Oxis Batteries to Fly in Two Airplanes

While we wait yet another five years for commercial development of each newly announced but promising battery chemistry, one company has its cells ready to fly in Bye Aerospace’s eFlyer 2 and in Texas Aircraft’s Colt S-LSA.  Oxis Energy has managed to leapfrog lithium-ion makers with its lithium-sulfur battery packs packing 400 Watt-hours per kilogram.  Considering the best announced pack-level li-ion performance has been 260 W-hr/kg, the leap is significant.

Batteries, for now, are at the heart of electric aircraft.  Until Doc Brown’s Flux Capacitor or a hydrogen fuel cell with Dollar Tree refills comes along, batteries are battling it out for our airborne dollars.  Lithium-ion remains in the forefront, with Tesla staging its shareholders’ meeting and its long-anticipated “Battery Day” on September 22.  Elon Musk has been dangling the promise of a million-mile battery for the last year, which may tie in with Chinese manufacturer Contemporary Amperex Technology (CATL).   According to Bloomberg, CATL’s, “Chairman and founder Zeng Yuqun said the company is ready with a battery pack that’ll last 1.2 million miles before needing to be replaced.”  Ostensibly, Tesla is a customer.

Discounting the lack of performance data and despite a ten-percent price differential over existing Li-ion cells, CATL’s batteries may be good investments for the long haul.  Most electric vehicles currently come with an eight-year, 120,000-mile warranty, so ten percent more for 10 times the mileage and a potential eighty years’ usage is a bargain.  (Your batteries will outlast you and your parrot.)

Overcoming the Longevity Gap

Longevity has been a big issue with lithium-sulfur so far.  Mark Crittenden, head of battery development and integration at Oxis Energy, explains that lithium-sulfur cells tend to degrade in a different way than lithium-ion cells, described concisely in his IEEE Spectrum article.

Oxis in cell, pack and casing formats, adding weight to provide protective shielding to cells

The Oxis Energy Technology page indicates a cell life of 250 charge/discharge cycles (the company hopes to double this to 500 cycles “within the next two years.”  Even given the low number, the average light aircraft in this country flies only about 80 hours per year (a terrible utilization rate) and the average light aircraft pilot flies only 40-80 hours.  Even business craft average only about 30 hours per quarter.  This would give about three years’ use at 250 cycles or six years at 500.  If as claimed Oxis batteries are substantially less expensive than Li-ion equivalents, this may be to their advantage.

Other Benefits

Oxis demonstrates their batteries’ ability to take bullets and nail punctures while remaining fully active and not bursting into flames – something with which Li-ion cells don’t fare so well.

Their environmental friendliness comes from their being made of sulfur rather than cobalt and nickel.  Lithium-sulfur cells are claimed by Oxis to be more easily recycled, a major problem for Li-ion cells, which are blamed for major recycling center fires.  Cobalt also bears the burden of being a conflict mineral, extracted in places like The Congo using child and slave labor.

Sulfur is far more abundant and not subject to battles for ownership.  Tenth most common element in the universe and fifth most common on earth, sulfur is found everywhere and has played a part through the history of materials development.

Cells can be fully charged and discharged, unlike lithium-ion cells that cannot be fully charged or discharged without potential damage or shortened service life.

Oxis Powered Aircraft Arriving Soon

Oxis cells are being incorporated in the design of two new craft coming to market soon.  Bye Aerospace, which previously had lithium-ion packs capable of 260 Whr/kg will now have Oxis packs that promise 400 Whr/kg to begin, 470 recently demonstrated and 500 “within a year.”  Oxis hopes for 600 Whr/kg by 2025.

Bye and Texas Aircraft will power their craft with electric motors.  “The all-composite eFlyer 2 is powered by a 120hp (90kW) Rolls-Royce RRP70D electric motor coupled to a 750V battery system. It delivers speeds of over 135 knots (250km/h or 155 mph) and has an endurance of over 3 [hours],” according to Flight Global.  The craft was designed from the start to be electrically powered.

Texas Aircraft’s Colt was introduced at  AirVenture 2019 as a Light Sport Aircraft with the ubiquitous Rotax four-cylinder engine.  It was also shown with a Siemens SP-55D producing 72 kilowatts (96.5 horsepower) AT 3,000 rpm.  Siemens electric aircraft division was purchased by Roll-Royce, so the Bye eFlyer2 and the Colt will share the same motor heritage and similar powerplants.

One can make a reasonable guess as to whether the Rotax or electric version of the Colt is an approximation of the other.  The Rotax engine weighs around 135 pounds and the R-R motor about 62 pounds.  The gas version carries 31.7 gallons of fuel – about 192.5 pounds.  The electric version’s 90 kilowatt-hour battery pack will weigh about 225 kilograms, or 495 pounds.

495 pounds of batteries minus the 192.5 fuel weight gives 302.5 pound difference.  Discount the electric motor weight vs. the gas engine and that gives up 73 pounds, ending up with a roughly 230 pound penalty for the electric Colt.  We have seen, though, that electric motor torque might be an equalizing performance factor, although this editor needs more study on the matter.

Texas Aircraft and Pipistrel will have electric and gas versions of three different models (the Alpha and Velis for Pipistrel).  These craft should provide excellent points of comparison.

Related Uses

Oxis sees its batteries as plausible in ground, air, and unmanned aerial vehicle applications, and others having experimented with lithium-sulfur have demonstrated reliable use.

A Parting Gift

Oxis has a 2018 brochure on line, extolling the virtues of their product.  One promise is eye-opening, comma splice and all.  “OXIS will be instrumental in moving the aviation sector away from lead-based fuel, the objective is to extend flight time eight fold by 2025, without increasing the weight of the aircraft.”


Electrifly-In: A Big Show in a Small Space

For those of us who find trudging over miles of airfield, such as Oshkosh’s AirVenture, or even local fly-ins spread along a runway tiring, Grenchen, Switzerland’s Electrifly-In may be welcome relief.  The event, previously called the Smartflyer Challenge, is planned for September 12 and 13 and should draw electric aircraft from all over Europe.

Grenchen, a town of just over 2,000, has an airport with a single runway of only 865 meters (2,838 feet), enough to enable a Cessna Citation CJ3 to land (and presumably depart).  The runway will host this year’s newly re-named Electrifly-In, devoted to promoting electric aviation.  All the activities will be held in a small, easily-accessible area.

Compact area makes touring all the attractions at Electrifly-In easily done

All Electric Aircraft – All Day

A baker’s dozen aircraft have been promised for the event, ranging from ultralight motorgliders to more advanced sailplanes with front electric sustainer motors, to four-seat hybrid tourers, two-seat trainers and even an e-race airplane.

AlpinAirPlanes GmbH, will bring their Pipistrel Velis E.

Martin Stepanek will bring his two-seat, MGM Compro-powered U-15E Phoenix from the Czech Republic.

Two Swiss owners will have their Lange Antares E self-launching sailplane on display.

Cornelia Ruppert, director of communications and flight instruction for Ruppert Composite GmbH, will have an Archaeopteryx Electro on the flight line.

Eck-Geiger motor in nose of Ikarus C42, with batteries charged by small 4-stroke engine behind cabin

Flugsport Toni Roth from Germany will bring Toni’s Ikarus C-42 CS Electro, a hybrid craft in the light sport aircraft size and weight range.

DG-1001e-neo, with FES propulsion from LZ Design in nose

DG Flugzeugbau  will bring its DG-1001-neo from Bruchsal, Germany.  This two seat machine uses the Front Electric Sustainer System – FES from Slovenia to enable level flight or climbs after a more normal sailplane launch.

Solar Flight Europe, Eric and Irena Raymond’s pioneering enterprise, will have Sunseeker Duo, the world’s only two-seat, solar-powered aircraft available for view.  Eric will also discuss the aircraft during the event’s symposium

Alisport Swiss will display its Silent 2 Electro, another craft with the FES power system on board.

Smartflyer display will be joined by real aircraft

The SFX1, from Team Smartflyer Ltd on the Grenchen airfield, will show its hybrid power system.

Urs Villiger sports UGM motor, hybrid drive

A similar craft, the Urs Viliger being developed by Evolaris, has a tail-mounted electric motor driving a propeller and a nose mounted hybrid generating system.

Pipistrel will bring its Panthera, the hybrid version currently in development, from Slovenia.

Zurich’s ETH will have e-Sling project on display

ETH, the Swiss Federal Institute of Technology in Zurich, will show progress on its e-Sling, an electric conversion of a South African four-seat tourer.

Taking design cues from Mike Arnold’s AR-5, UR1 is designed to hit 320 mph

Pie Aeronefs of Lausanne, Switzerland will show its UR-1 electric raceplane, set to compete in Air Race E in 2021.  This is slated to hit a top speed of 520 kilometers per hour (323 mph)!

A Symposium with Expert Speakers

On Saturday the 12th or Sunday the 13th from 10:30 a. m. to 12:30 p. m., The Grenchen Motorfluggruppe training room will host a symposium featuring:

  • Solar flight in the Sunseeker Duo
  • A “Made in Switzerland” Air Race E 2021 participant, the Pie Aeronefs – UR-1 aircraft
  • A recounting of a world record flight from the Alps to the North Sea (German) in a Pipistrel Velis– reported on here last week
  • ETH Zurich will present its academic focus project, the eSling, an adaptation of a popular South African airplane.

Organizers promise even more talks, with ample time over the two days to meet presenters and others.

From 2:30 p. m. to 5:00 p. m. on Saturday, a panel discussion, “THE eTALK,” will bring together, “Specialists and experts from the fields of technology, training, politics, regulations, pilots, etc. [who] will address current and controversial questions.  Hansjörg Bürgi, publisher of the magazine SKYNEWS, will moderate.

Best of all, if you’re flying your own electric aircraft, Grenchen Airport will waive landing fees for your entrance to the event.

Participants can also compete in the second edition of the eTrophy competition, which will reward the longest non-stop flight with electric power.    Read the rules and regulations here.  Registration Rules   First, second, and third prizes range from 1,000 to 3,000 Swiss Francs.  During the award ceremony on Saturday evening the winner of the challenge will get the eTrophy for the longest electric non-stop flight.

All in all, this would be a grand two days out, with a good compendium of the world’s electric sport aircraft on display.


Two New Electric Sailplanes

Two electric sailplanes come from different ends of the soaring spectrum and each shows its own unique character.  Their differences are as noteworthy as their geographic separation.


Birdy is a single-seat, electrically powered motor glider that fits the European Union 120 kilogram class.  The 264-pound empty weight puts it 10 pounds above America’s FAA Part 103 254-pound limit.  But Euro craft in that category are not as limited in top or cruise speed.

Birdy in alpine setting showing its folded propeller for minimum drag

Birdy’s light weight required clever arrangement of components to enable a maximum takeoff weight of 280 kilograms (616 pounds) and pilots up to 1.95 meters (6’ 5”) tall.  Its 13.5-meter (44.29-foot) wingspan carries only 13.9 pounds per foot, enabling 40:1 glide ratio at around 90 kilometers per hour (55.8 mph).  Its 8.3 square meter (89.3 square foot) wing area lifts only 6.89 pounds per square foot, enabling a 63 km/hr (39 mph) stall speed with flaps.  Birdy can top out at 180 km/hr (111.6 mph), well above FAA ultralight constraints.  Since it’s a sailplane, that may not count here.

It can operate in a highly independent way, able to take off on its own power and capable of being recharged by its “optional trailer with photovoltaic modules, [and] does not require any other infrastructure or auxiliary personnel other than a take-off and landing field.”

The maker explains, “The CFRP / GFRP structural components are manufactured by the German aviation company Klenhart-DESIGN and partner companies in NC-milled GFRP molds from the most suitable composite materials in order to achieve high overload capacity, practical surface robustness and still low empty weight. Hans-Peter Schneider (Technical Director of the DVLL, experienced aircraft manufacturer and approval expert) is responsible for the independent quality assurance of production.”

Lightweight, High-Torque Electric Power

An Eck-Geiger electric drive in the area of ​​the center of gravity with 12 kW or 16 kW continuous-power motor drives the removable, folding 1.3-meter (4.27-foot) propeller through a long shaft. This type of drive starts immediately when required, does not require motor extension or retraction “and avoids the otherwise unavoidable, strong increase in aerodynamic drag in motorized cruise flight.”

Three potential motors from company’s selections have rather amazing specifications.

Where the power comes out. Birdy has a centrally-mounted motor and batteries, with a folding propeller on the tail

The HPD12 produces 12kW continuously and /15kW peak from a weight of only 3.75 kilograms (8.25 pounds).  Turning over at a leisurely 2,180 rpm, these little disks can spin a fairly large propeller slowly and still produce substantial thrust.

The slightly larger, 4.7-kg (10.34-pound) HPD16 puts out 16 kW continuously and 20 kW at peak at 2,280 rpm.  For the same weight, the HPD20SD generates 20kW continuously and 25 kW peak at 2,600 rpm.   All of them use an MC300 Motor Management System which can pass 300 Amperes of current continuously, 400 Amps for approximately three minutes, and 600 Amps for around 30 seconds.

Enough Energy to Have Some Real Fun

Birdy can carry single or dual Geiger battery packs of three kilowatt-hours or six kWh enabling ranges of more than 200 kilometers in pure powered flight.  Each battery pack holds 3.6 kW-hr of energy and has its own battery management system (BMS) to enable monitoring and optimal charging.  A possible range extender could increase endurance “almost at will in the future.”

Sailplanes are tougher than they look. Spar test shows Birdy’s high strength

Since Birdy can maintain level flight at about 80 to 90 kilometers per hour (49.6 to 55.8 mph) on a mere 3 kW (4 hp), even a single battery pack will allow some thermal hopping and safe returns to the pilot’s home field.  A rate of climb of three meters per second (590 feet per minute) should require full power for only a few minutes, leaving a reasonable “cruising” range.

A brochure in German highlights the little sailplane’s features.

120-Kg Aircraft

In Europe, Airplanes up to an empty weight of 120 kg allow for de-regulated and easy flying.  Pilots need a sports pilot license, but no medical certificate.  With access to a runway or field, a Birdy pilot can have the sky to him or herself, and search for adventures in “green air,” sailplane pilots’ lingo for rising air.

Jonkers JS-3 RES

Jonker JS-3 with motor extended

Far larger, faster, and heavier, the JS-3 RES (Retractable Electric power System) from South Africa’s Jonker Aircraft puts its pilot in full competition mode.  The company notes they are a relative newcomer to the ambitious high-performance sailplane world, with three major competitors sharing the world market for decades.  When the Glaser-Dirks DG-400 took to the skies, extreme motor-gliding became a reality, and others have taken on the challenge.  Jonker started a decade ago with their JS-1 Revelation (now with over 100 sales), and has reached the JS-4 – due for flight testing soon.

We will focus on the JS-3 here, with its Slovenian Emrax 188 motor, a Roman Susnik design that produces 40 kW maximum and 25 kW continuously for climbing.  This allows self-launching, although a ground handler or two might be necessary because of the JS-3’s 15-meter to 18-meter wingspan.  Only 188 millimeters (7.4 inches) in diameter and 77 mm (3.03 inches) thick, the motor weighs a mere seven kilograms (15.4 pounds).  Axial-flux motors in the Birdy and the JS-3 show a dramatically light weight for the power and torque they produce.

SOLO Aircraft Engines, well known for their two-stroke gasoline engines, helped design the electric power system on the JS-3.  They aimed to contain the retracted propeller, motor and mast within the “smallest possible modern fuselage”.   To enable self-launching, battery capacity was set at 9.4 kWh running at 400 Volts, and a large, efficient propeller “was matched with the motor torque curves to minimize losses.”Two battery packs weigh 22 kilograms each, and have standalone battery management systems much like those on Birdy.  Internal current sensors and fuses help prevent thermal runaways and the ever-inconvenient smoke release.

JS-3 can hold up to two battery packs

Buyers can have a “pure” JS-3 with no additional power system, and use all their skills to ensure a safe trip to a planned destination.  Or they can choose from an MD-TJ 42 jet sustainer system , or the Solo electric sustainer/self-launch system.

The Emrax motor drives a two-bladed, 1.2-meter (3.94-foot) propeller the can produce up to 90 daN (90 decaNewtons =202.3 pounds of force).  The retractable part of the system weighs 21 kilograms (46.3 pounds) and can get the 500 kilogram (maximum takeoff weight) craft off the ground in 500 meters (1,640 feet) and establish a rate of climb of 2. 3 meters per second (453 feet per minute).  Note the heavier craft, even with more power, climbs more slowly than Birdy.  Still, it reaches 500 meters, 1,640 foot) altitude having used only 2.5 kWh from its battery pack.

RS-3 performance enables short takeoffs and long potential cross-country flights

The JS-3 can fly in standard class with 15-meter (49.2-foot) wings. Or with longer wingtips that give an 18-meter (59-foot) span.  In 15-meter configuration, the JS-3 has a 50:1 glide ratio, slipping forward 50 feet for every foot it loses in altitude.  It drops only 104 feet every minute.  If the plane is one mile high, it would take over 50 minutes to touch down.  With the 18-meter tips, the glide ratio goes up to 56:1 and the rate of sink sinks to 94 feet per minute, giving over 56 minutes of flight before reaching the ground.

Powered Sailplanes – a Great Proposition

With the potential to take one flying in the cleanest possible way, and promising high performance on small power, Bird and the JS-3 show what can be done within the limits of today’s batteries.  Imagine what their future can be as energy storage matures.


Regenerative Gas Turbines for Hybrid Aircraft

Beth Stanton shared an email she received from Alex Kovnat, EAA #452346, telling of Turbotech S. A. S., “A startup company” making very efficient gas turbines.  Turbotech “has patented a regenerative, high-temperature heat exchanger that increases the efficiency of low power turbines by a factor of 2–3. They achieved this by recycling what would normally be waste heat in the exhaust gases to preheat the air entering the combustor, resulting in less fuel required to generate the same amount of power. Turbotech views the turbogenerator as the ‘missing link”’ that will enable the future of hybrid-electric aeronautical propulsion.”

This regenerative ability reduces the amount of fossil fuel required to make things work – a valuable criterion while we await better batteries and cheaper fuel cells.  The French company makes both a small turboprop engine, looking very much like “A downsized version of the AGT-1500 regenerative gas turbine that has served since the 1980’s as the power plant for the Army’s M1 Abrams main battle tank.  Their turbine generator, shown below, would be used as a range extender for small aircraft.

Turbotech TG-R55 turbogenerator can run on jet fuel, biofuel, or even hydrogen

According to Aerospace and Defense Technology, “The TG-R55 turbogenerator is the first onboard electric genset dedicated to the hybrid-electric aircraft industry.”  Consuming a mere 15-22 liters (4 to 6 U. S. gallons) per hour at cruising speed, the TG-R55 manages to provide range extension at a low cost.  Depending on what that unit costs, it may be a viable way for electric aircraft designers and builders to make their craft capable of extended flights.

Turbotech twin generators installed in light aircraft to charge battery pack, extend range

The cutaway shows and internal installation for the turbogenerators, although one or more could be installed on external parts of the aircraft.  Mike Friend, former Technical Director for Boeing, designed a similar external generator range extender using a small internal combustion engine for power.  Several manufacturers are working on hybrid systems to overcome the range limitations of current batteries.

At a weight of 55 kilograms (121.25 pounds) and producing 55 kilowatts (74.8 horsepower), the generator is considerably lighter than an equivalent battery pack.  Turbotech claims that a 92 kilogram (202.8 pound) “TG-R55 system carries the same energy as 1000 kg (2,200 pounds) of Lithium-Ion batteries.”

Schematic of turboprop engine shows fuel-saving heat exchanger/regeneration process.  Generator works in similar way

According to Turbotech, “Used in conjunction with batteries, it can offer up to 10 times more range than a full-electric plane.”

Light aircraft with Turbotech generators under wings

The company sees this unit used as part of a hybrid system for aircraft and electric Vertical Take Off and Landing (eVTOL) vehicles.  The low fuel usage and energy storage compared to batteries makes an inviting comparison with battery-powered systems.  Even better, the system can be fueled with liquid hydrogen, eliminating any carbon emissions.  That will increase system weight for pressurized H2 tanks.  Designers will have to perform weight and performance comparisons to make sure they achieve best outcomes for their craft.

The company and its systems are an innovative approach to providing greater range for electric aircraft.  We will be anxious to see who makes the first practical application of their products.


We’re still early in attempts to set world records with electric airplanes.  Jean-Luc Soullier, a friend of the blog, held many of them a decade ago, flying a little Colomban MC-30, an ultralight designed by one of Concorde’s engineers.  At the other end of the size scale, Solar Impulse set many records on its globe-girdling treks.  Now, a five-member mostly German team hopes to set seven world records “in one fell swoop” as they electrically traverse 700 kilometers (435 miles) between the Schanis, Switzerland airport and Norderney Airport on Germany’s North Sea.

Friends of Electric Mobility

The five have interesting professional lives beyond their love of flight.  “Futurologist Morell Westermann, Swiss pilot Marco Buholzer, the Norderneyer brewer Tobi Pape, the video and music producer Tom Albrecht and the podcaster Malik Aziz, who founded the association ‘Friends of Electric Mobility’ want to start on August 31,” according to Electric-Flight.eu.  They will fly Pipistrel’s recently certified Velis Electro.  The team adds, “Above all, we want to prove its suitability for everyday use. That is why we do not fly prototypes specially designed for such record missions that only work under laboratory conditions.

700 kilometers (435 miles) by air -considerably farther by car: 1,246 kilometers (772.5 miles)

They hope to achieve their records during the planned three-day flight, including:

  • Lowest energy consumption (kWh / 100 km) over 700km
  • Highest average speed over 700 km (km / h)
  • Highest flight altitude ever reached with an electric aircraft (meter above main sea level)
  • Fastest climbing performance from 0-1000m / 1000-2000m / 2000-3000m (m / s)
  • Fastest average speed over 100km (km / h)
  • Lowest number of stops at 700km distance (number of stops)
  • Longest electrically flown route in 24/48/56 hours (km)

The team’s Velis, based at the Schanis, Switzerland airport (LSZX), will make a three-day flight of the 700 kilometers.   That’s an average of only 144.6 miles per day, which may not seem all that adventurous.  Flying a light airplane over the Alps certainly counts, and finding chargers along the way adds to the venture.

Comparing This to a Nissan Leaf’s Trip

Only 8 years ago, your editor wrote about Tony Williams, a then unemployed airline pilot who drove his daughter from Baja, California to Victoria, B. C. in his Nissan Leaf for a relative’s wedding. Early editions of that car managed around 100 to 125 miles on a charge, so Tony counted on the still-under-development network of charging stations along the I-5 to ensure that stops would be productive.  Today, motels, restaurants, gas stations, and Kohl and Walgreen’s parking lots have chargers.

Tony Williams’ Baja to B.C. Nissan Leaf was highly recognizable on its journey up the I-5

The sparseness of charging stations meant Tony had to plan carefully.  Similarly, our Swiss pilots will need to be prepared for a paucity of airports with the necessary support gear.

Overcoming the obstacles of terrain, aircraft range limitations (not too different from the 2012 Leaf) and relative lack of airport accommodations for electric craft today, the crew hopes to prove five big points.

  • “Electric flying is 4x more efficient than fossil drives
  • “E-planes are as efficient as e-cars
  • “CO₂-neutral flying is already possible today
  • “Electric flying is considerably quieter
  • “No contrails, exhaust fumes and kerosene stank” (We all need to add this to our descriptions of fossil-fuel fumers, ground-bound or aerial.)

 “Climate friendly, quiet and a little bit crazy” (their words)

The partners compare their adventure to that of Charles Lindbergh, who managed a solo flight across the Atlantic in 1927, winning the $25,000 (about $370,000 today) Orteig Prize, the largest such award up to that time.  The partners, however, have calculated they will have to pungle up between 50,000 and 80,000 euros to pull off their expedition.  Part of that will finance their application for the Guinness World Records acknowledgements.  Here your editor thought the Guinness folks showed up with plaques and medals when someone did something noteworthy.  It turns out they have to be lured to the scene and rewarded themselves.  Needless to say, they are looking for willing funders.

“Flying is not necessarily harmful to the climate”

The Friends of Electric Mobility will attempt to set seven world records in one flight

Pilot Marco Buholzer explains the grander goal.  “Flying with kerosene is extremely harmful to the climate. Aviation currently accounts for around five percent of the global warming, and the trend is increasing. The emissions at high altitude are a particular problem that arise from air traffic. We want to show that there are alternatives, even if we don’t manage the whole route in one go, CO₂-neutral flying is already possible today!”

Brewer Tobi Pape adds, “Most small planes fly distances shorter than 200 kilometres anyway, you could do that electrically.

Marco emphasizes, “On August 30th we will prove with our extraordinary flight that the time of electric planes has come.”  The landing is scheduled for September 1st.

Flight Following

The blog will follow this adventure and those playing at home can track the flight beginning August 30 here or here.  Stay tuned.


SolarStratos Returns to Service

SolarStratos, a mission envisioned by Raphaël  Domjan and an airplane designed by Calin Gologan,  returns to the skies after suffering a literal break in its program in 2018.

During a series of tests that put increasingly heavy loads on the wings, its left wing broke with what was called a “technical damage.”  This type of breakage during stress testing is not uncommon, especially on what are special machines such as SolarStratos and Solar Impulse.  Solar Impulse 2 suffered a similar break when its newly-designed wing was being tested.  As noted, this type of setback takes the team back to the drawing board, but also besets them with new reflections on their ongoing decisions.  If it were easy, everyone would be doing it.

“This pioneering spirit involves a real technological challenge, and takes us to unknown territories. Risks are an integral part of such a project, even if our objective is to anticipate them as well as possible; this is why we carry out many tests.”


Building a 24.9-meter (81.69-feet) wing for a powered aircraft that will gross only 450 kilograms (992 pounds) is a great challenge, but one that designer Calin Gologan has faced with his range of solar-powered vehicles.

As noted here five years ago, The airplane will carry two “big” pilots in tandem and 30 kilowatt-hours of batteries.  With the entire craft weighing only 200 kilograms (440 pounds) empty and 450 kilograms (990 pounds) loaded, the HPD-25D dual motor (32 kilowatts/43 horsepower) will be able to loft the efficient airframe to its goal altitude in about an hour, according to Calin.   The motor contributes a mere nine kilograms (19.8 pounds) to the airplane and Calin notes that the dual motor controllers are each the size of a deck of cards, enhancing the craft’s light weight.

The aircraft foregoes pressurization, helping make it a great deal lighter than the Perlan 2 sailplane, which weighs in at around 1,800 pounds.  SolarStratos will have to hoist two pilots with pressure suits, though, about 44 percent of the airplane’s gross weight.

 A Visit to Patagonia

Following the August, 2018 break in their wing, and waiting for the new design, Raphaël Domjan, Frank Bormann and Raphael Javet visited the Perlan Mission 2 team quartered at Al Calafate International Airport in Patagonia.  The two groups, both headed toward stratospheric goals, were able to discuss the challenges involved, “and Raphaël was able to gain the detailed insights of a highly motivated and dynamic team.”

Perlan acted as an inspiration for SolarStratos, with the power team reporting, “While the SolarStratos team was in Argentina, Perlan II broke a new record under tow, climbing to more than 40,000ft (12,192 m), beating the 30,000 ft (9,144 m) former record. An historic moment!

“Since the 27 August, the glider has broken the record again, posting an all-time altitude record for a glider of 76,000 ft (over 23,000 m) – a monumental achievement for this extraordinary aeronautical project.”

Miguel Iturmendi

Miguel A. Iturmendi, “Holds degrees in Aeronautical Science, Space Studies and Flight Test Engineering, and graduated as a Test Pilot from the National Test Pilot School.”  He was part of the Perlan team in Argentina, and flew with Jim Payne to 65,000 feet in 2018 in the Perlan 2.  Having flown over 160 different aircraft types, perhaps the most unique are the Perlan and the SolarStratos he is now test flying.

Miguel will have achieved record heights in both sailplane and power plane mode, with pressurization coming from a sealed cabin in Perlan and from a Russian-designed pressure suit in the SolarStratos. Both types of flights will share temperatures below -40° F or C (both identical at that temperature).

Resuming Flight

Miguel helmed the first flight of the re-designed and rebuilt SolarStratos on July 23.  The organization reports on the early morning flight.  “The aircraft soared effortlessly on its elegant new wings equipped with winglets at 800 meters (2,625 feet) above the Payerne aerodrome for twenty minutes before touching down again.”

Its new wings and wingtips catching the light, SolarStratos awaits the full light of the sun

Raphael Domjan expressed happiness with the results.  ““The plane is more stable and reliable than during our first round of test flights. Today we are beginning a new chapter that will allow us to reach extraordinary goals, to make the public dream and to convey a positive message on the potential of solar energy to fight climate change.”  Miguel and As flight testing continues, we will continue to report on the team’s progress.

Your editor as delighted to see a true pioneer in solar-powered craft counted as a member of the SolarStratos team.


Fred To was the first solar airplane designer, successfully designing and flying Solar One in late 1978.  SolarStratos, considerably advanced technologically, has the benefit of much better solar cells, batteries and motors than were available to Fred.

Fred reflects, “These are exciting times; from the humble beginnings in the 1970’s solar powered flight has come a long way. The pioneering spirit and dedication of Raphaël Domjan and team is now raising solar powered flight to a new and important level. I wish Solarstratos every success in this challenge.”  From the inspired inception of the concept Fred To gave us in 1978 to the sophisticated platform Raphael Domjan is using to explore extreme altitudes, it all seems of a wondrous thread tying past, present, and future together.


Electric Aviation Group Goes Big

Emulating bird flight has been a big part of man’s desire to fly through the years.  The latest in ornithological look-alikes comes from the Electric Aviation Group in the United Kingdom.  Their creation seem to be an outgrowth of last year’s somewhat controversial Bird of Prey concept displayed by Airbus at several prominent airshows.

Designed to have a “certain ‘Wow’ factor,” the model took its cues from hawks and eagles, including a high-arched wing blended into the upper fuselage.  It featured wingtips much like a bird’s, with primary feathers ostensible capable of morphing to control banking and even adverse yaw in a turn. Even its patriotic tail feathers were indeed feather-like and added to the avian quality of the aircraft.

Sailplane designers in the 1930’s tried similar imitation, with craft like the German Fafnir reaching an arch-winged perfection.

High-aspect ratio wing with distinctive bird-like shape helped German Fafnir glider achieve several world distance and endurance records.

Its flight, at least in this video, would be a model of grace and smooth, flowing motion – a bit dreamlike.

Hybrid Electric Regional Aircraft (HERA)

The British have always been good at giving their aircraft mythological appellations.  According to Greekmythology.com, “Hera is the wife of Zeus, the Queen of Olympus, and the Olympian goddess of marriage. As such, she is also the deity most associated with family and the welfare of women and children. Her marriage, however, was an unhappy one, since Zeus had numerous affairs. Jealous and vengeful, Hera made sure to give each of his consorts some hard time.”

Others have used the acronym, with one example four years ago from Imperial College in London.

Substantially different in configuration and with a distributed electric approach to propulsion, this aircraft has the same basic mission and requirements for quiet, economical, clean operation as the EAG proposal.


Perhaps short for EAGle, the resurrected design seems to be a more plausible version of the Bird of Prey, and has solid corporate and aerodynamic backing.

Mission parameters include reducing carbon dioxide emissions 75 percent per passenger kilometer over regular jet aircraft, dropping nitrogen oxide emissions 90 percent, and lowering noise by 65 percent.  EAG embraces these goals enthusiastically, seeing a slowdown in cleaning up existing craft.  “While the sector has made substantial progress over the last 50 years in addressing some of these factors, the pace of improvement is slowing as opportunities to do so on existing aircraft diminish and we remain a long way from reversing the impact on the environment. Hence it is time for the industry to embrace a paradigm shift. If we are to realize improving emissions that are moving towards the 2050 targets, then this paradigm shift needs to be embraced now and wholeheartedly.”

EAG’s HERA will have a tail perhaps inspired by aerodynamicist Bruce Carmichael rather than that of the earlier birdlike Airbus design

According to notes released for the beginning of the (virtual) Farnborough International Air Show, EAG’s HERA will be endowed with the following virtues:

  • Whisper-quiet operation reduces noise pollution
  • Innovative airborne battery regeneration to minimize turn-around time
  • Efficient battery integration
  • Thermal management of motors and power electronics
  • Gear Assisted Take-Off Run (GATOR) gives rapid acceleration for a quick lift-off reducing energy requirements
  • Short take-off-and-landing (STOL) performance enables new route opportunities affording greater profitability to operators
  • Cabin-flex design enables passenger operation during the day and cargo operation at night
  • Suitability for operating from regional airports brings convenience to travelers and gives increased proximity to warehouses, enabling private sector cargo to optimize last-mile terrestrial logistics and delivery systems and reduce carbon emissions
  • Future-proof design to accommodate alternative energy sources if available before 2030
  • Flexibility to transform into an all-electric or carbon-neutral as the battery density improves or alternative fuels and associated powertrain technologies mature and become affordable.

The design, has received additional support from EAG’s JetZero consortium, which includes some of the UK’s leading engineering and manufacturing organizations and senior academic advisors.

There will be competition, perhaps.  With larger and longer-range craft such as Jeff Engler and EasyJet’s Wright 1  making headway, HERA will find itself in a new and competitive environment.  Its medium size and medium-range capabilities should make it a desirable aircraft for that part of the market.


Honeywell’s New UAM Business Unit

Honeywell, long involved in avionics and other aviation-related instrumentation and equipment, has created an entire, new business unit devoted to unmanned aerial systems (UAS) and urban air mobility (UAM).  If any indication is necessary to show that urban air is not a passing fad, it’s the investments being made by major entities – from Toyota to Honeywell, from NASA to Mercedes.

Honeywell’s contributions to future UAM flight include avionics – devices that combine aviation with electronics.  Honeywell’s portfolio includes a miniaturized fly-by-wire system, electromechanical actuators to take the place of traditional control cables and pushrods, and systems to help integrate the UAM into existing and future air traffic control systems.

These systems will work for electric Vertical Take Off and Landing (eVTOL) machines or more conventional fixed-wing configurations, represented by Tine’ Tomazic from Pipistrel in the following video.

Multi-rotor craft can benefit from Honeywell’s lightweight auto-pilot and fly-by-wire systems.  Integration into the overall aircraft enables precise control and the ability to program systems and components for heightened efficiency, as shown with this Vertical Aerospace proof-of-concept vehicle.  You can find a white paper on the collaboration between the designers and Honeywell here.

Flight control passes to electro-mechanical actuators, another part of the Honeywell component lineup.  Having everything come from one source means more secure integration of those control systems and components.

Within the UAM and within the airspace in which that UAM flies, a maze of mission requirements and government regulations require the aircraft designers to integrate their craft into a complex flow of other vehicles.  That could be daunting in the not-too-distant future, with Uber, GrubHub, and Dominoes pizza deliveries competing for airspace.  Honeywell has thought about that future and launched a response.

Honeywell’s Consolidation of Resources

Mike Madsen, president and CEO of Honeywell Aerospace sees UAMs and UAS’s as a vital part of Honeywell’s future.   “Urban Air Mobility and Unmanned Aerial Systems will play an increasing role in the future of aerospace, with potential applications in all-electric urban air taxi vehicles, hybrid-electric unmanned cargo drones, optionally piloted airplanes, delivery drones and everything in between.”

Honeywell has chosen a skilled entrepreneur to lead the business unit, Stéphane Fymat, who your editor knows through his work with the Perlan Project.  Perlan holds the world altitude record for sustained, unpowered flight at over 76,000 feet.  This rarified atmosphere and almost unexplored height is significantly different from the low-altitude, potentially crowded urban airspace of the UAM world.  He did, as noted in his Perlan Project biography, found “Smartplane Inc. in 2011, a company developing a semi-autonomous personal aircraft.”  That experience will help him integrate well with his new business unit.

unmanned aerial systems (UAS) and urban air mobility (UAM)

The Perlan Project Biography

Stéphane Fymat : Board Member: Biography

“Stéphane has 25 years of experience in the aerospace and computer industries. He began his career as an engineer for Aerojet-Electrosystems, now a subsidiary of Northrop Grumman Corporation. At Wang Laboratories, he was part of the founding team of its document imaging software business unit which grew from $0 to $50M in 3 years, when it was carved out and sold to Kodak for $260M. He then joined cyber-security company Passlogix as Vice President. As part of the executive team, he lead the company from start up to mature market leader with #1 market share and 20M licenses sold to the largest companies worldwide. Passlogix was acquired by Oracle. He founded Smartplane Inc. in 2011, a company developing a semi-autonomous personal aircraft, and is its Chief Executive Officer. He has an MBA from Columbia University and a B.S. in Mechanical Engineering and Computer Science from UCLA. He is a private pilot, and sits on the ASTM F44 committee for FAA Part 23 Certification. He has two patents issued and one pending in avionics.”

Even more apropos to the needs of the AUM/UAS world, his work with the ASTM (American Society for Testing and Materials) F44 committee will be invaluable.

“This Committee addresses issues related to design and construction, systems and performance, quality acceptance tests, and safety monitoring for general aviation aircraft (also known as Part 23) that is less than 19,000 pounds and 12 passengers.”

It will be fascinating to see how Stéphane will expand his horizons and those of his employer in coming years.  Best wishes to all.


HyPoint and Hydrogen Flight

Their web site proclaims, “HyPoint, Inc. is developing the next generation hydrogen fuel cell system with zero CO2 emissions and game-changing energy performance for the air transportation and urban air mobility market.”  Pointing out a “fundamental barrier at a chemistry level” for lithium-ion batteries, the fuel cell maker launches some seemingly outrageous claims.

HyPoint states, “Our patented technology increases operational time and utilization rate while decreasing TCO (total cost of operation) of any flying platform.”  They claim “5X operational time, 10X utilization rate, 20X faster charge,” and a TCO 90 percent of equivalent battery-powered systems.

As we have reported here, demonstrated outputs for lithium-ion cells are around 350 Watt-hours per kilogram, and about 260 Whr/kg at the pack level.  HyPoint says it can already demonstrate a system-level specific power of 1,000 Watts per kilogram and an energy density of 530 kW-hr/kg.   The company points to its next generation of “turbo air-cooled” units to produce even more power and show better energy density.

These improvements would make the fuel cell a candidate for aircraft use, according to HyPoint.  Already collaborating with ZeroAvia and Urban Aeronautics, HyPoint hopes to supply airworthy systems by next year.

Urban Aeronautics, which is pioneering the next generation of eVTOL aircraft for commercial air taxi and air rescue roles, and HyPoint, a leader in next generation, high power (HTPEM) hydrogen fuel cell systems, will explore the development of an advanced version of Urban Aeronautics’ CityHawk eVTOL powered by HyPoint’s cutting-edge, hydrogen fuel cell stack technology. As currently designed, CityHawk relies on hybrid propulsion. 

  True Costs of Operation?

Mass-produced,HyPoint’s current fuel cells would cost about $800 to $1,000 per kilowatt.  The cost per kilowatt-hour would depend on the cost of hydrogen flowing through the cell.  HyPoint is apparently counting on their new “turbo air-cooled” units to lower that cost, although they are reluctant to disclose what the cell costs will be.

Tesla’s “Roadrunner” project aims to lower battery prices to $100 per kilowatt-hour.  For battery electric vehicles, that is a set rate (increasing slightly over time as the battery capacity is reduced in use).  Charging costs should decline over time, as solar cells and wind turbines become more efficient and less costly.

Several sources challenge the idea that hydrogen power can operate cars (or airplanes) more cheaply than electricity stored in batteries.  Inside EVs, for instance, reports that Volkswagen is trending toward batteries exclusively, stating somewhat provocatively, “In the case of the passenger car, everything speaks in favor of the battery and practically nothing speaks in favor of hydrogen.”

The efficiencies in comparison, as described by Volkswagen, which has a preference for batteries. Would another comparison from a different perspective yield a different preference?

Fred Lambert, writing in Electrek predicts, “Though hydrogen certainly has more potential with semi-trucks than passenger cars, it’s still not likely to triumph over batteries for powering the next generation of zero-emission transport.

“As we have often explained before, the entire end-to-end process from production to consumption is 3x times more energy efficient for battery-powered vehicles than hydrogen fuel cell vehicles.”  This was written three years ago, and things in both battery and fuel cell worlds have changed considerably.  It’s interesting that Lambert felt enthusiastic enough about his ideas at that time to use no less than four exclamation points in his caption to the diagram below.

What hope is there for hydrogen fuel cells in aircraft if the numbers tend to favor large stationary installations or their use in large vehicles such as buses or class 8 trucks?

Use in Aircraft

As we described 11 years ago, “Gerard Thevenot, a long-time championship-level hang-glider pilot, celebrated the centennial of Louis Bleriot’s flight across la Manche (the French name for the English Channel) by flying his hydrogen-powered La Mouette hang glider over roughly the same route Bleriot took between Calais and Dover on August 6, 2009.”  Later reports showed the flight used 755 grams (1.66 pounds) of H2, a great deal less than the amount of fuel a howling two-stroke engine might have consumed.

At current prices for hydrogen, at $1 to $1.40 per pound liquefied and transported to the user, the trip would have cost $1.66 to $2.33.  Try flying 22 miles any cheaper than that.

Today, several firms are exploring H2 aviation.  ZeroAvia, flying both Hollister, California and Cranfield, England, is using avgas and hybrid setups so far, but will switch its proof-of-concept Piper Malibus to hydrogen power in the near future.  They are partnered with HyPoint, so we look for flight tests by next year.

The Alaka’i Skai is intended to fly on H2 from the beginning.  The four-rotor UAM will have a range of hundreds of miles, rather than dozens like its battery-powered competition.

Reported in New Atlas, Rafi Yoeli, CEO of Urban Aeronautics says, “We look forward to collaborating with HyPoint on the integration of the next generation of hydrogen fuel cell systems for eVTOL transportation and the urban air mobility market. As a high-power, 100 percent environmentally friendly fuel, hydrogen is key to the future of eVTOL aircraft.”

Red Jensen shared this photo of a strange craft at Mojave Airport.  One Redditor speculated, “The tail number N971YT is registered to Toyota. It’s an electric aircraft which I find interesting considering their vehicle’s are known to favor hydrogen fuel cells as their alternative fuel choice instead of electric.”

Toyota promotes fuel-cell-powered trucks and its Mirai passenger car.  It gave Joby Aviation $394 million in January, so one wonders about the direction future flight might take with this partnership.

Where Will This All Go?

Obviously, proponents on both sides of the fuel cell/battery debate are well dug-in on their positions.  We need to do a less biased, more measured look at the trends and potential for each system.  In coming entries, we’ll try to give as objective a look as possible at these energy sources.


Wisk Tests Cora in US, New Zealand

Recently renamed Wisk (formerly KittyHawk) has resumed flight testing of its Cora eVTOL (electric Vertical Take Off and Landing) machines following a cautionary corona virus shutdown.  It’s already got a fleet, with several prototypes in the U. S. and at least four in New Zealand.

Four Cora’s on the ramp

New Zealand seems to have a lock on flight testing for unpiloted aircraft, with Pyka and Cora both finding amenable administrators willing to allow flight tests.  Boeing and Wisk are collaborating on achieving urban air mobility with the two-seat machine, and getting a lot of positive vibes from the locals.  Partly from the NZ government, partly from local businesses, and partly from indigenous Maori tribes’ people, Wisk and Cora have found wide-spread acceptance down under.

Government Support

Research, Science and Innovation Minister Megan Woods announced last October that, “The Government is establishing an Airspace Integration Trials Program to support the safe testing and development of advanced unmanned aircraft and accelerate their integration into the aviation system.”

The Ministry of Business, Innovation and Employment (MBIE), “Is committed to supporting the growth of an innovative unmanned aircraft sector in New Zealand. We’re creating opportunities to test and develop these emerging technologies to help make this happen.”

Working Zephyr Airworks, the New Zealand affiliate of Wisk, the MBIE has transferred $2.1 million to the Civil Aviation Authority to “build capability” and hire technical experts.  The Ministry gave an additional $900,000 to the Ministry of Transport to “support policy development related to regulatory settings.”

The government will also partially reimburse 4,000 aircraft owners for the costs of installing ADS-B (Automatic dependent surveillance–broadcast) transponders in their airplanes.  Such units will become essential as the number of autonomous craft grows.

Maori Support

Wisk reports (as of October, 2018), “Our time in New Zealand has also empowered many other important milestones. We have achieved seven hundred flight tests globally (now well over 1,000)–– a major step forward toward ensuring Cora is one of the most reliable and advanced aircraft ever to take to the sky.

“We have built lasting bonds with the community. The young leaders of Ngai Tahu Iwi (a Maori tribe in New Zealand’s South Island) recently visited our headquarters in sunny California. And we have benefited from hiring incredible local talent as the Kiwi cohort on the Cora team grows.

Kids, chalk, and Cora – a great outing for the family

Recently, we also celebrated the opening of our hangar in New Zealand. It was an exciting moment. The hangar will serve as our first base of operations as we grow our fleet of Coras and build toward the world’s first electric, autonomous air taxi service.”

In a hangar opening ceremony attended by Minister Woods, local school children, and Maori tribes people, “We were privileged enough to have Ngai Tahu bless our hangar. They led us on a procession in a timeless ceremony for invoking wellbeing and prosperity. It was one of the many priceless opportunities we have had to engage with the rich tikanga of the Māori culture… Together, we are building a world where the freedom and power of the sky connects all our lives.”

Cora Itself

An outcome of a decade’s development, Cora takes off vertically with no less than 12 propellers, apparently on pivoting mounts, paired on six under-wing booms.  Wisk describes the safety factor inherent in the design: “Rotor Safety System: Our vertical lift system features 12 independent rotors. Each direct drive motor combination has only one moving part: the fan. Flight tests have shown that an issue with one rotor is automatically handled with no discernible change in the flight path.”

Autoblog has a somewhat unique take on the “flying taxi.”  The Kittyhawk offerings are no longer available.

To keep things on a planned course, triply redundant flight controllers process navigation.  If any one encounters a problem, the other two maintain the plan.

Finally, in the Hail Mary type of safety measure all UAMs seem to choose, a total failure of all power plants on Cora would enable use of a ballistic parachute that would lower Cora and its occupants safely to the ground.  Your editor has a nit to pick with this, even though most UAM makers extol its virtues. It may be great for the craft and its passengers, but what about the unsuspecting groundlings who may have even the lightest of craft land on them – however slowly?

Cora has one saving grace in this, with its aerodynamics enabling controlled forward flight even with all power off.  A pilot (or an autoland system) could still maneuver Cora to a relatively safe landing.

Wisk does not elucidate on the power of the large pusher motor, or of the 12 fans.  It lists only the 400-pound payload, allowing us to make some admittedly loose speculations about the rest of the package.  The 12 fans will have to produce at least 100 – 135 pounds of thrust each to lift a 1,200 -1,600 pound Cora and passengers.  That gross weight will probably be more, so thrust will need to be greater.  Let’s guess 15-to-20 kilowatts (20-to-27 horsepower) per fan.  That’s 180-to-240 kilowatts total (240-to-324 horsepower).

Wisk lists Cora’s range at, “Initially about 25 miles (40 kilometers) plus reserves.  This is less than eVTOL News’ endurance listing of a flight time of 19 minutes with a 10-minute reserve.  At 110 mph cruising speed, 19 minutes would take the craft 34.8 miles (not counting power required to gain cruising altitude and set back down).  Let’s guess that cruising on the one pusher motor takes much less power than that required for vertical lift.  Just for fun, let’s add two minutes of total power lift and two minutes of total power descent.  (All these assumptions and calculations are open to scrutiny, of course.)

Four minutes of full power and 25 miles of 70-percent power would require 16 kilowatt hours for lift and descent and about one kilowatt-hour per minute in level flight or 29 kWh (with reserve).  16 + 29 = 45 kWh for the 19-minute flight.   We’re basing the power required for level flight on that for a Cessna 152, a roughly equivalent but radically different craft.   To lift the 400-pound payload, aircraft structure and motors, and batteries keeps the range short, and the total weight probably close to that of a 152 – 1,670 pounds.

Wisk Cora’s FAA application drawing

George Bye of Bye Aerospace has what are probably the highest power battery packs (as of now) on his eFlyer aircraft.  They are rated at 260 Watt-hours per kilogram.  If equally efficient packs were installed in Cora, it would take 981 pounds of batteries to maintain 29 minutes of full-power lift.  This would be inconceivable – if not impractical.

For the 19-minute flight noted above, batteries to obtain the 45 kWh would weigh around 173 kilograms, or 380 pounds.  That’s close to the one-third total weight that would make this a viable flying machine.

Wisk is doing a great job in promoting its aircraft, involving talent in both hemispheres, and being a good corporate citizen.  Its examples now flying are showing their merit and we may see the skies filled with their machines sooner than later.