The S.21H was much used as a trainer and also set new Swiss national records in all the two-seat class categories. At least ten of this version were produced, all of which appeared on the Swiss register.

The Spalinger S-21 is a Swiss gull-winged, two-seat trainer glider flown in the late 1930s. The S-21H (also called the S.21-I) was wooden-framed and ply-covered with an oval section fuselage along with tandem seats. At least ten were built and this example is on display in the aviation hall.

Of this tandem arranged two seater just over ten were built in the late 1930's.