Peretz P. Friedmann | Faculty
Francois-Xavier Bagnoud Professor, Aerospace Engineering
Peretz P. Friedmann is currently the François-Xavier Bagnoud Professor in the Aerospace Engineering Department at the University of Michigan, Ann Arbor. He is also the Director of the FXB Center for Rotary and Fixed Wing Air Vehicle Design, and the Associate Director of the Vertical Lift Research Center of Excellence (VLRCOE) which is a partnership between Georgia Tech (lead university), University of Michigan, Washington University in St. Louis and Utah State University. He has been with the University of Michigan since January 1999. Between 1972 and 1998 he was a Professor, 1972-1977 Assistant Professor, 1977-1980 Associate Professor, 1980-1998 Professor) in the Mechanical and Aerospace Engineering Department of the University of California, Los Angeles. Between 1988 and 1991 he served as the Chair of the Department. He recieved his B.S. and M.S. degrees in Aeronautical Engineering from the Technion - Israel Institute of Technology and his Sc.D. (1972) in Aeronautics and Astronautics from the Massachusetts Institute of Technology. Prior to entering the Academic world, Dr. Friedmann was a Senior Engineer at Israel Aircraft Industries and an engineering officer in the Israeli Air Force.
Dr. Friedmann has been engaged in research on rotary-wing and fixed wing aeroelasticity, on blade control of rotor vibration and noise, hypersonic aeroelasticity and aerothermoelasticity, structural optimization with aeroelastic constraints, and jet engine aeroelasticity. He has published extensively, 350 journal and conference papers. A total of 35 Ph.D. students have graduated, under his guidance, several of them hold faculty positions as well as senior positions in the aerospace industry in the US. He was Editor-in-Chief of the AIAA Journal (2009-14), Editor-in-Chief of Vertica - The International Journal of Rotorcraft and Powered Lift Aircraft (1980-90), Associate Editor of the Journal of the American Helicopter Society (2004-9) and AIAA Journal of Aircraft (2005-9). He is on a number of national award boards and review committees engaged in review of research funding, as well as review of Aerospace Departments. He has been a naturalized US citizen since 1977.
Professor Peretz Friedmann has made outstanding and lasting original contributions to rotary and fixed wing aeroelasticity and structural dynamics, on blade control of vibration and noise in rotorcraft, optimum design of low vibration helicopter rotors, rotorcraft aeromechanics and unsteady aerodynamics. These contributions had a major impact on understanding the aeromechanical behavior of helicopters and have advanced the state of modern helicopter design. He has also made major contributions to hypersonic aeroelasticity and aerothermoelasticity as well as jet engine fan blade aeroelasticity. A number of other areas where he has contributed are described in his CV.
His research has addressed the major technical challenge for civilian and military rotorcraft i.e. vibration reduction to improve passenger comfort, pilot performance and ensure structural integrity. He originated the concept of on-blade control for vibration reduction in helicopter rotors implemented by partial span actively controlled trailing edge flaps, and was the first to demonstrate its feasibility in 1991. For on-blade control both the control surfaces (flaps) and actuators are on the rotating blade. During the past 24 years he has extended on-blade control to encompass combined vibration and noise reduction and turned the concept into a practical tool suitable for implementation on full-scale rotors [see - Friedmann, P. P., “On-Blade Control of Rotor Vibration, Noise and Performance: Just Around the Corner?,” Journal of the American Helicopter Society, Vol. 59, No. 4, October 2014, pp. 041001-1 to 041001-37]. Since conceiving on blade control, the subject has blossomed into a fertile and promising field of research with over 500 papers published.
Another thrust of Professor Friedmann’s research, during the last 20 years has focused on the aeroelasticity and aerothermoelasticity of hypersonic vehicles. In these vehicles the aerodynamic loading, the dynamics of the structure, the aerodynamic heating and the propulsion system are tightly coupled. This problem represents one of the last frontiers of aerospace research and his contributions have improved substantially the fundamental understanding of this multiphysics problem.
Professor Friedmann’s accomplishments have been recognized by several awards, for details see Honors and Awards tab below.
Massachusetts Institute of Technology
DSc Aeronautics and Astronautics
Technion-Israel Institute of Technology
MSc Aeronautical Engineering
BSc Aeronautical Engineering
- American Institute of Aeronautics and Astronautics,Fellow
- American Helicopter Society, Fellow
- American Society of Mechanical Engineers, Member
POSITIONS HELD AT MICHIGAN
- François-Xavier Bagnoud Professor
- Director of FXB Center for Rotary and Fixed Wing Air Vehicle Design
Rotary and fixed wing computational aeroelasticity, vibration and noise reduction in helicopters using actively controlled flaps, hypersonic vehicle aerothermoelasticity, multidisciplinary optimization, and turbomachinery aeroelasticity.
- Aeroelasticity (Aero 544)
- Helicopter Aeromechanics (Aero 545)
- Structural Dynamics (Aero 543)
- Aircraft and Spacecraft Structures (Aero 315)
- Aircraft Design (Aero 481)
- Meir Hanin International Aerospace Prize (2016), awarded by The Technion, Israel Institute of Technology (2016)
- AHS Alexander A. Nikolsky Honorary Lectureship (2013)
- AIAA Ashley Award for Aeroelasticity (2009)
- AIAA Dryden Lectureship in Research (2009)
- American Helicopter Society (AHS) Fellow Award (2004)
- Spirit of St. Louis Medal, awarded by ASME (2003)
- AIAA Structures, Structural Dynamics and Materials Lecture Award (1997)
- AIAA Structures, Structural Dynamics, and Materials Award (1996)
- Fellow AIAA (1991)
- ASME/Boeing Structures and Materials Award (1984, 2004, 2010)
- Note - the last award is an award for the best paper given at the SDM conference in the previous year, the year indicates the year in which the award is given.
Helicopters are generally perceived as the workhorses of the aviation world. They hover over traffic, pluck people off mountains and burning buildings, fly people to hospitals, ferry workers and equipment to offshore oil drilling platforms.
With their unique capabilities they could make short-range air travel as commonplace as taking a bus - if engineers could just solve a couple of persistent problems.
A helicopter’s rotating blades generate a loud “wop wop wop,” noise that makes the prospect of landing in a residential neighborhood less than appealing. And cabin vibration can make a helicopter ride feel like traveling down a dirt road in a jeep.
The helicopter industry has been searching for answers to its noise and vibration problems for decades. Peretz Friedmann, the François-Xavier Bagnoud Professor of Aerospace Engineering, is closing in on a solution.
Friedmann, who is also the Director of the FXB Center for Rotary and Fixed Wing Air Vehicle Design, has devoted much of his career to tackling the problems of noise and vibration in helicopters.
Before coming to Michigan in 1999 he spent 26 years at UCLA where, among several pioneering contributions to rotorcraft aeromechanics, he developed an efficient way to design the low-vibration rotors that many helicopters use today.
Friedmann has spent more than two decades seeking the “jet-smooth ride” that is the helicopter industry’s holy grail, eventually developing a system that includes two very small, actively-controlled flaps placed at intervals on each of the helicopter’s blades. A sensor measures vibration at the hub of the rotor and a microphone mounted on one of the helicopter’s skids measures noise. The system uses those two measurements to adjust the flaps, reducing both noise and vibration.
Friedmann has been working on this concept since 1991, and devices he designed are now flying on pre-production experimental helicopters.
Helicopters’ utilitarian nature masks an incredible complexity. They are an order of magnitude more complicated than their fixed-wing counterparts. To design a helicopter an engineer must be adept in aerodynamics, structural dynamics, active control and aeroacoustics - all the disciplines that make up rotary-wing aeromechanics.
Friedmann specializes in an area called aeroelasticity, which involves the interaction of fluid (in this case, air) and structure. His active-flap system was initially inspired by a servo-flap system used as the primary flight control on all Kaman helicopters. He decided to investigate whether something similar might help address the issues of vibration and noise.
“Fortunately, at the university, you can always ask a very smart student to work on the problem,” he said. “The first student who worked on the problem is now the chief of dynamics at Sikorsky, which is the one of the leading helicopter companies in the world.”
Friedmann also works at the other end of the velocity spectrum, on fixed-wing hypersonic vehicles. Flying at speeds in excess of five times the speed of sound, they encounter a different and very fundamental set of challenges. Aerodynamic heating at that speed can raise temperatures to more than 2000 degrees Fahrenheit. Once engineers find structures and materials that can withstand the heat, they still face the challenge of developing an air-breathing engine that can function at that speed. Then there’s the issue of combining the two into a vehicle capable of sustained hypersonic flight.
As a 5-year-old boy, Friedmann was enthralled by the planes he saw in the sky over his Romanian hometown, and he decided then to become an “airplane engineer.” His parents moved to Israel when he was 12 years old, and he grew up in Haifa, Israel. He would eventually study aeronautical engineering at the Technion-Israel Institute of Technology in Haifa and later serve as an engineering officer in the Israeli Air Force. Many of his friends were pilots, and Friedmann would hitch a ride on anything with wings.
He came to the U. S. in 1969 and earned his Sc.D. at Massachusetts Institute of Technology. Friedmann studied under Rene Miller, a rotorcraft pioneer who dreamed of a future where tilt-rotor vehicles (similar to today’s Osprey) would be a commonplace means of short-range transportation.
Miller was head of the Aeronautics and Astronautics Department at MIT, and Friedmann has never forgotten how it felt as a graduate student to walk into Miller’s office and receive the department head’s undivided attention. As a professor, he’s tried to emulate the way Miller always put his students first. He says interacting with his students keeps him young.
His former graduate students have important positions at Sikorsky, Boeing and NASA, and five are professors at highly ranked universities. Young PhD students approach him at conferences and introduce themselves as his academic grandchildren.
“I’m more pleased with the success of my students than with my own accomplishments,” he said. “I feel like I’ve done something useful.”