People's Republic of China
Professor Pinqi Xia, PhD, Dean of Graduate School, Nanjing University of Aeronautics and Astronautics (NUAA)
As a professor of structural dynamics and aircraft engineering in the NUAA College of Aerospace Engineering and dean of the NUAA graduate school, Professor Pinqi Xia both teaches rotorcraft fundamentals and leads advanced research and graduate studies. Some of his student-researchers have gone on to work with Chinese industry on current helicopter programs. Prof. Xia observes, “The most difficult challenges in modern rotorcraft are how to effectively reduce noise and vibration and how to make rotorcraft easy to pilot.” He adds, “With the gradual opening of lower-altitude airspace in China, the civilian helicopter industry will grow at an unprecedented pace and promote rapid development. The most promising rotorcraft research in China will be for civilian helicopters to address the challenges.
“Civilian helicopters have more demanding requirements for low noise and vibration and easy piloting than military helicopters. Piloting a rotorcraft as easily as driving a car is a dream of many people. I hope this dream can be realized in the near future.”
Nanjing University of Aeronautics and Astronautics was founded in 1952 and today has about 24,600 students and 1,600 teachers and professional researchers. It is the only university with a specialty helicopter program in China. NUAA performs basic, applied and national defense research, and its faculty and students have developed more than 20 types of aircraft, including China’s first helicopter and China’s first unmanned helicopter. Within the College of Aerospace Engineering are the dedicated Helicopter Research Institute and National Key Lab for Rotorcraft Aeromechanics. The lab has an enclosed wind tunnel, whirl test machine, rotor test stand, vibration and fatigue testing systems, and computer-based simulators to support research efforts.
“About 60 bachelor’s degree students, 30 master’s degree students, and five PhD students in helicopter engineering graduate every year,” explains Dr. Xia. “Unfortunately, only about one-fifth of the students go on to work in the helicopter industry. Most of the students are only willing to work in modern cities such as Shanghai, Nanjing, Beijing, Guangzhou, etc.” China Helicopter Design Institute and Changhe Aircraft Industries Corporation, designer and maker of the Z-10 attack and Z-11 light utility helicopters, are based in Jing Dezheng, a small city in Jiangxi Province. Harbin Aircraft Industry, maker of the Z-15/EC175, Z-9 series, and other helicopters is in Harbin, a big city in Hei Longjiang Province. Both are considered less developed areas in China. [All of the manufacturing companies are part of the Aviation Industry Corporation of China (AVIC) under the Avicopter banner. See www.vtol.org/avicopter – Ed.]
Prof. Xia grew up in Zhouzhuang, a small town with a long history located on the south bank of the Yangtze River in Jiangyin County, China, “I keep a family genealogy that traces back 30 generations of the Xia family,” he notes. “When I was a child, I enjoyed making bamboo-copters with my father’s help. Just by rubbing my hands together, the bamboo-copter would rotate and fly. Also, I often built kites. As long as I pulled the string back and forth, the kite would fly. At that time, I recognized that the wind could blow things upward and have a magic power.”
Dynamists and Researcher
Pinqi Xia entered Nanjing Aeronautical Institute to study aircraft design in 1980 and received his bachelor’s degree in aeronautical engineering in 1984. He recalls, “When I filled in the application form for specialty study after taking the university national entrance examination, the first specialty I selected was aerodynamics at Nanjing Aeronautical Institute, NAI (later renamed NUAA). However, I was admitted in the specialty of aircraft design which is related to aerodynamics.”
Graduate studies led the young engineer to a master’s degree in solid mechanics in 1989 and helicopter investigations in 1991. Prof. Xia explains, “I did my first work on rotorcraft projects -- an experimental stability investigation of an isolated hingeless rotor – on the rotor test stand in the Rotorcraft Aeromechanics Lab at NAI. I designed a new and simple experimental method for measuring rotor aero elastic stability.
“At that time, the method in the literature was first to excite the rotor test stand horizontally. When the horizontal vibration of the rotor or the lag vibration of the blade reached a steady level, the exciter was stopped, the test stand was immediately clamped, and the lag vibration signal was measured. The test stand needed to be elastically supported, and a complicated clamp was required.
“The method I presented used a hydraulic actuator to excite the swash plate vertically. The rotating blades produced horizontal or lag vibration due to the Coriolis force. When the vibration reached a steady level, the hydraulic actuator stopped excitation, and the lag vibration signal of the blade was measured.”
The graduate researcher went on to Hong Kong Polytechnic University. “I did research work on dynamic response analysis of a thin beam structure under blast load as a research assistant in 1993.” Dr. Xia earned his PhD in structural dynamics from Nanyang Technological University in Singapore in 2001. “My research has focused on the structural dynamics such as vibration, vibration control, and dynamic stability of structures including airplanes and helicopters.”
In August 2012, Prof. Xia was invited by NASA research fellow Dr. Wayne Johnson to present a seminar for the AHS San Francisco Bay Area Chapter of regarding a wake bending unsteady dynamic inflow model of a tilt rotor in conversion flight and the aero elastic stability of tilt rotor aircraft in forward flight.
Prof. Xia continues his research focus on rotorcraft vibration. “At present, the noise both inside and outside the cabin is unbearable,” he says. “A ‘quiet’ helicopter is necessary. Although the vibration level of rotorcraft has been reduced to 0.05g by using active vibration control, the weight of the inertia actuators used is about 2.5% of the gross weight of rotorcraft, which is too heavy. A less-than-1% solution should be acceptable if we use a new actuating technology such as piezoelectric stack actuators. My relevant paper on active control of helicopter vibration driven by using piezoelectric stack actuators will be published soon in the Journal of the American Helicopter Society.”
According to Prof. Xia, “AHS provides a valuable platform for academic exchanges on helicopter technologies. Everyone can benefit from exchanging academic information, sharing the latest research developments, broadening academic vision, and expanding our academic network.”
NUAA and AHS have long fostered links between China and the international helicopter community. “As the Chairman of the Organizing Committee, I hosted the 2nd International Basic Research Conference on Rotorcraft Technology (IBRCRT) at NUAA with AHS in 2005,” notes Prof. Xia. “Twenty years had passed since the 1st IBRCRT was held at NUAA. I would like to thank Dr. Chee Tung, Co-Chairman of the Organizing Committee for his great effort on behalf of the 2nd IBRCRT. Rhett Flater, then the Executive Director of AHS, sent a special congratulatory letter and suggested that the international helicopter conferences held in Asian countries should be unified into an Asian Rotorcraft Forum (ARF), like the European Rotorcraft Forum.”
The suggestion resulted in more successful collaboration. “Starting from 2005, I focused on hosting the Asian Rotorcraft Forum and visited Japan and Korea to discuss China’s relevance to the ARF. In 2009, as the Chairman of the Organizing Committee, I again hosted the 3rd IBRCRT at NUAA with AHS. I would like to thank Prof. Edward Smith from Penn State University and co-chairman of the Committee, for his great effort on behalf of the 3rdIBRCRT.
“In 2011, five representatives: myself, Dr. Arvind Kumar Sinha, Dr. Prashant M Pawar, Dr. Yasutada Tanabe, and Dr. Duck-Joo Lee – from China, Australia, India, Japan and Korea respectively – signed the memorandum on holding the Asian/Australian Rotorcraft Forum at Busan, Korea. According to the memorandum, the ARF has been held in rotation between Korea, China, Australia, Japan and India every year starting in 2012, and the five representatives formed the ARF Executive Committee.
“In 2013, as the General Chairman, I hosted the 4th IBRCRT and the 2nd ARF at Tianjin, China, during the China International Helicopter Exposition which was also being held at the same location. The conference attendees enjoyed a wonderful flight demonstration of the Z-10 helicopter. Mike Hirschberg, the Executive Director of AHS, attended the conference and presented a keynote speech at the opening ceremony of the conference.”
Prof. Xia says, “I have always encouraged my students to join in the AHS. I advised my students to join in the AHS Student Design Competition in 2008, 2009, and 2011, and our team captured the prize for the best new entry in 2009. In the 4th IBRCRT and the 2nd ARF, Mr. Jinsong Yang, my PhD student, received the award for the Best Student Conference Paper. Dr. Wayne Johnson of NASA personally presented his book Rotorcraft Aeromechanics with his signature to Mr. Yang.”
Leadership Profile: Vertiflite November/December 2014