Rotorcraft research must address the needs of society, industry, and the military in the field of rotorcraft. Increased automation, reduced pilot workload, improved performance, and quieter rotor blades are needed. These topics are covered by traditional rotorcraft disciplines. However, new challenges also arise. For instance, we must reduce CO₂ emissions by using hybrid or fully electric power trains and sustainable aviation fuels. Additionally, we must address new threats and operational concepts in today’s military environments. Uncrewed air vehicles with a high level of automation or autonomous operations are changing the landscape of civil and military operations. Well-established and new companies are trying to address these challenges with new approaches and configurations. As with any vehicle with a thrust-to-weight ratio greater than one, a technical solution for a rotorcraft must be highly efficient, limiting the innovative designs that can be considered. [...]

Rotorcraft technology is living in a moment of intensive development. Alongside traditional disciplines—aeroacoustics, aerodynamics, dynamics, flight dynamics, human factors, structures and materials, to name a few, other aspects are emerging. Uncrewed air vehicles and their autonomous operation, automation in support of crewed ones, crew management and coordination, special operations with a particular focus on those on ship decks, and lots, lots of interdisciplinarity surfaced as the topics most addressed in the papers selected for this issue. All selected papers have been extensively edited by the authors and peer-reviewed according to the standards of the CEAS Aeronautical Journal. [...]

Advanced data processing methods for detecting unsteady boundary layer transition in periodic aerodynamic processes by means of infrared thermography measurements are presented. The thermal radiation emitted from the heated suction surface of a pitching airfoil model in subsonic flow is measured with an infrared camera. The unsteady boundary layer transition location is detected by analyzing the difference in the infrared radiation signal over short periods of time with differential infrared thermography (DIT). The DIT method is optimized and automated in the present study, which facilitates the extension of the part of the motion period where valid DIT transition measurements are produced. Additionally, a new infrared thermography data processing method is introduced in this study. The extraction of the extrema of the measured radiation signal at fixed locations on the model surface yields instants of the motion period that relate to the occurrence of boundary layer transition. The local infrared thermography (LIT) approach can be extended to measuring the two-dimensional unsteady boundary layer transition front.

Abstract: Differential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar–turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short-time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward flight. The current study investigates a pitch-oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long-term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement-related lag for relevant pitching frequencies. Graphical abstract: [Figure not available: see fulltext.]

Differential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar–turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward 2ight. The current study investigates a pitch–oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long–term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement–related lag for relevant pitching frequencies.