We have proved the commercial profit of sun power in the tropics and have more particularly proved that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the sun.—Frank Shuman, inventor, writing in the New York Times, July 2, 1916
In 1917, Emanuel Victor Rousseau, British writer of pulp fiction, had his latest adventure, The Messiah of the Cylinder, serialized in Everybody’s Magazine. Set in the year 2010, it envisages both airplanes and ray guns powered by solar energy.
Another who envisaged solar aircraft was John Wood Campbell Jr. In 1930, Campbell had his first short story, “When the Atoms Failed,” published by Science-Fiction magazine. At that time, he was twenty years old and still a student at college. But as the title of the story indicates, he was even at that time occupied with the significance of atomic energy and nuclear physics. Born in Newark, New Jersey, to a father who was a cold, impersonal, and unaffectionate electrical engineer, the son was allowed to carry out his own experiments, going on to study at Duke University and then the Massachusetts Institute of Technology. In one of Campbell’s stories, “The Black Star Passes,” published by Amazing Stories Quarterly in 1930, then extensively edited for book publication in 1953 by Fantasy Press, the boy says to his father, “Dad, I believe that you have been trying to develop a successful solar engine. One that could be placed in the wings of a plane to generate power from the light falling on that surface.…” To which the engineer replies, “[T]he one big trouble with all solar engines, eliminating the obvious restriction that they decidedly aren’t dependable for night work, is the difficulty of getting an area to absorb the energy.” Despite this a huge aircraft, the Solarite, is built and flies:
The invisible ship darted forward. They sped past the barrier of low hills, and were again high above a broad plain. With a startled gasp, Arcot cut their speed. There, floating high in the air, above a magnificent city, was a machine such as no man had ever before seen! It was a titanic airplane—monstrous, gargantuan, and every other word that denoted immensity. Fully three-quarters of a mile the huge metal wings stretched out in the dull light of the cloudy Venerian day; a machine that seemed to dwarf even the vast city beneath it. The roar of its mighty propellers was a rumbling thunder to the men in the Solarite.
Although it had nothing to do with solar energy, from 1929 the Solar Aircraft Company Ltd. of San Diego, California, was registered, although it only ever built a single airplane. This was Solar MS-1, an all-metal biplane (sesqui-plane) with a 420hp Pratt & Whitney Wasp avgas engine. It carried eight passengers, with a range of about 500 miles.
On April 25, 1954, Daryl Chapin, Calvin S. Fuller and Gerald Pearson publicly demonstrated the first practical silicon solar cell at Bell Laboratories, Murray Hill, New Jersey. They demonstrated their solar panel by using it to power a small toy Ferris wheel and a solar-powered radio transmitter. This created a sensation, and by July 4, 1955, Time Magazine had more to report: “When Bell Telephone Laboratories announced its silicon solar battery, it fired the imaginations of the science fictionists, and the solar system was soon abuzz with solar-powered space ships. Trimming their silicon sails to catch the sunlight, spacemen used the electricity generated by the batteries to push themselves from planet to planet.”1
The color front cover of the October issue of Modern Mechanix (erroneously dated 1934, twenty years too early) showed a solar-powered aerial landing field. The article inside states:
Recent experiments in the conversion of the sun’s rays into electric power have led to an unusual idea in aerial equipment. It is a dirigible that would not only get its power from the sun but also provide space for a landing field in the air. The ordinary cigar-shaped dirigible would in effect have a slice taken from the upper half of the gas bag. This would provide a large deck on which could be mounted solar photo cells, an airplane runway, and a hangar. Planes could land on the dirigible, floating over the sea, to refuel for trans ocean passenger service. Another unusual feature of this design, in addition to the landing field, is the use of the sun’s rays to power the motors of the dirigible.
Another who was inspired by the Bell breakthrough was André North, the pseudonym of Alice Mary Norton, also known as Andre Norton. Her 185-page book Sargasso of Space was published in 1955 in an edition of 4,000 copies by Gnome Press, a small publisher in New York City that focused on science fiction. Fresh out of Training Pool, a trade school for spaceship crews, Dane Thorson discovers that his first assignment as apprentice cargo master puts him on the free trader (basically an interstellar tramp freighter) called Solar Queen. During the years to come, Andre Norton would write another six novels in the Solar Queen series, during the last three of which solar airplanes had become a reality.
In 1973, two years after John W. Campbell’s death, sci-fi became sci-fact when Roland Boucher at Astro Flight turned his attention to the creation of a high-altitude solar-powered aircraft that would have unlimited endurance:
Heliotek in Sylmar, California, had developed a new high efficiency light weight solar cell for the Hughes Space Satellites with a power density of 100 watts per pound and a solar efficiency of 14 percent. Since this power density was comparable to the NiCads we were using in our previously successful electric powered models we knew that an airplane powered only by solar cells would fly. This was a trivial problem. But if somehow we could store enough of the sun’s energy during the day, we could then use that energy to continue flying all through the night. We could theoretically fly forever. But no suitable battery was available. My brother Roland came up with the following scheme. Store the energy in the Earth’s gravitational field!!! If we could build an airplane that could climb high enough during the day to be able to glide all through the night and still be at some reasonable altitude, say at 30,000 feet at dawn, we would have created perpetual flight. It all looked feasible. It would be difficult but with careful attention to detail it could succeed. We filed our patents and submitted our proposals to our prospective customer Kent Kressa of DARPA. We called our invention Sunrise. Our proposal to DARPA was to build a 100 foot wing span vehicle to carry the 50 pound tactical payload envisioned by the customer. ARPA counter offered to pay for a paper study to prove feasibility. Administration was by the Lockheed Aircraft Corporation of Sunnyvale, California.2
Astro Flight would build a ⅓ scale model of Sunrise, fly it on a government test range, and share the flight test data with DARPA. The Bouchers had expected to receive their contract in January 1974 so that they might make their initial flight tests in the summer months when the sun is highest in the sky and the days are longest. With the late starting date they had to work many long days from 7 a.m. to midnight to get Sunrise I ready for flight a few days after Labor Day.
Roland Boucher took on the task of the structural design, aerodynamics, telemetry, control and navigation. He also designed the integration of the solar panel, electric motors, gearbox and propeller. He selected an Eppler 387 airfoil for the wing. The Heliotek solar cells were 5 cm (2.0 inch) round commercial units with a 12 percent efficiency. A primary lithium booster battery capable of about one hour duration was installed to power Sunrise through any cloud layer and then be jettisoned. The actual airframe was constructed by a team under expert model builder Phil Bernhardt. The Sunrise’s wing span was 32 ft. (10 m) and the aircraft had a gross weight of 22 lb. (10 kg). The wing loading was a very low 4 ounces per square foot (0.011 kg/sq m). The aircraft structure was built from spruce, balsa and maple. Due to their roughness the solar cells were only mounted on the aft two-thirds of the wing’s upper surface. The wing spars were built from spruce spar caps with maple doublers at all attachment points and two 3/32-inch (2 mm) balsa shear webs attached to ⅛ to ⅜-inch (3 to 10 mm) balsa strips on the wing spars. The ribs were made from 3⁄32-inch (2 mm) balsa. This construction resulted in a balsa spar box with tapered spruce caps. The leading edge was covered with 1/32-inch (0.8 mm) balsa to form a leading edge D spar. The trailing edge was formed by two 2-inch (51 mm) wide 1⁄32-inch (0.8 mm) sheets forming a triangle with ⅛ to ⅜ inch (3 to 10 mm) vertical spar sections in between the ribs. The covering was ½ mil Mylar. The 32-ft (10 m) span wing weighed 5 lb. (2 kg) and was capable of loads up to 100 pounds. Control was via an S&O Radio–designed and built telemetry transmitter and receiver. The standard S&O six channel radio had channels for elevator, rudder, motor on and off and solar cell operating mode. The solar cells could be set for either series or parallel operation. The telemetry functions provided gave data on motor current, motor voltage, motor RPM, airspeed and two heading references from a sun compass for navigation.
Astro Flight Model 7404–1 (Sunrise) made its first test flight under battery power on September 17, 1974. Shakedown flights showed that the propulsion system and the command and control systems were OK and that Sunrise I had an excess power ratio of seven. That meant that Sunrise I could maintain level flight on one-seventh of its maximum power. It could maintain altitude on 85 watts. Sunrise I had a wing span of 32 feet (9.8 m) and weighed 19 pounds (8.6 kg). At this weight and with this power level, the Bouchers calculated its service ceiling at 75,000 feet (23,000 m). Heliotek delivered the solar panels but they were overweight and underpowered. The panels weighed 6.5 pounds (3 kg) instead of the promised 4.5 pounds (2 kg) and the power output was only 450 watts instead of the 600 watts promised. To make matters worse, the overweight solar panels mounted on the upper surface of the wings were behind the center of gravity, so they had to add two pounds of lead ballast to the motor compartment to rebalance the airplane. Sunrise I now weighed 27½ pounds (12 kg) ready to fly with lead ballast, telemetry downlink and radar beacon. They recalculated the probable service ceiling to be 25,000 feet (7,600 m) in June and 10,000 feet (3,000 m) in December. It was by now late in October and the rainy season in California had begun. A very wet and windy winter was forecast that year. Astro Flight argued with DARPA that the prudent course would be to put the solar flight tests on hold until late spring of 1975 or to move the flight tests to Australia. But they were instructed to fly at the earliest possible date at Bicycle Lake, California, a dry lakebed on the Fort Irwin Military Reservation.
November 4, 1974: Bicycle Lake, a dry lakebed on the Fort Irwin Military Reservation, California: the Boucher twin brothers, Bob and Roland, prepare to launch their Astro-Flight solar glider, Sunrise I. It was powered entirely by 4,096 Heliotech solar cells on its wings (Bob Boucher collection).
The first flights would be conducted on battery power, using a bungee cord launch to 20 ft (6 m). Then at 10:00 a.m. on November 4, 1974, Sunrise I rose slowly and silently from the dry lake bed at Camp Irwin. It was powered entirely by the 4,096 solar cells on its wings.
The age of Solar Flight had arrived. Roland Boucher reported:
The first flight test was on battery power prior to the attachment of the solar cells. Sunrise was launched by a bungee cord to about a 20 foot altitude, and then the electric motor was activated. The plane climbed to about 500 feet (150 m) by the end of the runway. It then glided in a rectangular pattern turning left to fly crosswind, then left again to fly downwind, then left again on base leg and finally left again to final approach. On the first pass sunrise still had over 50 feet (15 m) altitude when passing the operators located about 300 feet (28 m) down the runway. The power-on portion was reduced gradually until an accurate measure of the average power required was established. This flight test on battery power was a complete success.
The solar panels which had been under construction at Heliotech in San Fernando California were mounted, and the electrical power verified with the aircraft in our parking lot. The aircraft was returned to Bicycle Lake, a final full power check of Solar panel and electric motor was performed, and Sunrise made its first flight powered solely by incident sunlight on the flying surfaces. The weather was extremely cloudy that year even in the desert, and for some weeks we would wait in vain for clear skies and low wind. In all, 28 flights were made on solar power alone. Take off was sluggish, but once an altitude of a few thousand feet was achieved, the cells cooled down, power increased and Sunrise maintained a respectable rate of climb. The Telemetry and control system worked flawlessly and navigation by means of the sun compass was demonstrated. The final flight was made with cumulus clouds covering about 15% of the sky. The pilot flew too close to a cloud at about 8,000 feet (2,400 m) and Sunrise was destroyed in severe turbulence. We were disappointed that an altitude of 78,000 feet had not been achieved. However, there was no longer any doubt that Project Sunrise had demonstrated the feasibility of solar powered flight to extreme altitudes.3
DARPA was sufficiently encouraged to authorize construction of an improved version, and Astro Flight received a contract on June 10, 1975, to proceed with construction of Sunrise II. The Boucher brothers worked 16 hour days all that summer. Roland Boucher had become physically exhausted from his work on the initial Sunrise and he suffered from congestive heart failure. He was admitted to intensive care at Santa Monica Hospital. While in the hospital, he resigned from Astro Flight and sold his interests in the company to his brother Bob Boucher, who continued work on the second Sunrise aircraft. A new digital telemetry system was built and tested and a single new samarium cobalt Astro 40 motor replaced the two Astro 40 ferrite motors used on Sunrise I. Heliotek was now owned by Hughes Aircraft and had a new name, Spectrolab. Bob Oliver and his Spectrolab team had developed a new high-efficiency solar cell that measured 2 × 4 cm by 8 mm thick and delivered 14 percent efficiency. The new solar panel weighed 4½ pounds and delivered a full 600 watts. This was much better than the original 100 watts per pound that was originally promised.
Sunrise II made its maiden solar power flight on a dry lake at Mercury, Nevada, that was controlled by Nellis AFB on September 12, 1975, just three months and two days after contract award! Flight tests indicated that Sunrise II should have a service ceiling of 75,000 feet (2,290 m) in summer and 25,000 feet (7,600 m) in winter at the 30 degrees north latitude of the test range. At this latitude 24-hour flights would be possible during the months of May, June and July. After many months of flight testing, Sunrise II was damaged when a failure in the command and control system caused an airframe structural failure. After recuperating, Roland Boucher returned to work at Hughes Aircraft on classified military programs.
Meanwhile, in Germany, Helmut Bruss was working on a solar model airplane in summer 1975 without having heard anything about Boucher’s project. It operated without a storage battery but could only climb in a cloudless sky. Unluckily, due to overheating of the solar cells on his model, he didn’t achieve level flight. Bruss was a major pioneer and sponsor of solar aeromodeling. As a physics teacher, he was able to inspire numerous youngsters to become enthusiastic about solar flying—both inside and outside school. He also wrote several successful technical books and reports on the subject of electric and solar-powered model aircraft.
But it was Bruss’s friend, the veteran Fred Militky of Graupner, who produced his version, the Solaris, its solar cells running along the fuselage. On August 18, 1976, he completed three radio-controlled flights of 150 seconds and reaching an altitude of 50 meters (160 ft). This was probably Militky’s final model as he died of leukemia the following September, aged only 55. This pioneer’s name is still revered with the Militky Cup at the International Electric Flight Meeting held annually at Pfäffikon in Switzerland. Soon after, in 1978, Prof. V. Kupciks, Roland Stuck and Helmut Schenk were experimenting with solar model airplanes. At the 5th International Militky Cup in Switzerland in 1978, Helmut Schenk demonstrated his radio-controlled solar-powered model. It operated without a storage battery but could only climb in a cloudless sky.
The world’s first official flight in a solar-powered, man-carrying aircraft took place on April 29, 1979. The Mauro Solar Riser was built by Larry Mauro, president of Ultralight Flying Machines, and was based on his UFM Easy Riser as a swept-wing, tailless biplane. It had been flown both as a hang glider and as a gasoline-powered ultralight. Normally foot-launched, the Solar Riser had wheeled landing gear added. Power was supplied by a Bosch electric starter motor of 3.5 hp (2.6 kW) connected to a 30-volt DC nickel-cadmium battery pack taken from a Hughes 500 helicopter, powering a 41-inch (104.1 cm) propeller through a reduction drive made from a timing belt and two pulleys. The battery was charged by a series of photovoltaic solar panels mounted in the top wing that provided 350 watts of power. The solar cells were not sufficient to provide power in flight. All flights were made by recharging the battery on the ground from the solar cells and then using energy stored in the battery to fly. A charge in bright sunshine for an hour and a half yielded a flight of 3 to 5 minutes.
August 18, 1976: Fred Militky (right), with an unidentified friend, holding his final prototype, which he radio-controlled while completing three flights of 150 seconds and reaching an altitude of 50 meters (160 ft.). Militky died of leukemia the following September, aged only 55 (Fred Militky collection Giezendanner).
Following a successful model test in 1974, it was Mauro’s thought to demonstrate the airplane to the large crowd at the EAA fly-in, but the FAA nixed the idea. Mauro took his airplane to nearby Flabob Airport, in Riverside, California, where owner Flavio Madariaga encouraged innovation, and let aviators do pretty much as they pleased, so long as they did not get him into too much trouble. So it was that the world’s first official flight in a solar-powered, man-carrying aircraft took place on April 29, 1979, at Flabob Airport. The aircraft reached a maximum height of about 40 ft (12 m) and flew 0.5 mi (0.8 km). The Mauro Solar Riser used photovoltaic cells to deliver 350 watts at 30 volts. These charged a small battery, which in turn powered the motor. The battery alone was capable of powering the motor for 3 to 5 minutes, following a 1.5-hour charge, enabling it to reach a gliding altitude.
Larry Mauro was quick and prophetic to point out that, while his Solar Riser really and truly flew entirely on electricity made from sunshine, he considered his April 29 flights to be only
… previews of coming attractions. The solar cells we’re using are not really as efficient as some others currently on the market, and we can install at least twice as many of them on our machine as we’ve been using. We’re also looking for a better battery. As things now stand, we have to charge for at least an hour and a half just to get a three-to-five minute flight. That’s not as bad as it sounds, though, since it’s theoretically possible for the rig as it is to take off, fly for three or four minutes until it catches a thermal, and then soar—shut down—for an indefinite period of time while the solar panels recharge the battery in preparation for a power assist to another updraft. Still, that’s not the kind of flying I want to do. I want to improve this set-up until we can regularly take off and fly around all day on nothing but the solar-generated electricity that we’re producing as we buzz along.4
A number of other flights of the Solar Riser of similar height and duration were flown, including demonstration flights at EAA AirVenture Oshkosh, before the aircraft was retired to a museum.
The next breakthrough for solar-electric aircraft came indirectly from a £50,000 prize offered back in 1959 by an industrialist called Henry Kremer for almost impossible human-powered flights across the English Channel. Hanoch Kremer, born in Latvia, had immigrated to England after World War I and was educated in Switzerland. He became an inventor of wood products and in 1941 he developed a process for making a plywood substitute from sawdust, wood shavings and resin. Structural molded boards replaced natural timber, which was then unobtainable, and were used in the war effort and later commercially. This was the first product of its type in Britain and it grew into the particleboard industry. The De Havilland DH98 Mosquito, an amazing World War II fighter aircraft with a service ceiling of over 10,000 meters (33,000 ft.), was built from Kremer’s special laminated plywood; over 7,000 were built. Postwar, since working with De Havilland, Kremer had maintained his interest in aviation, and he was also very interested in physical fitness. Intrigued by the challenge of human-powered flight, he set up the monetary prizes that carried his name.
Freddie To, an architect and a member of Royal Aeronautical Society Kremer prize committee, was one of those who asked David Williams to start a project to produce a pedal-powered aircraft to compete for the prize. The resulting aircraft, at 230 lb. (104 kg), proved too heavy for human-powered flight and so was converted to solar power instead. A nose-mounted pod powerplant was installed consisting of four 1 hp (1 kW) permanent magnet 36-volt DC, 12 amp Bosch electric motors, powered by 750 solar cells of 3 inch diameter and a 65-lb (29 kg) nickel-cadmium battery pack of 24 cells with a 25 amp hour capacity, connected in series. The motors were connected by a 3:1 bicycle chain reduction drive to a 63-inch (160 cm) wooden two-bladed propeller, which turns at a maximum of 1,100 rpm, decreasing with battery discharge. The engines are controlled with a simple on/off switch. For flight the aircraft used its on-board solar cells to recharge the battery array on the ground, and then the batteries provided power for flight as the aircraft had insufficient solar cells for sustained flight. This shortcoming was not a design feature, but a problem of the cost of the solar cells as the limited project budget of £16,000 did not allow the purchase of sufficient cells. The 750 installed solar cells cost £6,000 and were the most expensive part of the aircraft.
Solar One’s first flight was a short hop that occurred at Lasham Airfield, Hampshire, United Kingdom, on December 19, 1978. Freddie To was not present when this occurred, and the pitch of the propeller was found to be incorrectly set, which was why it was a short hop. Subsequent flights occurred in 1979, and those are often mistakenly taken as the first flights of the aircraft, as confirmed by Barry Jacobson, a member of the Solar One team. The 1979 flight took place on June 13 and covered just under 0.75 mi (1.2 km). The pilot was Ken Stewart and the aircraft lifted off at 18 to 20 kn (33 to 37 km/h) and reached 35 kn (65 km/h) and 80 ft (24 m) in height. A second flight on the same day by Bill Maidment achieved a speed of 42 kn (78 km/h). All flights were made on battery power that had been recharged on the ground from the installed solar cells. An intended flight across the English Channel was abandoned when the aircraft did not reach intended endurance targets.
Enter Dr. Paul MacCready: “The perfect combination of pilot-engineer who dared to build lighter than anyone else.”5
Paul Beattie MacCready was born on September 29, 1925, in New Haven, Connecticut, where his father was a physician and his mother a nurse. He was dyslexic and had trouble concentrating, but showed passion for things that interested him, in particular insects. He collected them on the Connecticut shore and pored over the exquisite studies of John Henry and Anna Botsford Comstock, two 19th-century naturalists, to explore the evolution and the vein structure of the wings of lepidoptera. Nerdy already, small and unsporty, he then buried himself in making and flying model aircraft: fixed-wing and flapping-wing, out of a kit or out of his head, propelled with rubber bands or with tiny gasoline engines. He had little use for commercial kits. By the age of 15, McCready won a national contest for building a model flying machine.
Graduating at Hopkins School in 1943, McCready studied mechanical engineering at Yale, then was training as a U.S. Navy pilot when World War II ended. He returned to Yale, where he obtained a B.S. in physics in 1947, an M.S. in physics from Caltech in 1948, and a Ph.D. in aeronautics from Caltech in 1952.
During this time he became enraptured with the sport of soaring. He set an altitude record, and was a three-time winner (1948, 1949, and 1953) of the Richard C. du Pont Memorial Trophy, awarded annually to the U.S. National Open Class Soaring Champion. In 1956 he became the first American pilot to become the World Soaring Champion with a borrowed sailplane he had not flown before. He did this by taking extreme risks; in one leg of the competition he flew his sailplane far past any airport in southern France and landed after dark on the beach just to set the greatest distance flown in one day.
In 1951 MacCready founded his first company, Meteorology Research Inc., in the new field of weather modification. He was the first to use small instrumental aircraft to study storm interior atmospheric research. In 1971, McCready guaranteed a loan for a friend who wanted to start a business building fiberglass catamarans. When the company failed, MacCready found himself $100,000 in debt. Casting around for a way to deal with that problem, he recalled the Kremer cash prize for anyone who built a human-powered plane capable of sustained, controlled flight. On August 23, 1977, McCready and his colleague, South African–born Dr. Peter B.S. Lissaman of Caltech, who had recently established AeroVironment, began to recuperate that debt when Gossamer Condor (its name chosen by MacCready), piloted by amateur cyclist and hang-glider pilot Bryan Allen, won the first Kremer prize by completing a figure-eight course specified by the Royal Aeronautical Society, at Minter Field in Shafter, California.
Subsequent to the successful flight of the Gossamer Condor, winning Kremer’s cash prize that had gone without a winner for 17 years (in fact, doctoral theses had been written explaining in detail why the prize was not achievable), Henry Kremer issued a second prize, this time £100,000 (approximately $200,000) for the first successful human-powered flight across the English Channel. It was assumed that, given the shortest distance across the channel was 22 miles (35 km), and the weather was usually unfavorable, it would probably be another 20 years before that prize was won. However, MacCready was undaunted. Cashing in on his publicity from the Condor (with the help of a publicist he hired, Tom Horton), he sought and received sponsorship from DuPont, maker of the plastic covering used on the Condor, to cover much of the development cost for the Albatross. The Albatross, similar to the bird, was to be a much sleeker version of the Condor, and used primarily carbon fiber reinforced plastic resin for its structure, allowing for light weight as well as a much improved lift-to-drag ratio. On June 12, 1979, Bryan Allen pedaled her across the English Channel from Folkestone to Cap Griz-Nez, a distance of 22.2 mi (35.7 km).
MacCready’s team had actually been building three aircraft for the cross-Channel flight. The first (Gossamer Albatross I) was used for most of the flight testing and pilot training, where the airframe was optimized by repairing things that broke during a flight and making lighter things that did not, along with some aerodynamic refinements. The second was the “good” Gossamer Albatross II, meant only to be used on the Channel crossing. The third was a 75 percent sized version of the Albatross, named the Gossamer Penguin. This one, at approximately twice the wing loading, would fly faster than the Albatross (albeit requiring about 35 percent more power), in case the headwinds were too great an obstacle for the bigger, slower Albatross to make it across. (Some of the team members joked it was made so Marshall, the youngest of Paul’s three boys, would have his own plane to play with after the channel had been crossed. In fact, this supposition is very close to what later occurred.) Most of the structural frame of the Penguin had been completed, but it was not finished at the time of the Albatross’s success. The actual cross-Channel flight was accomplished with the old, much repaired, first Albatross, because the first attempt was on a marginal weather day, and the team did not want to risk losing the “good one.”
An engineer at Arco Solar (later purchased by Siemens) in Camarillo, California, had been following MacCready’s human-powered flights. He contacted Paul shortly after the Channel flight, suggesting Paul develop a solar-powered aircraft to fly the Channel using Arco Solar cells (developed for the expected terrestrial market since the oil crisis of the 1970s). He had pitched the idea internally, and received a favorable response from his management as a possible publicity showcase for the solar cells they produced. He had even picked a name for the aircraft—Archaeopteryx (considered an evolutionary link between dinosaurs and birds). Paul became excited by the idea. It would not only be fun to do, he felt it would show the world the potential for solar energy, steering the energy demands toward more benign, non-polluting, and renewable sources.
However, due to concerns about the financial impact on Paul’s environmental consulting company, AeroVironment, as a result of becoming involved in outside projects, Paul decided to bring this project “in house.” Since he had neither the staff nor facilities to run such a project inside the company, he began searching for a project manager to run this project, which included finding a building to rent, hiring the people to develop the aircraft and running the development program. He sought recommendations from several of his friends from the sailplane world, which included a gregarious, talkative fellow named John Lake, who also had become heavily involved in the budding hang-gliding industry. John had a friend named Ray Morgan, an aerospace engineer (then working in the Lockheed “Skunk Works”), whom he had met through Joe Greblo and Rich Grigsby, because Ray was teaching ground school for hang-gliding at Joe and Rich’s Southern California Hang Gliding school. Morgan recalls:
MacCready’s children were learning to fly at my club. He wanted me to start a group within his company, and then find a place to design and build the new airplane. There were two unique qualities Paul possessed that all who worked with him could appreciate. Persistence, he was relentless in pursuit of a goal, once he’d made up his mind to do something. Optimism, he considered any failure a better learning experience than a success. Of course, the other side of optimism—that others did not always appreciate, was a tendency to under-estimate the time, cost, and difficulty of his pursuits … some said by factors of 3 to as much as 7. He was good at coming up with what sounded like crazy ideas and convincing somebody to pay for them. He was intellectually fearless; he welcomed ridicule, not bothered at all about people thinking he was crazy. He was small in stature and was not athletic. He rarely smiled and spoke in a monotone, continuously sliding one sentence to the next until he was through with what he wanted to tell you and would then walk away.
A series of phone calls and negotiations led to Ray’s taking a leave from Lockheed California (for 8 months, predicted by Paul to be the time it would take to achieve the cross-Channel flight under solar power) to manage this project for Paul. Unfortunately, in the interim, ARCO Solar decided against sponsorship of the Archaeopteryx. Fortunately, Paul and Tom approached DuPont, which had gotten a good deal of favorable publicity from the Albatross flight, and convinced them to fund AeroVironment the $500,000 cost of developing a solar-powered, piloted aircraft that would showcase much of DuPont’s engineering plastics and fibers, and fly not just across the Channel, but from Paris to London (approximately 150 miles/240 km).
The plan was to finish the Gossamer Penguin, but converting it to solar-electric flight, as a testbed to learn the nuances of solar-powered flight before beginning the design of the Paris-to-London aircraft, now renamed Solar Challenger.
Ray’s first task was to find a location that could be used to complete and modify the Gossamer Penguin as well as provide office and shop space for the design, construction, and ground tests of the intercontinentally capable Solar Challenger (as yet unnamed), and hire some folks to do that. Fortunately, there was a new, light industrial complex just being completed less than two miles from his house.
Their Gossamer Penguin was a ¾-scale version of the Gossamer Albatross II, and had a 71 ft. (21.64 meter) wingspan and a weight, without pilot, of 68 lb. (31 kg). The powerplant was an Astro Flight Astro-40 Ferrite electric motor, supplied by a 450-watt solar panel consisting of 3,920 Spectrolab solar cells loaned by Astro Flight and formerly used on their Sunrise II and repaired by DuPont.
Because the Penguin, like its human-powered predecessors, was unstable and fragile, only suited to fly in the calm air of the early morning, a solar panel would be attached to the “kingpost” above the wing, which could be tilted to the sun, low on the horizon to maximize solar power collected (the team referred to “the power in the shadow” when adjusting the panel angle). The plan for continuous, racetrack flights was to climb up to about 25 feet (7 m) above the runway, then turn and glide while flipping the panel to the other direction with a “halyard” pulled by the pilot, and then resuming solar-powered flight in the other direction. They actually flew with an empty panel initially to explore the aerodynamic effects of this large panel.
Initial test flights were performed using a 28-cell NiCad battery pack instead of a panel. The test pilot for these flights was MacCready’s 13-year-old son Marshall, who weighed 80 lbs. (36 kg). The Penguin, like a high-aspect sailplane, had some nasty stall characteristics, and MacCready Junior got into a tip stall while practicing the “climb, turn and flip the panel” maneuver. He had quite a bad crash, escaping with nothing more than shock and bruises, but pretty much demolishing the Penguin wing. Fortunately, the solar cells had not been installed yet, and the crew was able to repair the Penguin in a few weeks, including replacing the NiCad battery pack with 350 watts of silicon solar cells gotten from Boucher. At 8 a.m. on May 18, 1980 (20 minutes before Mount Saint Helens blew up, killing any news release), the Gossamer Penguin was hand-towed to an altitude of about two feet and then released. Marshall MacCready guided the Penguin straight down the runway while climbing to an altitude of about five feet. He held this altitude for a distance of about 500 feet (150 m) before Paul asked him to land. The era of true, manned, solar-powered flight had arrived.
The official demonstration pilot for the project was Janice Brown, a schoolteacher and Piper Cherokee charter pilot with commercial, instrument, and glider ratings who weighed slightly less than 100 lb. (45 kg). She flew the Penguin approximately 40 times before a 1.95 mi (3.14 km) public demonstration at NASA’s Dryden Flight Research Center on August 7, 1980.
After about a month spent by MacCready, Morgan and Henry Jex considering different conceptual design approaches, including both Gossamer’s canard design and being foot-launched, in June 1980 a second powered aircraft concept, the Solar Challenger, was finalized. It was over three times as heavy (without pilot) as the Penguin and had a shorter wingspan, but was proportionately more powerful, equipped with what appeared to be two wings, the main lift-producing wing of normal proportions in the front, and also an oversized horizontal tailplane covered with solar cells. To find the required cells, as DuPont did not make solar cells, Ray Morgan visited all the nearby Southern California manufacturers:
None of the commercial guys had anything that was efficient enough to do what we needed to do. I went to Hughes Spectrolab in Sylmar, Calif., a maker of space grade solar cells for USAF and commercial satellites. I was told that 1) we were asking a quantity that would be 4% of their entire United States production of solar cells the previous year; 2) they could not start building them for a year due to backlog of orders; (Paul wanted this project over in eight months.); 3) that the amount of 16,000 solar cells we needed would cost us one quarter of a million dollars of, which, unfortunately, Paul had not accounted for when making his estimate to DuPont for the project cost. I felt as if I had been punched in the stomach, and the project and airplane of a lifetime was just not going to happen.
However, as I was leaving, the Spectrolab head of marketing told me about some solar cells they had built for an Air Force satellite that had been rejected for low efficiency (by satellite requirements of 14%), and that were, in fact, in the Hughes Government stores facility by L.A. Airport … suggesting that we might get them loaned or scrapped to us. I then found out that they, the Air Force, could not scrap them to a private concern like AeroVironment, but they could loan them to another Government agency. Dale Reade, a fan of Paul’s, as well as solar powered aircraft that could potentially fly into the stratosphere, was working as an engineer at NASA Dryden Flight Research Center. He had arranged funding for AeroVironment to perform a series of flight tests of the Gossamer Albatross’ stability and control, and write a whitepaper defining its unique characteristics associated with the very low mass of the airframe relative to the mass of the air influenced by the giant wing. It turned out that the flights had been completed and the data had been taken, but Paul and Henry Jex had never quite gotten the paper complete, and had asked for and received a no-cost contract extension to do so, leaving that contract still open. Consequently, if NASA were to ask to take possession of the Air Force rejected cells, Dale could sign the paper that would “lend” those cells to AeroVironment for the Solar Challenger. He told Paul that he was willing to support getting those rejected cells loaned to us for the Solar Challenger provided, after we did the flight across the Channel, we would let Dale fit the airplane with a remote control system to see how high it could fly after we did the flight across the Channel. Paul agreed verbally. Soon after, I got in my old ’65 Ford van and drove down to LAX, where I signed for 250,000 dollars’ worth of space-grade photovoltaic cells (over 16,000) then and took them back to our Simi Valley shop in my van. In fact, this quantity of cells was more than we first calculated we needed when sizing the aircraft, so we enlarged the horizontal tail (easiest and quickest part to change at that point) by a factor of about 3 beyond what we needed for stability, just so we had a place to put more cells, which meant more power!
The design incorporated advanced synthetic materials with very high strength-to-weight ratios, including Kevlar®, Nomex®, Delrin®, Teflon®, and Mylar®, all supplied by the aircraft’s sponsor, DuPont. The bulk of the load-carrying structure was carbon-fiber, stabilized with Nomex® honeycomb and Kevlar® fabric overwrap. “We also used Lucite® (Dupont’s proprietary formulation of acrylic, with excellent transparency, flexibility, and scratch resistance qualities) for the wind screen.”
1981: Solar Challenger’s two 2.75 hp Astro Flight samarium-cobalt permanent magnet motors operated on a 70-volt system run in tandem on a common shaft to drive a single propeller (Don Monroe).
This 1981 technical drawing of Solar Challenger shows the use of her 16,000 NASA solar cells (author’s collection).
Boucher and Astro Flight supplied the two 2.75 hp motors operating on a 70-volt system. Each measured 3 inches (7 cm) wide and 17 inches (43 cm) long and incorporating samarium-cobalt permanent magnets, run in tandem on a common shaft to drive a single, controllable-pitch propeller. Solar Challenger in its ultimate form would have no batteries; it collected sufficient energy from sunlight to take off, climb to 14,300 feet (4,360 m), and cruise at 40 mph (64 kph).
Flight tests of the Solar Challenger began in October 1980. The airplane was first flown under battery power (36 lbs./16 kg of NiCad cells) because the team didn’t want to risk losing any of the 16,128 solar cells in an inadvertent mishap while testing and learning to fly the airplane. The cells also had to be tested, matched to others in a string, and soldered together before installation, a process that overlapped the first flights on battery power. Starting with short hops down the runway, the team quickly developed enough confidence to attempt higher and longer flights.
Morgan: I don’t believe we ever measured more than 24001 watts in steady state conditions. But takeoffs in morning were usually made on about 1800 watts, about 1500 Watts appeared to be the absolute minimum to take off. This power increased with increased solar intensity, reduced temperature, and improvement in angle of array to sun. First two factors were improved as we climbed higher, and, of course the sun rising higher through the morning increased the angle. Early on we were hoping for 3200 watts, but didn’t get expected power from cells. After all, they were rejects!
This phase of testing, at Minter Field near Shafter California, was concluded with a 1½-hour flight at heights reaching 1,650 ft. (500 m) above the ground. The motor was used for only 15 minutes; the remainder of the flight was conducted using indirect solar power, in the form of rising air (thermals). Two days before Thanksgiving Day, on November 30, 1980, at El Mirage field in Southern California’s Mojave Desert, Janice Brown made the first serious solar-powered flight of 2 minutes of the Solar Challenger.
Brown recalls:
Each time we flew the solar powered aircraft, we often had a group of enthusiasts that came to witness the event. I sometimes wished that we were able to work out all the bugs before the flight but this was never the case. The stress to succeed was always present. The flight plan for the day was to conduct a couple of flights down the runway and then fly over the desert and return to El Mirage airport. On that November morning, the air was crystal-clear and cool. It was perfect weather for a solar powered flight. For the first flight, the airplane was placed at the end of the runway and the wing-walkers, who are necessary to keep the wings level for takeoff, were in place. I toggled on the five electrical switches which activated five solar panels and the Solar Challenger took off with only a 20 foot ground roll. This was its first take off and the shortest take off that it ever accomplished. The airplane flew down the runway flawlessly and landed. The aircraft was then repositioned to the end of the runway again for another take off. Once again, the aircraft took off with ease, climbed sunward and began a cross-country flight over the desert. This turned out to be a short flight because the electric motor overheated and failed. As safety precaution, we always made sure that we had an acceptable landing spot below us. Down came Solar Challenger to the dry lake bed. The aircraft turned out to be an excellent glider which was fortunate because it saw many unscheduled, off-field landings during its test flights.6
1981: Paul MacCready holds a prop blade, while pilot Janice Brown prepares for the next test flight in Solar Challenger (Don Monroe).
There followed a week of 3- to 7-minute flights using the low winter sun (which provided only a fraction of the energy that would be available in late spring and summer, with the midday sun more directly overhead). MacCready and team then took the airplane to Marana Air Park, near Tucson, Arizona. There, they hoped to make a 60-mile (100-km) flight attempt from Marana to Phoenix. Despite unusually cloudy weather, many flights were made nonetheless, and Janice Brown was able to leave the airport twice for short distances, gaining valuable off-field landing experience.
Ptacek recalls:
Although we should not have risked it, we just started putting anyone in the cockpit to have a go at flying the airplane. When Paul got in, he couldn’t get the airplane off the ground. He over-controlled it terribly and the Solar Challenger was not an airplane that responded well to anything other than a very light touch. It’s my understanding on a successive flight when I was in the cockpit, that Paul said to one of the crew members (I think Martyn Cowley), “It’s not as easy as it looks,” Martyn relayed this bit of information to me later that day. That’s as close as I ever got to a compliment from Paul MacCready. He spoke in the third person a lot. On one occasion time, during a (casual) meeting, that he had called, with Janice, Ray, Bob (Boucher), and me, while he was talking, Paul paused momentarily, and fell asleep! We sat scattered around Janice’s hotel room in chairs and on the bed. We sort of looked at each other with incredulity and then one by one left poor Janice with Paul fast asleep in a chair.
After a week in Arizona, they returned to their rented hangar at Minter Field, California, to test new motors and other components, as well as expand the flight envelope up to approximately 14,000 feet (4,200 m), and durations of up to 8 hours. In its last flight, lasting 1 hour and 32 minutes, Solar Challenger made it about halfway to Phoenix, the intended destination, when it encountered a thunderstorm near Picacho Peak (about ¼ the way to Phoenix), and Janice Brown was forced to land in a clear spot among the saguaro cacti.
Solar Challenger airborne in 1981. DuPont provided advanced synthetic materials with very high strength-to-weight ratios, including Kevlar®, Nomex®, Delrin®, Teflon®, and Mylar®, all supplied by the aircraft’s sponsor, DuPont. The bulk of the load-carrying structure was carbon-fiber, stabilized with Nomex® honeycomb and Kevlar® fabric overwrap (Don Monroe).
Due to funding limitations and concern over motor reliability, flights were terminated and the crew returned to Simi Valley. Bob Boucher developed a more reliable samarium-cobalt tandem motor system. Improvements were made by the AeroVironment team in power tracking and the manually controlled, variable-pitch propeller system (critical to drawing “peak” power from the solar array in varying conditions of speed, sun angle/intensity, and temperature—a major workload on the pilot), and provisions for cross-Channel flight, such as life jacket, wet suit, improved radio (with its own small solar array charging batteries for avionics), oxygen system, and basic instrumentation to permit emergency flight in IFR conditions.
After funding go-ahead, MacCready and team went back to Minter Field for a series of flight tests, trading off between Janice Brown and 28-year-old Steven R. Ptacek. The latter already had 4,600 hours of pilot-in-command time. He had flown a wide variety of aircraft, including some that were compromised with regard to flying at maximum gross weights and in marginal conditions, strong weather events, high density altitude airports, short and unimproved runways, strong and gusty crosswinds, etc.: “My experience up that point had prepared me to step in and fly Solar Challenger at a high level. Just dumb luck for me, and it made me appear to be better than I was when it really was just fortunate timing.”7
During this period Janice made a flight to a reported 14,000 feet (4,200 m) (the team’s Cessna 150 chase plane could not climb above 10,000 feet), and Steve Ptacek made a flight at around 11,000 feet of 8 hours’ duration. Both these flights set informal records for solar (and electric) powered aircraft. Sixty-nine flights with a total of 6 hours and 4 minutes engine time had been accumulated during these tests. Ptacek actually lost about 40 pounds—slimming down to 120—that spring to reduce the power required for him to fly the Challenger.
That summer the Challenger was air-freighted across the Atlantic by Flying Tigers Air Cargo.
Ray Morgan:
We had one day out of thirty that was good and we had to take that chance. We tried to make it that either Janice or Steve could fly the SC, so one would be reserve pilot. Janice had logged up 500 hours in the Piper Cherokee, but Steve had accumulated almost 5,000 hours in nearly everything that flew, including gliders. Not only would the pilot have to fly that airplane perfectly, but at the same time they must constantly look at a meter which told them how much power they were getting from the solar cells and work an overhead mechanical handle to adjust the feather angle of the propeller blades. Out of our concern for safety, Steve was chosen in the end. The 163 mile (261 km) trajectory was from Cormeilles-en-Vexin Airport near Paris across the English Channel to RAF Manston about 75 miles east of London; Air Traffic Controllers at Paris and Heathrow had rejected the idea of capital to capital.
Multiple attempts were made to fly from France to England. We found difficulty from two sources. We discovered that Cormeilles-en-Vexin was actually at the bottom of a very shallow valley, not really discernible at first, and also we had a very strong north wind blowing. First time we tried the flight, Ptacek took off to the north and flew straight. However, in the early morning haze, his climb rate was only about 25 feet (7 m) per minute. Consequently, he stayed near the ground, even while climbing, until about 1 mile north of the runway, he was faced with going either over or under a set of power lines. Steve reported later that he watched a tuft of dandelion, and saw it rising above the lines, so he knew he could stay above the lines without a downdraft pushing the Challenger down. However, after clearing the lines, he saw a forest that continued another mile in front of him, so he wisely set the Challenger down in a farmer’s freshly planted field, rather than risk hitting the trees, if he encountered a downdraft or a power failure. Subsequently, we reverted to the fly plan developed in Arizona, where Steve climbed up to 2,000 feet (600 m) in a thermal before departing the airport (if he didn’t catch a thermal before the end of the runway, he landed again).
Second attempt, the winds were blowing so hard that, after 4 hours, and climbing to 10,000 feet, he’d barely gotten a mile north of Cergy-Pontoise, so he returned to the airport, abandoning the attempt. Considering the predicted persistent north winds, and having been in France now almost three weeks, with our budget running out, Paul decided we should travel by land and hovercraft up to RAF Manston, figuring, if we could just get into the air at Manston, the Challenger could fly a zig-zag flight, keeping the solar array tilted mostly to the sun at the south, and let the winds blow us back to France. Unfortunately, the clouds socked in after arriving at Manston, and the winds became so strong that we wore out a tire from side forces scrubbing the Challenger sideways just rolling it out on the runway for flight attempts and back. After about a week and a half in the UK, we received a forecast for two days of calm wind, so we rapidly packed up and rushed back to Cergy-Pontoise, reading for flight the next day, south to north.
On July 7, 1981, pilot Ptacek took off in the Challenger and made multiple attempts at capturing a thermal for climb out, finally hooking into one just to the right of the runway, over a cloud of onlookers. He climbed to 2,000 feet (600 m), and radioed the ground crew and chase plane that he was departing for jolly old England.
Ptacek recalls:
It was the day we had been waiting for, clear and a relatively dry air mass. And most importantly light winds aloft for the entire route from Pontoise, our airport just Northwest of Paris, and R.A.F. Manston, Kent, U.K., the intended landing site. We had decided to start early, earlier than we really thought the solar intensity would provide enough direct sunlight to the solar cells on top of the wing and tail. So, at the end of the runway with Ray [Morgan] on the wingtip and Paul [MacCready] in the Cessna chase aircraft we began our take-off attempts. There were 7 altogether where I’d get airborne but only enough to land straight ahead on the remaining runway (during another attempt a few days earlier we took off and headed out at low altitude counting on the Solar Challenger’s ability to climb as solar intensity increased but landed but a few miles away in a bean field because I was unable to climb enough to clear a forest ahead on my flight path). Paul’s son, Parker, was positioned at the far end of the runway to assist me turning around to taxi back for another takeoff attempt. In this way, there was no interruption so we were assured to get off at the first opportunity. Then, on 8th takeoff, I sensed a weak but lifting air mass about mid-field just over the small group of onlookers gathered off the right side of the runway. Coincidentally, or because of them, it was over their heads that I found lift. I stayed in this thermal until about 2,600 feet above the field and then pointed the nose at a 90-degree angle to the rising sun and headed West.
The Solar Challenger has a light wing loading and slow speed, 23 mph [37 kph] climb speed that day. For this reason and that I felt what winds aloft there were would increase as the day progressed, I thought it important to fly as far West as possible early and then later I could take advantage of the winds aloft and keep the sun normal to the solar cells on the northbound leg to Manston. This route put me longer over the English Channel both in distance and time but I had a strong sense that getting West was not only desirable but of paramount importance to the success of the flight. Once away from Pontoise, I settled down to trimming the Solar Challenger to achieve maximum solar intensity on the solar cells. I fly mostly by feel and then crosscheck the instruments. As I’ve found with most machines, there was a sweet spot where you could feel and hear that everything was where it needed to be. I found a small envelope where the airplane was most efficient and stayed there and not squander altitude. Fly too slow and the airplane would descend, fly too fast and it wasn’t efficient and maybe descend. While I was never told how to fly the airplane, it was decided by common agreement that I should climb as high as possible and store energy in the form of altitude.
Because of concerns flying over the English Channel it was decided by some that I should wear a wetsuit just in case.… We didn’t have a real good ventilation system in the cockpit of the Solar Challenger and the seat was hard and not at a very comfortable angle (for me) but to fly the aircraft, I never mentioned it to anyone. Apparently, I was working harder than I realized to get airborne initially and climbing through 10,000 feet [3000 m] encountered cold temperatures. It was enough that I had at least very cold water if not ice running down my back for the first few hours of the flight. Having the 16,128 solar cells positioned correctly in the sunlight meant that the pilot was always in the shade.
Just prior to the French Coast I climbed up the side of a towering cumulus cloud in blinding-refracting-light. That was the most fascinating part of the flight, simultaneously unnerving and spectacular. Unfortunately, I was unable to derive any meaningful power settings as everything was changing so rapidly. At the same time I was dodging at least one helicopter and more than one airplane presumably with media people onboard. It had been agreed upon that media representatives would ride in the MacCready aircraft and then share photos with other interested media organizations. These aircraft either didn’t get the word or chose to disregard the agreement.
As things became more interesting, I purposefully flew into the cloud. “Cloud flying” as it’s called in Europe is legal and I was at the time very familiar with flying without visual cues using basic instruments, something all instrument pilots practice in training. Later in the flight I had one more encounter that would be the only other trial of the day. A four-engine Lockheed Electra had descended lower than their assigned altitude and its flight path was directly ahead of mine. I waited for what I thought was a reasonable amount of time and climbed to what I thought was a safe altitude before crossing its path. What I didn’t know and subsequently learned is that aircraft wakes do not always descend but can climb. This one did. I thought it was possible that the airplane might break up. But it did a great job and while the ride was exciting it survived intact and we continued on.
The remainder of flight over the Channel, the portion of the flight that I had prepared for the most, was actually very easy. I turned north, ran with the wind as I had earlier planned and I could really enjoy the beauty of where I was and the magnificent coasts of France and England. Witnessing the White Cliffs of Dover rising out of the haze is an image I will never forget. I circled Manston for about 45 minutes before landing while the chase plane landed and cleared customs, so that Paul would be available to catch the wing tip after touchdown, so the Challenger could be brought to a safe stop.
My only regret is for the Solar Challenger crew. Not only were they not there for the landing but most were unable to come to Europe at all because of the financial constraints. I was probably the least deserving person on the team as my contribution to the project was so small. I felt at the time and still contend that this was a flight that was going to happen one time ever and to that end while there was a certain degree of danger during the cumulus cloud event, I survived and experienced something that I will never forget. Granted to not experience this part would have been okay with me but I have no ill feelings to those others involved as I recognize that the media aircraft and helicopters were 1) just doing what they were told, and 2) didn’t realize the impact of what they were doing had on my aircraft. I have loved aviation and flying my entire life and to experience this flight and all my flights in the Solar Challenger was the chance of a lifetime. I am very thankful, grateful, and honored to have been part of the Solar Challenger Team.8
Ray Morgan adds:
By common consent, for safety’s sake, only one plane had been cleared to film the flight, the FIA chase plane with Paul on board communicating to Steve. But during the flight, which took 5 hours and 23 minutes, a helicopter chartered by the Press was hovering over Solar Challenger creating extreme turbulence that was lethal for our low wing-loaded airplane. Despite Paul’s telling the Press to keep their distance it was impossible. Steve described it as like trying to order sharks in the ocean not to bite you!… We had a parachute in there above the pilot’s head so that if he got in trouble he could pull it down and throw it out the side. When he hit the Electra’s vortices, Steve had his hands on the parachute ready to abort when somehow the SC managed to right itself and pull out! As for the solar energy, he had reported a momentary peak power approaching 3000 watts when over the English Channel at 11,000 feet, and adjacent to a very bright cumulus cloud which added reflected light to the direct sunlight on the array.
Solar Challenger never flew again. She is now in storage at the Smithsonian Air and Space Museum, Washington, D.C.9 But she has become a legend worldwide. Solar Challenger’s flight was reported around the world.
In 1980, a French-Japanese animation studio, Pierrot, made a television series called Estaban, Child of the Sun. Set in 1532, it follows the adventures of a young Spanish boy named Esteban who joins a voyage to the New World in search of the lost Cities of Gold and his father. Among their discoveries of the technological wonders of the Mu Empire are Solaris, a solar-powered ship, and the Golden Condor, a huge solar-powered ornithopter (mechanical bird), capable of traveling considerable distances under the sun’s power alone. Taiyō no ko Esuteban was premiered on NHK in 1982 and has become one of the best-loved animated series of all time.
There were those who began to use the sun differently for aerial flight. In 1972, Dominic Michaelis, a British architect and the inventor of many solar utilities and projects, invented and built the first lighter-than-air solar balloon (1 cubic meter) with a double skin Melinex polyester film envelope with a clear external surface and dark, heat-catching internal walls. The temperature difference taken inside and outside was about 27°C, which corresponds to a lift of approximately 100 grams per m3. Then, after building a few small balloons, Michaelis built a large one (diameter 10 meters) that was able to lift his son Stéphane (30 kg), whose captive flight saw him become the first solar balloon human pilot! But one day the balloon broke loose from its moorings and disappeared into the Oxfordshire skies. In 1981 Julian Nott piloted Michaelis’s 3rd solar balloon across the English Channel. No electric motor or batteries were used.
Over in Solln, a suburb of Munich in Germany, a long-haired, bearded, almost Biblical-looking industrial designer called Günter Rochelt was preparing his plane Solair I. Born in 1939 in Česká Kamenice, Bohemia, when his parents moved to Memmingen in Bavaria, the young Rochelt obtained blueprints for model airplanes but then modified them to fly better. After two terms at the engineering faculty of Munich Technical High School and two years studying industrial design at the Ulm Design High School, he began to invent. He designed a new clothes hanger, quick-change picture frame, and an energy-efficient electric shaver, which he sold to a Japanese firm.
Günther Rochelt (1939–1998), “hippie” inventor of Munich, helped by his wife and friends, designed and built his own solar airplane in the garage in 1980 (Carolin Scheuermann).
Meanwhile, in his enthusiasm for flying, he was frustrated by the short life of the batteries, and so started to consider solar power. On June 24, 1979, Günter flew his model airplane Silver Fox for 3 hours and 41 minutes—the longest described solar flight yet known. Then, with his own finance and just a little help from his wife and his friends, Günter Rochelt decided to build a full-scale solar airplane in a Munich garage. He called it Solair I. He took a canard design by the Swiss Hans Ulrich Farner, but enlarged it from 13 to 16 meters (43 to 53 ft), extending its area by 70 percent, and overcoming the difficulty of applying 2,499 monocrystalline rigid solar panels on curved wings, to give an output of 1.8 kilowatts (kW). He used a somarium-cobalt motor built by Karl Friedel, with an output of 2.2 kW (3.0 hp). Rochelt approximated the airfoil with a number of straight-line segments, then filled in the remaining space with clear silicone rubber. It took him and his wife three months to sand the silicone to a smooth aerodynamic shape. He then covered the silicone with a layer of ½-mil Mylar. The result was a glass-smooth finish, but Rochelt estimated that the process added about 35 pounds to the airplane. Also, after being installed in the wing, the panels delivered only 1,800 watts instead of the 2,200 watts measured before covering.
Bob Boucher recalls:
Günter took Solair I to Biggin Hill airport about 60 miles from Manston RAF Base where we were with our Solar Challenger. Günter was attempting a channel crossing at the same time that we were! We had heard some vague rumors about his airplane but we had no solid information. Then a few days after we got settled in at Manston we received a phone call from Günter inviting us to come to Biggin Hill to see his airplane. Martin Cowley and I drove over to Biggin Hill that afternoon. Günter was waiting for us with Champagne and Cognac to brighten our spirits and get us into the proper mood to witness the unveiling of his creation. The airplane was absolutely superb, the workmanship was flawless, and Günter had even installed a digital instrument panel.
On August 21, 1983, Rochelt piloted his Solair I for a record 5 hours and 41 minutes, at Unterwössen, Germany. By making it and its pilot lighter, Solair I was eventually able to clock up a total of 100 hours in the air. The Oskar Ursinus Association awarded Rochelt its prize for the most advanced design. (Solair I is now at the German Museum in Munich.)10
1980: Günther Rochelt carefully checks his Solair 1, its 16-m (53-ft.) Farner canard covered with 2499 monocrystalline solar cells to provide an output of 1.8 kilowatts (kW) to the 2.2 kW (3.0 hp) somarium cobalt Friedel motor (Carolin Scheuermann).
Ever innovative, Rochelt next turned his mind to a pedal-powered airplane which he named Musculair and built using ultra-light carbon fiber. It was flown by Rochelt’s 17-year-old son Holger to win two Kremer prizes for the flight over “the eight” in four minutes and 25 seconds in 1984. In the same year, Holger set a world speed record at 35.7 kph (22.2 mph) to receive a second Kremer prize. Later that year, Holger Rochelt and his sister Katrin, at that time still a child, flew the first passenger flight in a human-powered aircraft. In 1985, the Musculair II set a new speed world record of 44.26 kilometers per hour (27.50 mph). Günter’s Flair, for which the inventor finally proposed a bridge between gliding and hang-gliding, was first conceived in 1984, but its airframe in fiberglass, carbon and Kevlar was not finished until spring 1987. After a few test flights, in which the performance was confirmed but the rudders were found to be somewhat ineffectual, Günter decided not to put the Flair into production, concluding that he could improve performance further with some changes to the design. This led to an ultralight glider (36 kg/80 lb.), Flair 30, whose design goal was to reach a 30:1 glide ratio with the pilot launching by foot, then lying prone in a special harness, and finally landing on a skid. It first flew in 1990. For his innovative aircraft concepts Rochelt was awarded the Philip Morris “Future Challenge” Research Prize. With his 90 kg (200 lbs.) MinAir of 1992 there was a solar-electric option, with twin motors and Heck folding propellers.
Finally the Solair II was built to compete for the Berblinger Prize. Modeled on glider construction, the airplane had a V-tail with electric motors mounted at the tips and trailing fins on each propeller. It was manufactured in half-shells sandwich construction with honeycomb cores. With charged batteries, it required an input of 755w power for the straight flight. Despite two 2kW electric motors and a heavy battery, Solair II weighed only 140 kg (300 lbs.).
Günther Rochelt in Solair II in 1996, waiting for some sunshine. Notice the V-tail, at the tips of which are the propellers. Rochelt’s premature death precluded any further development (Carolin Scheuermann).
Its test flight was on July 7, 1996, at the Laupheim Army Airfield near the city of Ulm. But there were teething troubles; the propulsion system was overheating. Sadly, development stopped in September when Rochelt, aged only 59, died suddenly from pancreatic cancer. Eric Raymond recalls: “Gunther had a very pure design philosophy that bordered on the religious. He instinctively knew how to optimize every part, large or small, and combine them into beautiful, efficient aircraft. All his aircraft were thoroughbreds, pure Rochelt.”11
Some continued to believe in a “pedalectric” approach, without solar panels. The Massachusetts Institute of Technology Monarch aircraft project was a series of two aircraft designed to win the Kremer prize for human-powered aircraft speed record, administered by the Royal Aeronautical Society. The aircraft used an electrical motor along with batteries that were charged by the pedaling action of an athlete piloting the aircraft. From the 1970s until the early 1990s, MIT had a succession of student-led projects that designed, built, and flew human-powered aircraft (HPA), starting with BURD and BURD-II, and evolving into the flight of the Chrysalis in 1979, the first of the MIT HPA to fly successfully. Chrysalis went on to have over 44 pilots, including the first female pilots of an HPA. The Monarch B was a human-powered aircraft built by a student team in 1983 which won a Kremer Prize of £20,000 for sustaining a speed of over 30 kph (20 mph) over a 1.5 km (1 mi) triangular course. It was a precursor to the Daedalus effort, which flew a human-powered aircraft from Crete to the island of Santorini off the Greek mainland in 1988.
Another contender, AeroVironment’s Bionic Bat, was an aircraft built to compete for the Kremer Speed Challenge. It incorporated an electric motor that doubled as a generator while on the ground, with pilot Bryan Allen’s pedaling action recharging nickel-cadmium batteries. The stored energy was used to supplement pedal power from the pilot during record attempts. In 1984, Bionic Bat won two segments of the Kremer Speed Challenge.
At the time of the Solar Challenger’s success, it was reported that its solar cells, valued at one quarter of a million dollars, had been on loan from the USAF. Unfortunately, in the team’s haste to fly the Channel, the NASA plan had apparently not been coordinated with DuPont, and consequently, the planned unmanned high-altitude flights of the Challenger never took place. (The story of AeroVironment’s entry into UAVs is told in Chapter Nine of this book.)
In July 1985, Bob Boucher presented a paper, “Starduster, a Solar-powered High Altitude Airplane,” at the 21st joint propulsion conference of the AIAA/SAE/ASME at Monterey, California. The proposed Starduster, an improved version of Sunrise II, was designed to reach extreme altitudes of 200,000 feet, and although flight would be limited to daylight hours, long-distance flights over thousands of miles would be possible. In his paper, the visionary Boucher concluded: “Perhaps in this second decade of solar flight we will see solar airplanes circle the globe nonstop!” Without funds, Starduster, ahead of its time, was never built.
Alongside AeroVironment, others were busy. Like Paul MacCready, Eric Raymond, born in 1956 in Tacoma, Washington, had flown model airplanes at an early age. In his teenage years he started flying sailplanes, but switched to hang-gliding. While studying photography at the Rochester Institute of Technology and aeronautical engineering at University of California San Diego, Raymond won the 1979 U.S. Hang Gliding Championship. He also set world hang-gliding records and in 1983 and 1984 became world aerobatic champion. He went to work for Paul MacCready on his unmanned aircraft, meeting Günther Rochelt and flying the Musculair II human-powered aircraft.
From this experience, and with help from Rochelt, Raymond determined to design a solar-powered aircraft. He founded Solar Flight and in 1986 began construction of his design in his 2-car garage, in Lake Elsinore, California. It was built using usual carbon pre-preg, Nomex honeycomb, Rohacell foam, and thin film solar cells. Günther Rochelt sent Raymond the airfoils he used, and taught him the layups. Sunseeker I was partly assembled out on the front lawn. The solar sailplane was never fully assembled until Raymond and his team took it to the abandoned runway in Desert Center, where it made its first flight as a glider in 1989. In early 1990 solar-powered flights were made with two brush motors driving a variable-pitch propeller, and then with a brushless motor driving a folding propeller. In 1990 Raymond flew Sunseeker I with only 400 Wh of Sanyo battery energy across the USA from the Southern California desert, and after 21 flights ended in North Carolina, all the time flying just with natural and renewable energy sources. Two flights, covering 247 miles (398 km) and 249 miles (400 km), involved 8.5 hours in the air. The solar airplane often climbed to 15,000 ft (4,570 m) at about 35 mph (56 kph), but sometimes reached 85 mph (140 kph) on final glide when Raymond was too high. The Sunseeker I went on to break all previous records for solar-powered aircraft.
In 1990, Eric Raymond flew his Sunseeker I with only 400 Wh of Sanyo battery energy across the USA from the Southern California desert. After 21 flights, he ended in North Carolina, all the time flying just with natural and renewable energy sources. Two flights, covering 247 miles and 249 miles, involved 8.5 hours in the air (Eric Raymond).
Raymond recalls: “Since the sun was stronger in the West, as I got further east, it became harder to get up and make progress. In the Appalachians, with only 2.4 kW of climbing power, I was sometimes corralled by the trees around the airfield, flying circuits inside the tree line until I gained some height. I often flew with birds, and the day I crossed the Appalachian ridge, I had 3 birds in tight formation with me when I climbed into the clouds, and they tucked in tight and flew with me the whole time I was IFR.”
Sunseeker II, built in 2002, was updated in 2005–2006 with a more powerful motor, larger wing, 1,953 Wh lithium battery packs and updated control electronics. Sunseeker II’s use of the lithium battery announced a new chapter in the development of electric airplanes. As of December 2008 it was the only manned solar-powered airplane in flying condition and was flown regularly by Solar Flight, using 2,841 Wh of Lipo cells. In 2009 Raymond flew Sunseeker II all over southern Europe, becoming the first solar-powered aircraft to cross the Alps, from Butwill, near Zurich, to Turin, Italy, 99 years after the first crossing of the Alps by an aircraft. In June, at the World Air Games in Turin, Raymond flew the Sunseeker for demonstrations and won a Gold Medal for the best experimental aircraft. He also set two world records for solar-powered aircraft during the event: one for time in the air, the other for absolute altitude, about 20,380 feet (6,211 m).
During this time, China had also been testing its first unmanned solar aircraft. Danny H.Y. Li had had a great longing for flying since childhood. He became a test pilot, piloting different kinds of airplanes, helicopters and gyroplanes. He had twice escaped from airplane crashes during his test flight career. In 1989, he and his friends flew across China with ultralight planes that set the world record for long-distance formation flight. Li obtained his Ph.D. in aeronautics and astronautics at Beijing University. In 1991, Li and Zhao Yong teamed up with Matsushita Electric Industrial Co. to create a pilotless solar aircraft. The body and wings were hand-built predominantly of carbon fiber, Kevlar and wood. The design used winglets to increase the effective wingspan and reduce induced drag. On August 19, 冲天 (Soaring) successfully completed its first flight in northern China. Li and Zhao were granted a patent license from the Chinese State Patent Office to further develop the aircraft.12
Rudolf Voit-Nitschmann, born in 1950 in Eisenach, studied aerospace engineering at Stuttgart University. He then became senior engineer at aerospace companies such as Gyroflug and Dornier, then in 1995 became professor of the Aircraft Institute in Vaihingen. Two years later, a project was launched at the University of Stuttgart to build a practical solar aircraft. Voit-Nitschmann joined the Akaflieg (Academic Flying Group), a team of 45 students, for the project they called Icaré, a combination of the name of Icarus, the hero of the Greek mythology, and Re, the Egypt sun god. With the help of sponsorship of the State of Baden-Württemberg, Icaré II was built. The 12 kW electric motor was mounted on the tail fin so as to increase the efficiency. For the self-launch, a 915 Wh NiCad battery was used, charged by the photovoltaic panels on the wing, enabling the Stuttgart sailplane to rise up to 400 meters (1,312 ft). After the first solar long-distance flight on July 7, 1996, over more than 350 km (218 mi) from Alen to Jena with Rudolf Voit-Nitschmann at the controls, Icaré II won the Berblinger Prize in Ulm for the most efficient solar plane, followed by the EAA Special Achievement Award in Oshkosh, the Golden Daedalus Medal of the German Aeroclub, and the OSTIV-Prize in France in 1997. Increased altitude and range became possible by the installation of lithium ion batteries.
Danny H.Y. Li continued to develop his solar-powered aircraft. During 2000 to 2002, directing New Concept Aircraft (Zhuhai), the China Aviation Industry Development Research Center, and the China Academy of Space Technology, Li developed the Green Pioneer, an integrated-wing solar powered aircraft with optimized aerodynamic design. Green Pioneer made its test flight in 2004.
Another approach was adopted by Alan Cocconi of San Dimas, California, a Caltech-trained engineer. Cocconi had served as an engineering consultant and developed the drive and solar tracking systems for the General Motors SunRaycer car, which won the 1987 World Solar Challenge, a cross-country race for solar-powered vehicles held in Australia. He designed and built the controller for the original GM Impact that was introduced at the 1990 LA Auto Show, and which evolved into GM’s EV-1. In 1992 Cocconi and Wally Rippel founded AC Propulsion specializing in AC-based drive train systems for electric vehicles.
In 2005, to prove the sustainability of solar-powered flight, Cocconi built an unmanned solar glider he called SoLong with the goal of making a 48-hour nonstop flight around-the-clock. SoLong had a wingspan of 4.75 m (15 ft.) and weighed 12.6 kg. (28 lbs.). Power from 76 SunPower Corp. (Sunnyvale, California) solar cells supplied the plane’s energy. Power distribution among the onboard systems was controlled by management software developed by Cocconi. Twelve PIC18 microcontrollers from Microchip Technology Inc., of Chandler, Arizona, controlled and monitored all vehicle systems. Systems under control of the PICs included the autopilot, motor drive, power tracker, six servomotors, the battery monitor, and a tracking downlink antenna. For example, the autopilot controller decoded 13 PWM control signals from the uplink receiver, input serial data from the GPS module, and monitored 23 analog sensor channels.
During daylight flight the nominal 225-W solar array powered all systems and recharged 120 Li-ion cells from Sanyo Corp. The Li-ion cells fulfilled the craft’s energy demand at night. Propulsion came from a high-efficiency electric motor driven by a split-phase power controller developed by AC Propulsion. A variable-pitch propeller fine-tuned thrust for different rpm and power settings using a load cell for in-flight thrust measurements.
An earlier 24-hour test flight showed the original battery reserve couldn’t keep the craft airborne. “We split the first test flight’s night in two, flying midnight to midnight,” said Cocconi. “We were getting enough solar energy during the day but we didn’t have quite enough battery to take us through the night.” The Sanyo cells pack 220 W-hr/kg and have a charge-discharge efficiency of over 95 percent. “That made the difference,” Cocconi stated, allowing the SoLong to pass the 48-hour mark.
SoLong took off at 4:08 p.m. on Wednesday, June 1, 2005, from the sun-baked runway at Desert Center Airport just east of Eagle Mountain in California’s Colorado Desert. It remained aloft until Friday, when it skidded to a stop at 4:24 p.m. after 48 hours and 16 minutes in the air. From the 5 ft × 8 ft (1.5 m × 2.44 m) SoLong trailer serving as ground station, Cocconi and the team of seven crack radio-control and hang-glider pilots took turns monitoring flight conditions from the twenty-three channels of telemetry plus GPS navigation and video downlink data available in the ground station. Nothing, save the flagging energy of its pilots on the ground, kept the SoLong from flying for another two days, or ten, or a whole month! Equipped with a video downlink, SoLong was the first solar electric airplane to take film images from the sky.13
Lockheed Martin’s 240 ft × 70 ft (70 m × 21 m) HALE-D (High Altitude Long Endurance-Demonstrator) was built and tested as a remotely controlled solar-powered UAV airship designed to float above the jet stream at 60,000 ft (18,000 m). Its 15 kW thin-film solar array supplied energy to 40 kWh Li-Po for two 2kW motors. On its maiden flight on July 27, 2011, from Akron, Ohio, the Lockheed HALE-D reached 32,000 ft before a problem with the helium levels cut the test short, forcing an emergency landing in the deep woods of southwestern Pennsylvania. Two days after the landing, before the vehicle could be recovered from the crash site, it was destroyed by fire.
Meanwhile, the Institute of Aircraft Design (Institut für Flugzeugbau) continued to pursue its R&D. e-Genius was built for the CAFÉ 3rd Green Flight Challenge sponsored by Google to be held in late September 2011 at the CAFE Foundation Flight Test Center at Charles M. Schulz Sonoma County Airport in Santa Rosa, California. The design was a converted motorglider using a tailfin-mounted 80 hp (60 kW) electric motor. The e-Genius performed its first 20-minute flight on May 25, 2011. In July 2011 the aircraft flew for over two hours between two points near Mindelheim, Germany, at an average speed of more than 100 mph (161 km/h). During the Challenge, held July 10–17, three aircraft competed and two met the challenge requirements to fly 200 miles (320 km) in less than 2 hours and use less than one gallon of fuel (or energy equivalent) per passenger. The first place prize of $1,350,000 was won by the Pipistrel USA.com team led by Langelaan LLC of State College, Pennsylvania. Second place prize of $120,000 went to the e-Genius team led by Eric Raymond of Ramona, California.
On June 20, 2013, Eric Raymond test-flew his new two-seater Sunseeker Duo from Milan, but with a takeoff tow from his car. On December 17, 2013, he used the Duo’s motor to take off. The Duo has 1,510 solar cells on its 72-ft span (22 m) wing and on its empennage surfaces, plus 8,158 Wh of Li-Po batteries, driving a tail-mounted 16 kW electric motor. During 2014 Eric Raymond and his wife Irena, a fully qualified pilot, took a number of passengers for flights in the Duo. But to go one further, the Raymonds decided to repeat the 2009 adventure of the Sunseeker II, a crossing of the Alps in both directions, this time with the Sunseeker Duo. The mission was to stop and show the airplane at different airports. For the final destination, Munster-Geschinen airfield in Switzerland was chosen: “This is a perfect starting point to explore the Swiss Alps and visit the highest peaks and glaciers. We decided to fly to Torino Aeritalia airport on 2 August 2015 and then continue to Switzerland. On August 3rd, we climbed up the foothills, with low clouds at the base of the Italian Alps. We crossed the high mountains near Zermatt and then detoured to the Aletsch Glacier, Jungfrau, Eiger and Mönch. The distance flown was 384 km and the maximum altitude reached was 4090 m. The battery pack was completely charged after we landed.”14
The weather on August 5 was very promising, so Raymond and his hang-gliding friend Stefan made a flight over the Aletsch Glacier. On August 7, 2015, Eric and Irena Raymond took off for the flight to their home base.
We headed first to the Matterhorn and then direction south, toward Genoa. The flight was very easy in comparison to the crossing of the Alps a few days earlier, in the opposite direction. The weather in the Alps was more than perfect. The Matterhorn just got covered with a cloud cap when we approached it, however, the view on this giant, steep mountain was spectacular. The maximum altitude we climbed was 4,545 m. We could easily go much higher, unfortunately we do not have a dual oxygen system yet. Descending toward the Po Valley the air became hotter and the visibility was poor. After 230 km and less than 4 hours our Sunseeker Duo reached her home base.
The Duo has since been used to train a number of pilots.
At the Sustainable Aviation Symposium held in San Francisco in May 2016, Eric Raymond stated that Solar Flight was ready to build and fly a solar-electric six-seater, called the Observer, based on an Italian design, the Partenavia. The wing is optimized for best aerodynamic efficiency with a large camber changing flap for short takeoff and landing capability. The main power source is a lithium battery pack, but an optional range extender can be fitted into part of the baggage compartment. It consists of a generator running on unleaded auto gas. A ten-seater would follow.
Irena Raymond braves the cold on a winter 2015 flight in Sunseeker II over the Apennine Mountains in Northern Italy. To date she has flown 110 hours in solar-powered airplanes (courtesy: Irena Raymond).
Then there is the Sun Flyer, under development by George Bye of Aero Electric Aircraft Corporation (AEAC) of Denver, Colorado. An engineering graduate of the University of Washington and an indefatigable entrepreneur, Bye has immersed himself in aviation for decades. After earning a bachelor of science degree in civil engineering from the University of Washington, from 1981 to 1993 he was a U.S. Air Force instructor pilot flying Northrup T-38 and C-141B strategic transport, accumulating over 4,000 flying hours in aircraft. Once in mufti, Bye began designing aircraft and developing businesses. In 2005 Bye designed and developed the Javelin Jet, a lightweight category twin turbofan, tandem-seat jet aircraft. In 2007, he created Bye Energy, an engineering services organization, with a special concentration on various unmanned aerial vehicle projects. In July 2010, Cessna announced it was developing an electrically powered 172 as a proof-of-concept in partnership with Bye Energy. In July 2011, Bye Energy, whose name had been changed to Beyond Aviation, announced the prototype had commenced taxi tests on July 22, 2011, and a first flight would follow soon. In 2012, the prototype, using Panacis batteries, engaged in multiple successful test flights.
To further exploit recent advances in battery and solar technology, George Bye founded AEAC in 2014 with the goal of putting an all-electric trainer aircraft into production. Joining him was Charlie Johnson, the former president of Cessna. He then obtained a license agreement and engineering contract with Calin Gologan’s PC-Aero to incorporate the work done in Germany on the Elektra One, which AEAC then modified with new landing gear, prop and instrumentation. The two-seat prototype was installed with the EnstrojEmrax 268 high voltage electric motor, rated at 100 kW and 400 volts nominal supplied by four Panasonic lithium-ion battery packs and solar panels on the wings and the horizontal tail and behind the canopy. A regenerative propeller is also used. The solar panels energize the batteries whenever the sun is shining, whether the plane is in the air or on the ground. This brings over three hours of endurance and a 30-minute recharging time. To enable this swift recharging, Sun Flyer partnered with the Bloomington Corp. of Orlando, Florida, now working on a national network of battery charging stations. Alternately, for more advanced flight schools, it is possible to replace depleted batteries with fully charged ones in a matter of minutes. When a line-up of Sun Flyers is parked on the airfield, they can use their solar panels to supply electrical energy to the local grid. Sun Flyer will use broadband and iPad connectivity as part of a high-tech flight training system to enhance the student pilot-instructor experience. The Redbird Flight Simulations Sidekick will keep track of motor parameters, as well as flight time, airplane position, attitude, and landings, and wirelessly transmit the data to the flight school or ground station where the operator can track it via Redbird’s customizable Sidekick software.
Flight schools seriously need this product. In May 2016, AEAC hosted a rollout event of its proof of concept (POC) Sun Flyer, built by Arion Aircraft of Nashville, Tennessee, at Centennial Airport. Performance data from the POC prototype airplane would be used to help finalize the design for the FAA-certified production version. During late 2016 the POC was put through extensive ground testing. Following 10 deposits received for the electric airplane unveiled at EAA AirVenture Oshkosh, in September 2017 AEAC gave a ground test to their POC, registered N502. Spartan College of Aeronautics and Technology and a local flight school signed for the first 35 Sun Flyers. In addition, a Centennial Airport–based school, Independence Aviation, also just recently signed on. Bloomington Corp. ordered 30 Sun Flyers. An agreement was also signed with the Aero Touring Club de France, based at Toussus le Noble, to purchase Sun Flyers for their club.
Bye referred to Boeing’s estimate that 533,000 commercial pilots will be needed by 2033, and that with the current training fleet being 40 years old, something has to change. Bye noted the high cost of flying, the high demand for new pilots, and the need for an answer to these problems, and then asked, “What is the solution and how do we get it?” Cessna delivered the first 172s in 1956. As of 2015, Cessna and its partners had built more than 43,000, a large number for pilot training.
For those pilots training to fly the new generation of electric airplanes, all-electric flight simulators, more energy efficient and easier to maintain, are already the standard. Recall how in 1929 J.P. Buckley patented an electrically driven aeronautical instructing device (or flight simulator) for pilots of biplanes. The first manufacturer to tap improved electric technology and apply it to flight simulation was Moog Inc. of East Aurora, New York. Moog presented the concept of all-electric motion systems for full-flight simulators with several FFS manufacturers that already used Moog’s high-performance servo valves in their hydraulic motion systems. In 1994, Moog engineers had designed and tested their first 4,500 kg (10,000 lb.) electric platform. But going from hydraulics to electric actuation posed a number of engineering challenges—among them, handling heavier payloads, providing smooth motion, ensuring safety, and preventing unwanted noise. Moog teamed up with Ron Jantzen and Niddal Samur of Flight Safety International of Broken Arrow, Oklahoma, the world’s premier professional aviation training company and supplier of flight simulators. This involved the development of 36- and 60-inch actuators, a 12-pole, brushless servo-motor with custom rotor and stator design to deliver 5,600 lb.-in (633 Nm), and motion control software. The work paid off, and in May 2006, the FAA granted first Level D Certification to the first all-electric high-payload flight simulator. Since then adoption of all-electric FFSs has grown quickly. Civil Aviation Training magazine recently noted there are 1,150 FFSs in use around the world built by companies such as FSI and CAE in Montreal, Canada. Of the motion-control solutions for flight simulators now being built and sold, industry experts say more than 85 percent are electric.
A second AEAC airplane envisaged by Bye is the graphite composite solar-electric StratoAirNet, with solar cells on its 15-m (49-ft.) wing, supplied by SolAeroTechnologies. It will be used as a prototype for a medium-altitude, multi-day persistent unmanned aircraft. In August 2017 SolAero Technologies Corp (SolAero) delivered the first solar wing for the StratoAirNet. The initial wing-solar cell configuration will deliver sufficient power, approximately 2,000 watts, under suitable daylight conditions at altitude. The Bye Aerospace StratoAirNet family of “atmospheric satellites” are intended to provide support for commercial and government security requirements. Final assembly and integration of the wings and power systems began in November 2017, with ground and flight tests to follow from Bye’s new facility at the Northern Colorado Regional Airport.
On July 23, 2017, at EAA AirVenture, AEAC announced plans for a four-seater pure-electric airplane, Sun Flyer 4, with an autonomy of four hours. In addition, Spartan College of Aeronautics and Technology was the first flight school to hold a deposit for a Sun Flyer 4. The two-seat Sun Flyer, Sun Flyer 2, will be the first FAA-certified all-electric trainer aircraft under FAR Part-23. The new four-seater will closely follow the certification of the two-seat version. Features of the Sun Flyer 4 included a 46-inch cabin width, 38-foot wing span, ballistic parachute recovery system and a gross weight of 2,700 lbs., with a full 800 lbs. of payload for pilot and passengers.
Not related in any way to solar power, in March 2017, Bye Aerospace also allied itself to XTI of Denver to develop a hybrid/electric prototype of XTI’s revolutionary TriFan vertical takeoff airplane. Transmission, gears, two large heavier engines, and other components would be replaced with electric motors, batteries, generators, and a single smaller turboshaft engine. The TriFan 600 is designed to travel at over 300 mph (480 kph), with a range of over 1,200 miles (2,000 km). Using three ducted fans, the TriFan would take off vertically, and then its two wing fans would rotate forward for a seamless transition to cruise speed and its initial climb. It would reach 35,000 feet (10,000 m) in just ten minutes and cruise to the destination as a highly efficient business aircraft.
In 2012, Anne Réale, a painter and writer, with Thierry Vigoroux, journalist and pilot, published De Glace et de Lumière (Of Ice and Light) with Editions Pascal Galodé, an adventure novel about a solar-powered amphibian that takes off from the French Alps, crosses the Atlantic, and lands on the Greenland glacier. The authors may have been inspired by the Hy-Bird, a solar-powered hydrogen fuel-cell amphibian, with foldable wings as projected by Erick Herzberger of the LISA Aeroplane Company in Savoy, France, at the side of Lake Bourget. The plan was to fly it around the world, landing on land, water and ice. Such an electric aircraft is still to be built.
Another e-airplane, which on June 10, 2016, was test-flown for ten minutes in the skies above Calverton Air Base, New York, was the solar-wing-powered Luminati Aerospace VO-Substrata prototype, with Robert Lutz at the controls. After the flight, Lutz described the flight as “very birdlike. You feel like you’re in the environment up there with the creatures. Hawks will be circling around, and they kind of flock to you. It’s the only aircraft I’ve ever flown where I can hear a helicopter next to me. It’s a little spooky but pretty cool.”
The Luminati project was to manufacture a fleet of manned and unmanned aircraft for perpetual, solar-powered electric flight in the stratosphere, as a platform for commercial Internet and government ISR (Intelligence, Surveillance, and Reconnaissance) applications, also to provide aerial Internet service for an estimated four billion people worldwide. The founder of Luminati Aerospace, Daniel Preston, brought together an “enlightened” team of engineers, professors and advisors from MIT, UIUC, and Georgia Tech, leading industry professionals, and visionary technological advisors such as Dr. Anthony Calise, former professor of aerospace engineering at Georgia Tech. Their prototype airplane was based on a modified “Elektra One Solar,” bought from the German company PC-Aero, with its four-hour flight autonomy, but with its aileron span increased, wing flaps excluded, and rudder chord slightly increased. In 2015, Luminati Aerospace paid $3.4 million to acquire the old Calverton Air Base, 16.3 acres (6.6 hectares) of land on Long Island. In June 2017, it was announced that Luminati was searching for new sponsors after ties with its earlier backer, Facebook, were severed. To buy the sprawling Enterprise Park at Calverton, an approach was made to John A. Catsimatidis, Greek-American billionaire. The departure of key members of what Preston called his team, and revelations about the startup founder’s past and current legal troubles, have cast doubt on his ability to fulfill his promise to bring the defense aerospace industry back to Calverton.15
Although still in the embryonic phase, the solar helicopter now exists. After successfully completing the longest duration flight for a human-powered helicopter in fall of 2013, the University of Maryland Gamera Team, a student team originally inspired in 2012 by the American Helicopter Society’s Sikorsky Prize, has continued raising the bar. In 2014, a new group of undergraduate students took over Team Gamera, reinventing itself as Solar Gamera to test the feasibility of applying solar power in achieving human helicopter flight. Solar Gamera is powered solely by four banks of solar panels, with lift provided by four sets of rotor blades. It measures 100 ft (30.5 m) square. On August 26, 2016, it successfully carried a passenger, the lightweight Michelle Mahon, over one foot (0.3 m) into the air, staying airborne for nine seconds. According to the team, once its electronic control system is better able to compensate for drift, that duration figure should rise significantly.16
If ongoing progress with solar cells is observed, solar airplanes and UAVs have a promising future. From 2009, the University of Washington’s Multidisciplinary University Research Initiative (MURI) project team, with lead researcher Dr. Minoru Taya, has been working on the airborne solar cells and found that dye-sensitized solar cells made from organic materials, which use dyes and moth-eye film, are able to catch photons and convert them into synthesized electrons that can harvest high photon energy. As an optimum energy-harvesting source, DSSC may lead to longer flight times without refueling.
Alta Devices of Sunnyvale, California, made up of scientists from Caltech and the University of California, Berkeley, have developed the flexible AnyLight™ cells to give as much as 5 times more daytime endurance, and at one gram per watt of power, with virtually no impact on aerodynamics. Based on gallium arsenide (GaAs) which is a III-V semiconductor with a zinc blende crystal structure, Alta’s units hold single- and dual-junction solar efficiency records at 28.8 percent and 31.6 percent respectively. AnyLight has a solar cell thickness of 110 mm, a mass of only 170 g/m2, and the ability to bend to cover curved surfaces. Equipped with AnyLight cells, in March 2008, an AeroVironment RQ-20 Puma UAV, which normally has an endurance of 2 to 3 hours, flew for 9 hours 11 minutes and 45 seconds.
More experimentally, Martin Kaltenbrunner, Niyazi Serdar Sariciftci, and Siegfried Bauer of the Department of Soft Matter Physics, Johannes Kepler University, Linz, Austria, have shown perovskite solar cells just 3μm thick can power miniature model aircraft for several hours. Plastic foil substrates and chromium oxide interlayers are used in a novel technology that combines high efficiency, low weight, and extreme flexibility in a single platform. For these tests, they powered a 4.8 g model airplane with a 58-cm (23-in.) wingspan with a 3μm-thick, 5.2g/cm, light solar panel (with 64 individual cells) on the tailplane and flew it on a sunny winter afternoon above the campus of Johannes Kepler University. A lighter-than-air model blimp and a “solar leaf” were also tested. These three aeronautic models were still fully functional more than six months after their initial flights. In their future research, the Koblenz team plans to focus on realizing perovskites with improved efficiency and moisture resistance, by exploring electrode transport materials, alternative metals, and superhydrophobic coatings. They suggest their design could initially find applications in robotic insects and drones.17