Beam Me Up: Flying on Sunshine™

We recently reported on two electrically-powered cross-country flights for which the big issue was lack of battery-charging facilities at airports along the way.  Both “teams” had their chargers carried by an accompanying airplane or automobile.  Now, with a public demonstration a Beam Global charger at Reedley Municipal Airport in Fresno County, California, we see a no-fuss way to bring EV charging to aviation – even in remote locations.

Beam Global premises its installations on a foursome of negatives: No permitting, no construction, no electrical work, and no utility bill.  Installation, if one believes Beam’s video, is almost a non-event.

Beam, formerly Envision Solar, produces pre-fabricated EV ARC solar-powered charging stations.  Like a vacation camper, the ARCs can be towed right onto a level piece of property and dropped off.   The units are self-contained and can produce electricity from the sheltering overhead solar panels.  A driver or pilot can park on or next to the metal platform and charge their electric car, motorcycle, or even airplane.   Demonstrated in late October when Beam Global CEO Desmond Wheatley, and pilot Joseph Oldham charged a Pipistrel Alpha Electro and took flight, the system works well and can charge the pilots’ cars while the aviators are in the sky.

Joseph Oldham is the founder of New Vision Aviation, “a 501 (c) 3 non-profit charitable organization dedicated to providing residents and youth from disadvantaged communities in the San Joaquin Valley with the opportunity to experience flight and begin training for careers in aviation.”  Because of their low operating costs, New Vision chose Pipistrel Alpha Electros as their training vehicles, and awaits full certification to allow their use in an educational program.

Joseph Oldham and Desmond Wheatley stand next to one of four NVA Pipistrel Alpha Electros which will soon be training young pilots.  Note the Pipistrel, Wheatley’s motorcycle and Oldham’s Tesla 3 share the same charging station.

Oldham took Beam Global CEO, Desmond Wheatley for a trip around the patch as an active participant in the first “Flying on Sunshine™” event, powered by electricity that is “off-grid, sustainably generated, [and] locally stored.”  Wheatley reflected on the importance of the event. “The electrification of transportation is taking to the skies, powered by Beam Global. With 40 percent of greenhouse gas emissions coming from transportation in California, it’s imperative to push the envelope in every form of mobility.  Whether it has two, four or 18 wheels, a propeller or four rotors, Beam is developing sustainable solutions to deliver clean mobility to all. An important differentiator for us is that our products can charge any form of transportation, enabling us to take advantage of growth across this massive but diverse sector.”

Flying on Sunshine may become a common label in the skies above the San Joaquin Valley

Beam describes the ARC solar charging station and its potential: “The EV ARC™ 2020 being used to power the Pipistrel plane is equipped with [two] Enel X JuiceBox® Pro EV chargers and one (unspecified) 15kW aircraft charger and is capable of charging two vehicles and one electric plane. 100-pertcent solar-powered EV ARC™ units are off-grid so require no permitting, no construction, no electrical work and generate no utility bill. Designed to fit in a standard parking space, without reducing available parking, the small footprint and construction-free deployment does not disrupt city or airport planning efforts and can be rapidly deployed. Beam Global EV charging products enable municipalities and states to build zero-emissions infrastructure that is rapidly scalable as charging needs evolve.”

The latter point will be of interest to municipalities that were otherwise concerned with the possibility of overwhelming the grid when electric vehicles became a dominant factor.  Beam’s web site is light on details as to who pays and how they are charged, but that may vary by user.  Likewise, charger plugs can be varied as required.

Oldham’s organization sees the human potential in the enterprise.  “NVA is an all-volunteer organization and believes that investing in ‘human capital’ is the best ROI possible for our communities and our world!!  That is why we exist and why our team is investing our time, money, and resources into helping open doors for young people that otherwise would not be possible on their own.”  We can hardly wait to see how many new pilots are beamed up in the near future.

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In a recent AVWeb Vodcast, Paul Bertorelli interviewed Embry Riddle’s Dr. Pat Anderson on the topic, “Why Electric Airplane Designers Are Turning to Hybrid Drives.”  Battery energy-carrying capability has not fulfilled its promise yet, according to Anderson.  The difference in energy density between fossil fuels and batteries is still too great to fulfill missions involving more than small craft and short distances for the most part.  This outlook caused Dr. Anderson’s associates, Eric Lindbergh and Eric Bartsch to form Verdego Aero, dedicated initially to developing a Diesel-hybrid generator system.

They corroborate Dr. Anderson’s sense of current battery technology, their web site answering “Why hybrid?”  They explain, “Electric aircraft are at the forefront of aviation technology, but the energy density of current batteries isn’t yet high enough to support many mission types or aircraft designs.  The power generation systems in the VerdeGo IDEP (Integrated Distributed Electric Propulsion) systems, which use Continental Jet-A Piston Engines, offer 4-8x the equivalent energy density of today’s battery systems.  As battery technology evolves sufficiently, the onboard hybrid power generation units can be removed and replaced with batteries.”

TransportUp.com reports on their recent test runs of the IDEP system on an “iron bird” test fixture.  “The VerdeGo Aero team has successfully performed the first test runs of their ‘Iron Bird’ prototype diesel-hybrid (Jet A fuel) generator system in early August. Full-power testing is now underway to accelerate development of VTOL and CTOL electric aircraft utilizing VerdeGo’s high-performance hybrid-electric powertrain to perform demanding commercial missions.”

Verdego’s history of aviation powerplants – culminating in their IDEP hybrid system – with the implication there’s more to come

Tests reached over 150 kilowatts (201 horsepower), with the certified Continental CD-265 Diesel aircraft engine offering 40-percent lower fuel consumption than “competing turbine-hybrid offerings, while providing between four and eight times the endurance of competing battery-only powertrains.”  Since the engine can burn Jet-A fuel or other bio-based fuels, it avoids the future supply issues of LL100-fueled engines.  Since tetraethyl lead is made only for the 230,000 aircraft that still require leaded fuel for safe operation, all that will change as that aging part of the fleet leaves service.

“Key Assets”

Dr. Anderson has worked on a variety of electric and hybrid projects at Embry Riddle Aeronautical University, many of which are featured on a “key assets” page.  Partnered with Lindbergh and Bartsch, the team helped create the Eco-Eagle, a hybrid conversion of a Stemme motorglider that participated in the 2011 Green Flight Challenge.  Other projects led to the latest iteration of the “Iron Bird” ground-based test system.  Note they have crafted both serial and parallel hybrid systems.  Serial hybrids use the fuel-powered engine/generator to charge batteries that power any number of electric motors.  Parallel systems use the engine/generator and the electric motor(s) to propel the aircraft.

On his LinkedIn page, Bartsch makes a case for continuing hybrid evolution while waiting for the battery revolution, using Elon Musk’s recent Battery Day unveiling to bolster his argument.

Bartsch writes, “The big news this week is that a 5X LARGER cell is being launched that is 50% cheaper to make and maybe 8% to 16% more energy dense due to form factor and chemistry modifications, and therefore the electric car market can grow further into the mass market. That’s HUGE news for cars and Tesla deserves credit for it, but that doesn’t address the gigantic performance shortfall we have in aerospace.

“Right now electric aviation is where electric cars were in the mid 1990s. Hybrid-electric cars like the Prius launched almost simultaneously with Battery-electric cars like the GM EV-1. However one of those approaches went on to sell millions of cars worth tens of billions of dollars, while the other sold a few units and was cancelled because the value equation and performance wasn’t there yet.”

Continental CD-265, Diesel-fueled engine powers VerdeGo generator, can run on biofuels

And because that value and performance are not yet there for electric aircraft, Bartsch would argue, current efforts should focus on an interim hybrid solution.  Verdego Aero is his and Erik Lindbergh’s firm to develop such solutions in partnership with Continental Aerospace Technologies™.  The company claims their serial hybrid system will be clean and quiet, economical, and capable, “with 4X range and 12x refuel/recharge speed compared to all-battery approaches.”

Using a Continental CD-265, four-cylinder Diesel engine, the system can run on a wide range of non-fossil fuels (Diesel designed his original engine to run on peanut oil).  Diesels generally get better “mileage,” their high compression squeezing more power from each gram of propellant.  The engine weighs 198.8 kilograms (438.3 pounds), producing one horsepower, peak, for every 1.83 pounds of engine mass – comparable to the best gasoline-powered engines.

Even with an engine and exhaust, attached generator, heat exchangers, cooling fans, and power distribution, the core IDEP unit weighs 277 kilograms (609 pounds) for a combined output of 184 kW (247 hp).  Partner Seyer Industries provides custom-made parts for the IDEP package.

VerdeGo’s flexibility of configuration enables placement for different weight and balance, configuration considerations

To make their claims pay off, VerdeGo must displace the weight of batteries that would supplant the generating system and provide the greater range and endurance.  Allowing flexibility of design, one or two IDEP packages can be installed in the aircraft and supply electrical power to any number of distributed motors.  Applications can include conventional fixed-wing aircraft, multi-rotor systems, or designs relying on distributed electric propulsion.

Competing Systems

VerdeGo positions its technology against turbine hybrid-electric systems and battery-electric systems.  The firm promotes its strengths against turbine setups as (presuming equal output):

  • 35% Lower carbon emissions
  • 35% Lower fuel burn
  • 30% Powertrain acquisition cost savings
  • ~10-20 dB Quieter (exhaust note)
  • 45% Lower overhaul cost per hour
  • 40% Lower cost per flight cycle

VerdeGo claims its IDEP system fares well against battery-electric systems, too (again, presuming equal output):

  • 10x Smaller battery size
  • 25% Lower power system weight
  • 12x Faster recharge/refuel time
  • 4x+ Endurance/range
  • Longer battery cycle life
  • Full FAA / EASA (European Union Aviation Safety Agency) ENERGY reserve energy
  • Up to 25% Lower cost per cycle
  • Potential to be quieter (by increasing power to support low-noise rotors)

Verdego IDEP can work with fixed wing or multi-rotor concepts

Certainly fleet operators such as Uber would welcome operating savings in which reduced expenses for individual units are multiplied by the number of craft in the fleet.  Prospective clients willing to sign a non-disclosure agreement, “VerdeGo is able to provide the equivalent of a traditional engine deck. This proprietary software utilizes data from the full-scale hardware testing and includes a hybrid simulation model for airframers to use that includes both the hybrid generator and the battery solution that goes with it.”

David Eichstedt, Director of Advanced Concepts, explains the benefits of such simulation.  ““It’s a powerful way for customers to validate the economics of their aircraft designs value proposition using real powertrain hardware without leaving the ground.”

Under development and with ambitious goals, VerdeGo has performance and environmental targets to hit, and it seems well on its way to doing so.

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H3X – A Motor with High Power Density

H3X, a motor company started by three University of Madison, Wisconsin graduates, promotes its integrated motor/inverter power plant as “the next step in the evolution of electric propulsion technology.”  With Their HPDM-250’s 13-kilowatt-per-kilogram continuous power ability, it meets ARPA-E’s (Advanced Research Projects Agency–Energy’s) criteria for powering large, 737-type aircraft.

Electronics Weekly reports, “ARPA-E has determined that for a Boeing 737 to complete a typical five hour flight, the propulsion system must be >12 kW/kg continuous.”  H3X adds, “These specifications are estimates based on electromagnetic thermal and structural simulations. Data from dynamometer will be available Q2 2021.”

Their motor is roughly twice as power dense as MagniX motors of similar power, according to H3X.

Weight reduction is an intrinsic part of aircraft design.  In the days of internal combustion engines (still very much with us), conventional wisdom held that reducing power plant weight by one pound could help take two pounds off the airframe.  Even today, ICE engines generally produce only one horsepower for every two pounds of engine weight.  The HPDM-250 produces 7.92 horsepower per pound.  Couple that with modern composite airframes and one can see design possibilities lighting up the skies.

H3X describes its motor drive, a combined motor/controller unit: “The HPDM-250 is an ultra-high power density integrated motor drive for electric aircraft. It combines the electric motor and inverter (+ optional gearbox) into one powerful unit. It is the culmination of H3X innovation in multiple areas including:

“Electromagnetics design optimization

“DMLS (Direct metal laser sintering) 3D printed synergistic cooling jacket

“SLM (Selective laser melting) 3D printed copper stator coils

“Robust fault tolerance

“Thermal resistance reduction

“High frequency SiC (Silicon Carbide) power electronics”

H3X explains their 3D printed stator coils add to the lightness and robustness of the motor.

with >93% IACS (International Annealed Copper Standard) conductivity. “Our AMcoils achieve >70% copper fill factor in the HPDM-250 and offer a 40% improvement over conventional windings in terms of maximum continuous current density.”  They help cool the motor and achieve higher output while being relatively easy to manufacture.

Of course, that’s going to depend, too, on batteries of highly-improved capabilities.  We seem to be able to craft incredibly power-dense motor capabilities only short of dilithium crystals, but lag on energy storage.

Vertical axis is torque in Newton-meters: horizontal axis is RPM x 10 to the fourth power

More detailed specifications show a 250kW (335 hp) peak output for 30 seconds, and 200 kW (268 hp) continuous.  The little motor generates 95 Newton-meters (70 foot-pounds) of continuous torque.  It can manage up to 800 Volt DC with 96.7-percent peak motor efficiency, 99-percent peak inverter efficiency, and a combined peak efficiency of 95.7 percent.  Its 15-kilogram (33-pound) mass fits within a 6.75 liter volume – about three-and-a-half large soda bottles.

The motor’s efficient speed of 20,000 RPM means it needs a propeller speed reduction unit (PSRU).  H3X’s is a 4:1 unit, meaning the prop would still spin at 5,000 RPM at top speed, something that might cause blade tips to approach or exceed supersonic speeds  and generate a terrible racket.  The reduction unit adds only three kilograms (6.6 pound), quite good for a reduction system that can absorb all that power.

H3X founder and CEO Jason Sylvestre explains that without the gearbox, the overall efficiency and power density would be lower.

There’s some question as to whether there is a functional reduction gearbox at this point, since H3X says they “…can design a high torque density planetary gearbox that is integrated into the front end cap of the machine to achieve your desire torque speed requirements.  The example 4:1 planetary is based on a real design that is 3kg and 97% efficient.”

3D printed copper coils increase copper fill, energy density

Keeping it cool helps improve performance and lower weight.  Sylvestre explains, “… We use a single, synergistic cooling jacket to simultaneously cool both the power electronics and motor. This integration reduces system mass and volume. Additive manufactured copper stator coils are used to increase copper fill factor and improve continuous current density capability. This is a new technology that has the potential to revolutionize the motor manufacturing industry as it offers faster development, better performance, and greater design flexibility.”

Primary near-term applications for this motor, said the company, are urban air mobility, EVTOLs, UAVs, “military jets and select regional aircraft markets. Primary long-term applications: large commercial electrified aircraft, such as the Boeing 737.”

Sylvestre projects an interesting future.  “In the next five years, we’re going to see those eVTOLs and small electric aircraft.  But by around 2030, we’ll start to see electrification of large commercial aircraft. That’s really what you want to go after. Aircraft around the size of a Boeing 737, those account for around 50 percent of all the greenhouse gas emissions in the aircraft sector. An aircraft that uses distributed propulsion with multiple 250-kW motors, maybe 16 or so, along each wing. You can imagine the weight of those will add up, and that’s where a motor like ours could make a huge difference.”

The firm intends to start testing by mid-2021 and is seeking letters of interest from potential clients.  We can only hope that companies like H3X and MagniX continue their drive toward lighter, more powerful motors.  The competition will benefit all.‍

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What’s the HAPS?

What do a Japanese investment bank, a software network, balloons and a gigantic stratospheric flying wing called HAPS have in common?   Let’s look at the players and then piece together this puzzle.

Softbank

According to Wikipedia, “SoftBank Group Corp.[11][12] is a Japanese multinational conglomerate holding company headquartered in MinatoTokyo. SoftBank owns stakes in many technology, energy, and financial companies. It also runs Vision Fund, the world’s largest technology-focused venture capital fund, with over $100 billion in capital.[13][14]

“The company is known for its leadership by founder Masayoshi Son.[15] It operates in broadband, fixed-line telecommunications, e-commerce, internet, technology services, finance, media and marketing, semiconductor design, and other areas.

“SoftBank was ranked in the Forbes Global 2000 list as the 36th largest public company in the world,[16] and the second largest publicly traded company in Japan after Toyota.”

SoftBank’s web site promotes the “Information Revolution” as “Happiness for everyone.”  The bank explains, “Since our founding, the SoftBank Group has sought to promote the Information Revolution to contribute to the wellbeing of people and society.”

The Group expands on this with a vividly-produced video promoting their idea as to how using high technology can bring about a Utopia long dreamed of by philosophers and inventors.  (Your editor is a bit skeptical, having seen large display ads in year 2000 Silicon Valley airports extolling the coming millennium because of 13-micron lines on new computer chips.  Somehow, the world did not change in a dramatic or blindingly positive way.)  The technology is wonderful, but maybe over-rated here for its effects on our collective soul.

SoftBank has a more upbeat end to the story, though.  Their investments will bring happiness to all. “The answer is simple: to bring happiness and give inspiration to people — a vision that has guided us since our founding and is encapsulated in our corporate philosophy.

At a more pragmatic level, the means by which SoftBank and its partners have managed to create a worldwide communications network are truly wondrous.  Their aspirational corporate video shows an optimism rarely found in the modern world.

SoftBank has an ambitious agenda for the new technology it is to employ in its sky-borne 5G/LTE networks.

LOON

LOON, a Google Alphabet project, uses balloons to transmit Internet communications to ground-based users.  Up until now, such signals came from ground-based stations or satellites.  LOON fills in the celestial/terrestrial gap with stratospheric balloons that can fill in electronic communications gaps for half the world’s land mass, the 3.8 million people who don’t have access to the internet, and those who lack adequate access.

Loon recently achieved an important milestone: “Our balloons have flown over 1 million hours in Earth’s stratosphere. In all of those hours aloft, Loon’s balloons have traveled nearly 40 million kilometers — enough to make 100 trips to the moon or circle the Earth 1,000 times.”

Flight of the LOON: 312 days around the world from Puerto Rico to Mexico

One LOON managed to take a world tour lasting 312 days, a meandering journey that took it from its launch site in Puerto Rico to a landing in Mexico.  TechCrunch.com reports, “The balloon in question took off from Puerto Rico in May 2019, and then made its way to Peru, where it took part in a service test for three months. It then headed south over the Pacific Ocean, and finally ended up in Baja, Mexico for a landing in March this year. Loon’s CTO Sal Candido said in a blog post that the record-setting flight is the result of the company’s continued work on advancing its technology and pushing both hardware and software forward in new and innovative ways.”

Like traditional balloons, LOONs drift on wind currents, but at stratospheric altitudes between 50,000 and 70,000 feet.  The folks at LOON explain, “We’ve created what is essentially a stratospheric submarine that utilizes the sun, the air, some pretty cool machines, and a collection of smart algorithms. A solar-powered pump* adds or subtracts air from the balloon. That air makes the balloon heavier or lighter, allowing it to ascend or descend in altitude. Rather than fight against the wind at one altitude, the balloon moves up or down until it finds a favorable wind current. By repeating this thousands of times over the lifespan of a balloon, we can drift on the winds to get to locations around the world.”

Navigation require algorithm-driven selection of altitudes, winds to find LOON’s way

This artificial intelligence approach would probably exhaust a human aeronaut, and the people at LOON have a bit of fun with a Saturday Night Live reference to their AI version.  “We’ve called various versions Hans and Franz because, of course, they’ll pump you up.”

HAPSMobile

HAPS, High Altitude Pseudo Satellite (or High Altitude Platform Station in HAPSMobile terminology) comes from AeroVironment, and is an improved version of its earlier segmented flying wings that achieved altitude records.  Like a satellite, it flies in a regular pattern – unlike a LOON, which is subject to winds aloft.  It fits in the altitudes between geosynchronous near-space satellites and ground-based transmission towers.  That means it can cover a broader area than terrestrial antennas.  HAPSMobile estimates it would take tens of thousands of existing terrestrial base stations to cover the entire Japanese archipelago.   The same area could be covered by just 40 HAWK30s.

 

Think, too about satellite radio, which overcomes signal blanking from tall buildings and hilly or mountainous areas that interfere with high-frequency signals.  Placing transmissions towers, usually on the tallest promontories in a region, is a dangerous enterprise: launching and retrieving large HAPS a much less hazardous business.

Even better, airborne or satellite transmitters are impervious to disasters on the ground.  Transmission towers can be brought down by fires, earthquakes and other catastrophes.  Maintenance of terrestrial towers is itself a dodgy thing, and fatalities are common.

HAPSMobile explains that, “The ‘30’ in the HAWK30 name refers to the fact that, at a latitude of plus or minus thirty degrees from the equator, the HAWK30 can fly 365 days a year. In fact, the HAWK30 can fly even in high-latitude areas like Japan, which lies between the 24th and 46th northern parallels, most of the year, with the exception of winter months when daylight hours are few. A ‘HAWK50’ model, which can fly plus or minus fifty degrees from the equator, is now in development with the goal of enabling stable service regardless of the season.”

HAPSMobile makes another interesting point.  Light and radio waves travel at the same speed – about 300 million meters per second (3.0 x 108 m/s) or 186,300 miles per second.  With earth orbit satellites about 36,000 kilometers (22,369 miles) above the earth and low-orbit satellites at about 1,200 kilometers (746 miles), times for transmission and reply (RTT) vary greatly.  The high-orbit satellite takes 400 milliseconds for an RTT, while the low-orbit can perform an RTT in 18 milliseconds.  A HAPS base station in the stratosphere reduces RTT to 0.6 milliseconds.

Because HAPS is closer to earth, signal power density “is approximately one million times that of a GEO satellite and approximately ten thousand times that of a LEO satellite, allowing HAPS to provide high-quality communication services to existing mobile devices.”

*RTT (Round Trip Time): The time it takes to transmit a signal or data and receive a reply. RTT is affected by distance, the number of relay/transfer devices on the route, and the processing time.

Above the clouds in the stratosphere, HAPS receives all the sunlight possible, enabling it to stay up as endlessly as an operator desires.  Being able to “loiter” at altitude enables long-term transmission.  Its solar panels and ten propellers are able to keep the 78-meter (256-feet) wing cruising at an average 110 kilometers per hour (68.4 mph).

The HAWK30 supports an atmospheric communications platform, “Capable of providing coverage for a radius of about 124 miles while staying aloft continuously for six months, SoftBank said. The longest solar-powered flight with a previous-generation AeroVironment HAPS drone was for 18 hours in 2001.”

HAPSMobile makes the point that, “There are still many countries and regions around the world where the development of the Internet has been delayed due to insufficient power supply, security issues and other barriers. Some of these areas have access to satellite-based Internet, but satellite technologies have their own barriers, such as hardware failures, speed and bandwidth issues, and pricing. With stratosphere-based technology, however, it will be possible to provide high-quality Internet services that are fast, affordable and with high bandwidth across all areas. For that reason, HAPSMobile is strongly committed to this new technology.”

We can hope that the convergence of ground-based, stratospheric, and extra-terrestrial signals will bring the opportunities inherent in the Internet and other communications links to the entire world.

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DLR’s Novel Configurations

Researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) conducting research into the potential of new types of design have crafted novel configurations for future flight.  The DRL and BDLI (German Aerospace Industries Association or Bundesverband der Deutschen Luft- und Raumfahrtindustrie)  have published a white paper: “Zero Emission Aviation – Emissionsfreies Fliegen” explicating these configurations.

FutPrInt 50 unique configurations

Surprisingly, one of their major findings is that “Electric flight enables lighter aircraft with smaller wings and distributed propulsion systems.”  Battery weight has caused MagniX and Ampaire to reduce the number of passengers or the cargo loads on conversions of existing airframes.  To counter those issues, “An EU research project is investigating the potential for new propulsion systems and aircraft concepts.”  Obviously, these new concepts will need to take advantage of advanced materials to lower airframe weight.

Hybrids and Hydrogen

Thousands of airliners parked in dry desert locations highlight how the COVID crisis has affected air travel.  Despite the ongoing interlude in travel, we should experience five percent per year growth in air traffic every year until 2030, according to forecasts reported in Horizon magazine.

DLR study for 19-seat regional airliner with multiple propellers – similar to X-57 Maxwell concept.  This would be hybrid, though, with turbine-driven generators

Countering that rosy outlook, Horizon reports, “As a result of the COVID-19 pandemic, U.S. airlines have cut capacity by more than 1.4 million seats, or 6 [percent] in the last week alone, according to OAG, an airline data company.”  At some point in the future, though, threats of being enclosed in a tube with contiguous and contagious fellow passengers will finally dissipate and people will fulfill their wanderlust.  Then it will be up to aircraft designers and makers to prevent a return to the spread of something even more of an existential risk – air-borne pollution.

The need to jumpstart the economy is great worldwide, but the necessity of reducing airline emissions is also great.  Aviation, already responsible for two percent of global greenhouse emissions, will grow that share unless it can be brought into line with the European Union’s target of net-zero greenhouse gas emissions by 2050.

Aviation contributes significantly to the European economy, generating more than €500bn per year and supporting 9.3 million jobs.  To help maintain that benefit, hybrid-electric aircraft will probably be a short-term fix.

Dr Xavier Roboam, a senior scientist and deputy director at the LAPLACE lab at the University of Toulouse in France, explains, “By hybridizing sources, you can reduce the fuel burn of aircraft and therefore the environmental impact.  It’s the first step before the final step, which may be zero-emission, fully-electric aircraft.”  Since the best batteries are still only about three percent as energy dense as kerosene jet fuel, an engine/generator and small fuel load can extend the range of electrically-propelled aircraft.

Light weight structure and hybrid propulsion systems can be contained in unique configurations

Hybrid planes will also have to reduce enough weight over battery-powered aircraft to compensate for the fuel load and any additional battery weight.  Dr. Roboam and associates, working with the HASTECS (Hybrid Aircraft; academic reSearch on Thermal and Electrical Components and Systems) project, are focused on systems that convert power between batteries, generators and electric motors.  Roboam explains the group’s goal: “We are trying to maximize the ratio between the power you are able to deliver and the weight that is necessary to deliver that power.”

The team aims to “design an electric motor that would double the power-to-weight ratio of electric motors used today, such as in a Tesla electric car, to achieve 10 kilowatts per kilogram by 2035. They also want to increase the power-to-weight ratio of power converters to 25 kilowatts per kilogram by the same period.” This could lead to lighter aircraft burning up to 10 percent less fuel.

The team claims to have met their goal for the electric motors, optimizing their structure by using electromagnetic materials, for example, and special Litz wires (a special type of multistrand wire or cable used in electronics to carry alternating current (AC) at radio frequencies) to help improve performance.   Smaller motors heat up more, so the team also came up with a more efficient way to cool them using an internal cooling system.  Their power conversion system met similar goals, “…beyond the target which is very successful for the project.”  Dr. Roboam thinks a hybrid aircraft using their concepts could fly in five to 15 years.

Professor Andreas Strohmayer, head of the Department of Aircraft Design at the University of Stuttgart in Germany, and his colleagues are also working on a hybrid-electric aircraft with up to 50 seats that would start providing commercial flights in 2035 as part of the FutPrInt50 project.  Professor Strohmayer relates, “The 40 to 50 seat range is the first commercial tool to have an impact (in terms of) transport capacity.  The larger you go from there, the more issues you have, so I believe in a step-up approach.”

Hydrogen

Airbus takes a next step, hydrogen, with their September 21 announcement that they plan for the world’s first zero-emissions aircraft using hydrogen as a power source*.  Professor Strohmayer adds, “We are working on our reference aircraft so that we have a one-to-one comparison of our design against a conventional aircraft of the same size.”  Several possibilities, shown in the following video, help explain that hybrid and hydrogen concepts could even be combined.

DLR and various academic groups can pull information from NASA in America, ONERA in France, and agencies in South America and the Netherlands. Research groups will also focus on harvesting energy from the airflow to help reduce battery and fuel weight in hybrid aircraft.

By the end of the project in 2022, the team will have developed a technology roadmap for all the different components needed, as well as a roadmap for the standards that need to be met for certification. It will be accompanied by a hybrid aircraft design that could be transferred to an aircraft manufacturer for production and development. Strohmayer concludes, “My vision is that my grandchildren can sit with me onboard one of these aircrafts in 20 years from now. I want to see this built.”

Less Noise with More Propellers

Fans and propellers produce aircraft noise during flight but total noise in flight is largely determined by aerodynamics, “produced by the propellers or fans of the engines and the airflow around the fuselage and wings.” Researchers have found that many small propellers create a different sound from that of two large ones, and examined the flow acoustics in depth.

Martin J. Hepperle of the DLR Institute of Aerodynamics and Flow Technology, cautions, “The reductions that our concepts are calculated to achieve are in the single-digit range. Our preliminary investigations indicate that hybrid-electric regional aircraft with distributed propulsion systems would result in a 10 percent noise reduction.”   He retains a realistic outlook, noting that although hybrid systems would allow power to be generated directly on board, this would increase weight.  Further, “Conversion and transfer of electricity would also result in some power losses.”

Hepperle ran up against the weight of energy storage, since present-day batteries add to the aircraft’s mass and and yet do not allow long range.  Near-term, Hepperle sees battery-only systems as practical only for “small sports aircraft,” and hydrogen fuel cells as very expensive and complicated.

University of Stuttgart hybrid electric 50-passenger regional airliner concept

He sees kerosene-fueled hybrid propulsion systems as a practicable transitional solution. Although carrying a complex propulsion system, this type of electrically powered regional aircraft could “easily” carry 100 passengers for up to 2000 kilometers.

Despite the many issues being sorted out by researchers, Current findings and concepts for electric aircraft can be an option for short-haul routes.  The DLR cooperates with research as part of the European Clean Sky 2 Advanced Engine and Aircraft Configurations (ADEC) projects, ONERA,  TU DelftNLR (The Royal Netherlands Aerospace Center) and industry partners Airbus and Rolls-Royce to determine the potential of innovative propulsion systems and aircraft concepts.  DLR is working with the Synergetic integration of distributed hybrid-electrical propulsion systems (SynergIE) project, part of Germany’s national aviation research program.

While many of these efforts will mirror configurations such as the NASA X-57 Maxwell or other American research programs, all such projects help point us toward a clean sky future.

*This is preceded by aircraft such as Pipistrel’s Hy4, already flying at least partially on hydrogen and e-Genius, a product of Stuttgart’s aerodynamic programs.

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Peter Sripol’s Mk. IV is Paramotor Powered

Peter Sripol creates interesting ultralight aircraft, among other, sometimes scary projects. His latest is pulled along by a paramotor motor.  Because of the small aircraft’s low and slow performance, the low-power (and very low noise) motor seems more than sufficient to the task.

His fourth design, the Mk IV has no ailerons, much like an earlier ultralight, the Skypup.  After initial tests showed shortcomings with the Mk. IV,  quickly modified wings allowed Peter to return to the air quickly.  As he explains, there won’t be plans for this airplane because it has too many not as yet time-tested innovations.  The hot-wire-cut foam structure and vinyl wrapped wings are an unknown in terms of longevity, so it’s probably best to let Peter make his determination on that.

Skypup was Rotax 277-powered ultralight that flew without ailerons

Note the machine seems to be remarkably quiet, the OpenPPG motor drowned out by propeller noise.  (That’s also low because of the e-Prop’s design.)*  When Peter is able to shout down to his father and crew on the ground, he is easily heard.  The SP140 motor comes from a paramotor supplied by the open-source group that started with a four-motor collapsible frame system.  Note that the four little propellers turning over fast come through loud and clear.  Bigger motors turning slower, larger props make less noise.

The OpenPPG team now sells both the four-motor and single-motor versions.

A Little History

Sripol has cranked out four airplanes in the last three years, each a learning experience and a venture into Peter’s seeming insistence on trying out new things.  His Mk. III used a small two-stroke engine, noisier than any of the electric craft.

His Mk. II used two small model aircraft motors, the first pair not providing the power for which he had hoped.  There seems to be no news about what happened with the SunnySky replacements he displays toward the end of this video.  It would be nice to know if he sorted out the landing gear issue, too.

Finally, all the way back to Peter’s first effort, this too used hobby motors and model aircraft propellers and battery packs.  Peter has long been involved with the hobby industry and the increasing size of electrically-powered model aircraft seems to be overtaking the 100-percent scale machines.  When displayed at AirVenture, this machine drew crowds.

It’s exciting to see someone willing to learn, open to new ideas, and willing to reflect the spirit of experimental aviation.  We can only wonder what Mk. V will look like.

*An interesting footnote: e-Props just celebrated delivery of its 100,000th carbon fiber propeller blade, evidence of a strong market for quiet flight.  They sell 45,000 propellers a year in more than 80 countries.

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DLR’s Future Visions

One Size Does Not Fit All

DLR (Deutsches Zentrum für Luft- und Raumfahrt or German Aerospace Center) and the German Aerospace Industries Association (Bundesverband der Deutschen Luft- und Raumfahrtindustrie; BDLI) present future visions of electric aircraft.  These range from a four-seat hydrogen-powered repurposed Pipistrel that nine years ago won the NASA Green Flight Challenge to large, multiple propeller, medium-range airliners.

Their White Paper, “Zero Emission Aviation – Emissionsfreies Fliegen” (unfortunately available only in German) promotes the promise of “energy transition in air transport, with the goal of zero emissions,” and claims this is “possible by mid-century but requires a considerable increase in innovation.”

DLR, BDLI investigate multiple possibilities for future electric aviation

Rolf Henke, the member of the DLR Executive Board responsible for aeronautics research and technology, explains, “The time has come to start a new chapter in aviation. Our white paper shows the path to emission-free flying for the ‘Green Deal’ in aviation, which will lead to new technologies, attractive high-tech jobs, fascinating products and the promotion of social prosperity in Germany and Europe.  With the transformation of an entire industry, however, this path also involves major research efforts. In particular, flying demonstrators will be an essential element in the areas of electric flight, hydrogen, new fuels and new aircraft configurations.”

“Reiner Winkler, BDLI’s Vice President for Aviation emphasizes: ‘We are currently facing two unprecedented challenges. On the one hand, the coronavirus pandemic has triggered the most severe economic crisis in our industry. The collapse of global air traffic creates a dramatic situation for manufacturers as well as for our deeply rooted supply chain, which is located throughout Germany. On the other hand, aviation is on the threshold of climate-neutral flight. We have set ambitious goals for ourselves; by 2050 we will achieve climate-neutral flight. That is why up to 90 percent of our investments in research and development have long been directed at reducing emissions.’”

Research, Research, Research

The DLR, BDLI and participating academic and industry partners are researching “several radical technologies… in parallel” for missions from urban aeronautics to large airliners capable of trans-continental trips

Zero-emission aviation requires a great deal of research. To achieve this goal, and their use evaluated in relation to the size and range of aircraft. In the field of battery-electric urban air mobility to hybrid and fuel cell power for regional aircraft, and sustainable fuels, in combination with new gas turbine concepts for emission reductions on medium and long-haul flights. Directly-burned green hydrogen may become a factor on long-range flights.

On an economic standpoint, the white paper predicts, “Until the global aircraft fleet is replaced by the next generation in around 20 to 30 years, financial resources will be needed to improve the climate impact of current aircraft, in addition to investments in new technologies… Studies by DLR show that even small changes in flight guidance with an increase in operating costs of only one percent could lead to a reduction in climate impact of up to 10 percent.”

Different Approaches to Different Missions

The Hy4 Regional Commuter

Hy4, derived from GFC winning PIpistrel G4, would fly regional commuters on Hydrogen power

The Hy4, powered by a hybrid drive concept comprising a low-temperature hydrogen fuel cell and a high-performance battery works successfully. André Thess, Director of the DLR Institute for Engineering Thermodynamics, explains, “The major challenge for the future is to create electric drive systems for large passenger aircraft as well. With this vision in mind, we are currently working to continue improving the fuel cell powertrain.”  This aircraft, originally powered by a 200 horsepower electric motor, won the Green Flight Challenge in 2011, with a passenger mile per gallon energy equivalent of 403 mpg.  This clean design would enable it to transport four passengers in unpiloted mode between Germany’s 60 regional airports, a short-range convenience for many users.

Hy4’s hydrogen fuel cells replace original G4 batteries, 200 hp motor

19 Seats – a Popular Number

A cooperative effort between The German Aerospace Center and Bauhaus Luftfahrt,  the CoCoRe (Cooperation for Commuter Research) project examines the possibilities and potential for hybrid-electric 19-seater aircraft. These craft would fly missions up to 350 kilometers (217 miles), not uncommon distances for such air service.

19-seat concept for hybrid-electric regional airliner as part of CoCore project

This is a popular market segment, with approximately 3000 commuter-class aircraft in use worldwide.  But only just over a dozen new 19-seaters have been delivered to the civilian sector annually in recent years.  Project Manager Wolfgang Grimme of the DLR Institute of Air Transport and Airport Research explains, “In our study, we investigated a sample configuration that, with a few modifications, is based closely on the 19-seater Do 228 and, in particular, the Jetstream 31, which are currently flying.”

Envisioning flights of 200 kilometers (124 miles) on battery power alone, DLR researchers expect a battery weight of two tons and a maximum total take-off weight of 8.6 tons.  With this in mind, they propose mounting easily replaceable batteries in nacelles over the landing gear.  Such distances are not uncommon for routes even in America.  Southwest Airlines, for instance, just added a new route between Colorado Springs, Colorado, and Denver on March 11, with service four times daily. At only 63 nautical miles long (73 miles), the flight will be the shortest in the Southwest route network, according to the airline.

Grimme adds, “This allows us to place the weight of the batteries, which are comparatively heavy, exactly where it is most convenient during take-off and landing – directly above the landing gear. This also means that empty batteries can be replaced quickly and easily.”

Dornier 228 as reconfigured with electric-hybrid system in DLR concept rendition

Range extenders in the form of two gas turbines that can be coupled or decoupled from the propellers could allow trips up to 1,000 kilometers (620 miles). DLR research shows 56 percent of 19-seaters worldwide fly distances of less than 200 kilometers and 83 percent fly less than 350 kilometers (217 miles).

Annika Paul of Bauhaus Luftfahrt  explains, “This usage pattern means that the combination of fully electric flight enhanced by range extenders will prevent the majority of carbon dioxide emissions caused by commuter aircraft.”   Ranges extenders would enable diversions to alternative airports and allow longer fully electric flights.

Improved batteries could lead to even better fully-electric ranges in the near future.  Smaller battery-powered and range-extended machines would also provide more trips to remote regions with lower passenger volumes, expanding the possibilities for more flights to more destinations that otherwise can’t support 737 or A320 size aircraft.  The economics of batteries with greater numbers of charge discharge cycles will enhance electric aircraft use and again lead to more small craft making more trips to otherwise little-served communities.

Next: DLR’s Novel Configurations

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Ampaire’s Second Electric Eel Sets Record

There are now two Ampaire electric EELs* flying, courtesy of Ampaire Aviation.  The second test vehicle recently set a world record, staying in the air for two hours and 32 minutes, covering 341 miles at an average speed of “around 135 mph.”
A six-seat Cessna 337 “Skymaster,” the “push-pull” twin has been modified by Ampaire “with an electric motor in the nose and traditional [internal] combustion engine in the rear.  The paired powerplants act as a parallel hybrid, both electric and ICE units providing thrust simultaneously.

Ampaire flew an electric-and-gas-powered Cessna 337 this year. With assistance from Ikhana, a modification and conversion specialist,  Ampaire replaced the 337’s rear engine (which drives a pusher prop) with an electric propulsion system, leaving the forward engine in place.

It is now swapping the configuration around – putting the engine in the back and moving the electric system forward, with batteries removed from the cabin and installed in a pod under the aircraft.

Ampaire’s partner on the 337, Hawaii-based Mokulele Airlines, will fly the aircraft in this new configuration in the first quarter of next year, according to Brice Nzeukou, Ampaire Product Manager.

A Quite Normal Cross-Country Flight

Ampaire reported, “The craft took off from Camarillo Airport just north of Los Angeles at 12:20 PM. Test pilot Justin Gillen and Flight Test Engineer Russell Newman, flew up California’s Central Valley at 8,500 feet, landing at Hayward Executive Airport at 02:52 PM.” Gillen explained, “The mission was a quite normal cross-country flight that we could imagine electrified aircraft making every day just a few years from now.”

The record flight followed four weeks, 23 flights, and 30 hours (“with 100-percent dispatch reliability) since the Hawai‘i Bird first took to the air.  Ampaire’s general manager Doug Shane said, “Our success in taking this aircraft in a short period from the test environment to the normal, everyday operating environment is a testament to our development and test organization, and to the systems maturity we have achieved with our second aircraft.”

Flying over California’s Central Valley, Ampaire’s second electric EEL sets record distance for hybid electric flight

The Hawaiʻi Bird, so named because it will take part later this year in a series of demonstration flights with Hawaiʻi-based Mokulele Airlines on its short-haul routes, will be partially disassembled in Hayward for shipment to Hawaiʻi. The Hawaiʻi flight trials are funded in part by Elemental Excelerator, a cleantech incubator headquartered in Honolulu.

Ampaire’s  electric EEL will serve as “a testbed aircraft for the development of high-powered electronics, inverters, motors, and related systems.”  A platform for developing scalable technology and certification processes, the EEL can also serve owner-flown, charter and short-haul regional airline/cargo carriers.  The EEL will have operational costs cut with fuel savings of 50 to 70 percent and maintenance costs only 25 to 50 percent of the conventionally-powered original.  The hybrid electric system will provide safe transport between islands, able to hop 200 miles with reserves while carrying three passengers or 450 pounds of cargo.

According to Ampaire, “These flight demonstrations will mark the first time an electrically powered aircraft has flown under an FAA ‘Market Survey’ experimental aircraft certificate in order to gain real-world flight experience.”  Beyond Mokulele’s interest, PAX (Personal Airline Exchange) ordered 50 EELs last year.

*According to Wikipedia, “EEL refers to the original 337 designation, with the characters reversed.”

A Four-Motor Electric Otter

Ampaire’s CEO Kevin Noertker said, “The Electric EEL is our first step in pioneering new electric aircraft designs. Our next step will likely be a 19-seat hybrid electric retrofit program that will lower emissions and operating costs, benefiting regional carriers, their passengers and their communities.”

Ampaire and aircraft services company Ikhana have been designing a 19-seat (or 4,000 pounds of cargo) hybrid-electric aircraft based on the popular de Havilland Twin Otter aircraft, to be called the Eco Otter SX, since October 2019 as part of a NASA-funded project.

“Twin” Otter as shown at DLR symposium, but with four motors

Like the EEL, the Otter will save 20 to 30 percent on fuel and 10 to 25 percent on maintenance. The Twin Otters may become four motor craft with hybrid propulsion using a Diesel engine to generate electricity and a full electric system, according to Brice Nzeukou.

The companies expect to complete their study by the end of the year and have the modified 337 certificated by the end of 2021.  Even grander plans are on the horizon.

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If, as the infamous cartoon in the New Yorker proclaimed, “Money is life’s report card,” Jeff Engler’s Wright Electric got a least a B+ for its current semester.  While not as flush with cash as firms like Joby Aviation, eHang, or Volocopter, Wright received significant recognition for its initiative in designing high-efficiency electric motors with a high-frequency inverter and “an aggressive cooling strategy.”  The $647,039 ARPA-E grant will further Wright’s work on the ARPA-E ASCEND Project.

ASCEND stands for Aviation-class Synergistically Cooled Electric-motors with iNtegrated Drives, a sure-fire Scrabble winner and pretty tortuous acronym. Phase one of the project takes the team through the detailed design and subcomponent testing for the system.  Phase two will see Wright build and demonstrate the system.

Only a startup in 2017, Wright Electric has managed to partner with easyJet, a European budget airline, to develop a 186-seat electric aircraft called Wright 1.  With others in startup mode flying six and ten-passenger aircraft and looking forward to 19-seaters, Wright’s plans are ambitious indeed.  To help create their hybrid electric aircraft solution they also partnered with Airbus, hoping to reach power densities beyond 12 kilowatts (16 horsepower) per kilogram.  GreenCarCongress offers the comparison of current jet fuel-burning turbine engines that achieve approximately 6-9 kW/kg.

GreenCar Congress adds that, “The innovations across the electric propulsion system will aid the development of aircraft flying entirely on electric power. Single-aisle and twin-aisle aircraft that carry 100 or more passengers account for more than 90 percent of global emissions from commercial aircraft.”

That is very much the market in which EasyJet is involved and fits very well with their plans with Wright “to develop an all electric aircraft program as part of a shared goal to decarbonize aviation.”.

David Morgan, Director of Flight Operations for easyJet commented: “We are excited to see this news as funding is going to be so crucial in unlocking the potential of new technologies so this marks another step on their journey to developing their all electric aircraft.

easyJet remains absolutely committed to more sustainable flying and we know that technology is where the answer lies for the industry. We are committed to collaborating on the development of these new technologies – as demonstrated by our support of Wright Electric – with the aim of being an early adopter when they come to market.”

Jeff Engler, CEO of Wright Electric said, “We could not be more happy to collaborate with the experts at ARPA-E on the future of aircraft design. Since 2016, Wright Electric have pioneered efforts to advance aerodynamics and propulsion technologies and we remain focused on our ultimate goal to produce a fleet of zero-emissions commercial airplanes.”

The Centre for Aviation reports, “Since last November, easyJet is the first major airline to operate carbon neutral flights across its whole network. The airline is achieving this goal by offsetting the carbon emissions from the fuel used for all of its flights. The airline sees this as an interim measure until new technology becomes available to decarbonize aviation. In the meantime, easyJet remains focused on operating its fleet as efficiently as possible using modern, fuel efficient engines which are quieter and burn less fuel. Since 2000 easyJet has reduced the carbon emissions for each kilometer flown by a passenger by over one-third (33.67 percent) and has a target to reach a 38-percent reduction by 2022.”

You will notice variations in the Wright 1’s configuration over the last few years.  This image shows the most current.

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Aalto University in Espoo, Finland has announced a seemingly impossible breakthrough – black-silicon solar cells that exceed 100-percent efficiency.  This breaks the Shockley-Queisser limit, previously thought to be an unbreakable barrier to any solar cell generating more than 33.7-percent efficiency for a single p-n junction photovoltaic cell.  The 1,000 Watts of sunlight falling on a square meter of single-junction solar cells could never produce more than 337 Watts to a battery or other receiving mechanism.  William Shockley, a co-winner of the Nobel Prize in Physics for his co-creation of the transistor and Hans-Joachim Queisser defined this limit at Shockley Semiconductor in 1961.

Light landing on forest-like black silicon generates more electrons than photons striking cell: 30-percent more in Aalto cells

In a traditional solid-state semiconductor such as silicon, a solar cell is made from two doped crystals.  One is an n-type semiconductor, which has extra free electrons, and the other a p-type semiconductor, which is lacking free electrons, referred to as “holes.” When initially placed in contact with each other, some of the electrons in the n-type portion will flow into the p-type to “fill in” the missing electrons.

For an overview of the limit and the physics involved, this link provides some insights.

Even the Researchers Disbelieved

Aalto reported the new solar cell’s “efficiency was so high that at first the researchers had a hard time believing the result.”  Their black silicon photodetector reached above 130-percent efficiency, exceeding the 100-percent external quantum efficiency limit at ultraviolet wavelengths.

Professor Hele Savin, head of the Electron Physics research group at the University explained, “When we saw the results, we could hardly believe our eyes. Straight away we wanted to verify the results by independent measurements.”  To confirm the findings the German National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB), known for accurate and reliable measurement services, performed independent measurements.

Dr Lutz Werner, head of the PTB Laboratory of Detector Radiometry, commented, “After seeing the results, I instantly realized that this is a significant breakthrough – and at the same time, a much-welcomed step forward for us metrologists dreaming of higher sensitivities.”

 Unique nanostructures

If one photon hits the surface of a solar cell and generates one electron to an external circuit, the efficiency of the solar cell would be 100 percent.  Most solar cells remain well below the Shockley-Queisser limit giving in electrical current only a portion of the solar energy striking them.  Aalto’s black silicon cells are unique in sending 1.3 electrons into the circuit for every photon strike.

The University explains, “The researchers found out that the origin of the exceptionally high external quantum efficiency lies in the charge-carrier multiplication process inside silicon nanostructures that is triggered by high-energy photons. The phenomenon has not been observed earlier in actual devices since the presence of electrical and optical losses has reduced the number of collected electrons.”

Black silicon enables broader responsiveness to wider range of light wavelengths

Professor Savin adds, “We can collect all multiplicated charge carriers without a need for separate external biasing as our nanostructured device is free of recombination and reflection losses.”

Looking at the improvements possible in devices relying on solar cells, Dr.Mikko Juntunen, CEO of Aalto University spin-off company, Elfys Inc., notes, “Our detectors are gaining a lot of attraction at the moment, especially in biotechnology and industrial process monitoring.”  Elfys already manufactures these black-silicon cells for commercial use.

Implications for Aerospace

Imaging a Solar Impulse or Sunseeker Duo which needs far smaller wings and solar cell arrays.  Aircraft performance could be enhanced, construction costs reduced, and general utility bordering that of many general aviation craft engendered.  Reportedly lower costs of black silicon cells would certainly make their use an attractive proposition.

More efficient solar cells would make smaller solar aircraft plausible as shown with early version of Calin Gologan’s PC Aero design

Published Results

M. GarinJ. HeinonenL. WernerT.P. PasanenV. VähänissiA. HaarahiltunenM. Juntunen, and H. Savin published their findings under the title, “Black-silicon ultraviolet photodiodes achieve external quantum efficiency above 130%,” in the journal, Physical Review Letters.

The abstract provides an overview and implications for further research.  “At present, ultraviolet sensors are utilized in numerous fields ranging from various spectroscopy applications via biotechnical innovations to industrial process control. Despite of this, the performance of current UV sensors is surprisingly poor. Here, we break the theoretical one photon – one electron barrier and demonstrate a device with a certified external quantum efficiency (EQE) above 130% in UV range without external amplification. The record high performance is obtained using a nanostructured silicon photodiode with self-induced junction. We show that the high efficiency is based on effective utilization of multiple carrier generation by impact ionization taking place in the nanostructures. While the results can readily have a significant impact on the UV-sensor industry, the underlying technological concept can be applied to other semiconductor materials, thereby extending above unity response to longer wavelengths and offering new perspectives for improving efficiencies beyond the Shockley-Queisser limit.”

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