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. [...]

This paper investigates the effects of different automation design philosophies for a helicopter navigation task. A baseline navigation display is compared with two more advanced systems: an advisory display, which provides a discrete trajectory suggestion; and a constraint-based display, which provides information about the set of possible trajectory solutions. The results of a human-in-the-loop experiment with eight pilot participants show a significant negative impact of the advisory display on pilot trajectory decision-making: out of the 16 encountered off-nominal situations across the experiment, only 6 were solved optimally. The baseline and constraint-based display both lead to better decisions, with 14 out of 16 being optimal. However, pilots still preferred the advisory display, in particular in off-nominal situations. These results highlight that even when a support system is preferred by pilots, it can have strong inadvertent negative effects on their decision-making.

This paper investigates the effect of employing different display design principles for human–machine interaction in helicopters. Two obstacle avoidance support displays are evaluated during low-altitude forward flight. A baseline head-up display is complemented either by a conventional advisory display or a constraint-based display inspired by ecological interface design. The latter design philosophy has only been sparsely applied in the helicopter domain. Twelve helicopter pilots participated in an experiment in a research flight simulator. We found no significant effects of the displays on objective performance measures. However, there was a trend of decreasing pilot workload and increasing situation awareness when employing the support displays, as compared to the baseline display. The constraint-based display had the largest positive effect and increased the resilience of the pilot–vehicle system toward unexpected events when considering the safety of the flown trajectories. Pilots preferred the advisory display in nominal situations and the constraint-based display in off-nominal situations, reproducing similar findings from research in the fixed-wing domain. This experiment showed the potential of the developed constraint-based display to improve subjective pilot ratings, pilot preference, and safety during unexpected events. Future research will investigate more complex scenarios with longer time frames, possibly eliciting more divergent effects of different display design principles.

This paper aims to reveal the effect of different display design principles in the helicopter domain. Two different obstacle avoidance support displays are evaluated during low-altitude, forward helicopter flight: a baseline Head-Up Display (HUD) is complemented either by a conventional advisory display, or a constraint-based display inspired by Ecological Interface Design. The latter has only been sparsely applied in the helicopter domain. It is hypothesized that the advisory display reduces workload, increases situation awareness, and improves performance measures in nominal obstacle avoidance situations, while the constraint-based display increases the resilience of the pilot-vehicle system towards unexpected, off-nominal situations. Twelve helicopter pilots with varying flight experience participated in an experiment in the SIMONA Research Simulator at Delft University of Technology. Contrary to expectations, the experiment revealed no significant effects of the displays on any of the dependent measures. However, there was a trend of decreasing pilot workload and increasing situation awareness when employing any of the support displays, compared to the baseline HUD. Pilots preferred the advisory display in nominal and the constraint-based display in off-nominal situations, reproducing similar findings from research in the fixed-wing domain. The relatively short time-frame and monotony of the control-task, an already cue-rich baseline HUD condition, and similarity between the displays possibly prohibited revealing larger differences between conditions. Future research will analyze the obstacle avoidance trajectories of this experiment, possibly revealing changes in control strategy caused by the displays, even when the lumped performance measures are similar. A follow-up experiment will focus on a longer task time-frame, more variable situations, and a truly ecological display to investigate the effect of applying Ecological Interface Design and different automation systems in the helicopter domain.

Head-down hover displays and instrument panels theoretically provide all necessary 2ight data information to control low-speed helicopter manoeuvring. However, past experiments have shown that head-down displays can incur high workload, control instability, and even loss of control when used as the sole 2ight data source. This paper investigates the reasons for this instability incurred by replacing good outside visuals with a head-down hover display and an instrument panel. A pilot model based on crossover theory is developed for a linear six-degree-of-freedom Bo. helicopter model. Utilising a target trajectory based on-theory and assuming perfect information availability, the developed model can perform the required manoeuvring task with a control time-delay stability margin of . s (with SAS) or . s (without SAS). Then, the actual information availability based on human perception methods and limitations is discussed. A pilot-in-the-loop experiment in the SIMONA Research Simulator qualitatively validates the developed pilot model for good outside visuals. However, the pilot model does not capture the added diZculties of having to utilise the hover display and instrument panel instead of good outside visuals; during the experiment, the task was impossible to complete with only these displays. This is likely caused by an increase in control time-delay, which in turn is caused by the loss of peripheral and flow 1eld information, a more abstract information representation compared to good outside visuals, and the fact that the pilot now needs to scan multiple displays to acquire all necessary 2ight state information. Improving head-down hover display symbology and scaling factors might rectify some, but probably not all of these effects.

The paper investigates the basic mechanism of aeroservoelastic pilot-assisted oscillation about the roll axis due to the interaction with pilot’s arm biomechanics. The motivation stems from the observation that a rotor imbalance May occur as a consequence of rotor cyclic lead–lag modes excitation. The work shows that the instability mechanism is analogous to air resonance, in which the pilot’s involuntary action plays the role of the automatic flight control system. Using robust stability analysis, the paper shows how the pilot’s biodynamics May involuntarily lead to a roll/lateral instability. The mechanism of instability proves that the pilot biodynamics is participating in the destabilization of the system by transferring energy, i.e., by producing forces that do work for the energetically conjugated displacement, directly into the flapping mode. This destabilizes the airframe roll motion, which, in turn, causes lead–lag motion imbalance. It is found that, depending on the value of the time delay involved in the lateral cyclic control, the body couples with rotor motion in a different way. In the presence of small or no time delays, body roll couples with the rotor through the lead–lag degrees of freedom. The increase of the time delay above a certain threshold modifies this coupling: The body no longer couples with the rotor through lead–lag but directly through flap motion.

Nowadays, the complexity of high speed civil transport and highly-augmented rotorcraft, has led to an increase in the chances of encountering unwanted unstable phenomena, such as the so called Aircraft/Rotorcraft-Pilot Couplings (A/RPCs) or Pilot-Induced Oscillations (PIOs), whose unpredictability has given rise to a serious problem concerning the safety of a mission. When talking about PIOs, McRuer de- 1ned them as “inadvertent, sustained aircraft oscillations which are a consequence of an abnormal joint enterprise between the aircraft and the pilot”. However, A/RPCs, these undesirable events associated with the interaction between pilot and aircraft, have become diverse and more complex than those encountered in the past. At the moment, there are different methods available to prevent and detect Cat. I/II A/RPC, but particular interest has recently arisen in this topic for 2ight simulation applications as any enhancement of these tools in order to accurately and objectively predict, detect (in real-time) and alleviate RPCs will be greatly welcomed. One of the main questions to be answered through the efforts carried out within this work is related to the better detection in real-time of embedded tendencies to RPCs in modern aircraft. To answer this question, initially an assessment of the eZcacy of the Phase-Aggression Criterion (PAC), which has been designed a few years ago at the University of Liverpool, will be undertaken either: as a means of alerting the pilot to conditions likely to lead to the onset of a PIO; or, given that the time available for the pilot to counteract may be extremely limited, as a means to assist him/her in alleviating (automatically) the PIO condition itself. Preliminary results from 2ight simulation trials to explore how best to achieve this will be reported. Moreover, this work will report on the development of PAC boundaries for more highly augmented response types. Furthermore, as classi1ed by McRuer, Cat. III PIO, which is nonlinear in essence, is the most complex one. However, the researches on Cat. III PIO are rare. This paper will reveal some elementary results of Cat. III PIO. Since there is no existing method used for predicting and detecting Cat. III PIO, this paper utilized the characteristics of PIO, such as the amplitude, the oscillation frequency and ultimate tendency of key aircraft response states to judge Cat. III PIO preliminarily. By using this elementary judgment of PIO, we studied the following factors: time delay of pilot input and helicopter main body, actuator position saturation, actuator rate limit and SCAS control authority in triggering PIO. Results show that PIO induced by actuator position saturation, actuator rate limit and SCAS control authority can be regarded as Cat. III PIO as the variation of these factors can be viewed as a kind of transition of effective controlled vehicle dynamics. These kinds of transition can cause a mismatch between the effective controlled vehicle dynamics and pilot control strategy, which is the main cause of Cat. III PIO. Copyright Statement The authors con1rm that they, and/or their company or organization, hold copyright on all of the original material included in this paper. The authors also con1rm that they have obtained permission, from the copyright holder of any third party material included in this paper, to publish it as part of their paper. The authors con1rm that they give permission, or have obtained permission from the copyright holder of this paper, for the publication and distribution of this paper as part of the ERF proceedings or as individual offprints from the proceedings and for inclusion in a freely accessible web-based repository.