The elfin Story

Success is the glory of the effort

The innovative e-motor glider Stemme elfin is the advanced-career masterpiece of Reiner Stemme, a resourceful plane designer and lifelong aviation enthusiast

Reiner Stemme’s latest aircraft is once again sleek and technologically forward-looking. Still, pushing forward the root concept of the elfin, a cutting-edge electric motor glider, spanned almost the entire professional life of its German inventor. His vision of a glider capable of taking to the skies by own motor power, as well as for a plane suitable for relaxed “safari” tours, brought Stemme into developing aircraft as a young man. Hence some unique features of the elfin model, the retractable propeller, foldable wings or side-by-side cockpit, had their debut already in a legendary precursor – the STEMME S10 motor glider that, since launch in 1990, became a aeronautical household name for its outstanding technology and performance.

So, even if the new e-powered plane might bring another revolution to glider flying, it is built on  technologies that where carefully iterated over decades by one of Germany’s most prolific aircraft designers. At age 81, the evangelist Stemme still stands by his trademark battlecry “mankind needs wings” he coined as a little boy. Born into a technology-minded family, the three words became his creed once he found himself parked by his elder brothers on top of a wardrobe so that he couldn’t take part in their “prototyping” of all sorts of apparatuses made from cardboard, paper, straws and glue. The awkward feeling, not being able to overcome gravity, fanned his urge to turn aeronautical dreams into reality. “Believe it or not – it was my career-building moment. I was five years old. From then on, I wanted to be involved in designing high-performance aircraft, nothing else”, he recalls now sitting behind his desk at RS.aero’s headquarters at Schönhagen airfield in Brandenburg, Germany.

Truly innovative glider designers hang on to their visions from young age

The path from the child with a knack for technology, growing up in the sleepy 1950ies German town of Philippsthal, to the mild-mannered octogenarian launching his latest aircraft model for a global glider audience, resonates in many ways with the careers of other modern-day tech innovators. “Being stubborn, setting your determination, visions and energy against the unavoidable wall of sceptics, was as powerful for getting things done, as it is today. Such uncompromising attitude can raise the enthusiasm and, not to forget also the funding, you need from other people to bring entirely new aircraft types to market”, Stemme says. “I also know how much I owe to the numerous loyal investors and aviation enthusiasts who cash my projects for decades now – I hope the results and the success we have in the markets is a pleaasing dividend to them.”

Like other contemporary breakthrough innovators, Stemme too passed critical milestones at a tender age while taking risky turn-offs in his later career. Building model planes from early childhood, Stemme was only a teenager when he put together his first real aircraft during the off-time hours from his apprenticeship as a fitter in the local potash plant. Being one of the youngest members of the newly-founded aeroclub Segelfliegergruppe Kaliwerk Hattorf, he reached for the blueprints of a Rhönlerche, a well-known German aircraft model designed by Alexander Schleicher. “Building this type of glider, I learned a lot about every aspect of aircraft construction. I took my first pilot training on this self-built plane at the age of sixteen. So I knew it inside out”, he recalls.

Where cold war collides with hot developer enthusiasm, pragmatism results

Feeling still limited in his options, Stemme made the most of the financial tailwind his siblings offered for further education. He took evening classes, earned a high school degree and capped his educational sprint with an MA in physics from the prestigious Berlin Technical University (TU). “Analysing nature at fundamental levels, gives you also a deep understanding of what you need to know for designing aircraft”, Stemme says, who earned his formal glider license in 1963 after joining the Akaflieg Berlin, the TU’s glider club where student members honed their skills as aircraft innovators. There, he spent as much time as possible at the controls in glider cockpits. Pursuing his passion helped him to find out as much as he could on different airframes‘ behaviours in different thermal and weather conditions.

“Flying was far from an easy undertaking in the cold-war days. The airspace above West-Berlin was open to allied aircraft only. We had to decamp to a little airfield near Celle in West Germany to gather experience, study various aircraft types and learn”, Stemme recalls. The Akaflieg club was well known for building self-designed prototypes at advanced technological levels. Conducting the necessary research during the dark winter days, its members tried to maximize their flying hours in the summer. This unique environment of flying, testing, researching, designing and adapting sailplanes with other enthusiasts,  shaped Stemme deeply. “It gave me the self-confidence to really see what is feasible in glider construction and to eventually come up with my own designs and features. I can safely say: the elfin is still benefiting from my time at Akaflieg”, he says.

Flying propelled and in soaring mode with one aircraft resolves ‘Hirth’s dilemma’

From the start of his design career Stemme was convinced that Wolf Hirth’s 1930’s dream of recreational cross-country flying in a high-performance glider would sooner or later become reality. The vision of Germany’s ‘godfather of gliding’ could come true with an airplane that ties powered flying to excellent soaring capabilities, Stemme reasoned. “In those days solutions fell into two categories. You would either extend the wings of a powered plane to improve, rather inefficiently, its soaring profile. Or you could add a small engine to a sailplane, which brought about its own troubles, such as the dodgy weight distribution the motor creates, plus the unavoidable drag when the engine is put into its optimal position. None of this was very efficient”, Stemme says.

From early on Hirth’s dilemma sparked a fire that would never die down in Stemme’s plane designer mind. The enabler in him, who resolves things once and for all, eventually put forward a viable construction idea – with a workable technical concept following suit after months of head-scratching and napkin scribbling about systems, aerodynamics, engine shapes and designs. To keep the envisioned glider’s balance uncompromised, the motor would be placed mid-ship and its power transmitted to a retractable front-propeller via a drive shaft running between pilots that are seated side-by-side. “This was a breakthrough”, he says. “The setup allowed for an aerodynamically clean fuselage during soaring flight but also for instant access to engine power if needed while drag and trim remained untouched”. Stemme rushed to get the fruit of his light-bulb moment patented straightaway. It is an invention that helped to get him awarded the exclusive German Otto Lilienthal Medal for his life achievements as aircraft designer in 2015.

The elfin e-glider rises from a cradle prominent ancestor models had soared from

Before Stemme went about to resolve Hirth’s dilemma though, the aircraft manufacturer in waiting moved to Switzerland with his young family and two kids to earn a doctorate in physics at the university of Bern while having a stint at a local laser manufacturer for the watch and medical industry. His newly-won academic degree opened up new career paths and the family decided to relocate back to Germany where „Dr. Reiner Stemme“ took over the management of a VDI Technology Center – a precursor of today’s incubator and accelerator hubs where he allocated funding and controlled the performance of young technology start-ups. It was an occupation that also led himself come up with patents covering crucial features of his envisioned aircraft concept.

Stemme knew a thing or two about nurturing businesses to success when he started his own aircraft firm, Stemme Ltd, in Berlin. It was the point where he went full risk and took the plunge to commercialise his new aircraft brainchild rather than pursuing a safer career based on his solid scientific education. The upstart was up and running soon at a former AEG plant located in Berlin’s Wedding neighbourhood from 1984. His first enterprise, though, needed a licence for building aircraft on West-Berlin soil from the controlling allied forces, which Stemme received to become the one and only plane maker in the walled-in city. Its team worked day and night towards launching Stemme’s first motor glider model S10 and its prototypes had to be moved again to West-German for test flights. Looking back he can laugh about the awkwardness of this approach.

“You can imagine the ballyhoo and paper work it involved, getting whole planes back and forth over hundreds of road kilometers and through hostile GDR border checks to Westdeutschland and then back to Berlin.” It took the firm’s head designer and team just two years to get its new aircraft class ready for takeoff. Self-launching and fossil-fuel-powered it passed its maiden flight in July 1986 while full certification followed in 1990. The S10 formed in many respects the technological root for other aircraft Stemme has developed ever since – from the S6, an outlier single engine plane, to the elfin whose maiden flight is imminent. “No winch, no aerotow anymore. We married launch independence with long distance capability. That became our main marketing line for our aircraft which globally sold more than 300 times. Without S10’s success we would not have been able to push our ideas forward and arrive at our current designs”, Stemme remarks. The new plane even earned him a visit on deck of the WWII US aircraft carrier ‘Intrepid’ where Stemme received a Popular Mechanics Award for his invention.

Stemme’s new e-motor glider offers contemporary comfort and safety

Still, on a ‘tree of life’ of the plenty of aircraft concepts and solutions Stemme has come up with in his long career, the elfin would make a new branch. “Yes, the plane is based on things glider pilots will know from the S10. However, it is the raft of innovations and the use of state-of-the-art technology that make elfin a new aircraft type”, Stemme insists. “The trademark collapsible propeller is extended by one blade. It is now fully carbon and has better aerodynamics. The foldable wings got their design likewise improved. And if we think of the new e-propulsion unit or of the added performance, handling and safety features, elfin is clearly a beast of its own”. More than before, Stemme has embedded his current design firm, RS.aero, into a european-wide network of suppliers – a modern approach to bring high-tech products to market at speed. The ‘agile’ ecosystem comprises external suppliers for elfin’s propeller blades, made in France, its wings, produced in Poland, the electric engine and generator, made by Slovenian specialists. The availability of much stronger batteries powering much more efficient propulsion systems allowed Stemme to include viable e-power into his new plane. “It is not anymore about where the drive shaft goes. The propeller is now moved by a compact e-engine sitting right behind the plane’s nose, giving passengers in the cabin more space and calm to enjoy a real glider feel”, he explains.

The elfin is only just the start of a journey to an even wider horizon in aircraft building

Environmentally friendly, the elfin offers more performance in e-powered flight than any other electric motor glider on the market. And it still can enlarge its reach considerably with the help of an attachable fuel-cell engine that allows for a non-stop 460 air miles range – the distance between Berlin and Paris. “We considerably heightened air safety too”, Stemme adds. “The elfin is fitted with a rescue system that would vertically land the aircraft safely, suspended from a massive parachute, in case something goes wrong mid-air. Plus, we picked a cockpit with the highest possible crash safety properties.“

Pulling all this off, getting the full regulatory greenlight and making sure that all falls into place once elfin starts normal series assembly, is quite a task for an octogenarian who is an active member of the venerable German aviation club “Alte Adler” (Old Eagles) and whose fitness compares favorably to many peers of his age group. What is for sure though, is that the Stemme family has a thing with flying. And there is a vague dynastic horizon emerging for the firm, as Stemme’s elder daughter Karen Stemme, and even her elder son Simon, are likewise involved in aviation way beyond the mere private pilot licence. Yet for now it is Reiner Stemme who harbors plans for aircraft building beyond elfin. A string of further designs are waiting in the drawers at RS.Aero. “We live in an age of breakthrough technologies. Their possibilities are amazing and it is my great challenge to point out their way into aviation”, he remarks with a smile, rushing out of his office to hold a meeting with his design team. This man needs wings – there is no doubt.