**Sergei Chaplygin** was a Russian physicist and mathematician who did important work in hydrodynamics and aerodynamics.

- Sergei Alekseevich has a great future.
- In the autumn of that year, at age seventeen, Chaplygin packed a small suitcase and, with 200 rubles in his pocket, set off from Voronezh to Moscow to begin his university studies of mathematics.
- At the University of Moscow Chaplygin studied in the Physics and Mathematics Faculty and, for the first two years, he concentrated exclusively on mathematics courses.
- After Chaplygin graduated with his first degree in 1890, Zhukovsky persuaded him to continue to study for his university teacher's qualification.
- In 1893 Chaplygin published On certain cases of the motion of a solid body in a fluid and the quality of this work was so outstanding that he was awarded the N D Brashman Prize for this contribution.
- Chaplygin had begun teaching in Moscow in the year 1893.
- After the award of his Master's Degree (equivalent to a Ph.D.), Chaplygin worked on two classic problems of theoretical mechanics.
- Three decades later, however, Chaplygin's dissertation served as a starting point for many studies by aerodynamics specialists and provided the basis for the solution of problems of subsonic flows.
- Chaplygin wrote his remarkable dissertation while he was on vacation at a resort in the Crimea.
- Nevertheless it continued to operate as an excellent university, providing Chaplygin with a very good education.
- Chaplygin was one of the professors who resigned in 1911 along with a number of his colleagues in mathematics such as Boleslav Kornelievich Mlodzeevskii (1858-1923), who was very active in the Moscow Mathematical Society.
- Zhukovsky was the president of the Moscow Mathematical Society at this time which gave Chaplygin more reason to maintain a high level of involvement.
- Chaplygin read papers on mechanics and on approximate methods in analysis to the Society.
- This postulate - the so-called Chaplygin-Zhukovsky postulate - gives a complete solution to the problem of the forces exerted by a stream on a body passing through it.
- This article includes the fundamentals of plane aerodynamics, particularly Chaplygin's celebrated formulas for calculating the pressures exerted by the stream of a fluid on an impeding body.
- These formulas were applied by Chaplygin to the calculation of the stream pressure on various wing profiles for which he gives the construction.
- Chaplygin's important paper Theory of cascaded airfoils (1914) presented the basic theory of circulation round cascades, the theory which is used in the design of propellers, turbines and other hydraulic devices.
- Together with Zhukovsky, Chaplygin planned for the setting up of an aeronautical research centre in Moscow.
- On the death of Zhukovsky in 1921, Chaplygin became Chairman of the Board, a position he held until 1930.
- Lazar Aronovich Lyusternik became a research student in the Moscow Institute of Mathematics and Mechanics in 1922 where he was taught by Chaplygin.
- But Chaplygin had not published this paper, since this theory did not have a mathematical basis.
- Chaplygin took charge of the Novosibirsk branch of the Institute and rapidly organised the building of a wind tunnel and research laboratories.
- Further honours were given to Chaplygin following his death.
- Ranenburg, the town of his birth, was renamed Chaplygin in 1948.
- A crater on the moon has been named for Chaplygin.
- Finally let us mention that Chaplygin loved playing chess and spent many hours playing against friends in the staff club.

Born 5 April 1869, Ranenburg (now Chaplygin), Russia. Died 8 October 1942, Novosibirsk, USSR.

View full biography at MacTutor

Origin Russia

**Oâ€™Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive