - the 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.

Electric Power - the 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 E-Flight design team has engineered and constructed 10 battery “safe boxes” intended to contain 8 Li-Poly battery packs per box and consolidate their charge/discharge and balancing wiring into two sets of multi-pin connectors. The Boxes will accommodate natural cell expansion and contraction while safely securing each cell pack and facilitating cell cooling with “cooling foam” padding. Cooling will further be aided by heat sink surfaces on each box that will have cooling inlet air directed over them. Additionally, the boxes are designed to contain and safely direct fire or explosion within the box through a “blow hole” in the box that will be connected to a small exhaust manifold.

For the proof-of-concept aircraft, the battery boxes will be removed from the aircraft and charged individually. The charging units need to be configured to safely keep all cells balanced during charging. Lessons learned from the proof-of-concept systems will lead to the design of more advanced charging and balancing systems allowing safer battery handling by consumers, including a single-plug charging system that may remain in the aircraft at all times, featuring easy exchange of battery boxes to enable consecutive back-to-back flights in a short period of time by pilots who wish to invest in spare batteries.

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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