Jakob Ackeret (1898–1981)

Professor of Aerodynamics at ETH Zurich

Jakob Ackeret was born in Zurich on 17 March 1898 to locksmith Jakob Ackeret and his wife Anna Maria (née Oberer). In 1916 he enrolled at ETH Zurich's Department III for Mechanical Engineering. After obtaining his diploma in March 1920, he became an assistant for caloric machines under Professor Aurel Stodola. By this point, Ackeret had already developed a keen interest in aeronautics and was involved in the foundation of the Academic Aviation Society (Akademische Gesellschaft für Flugwesen (AGIS).

Stay in Germany

In the autumn of 1921, he joined Professor Ludwig Prandtl in Göttingen, Germany, where he mainly devoted himself to aircraft aerodynamics. In 1922 he took charge of aerodynamic testing and continued his studies in mathematics and physics. From 1925 to 1926, he headed the expansion of the Kaiser Wilhelm Institute for Flow Research (now the Max Planck Institute for Dynamics and Self-Organisation), using the new facilities to conduct research on gas dynamics and cavitation (the formation of cavities). However, he primarily focused on the problems of flying at high speeds.

Return to Switzerland and doctorate

In 1927 Ackeret returned to Switzerland to take up the position of chief hydraulics engineer at the Laboratory of Hydraulics and Flow Machines at Escher Wyss AG in Zurich, where he was highly successful in establishing hydraulic testing. He also endeavoured to apply the insights gained to aero, hydro and gas dynamics in steam turbines, gas turbines and compressors.

Ackeret completed his doctorate in 1928 with his dissertation "Über Luft-Kräfte bei sehr grossen Geschwindigkeiten insbesondere bei ebenen Strömungen" (About Aerodynamic Forces at Very High Speeds, especially in Even Currents) and was appointed as a private lecturer at ETH Zurich. In his postdoctoral thesis, he coined the popular term "Mach number" to describe the ratio of the velocity of a flying object to the speed of sound v/a – in honour of the physicist Ernst Mach.

Nomination as associate professor

He became associate professor of aerodynamics in 1931, full professor in 1934 and simultaneously dean of the newly founded Institute of Aerodynamics. In collaboration with the local machine industry, the institute developed the world’s first supersonic wind tunnel that worked in a closed circuit in 1933/1934. For the first time, the facility enabled observation of the flow phenomena around airfoil profiles close to sound velocity  . Together with his team, Ackeret made key contributions towards the development of aerodynamics and flow physics. His research on the topic finally drew to a close on 10 June 1967 with his farewell lecture on the topic of "the path towards supersonic aircraft".  

Ackeret died in Küsnacht on 27 March 1981.


Ackerets Handschrift

Ackeret's broad horizons are reflected in his study of the history of the technical sciences, such as for the edition of the complete works of Leonhard Euler, one of the leading mathematicians and physicists on the eighteenth century. The document depicted above comes from a manuscript explaining Euler’s turbine theory by comparing the size of Marly’s machine with a modern system with the same output (Hs 552: 139).


The ETH Zurich University Archives contain numerous manuscripts from Jakob Ackeret's research and his extensive correspondence. The inventory (external link) can be viewed via the internet and downloaded as a PDF document. Information on the life and work of Jakob Ackeret is gathered in the Biographical Files. The Image Archive contains some photographic documents on Ackeret. ETH-Bibliothek's exhibition to mark the twentieth anniversary of Ackeret’s death is available on the internet as a virtual exhibition (external link). ETH-Bibliothek owns numerous publications by and on Ackeret, which can be ordered via ETH Library's Search Portal (external link).