Recently, the history of Turkish aviation has primarily centered around the notable figures of Vecihi Hürkuş and Nuri Demirağ. However, this narrative approach is incomplete and overlooks the critical detail: the technical training and education. During the early days of the Republic of Türkiye, there was a strategic emphasis on education, leading to the opportunity for young citizens to pursue modern education abroad. Students that were selected through rigorous examinations were sent abroad starting in January 1925 and continuing through World War II.  Among those who were sent to Europe, Ertuğrul Esat, a scholarship recipient of the Turkish Aeronautical Association (THK), holds significant importance as the first verified individual to achieve a doctorate degree in aircraft engineering. His path crossed with famous scientists Theodore von Karman and Ludwig Prandtl during his time there.

Esat, also known as "Ertogrul Essad" in the records, is documented in the archives of the Technical Universities of Berlin, Braunschweig, and Aachen, as well as the Max Planck Institute. As the son of a legal advisor and a faculty member, Esat embarked on a journey to Germany after a short period at the Advanced School of Engineering (predecessor of İTÜ - İstanbul Technical University). His autobiography, penned in 1932, can be found in the archives of Aachen, where he prepared his doctoral dissertation. Esat introduced himself with the following lines:

“I, Ahmet Ertuğrul Esat, was born in Istanbul on March 17, 1903, as the son of the late university professor Mahmut Esat.1 After completing elementary school, I attended the 'Menba-ül-irfan' school and later graduated from high school in 1923. During the Allied forces' occupation of Istanbul, I attended the Advanced School of Engineering for a short time before coming to Germany for my university studies. Initially, my high school graduation degree was not recognized for university education, so I attended lectures at Technische Hochschule Braunschweig as an observer. Subsequently, I joined the Institute for Foreigners at the University of Berlin and passed the external graduation exams according to the Prussian system, which allowed me to enroll in Braunschweig. However, shortly after passing this exam, the German Ministry of Education informed me that my Turkish high school diploma was now recognized.

At Technische Hochschule Braunschweig, I completed the pre-diploma program in April 1926 and the graduate program in March 1927, earning the title of mechanical engineer. During the summer vacation, I took advantage of the time to gain practical knowledge and experience.

After graduating from Braunschweig, I received a scholarship from the Turkish Aeronautical Association and enrolled at Technische Hochschule Berlin-Charlottenburg in the Department of Aircraft Design . My pre-diploma from Braunschweig was recognized, allowing me to start from the fifth semester. In April 1930, I successfully completed my second graduate program in Berlin and was granted the title of aviation civil engineer. To gain practical experience, I worked at the Aerodynamics Research Institute in Göttingen (AVA, from May 12 to November 29, 1930), and later at Junkers Flugzeugwerke A.G. in Dessau (from December 8, 1930, to January 5, 1932.) During this period, I served to various departments, including fluid mechanics, statics, and construction.

In February 1932, I came to Göttingen to conduct the experimental part of my doctoral dissertation. 

Aachen, November 20, 1932 (-signature-)”

His school number in Berlin, where he came as a scholarship student of the Turkish Aeronautical Association, was 39161. He studied at this school between the fall semester of 1927/28 and July 7, 19302.   During his time there, he had the privilege of being a student of Wilhelm Hoff and Hermann Föttinger, renowned German professors in the aviation field. In his PhD dissertation titled "Tandem Propellers: Their Most Favorable Arrangement and Comparison with Single Propellers," he provides extensive information about his scientific work and mentions the support he received from Philipp von Depp, Head of the Fluid Mechanics Department at Junkers. Esat discovered that Gustave Eiffel and Karl Schaffran had also conducted experiments on this subject, but they could not effectively integrate it with theoretical calculations. He believed that no satisfactory research had been conducted worldwide on the efficiency analysis of two propellers placed one behind the other in tandem arrangement. Recognizing the gap in the scientific literature on aircraft propulsion systems, Esat decided to shift the focus of his doctoral dissertation to this area.

The 106-page study takes the propeller examined in Fred Weick's 1929 NACA report No. 306 as its reference.3 The reason for this choice is the claim that it may be the most suitable for optimal performance in a tandem arrangement. The first 42 pages of the study delve into topics like velocity distribution of the blades of this propeller, the mutual influence of both propellers, thrust and torque coefficients, and changes in the pitch of the propeller, all analyzed through mathematical calculations. To verify the theoretical findings at experimental environment, tests were conducted at the research center in Göttingen.

The experimental investigations are mainly concerned with measuring the thrust and moment coefficients at three different distances between the two screws and at different pitches of the rear propeller. An important result is that the rear propeller has no influence on the front propeller even at the smallest distance (1/2 propeller diameter). Finally, the velocity field in the jet is examined and compared with the calculated values. The conclusion of Esat's dissertation includes the following statements: Full recovery of the twist loss of the puller propeller is possible if the pusher propeller is dimensioned appropriately. In this case, the tandem arrangement works without twist loss. However, the torques of both propellers are not equal. The tandem's thrust is greatest when the full swirl energy is recovered.

(20 Kasım 1932’de fakülteye tezini teslim edip savunma tarihi için başvuran Esat’ın tez danışmanları Aachen Mühendis Mektebi’ndeki ünlü bilim insanları Carl Wieselsberger ve Ludwig Hopf’tur. İki profesör de 14 Aralık 1932’de tezin yazılı kısmı hakkında değerlendirme raporunu fakülteye gönderir. Prof. Hopf, değerlendirmesinde şu tespitlerde bulunmuştur:)

On November 20, 1932, Esat submitted his dissertation to the faculty and requested a defense date. His dissertation advisors were Carl Wieselsberger and Ludwig Hopf, renowned scientists at Technische Hochschule Aachen. Both professors submitted their evaluation reports on the written part of the dissertation to the faculty on December 14, 1932. In his evaluation, Prof. Hopf made the following observations:

“...There may be little of direct practical use, but the insight into the conditions of tandem propellers is very useful. The author shows theoretical understanding and experimental skill to an appreciable degree.”

Prof. Wieselsberger concludes the report with the following sentences: 4

“...This work demonstrates a good understanding of the fundamentals of propeller theory. The theoretical and experimental results contribute significantly to the clarification of the processes occurring in tandem propellers. I therefore recommend the work for acceptance as a doctoral dissertation.”

On Wednesday, December 21, 1932, Ertuğrul Esat successfully defended himself before a jury chaired over by Otto Blumenthal, a renowned mathematics professor who tragically lost his life in a concentration camp during World War II. As a result of his defense, Esat was granted the prestigious title of "Doctor of Engineering" on February 9, 1933.5 The Aerodynamics Research Institute in Göttingen, where the experimental work was carried out, and the Kaiser Wilhelm Institute for Flow Research conducted joint studies on the same campus at that time. Another document from Esat's time in Göttingen is found in the archive of the Kaiser Wilhelm Institute, which was later renamed the Max Planck Institute. In a folder that lists foreign researchers, Esat's name appears as an employee of Junkers, with his residence address mentioned as "Herzogsallee 44, Dessau." This significant detail indicates that Esat's doctoral dissertation was conducted in collaboration with the renowned German aircraft manufacturer, Junkers.6

In the July 1, 1935 issue of "Aviation and Sports" magazine, the publication organ of the Turkish Aeronautical Association, an article titled "Our students in Europe: Engineer students trained in Europe by the Turkish Aeronautical Association" features a list of 19 individuals. Among them, Ertuğrul Esat stands out as the only engineer holding a PhD degree. The information regarding Esat’s assignment to Kayseri Aircraft Factory as part of his compulsory service in return for the scholarship he received is documented in the memoirs of Wilhelm Gibałka, one of the Polish engineers employed in Kayseri. Osman Fırat Baş, referring to Gibałka's memoirs published in 1960 in the aviation magazine "Skrzydlata Polska" in his own country, describes the situation as follows:7

“...The acceptance of each part produced in Kayseri is subject to technical control. Initially, the technical control process progressed smoothly with cooperation between the Poles and the Turkish personnel. Although the Turkish team made occasional evaluation errors due to their unfamiliarity with the P-24s, they generally did not intentionally create difficulties for the Poles. However, this dynamic underwent a radical shift with the appointment of Ertuğrul Esat as the Head of Technical Control. Esat, a Turkish engineer specialized in aerodynamics, who had studied and interned abroad and was married to a German woman, seemed to harbor little fondness for the Poles, as sensed by Gibałka. During inspections, even the most trivial issues would lead to a complete halt of work in the hangar, with long meetings attended by the Technical Manager. Despite Gibałka's warnings about potential delays, his concerns were disregarded, and this even earned him a new adversary...”

Dr. Ertuğrul Esat was a prominent engineer who pursued his education in Germany and had the privilege of working in esteemed research institutes alongside notable figures in the field such as Theodore von Karman and Ludwig Prandtl. As a recipient of the Turkish Aeronautical Association scholarship and an employee at Kayseri Aircraft Factory, compiling a comprehensive biography of Dr. Esat would necessitate access to relevant documents from both institutions. His biography is expected to provide valuable insights into the specific areas within the Turkish aviation industry where he applied his knowledge acquired abroad. The fact that Dr. Esat’s contributions remain relatively unknown to this day is a poignant reminder of the lack of interest in the history of engineering in Türkiye