This week we brought the Sunseeker Duo to AERO Friedrichshafen for its public unveiling. The airplane is fresh out of the paint shop, and since it is too large to fully assemble in the Slovenian workshop, it is also the first time that we got to see the airplane in its full glory!

AERO is always a special event, a convergence of the best sport aviation manufactures and many interesting projects in development, this year was especially good. Not only do we have a new airplane to show - we were treated to the central display space at the main entrance.

Today we assembled the major components of Sunseeker Duo out on the ramp for the first time. There is a lot of work left to do, but it is encouraging to see the ship start to look like an airplane! Compared to the original Sunseekers, the Duo is a giant. The switchblade function of the wings reduce its footprint to a managable size for hangar storage.

The Sunseeker Duo is truly an international effort. Consider that the fuselage was molded at Allstar Gliders in Poland. With extensive support from Germany and Slovenia, the project is gathering momentum. Construction moves ahead, with high quality parts as the rule.

Here we introduce the engineering effort on the nose gear from our friends in Santa Paula, California.

The nose gear is a crucial assembly, requiring shock absorbtion, steering, and retraction, all in a reliable light weight package. Rick McWilliams (http://www.tangentinstruments.com/) designed the trouble free nose gear for the Mermaid amphibian, so he got the job of designing our nose gear under very demanding weight and space constraints.

Partnered with him is John Lynch, whose shop is also at the Santa Paula Airport, to turn the computer files into parts. While most of the parts of the new plane are composite, this assembly will utilize aluminium. The shock absorber is integrated co-axially into the strut to save weight. A carbon pre-preg fork will be tested with the assembly, attaching to the nylon wheel.

We are making good progress on the wing at the moment. Karl Kaser leads the engineering team starting work on the center section and main landing gear.

The campaign to build the fuselage was completed at the Allstar Glider factory in southern Poland. Andrej Papiorek, the owner. helped us with materials and construction techniques, not to mention full use of his well equipped workshop.

Many parts, and the molds themselves are provided by Stemme GmbH. The window is from Mecaplex in Switzerland, and was installed by experts in Poland, a tricky job!

The fuselage is molded from carbon fiber, with 100% Nomex honeycomb sandwich.

Roman Susnik brings to our attention the housing for the new motor he is developing.

After a successful hang gliding career and constructing several of his own gliders Eric Raymond was invited by Rochelt to fly his human powered airplane, Musculair II. Musculair II was groundbreaking in its simplicity and to this day remains the fastest human powered aircraft ever built. With Rochelt's encouragement, Raymond conceptualized the original Sunseeker. The configuration was based on that of Musculair II and Rochelt passed on the novel construction techniques that he used to acheive phenomonally lightweight, yet robust structures.

In addition to the series of human-powered airplanes, Rochelt built two significant solar-powered ships. Solair 1 was based on a Hans Farner canard design. It employed 2499 wing-mounted solar cells giving an output of between 1.8 and 2.2 kW. The aircraft first flew at Unterwössen, Germany on 21 August 1983. It flew for 5 hours and 41 minutes. The airplane is now displayed at the German Museum in Munich Rochelt's second solar-powered airplane, Solair II, made its first flight in May 1998 and further test flights that summer, but the propulsion system overheated too fast and development stopped when Günther Rochelt suddenly died in September 1998. More information about Rochelt's many projects can be found at solair.de

Solar Flight's efforts are dedicated to the memory of Professor Günther Rochelt.

Solar flight was established to further the development of solar powered and electric sport aircraft. Eric Raymond's dream of solar powered flight began in 1979, when Larry Mauro demonstrated his solar powered ultralight glider, named Solar Riser. 1981's debut of Paul MacCready's Solar Challenger added credibility to the concept. The revelation, after flying Günther Rochelt’s Muculair II, that a fast, streamlined aircraft could be built for incredibly low weight was the impetus that led to the construction of the Sunseeker. Design of Sunseeker I began in 1986. Progress was slow until 1988, when support was found in Japan. With the help of several corporate sponsors. Sunseeker I was test flown at the end on 1989 as a glider.

In early 1990 battery powered flights were made with two brush motors driving a variable pitch prop, which could be feathered for gliding. The motor and prop mechanism were not satisfactory, so an A.C. brushless motor and a folding prop were installed.

Across America

Solar Flight’s first airplane, Sunseeker I, was designed for a mission to cross America, a feat it accomplished during the summer of 1990. The expedition began in the Southern California desert and with 21 flights ended in a field near the site where the Wright Brothers first flew.

"With average conditions, I could cross about one state per day, with the first landing being just northeast of Phoenix AZ, after an 8 hour flight.

At my slow flying speed, I often flew in formation with flocks of birds. Nearing the Appalachian Mountains, I flew with the same three black birds two days in a row. They were still following me when I reached the highest part of the mountain range that I needed to cross. I decided the safest thing to do was to fly up through the clouds, so I could fly over the tops of all the clouds and mountains.

I switched on my simple blind flying instruments, but even with my head down, I noticed the three black birds, hovering just above and to the sides of my window. The thicker the cloud, the closer they stayed, but they never left, until we were in the clear again."

• Eric Raymond

It was the first crossing of the United States made by a solar-powered airplane; an affirmation of the technology's potential and a milestone in aviation history.

The Edelweiss was the second airplane produced by Solar Flight. It was built in response to a debate as to whether it was possible to construct a high performance sailplane that weighed less than the ultralight category weight limit of 154 pounds. AlthoughSunseeker I was initially flown as a glider with an empty weight of only 100 lbs, it was considered too fragile to be practical. More durability was built into the Edelweiss, with less wing span for better maneuverability and a higher top speed. It is designed for a top speed of 120 knots and is fully aerobatic. One of its design features is the inclusion of water ballast tanks in the wings, capable of carrying 150 lbs of water. The wings were load tested to 6.6 g before flight testing.

In 2006 many improvements to the original Sunseeker were completed. The new airplane, dubbed Sunseeker II, featured a redesigned wing with more area for solar cells, a more powerful motor, new lithium polymer batteries, and an updated electrical system. In 2009, again with Eric Raymond in the cockpit, Sunseeker II completed a vast flying tour of Europe. The tour began with the first crossing of the Alps ever made by a solar powered airplane and continued down the length of Italy to Sicily, followed by a route along the Dolomites through Austria and Slovenia, and finally a journey through the South of France and Spain ending at Spain’s southern coast.

Sunseeker I and II have logged, by a huge margin, more flight hours than any other solar powered airplane. The Sunseeker, unlike other solar powered aircraft that have been flown in ideal conditions under strict ground supervision, is the only solar powered aircraft to have been tested and proven in continuous real world operations.

First Alps Crossing

99 years after the first crossing of the Alps in an airplane by Geo Chávez flying a Blériot XI, Eric Raymond completed the first crossing of the Alps made by a solar-powered airplane flying Sunseeker II.

"It was one of the most difficult things that I have ever done, but it was also the most beautiful flight I have ever made. It was very cloudy, but after fighting to gain altitude I got over the clouds and cruised on direct solar power, eventually climbing to 13,700 ft. It was amazing to see the peaks of the mountains coming upthrough the clouds. I could clearly see the Matterhorn and Mt Blanc over the clouds. I could not see anything in the direction of Italy, except a solid wall of clouds. I tried to climb over them on course for Torino, but I had to fly between towering cumulo-nimbus clouds. I was in bright sun, when I noticed that I was flying through large snowflakes. That was the first sign of trouble. Soon I was trapped over these rising clouds, with my escape closed off. I was climbing at full power, but the clouds were rising faster. It was snowing on me, even though I was in the sun! Desperately flying around in my shrinking trap I found a small hole, where I could see the ground. Just snow and trees. I turned off the motor, set the airbrakes, and spiraled down 7000 ft, until I was just under the clouds. I wanted to take a picture of the snow, but I couldn’t take my hands from the controls. After feeling desperate about flying through clouds in a blinding snowstorm, I felt much better seeing that the clouds did not go all the way to the ground. I even flew with a sailplane and a paraglider, so I did not feel so alone. Because of the thunderstorms, I left the Alps early, and had a long crossing over the Italian flats. It seemed to take forever to get to Torino, but in reality the entire flight took less than 5.5 hours. TV crews were waiting, and we saw the story on the national news that night in our hotel, just before a nice dinner with our hosts, the organizers of the World Air Games 2009. We are now preparing to continue down the length of Italy, to Sicily."

• Eric Raymond