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Dynamic people: Bill Milliken

Low flyer

William F. ‘Bill’ Milliken’s pioneering vehicle dynamics research stemmed from a love of all things automotive and aeronautical

By Joe Walter

Adventure, innovation and risk have been part of William F. ‘Bill’ Milliken’s career in aircraft and vehicle dynamics for more than 75 years. He designed, built and crashed his own wood and fabric airplane in 1933 before finishing college. He then graduated from Massachusetts Institute of Technology (MIT) with a degree in mathematics, which was more attractive to him than the two years of German language study involved in an engineering degree, although he did devour elective courses in MIT’s renowned aeronautics department. True to his genetic profile, he went on in later years to design, build and/or crash several race cars.

Milliken spent most World War II actively engaged in flight testing of prototype military aircraft such as Boeing’s B-29 and Avion’s flying wing (XB-79). At the end of the war, engineers with this expertise in aircraft stability and control began to apply mathematical modeling to similar problems in vehicle dynamics. Milliken joined the Cornell Aeronautical Laboratory (CAL) where he spearheaded the application of fundamental math and physics principles, first to the motion of aircraft, and then to automobiles. He was driven by necessity to tire testing because proper vehicle modeling required tire force and moment data.

Now nearing his 100th year, Milliken is well known in racing circles for his basic research in automobile handling, but is less well known for his early creative work with tire testing and cornering behavior. For example, he demonstrated the validity of using quasi-static tire properties in modeling vehicles at highway speeds subject to non-steady-state steering commands. This fundamental understanding of tire-vehicle response underpinned subsequent research dealing with the Milliken Moment Method and the ‘g-g’ diagram. His passion for race cars convinced him that you can’t drive one successfully without becoming involved in the finer points of handling. Extant aircraft textbooks provided the necessary basic theory for motion in flight. Because the automobile had been around much longer than the airplane, he assumed that there must be equivalent texts for vehicles traversing roadways.

But other than a 1947 paper by Maurice Olley, Milliken found nothing that met his needs. He visited General Motors in 1952 in search of such information, but unexpectedly met Olley, and then received a sizeable grant from GM to undertake studies on transient behavior of tire-vehicle systems. This research sponsorship continued until 1963 and was the beginning of the modern vehicle dynamics era in the USA. This built on Olley’s seminal work of the early 1930s at GM dealing with steady-state behavior. Research was largely based on technology transfer from the aircraft field. As a matter of policy, Milliken laid great emphasis on physical understanding of equations because investigations of vehicle handling at the time tended to be more art than science.

Milliken knew that the maneuvering forces for aircraft are aerodynamic in nature and could be measured in a wind tunnel; for automobiles, the forces principally arise from tire-road interactions and had to be obtained by other methods. Both aircraft and automobiles have operational limits based upon available external forces that, when exceeded, can result in dramatic changes in stability and control such as stalling and skidding. Thus, in 1952, Milliken secured a USAF contract to design and construct an on-road tire tester that enabled accurate measurements of the six-tire force and moment components over a large range of slip and camber angles under variable braking conditions. This machine was a major advance over previous tire testers and served as a basis for subsequent machines placed in operation elsewhere.

One major result obtained early on was that tire stiffnesses changed during service due to tread wear. CAL then received grants from many tire companies to measure tire force and moment properties – principally lateral force and aligning torque. Toward the end of Milliken’s career at CAL, the first commercially viable, flat-surface, high-speed laboratory tire force and moment machine, TIRF was placed in operation – and is still running today.

No sign of a slowdown

Although he formally retired from CAL (now known as Calspan) in 1976, Milliken has maintained an incredibly active professional life as a consultant and writer. In 1995 he co-authored the successful Race Car Vehicle Dynamics, which has sold more than 20,000 copies; he discerningly profiled the career and research of Maurice Olley in Chassis Design (2002); and most recently he published his autobiography, Equations of Motion (2006).

Who knows what might originate from the active mind of this nonagenarian in the future?