INVENTING ROOT LOCUS:HOW ONE MAN REPLACED CHAOS WITH CLARITY

   Evans had many innovative ideas, frequently years ahead of their time, but root locus arrived at the perfect moment. Now, decades later, its significance has only grown with time. One colleague called it among the aerospace industry's greatest contributions.  Perhaps it was.

Root locus revolutionized automatic control systems design in the last half of the 20th century. With simple tools—a Spirule and graph paper—engineers could solve problems and gain valuable insights in seconds. It would take another 15 years for programs like MATLAB to solve these problems, though without the same intuitive understanding.

A  friend wisely advised me to highlight root locus's significance at the book's start. I agree. Chapter 1, mostly written in 2004 by Stanford Aeronautics Professor Robert H. Cannon  for the author’s use, explains the transformative leap root locus brought to control system design.

1920-1937

Walter Evans, the youngest of four children born to Gomer and Syblia Evans, grew up in St. Louis at 7048 Nashville Avenue. His paternal grandparents and maternal grandfatSher were also born in St. Louis, while his great-grandparents hailed from the working classes of Britain, converted by early Mormon missionaries. His grandparents and parents later connected through the Reorganized Church of Latter Day Saints, a branch of the LDS church that rejected polygamy . 

Walter was born on January 15, 1920. 

I was also born in St. Louis, in August 1947, like my parents and grandparents before me. That same month, while working at Emerson Electronics and living in St. Louis, Dad submitted the first of two papers to the A.I.E.E., marking a pivotal moment in his career. As this book unfolds, it reveals how my dad's life choices profoundly shaped my own, making this writing journey a tribute to his enduring spirit.

 1937-1941

 Evans' boyhood home at 7048 Nashville Avenue was, at 1.8 miles, a short jaunt on his bicycle to the campus of Washington University. Moreover, his brother, Cedric, his father, and uncle, had earned degrees, and his brother, Sam, was a student. Life-altering decisions lay head, but his immediate future was set: Washington University

Between 1937 and 1941 Evans formed relationships with his future wife and engineering school dean Alexander Langsdorf, professors Roy Glasgow and - Middlemiss that would last a lifetime.

1941-1946

During World War II, General Electric's (GE) Schenectady plant was a pivotal contributor to the Allied war effort. GE implemented the Advanced Course in Engineering, a rigorous three-year, in-house program designed to develop engineers capable of identifying and solving real-world engineering challenges. This program not only enhanced the technical expertise of GE's workforce but also ensured a steady supply of skilled engineers who could innovate and maintain the sophisticated technologies essential for the war effort. Assigned to a project whose goal was an innovative new gun-turret for the B-29, Evans' work exposed him to servo-mechanisms and the limitations of design tools.  He found hope in a new graphical analysis in a journal article by Swiss Engineer Paul Profos.

  1947-19948

Letter written by Evans on August 11, 1947  to P. Profos

… “Your idea of using the Nyquist plot as a single line of a conformal map to determine the complex root of the differential equation seemed to me to be the basic idea for a very practical method. In September 1946 I became an instructor of Electrical Engineering at Washington University in St. Louis, Missouri and worked off and on with your idea during the fall and winter. … I believe that you made a real contribution to the analysis of regulators and hope that this paper succeeds in calling attention to it. It has certainly provided me with the opportunity to write a worthwhile paper which otherwise not have occurred for several years.

1948-1955

In June 1948, at the end of WashU's academic year, Evans accepted an offer from his classmate, friend, and mentor John R. Moore to explore full-time employment. Two months later, in August, he returned to St. Louis, packed his belongings, wife, and two children into a two-tone, brown-and-grey 1947 Oldsmobile, and drove cross-country. 

In September, they   settled in Whittier, California.

Walt Evans’ arrival at NAA in 1948 placed him at the heart of a transformative era. Working in the Aerophysics Laboratory, he joined a pioneering effort to push the boundaries of aviation and technology. As the industry faced an uncertain future, a wave of young engineers, many from the Midwest like Evans, moved to Southern California. With their expertise and creativity, these engineers played a vital role in shaping American aerospace innovation. This chapter of Evans’ life highlights his contributions while reflecting the broader challenges and triumphs of a pivotal moment in technological history.

September 7, 1948?

Evans credited a question from a student as the inspiration for his breakthrough. The student asked how the root locus would be affected if the characteristic equation was not perfectly quadratic due to a small third-order delay element in the feedback loop. Evans referred to it as his "slightly cubic" question. In his September 14 servo class notes, which included a key diagram, Evans addressed this question. He realized that the solution to the "slightly cubic" problem could be generalized to any characteristic equation, regardless of its order.

This realization marked a turning point in Evans's career, a moment made possible by the unique convergence of research, education, and industrial design at the Aerophysics Lab. As Evans shared his insights with engineers working on real systems, his methods gained rapid traction, illuminating new possibilities in their work.

1948-1950

Two months later, in November 1948, Evans submitted his manuscript to the IEEE, presenting the fully developed "Locus of Roots" method. The name was  shortened to "root locus" in a March 1949 rewrite.  Despite positive feedback from practicing engineers, theoretical reviewers found the paper confusing, and Evans faced significant challenges in getting it published. This chapter recounts Evans's struggle to bring his ideas to light—a journey that culminated in the paper's publication in January 1950.

1948-1951

 Evans collaborated with colleagues at North American's Aero-physics Lab, especially Jeff Schmidt, to develop the device colleague DeWitt Lyon first called a Spirule. This chapter is an account of the invention of the device, the first sales of the now-iconic device in December 1950, and events leading up to the creation of the Spirule CompanY.

1949-1954

As Yogi Berra might say, "it was Deja vu all over again." in this reprint of a paper entitled Bringing Root Locus into the Classroom, published in 2004 on the 20th anniversary of its publication, this chapter once again finds Evans jousting with his publisher in the course of writing his textbook, Control Systems Dynamics. One contentious issue was Evans unorthodox stand on the role of the Laplace Transform in the introduction of root locus. Evans opposed it because in his experience students did not understand the Transform.

 1955-1959

There is certainly no question that Walt was an outstanding technical talent.

However, he was also an outstanding manager of people. Either explicitly, or perhaps implicitly, everyone in the group knew that Walt’s position was that we worked for him and that he had complete faith in us. As I recall, he said in effect, “If anyone outside the group has any complaint about how you are doing your job, send them to me. I gave you the job and I am responsible for how you do it.” This kind of management support resulted in people being unafraid to stretch their talents to the greatest extent. You learned to act and complete work without fear of possibly making a mistake. Walt’s support and management style created some of the finest leaders in the Navigation Systems Division (NSD) and Autonetics. Sam Carson became the head of NSD later and went on to manage the start of the Autonetics electronics components business, now mostly nonexistent. George Leisz, another supervisor in Walt’s Group 64 followed Sam as head of NSD and later became head of all of Autonetics when John Moore went to the corporate office. As you know he was a great man.

Hal Engebretson

Yorba Linda, CA

1952-1980

The Spirule Company was a virtual non-profit enterprise operating out of Evans's Whittier residences on Maple Street and El Venado Drive.  Over 100,000 units were sold at Evans's cost for decades, as root locus was embraced by academics and engineers world-wide.  Today computer programs such as MATLAB compute answers.