Irmgard Flügge-Lotz was born Irmgard Lotz on 16 July 1903 in Hamelin, Germany. Her father, Oscar Lotz, had a gift for mathematics and worked as a journalist. Her mother, Dora Grupe, came from a family that had been in the construction business for generations. Those two inheritances shaped her early life. She spent hours on building sites with relatives and watched Zeppelin tests near her home. She later said she wanted a life that would never be boring, a career that would keep producing new problems even if she never married.
She finished secondary school in 1923 and entered the Technische Hochschule in Hanover to study applied mathematics and engineering. She was often the only woman in her classes. In 1927 she earned the Diplom-Ingenieur. Two years later she received the Doktor-Ingenieur for a thesis on the mathematical theory of heat conduction in circular cylinders, work that grew out of practical questions about the heating of a forging stamp. She was the only woman to take that doctorate at Hanover that year.
In 1929 she joined Ludwig Prandtl’s group at the Aerodynamische Versuchsanstalt in Göttingen, the leading center of theoretical aerodynamics in the world. Prandtl’s lifting-line theory described how lift is distributed along a wing, but the equations for three-dimensional wings of arbitrary planform were hard to solve. In 1931 Lotz published a practical numerical method that turned the problem into a tractable calculation. The Lotz method quickly became a standard tool in aircraft design offices. By the mid-1930s she headed the theoretical aerodynamics group. When Prandtl recommended her for a research professorship in 1937, the Reich Aviation Ministry refused, almost certainly because she was a woman.
In 1938 she married Wilhelm Flügge, a civil engineer and privatdozent at Göttingen who had been labeled politically unreliable by the Nazi authorities. The couple moved to Berlin, where Flügge took a post at the Deutsche Versuchsanstalt für Luftfahrt. Flügge-Lotz worked there as a consultant on aerodynamics and flight dynamics throughout the war. Both of them were anti-Nazi, yet Hermann Göring’s institutes valued their technical skill more than their politics. In 1944 the laboratory was evacuated south to the French occupation zone.
After the war the French recruited the couple to the newly expanded Office National d’Études et de Recherches Aérospatiales in Paris. There they served as equal group leaders. In 1948 Wilhelm Flügge received an offer from Stanford University, arranged in part through Stephen Timoshenko. Irmgard followed. He was appointed professor at once. She was given the rank of lecturer, even though she taught the same graduate courses in hydrodynamics, aerodynamics and automatic flight control, supervised doctoral students, and published at the same pace as a full professor. She became a naturalized American citizen in 1954. Only in 1960 (some sources say 1961) was she appointed Professor of Applied Mechanics and of Aeronautics and Astronautics, the first woman to hold a full engineering professorship at Stanford.
At Stanford her research shifted toward automatic control. High-speed aircraft and later spacecraft needed simple, robust regulators. She developed the first systematic theory of discontinuous, or “on-off,” control systems—the bang-bang controllers that switch fully on or fully off rather than modulating continuously. The same mathematics applies to thermostats, fire-control systems, guidance loops and satellite attitude control. Her 1953 book Discontinuous Automatic Control and the later Discontinuous and Optimal Control became standard references. She published more than fifty technical papers and helped build Stanford’s graduate programs in mathematical aerodynamics and hydrodynamics.
Recognition came late. In 1970 she received the Achievement Award of the Society of Women Engineers and became the first woman elected a Fellow of the American Institute of Aeronautics and Astronautics. In 1971 she delivered the Institute’s von Kármán Lecture, “Trends in Automatic Control in the Last Two Decades.” The University of Maryland awarded her an honorary Doctor of Science in 1973, citing her lifetime of work in a field dominated by men.
She retired in 1968 at sixty-five but continued research on satellite control, heat transfer and high-speed drag. Arthritis gradually immobilized her. She died in Stanford Hospital on 22 May 1974 at the age of seventy. Wilhelm Flügge survived her. They had no children.
Flügge-Lotz’s career spanned the transition from wooden biplanes to jet aircraft and early spacecraft. The Lotz method made three-dimensional wing design calculable; her control theory made discontinuous regulators predictable. She did that work first as an unofficial department head in Göttingen, then as a consultant in wartime Berlin, then as an under-ranked lecturer at Stanford, and only at the end as a full professor. The technical results outlasted the titles.