Siebel was a German aircraft manufacturer founded in 1937 in Halle an der Saale. ==History== It originated in the Klemm-Flugzeugwerke Halle that had been founded in 1934 as a branch of Leichtflugzeugbau Klemm in Böblingen. Its name changed to Siebel Flugzeugwerke when it was taken over by Friedrich Siebel in December 1937. After World War II the ...