Convergence at CAFE’s Electric Aircraft Symposium


The 10 Annual CAFE Electric Aircraft Symposium, held at the Marriot San Francisco Airport on May 19 and 20, visited topics of electric propulsion, aircraft, airspace, and control of the various types of craft that will be sharing the skies in the near future.

Yolanka Wulff organized the event, gave the opening remarks and introduced Jo Dempsey of the CAFE Board, who shared the 34-year history of the CAFE Foundation, its many test programs and the Green Flight Challenge, which awarded the largest prize in aviation history.  She finished by welcoming attendees to the 10th Annual Electric Aircraft Symposium.

Yolanka discussed the many challenges facing green aviation, including implementing the technologies being developed, funding the activities going forward, and reaching consensus on targets, strategies and priorities for that future.  She concluded that CAFÉ’s new mission was to advance development of low-emission flight by fostering and promoting early entry of early entry market opportunities.  Yolanka explained we need solutions that are technically feasible, environmentally beneficial and economically reasonable – and we need to work collaboratively to find them.

Star Ginn, Spiral Development of Electric Propulsion Though Flight

Starr Ginn, Deputy Aeronautics Research Director at NASA’s Armstrong Flight Research Center, Edwards Air Force Base, heads up a group of innovators pushing the envelope with new X-planes.  X-planes of the past were all about going higher and faster, but the new breed is trying to be quieter, more efficient, and better world citizens.

She’s involved with structural questions for coming electric aircraft, having worked on MADCAT (Mission Adaptive Digital Composite Aerostructure Technologies).  There, as with later projects, she started small and worked up, an overall approach that ties in with NASA’s current high-speed culture to build, test, and fly – then start over with the next iteration. She notes it took 40 years to get from the Wright Brothers’ initial flights to the ability to craft a 40-passenger airplane.  She and her group hope to create an electric 40-passenger airplane in 20 more.

Much of this will be possible through the synergistic integration of distributed electric propulsion into airframes, structures and systems optimized for such power.  This may require hybrid architectures, advanced air transport technology and convergent aeronautic solutions – a phrase heard frequently during the symposium.  Testing flows quickly, relying on “pitching” of ideas, fast development and rapid follow-up.

Creative approaches abound – the HEIST (Hybrid Electric Integrated Systems Testbed) Peterbuilt speeding along the desert floor is an example, inexpensive compared to wind tunnels.  The LEAPTech (Leading Edge Asynchronous Propeller Technology) spreads distributed electric power (DEP) across 18 motors on much smaller wing than the Technam P260 fuselage originally carried.  The test vehicle, now known as SCEPTOR (Scalable Convergent Electric Propulsion Technology Operations Research) shows that acronyms and abbreviations abound as readily as creativity on this project.

One finding is that electro-magnetic interference (EMI) may prevent accurate pilot control of motors on such a complex bus arrangement.  The fly-by-wire (FBW) system must overcome any such issues.  Motors, batteries, controllers, propellers and other elements of an electric power system are characterized individually on a single-string propulsor test AirVolt system.

Other speakers from Armstrong Flight Research Center filled in additional details on Starr Ginn’s project.  More to come.

SCEPTOR with research team and pre-makeover Technam twin engine aircraft.
SCEPTOR with research team and pre-makeover Technam twin engine aircraft.

George Bye and the Ready-for-Part 21 Sun Flyer

George Bye, head of Aero Electric Aircraft Corporation (AEAC) told of the recent rollout of his Sun Flyer trainer, comparing it to his initial foray into electric trainers, a Cessna 172 that was test flown over 20 times five years ago.  He pointed out that such an airplane needs a reason for being, a business solution that needs a compelling aspect for the utility of the concept.

Because of its size, and possibly because the battery weight made the four-seater into a two-seater, George and his partners reviewed their approach.  The resulting Sun Flyer is half the structural weight of the Cessna, has a lift-to-drag ratio of 20, twice that of the 172, and requires about 1.5 square feet of cooling area to keep the Enstroj Emrax 268 high voltage electric motor, (rated at 100 kW and 400 volts nominal) running at an acceptable temperature.  The 172 has 11 square feet of open cowling to keep things cool – a significant drag penalty.

George explained that almost the entire span of Sun Flyer’s propeller converts torque to thrust, which coupled with the highly-efficient electric motor allows the airplane to outperform a Cessna 172.  He emphasized that there is no technology we are waiting for that prevents moving forward into practical electric aircraft.

General Aviation history showing sharp drop in sales around 1980. George Bye hopes to reinvigorate the market with the Sun Flyer.
General Aviation history showing sharp drop in sales around 1980. George Bye hopes to reinvigorate the market with the Sun Flyer.

Sun Flyer, sporting LG 260 Watt-hour-per-kilogram batteries, airbags and a BSR whole-airplane recovery parachute, can achieve an 85 knot cruise and a top speed of 120 knots.  Its low noise levels were recently tested by the National Park Service, which found a flyover by the single-seat proof of concept demonstrator was impossible to hear against ambient noise.  The 30 dB reading (about 1/1,000th that of a conventional plane) should increase the airplane’s utility.

He has been working with the FAA to enable Sun Flyer to meet Part 21, not LSA standards, and thus find a place in training new pilots at much lower costs.  George estimates charging the batteries at $1 per flight hour, with a total operation costs around $24, including battery replacement, maintenance and regular inspections.  A 172 costs around $107 per hour, total, making it hard to lure new students into flight schools.  According to George, General Aviation production fell off a cliff around 1980, and is struggling to recover.  These savings might help.

David Josephson and Community Noise Standards

Josephson, the Principal at Josephson Engineering, Inc., has taken on the kind of challenge he enjoys, predicting the acoustic impact of electric aircraft on neighborhoods bordering airports.  Designer of several high-end microphones used in recording and sound measurement, he often works with unconventional applications and wonders if traditional ways of sound measurements are adequate.  Is there a need for a different metric for electric aircraft?

On-demand mobility (ODM) will essentially require the quiet of electric aircraft to be successful.  One can imagine neighbors calling up an air taxi at all hours.  Even a conventional ground taxi or shuttle can disturb neighbors.  We will, according to Josephson, measure the impact of such activities on a social basis.  For how many houses will an airport pay to install soundproofing, for instance?

David Josephson argues we want to measure quiet rather than noise, based on factors other than sound pressure levels (SPL) usually measured in decibels (dB).  Such measurements were originally made to determine how loud a telephone ringer needed to be to be heard from other rooms, but depend not just on loudness (audibility) but things like annoyance for the listener.  The level of aversion experienced by an airport neighbor depends as much on perceptual factors as on actual sound measurements.  Other factors, such as the number of times per day the listener is subjected to a noise, the length of each exposure (a helicopter hovering for half-an-hour), and things like rate of change in direction and modulation affect the acceptability of noise in our environment.  The cumulative effects of such exposures have a strong effect on neighbors.

He shared some wisdom on improving noise levels, noting that, “If you can’t measure it, you can’t improve it.”


Robert Bulaga Trek Aerospace

Seeing the 2000 SoloTrek XFV (exoskeletal flying vehicle) at the Hiller Aviation Museum a few weeks before attending the CAFE Symposium, I was ready to hear from its designer.  Robert Bulaga, head of Trek Aerospace, Inc.  The Springtail, fourth in a series, was the first Trek device to fly untethered.

After months of working with “buggy” Computational Fluid Dynamics (CFD) code, Bulaga was able to test Springtail for 10 weeks in the Ames NASA wind tunnel.  The code predicted within two percent what the wind tunnel proved.  Bulaga and crew optimized duct geometry, finding an inlet duct radius of 8-10 percent performed well, and a propeller geometry blowing 650 feet per second was acceptable.  Control surface optimization, including selection of airfoil shapes and flap size and type helped maneuvering.

The XFV drivetrain, a mechanical system that would be better served with electrical power and components.
The XFV drivetrain, a mechanical system that would be better served with electrical power and components.

The airframe, a welded-steel frame with aluminum honeycomb and fiberglass skins, mounted two ducted fans powered by two-stroke Hirth engines, driving the fans through 98-percent efficient – but noisy – gearboxes.

Because everything was connected mechanically, controls required “extreme hand movements” to hover Springtail for even 15 seconds.  He noted that a stability augmentation system was necessary, otherwise perturbations double in a short time and it takes a mere eight-tenths of a second to lose control.  At least for that reason, safety systems like quick-release harnesses, base-jumping parachutes and even ballistic recovery chutes were necessary.

The ducted fan system worked well, with its carbon-infused fan blades and light, stiff ducts that stayed round and avoided resonant frequencies.

Publicity for the XFV turned out to be a two-edged sword, with DARPA’s Defense Science Office (DSO) and Tactical Technology Office (TTO) asking designers and inventors to “share their most audacious ideas,” while the FAA took a more measured response.  He and fellow presenter Joshua Portlock had a surprise for attendees later in the meeting (report soon).

Frank Taylor and Ultimate Next Transportation

Frank Taylor founded Ultimate Next Transportation LLC to design an aircraft suited to the demand for added mobility in an increasingly crowded world.  He noted we are “pretty much where we were in the 1970s, looking for flying cars in every garage, and stifled by traffic jams instead.

He talked about how major changes, such as personal computers displacing mainframe computers in remarkably short order, could be models for how we will jump from the crowded highways to well-organized paths in the sky.  He sees the use of “killer apps” and Next Ultimate Airspace vehicles as means to achieve safety, control and efficiency in the new airspace.  Like telephone networks in 1910, air traffic control will require lots of talking, but through modern, non-verbal, digital communication links.

These wireless networks would establish more layers and boundaries for control, separating aircraft including UAVs, personal air vehicles, and larger commercial craft.  Integration of iPhones, iPads, and PC-based high-frequency radar would allow shared data to keep things moving safely.

Rather than set rules, administrators would define performance specifications for a distributed and available data system.  With everyone communicating, everyone would “see”even a non-compliant aircraft.  This type of control would allow change and evolution over time, and possible expansion as the GA fleet and drone deliveries grow.

David Jenson and the FAA’s Electric Flight Efforts

Aircraft certification services (AIR) for standards, policies, certification and production of components, and COS management come from regional offices, with the Kansas AIR serving as the lead office for electric flight.  Jenson’s talk emphasized the several certification projects currently underway for manned and unmanned aircraft.

The goal of integratimg new technology into the mix safely requires a proven, risk-based approach.  Looking at the continuum, acceptable levels of safety and certitude need to be integral to regulations.  Standards require an acceptable level of oversight – too little rigor and we all face safety problems: too much and we stifle innovation.  Zero risk means grounding all airplanes – where they are safe indeed.

Several FARs are applicable.  For now, light electric aircraft may be treated as a special class under part 21.17 (b).  Electric aircraft will be handled on a custom certification basis.  Electric propulsion system and installation aspects will be handled under part 33, certification of uas and experimentals and help the FAA gain experience in this new area.  He explained that European certification of powered gliders such as the Lange Antares allowed operation here under existing rules.

Jenson feels the confluence of tech and demand makes the time right for moving forward.  His last slide had this to ponder, “The thing about smart people is that they seem like crazy people to dumb people.”

Dr. Don Hillebrand, Argonne labs and Advanced Technology Vehicles – Status and Outlook

Dr. Hillebrand, director of electrical systems at Argonne, thinks electrification of transportation is underway, and that advances are steady, with spillover occurring on the grid, and that these changes are permanent.  He notes that even though advances are steady, dual use and spillover technology have not been exploited fully.  The U. S. Department of Energy is staging EV Everywhere as a clean energy grand challenge.  “EV Everywhere is the umbrella effort of the U.S. Department of Energy (DOE) to increase the adoption and use of plug-in electric vehicles (EVs).  EV Everywhere was launched as one of a series of Clean Energy Grand Challenges that set ambitious, far-reaching, national goals that will help the U.S. become more energy secure and environmentally sustainable.”

17 national labs are taking part with Argonne as the principal lab to evaluate EV drive technology.  These efforts are already bringing about results, with development of advanced battery having reduced costs by 70 percent, and increased energy density.  Integrating these vehicles (and possible future electric aircraft) into the national smart grid would aid in creating more reliable electricity.

With the one millionth plugin electric vehicle sold in September 2015 and CO2 emissions at a 27-year low, optimism seems a natural feeling.   The bad news, though, is that aviation seems to have no home for federal research


John Brown: Electric Flight and Unmanned Aviation

Brown, the President and CEO of Silent Falcon UAS Technologies, has an all-seeing eye in the sky that can stay aloft over five hours at a time – seven under ideal conditions.  This persistence is a prime factor in surveilling and mapping large areas.  Most fixed-wing UAS’s are limited to a five-kilometer (15 maximum) out-and-return mission: the Silent Falcon can do 100.

Its three-kilogram (6.6 pound) payload allows it to carry 10 different kinds of systems, including a – spectrometer for spotting mine damage, leak detection on pipelines, and other hazards.  Other payloads can monitor crops, and perform mapping surveys.  Law enforcement can use the high-resolution cameras and infrared sensors to track down bad guys, and foresters can oversee forest fires and make decisions regarding conservation of natural resources.

Flying over a t 200 meters (650 feet), the UAS can’t be heard.  At 500 meters (1,640 feet) it can’t be detected audibly or visually.

The open-interface bus architecture on board allows future inclusion of new systems.  Silent Falcon’s autopilot system can maintain a pre-planned flight path.  Brown refers to human pilots as “weak servos.”

Next, day two with international participation


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