Hirth aircraft engines have a tradition dating from 1926. Hellmuth Hirth (1886-1938) was a son of Albert Hirth, a notable engineer and tool designer, and the brother of Wolfram (Wolf) Hirth (1900-1959), a famous sailplane designer and pilot. Hellmuth Hirth was a pioneer, pre-WWI, German military pilot. His engine company built mainly air-cooled, inverted inline engines for light aircraft from the 1920s through WWII. After his death, the firm was operated by the Civil Aviation Reichsministry in Germany until 1941, at which time the Heinkel organization took over Hirth operations. After WWII, Hirth became independent again and specialized in building two-stroke cycle engines for stationary use, snowmobiles, and then aircraft from 1965 to 1974. The Hirth firm went into voluntary liquidation in 1974. The assets were acquired shortly thereafter by Hans Göbler, who has built a broad range of two-stroke engines for many applications as the Göbler-Hirthmotoren GmbH of Benningen, Germany. In the 1980s, two-stroke Hirth engines were again built for light aircraft and production continues to the present. Two-stroke cycle HOAEs are part of the Hirth line, which also includes one-cylinder and two- and three-cylinder inline engines. Hirth is the major manufacturer of two-stroke HOAE in the 65-110hp range at the present time. Historical information can be found on the Hirth Website. The Type Certificates (TC) listed below as LBA refer to certification by the Luftfahrt Bundesamt (Federal Office of Civil Aviation), the German equivalent of the FAA in the US. Certification is to the European JAR requirements.
These are the engines built from 1965 to 1974 by the post-WWII Hirth company for light aircraft applications.
O-35 (2-Stroke) -- {2.283 / 2.126 / 34.8} / {58 / 54 / 571}
4cyl; F10A; 24hp@4800rpm, 26@5000 (TO); 1965-1974; Wt = 56#; LBA TC = 4568.
Single-ignition, geared, and produced in the following models:
F10A 1a, b, c with propeller shaft above the crankshaft; geared to 0.536, 0.455, 0.388, respectively;
F10A 2a, b, c with propeller shaft below the crankshaft; geared to 0.536, 0.455, 0.388, respectively.
F10K engines with the same 1a to 1c and 2a to 2c models are listed under the LBA TC; details of the differences have not been found. All applications are for powered gliders.
J65-66toJ75-76; W66-67.
Applications: (France) Fauvel AV.45. (Germany) Scheibe SF-24B Motorspatz, SF-25B Motorfalke, SF-27M self-launching sailplane with retractable engine above and behind the pilot; Schleicher K-12.
Data and information on the current Göbler-Hirthmotoren engines can be found on the Hirth Website, and also from the US Hirth distributors, namely Adventure Ultralights, Inc. and Recreational Power Engineering.
O-23 (2-Stroke) -- {2.598 / 2.205 / 23.4} / {66 / 56 / 383}
2cyl; F22; 23hp@5000rpm; 1989-1993; Wt = 44-51#.
It is not clear whether it was produced in any quantity.
BGP; Brinks; J89-90toJ92-93.
Applications: None found.
O-32 (2-Stroke) -- {2.835 / 2.520 / 31.8} / {72 / 64 / 521}
Same bore and stroke as O-64.
2cyl; F23A; 40hp@5500rpm; 1988-present; Wt = 52-62#.
Dual-, capacitive-discharge ignition, direct drive available or reduction by belt drive (or gearing) to N/A; higher weight includes the gearing. An improved version was tested in 2002 and produced 50hp@6350rpm, as reported on their Website.
BGP; J89-90to present; KP4/05.
Applications: (Czech Republic) Airox F-31A twin. (Germany) Dornier MTC 11 helicopter. (US) Fisher 303, Skylight.
O-64 (2-Stroke) -- {2.835 / 2.520 / 63.6} / {72 / 64 / 1042}
Same bore and stroke as O-32.
4cyl; F30 series; 65hp@4500rpm-110@6500; 1987-present; Wt = 79# for direct drive, up to 130# with gearing.O-78 (2-Stroke) -- {N/A / N/A / 77.5} / {N/A / N/A / 1270}
4cyl; F30A; 80hp@4500rpm-130@6500; 1987-1993; Wt = 77# for direct drive, N/A for geared version.
Larger displacement version of O-64 with and without gearing to N/A; did not go into production. Performance and weight varied with the version chosen; the horsepower range was from 80 to130 depending on the gearing and state of tune.
BGP; J87-88toJ92-93.
Applications: None found.