Sunseeker Seeks New Records
By Bill Moore
Imagine flying an aircraft whose power-source is 93 million miles away. An aircraft so clean that it generates no air pollution and little noise pollution.. And according to its creator and pilot, birds often soar within a few feet of it.
You don't have to imagine. It's very real and its creator and pilot is not unfamiliar with the electric vehicle industry. AC Propulsion's Alan Cocconi, the engineering genius behind the tzero and other electric automobiles, contributed to the development of Eric Raymond's solar-powered sailplane, the Sunseeker, the first solar-electric aircraft to fly across the North American continent. The trim and tanned Raymond also has flown Aerovironment's Solar Challenger. He's even been at the controls of the current record holder for the fastest -- at less than 35mph -- solar aircraft, one developed in Munich, Germany.
Raymond told EV World that it was the Germany aircraft, which weights a mere 52 pounds and requires only 250 watts of solar-energy to keep it airborne, that inspired him to eventually build his own solar plane, the Sunseeker. His experiences with both of these early airplanes equipped him with the necessary skills and insight to build a plane that could fly cross-country, west-to-east. He points out that Solar Challenger was the first machine to run entirely off of its photovoltaic cells, instead of its batteries. However, it could only fly heading north during the noon hour because it had to keep sunlight falling on its large, broad wing or risk losing power. Still, it proved it could be done.
"My design was a complete departure from anything that had been done previously," Raymond explained to me. "I made a very small wing, which could only generate enough power for level flight. The idea was to take-off on battery power, then to transition to thermal lift or on continuous, sustained mode on photovoltaics."
His efforts attracted the support of Sanyo, who provided him with experimental, amorphous, thin-film solar cells, which in 1990 were only about two percent efficient at converting sunlight into electric power. It wasn't as much as Raymond would have liked, because it would require more surface area on the parasol wing he was envisioning, but in his words, Sanyo's "publicity machine was cranked up." This compelled the Californian to keep his sailplane idea moving forward although he had to give up on managing sustained flight on sunlight. Instead, he'd take off on battery power and soar until the PV panels built into his long, thin, parasol wings could recharge his NiCad batteries.
Since his 1990 transcontinental flight -- which still remains the record -- Raymond has built a new wing that incorporates monocrystalline silicon cells efficient enough to generate 1,800 watts of energy. He noted that he only needs about 1,100 watts to maintain sustained flight in Sunseeker.
Flying on solar power across North America was not Raymond's first objective; he had much grander plans in mind: a solar flight around the world, but the technology just wasn't available a decade and a half ago. When he isn't hang gliding or dreaming of world-girdling solar sailplane epics, Raymond works at Aerovironment, Dr. Paul McCready's R&D firm; they're the folks who built the first human-powered plane to cross the English Channel and the prototype of the EV1 electric car. Raymond tells me that his colleagues now think an around-the-world flight is now possible... barely.
It's the "barely" part that I think intrigues Raymond the most, but he now has competition in the form of the Solar Impulse team in France who have a large, two-place machine on the CAD system. What Raymond needs to beat them is some deep-pocket sponsors, but in the interim, he is working on perfecting a solar wing skin system that can be seamlessly integrates the photovoltaic cells into a super-smooth, laminar airfoil.
Thoroughly Modern Icarus
Sunseeker is constructed out of ultra-light, carbon-fiber bonded with high-temperature resins, unlike most other carbon-fiber, "plastic" sport planes built today, which use low-temperature resins. While the later is easier to work with and lets hobbyists build high-performance, sophisticated aircraft, it is unsuspecting to heat, in large part because the carbon fiber framework is jet black and can get very hot in the sun, causing low temperature resins to soften and delaminate with potentially catastrophic consequences. Raymond explained to me this is why carbon fiber sport planes are almost invariably painted white, in order to keep down the temperature of the underlying material.
In contrast, and at substantially higher cost, Sunseeker's carbon-fiber components have to be baked in a special "oven" in order to cure properly. The oven for one wing is twenty-four feet long, so it's not something the average hobbyist can afford to build or acquire, which is part of the reason Raymond hasn't followed the lead of other sport plane designers in offering plans and/or kits for the Sunseeker or its non-solar, ultralight sailplane successor, Eidelwess.
The finished empty weight of the aircraft is a mere 100 pounds (45.3 kg). Include the complete instrumentation package, a ballistic parachute for safety, 35 pounds (15.8 kg) of NiCad batteries, 1,800 watts-worth of solar cells that completely cover the top of the wing, fuselage and horizontal stabilizer, and a 2.5 hp brushless DC electric motor plus a folding propeller and the ship still weights under 200 pounds (90.6 kg). Raymond admitted that while the Sunseeker conforms to European sailplane specifications in terms of its flight loading (6.6 Gs), he did eliminate what he calls some of the "garbage" loads in terms of structural reinforcements that make the vehicle less susceptible to damage during landings, take-offs and ground handling. From that perspective, Sunseeker is more fragile than the average sailplane.
While Raymond's technology might seem cutting-edge, he tells me that it really isn't. Pointing to the solar cells on this plane, which are more efficient than the original Sanyo cells on this first flight, he had to shop around for the best price since he is funding the project entirely on his own now. He tells me that even if someone gave him a million dollars worth of the more efficient solar cells available, it would still take a lot of work -- and money, presumably -- to tie them all together using the correct diodes, one for each cell.
Surprisingly, Raymond isn't working on Aerovironment's own solar aircraft program, the largest version of which, called Helios, crashed off of Hawaii last year, leaving its smaller prototype, Pathfinder to continue the research on what's left of government funding. Instead, he works in the Monrovia, California-based company's unmanned aerial vehicles (UAV) program under a Pentagon contract, developing very small, remote controlled reconnaissance aircraft.
Once being a licensed private pilot -- I haven't flown a plane myself in years -- I have to admit my envy of Raymond. I find sailplanes one of the "sexiest" machines ever invented by man, so I ask him to tell me what its like to fly a machine that gets all its energy from sunlight.
He says that it handles very well, but its also very, very slow. It has a wing-longing of three pounds per square foot and flies at between 30 and 35 mph, slow enough for curious birds to fly in close formation with him. He has gotten it up to nearly 100 mph in a shallow dive towards an airport. Going fast isn't what Sunseeker or Raymond are all about. He tells me that one of the great joys of this plane is flying with his canopy open, made possible by a special mechanism he invented, as well as the aerodynamics of the parasol wing. He says can almost reach out and touch the birds that soar in for a closer look. He half suspects they want to land on Sunseeker, but it hasn't happened yet.
AC Propulsion's experiments with off-the-shelf lithium ion batteries in the tzero haven't been lost on Raymond. He tells me that his friend, Alan Cocconi, is willing to put together a lithium-ion pack to replace the original NiCads that are still in the sailplane, but Raymond says he's a bit reluctant to commit just yet because the technology is improving so quickly. It seems to him that they are getting about 25 per cent better every year. Right now, lithiums have ten times the energy density of the NiCads he presently uses.
"If you're spending your own money, it's hard to know when to buy something like this," he comments. "I'll be kicking myself a year from now when I have obsolete batteries."
For the moment, he's content to stick with the NiCads, in part because Sunseeker is meant to be a solar-powered airplane, not a battery-powered one. He notes that the Germans are focusing on the latter because they have to contend with less available hours of direct sunlight than in the sun-drenched American southwest.
The original, record-setting flight from California to Kittyhawk, North Carolina, home of the first heavier-than-air powered flight, took place in an atmosphere Raymond calls a "media circus." It took him twenty-one flying days and just over 100 hours of actual flight time to complete the more than 3,000 mile journey in what he considers "sub-optimal" weather conditions into a predominately easterly wind. (Winds across America tend to blow west to east, not east to west). At one point, Raymond and his small support crew in a pair of vans and a chase plane, were grounded in southern New Mexico for a week while the winds blew at 20 mph out of the east.
During the journey he set several other records for a solar-powered aircraft including altitude (more than 16,000 feet), distance on a single leg of 249 miles, and duration in the air of eight and a half hours. Unfortunately, all are "unofficial" because the Fédération Aéronautique Internationale, which administers aviation records, hasn't set up a separate category for solar or electric-powered planes. Raymond attributes this to a lack of a precise definition of what is a solar-powered aircraft, which could potentially include numerous, subtle permutations. To be technically accurate, Raymond notes, the Sunseeker, as it was flown on its 1990 record attempt was a "an electrically-powered, self-launching sailplane with an onboard solar charging system."
Raymond emphasizes that at no time did he every charge Sunseeker's batteries from the power grid, although the Sanyo engineers who accompanied him on the ground did bring along some extra solar panels they could deploy on the ground just in case the batteries depleted overnight.
Instead, Raymond and his crew would have breakfast, usually out at the airport and watch for thermal activity over field, typically soaring birds that indicated an updraft. He'd take off on battery power, which gave him 12-15 minutes of run time, and then hit the thermal and slowly begin to gain altitude by flying tight circles inside the rising column of air. Sometimes he'd begin his turns just two-wing spans above the runway, admittedly breaking federal laws; but airport operators where cooperative and let him get away with, often halting their normal flight operations to let Raymond get enough altitude to fly to the next thermal and eventually out of their airspace.
"Sometimes I was up and way very quickly," he explains, adding that in Missouri he flew more than 100 miles below 1000 feet because there just wasn't enough thermal lift, forcing him to fly around radio masts. "There were times when I flew with no food, no shoes, because I was trying to keep it as light as I could just to get across the country. We knew the aircraft could do it, but it was close.
In still air, Sunseeker's 2.5 hp electric motor gives it a climb rate of 150 feet per minute, but Raymond says he never flew it in those conditions because it would have been pointless, especially when normal summer heat convection can create thermal updrafts with ten times that rate.
The motor not only came in handy during morning take-offs, but while crossing zones with little thermal updraft activity like forests and lakes, or on his first day from California to Phoenix, Arizona while crossing the Colorado River. In the evening, after a day of soaring had let the batteries recharge, he'd use the motor to extend his glide to just one more airport further east. When the motor wasn't be used, the propeller on the tail, folded back to eliminate its drag.
Raymond's flight took him from the sunny Southwest where he estimates he covered about a state a day, anywhere from 150 to 250 miles per day, across Tennessee and the Appalachian Mountains where he found the sunlight less intense and the distances harder to cross. Here it was harder to gain enough altitude to cross the mountains and he found himself doing as many a colonial pioneer had done, threading his sleek sailplane through the Cumberland Gap rather than over it.
After his record setting flight, he bought a two-place German motorglider and started a commercial flight service. Ever-enamored by his love affair with electric flight, he's endeavored -- without success -- to convince NASA officials to fund a conversion of this machine, considered the best motorglider in the world, to solar electric power as a demonstration of what can be done with the technology. Given the advances in solar cells, batteries and electric-drive technologies, not to mention the high cost of fuel, the time may be right, though the funds may have to come from sources other than NASA.
In the meantime, Raymond also dreams of solar-powered airships, a design of which is also on his web site. He notes that the first two powered flying machines were airships and the Wright glider. He foresees the natural evolution of modern solar flight following a similar pathway, though he admits that airships are a hard sell ever since the Hindenburg disaster in 1937. And unlike his little sailplane, which he could finance on his own, a huge airship will require a major government-business partnership, like the recent Lockheed proposal to build a solar airship for surveillance purposes.
Sky's the Limit
Although Sunseeker has more energy-productive solar cells, the rest of its technology is still a more than a decade out of date. According to Raymond, it is the Germans who have picked up the "ball" when it comes to solar-electric flight, and are running with it. His fear is that because of America's lack of interest in this pursuit, that it is fast becoming a technological "backwater," comparatively speaking.
The German system incorporates state-of-the-art lithium ion batteries with smart charging circuitry to prevent "run-away" overcharging that can cause the batteries to catch fire. This is packaged with a 45kW brushless motor, significantly more powerful than Sunseeker's modest 2.5 hp. He estimates that when mated to high-performance photovoltaic cells, the machine could remain airborne 5-6 hours.
Raymond envisions that someday all small aircraft will incorporate solar cells in their wings, if only to eliminate the aircraft generator. He says there are quite a few light, sport aircraft that don't carry generators in order to save weight. This is why he continues to work on perfecting his solar wing skin. He sees this technology as a way to greatly improve the reliability of an aircraft, much the way EV-proponents see electric cars as being much more reliable than complicated internal combustion engines.
Sound improbable? Not to Raymond who is convinced it will happen; it's only a matter of time.
"It's absolutely assured that it will happen. I am amazed that it's taken this long, because I started on this line of thought in 1979. There's been so much progress in other fields, and so little in this field," he laments.
Most electric car enthusiasts have often asked the same question.
He anticipates that eventually commercial airlines will use a propulsion system based on unducted fans, what are essentially very efficient propellers that lend themselves nicely to electric motors. The question then, as always, is the power source. Many might assume that this where fuel cells might come in, but Raymond tells me that none of his colleagues at Aerovironment who have actually worked with fuel cells to power their Helios solar aircraft believe they will be ready anytime in the foreseeable future to power an aircraft.
Instead, he sees far more promise in the near term in lithium ion batteries. He saving his pennies at the moment to buy a pack of lith ions to equip Sunseeker for yet another record breaking flight, this one of 1000 miles nonstop. He hopes the publicity from that event will help him keep alive his dream of solar-powered aviation.