9/7/2016 Diane Jeffers, AE Coordinator of External Relations, and AE Emeritus Prof. Harry H. Hilton
Written by Diane Jeffers, AE Coordinator of External Relations, and AE Emeritus Prof. Harry H. Hilton
September 5, 1919 – August 6, 2016
After earning his PhD, Yen became an assistant and, later, an associate professor of mechanical engineering at Kansas State University from 1951-56. He returned to Illinois as an associate professor of aerospace engineering, and was promoted to professor in 1962. From 1985 to 1987, Yen was acting head of the department. Retiring on May 20, 1990, he remained active in AE.
Yen’s incisive research contributions to rarified gas dynamics and computational hypersonics earned him national and international recognition. He often was invited to present lectures at the USSR Academy of Science and the University of Trondheim in Norway. Yen was selected to participate in an exchange program with the Computational Physics Group of the Moscow Computing Center. At Illinois, he collaborated with faculty in the Coordinated Science Laboratory.
Yen’s industrial experience included working three years as an engineer in Taiwan, and as a consultant over three summers at McDonnell Aircraft Company, Boeing Airplane Company and AVCO, respectively. Additionally, he consulted with Ballistic Research Laboratories, Convair, and the NASA Marshall Space Flight Center.
Both before and after retiring from AE at Illinois, Yen helped develop departmental educational policy. His students spoke highly of his teaching performance and continued to seek his professional advice after their graduations.
From Robert Liebeck, BS 61, MS 62, PhD 68, Senior Fellow, The Boeing Company
From David Riley, BS 77, Program Manager, The Boeing Company
I only took one course from Professor Yen, but was struck by his personable style and how he went out of his way to ensure that the students were learning the material. He was very engaged with the class and was always friendly and approachable when I had questions. Professor Yen was always interested in how I was doing when I came back to campus and was always glad to see me.
Professor Yen enjoyed following Illini football and was especially pleased when Illinois beat Michigan late in the 1983 season at Zuppke Field. He had two panoramas that were taken of Zuppke Field, with the final score, printed on poster-sized paper and gave out copies to everyone that wanted one. Obviously he was very proud of the Illini victory that day!
Yen also directed AE’s Graduate Extramural Program, providing a master’s degree-level program at the then-McDonnell Douglas facility in St. Louis.
From Steve D’Urso, BS 78 MechSE, MS 89, Coordinator/Lecturer of Systems Engineering, AE at Illinois
I had Professor Yen when I was pursuing my Master’s degree. He was teaching "Boundary Layer Theory.” It was one of my most memorable classes. It involved the study of theoretical boundary layers. One (of the problems) was an aircraft situation in which you would initially model the flow from the theory and then apply it to the situation. From that you make design decisions based on the data that you generated. This involved a fair amount of commuter programing to model the situation and interpret the results. Well, I was never a great programmer. We did all that programming in FORTRAN at that time, which is a very picky language. One misplaced digit or extra space could really foul things up. In one of my problems I couldn't get the program to converge on the shooting method of integration. After many runs, which took a lot of time back then, I finally decided I had to ask the professor what I was doing wrong. I spent the time on how I formulated the problem and my approach to programming it. He listened intently. Then he gave me his advice on how to fix the problem: "Just make the damn thing run.” Well I was puzzled but eventually found the small programing parameter to adjust making the program converge. He knew I would learn more by finding it myself. He was right.
Yen’s family and AE faculty and staff members remember him for his great sense of humor. He always had a story to tell about his early years in China, his time at college and his past graduate students. He was a devoted husband, father and grandfather, survived by his wife, Maria; daughters, Elizabeth, Debbie, and Frances; son, Robert; and six grandchildren.
Professor Yen shall be missed but not forgotten.
From Michael F. Lembeck, BS 80, MS 81, PhD 91
Early in the summer of 1985, I returned to the Urbana campus to explore the possibility of pursuing a PhD in Aeronautical and Astronautical Engineering. Dr. S.M. Yen was serving as the interim department head while a search committee looked for a replacement for the irreplaceable (Prof.) Harry Hilton. We talked about my desire to pursue research in the not-yet-explored implementation of artificial neural network-based control systems (now popularly called “deep learning” systems), and Dr. Yen proposed a path for-ward for me. Eventually, he, along with (Prof.) Ken Sivier, would become my co-advisors in this uncharted territory. Little did I know at the time, I would also be his last official PhD student.
Dr. Yen was world-renowned in computational hypersonics. But he resisted being pigeonholed by that discipline. To that end, he invited me into his office a couple of times a week for wide-ranging discussions. We both equally enjoyed those talks and genuinely learned from each other in the process. One of those conversations stands out in retrospect and would eventually guide my career trajectory. A peer of Dr. Yen’s had forwarded a note asking for a succinct description of “systems engineering.” In turn, he asked me to take a stab at defining what was becoming an oft-used, yet somewhat ill defined, term.
A day later I returned with a block diagram showing the path from customer requirements to delivered system. Dr. Yen was immediately able to convey the gist of the process to his friend and I had a graphic that I would use in tens of industry proposals since that day. Commenting on the speed of my response, Dr. Yen conveyed a compliment and a lesson as he sometimes would in compact, almost Zen-like, form. “A good engineer does things quickly and accurately. One without the other has little value."
On my return trips to campus after graduation, I would always be greeted by his quick step, an eager smile, and a firm handshake. For someone so focused on making contributions in his field, Dr. Yen would first ask about my parents, my former classmates, and my career. After he retired from campus, we still exchanged Christmas cards every year, even as his wife began writing the return greetings when he no longer could. For those of us who were privileged to have spent time with Dr. Yen, he – and his lessons – will certainly live on.