CAFE Symposium Celebrates the 'Dawn of Electric Flight'
By Patrick Panzera, Editor — Experimenter, EAA 555743
May 3, 2011 —Picking up where we left off in Part I of this series, David Calley, Co-Founder and Chief Technology Officer of Motor Excellence gave his presentation “Ideal Electric Aircraft Motors.” The primary point Calley made was that a key barrier to widespread adoption of electric vehicles is the additional cost above comparable internal combustion engine vehicles due to large, expensive batteries.
The focus of Motor Excellence has been to develop lighter, highly efficient, and thermally stable motors that provide the same power and torque at a lower power demand than the current state-of-the-art motor technology allows. This enables a significant reduction in battery size and cost, netting a result similar to increased battery energy density.
Coming from the wind generator side of the clean-energy movement, with generators and electric motors having much in common, Calley, the founder of Southwest Windpower, brings his decades of experience from creating highly efficient generators to the electric motor industry. Using what he refers to as "3-D construction" (where there is only a single winding made from heavier gauge wire resulting in less resistance), Calley has designed high-torque, low-RPM, thermally stable electric motors that are suitable for direct-drive use in bicycles and automobiles. In some aviation applications however, they might need to be geared up.
Motor Excellence feels confident that even with a shortage of rare earth magnets, they can still outperform conventional highly efficient electric motors.
Two additional points of interest Calley brought up were 1) the current rate of the world demand for eBikes is in the 30 million per year range, and 2) China controls nearly all the rare earths necessary for neodymium magnet (rare-earth magnet) production, essential in creating small, light and powerful electric motors.
While the focus of the Electric Aircraft Symposium would seemingly be electric aircraft, a lot of what was discussed was either in support of efficient flight or a seemingly practical application of electric flight where it could be potentially more efficient than an internal combustion engine.
Along the lines of supporting efficient flight, Professor Krish Ahuja of Georgia Tech University gave his lecture on “Quiet Propulsion Technologies”, in other words, how to make propellers quieter without losing thrust. Pointing out that the propeller tip is the dominate source of sound - with speed being the biggest factor - he also stated that the twist, chord, number of blades, as well as the leading edge sweep, were all contributors.
A scimitar planform is ideal, he said, as tip speeds approach .65 mach (which he considered the fastest speed a prop-tip should ever see). He showed that a high aspect ratio, six-blade prop can be quieter than a traditional two-blade prop producing the same thrust. However, when asked by an audience member about the test propeller RPM, Ahuja disclosed that of the props tested, the two-blade was spinning at 6,000 RPM and the six-blade at 3,000.
The McLaughlin controller is made from off-the-shelf parts and is intended to become open technology.
The most homebuilder-like presentation was from Patrick McLaughlin, founder of Mountain High Equipment & Supply Co. (the maker of state-of-the-art aviation oxygen equipment) who spoke on “Motor Controllers for Electric Aircraft.” Starting with a clean-slate, wishing to use off-the-shelf parts for constructing inexpensive controllers, his desire is that this type of information will become "open technology" where designers and developers can tweak, improve, or redesign for the betterment of the end product, which should be available to all. His work started with what is available from the radio control community, and he's built up from there, incorporating the differences required for manned flight. At this point, all research and development has been done in his "spare time."
McLaughlin finished his presentation with this image of his spare-time "lab."
Specifications for the controller 50-60 kW at 250 volts, using 4-6 ounces per square foot copper substrate, bolted to glass. The system could run up to 80 kW and the cost of the parts and raw materials is in the $280 range. An interesting angle McLaughlin touched on is the idea of multiple controllers and multiple motors used in series to vary power.
McLaughlin's polymodal controller has what he called a "memory function" that in addition to controlling the speed of the motor, the system knows where the propeller blade is at any given time, allowing for a stepper function (built into the controller) to be implemented for "parking" the prop when stopped; its accuracy is down to fractions of a millimeter. This function is particularly important to self-launch gliders that might have a retractable propeller like Pipistrel’s Taurus.
Pipistrel’s Taurus Electro G2 utilizes a retractable propeller that needs a stepper function to clock the prop blades in a vertical position.
The opening presentation was by Dr. Ben Santer, Climate Scientist for Lawrence Livermore National Laboratory, who spoke on climate change. This topic was brought up by virtually every speaker during the two-day event, as it seems to be one of the driving forces behind the move to electric vehicles, including aircraft of all sizes.
Part of Dr. Santer's program touched on the fact that computer models, those most responsible for forecasting long-term weather (including the earth's temperature), are designed to consider "natural background noise," i.e. natural phenomena such as volcanoes and the sun's 11-year irradiation cycle.
Carbon nanotubes, that during last year's symposium were reported to be technology that was still 10 years away, were on the lips of multiple speakers, even those whose work is vastly beyond theoretical. According to Karl Young, CEO, X-Cap who spoke on “10X Supercapacitor Energy Storage Using Carbon Nanotubes,” single-wall nanotubes have a surface area of 1,500 square meters per gram (16,145 square feet), which is three times that of activated carbon (charcoal), the main component in virtually all commercial supercapacitors produced since 2010, and the positive electrode in typical dry cell batteries.
In addition to the larger capacity from the greater surface area, carbon nanotubes are highly conductive netting fast charge and discharge speed. As an example, Young stated that carbon nanotubes are 1,000,000 times more conductive than copper. X-Cap has yet to produce a working prototype.
With nearly 30 presentations in all, each deserving their own article in any number of EAA’s publications, it's hard to cover it all. We will continue to report on this event, and other electric flight events. Although the battery technology is still lagging, advances in electric motors and their controllers, plus the awakening to the need to reduce airframe drag - even if it means clean-slate thinking such as Synergy and Seraph - commonplace electric flight may not be too far off.