Vertical Lift: Rotary- and Flapping-Wing Flight

Dear Colleagues,

Hovering is a fascinating ability in both engineering and biology, allowing rotary-wing vehicles and flapping-wing vehicles or insects (in contrast to fixed-wing vehicles) to remain stationary in the air relative to the ground. This shared capability places both rotary- and flapping-wing vehicles within the overarching category of vertical lift. This mode of flight presents significant challenges in terms of modeling and analysis due to its complexity. Challenges emanate from the multi-body, nonlinear, high-order, and time-varying dynamics inherent in these vehicles’ motion. In this type of locomotion, the time-varying wing/blade dynamics interact with the aggregate body dynamics and unsteady flow dynamics intricately and synergistically. Because the dynamics of hovering vehicles are typically unstable, high order, and with significant cross-coupling between motion axes, flight control design is often essential. Flight control systems are not only necessary for stabilizing the dynamics and imposing desired response characteristics but also, in the case of rotorcraft, for alleviating the workload of the pilot. Owing to these challenges, the study of vertical lift vehicles encompasses a wide range of multidisciplinary research areas. These include aerodynamics, flight dynamics, stability and control, structures, structural dynamics, aeroelasticity, propulsion, acoustics, autonomy, biology, and biomechanics. Therefore, this Special Issue is dedicated to showcasing the latest advancements in vertical lift and welcomes contributions in all the aforementioned areas, as they pertain to rotary- and flapping-wing vehicles.

Dr. Umberto Saetti
Dr. Bo Cheng
Dr. Pierluigi Capone
Guest Editors

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• rotorcraft
• flapping-wing flight
• aerodynamics
• fluid dynamics
• stability and control
• structures
• structural dynamics
• aeroelasticity
• propulsion
• acoustics
• autonomy
• biology
• biomechanics

Title: Influence of rotor inflow, tip loss and aerodynamics modeling on the maximum thrust computation in hover
Authors: Berend G. van der Wall
Affiliation: German Aerospace Center (DLR), Institute of Flight Systems, Braunschweig
Abstract: Comprehensive rotorcraft simulation codes are the working horse for design and simulation of a helicopter and its rotor under steady and unsteady operating conditions and also used to predict their limits until rotor stall occurs. This paper focuses on the prediction of hovering rotor maximum thrust (due to stall limits) and the thrust and power characteristics when the collective control is further increased. The aerodynamic factors that in parts significantly affect the results are: steady or unsteady aerodynamics, steady or dynamic stall, blade tip losses, curvature flow, yaw angle, downwash model, blade-vortex and fuselage-rotor interaction. The downwash model and tip losses are found to be the most important factors.

Title: Gaze Movements of Helicopter Pilots during real and simulated Take-Off and Landing Maneuvers
Authors: Daniel Heinrich Greiwe; Maik Friedrich
Affiliation: German Aerospace Center (DLR), Institute of Flight Systems
Abstract: Most accidents and serious incidents of commercial air transport helicopters occur during standard flight phases, whereby a main cause are pilots’ situational awareness. Enabling pilots to better assess their situational awareness can make an important contribution in reducing the risk of fatal accidents. One approach is to examine pilot’s gaze behavior with the help of eye tracking. This paper reports the results of eye tracking measurement during real flight and simulator studies of a standard mission profile. The general gaze behavior is characterized by a dominant, external view and the airspeed and altitude indicator as the most important flight instruments. A real-world applicability of gaze data obtained in the simulator could be shown.