Klaus Ohlmann is legendary in his accomplishments. Having surmounted Mount Everest in a sailplane, traversed the Alps and the Andes in sailplanes and battery- and solar-powered craft, and contributed to wave soaring studies, he is ready to set a new type of record – one with a Stemme hybrid power system.
Klaus Ohlmann’s and Karl Pickner’s modified Stemme S10 with Briggs & Stratton engine replacing batteries and acting as a range extender for flights up to 3,000 kilometers (1860 miles)
In its sadly last post, https://www.electric-flight.eu/ left us with this news. “With a modified Stemme hybrid S10, Klaus Ohlmann wants to fly 2000 kilometers (1,243 miles).” The publication missed its headline by 1,000 kilometers (620 miles), which would make Ohlmann’s goal 1,864 miles, requiring up to 20 hours of leisurely travel.
Stemme has long relied on a unique distribution of power components, with a fossil-fuel-powered engine behind the pilots, a shaft passing from its power takeoff between the two occupants to a forward-mounted, cleverly-concealed propreller tucked into a sliding nose cose. The layout is similar to that of the P-39, and later P-63 Bell Airacobras of WWII. Despite the clever engineering, they were not popular with American pilots and were often dispersed to our then Russian allies.
WWII Bell P-39 Airacobra had unique distribution of power drive componant, echoing that on Stemme S10
Working with Karl Pickan of PIMO Motors, Ohlmann’s Stemme S10 initially offers a pure battery version with a 30 kWh lithium battery with two redundant inverters. A Slovenian Emrax Motor replaces the normal Rotax 914 turbo internat combustion engine, which according to user reports consumes about 11 to 13 liters of fuel per hour, from a little under to around four gallons per hour. Like the layout of the Stemme or Airacobra, the total weight of fuel or batteries and their distribution is obviously a big part of the equation. This part of the design is a little trickier in a sailplane, with its narrow chord wings and limited center of gravity placement.
A second variant replaces the batteries with a Briggs & Stratton two-cylinder engine, which sips a mere 5 liters per hour. A 20-hour flight would require 100 liters, or 75 kilograms (165 pounds) of fuel. The same flight with the Rotax engine would require 165 to 195 kilograms (363 to 429 pounds) of dinosaur remains to cruise for the same 20 hours. That would certainly overload the Stemme, which has a normal all-up weight around 1,800 pounds. The hybrid configuration provides a viable alternative.
Pickan notes, “This smart consumption is only possible thanks to thehigh-quality wing of the S10. He adds, “A new certification is not required for the aircraft. Aan STC is sufficient purely from an approval point of view.”
Ohlmann gives a view of the missions planned and the technology involved in those missions. He and Pickan continue in their quest to expand the range and potential of an already highly capable soaring machine.
We look forward to sharing these new adventures.