Hanns Klemm – Light aircraft manufacturer and pioneer

As one of the best known aircraft designers of his time, Hans Klemm’s ideas of light and aerodynamic aircraft made his reputation as an aviation pioneer. The German engineer and entrepreneur developed exciting aircrafts such as the Klemm 35, which was a freestanding low-wing plane that was capable of performing stunt flying and which had a production run of over 1,300.

 © Gregor Behling

Hanns Klemm – Engineer, entrepreneur, and aviation pioneer

Hanns Klemm’s first encounter with the aircraft industry took place relatively late and almost by chance. He was born in Stuttgart in 1885, and as a young man, Hans Klemm began to work in the civil engineering field. Following four years of university study, he received a civil engineering degree from the technical university in his hometown and subsequently spent two years working for the Württemberg State Railway, where he learned about new building techniques using concrete. His subsequent employment involved building bridges and tunnels, as well as a year’s military service, and after which he was engaged as an engineer for steel reinforced concrete and steel frame construction at the Imperial Shipyard in Gdansk.

Only when working as a structural engineer and designer for the airship manufacturer, Luftschiffbau Zeppelin GmbH, did he begin to encounter the field of light aircraft construction. As the head of the research department, reporting to Claude Dornier, another notable aviation pioneer, Klemm became familiar with aircraft design and construction, primarily from the perspective of metals engineering, as a result he developed a remarkable passion for aeroplanes. After a short period at the Hansa-Brandenburg Aircraft Factory in Briest, Hanns Klemm returned to Stuttgart in 1918 where he became lead designer at the Daimler Aircraft Factory in Sindelfingen. While working to develop high-performance fighter aircraft such as the Daimler L 11, he became familiar with wood as a building material and learned to appreciate its virtues.

Klemm learned a great deal during his time at Daimler and, in doing so, developed a highly individual concept of what an aircraft could be. His concept involved the construction of highly aerodynamic, lightweight aeroplanes that would generate little drag and, as such, could provide acceptable performance with a relatively low power engine. As a result of aircraft designed and built in this way, Hanns Klemm would later become one of the most famous light aircraft designers.

In summer 1919, Hans Klemm built the Daimler L15, the first single-engine light aircraft in the world. Equipped with a motorcycle engine, made by Indian and developing just 7.5 hp, and following some initial setbacks, Klemm broke one light aircraft record after another with the L15. With its successor, the Daimler L 20 light aircraft, Klemm replaced the rounded fuselage with a square one and chose a 20 hp motor designed by Ferdinand Porsche. The L 20 attracted particular attention due to the spectacular trip around the world undertaken by Baron Friedrich-Karl von König-Warthausen, who used it on a non-stop flight between Berlin and Moscow in 1928 before spontaneously deciding to fly it onward to Persia and eventually spending a year and a quarter flying it around the entire world. Baron Friedrich-Karl von König-Warthausen was awarded the renowned Hindenburg Cup for his achievements as an aviator.


The Daimler L 20 – the aircraft used by Baron Friedrich-Karl von König-Warthausen to fly around the world

The Daimler L 20 achieved particular fame due to the spectacular circumnavigation of the globe by Baron Friedrich-Karl von König-Warthausen – © Flight XiX, 35 p.613 (1 July 1927), [CC-BY-4.0], via Wikimedia Commons

 

When the Daimler and Benz companies merged in 1926 and ceased building aircraft, Hans Klemm started his own company with Leichtflugzeugbau Klemm (LFK) GmbH in Böblingen near Stuttgart. LFK GmbH grew rapidly and, by 1933, it had around 250 employees. Klemm’s idea of simple, low-cost light aircraft was rewarded with great success and the successor to the L 20, the Klemm Kl 25, had a production run of over 6,000 examples and was also built under licence for export to Great Britain and the USA. Models such as the Klemm Kl 26, Kl 31, Kl 32 and Kl 35 continued this German engineering success story, graduating to bonded construction techniques in 1937 in the form of the Klemm partial shell construction method that he developed.

Following the end of the Second World War and the associated prohibition on aircraft building in Germany, Hans Klemm decided that he would no longer take an active role in his business. The town of Böblingen made the aircraft designer an honorary citizen in 1955. He died in Fischbachau in southern Bavaria 1961.


The Klemm Kl 35 – an acrobatic, training and sports aircraft 

The Model Kl 35, the successor to the Kl 25, became known as a free-standing low-wing aircraft, and was used primarily as a training aircraft and for sports flying. The mixed-method construction can be seen as emblematic of Hans Klemm’s vision of a light aircraft: whereas the fuselage was made of steel, Klemm used wood for the wings and tail using small amounts of lightweight metal for the surfaces. Fixed, singe-strut landing gear and spring damping complemented the mixed-method construction combined with a twin-timbered wooden frame.

Some of the unique characteristics of the Kl 35 light aircraft included the gull wings, which were partially made from plywood and which allowed a robust landing gear to be attached at the kink points. In comparison to its predecessor, the Kl 25, this free-standing low-wing aircraft differed primarily in the welded steel tube undercarriage that replaced the pure wood construction that had previously been used.


The Klemm Kl 35 light aircraft was used as a training and sports aircraft which also had aerobatic capabilities The Klemm Kl 35 with its distinctive gull wings, which were partly made of plywood – © Gregor Behling 

 

For the first production models, Klemm continued to opt for power from a Hirth HM 60 R engine, but this was soon replaced by an HM 504 A Series 2. The suspended, air-cooled 4-cylinder inline motor achieved a power output of 105 hp and accelerated the light aircraft to a top speed of 208 km/h. A fuselage-mounted 31-litre fuel tank and a 60-litre main tank enabled an impressive range of 600 km. A total of just over 1,300 Type Kl 35 light aircraft had been built by the time production of the model ceased in 1943.


Current light aircraft trends

Modern light aircraft are divided into a number of extremely different registration classes, provided that their take-off weight is below 5.7 tonnes. The classifications relate to the entitlement of different pilot’s licences, with well-known examples including Single Engine Piston (SEP) or Single Engine Turbine (SET) light aircraft, the best known among them being the Cessna 208 or the Piper PA-46. These should be distinguished from ultralight aircraft, which German regulations define as motorised sport aircraft with a maximum take-off weight of 472.5 kg for two-seater designs.

The most build aircraft ever, the Cessna 172, is also classed as a light aircraft. This tough, four-seater airplane became world famous under the “Skyhawk” name and around 44,000 examples have been built to date. As a single-seater monoplane, the Skyhawk is offered in a wide variety of different versions with power outputs between 145 and 180 hp with cruising speeds between 195 and 250 km/h. The Cessna 172 is regarded as a relatively easy to handle light aircraft and is therefore a particularly popular choice for pilot training. Outstanding low-speed flight characteristics and easy manoeuvrability have earned this model a reputation for being the archetypal “club aircraft.”


The Cessna 172 – a famous example of a light aircraft

The Cessna 172 is the most build aircraft ever

 

Hanns Klemm and his services to the light aircraft industry

Aircrafts built by the German engineer and aircraft designer, Hans Klemm, became the embodiment of the German light aircraft industry in the 1920s and 1930s. With his unconventional idea of an economical, light aeroplane that would be suitable for everyday use, Klemm revolutionised an entire sector and developed highly successful light aircrafts that were enthusiastically received all over the world. Hanns Klemm’s aircraft were not known for their power or speed – what was more impressive was their combination of startling simplicity and ingenious engineering.


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