HopFlyt Channels the Custer Channel Wing

HopFlyt is an enthusiastic young organization devoted to renewing the Custer Channel Wing, a lost remnant of attempts to create extremely short takeoff and landing (STOL) airplanes starting over 70 years ago.  Their web site explains their primary goal, which includes adding electrically-powered vertical takeoffs and landings to the channel wing’s repertoire. “HopFlyt is an aviation technology startup company [whose] main priority is to develop technology and ultimately build a sustainable electric Vertical Takeoff & Landing (eVTOL) aircraft. The goal of this aircraft is to help you beat the jam of traffic and reduce pollution in major urban centers around the world. We want to change your 2 hours of traffic into a short 20 minutes of flying.”

HopFlyt is an electrified extension of Willard Custer’s ideas, with eight semi-circular ducts channeling airflow for enhanced performance

Willard Custer’s Frustrated Search for High Lift

Willard Custer designed several approaches to using his unique ducts to channel air around the rotating propeller.  These are covered in at least 27 patents granted to him between 1929 and 1974.  He built and flew three aircraft, CCW 1, CCW 2, and CCW 5 all of which were twin engine, from 1940 into the mid-1950’s.

Early demonstrations for the military showed his semi-circle wing surrounding a propeller could draw enough air through the “channel” to pull the airplane off the ground with no forward motion of the airplane (not mentioning the wind speed during the test).  A French web site devoted to the channel wing describes this test.  “Willard decides one day to demonstrate the vertical flight of his device.  Attached to a rope stretched between two masts, the machine is indeed rising … naturally, hardly the engines set in motion.”  Custer claimed flight at speeds as low as eight to 11 mph with this CCW-2.

His later CCW-5 was a four-seater equally capable of STOL performance.

Its twin 225-horsepower engines certainly produce enough noise to be unwelcome guests at most airports today, and not likely to be approved for neighborhood airparks or rooftop arrivals and departures.  Perhaps electric propulsion can help solve part of the noise issue.

Custer’s experiments received a great deal of public interest and comment, and even tests in the NACA Langley wind tunnel, but no “takers” for certification and production.  High drag associated with the extreme STOL capabilities kept the airplane in lower speed ranges – but that’s not a problem for HopFlyt’s innovators.

HopFlyt’s Vertical Extension of Custer’s Ideas

HopFlyt’s mission limits trips to under 200 miles, so high cruising speeds will not be as important as the fact that commuters will avoid the gridlock below.

“At HopFlyt, we are designing an electric Vertical Takeoff & Landing (#eVTOL) aircraft that allows you to fly over the traffic, saving you precious time, so you can be more productive. Additionally, HopFlyt is exploring ways to reduce recurring energy costs and make urban transportation fast, safe and sustainable.”

The design combines tandem wings, eight electric powerplants, and eight channels surrounding multiple-bladed propellers to provide thrust.  With the wings pivoted perpendicular to the fuselage, the airplane can make vertical takeoffs.

Pivoting wings enable vertical takeoffs and landings

HopFlyt aims to make their craft accessible to all, with one possible means to achieve this being the use of automated manufacturing.  Their video of a 1/7-scale wing rib being 3D printed shows at least one possible way to achieve their goals.

Although there is little in the way of detailed specification at this time, it’s interesting to see the revival of Willard Custer’s dream.

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George Bye has spent the last decade developing a viable two-seat training aircraft that would be electrically powered.  His efforts included a Cessna 172 that took wing on battery power, and have evolved to the current product, a sleek two-seater that has 105 deposits to buy worldwide.

At AirVenture 2017, George displayed the Sun Flyer 2 and announced plans to introduce a four-seater, the Sun Flyer 4.  With ground tests complete on the aircraft and its 45-pound Emrax motor, George envisions flight tests coming this fall for the 2.  Even given successful flight tests, certification may take two to three years.  George has been working with the FAA to enable certification under Part 23 rules, and has made great headway in obtaining acceptance of electric powerplants on training aircraft.

Flying Magazine reported in February that, “Developers of electric aircraft are rejoicing now that the Part 23 rewrite is complete. Unlike before, the new rule will allow for certified airplanes to be developed with electric propulsion.”  The magazine quoted George on the gains to electric aircraft developers.  “One particularly important benefit for Sun Flyer is that by being able to increase the weight of the initial two-seat training airplane, additional batteries can be carried, resulting in improved flight endurance, greater utility and broader market acceptance.”

Sun Flyer 2 at Oshkosh AirVenture 2017

Training may be where it’s at in the new General Aviation.  Boeing predicts a need for 617,000 new commercial pilots by 2035, due to the retirement of currently licensed personnel and the anticipated expansion of airline and commuter travel.  Redbird Flight is partnered with Sun Flyer to help deliver simulators and ground school for all these new students.

Prices for the two airplanes, $249,000 for the 2 and $349,000 for the 4, may seem high, but compared to equivalent internal-combustion-powered aircraft, not out of line.  As Sun Flyer premises, operating and maintenance costs will be much lower – only $16 per hour in direct operating costs for the 2 and $18 per hour for the 4.  In what Sun Flyer describes as “disruptive affordability,” about $3 of those amounts pays for the electric charging bill for each hour of flight.  Compare that to the $88.31 per hour and $122 per hour operating costs Sun Flyer claims for a Cessna 172 and 182, respectively.

Emrax motor weighs a mere 45 pounds, hides neatly behind spinner

Brushless electric motors have only one moving part, and are extraordinarily reliable compared to their internal combustion cousins.  Lower operating and maintenance costs could bring more student pilots through the doors of flight training centers, something on which Spartan College of Aeronautics and Technology, is counting.  It has reservations for the first 25 two-seaters, after all.  The College is even implementing a course that will teach aircraft and engine mechanics the art of maintaining aircraft with this new technology.

George Bye’s aerospace endeavors extend to large drones, a high-speed, vertical takeoff and landing craft, and expanding the role electric aircraft will play in future flight training and general aviation.  The work he’s done in gaining acceptance for clean energy in light aircraft is a substantial first step.

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A123/Solid Power Partnership – A Safe Bet?

A123 Systems has worked with buffering chemistries to reduce the volatility of lithium batteries for the last decade.  Solid Power Inc. has taken a set of interesting new technologies to make batteries more energy dense and safer.   The two companies are combining efforts to make a more powerful, less-volatile battery, according to recent press releases.

A123 produces nanophosphate (lithium iron phosphate – LiFePO4) and ultraphosphate batteries.  Their nanophosphate batteries are used in Porsche’s 919 hybrid, a LeMans Prototype (LMP1) endurance racer that was outright winner of the event this year.  They also power Eva Hakansson’s Killajoule and Bill Dube’s Killacycle – both record-holding electric motorcycles.  Their Ultraphosphate line is designed to work at low voltages and low temperatures, including 48-Volt mild hybrid applications.

 

Porsche 919 hybrid won Le Mans outright this year. Photo: Porsche Motorsports

Solid Power, a startup based on research done at University of Colorado Boulder, combines (“an exceptionally”) high-capacity cathode with a high-capacity lithium metal anode and a high ionic capacity solid separator.  This combination produces, according to Solid Power, “provide substantially higher energy than conventional lithium ion (2-3X greater).”  Their inherently safer inorganic materials, with no flammable or volatile components, allow lower costs for modules, since they eliminate the need for complex battery management systems necessary with lithium-ion systems.

A123 delivers nanophosphate batteries in a variety of formats

Solid Power’s CEO Doug Campbell said, “We are committed to advancing the solid-state battery industry and pushing the limits on development as a way to improve battery-powered devices such as electric vehicles, portable electronics, and other applications. The investment from A123 will help us continue to make significant strides toward large-scale commercialization.”

This venture complements A123’s recent investment in Wildcat Discovery Technologies and its technical collaboration with Argonne National Labs, announced last year.  Although Campbell says Solid Power’s work is currently “pre-product,” he looks forward to having a viable commercial introduction in the next two years.

Jeff Kessen, A123’s Vice President of Corporate Strategy, promotes the early bird theory of venture capitalism.  “We acted early as a series A investor to support a promising solid-state technology and look forward to the commercialization of Solid Power’s innovations as they continue to mature.”

With the oft-promised output of the 2-3X battery and enhanced safety from the solid-state nature of the new batteries, we can only wish A123 and Solid Power “more power to you.”

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There are few times one will see more than one electric airplane at the same place – outside of perhaps, Friedrichshafen’s e-Flight Expo every year.  But to see them flying at the same field on the same day is an even grander delight.  That happened September 9 and 10 at Grenchen, Switzerland.  Grenchen hosted the world’s first all-electric fly-in – the SmartFlyer Challenge.  It drew an appreciable number of electric aircraft of all sizes and types despite the clouds and rain that kept some from scaling the mountains.

An Electric Three-Plane Formation Flight

The Siemens-powered Magnus e-Fusion from the Czech Republic, the electric Phoenix motorglider, and Stuttgart University’s e-Genius all flew formation with a Piper L-4, a World War Two liaison aircraft and camera plane.

A rare sight – a three electric airplane formation. Frank Anton pilots the Magnus e-Fusion (foreground), followed by the D-14 Phoenix motorglider, and e-Genius.  Photo courtesy of Jean-Marie Urlacher

They joined a commendable group of aircraft on the field.  All seemed to fly as much as possible during the event, including drag racing a Tesla S sedan down the runway.

Electric airshow action with a Tesla S sedan drag racing a Magnus e-Fusion. Photo courtesy of Jean-Marie Urlacher

Expatica.com noted, “Pilot Frank Anton had never heard applause upon landing. But when the head of electric planes at Siemens touched down in a Magnus E-Fusion craft powered by electricity, he was received like a rock star by photographers and members of the public.”

e-Genius does a low fly-by. Photo courtesy of Jean-Marie Urlacher

Aircraft on the field included e-Genius, second-place winner of the 2011 Green Flight Challenge.  It made the first landing at Grenchen by an electric airplane.  Another craft from Stuttgart, Icare 2, is a solar-powered sailplane flying since 1996 and holding many records, set first by its project leader, Rudolf Voit- Nitschmann, and followed with a series set by Klaus Ohlmann.

Both aircraft have the tail-mounted propeller configuration favored by Voit-Nitschmann, creating only a fraction of the skin friction a front-mounted propeller does.  This same configuration is used by the group designing the Smart Flyer, a four-seat hybrid with its base in Grenchen.

Several trikes flew in, including an A-I-R Atos, which made the first electric takeoff from the field.

Posted by Smartflyerchallenge on Friday, September 8, 2017

Another craft based on the field, the Votec Evolaris, has a modified Brusa motor and was undergoing runups prior to the fly-in.

Votec Evolaris, a powerful aerobatic contender, fills a small space. Note poster for Traveler Hybrid, a four-seat hybrid craft also based in Switzerland.  Photo courtesy of Jean-Marie Urlacher

Two presenters brought slides but no airplanes.  Tomas Brodreskift flew by commercial jet from Norway and explained why “The [Equator] P2 is the next big thing in aviation,” with its amphibious capabilities and advanced hybrid power system.  Tine Tomazic and Paolo Romagnolli discussed the creation of the Alpha Electro from design to serial production.

A full speakers list included an introductory talk by Jean-Luc Charron, president of the French Aeronautical Federation.  Frank Anton, head of Siemens electric aircraft motors program, discussed his company’s future in a growing and expanding market.  Axel Lange detailed the Antares E2, his still advanced electric sailplane.  Others filled in on regulations, technology, and new developments.

One Facebook picture shows a group with a Rotax engine and hybrid-looking hookup, but little information as to its intended purpose.  We will be happy to receive intelligence about this system.  This is possibly the power setup for the  Hybrid Traveler.

Possibly the Smart Flyer development team with a Rotax-based hybrid system

Another ultralight from the Czech Republic, the Ultralight Design Ego Trike, showed its clean lines on the tarmac, also topped by an A-I-R Atos wing.  In a display hangar, the French Electric Aircraft Whisper eight-rotor helicopter looked intriguing, but there is little detail on their web site to answer questions arising from the craft’s appearance.

Rendering of Whisper helicopter shows possible housing for hybrid drive. Web site does not fill in details

A Lange motorglider and Silent 2 showed that electric craft have been flying for several years, improving as better batteries become available.  A lighter machine, the Ruppert Archaeopteryx, was piloted by Cornelia Ruppert, a company principle.  She also made a presentation on her dream of flight, and how this airplane helps fulfill that.

Cornelia Ruppert pilots her Archaeopteryx over Grenchen

Short symposium sessions allowed time for participants to watch flight demonstrations and inspect craft indoors and out.  We can hope that next year’s Challenge, planned for September 1 and 2 has better weather and pulls in an even larger crowd.

A Note on Some of the Photographs

Jean-Marie Urlacher is a master photographer who raises standards for air-to-air photographs.  He kindly consented to allow some of his work to be used in this blog entry.  Please visit his web site to be astounded at the clarity and daring of his work.

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Equator P2 Makes First Taxi Test

Designing and building your own airplane is a chore most people will never accomplish.  It’s harder than it looks.  All the people your editor knows who have accomplished this, even “just” the building part, talk about the 90-percent rule: 90-percent done – 90-percent to go.

Getting the Nose Gear to Steer

Tomas Brodreskift of Equator Aircraft is probably at the 95-percent stage of aircraft completion on his hybrid P2 amphibian, but he and his team still need to drill new holes, make new fittings, laminate some additional pieces and finally get a nose-gear steering system in place.  Since his airplane doesn’t have a set of rudder pedals, steering is controlled by pushing on switches on an orange handgrip in the cockpit.

Motor Run Number 2

Since it last ran in April before being transported to the Friedrichshafen Aero Expo, the Equator P2 has waited for its nose gear and “steer-by-wire” controls, among other things, to enable it to make its way around the airport.  The quietness of the overall system is noteworthy.

Taxi Testing

Perhaps Tomas should consider putting a shroud around the propeller and using the P2 to commute on public roadways.  The control gear, which looks like a variation on rack-and-pinion steering, seems to do its job as planned.  Having a thoroughly different form of steering control on a retractable nose wheel is a great accomplishment in itself.

We can look forward to further progress in the near future, as Tomas and his team make ready for faster taxiing and that first lift-off.

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Cheaper Hydrogen and Fuel Cells

Hydrogen would be a wonderful fuel if it were easy to get and easy to use.  It makes up 90 percent of all atoms in the universe, equal to about 75 percent of all the mass.  Hydrogen has been expensive to obtain because quite often its extraction from other matter entails using expensive catalysts such as platinum.

Russia and America Team Up to Get Cheap Hydrogen

Scientists from the Argonne National Laboratory in Illinois, working with researchers at the Moscow Institute of Physics and Technology (MIPT) and in Jinan, China combined efforts to produce hydrogen using sunlight and photosensitive lipids.  We associate lipids with getting blood drawn at the clinic, and waiting patiently to see how our cholesterol and triglycerides are doing.  Lipids are water insoluble fats, and are a key to this inexpensive method of extracting hydrogen.

Using titanium dioxide as a photocatalyst, the teams “inserted a photosensitive protein into nanodiscs — made from circular fragments of cell membrane composed of a lipid bilayer — to mimic a natural cell membrane called bacteriorhodopsin.”

Combining fats (lipids) with titanium dioxide, immersing the nanodisc in water makes budget hydrogen.  Courtesy: Moscow Institute of Physics and Technology (MIPT)

Placing the nanodiscs, the titanium dioxide and a small amount of platinum (to increase reactivity) in water released hydrogen when the setup was exposed to green or white light.  White light generated 74 times more hydrogen than the green light, though.  According to Futurism.com, “MIPT’s Vladimir Chupin, whose work is usually in anti-aging research, said in a press release. ‘However, the recent joint study with our U.S. colleagues shows that by bringing together biological and technical materials, nanodiscs can be used to obtain hydrogen fuel.’”  Who know light and fats could make a clean energy product?

Durable and Frugal Fuel Cells

University of Delaware Researchers developed a new technology that could speed up the commercialization of fuel cell vehicles.  Since platinum is commonly used as a catalyst in fuel cells designed to burn hydrogen, this has slowed adoption because of high costs – about $30,000 per kilogram ($13,600 per pound).  The UD team used tungsten carbide, which sells for around $150 per kilogram ($68 per pound) and used a novel method to turn it into nanoparticles. Dionisios Vlachos, director of UD’s Catalysis Center for Energy Innovation, explains, “The material is typically made at very high temperatures, about 1,500 degrees Celsius, and at these temperatures, it grows big and has little surface area for chemistry to take place on.  Our approach is one of the first to make nanoscale material of high surface area that can be commercially relevant for catalysis.”

Making the nanoparticles through hydrothermal treatment, separation, reduction, carburization and other processes, “We can isolate the individual tungsten carbide nanoparticles during the process and make a very uniform distribution of particle size,” Weiqing Zheng, a research associate at the Catalysis Center, explains.

Like the nanodisc researchers who used titanium dioxide as a budget alternative to platinum, University of Delaware scientists incorporated their tungsten carbide nanoparticles into a membrane – but in this case, the proton exchange membrane in a fuel cell (PEMFC).  This membrane splits H2 into ions (protons) and delivers them to the cathode, which delivers current.  This membrane wears out from going through repeated wet/dry cycles, mainly because the reaction in the cell produces heat and water – the “exhaust” for a fuel-cell powered vehicle.

Placing tungsten carbide in the membrane humidifies the membrane at a level that optimizes performance.  Liang Wang, an associate scientist in the Department of Mechanical Engineering, says, “The tungsten carbide catalyst improves the water management of fuel cells and reduces the burden of the humidification system.”

Researchers found their fuel cells last longer than more traditional one, because the tungsten carbide captures free radicals before they damage the membrane.  Wang explains, “The low-cost catalyst we have developed can be incorporated within the membrane to improve performance and power density.  As a result, the physical size of the fuel cell stack can be reduced for the same power, making it lighter and cheaper. Furthermore, our catalyst is able to deliver higher performance without sacrificing durability, which is a big improvement over similar efforts by other groups.”

The UD research team used a scanning electron microscope and focused ion beam to obtain thin-slice images of the membrane to determine fuel cell longevity.  Again, like the American/Russian extraction effort, some aspects of the program rely on bio-medical-like technologies.  Zheng notes, “This is a very good example of how different groups across departments can collaborate.”

The group has applied for a patent and hopes to commercialize their technology.

They describe their results in a paper published in Nature Communications.

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Smart Fabrics Generate Energy Several Ways

We see a great deal about wearable energy-generating fabrics, garments that will help keep the wearer warm, or cool, or visible because of built-in piezo-electric generators in the makeup of the fabric.  Several researchers are taking this to the next level, creating new warps and woofs of materials that will create energy from a greater range of energy inputs.

Elias Siores and the University of Bolton

In 2011, Professor Elias Siores and associates at the University of Bolton in the UK created a flexible fiber that could harvest energy from movement and light.  Siores said it was flexible enough to be woven into “a sail, window curtain or tent and generate power”.  The material was recognized as a major innovation at the 2011 Energy Innovation Awards in Manchester.

Professor Elias Siores with a sample of his energetic fiber

In a 2013 paper, the team, led by described devising a “smart fabric.” “A smart material is one that shows extraordinary response when subjected to a stimulus. Piezoelectric materials are considered as smart materials because of their ability to generate electricity against the stimulus which is mechanical strain or vibration. This property of piezoelectric materials is known as direct piezoelectric effect. The reverse effect is also possible in that this material undergoes a slight deformation in shape when a small electrical field is applied.”

Coming up with a flexible fabric allow knitting or weaving it into fabric for clothing, cases for personal gadgets, and even sails, window curtains or tents, which could charge batteries on boats or portable electronics that could make camping more like glamping.  Siores had noted “renewable energy sources such as sunlight, wind and rain are not always available at the same time in the same location,” making this a more versatile material that could operate under a variety of circumstances.  A detailed paper on the team’s work can be found here.

Jayan Thomas and the University of Central Florida

Jayan Thomas and fellow researchers at the University of Central Florida added to the happy combination of energy-harvesting threads and added energy storage, with cotton, copper, perovskite solar collector and capacitor energy storage fibers cleverly woven into something wearable (and maybe even fashionable).

Simple loom for hand weaving energy collecting, storing fabric at UCF

We all dream of emulating our film heroes, but Professor Thomas took it to the next level, having seen Back to the Future“That movie was the motivation,” …Thomas, a nanotechnology scientist at the University of Central Florida’s NanoScience Technology Center, said of the film released in 1989. “If you can develop self-charging clothes or textiles, you can realize those cinematic fantasies – that’s the cool thing.”

The team’s paper in the journal Nature Communications explains how the woven materials collect sunlight, the flexed motion of the wearer, and store that energy for delayed use.  Thomas saw this as a way to help soldiers in the field, who often carry 30 pounds of batteries for the many communication and navigation devices a modern infantry man or woman must pack besides weaponry and ammunition.

The paper details how the researchers managed to meld the elements in their cloth.  “In this study, we report an all-solid-state, energy harvesting and storing (ENHANS) ribbon that integrates a perovskite solar cell (PSC) on top of a symmetric supercapacitor (SSC) via a copper (Cu) ribbon which works as a shared electrode for direct charge transfer. A highly flexible, thin, sandwich PSC with >10% conversion efficiency is developed by a solvent-assisted perovskite growth technique. The sandwich-type device configuration provides better protection for the solar cell against environmental effects due to an unexposed perovskite layer to the atmosphere. The Cu ribbon not only serves as an electron-collecting electrode for the solar cell but also as a substrate for generating copper hydroxide nanotubes (CuOHNT) for developing the supercapacitor.”

(a) Charge–discharge profile of the ENHANS ribbon. The solar side of ENHANS ribbon has been charged with the solar simulator for 1 min and discharged with electrochemical workstation at different current densities after 10 s photocharging (PC) off; (b) Ragone plots of an independent supercapacitor and an ENHANS ribbon to compare the energy density and power density at different charging–discharging rate (1, 2, 4 and 8 mA cm−2 current density); (c,d) photograph of the ENHANS ribbon being bent at different angles; (e) charge–discharge profile of the ENHANS ribbon after a different bending cycles (the ENHANS ribbon has been photocharged for 1 min, and then removed from light 10 s before discharge); (f) schematic illustration of the ENHANS ribbon after weaving with the cotton yarn to make a portable lightweight cloth and (g) ENHANS ribbons weaved with cotton thread to demonstrate the working of the lightweight fabric. The photograph shows the charge deliverability of weaved matrix as a result of one minute photocharging.

Zhong Lin Wang and the Georgia Institute of Technology

Zhong Lin Wang at the Georgia Institute of Technology, along with a phalanx of scientists in colleges and universities throughout China, devised a fabric described in their paper, “Self-powered textile for wearable electronics by hybridizing fiber-shaped nanogenerators, solar cells, and supercapacitors,” was published in the October 26, 2016 edition of Science Advances.

Sample of Georgia Tech energy cloth

Taking the manufacture of this material beyond small samples, Wang explains, “The backbone of the textile is made of commonly-used polymer materials that are inexpensive to make and environmentally friendly.  The electrodes are also made through a low cost process, which makes it possible to use large-scale manufacturing.”

Wenjie Mai and Researchers in China and Singapore

Researchers at Jinan University and Chongqing University in China, and Nanyang Technological University in Singapore took a similar approach, creating threads which store energy from piezoelectric reactions and solar energy. “The ‘threads’ (fiber electrodes) featuring tailorability and knittability can be large-scale fabricated and then woven into energy textiles. The fiber supercapacitor with merits of tailorability, ultrafast charging capability, and ultrahigh bending-resistance is used as the energy storage module, while an all-solid dye-sensitized solar cell textile is used as the solar energy harvesting module. Our textile sample can be fully charged to 1.2 V in 17 s by self-harvesting solar energy and fully discharged in 78 s at a discharge current density of 0.1 mA.”

Fiber supercapacitors and photoanodes woven together with cotton and counteranode fibers. Things are connected with conductors at fiber ends

Wenjie Mai, Department Chair and Professor in the department of physics at Jinan University (China) explains how these fibers are connected to produce a current. “We simply use metal wires to connect all these fibers at their extremities”   This may not look perfect, it was good enough to show the idea on a working prototype.

An Ending with a Twist

Twistron sounds like a commercially-viable product already, and the potential for this twisted carbon nanotube actually might exceed the performance of some lithium batteries. Developed by researchers at the Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas; the Center for Self-Powered Actuation, Department of Biomedical Engineering, Hanyang University, Seoul; the Department of Materials Science and Engineering, University of Texas at Dallas, and numerous other organizations, Twistron takes a literal twisting of the yarn-like material to produce energy.  The teams’ paper, “Harvesting electrical energy from carbon nanotube yarn twist,” appeared in the August 25, 2017 edition of the journal Science.

Twistron yarn comes close to rivaling lithium cells in energy density

According to Green Optimistic.com, “A twisted yarn that is stretched 30 times per second can generate a power of 250 watts per kilogram of the yarn. This rate is over a hundred times higher than other energy-harvesting fabric yet developed.”  (And similar in energy density to good-quality lithium cells.)

How these fabrics might be moved from fashion to structural use in aircraft is open to question, but the widespread research, of which only a handful of possibilities could be described here, show progress and potential.  Consider the idea of older, fabric-covered airplanes that could be restored and electrified, gaining a new lease on life after all the antique Continentals and Lycomings are reduced to scrap.  Or think of hang gliders and ultralights that might be at least partially powered by sunlight and the flexing of their fabric sails.

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Oliver Garrow has been pursuing the dream of vertical takeoff and landing (VTOL) flight for a decade, starting long before it became the currently fashionable ideal for “flying car” enthusiasts.  He sold a little over 1,000 simulation packages to enthusiasts, who could “fly” variants of the Verticopter™ ranging from three to 65 feet in span.  At the same time in 2010, Garrow was testing large radio-controlled models of the concept at NASA Ames, Moffett Field, California.

The craft’s configuration changed considerably as Oliver refined his concept, with a full-scale prototype displayed at the HAI (Helicopter Association International) Helicopter Expo in Orlando, Florida in 2015.  The company and vehicle names changed to VTOL Aerospace and Converticopter™.

Later, Garrow’s team tested the static thrust of the prototype, achieving close to 1,000 pounds of thrust at about 1/3 throttle on the 450 shaft horsepower turbocharged engine.

Here it’s shown in hover in 96-inch span model (CVC96) form earlier this year.  The use of electric motors may show a direction for future development of full-scale aircraft.  Such a design would probably simplify the drive system in the tilt-wing configuration.

Recent tests at Hayward, California with the CVC96 show great controllability and intriguing tuft testing.  The black yarn attached at regular intervals to the lower wing shows persistent attachment at all angles of attack, demonstrating excellent laminar flow throughout the model’s speed range.

Garrow reports on these latest flights.  “It was verified and corroborated through systematic simulations and flight tests, that the production airframe would benefit from a L/D (lift-to-drag) ratio above 15.0 at loitering speeds, allowing very efficient and extended flight time.

“The company highlights the features of a compact Converticopter version (CVC96) with a wingspan of 8-ft, allowing loiter flights up to 1.5 hour, only on battery power alone, and beyond 5 hours with an electric hybrid power plant. Larger payload sizes and longer flight times may be achieved by scaling up the airframe, and its power source, up to 40 ft in wingspan. Additional CVC models with various wingspans may be offered by manufacturing partners, who are to subscribe to a manufacturing license agreement.”

These ongoing experiments, including work in NASA Ames’ wind tunnel and at full-scale and model sizes, shows hope for Garrow’s ambitions for the project, including”

“·  Vertical take-off with considerable payload
“·  Self-stabilizing and self-rectifying hover flight transition
“·  Rapid and safe conversion to conventional flight
“·  Adaptive flight patterns based on the selected mission, including low-speed loitering.
“·  Extended flight time due to a low-drag, high-lift airframe
“·  Ability to land vertically any time in the midst and/or at the end of the mission.”

The appreciable glide ratio itself is a feature that many multicopters don’t enjoy, and the thought of failures dropping half-ton or bigger vehicles on the landscape below, even with parachutes,” is not comforting.  Converticopters at least have a controllable glide path that may avert such disasters.

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Electric Propulsion for Big Birds

Graham Warwick reports in the August 25 Aviation Week that NASA is investigating the creation of megawatt-scale electric propulsion systems for airliners.  These would be much more powerful than those in cars or even semi-trucks, and far lighter than equivalent units in ships.

NASA’s research involves partnering with the University of Illinois, Ohio State University, General Electric, and Boeing.  NASA Glenn Research Center is working on its own self-cooled, superconducting wound field synchronous motor as part of the overall effort.

Concept with boundary-layer-ingesting electric fan in the tail is an option for a 2035-time frame partially turboelectric commercial aircraft. Credit: NASA

NASA’s focus, according to the article, “is on electric machines that can be used as generators (sources) and motors (loads) and power electronics that convert AC to DC (rectifiers) and DC to AC (inverters).”  Research includes wiring systems that can distribute high levels of electrical power.  These efforts would support “near- or medium-term development of partially turboelectric and hybrid-electric propulsion systems for aircraft up to single-aisle airliner size.”

Ambitious Goals, Different Approaches

Goals are ambitious, with NASA Research Agreements (NRAs) awarded to the University of Illinois and Ohio State University to develop electric systems that can achieve 13 kilowatts per kilogram and efficiency greater than 93 percent.  NASA Glenn’s target is 16 kW/kg and 98-percent efficiency.

General Electric and the University of Illinois share an NRA to make power converters that produce 19 kW/kg and an efficiency target of 99 percent.  Boeing’s working on a cryogenic converter with goals of 26 kW/kg and an efficiency of 99.3 percent.  Compare these goals with the Energy Department’s 2020 goal of 14.1 kW/kg for vehicle power electronics.

Each NRA promotes a different kind of motor.  The University of Illinois’ one-megawatt permanent magnet synchronous motor is a large outrunner not unlike those on model aircraft with a carbon fiber overwrap and permanent magnets that rotate at 18,000 rpm.  The University has already done full-speed rotor testing and is working to integrate the air-cooled unit into a Roll-Royce Liberty Works Electrically Variable Engine.

The university has conducted full-speed rotor testing and design work on integrating the air-cooled motor into the Rolls-Royce Liberty Works’ engine.  This parallel hybrid-electric propulsion system uses a battery-powered motor to help drive the turbofan for taxiing, takeoff, and idle descent, reducing fuel consumption. The team has studied one-to-2.6 megawatt motors.

Concept with boundary-layer-ingesting electric fan in the tail is an option for a 2035-time frame partially turboelectric commercial aircraft. Credit: NASA

Taking a different approach Ohio State is working on a 2.7-megawatt ring induction motor. The one-meter (3.3-foot)-diameter ring rotates at 2,700 rpm, the outside rotor driven by magnetic induction from the magnetic field produced by the stator winding.  A tape conductor wound around the stator drives the rotor. Part of the conductor tape outside the active region has direct liquid cooling, allowing high current density in the stator and high specific power.

Ohio State’s three motors; 300 kW, one megawatt and 2.7-megawatt prototypes are supposed to validate cooling, manufacturing, and performance.  OSU also has a 10-megawatt ring motor integrated with a turbofan, spinning at 5,000 rpm.  This complicates structural design and leads to windage losses (caused by air resistance) at speeds between the rotor and stator approaching Mach 1.

NASA Glenn Research Center’s self-cooled, superconducting wound-field electric motor has the cryocooler integrated into the rotor. Credit: NASA

NASA Glenn’s 1.4 megawatt wound field synchronous motor combines a self-cooled superconducting rotor with a slotless stator to boost power density and efficiency without the weight of external cooling.  A cryocooler integrated into the rotor keeps the high-temperature superconductors on the rotor winding from overheating.  This motor might be able to directly drive a fan.

Noise considerations

NASA’s report on expected noise levels seems internally contradictory, with graphs showing stadium rock noise levels in some instances while the text claims lower than conventional jet noise levels for the Ohio State and U of Illinois motors.  One bullet point indicates, – Uncertainty is high.”

Further Research

Ralph Jansen of the University of Illinois project and a NASA Glenn Tech Integration Manager, discussed whether power should be distributed from direct current (DC) or alternating current (AC) sources.  “If the source is a battery, then it is clear DC makes sense. If the source is a turbofan, it works with AC or DC. There is work to be done to figure out which is best…[and] it gets down to the types of machines used.”

Voltages could run as high as 10,000 Volts.  The highest voltage used in aircraft currently (unavoidable pun) is 540 (±270 Volts), “but distributing megawatt-scale power in a single-aisle aircraft will require higher voltage.”  The higher the voltage, the lower the weight of cables required to connect things.  NASA calculates, “At 2,000 volts DC, cable weight to deliver 1 megawatt over 150 ft. would be reduced to 200 kg from 900 kg for a 540-volt system.”

Power Converters

Related, DC-to-AC converters with such high input voltages will take DC power from batteries and the distribution bus, for instance, and convert it “to controlled, variable-frequency AC that both drives the motor and regulates its speed and torque.”

Jansen explains material breakthroughs with silicon carbide (SiC) and gallium nitride (GaN) switchgear allows use of commercially available, high-efficiency gear that allows higher frequencies and lower losses.  GE and the University of Illinois are both crafting high-power, liquid-cooled inverters, while Boeing is developing a cryogenically-cooled unit.

The NEAT facility is designed to enable end-to-end ground testing of flight-weight electric powertrains for Boeing 737-size aircraft. Credit: NASA

Aviation Week reports that “The NRAs will be completed in fiscal 2019 and the internal NASA work by 2020”  NASA’s Electric Aircraft Testbed (NEAT) at Plum Brook Station in Ohio, will accept the full-scale, flight-weight products that will power Boeing 737-size aircraft.  This ambitious time frame and scope of the projects bodes well for timely adoption of greener, cleaner aviation in the near future.

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Lithium-ion and lithium-polymer batteries face several problems: they are not making great leaps forward that we hope for, they occasionally burst into flame, and they weigh too much to be all that practical in a pure-electric airplane.  Researchers peer over the alternatives, magnesium, manganese, aluminum, and now, after several false starts in recent years, zinc.

University of Sydney scientists claim to have found a three-stage method of charging zinc-air cells that promises greater energy density and longevity.  One selling point – the relative abundance and low cost of zinc, such cells are cheaper to produce than lithium equivalents.  They theoretically can store up to five times more energy than lithium-ion cells, are less prone to burst into flame, and are even more environmentally friendly.

What’s not to like?  Until now, they’ve been difficult to recharge.  ReVolt tried developing a rechargeable zinc-air battery with an ARPA-E (Advanced Research Projects Agency – Energy) grant, but gave up after two years. Explaining that the zinc-air batteries used in hearing aids were not rechargeable, ReVolt attempted to prevent the growth of dendrites, little follicles that eventually punch through the internal separators and cause short circuits.

Workings of a rechargeable zinc battery.  Sydney researchers managed simultaneous control of the composition, size and crystallinity of metal oxides of earth-abundant elements such as iron, cobalt and nickel

Stanford scientists had investigated a high-energy zinc-air battery in 2013.  Hongjie Dai, a professor of chemistry at Stanford and the lead author of a study published at the time, said, “Metal-air batteries offer a possible low-cost solution.”  He added, “”With [an] ample supply of oxygen from the atmosphere, metal-air batteries have drastically higher theoretical energy density than either traditional aqueous batteries or lithium-ion batteries.  Among them, zinc-air is technically and economically the most viable option.”

A lack of electrocatalysts that successfully reduce and generate oxygen during the discharging and charging of a battery have kept these potentially high-potential cells from success.  But the paper published in the August 14 on-line edition of Advanced Materials, explains how the Sydney team and their partners at Nanyang Technological University developed a new three-stage method to overcome this problem and create an oxygen electrocatalyst at the heart of the research.

According to Professor Yuan Chen, lead author for the paper, the new method can be used to create bifunctional oxygen electrocatalysts for building rechargeable zinc-air batteries from scratch.  He noted, “Up until now, rechargeable zinc-air batteries have been made with expensive precious metal catalysts, such as platinum and iridium oxide. In contrast, our method produces a family of new high-performance and low-cost catalysts.”

The paper explains the three-steps.  “These new catalysts are produced through the simultaneous control of the: 1) composition, 2) size and 3) crystallinity of metal oxides of earth-abundant elements such as iron, cobalt and nickel. They can then be applied to build rechargeable zinc-air batteries.

“Paper co-author Dr Li Wei, also from the University’s Faculty of Engineering and Information Technologies, said trials of zinc-air batteries developed with the new catalysts had demonstrated excellent rechargeability – including less than a 10 percent battery efficacy drop over 60 discharging/charging cycles of 120 hours. It also demonstrates an excellent energy density of 904 Watt-hours per kilogram.

Professor Chen added, “’We are solving fundamental technological challenges to realize more sustainable metal-air batteries for our society,’”

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