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There are a couple of other motorgliders out there worth considering, although none I'm aware of with the engine on AND engine off performance ot the Stemme. There is actually a bit of a tradition of european touring motorgliders, exemplified by the designs of Rene Fournier. The RF-4, powered by a Limbach VW conversion, was at one time fairly numerous both here in the US and in Europe. Mira Slovak, a famed aerobatic pilot, used to deliver them from France by flying them across the Atlantic! The EURAVIAL RF-47 appears to be a continuation of this line. I thing Diamond still makes the long-winged motorglider version of the Katana. And the venerable, all aluminum Czech Blanik is available in a powered version. And some of the high-zoot glass sailplanes are available in "self-launching" versions, with small two strokes and climb props that retract once they've gotten you in the air. Web search engines on these keywords should get you fresh links if you're interested.