Born: Romania
Primarily active in: Netherlands

From Leadership Profile: Vertiflite, Jul/Aug 2020

Marilena Pavel, Associate Professor, Delft University of Technology

In the Faculty of Aerospace Engineering at Delft University of Technology (TU Delft) in the Netherlands, Prof. Marilena Pavel teaches the school’s only graduate-level course on helicopter aerodynamics and modelling, and advises students conducting rotorcraft-related research. She explained, “At the moment, most projects relate to modelling and simulation of helicopters and compounds with an emphasis on building future urban air mobility. All of the modelling used to predict rotorcraft behavior can be translated into understanding how it affects the pilot and how it can be used for flight control. I’m very interested in how sensor-based control approaches can provide improved handling qualities for rotorcraft.”

Pavel noted, “We are on the brink of developing self-aware vehicle concepts with super-Level 1 handling [qualities]. The degree to which the pilot might be able to engage with the operation of a self-aware vehicle is still an open issue. Automatic equipment seems to function best in routine tasks when pilot workload is light. When the task requires more assistance and when workload is high, automatic equipment is often of least help — this is one of the ironies of automation.”

Pavel serves on the European Union-funded NITROS (Network for Innovative Training on Rotorcraft Safety). She also advises PhD students trying to understand the use of automation in helicopters, analyzing current systems and practices, and working on possible improvements in automation and the human-machine interface, especially in emergencies. “Accidents with helicopters show that while autopilots can greatly reduce pilot workload, they can also result in erroneous pilot actions and safety issues. Rather than striving exclusively to mitigate human error with more automated systems, the emphasis should shift to exploring ways in which technology can facilitate human adaptiveness and flexibility to cope with unforeseen events — to enhance resilience.”

TU Delft is the home of the SIMONA (Simulation Motion and Navigation) full-motion flight simulator for fixed- and rotary-wing research. Pavel said, “The simulator can be used as a laboratory for rotorcraft flight simulation technology and human-machine interaction. I develop rotorcraft models to be implemented in the SIMONA simulator, concentrating on enhancing real-world fidelity.” The generic physics-based rotorcraft models are validated for different helicopter types — such as the Airbus Bo 105, Boeing AH-64, Sikorsky UH-60 and Boeing CH-47 — and provide variable fidelity to ascertain performance, simulate maneuvers, determine response to external perturbations and design flight controls.

Pavel observed, “Thinking of fixed-wing aircraft, the concept of zero-flight-time training using simulation is accepted and considered necessary from a safety and cost standpoint. This is not the case for helicopters. Poor pilot cues have to be partly compensated for in the helicopter model to make the simulator satisfactory.” She continued, “Nowadays, we better understand the relationship between the simulator cueing environment and the behavior of the pilot. At Delft, we are trying to develop a practical and comprehensive methodology to expose the intricate three-way interaction between vehicle dynamics, task specification and execution, and simulator motion-cueing algorithms.”

Aeronautical Engineer
Marilena Pavel grew up in Brasov, Romania, under the dictatorship of Nicolae Ceausescu. “My father wanted to be a fighter pilot, but he had heart issues so finally had to stop. We had many books at home about heroic aircraft flights over the Carpathians.” Brasov is surrounded on three sides by the southern Carpathian Mountains. “It was there where I started my gliding training as a teenager and decided to go for an aerospace career. The air currents in the Transylvanian Alps have ‘long wave’ formations, with winds constantly blowing at high speed over the mountains for a long time and being amplified when they meet large obstacles. Many altitude records for gliding flight have been established in that region.”

As communism collapsed in Eastern Europe, Pavel pursued aerospace engineering at the highly competitive Politehnica University of Bucharest. She recalled, “The Faculty of Aerospace Engineering at that time in Bucharest was the only place in Romania to study for an aerospace career. To be a student at that faculty meant already being passionate about aviation.” Pavel completed an internship at the division of airplane assembly in Fabrica de Avioane Bucharest and earned her Masters of Science in aircraft structures. “I enjoyed the subject of aeroelasticity as a student. We had great teachers, professors from the same school of thought as, for example, Henri Coanda, Elie Carafoli, or Liviu Librescu. They taught us that the scientist extracts beauty from the phenomenon he is studying.”

Upon graduation, Pavel became a research engineer at the Aviation Research Institute in Bucharest in STRAERO — the Institute for Theoretical and Experimental Analysis of Aeronautical Structures. “It was there where I started my work with helicopters in the group led by Prof. Victor Giurgiutiu. It was a wonderful team with very talented people. We were trying to do aeroservoelastic optimization of helicopter rotors when computers were not as powerful as they are today. We had in-flight measurements from an IAR Puma helicopter manufactured in Romania so we could validate our theoretical codes. This showed me how different helicopter behavior can be throughout the envelope.”

Pavel became a senior researcher for the Institute of Flight Dynamics of Bucharest and worked with Dr. Alexe Marinescu, learning helicopter piloted simulation modeling. She acknowledged, “The situation after the fall of the communism in Romania was not easy. With an inflation rate of 200%, prices tripled regularly, so I had to pursue more jobs. I was also a teaching assistant professor for the Polytechnic Institute of Bucharest teaching mechanics and working with student researchers.”

Research Portals
TU Delft is the largest technical university in the Netherlands. Pavel recalled, “In 1995, I received a Nuffic [Dutch international education] scholarship at the Faculty of Aerospace Engineering. Here, I joined the Department of Flight Mechanics and Propulsion, led by Professor Theo van Holten, and participated in development of helicopter piloted simulation for the SIMONA simulator.” Doctoral studies in rotary-wing modeling considered both helicopters and wind turbines. “At that time, TU Delft was developing wind energy as one of the pillars of a renewable energy economy. From Professor van Holten and Koen Jessurun I got a lot of good advice on the real problems of helicopters and wind turbines.”

In 1996, Pavel met Prof. Gareth Padfield at the European Rotorcraft Forum. “He introduced me to the area of helicopter handling qualities but, most important, he was my mentor when I started thinking about what career path I should follow.” The meeting led to a collaboration with Padfield and the University of Liverpool. “The fruitful discussions I had with him on the subject of helicopter modeling and simulation were a blessing, and I am very grateful for this.”

TU Delft research also afforded Prof. Pavel opportunities to apply her technical skills to real-world problems and to help students develop their skills for the aerospace industry. “I remember the excitement of developing the Ornicopter, a tailless helicopter that flies by flapping the blades of the main rotor so that no reaction torque is needed. We could optimize the Ornicopter to have power requirements similar to conventional helicopters, as well as very close stability and controllability characteristics on the pitch and roll axes. I still hope the Ornicopter will find its application in the world of drones as, when thinking of flapping-wing robots, none of them would be as perfect as the Ornicopter for long hovering flight.”

From 2010-2016, Prof. Pavel was responsible for qualification and certification of the PAL-V ONE flying car, a Dutch design combining the principles of an automobile and a gyroplane. On the ground, the rotor and pusher propeller are stopped, and power is diverted to road wheels, allowing the vehicle to travel as a three-wheeled car. The single-seat demonstrator made its first public flight in 2012 and was used to explore stability and control. The two-seat PAL-V prototype is expected to complete all certification requirements by 2021.

Pavel offered, “The difficult/challenging thing about new flying machines — eVTOL [electric vertical takeoff and landing] and other transformative flight concepts — is that, for example in the area of stability/safety, over-confidence based on a cookbook modeling solutions can still lead to poor decisions. The only true way to determine if these critical stabilities are proper is to flight-test the result.”
Pavel also contributed to ARISTOTEL, the Aircraft and Rotorcraft Pilot Couplings Tools and Techniques for Alleviation and Detection program sponsored by the European Union. ARISTOTEL aims to advance the understanding, prediction and alleviation of particularly unfavorable rotorcraft-pilot couplings or pilot-induced turbulence. Pavel explained, “I tried to understand the mechanism of pilot destabilization in a coupled pilot-vehicle-trigger system. I found mechanisms where the advancing lead-lag mode was destabilizing the system motion.”

TU Delft provided other collaborative opportunities. Pavel said, “The sabbatical I spent in the United States between 2015 and 2018 was the greatest opportunity I had to connect to overseas research. I met wonderful people at NASA Armstrong Flight Research Center and the National Test Pilot School in Mojave. The Transformative Vertical Flight group which was set up at the time by the Vertical Flight Society [and NASA] gave me a wonderful opportunity to contribute to the common effort exploring electric VTOL as a future solution of air transportation systems.”

Prof. Pavel’s work on the GARTEUR HC/AG-30 Rotorcraft Simulation Fidelity program considered advanced aeromodeling for transformative flight configurations. “Our modeling tools need to be re-adapted to multi-copters, tilt-fans or compound configurations,” she said. “We need to understand these new configurations in different scales and be able to predict ride comfort — noise, vibration, space and amenities — and the ability to operate in high winds.” Pavel added, “While gust sensitivity has not been a serious problem for helicopters with articulated rotors, for such new configurations, it can be an important factor that must be dealt with during vehicle development. Super-Level 1 handling qualities and how to design for them are challenges for the rotorcraft community to be solved.”

Marilena Pavel joined the then-American Helicopter Society in 2001. “Every year, I look forward listening to the Alexander A. Nikolsky Honorary Lectureship at the Annual Forum and enjoy hearing about all the advances vertical flight has made. Especially now as the eVTOL Revolution is building a new future of air mobility, it is important that the Vertical Flight Society engages the whole rotorcraft industry.”