The Flying-V is a novel flying wing aircraft design that aims to improve aerodynamic efficiency and fuel consumption. In recent years, there has been an increased effort to evaluate the handling qualities (HQs) of the Flying-V, and to develop new flight control strategies. One of the latest flight control designs for the Flying-V uses Incremental Nonlinear Dynamic Inversion (INDI) with a Flight Envelope Protection system. The purpose of this research is to validate this FCS design and its conclusions on handling qualities by conducting piloted experiments. To facilitate a sound comparison, the aerodynamic model, flight control structure, and airframe characteristics are taken as is from the existing study. For the experiment, numerous maneuvers are designed and carried out. The experiment is performed on the SIMONA Research Simulator of the Delft University of Technology, with three real-life test pilots as participants. The results show a significant correlation with offline findings and demonstrate the improvement in HQs provided by the flight control system.@en

Providing adequate simulator motion cues for simulated upset and stall scenarios remains challenging. This paper evaluates the potential of novel optimization-based motion cueing algorithms for upset and stall simulation. An offline analysis is performed to compare three Model Predictive Control (MPC) algorithms with varying prediction horizon lengths and prediction strategies (i.e., "Oracle", "Perfect", and "Constant") against two baseline classical washout algorithm implementations from literature. The analysis is performed for a symmetric stall scenario flown with TU Delft's Cessna Citation II laboratory aircraft. Overall, the analysis shows that the objective motion cueing quality expressed in terms of the Root Mean Square Error (RMSE) improves by 29.8% (for specific forces) and 18.7% (for rotational velocities) with the "Oracle" and "Perfect" MPC implementations compared to the reference classical washout results. For the "Constant" MPC algorithm, which in fact does not include any explicit prediction across the MPC algorithm's future prediction window, only a marginal improvement in motion quality was found. Overall, these results imply that, assuming a sufficient future reference motion prediction can be achieved, optimization-based motion cueing algorithms have the potential to provide significantly better motion cueing quality compared to classical motion cueing algorithms.@en

This paper presents the development process of an aircraft control law. The control law is designed using a two-degree-of-freedom (2DoF) structured H∞ loop-shaping approach. This method allows the reuse of controller structures required by certification procedures while directly including handling qualities and robust stability requirements in the optimization process. This strategy is employed to develop a Rate Command and Attitude Hold (RCAH) demand system aimed at satisfying longitudinal handling qualities. First, the stability of the open-loop model and its compliance with the handling qualities guidelines are evaluated. Then, the control law is designed, with a detailed description provided of the design specifications and their formulation in the context of H∞ control. Subsequently, the controller parameters are optimized to satisfy the design specifications and a closed-loop analysis is performed. Finally, a simulator flight testing campaign is conducted to experimentally validate the designed control law. It is shown that the aircraft equipped with the RCAH system achieves better handling quality ratings (HQRs) and more favorable pilot feedback, providing a substantial improvement over the bare airframe.@en

Motion cues are one of the most challenging aspects of human-in-the-loop vehicle simulators. The real vehicle cues can only be presented in a highly distorted way, so it is important to understand what these cues look like and which aspects are important for the human controlling the vehicle. This paper describes two complementary ways of assessing (translational) motion cues: accelerations plus gravity, and specific forces. These perceived cues can be constructed from different components of Newton’s Second Law and are fundamentally equivalent. The paper shows how the situation heavily favors one representation or the other in understanding the motion cues to be presented. When assessing the cues in flight, the specific force formulation is superior as it leverages flight dynamics knowledge and intuition to predict and explain the form of the cues. The paper gives a number of examples to illustrate this claim, supported both by analysis and by measurements in an instrumented business jet and a motion-based flight simulator.@en

Previous research indicated a need to improve pilot training with regard to understanding of autopilot logic and behavior, especially in non-routine situations. Therefore, we tested the effect of problem-based exploratory training on pilots’ understanding of autopilot functions. Using a moving-base flight simulator, general aviation pilots (n = 45) were trained to diagnose failures either without foreknowledge and guidance (exploratory group), without foreknowledge but with some guidance (exploratory-guidance group) or with foreknowledge and full guidance (control group). They subsequently performed six test scenarios in which their understanding of the effects of failures was tested by requiring them to deduce the failures and select autopilot modes that were still functioning. Those who received exploratory training with guidance were significantly more likely than the other groups to diagnose failures correctly. The exploratory training group also selected the most appropriate functioning autopilot modes significantly faster than the control group. The results suggest that exploratory training with an appropriate level of guidance is useful for gaining a practical understanding of autopilot logic and behavior. Exploratory training may help to improve transfer of training to operational practice, and prevent automation surprises and accidents.

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This paper analyzes the effects of the helicopter dynamics on pilots' learning process and transfer of learned skills during autorotation training. A quasi-transfer-of-training experiment was performed with 10 experienced helicopter pilots in the SIMONA moving-base flight simulator at Delft University of Technology. Pilots had to control an in-house flight dynamics model setup to simulate two types of helicopter dynamics: (1) a "hard"dynamics characterized by a low autorotative flare index requiring high pilot control compensation and (2) a "easy"dynamics characterized by a high autorotative flare index with low pilot control compensation required. Two groups of pilots tested these types of dynamics in a different training sequence: hard-easy-hard (HEH group) and easy-hard-easy (EHE group). The main conclusion of this study proved that simulator training for autorotation can best start with pilots training in the most resource demanding condition. A more challenging helicopter's dynamics will require higher pilot agility and more rapid responses to his/her perceptual changes. This will result in pilots developing more robust and adaptable flying skills. Indeed, a clear positive transfer of training effect was observed in the experiment presented in this paper in terms of acquired pilot skills in the HEH group, but not the EHE group. Positive transfer was especially observed in terms of reduced rate of descent at touchdown. The two groups differed in the control strategy applied, with the HEH group having developed a control technique mimicking more closely the one adopted in a real helicopter.

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The Flying-V novel aircraft design aims at reducing fuel consumption by an innovative low-drag, fuselage-free geometry. Possible issues related to certification requirements have been noted, however, regarding longitudinal handling qualities at low speed, the pull-up manoeuver, and the flight-path-angle response. This study aims at investigating these issues through a pilot-in-theloop experiment. Starting with a mathematical model of the Flying-V, based on the vortex lattice method, a preliminary off-line analysis of the handling qualities is conducted. A sensitivity analysis is considered over the proposed operational center-of-gravity range, approach speed (between 0.225 and 0.3 Mach, 149 and 198 knots indicated airspeed, respectively), maximum deflection of the control surfaces (between 20 and 30 degrees), and flight control system (Direct Law or Pitch-Rate Command). The pilot-in-the-loop experiment, its design guided by results from the analytical assessment, shows that the handling qualities provided by the current design of the Flying-V with Direct Law at 0.3 Mach are satisfactory with minor improvements related to aircraft responsiveness. For lower speeds (0.225 Mach), the handling qualities degrade due to a sluggish response, high compensation workload, insufficient control authority, insufficient sight angle, and tendency to pilot induced oscillations. Shifting the center of gravity away from the nose provides larger control authority at the expense of a minor reduction of responsiveness. Control augmentation proves to be very effective at improving the handling qualities. It is expected that the go-around certification standards will be satisfied, but approach speed will remain critical for controllability and safety.

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A novel aircraft configuration, the tailless Flying-V, is examined for its longitudinal handling qualities in cruise by means of piloted simulations. The Flying-V is controlled by two aileron/elevator (elevon) surfaces on each side, and rudders on each wingtip. Two control allocation schemes were created: a conventional one where both inboard and outboard elevons deflect in the same direction, and one where the change in lift the elevons generate is countered by deploying the inboard and outboard elevons in opposite directions, allowing more direct control of the resulting flight path. The longitudinal handling qualities in cruise conditions were investigated by pilot opinion in a moving base simulator. Three experiments were conducted: a traditional pitch tracking experiment with the conventional control allocation, and a new flight-path-angle tracking experiment, using both the conventional and the flight-path-oriented control allocation. The pilots indicated the conventional pitch attitude control to have Level 1 handling qualities for the pitch control task, and Level 2 for the flight path control task. The flight-path-oriented control allocation improved the performance of the pilots during the flight-part tracking experiment, but the perceived control authority was considered too small for most pilots to consistently rate it at Level 1.@en

Background. Mnemonic procedures are currently being taught to airline pilots to manage startle and surprise. We previously tested the effectiveness of a four-item mnemonic. Pilots generally rated it as useful but some remarked that it induced too much additional workload. Therefore, we tested whether a simpler mnemonic, Aviate-Breathe-Check, would be more useful. Method. The experiment took place in a hexapod simulator with a Piper Seneca aerodynamic model and a generic cockpit. Airline pilots (n = 25) were divided into an experimental (“ABC”) and control group. All received ground training on startle and surprise, which included instructions on the ABC mnemonic for the ABC group. The mnemonic aims to support prioritization of flight-path management (Aviate), followed by physiological and mental stress management (Breathe), followed by troubleshooting (Check). All pilots performed four familiarization scenarios, during which the ABC group practiced the ABC mnemonic. Two test scenarios were then performed to evaluate performance, mental effort, stress, and pilot evaluations of the ABC mnemonic. Results. The pilots’ evaluations of the ABC mnemonic were significantly higher than those were for the previously-tested mnemonic in the same scenarios. There were no significant differences between the ABC and control group in mental effort and stress, whereas there were trends towards higher mental effort and stress with the previous mnemonic. No significant effects on performance were found. Conclusions. The results suggest that the ABC mnemonic was more useful and easier to apply than a previously tested mnemonic. This is promising for the development of effective pilot training interventions for startle and surprise. @en

Preventing Loss of Control In-flight (LOC-I) in commercial and general aviation is an active research area with numerous proposed solutions. One of these solutions aims to prevent lateral LOC-I, a special type of LOC-I, by presenting a roll-performance based minimum lateral control speed to the pilot in roll-limited situations, such as single-engine failure scenarios in multi-engine aircraft. This minimum lateral control speed is predicted by a system, named the Vc Prediction System (VPS), which continually predicts the minimum lateral control speed Vc at which an aircraft can still obtain a certain roll angle within a certain amount of time. It consists of three components; a linear model, a parameter estimation method and a Vc prediction model. These VPS components were designed for a simulation model of the Piper Seneca. This study analyzes the sensitivity of the VPS design to a change in aircraft dynamics and simulation model complexity by redesigning this system for a high-fidelity simulation model of the Fokker 50. The results show that both aircraft favor a small linear model and the Modified Kalman Method for parameter estimation. The original Vc prediction model however gives higher Vc prediction errors for the Fokker 50 than for the Piper Seneca. By simplifying the original Vc prediction model a stable, smooth and relatively accurate Vc prediction for the Fokker 50 can be obtained.@en

Flying wings are known for their limited lateral-directional stability and handling qualities. This study aims at assessing the lateral-directional handling qualities of a conceptual flying wing aircraft currently in development at TU Delft, the Flying-V, in a moving-base flight simulator. It focuses on two aspects: First assess the lateral-directional handling qualities of the bare-airframe Flying-V, and the compliance to quantitative requirements. Second, improve these handling qualities through a prototype flight control system, and assess its effect on the handling qualities and the requirement compliance. These assessments were performed both analytically and with a pilot-in-the-loop simulator experiment, in order to experimentally validate analytical findings and obtain new pilot-subjective insights. The analytical and experimental assessment for lowspeed flight conditions both show the lateral-directional handling qualities of the Flying-V to be insufficient for requirement compliance, due to a lack of pitch, roll and yaw control authority and an insufficiently stable Dutch roll eigenmode. The prototype flight control system, consisting of an adapted control allocation and a stability augmentation system, showed both analytically and experimentally to improve the control authority, stability, and handling qualities of the Flying-V. While the effect on the lateral-directional stability was sufficient for stability requirement compliance, the control authority was not sufficiently increased for maneuverability requirement compliance at low speed. Thus, if the landing speed is not increased from the current baseline, a challenge remains to improve the handling qualities of the Flying-V. An approximation of the control authority required for full requirement compliance in the low-speed flight conditions tested showed a control authority increase of over a factor four to be required in that case.@en

Background. Previous studies and accident analyses have shown that pilots can make roll reversal errors when responding to bank angles shown by the artificial horizon in the Primary Flight Display (PFD). In the current study, we tested whether adding stereoscopic depth cues to the artificial horizon may lead to better bank angle representation due to an improved figureground separation between the symbols. Method. Stereoscopic depth cues were created by using a half-silvered mirror multi-layer PFD, which presented the horizon symbol on a lower layer and the aircraft symbol on a higher layer. A group of 23 non-pilots and 18 general aviation pilots were shown left or right bank angles on this multi-layer PFD as well as on a normal single-layer PFD, with the task to roll the wings level using a joystick. Results. In the pilot group, a similar amount of roll-reversal errors was made with both displays (median = 3.3%) with no significant difference, p = 0.635. In the non-pilot group, fewer roll-reversal errors were observed with the multi-layer display, but this difference did not reach significance either (median = 3.3% vs. 5.0%, p = 0.182). In both pilots and non-pilots, the reaction time was longer in the multi-layer display, which reached significance in the non-pilots (p = 0.016) but not in pilots (p = 0.215). Participants noticed that the depth was only visible during the start of the session. Conclusions. The results suggest that using stereoscopic depth cues are not a viable manner to enhance the figure-ground relation in the artificial horizon. @en

Nonlinear dynamic inversion (NDI) is a nonlinear feedback linearization technique that has been widely applied to flight control systems [1,2]. Using state feedback and the inverted nonlinear system dynamics, NDI can significantly reduce controller development costs by avoiding gain scheduling and Jacobian linearization at a multitude of operating points. However, the control performance of NDI is directly dependent on required detailed knowledge of the model. As a simplified and enhanced NDI method [3], incremental nonlinear dynamic inversion (INDI) [4,5] has been proposed to reduce the model dependency and improve the robustness against model uncertainties. Instead of using a global nonlinear model, in INDI the dynamic inversion is implemented on a locally linearized system model that is updated at every sampling period, for which the control input is calculated in an incremental manner. Unlike NDI, for which full knowledge of the complete system dynamics is needed, INDI only requires explicit knowledge of the system’s control effectiveness matrix.@en

Fidelity is a fundamental concept for crucial decision-making processes during engineering design, test and evaluation of aircraft and rotorcraft. Fidelity, as applied to rotorcraft, proves to be a prerequisite for most human factors research and simulator development programs. This paper reviews the concept of fidelity, its metrics and methods concentrating on rotorcraft applications. The paper stems from the Applied Vehicle Technology (AVT) Panel of the NATO Science and Technology Organization (STO) work of NATO AV-296 concentrating on recent advancements on rotorcraft flight simulation model fidelity prediction and assessment. Starting from the question of what is meant with the term simulation fidelity, the paper will demonstrate that even though the term fidelity can be loosely translated as simulation goodness or faithfulness to reality, when it comes to fidelity assessment, this concept has a multidimensional and multifaceted character depending on the configuration considered. A key message of the paper is that simulation fidelity should be decomposed in different dimensions and attributes with their own metrics. Using multiple fidelity metrics is therefore meaningful for assessing simulation fidelity in general and in particular for the case of rotorcraft.

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Eigenmode distortion is a novel quantitative methodology developed to objectively evaluate motion cueing fidelity in flight simulation. It relies on an explicit coupling of linearized vehicle and Motion Cueing Algorithm dynamics. Modal analysis subsequently performed on this coupled system reveals the degree of distortion imposed by the Motion Cueing Algorithm on to the dynamics of the simulated vehicle. Eigenmode distortion thereby provides unprecedented insight into the combined dynamics of the two systems along modal coordinates. Compared with existing methods for motion cueing fidelity assessment, the eigenmode distortion method enables a systematic analysis of the coupled vehicle and Motion Cueing Algorithm dynamics. This is mainly because it does not consider the Motion Cueing Algorithm in isolation and does not inherently rely on assumptions regarding the excitation of the simulated vehicle dynamics. This paper outlines the theoretical foundation of the eigenmode distortion method and includes a case study on helicopter longitudinal dynamics and a sensitivity analysis to demonstrate its utility. The results presented in this paper shown that the eigenmode distortion method can reveal interactions between the Motion Cueing Algorithm and the vehicle dynamics that are currently not captured by other established methods, such as the Sinacori–Schroeder criteria and the Objective Motion Cueing Test.@en

Current aircraft flight deck interfaces do not provide information on how a performance-altering failure constrains an aircraft’s flight envelope. As a result, it is difficult for flight crews to plan maneuvers in order to reach navigation targets. This study presents the results of the conceptual development of constraint-based interface symbology that aims to address this issue. The proposed symbology is designed to integrate with both the primary flight display and navigation display. A small-scale, pilot-in-the-loop experiment (N=9) was conducted to assess the effectiveness of the used symbology in terms of flight performance and pilot usability. A simplified dynamic model with an asymmetric flight envelope was used to purposefully manipulate various levels of damage severity and corresponding flight envelopes. Results show that although the modifications to the primary flight display generally did not show statistically significant improvements, presenting flight envelope constraints as a reachable navigation envelope on the navigation display generally did do so for severe failures. The visualized envelope occasionally resulted in improved tactical control decisions at reduced workload levels. A future study involving a lager sample size and increased simulation realism should substantiate the discovered results.@en

Training has the potential to inject a “safety vaccination” into the rotorcraft community by reducing the number of accidents. The term training should not be intended only in a strict sense, i.e., as pilot technical skills training, but more broadly as risk avoidance and safety culture training. As in the case of vaccination, where immunity is created only when applied on a large scale, helicopter accidents will not be eradicated until every player in the rotorcraft community is involved in the safety enhancement process. In particular, as outlined by accident and safety reports, a reduction in the helicopter accident rate cannot be accomplished disregarding pilots’ training and the contribution that _ight simulators can provide to both training and certi_cation. This paper provides an overview of the research into simulator training for helicopter pilots conducted as part of the European Joint Doctorate NITROS (Network for Innovative Training on Rotorcraft Safety). An approach that requires an in-depth analysis of the actual training task is adopted for two different maneuvers, namely hover and autorotation. This approach enables the training developer to understand what are the aspects of the actual training situation that should be reproduced in the simulated training situation to avoid ineffective training and negative transfer of skills. Moreover, such an approach allows to identify differences in terms of requirements between the training of basic and advanced maneuvers and between initial and recurrent training. The results of three different pilot-in-theloop experiments, performed to explicitly con_rm the effectiveness of developed training programs and to understand whether certain elements of the simulation can foster the development of superior _ying skills, are summarized in this paper. @en

This paper analyzes the effects of the helicopter dynamics on pilots’ learning process and transfer of learned skills during autorotation training. A quasi-transfer-of-training experiment was performed with 14 experienced helicopter pilots in a moving-base flight simulator. Two types of helicopter dynamics, characterized by a different autorotative index, were considered: “hard,” with high pilot compensation required, and “easy,” with low compensation required. Two groups of pilots tested the two types of dynamics in a different training sequence: hard-easy-hard (HEH group) and easy-hard-easy (EHE group). Participants of both groups were able to attain adequate performance at touchdown in most of the landings with both types of dynamics. However, a clear positive transfer effect in terms of acquired skills is found in both groups from the hard to the easy dynamics, but not from the easy to the hard dynamics, confirming previous experimental evidence. Positive transfer is especially observed for the rate of descent at touchdown. The two groups differed in the control strategy applied, with the HEH group having developed a more robust control technique. During the last training phase the EHE group aligned its control strategy with that of the HEH group.@en

Ground-based demonstration of spatial disorientation (SD) has been recommended for military as well as commercial pilot training. Although the leans illusion is the most common form of SD, no data exist yet of an effective ground-based leans procedure for a hexapod simulator. In this paper we describe the development of such a procedure and its tuning with nine subjects. The procedure was then used in an experiment with 18 airline pilots, which is described elsewhere. The final procedure started with a prepositioning phase, during which the simulator platform was slowly tilted to a 3.5° prepositioning roll angle, while the pilot performed a distraction task and the instruments and outside visuals indicated level flight. Next followed an adaptation phase, during which the pilot's vestibular system adapted to the new angle, the outside visibility degraded to zero and the instruments were covered. Then the platform was moved back to level, above the perceptual threshold, after which the instruments were shown again. The pilot was then tasked to roll back to level. The addition of the motion cues caused an increase in roll reversal errors by a factor of 3 in airline pilots. The procedure can be implemented in a scenario for demonstrating the leans in a cost-effective simulator. @en

This paper investigates the interaction effects of motion filter order and break frequency on pilots’ manual control behavior and control performance using two simulators. Eighteen pilots performed the experiment in the Vertical Motion Simulator (VMS) at NASA Ames Research Center and 20 pilots in the SIMONA Research Simulator at Delft University of Technology. The experiment used a full-factorial design with three motion filter orders (first-, second-, and third-order) and two filter break frequencies (0.5 and 2.0  rad/s), in addition to reference no-motion and full-motion conditions. Key task variables, such as the quality of the motion and visual cues and the characteristics of the sidestick, were matched across both simulators. Overall, the expected effects of filter order and break frequency variations were found, with both increasing order and increasing break frequency causing pilots to use less motion feedback in their control strategy, resulting in lower tracking performance. Furthermore, across the wide range of filter orders tested in the experiment, the existing Sinacori–Schroeder motion fidelity criterion was found to be a good predictor of the interaction effects of both filter settings on pilot control behavior. For the same motion condition, there was a consistent offset in the results between simulators, due to the more high-gain control strategy adopted by a number of the VMS pilots. Still, the observed relative trends in pilot control behavior and performance between motion conditions were equivalent in both simulators and thus accurately replicated.@en