{"id":26660464,"date":"2026-10-05T10:38:28","date_gmt":"2026-10-05T08:38:28","guid":{"rendered":"https:\/\/migflug.com\/afterburner\/?p=26660464"},"modified":"2026-10-05T10:38:28","modified_gmt":"2026-10-05T08:38:28","slug":"eth-zurich-wind-tunnel-ackeret-supersonic-aerodynamics-history","status":"publish","type":"post","link":"https:\/\/migflug.com\/afterburner\/eth-zurich-wind-tunnel-ackeret-supersonic-aerodynamics-history\/","title":{"rendered":"Mach 2 in Zurich: How ETH\u2019s Wind Tunnels Made Switzerland an Aerodynamics Pioneer"},"content":{"rendered":"<style>.et_pb_title_container h1.entry-title { padding-top: 40px !important; }<\/style>\n<!-- mfsh:top -->\n\n<style>\n.mfsh-trigger{display:inline-flex;align-items:center;gap:10px;height:44px;padding:0 18px;margin:0 0 26px;border:2px solid #0F1720;background:#fff;color:#0F1720;font-family:inherit;font-size:14px;font-weight:700;line-height:1;letter-spacing:0;text-transform:none;cursor:pointer;box-shadow:none;transition:background 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Next door stood something even more unusual: a tunnel built to blow air past models at twice the speed of sound, in a closed circuit, for as long as the experimenters liked.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Behind both was Jakob Ackeret, a locksmith&rsquo;s son from Zurich who had learned his trade under Ludwig Prandtl in G\u00f6ttingen and who gave the world a term every pilot now knows: the Mach number. For the next half century, ETH&rsquo;s Institute of Aerodynamics was where Swiss military aircraft went to be tested before they ever flew.<\/p>\n\n\n\n<div style=\"background:#f5f5f5;border-left:4px solid #1a1a1a;padding:18px 22px;margin:24px 0\"><p style=\"margin:0 0 8px;font-weight:600\">Quick Facts<\/p><ul style=\"margin:0;padding-left:20px\"><li><strong>Founder:<\/strong> Jakob Ackeret (1898&ndash;1981), professor at ETH Zurich<\/li><li><strong>Institute:<\/strong> ETH Institute of Aerodynamics, head from 1934; closed 1988<\/li><li><strong>Low-speed tunnel:<\/strong> First run New Year&rsquo;s Eve 1934; test section 3 by 2.1 metres; up to 320 km\/h<\/li><li><strong>Supersonic tunnel:<\/strong> Closed-circuit, continuously running, about Mach 2; built 1933&ndash;35<\/li><li><strong>Named:<\/strong> The &ldquo;Mach number&rdquo;, proposed by Ackeret in 1929<\/li><li><strong>Tested:<\/strong> Swiss Army aircraft models including the C-35 and C-36; theory for the P-16 wing<\/li><li><strong>Today:<\/strong> The large tunnel survives as a protected monument; the supersonic tunnel was demolished in the 1980s<\/li><\/ul><\/div>\n\n\n<h2 style=\"padding-top:22px\">A Swiss in G\u00f6ttingen<\/h2>\n\n\n<p class=\"wp-block-paragraph\">Ackeret was born in Zurich on 17 March 1898, studied mechanical engineering at ETH and graduated in 1920. In 1921 he went to G\u00f6ttingen to work with Ludwig Prandtl, the father of modern aerodynamics, and helped expand Prandtl&rsquo;s Kaiser Wilhelm Institute for Flow Research. In 1925 he published a theory of the forces on wings moving faster than sound, translated by the American NACA the same year. It was one of the first practical theories of supersonic lift and drag, written at a time when no aircraft could get anywhere near Mach 1.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">In 1929, back in Zurich, he gave a lecture on air resistance at very high speeds and proposed a name for the ratio of an object&rsquo;s speed to the speed of sound.<\/p>\n\n\n\n<div style=\"background:#f8f9fa;border-left:4px solid #5C91FF;padding:20px 22px;margin:18px 0 24px;font-size:16px;line-height:1.7;display:flex;gap:20px;align-items:flex-start\"><div><em>&ldquo;Da der bekannte Physiker Ernst Mach auf unserem Gebiet die grundlegende Bedeutung dieses Verh\u00e4ltnisses besonders klar erkannt hat, scheint es mir sehr berechtigt, Geschwindigkeit durch Schallgeschwindigkeit als Mach&rsquo;sche Zahl zu bezeichnen.&rdquo;<\/em><div style=\"margin-top:10px;font-size:14px;color:#555\"><strong>Jakob Ackeret<\/strong> &mdash; Schweizerische Bauzeitung, 1929. (&ldquo;Since the well-known physicist Ernst Mach recognised the fundamental importance of this ratio particularly clearly, it seems to me entirely justified to call velocity divided by the speed of sound the Mach number.&rdquo;)<\/div><\/div><\/div>\n\n\n<h2 style=\"padding-top:22px\">The Army Wanted a Wind Tunnel<\/h2>\n\n\n<p class=\"wp-block-paragraph\">Switzerland&rsquo;s military had been asking for an aerodynamic test facility since the late 1920s, and in 1931 ETH decided to build one in its machine laboratory. Ackeret, an associate professor from 1931, became full professor and head of the new Institute of Aerodynamics in 1934. Construction of the main low-speed tunnel began in February 1934 and, by his own account, it ran for the first time on the last evening of the year.<\/p>\n\n\n\n<div style=\"background:#f8f9fa;border-left:4px solid #5C91FF;padding:20px 22px;margin:18px 0 24px;font-size:16px;line-height:1.7;display:flex;gap:20px;align-items:flex-start\"><div><em>&ldquo;Die ganze Anlage wurde schon vor zwei Jahren entworfen. Aus allgemeinen Gr\u00fcnden konnte mit dem Bau erst im Februar 1934 begonnen werden. In der Folge gelang es dann die Arbeiten so zu f\u00f6rdern, dass der erste Lauf noch am Sylvesterabend 1934 erfolgen konnte.&rdquo;<\/em><div style=\"margin-top:10px;font-size:14px;color:#555\"><strong>Jakob Ackeret<\/strong> &mdash; report on the new ETH wind tunnel, 1935. (&ldquo;The whole facility was designed two years ago&hellip; the first run took place on New Year&rsquo;s Eve 1934.&rdquo;)<\/div><\/div><\/div>\n\n\n\n<p class=\"wp-block-paragraph\">Its companion was the remarkable one. ETH describes its supersonic tunnel as the world&rsquo;s first to run in a closed circuit, recirculating the same air instead of blowing a short burst from a pressure tank. A 13-stage axial compressor from Brown Boveri, driven by a 700-kilowatt electric motor, pushed air through a test section about 40 centimetres square at up to twice the speed of sound. When Ackeret presented it at the Volta Congress on high-speed flight in Rome in 1935, the Italians were already building their own supersonic tunnel at Guidonia, which ETH&rsquo;s archive records as modelled on the Zurich design.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\" style=\"margin:0 0 24px;width:100%\"><img decoding=\"async\" class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" width=\"1024\" src=\"https:\/\/migflug.com\/afterburner\/wp-content\/uploads\/sites\/4\/2026\/10\/eth-zurich-supersonic-wind-tunnel-compressor-1934.jpg\" alt=\"The compressor and electric motor of the ETH Zurich supersonic wind tunnel in November 1934\" style=\"width:100%;height:auto;max-width:100%;display:block\"><figcaption style=\"font-size:13px;color:#777;text-align:center;margin-top:6px;font-style:italic\">The compressor of the ETH supersonic tunnel, with its electric drive motor, in November 1934. Photo: ETH-Bibliothek Z\u00fcrich, Bildarchiv, public domain<\/figcaption><\/figure>\n\n\n\n<div style=\"position:relative;padding-bottom:56.25%;height:0;overflow:hidden;margin:24px 0\"><iframe class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" src=\"https:\/\/www.youtube.com\/embed\/I2LuhgFeEBI\" style=\"position:absolute;top:0;left:0;width:100%;height:100%;border:0\" allowfullscreen><\/iframe><\/div>\n\n\n<h2 style=\"padding-top:22px\">Every Military Aircraft Through the Tunnel<\/h2>\n\n\n<p class=\"wp-block-paragraph\">The new facility went to work for the Swiss Army almost immediately. A model of the C-35 biplane was tested before the tunnel had even been fully calibrated, and models of the C-36 family followed, photographed hanging upside down in the test section with captions noting the work was done on behalf of the army. According to the curators of ETH&rsquo;s collection, from the 1940s onwards every Swiss military aircraft was tested in the ETH tunnel. Buildings, road tunnels and cars went through it too.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Ackeret&rsquo;s influence reached beyond the test section. He sat on the federal commission for military aircraft procurement from 1943 and chaired it from 1950. When Switzerland tried to build its own jet fighter, the FFA P-16 from Altenrhein, the theoretical basis for its thin, straight wing came from Ackeret and his colleagues Nikolaus Rott and Max Degen at the institute in 1950. After the P-16 was cancelled in 1958, Ackeret resigned from the commission.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\" style=\"margin:0 0 24px;width:100%\"><img decoding=\"async\" class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" width=\"1024\" src=\"https:\/\/migflug.com\/afterburner\/wp-content\/uploads\/sites\/4\/2026\/10\/ffa-p-16-j-3001-altenrhein.jpg\" alt=\"The first FFA P-16 prototype J-3001 at Altenrhein\" style=\"width:100%;height:auto;max-width:100%;display:block\"><figcaption style=\"font-size:13px;color:#777;text-align:center;margin-top:6px;font-style:italic\">The first FFA P-16 prototype, J-3001, at Altenrhein. The theory for its wing came from Ackeret&rsquo;s institute. Photo: Comet Photo AG \/ ETH-Bibliothek Z\u00fcrich, CC BY-SA 4.0<\/figcaption><\/figure>\n\n\n\n<div style=\"background:#f8f9fa;border-left:4px solid #5C91FF;padding:20px 22px;margin:18px 0 24px;font-size:16px;line-height:1.7;display:flex;gap:20px;align-items:flex-start\"><div><em>&ldquo;Sie k\u00f6nnen ein solches System von f\u00e4higen Mitarbeitern mit einem Beschluss zerst\u00f6ren, wiederaufbauen k\u00f6nnen sie es nie mehr.&rdquo;<\/em><div style=\"margin-top:10px;font-size:14px;color:#555\"><strong>Jakob Ackeret<\/strong> &mdash; on the cancellation of the P-16, as quoted by aviation historian Georges Bridel. (&ldquo;You can destroy such a system of capable people with a single decision, but you can never rebuild it.&rdquo;)<\/div><\/div><\/div>\n\n\n\n<div style=\"position:relative;padding-bottom:56.25%;height:0;overflow:hidden;margin:24px 0\"><iframe class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" src=\"https:\/\/www.youtube.com\/embed\/s7LhsWplOew\" style=\"position:absolute;top:0;left:0;width:100%;height:100%;border:0\" allowfullscreen><\/iframe><\/div>\n\n\n<h2 style=\"padding-top:22px\">From Zurich to Emmen<\/h2>\n\n\n<p class=\"wp-block-paragraph\">ETH&rsquo;s tunnels became the template for the federal aircraft factory at Emmen, which built its own wind tunnels and research facilities on the ETH model. The Large Wind Tunnel Emmen, begun in 1944 and fully working by 1946, has a test section seven metres wide and five high and is still in use 80 years later under RUAG, now testing electric vertical-takeoff aircraft as well as conventional designs.<\/p>\n\n\n\n<div style=\"position:relative;padding-bottom:56.25%;height:0;overflow:hidden;margin:24px 0\"><iframe class=\"skip-lazy\" data-no-lazy=\"1\" loading=\"eager\" src=\"https:\/\/www.youtube.com\/embed\/8bdFU5TkPrY\" style=\"position:absolute;top:0;left:0;width:100%;height:100%;border:0\" allowfullscreen><\/iframe><\/div>\n\n\n<h2 style=\"padding-top:22px\">An Engineer Beyond the Wind Tunnel<\/h2>\n\n\n<p class=\"wp-block-paragraph\">Ackeret&rsquo;s work went well beyond aircraft. With Curt Keller he patented a closed-cycle gas turbine in 1935, and the first two-megawatt plant of the type was built in Switzerland in 1939. In G\u00f6ttingen he had worked on the rotor ships of Anton Flettner, and at Escher Wyss he studied cavitation in pumps and turbines. Among his students were several who went on to shape aerodynamics, including Nikolaus Rott and Werner Pfenninger. He gave his farewell lecture at ETH in 1967 on &ldquo;the road to the supersonic airliner&rdquo; and died in K\u00fcsnacht in 1981.<\/p>\n\n\n<h2 style=\"padding-top:22px\">What Survives<\/h2>\n\n\n<p class=\"wp-block-paragraph\">The Institute of Aerodynamics closed in 1988, and the supersonic tunnel was demolished in the 1980s. The large low-speed tunnel survived. It is now a protected monument and is still used by ETH&rsquo;s Institute of Fluid Dynamics. In 2019 and 2020, around 430 objects from the institute, including wind tunnel models of Swiss military aircraft, passed to the ETH Library&rsquo;s collection of scientific instruments, and some are on show in the exhibition &ldquo;Modelle &ndash; Wissen formen&rdquo; at ETH until June 2027.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Sources: ETH-Bibliothek, short portrait of Jakob Ackeret; Swiss National Museum blog, &ldquo;Im Windkanal der ETH&rdquo; (15 September 2026); ETHeritage blog (2017 and 2020); ETHistory, Forschungspfade; J. Ackeret, NACA TM-317 (1925) and NACA TM-808 (1935); Schweizerische Bauzeitung 94 (1929); NDB-online, Jakob Ackeret (2023); higgs.ch; G. Bridel, SVFW presentation on the P-16 (2025); RUAG Aerodynamics; Aerospace Testing International (21 September 2026); ETH-Bibliothek Z\u00fcrich Bildarchiv<\/em><\/p>\n\n<!-- mfsh:bottom -->\n\n<button type=\"button\" class=\"mfsh-trigger mfsh-bottom\" data-mfsh-placement=\"bottom\" aria-haspopup=\"dialog\"><svg><use href=\"#mfsh-i-share\"\/><\/svg>Share this story<\/button>\n\n<!-- \/mfsh:bottom -->\n\n\n<style>.mfq{margin:34px 0 8px}.mfq h2{font:26px\/1.3 \"Gilroy semiBold\",Helvetica,Arial,sans-serif;color:#0d1117;padding-top:22px;margin:0 0 6px}.mfq .qa details{border-top:1px solid #5C91FF;margin:0;padding:0}.mfq .qa details:last-of-type{border-bottom:1px solid #e2e7ee}.mfq .qa summary{cursor:pointer;list-style:none;display:flex;justify-content:space-between;align-items:center;gap:16px;padding:22px 26px;font:18px\/1.7 \"Gilroy semiBold\",Helvetica,Arial,sans-serif;color:#0d1117}.mfq .qa summary::-webkit-details-marker{display:none}.mfq .qa summary::after{content:\"+\";font:24px Helvetica,sans-serif;color:#3568e0;flex:0 0 auto}.mfq .qa details[open] summary::after{content:\"\\2013\"}.mfq .qa details:hover summary{color:#3568e0}.mfq .qa .a{font:16px\/1.7 \"Gilroy regular\",Helvetica,Arial,sans-serif;color:#454e5e;padding:0 26px 24px}.mfq .qa .a a{color:#3568e0}@media(max-width:680px){.mfq .qa summary{padding:18px 14px;font-size:17px}.mfq .qa .a{padding:0 14px 20px}}<\/style>\n\n\n\n<section class=\"mfq\"><h2>Frequently Asked Questions<\/h2><div class=\"qa\"><details open><summary>Who coined the term Mach number?<\/summary><div class=\"a\">The Swiss aerodynamicist Jakob Ackeret proposed the term &ldquo;Mach number&rdquo; in 1929, in a lecture published in the Schweizerische Bauzeitung, naming the ratio of speed to the speed of sound after the Austrian physicist Ernst Mach.<\/div><\/details><details><summary>Who was Jakob Ackeret?<\/summary><div class=\"a\">Jakob Ackeret (1898&ndash;1981) was a Swiss engineer who studied under Ludwig Prandtl in G\u00f6ttingen and founded the Institute of Aerodynamics at ETH Zurich in 1934. He developed an early theory of supersonic airfoils in 1925, built a closed-circuit supersonic wind tunnel and named the Mach number.<\/div><\/details><details><summary>Did ETH Zurich have a supersonic wind tunnel?<\/summary><div class=\"a\">Yes. In the mid-1930s ETH Zurich built what it describes as the world&rsquo;s first closed-circuit, continuously running supersonic wind tunnel, reaching about Mach 2 in a test section roughly 40 centimetres square. It was demolished in the 1980s.<\/div><\/details><details><summary>Which aircraft were tested in the ETH wind tunnel?<\/summary><div class=\"a\">Models of Swiss Army aircraft including the C-35 and the C-36 family were tested at the ETH Institute of Aerodynamics, and according to ETH&rsquo;s curators every Swiss military aircraft from the 1940s onwards went through the tunnel. The institute also supplied the theoretical basis for the wing of the FFA P-16 jet fighter.<\/div><\/details><details><summary>Does the ETH wind tunnel still exist?<\/summary><div class=\"a\">The large low-speed tunnel opened in 1934 still exists as a protected monument and is used by ETH Zurich&rsquo;s Institute of Fluid Dynamics. The supersonic tunnel was demolished in the 1980s, and the Institute of Aerodynamics closed in 1988.<\/div><\/details><details><summary>What is the wind tunnel at Emmen?<\/summary><div class=\"a\">The Large Wind Tunnel Emmen in Switzerland was built from 1944 and fully operational by 1946, following the ETH model. Operated today by RUAG, it has a test section seven metres wide and five metres high and is used for aircraft, including electric vertical-takeoff designs.<\/div><\/details><\/div><\/section>\n\n\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"Who coined the term Mach number?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The Swiss aerodynamicist Jakob Ackeret proposed the term \u201cMach number\u201d in 1929, in a lecture published in the Schweizerische Bauzeitung, naming the ratio of speed to the speed of sound after the Austrian physicist Ernst Mach.\"}},{\"@type\":\"Question\",\"name\":\"Who was Jakob Ackeret?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Jakob Ackeret (1898\u20131981) was a Swiss engineer who studied under Ludwig Prandtl in G\u00f6ttingen and founded the Institute of Aerodynamics at ETH Zurich in 1934. 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Operated today by RUAG, it has a test section seven metres wide and five metres high and is used for aircraft, including electric vertical-takeoff designs.\"}}]}<\/script><div style=\"background:#f0f4ff;border-left:4px solid #5C91FF;padding:16px 20px;margin:32px 0 8px\">\n<p style=\"margin:0 0 8px;font-weight:600;color:#333\">Related Posts<\/p>\n<p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/nasa-wind-tunnels-langley-full-scale-ames-40x80-m2-f1-avrocar\/\">Monster Fans and a Flying Bathtub: Inside NASA&rsquo;s Giant Wind Tunnels<\/a><\/p>\n<p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/vortex-generators-wing-fins-explained\/\">Vortex Generators: The Little Fins That Fix Big Wing Problems<\/a><\/p>\n<p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/hidden-swiss-air-force\/\">The Hidden Air Force<\/a><\/p>\n<p style=\"margin:4px 0\"><a href=\"https:\/\/migflug.com\/afterburner\/variable-sweep-swing-wing-x-5-f-14-tornado-mig-23\/\">The Wing That Changed Shape in Mid-Air<\/a><\/p>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>In 1934 ETH Zurich switched on wind tunnels that tested every Swiss military aircraft of the era, including one of the first supersonic tunnels anywhere. The story of Jakob Ackeret, the man who named the Mach number.<\/p>\n","protected":false},"author":23,"featured_media":26659592,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"editor_notices":[],"footnotes":""},"categories":[666],"tags":[],"class_list":["post-26660464","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-history-and-legends"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>ETH Wind Tunnel: Ackeret and Mach 2 in Zurich | MiGFlug<\/title>\n<meta name=\"description\" content=\"In the 1930s Jakob Ackeret built a closed-circuit supersonic wind tunnel at ETH Zurich and named the Mach number. 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