The Hirth HM 506 was a six-cylinder air-cooled inverted inline engine that was developed from the earlier four-cylinder HM 504.
[1] The HM 506 was a popular engine for light aircraft of the 1930s to 1940s and powered the Bücker Bü 133A model trainer.
The engine featured a cast magnesium alloy crankcase.
Data from Jane's All the World's Aircraft 1938,[2] Flugzeug-Typenbuch.
Handbuch der deutschen Luftfahrt- und Zubehör-Industrie 1944[3]