Here is my replica Graupner Silentius model. It was constructed from an original plan obtained from the German Vintage Model Association, (akin to UK SAM35). The original Graupner/Faulhaber geared motor was fitted though it ran off 50mAh NiCad cells of the time (1990).
I had the great pleasure of chatting with the late, great Ron Moulton who kindly gave me several original Salt-Water activated battery cells and an original Graupner Silentius prop assembly. These had been subject of testing (Aeromodeller?) when the kit was originally issued circa 1961.
A very rough foam free flight model called the 'Electra' was produced at a similar time in America. This also used the salt water cells. I still have an unbuilt 'Electra' kit.
My 'Silentius' model flew superbly and despite the fuse thermaliser, flew high then away towards some woods never to be found alas.
In 1986, Graupner brought out another called 'Silentius '86', this was for R/C though and ran on 7-8 NiCad cells, driving the common Mabuchi 550 geared motor (Graupner Jumo 550) with its plastic folding prop assembly. This model fortunately still survives and with today's LiPo cells flies better than ever!