High Franz, Hello Everybody,
now, having that hint it's easy for me, as I had some interests in railway-technology in earlier times... long ago... 'bout twenty years...
Taddaaaah: for sure it's a Gotha GO 150!
Nice aircraft, FAI world record in July 1939 (hey, that's right 70 years ago...) for altitude: 8048m (about 26400 ft) one seated.
Greetings
Ulrich