More Haptic Aircraft

This paper presents a comprehensive review of haptic feedback in light aircraft control. It provides an overview of the results and experiences gained from a previous research project focused on the design and testing of pilot haptic feedback hardware. The objective of this paper is to outline a roadmap for the future development of “More Haptic Aircraft,” incorporating principles of human-centred design into light aircraft cockpits equipped with the presented haptic feedback device. The roadmap provides general requirements for pilot-aircraft interaction and highlights three specific levels of functions. These functions aim to reduce the pilot’s workload and enhance situational awareness.


Introduction
In modern aircraft control, the visual modality has become saturated [1].While this is not problematic under standard conditions, it can lead to a reduction in situational awareness during unexpected or emergency events.Another challenge, particularly in general aviation aircraft, is that the aircraft control still employs speed, rather than angle of attack (AoA), as its primary parameter.Both speed and AoA are conveyed through the visual modality.In contrast, flying animals gauge speed and angle of attack through tactile or haptic perceptions.For instance, birds detect speed based on the vibrations of their feathers, while insects do so through the vibrations of their hairs.This suggests potential ways to enhance pilot-aircraft interactions and improve pilots' situational awareness through haptic feedback, offering an artificial sensation of airflow parameters such as AoA and Angle of Sideslip (AoS).In this paper, the authors aim to explore the role of haptics in aircraft control, taking into account recent advancements in both the haptics and light aircraft control domains.The basic principles of human-centred design are also considered to lay out a roadmap for the new cockpit of light aircraft.

Background
Over the past century, primary aircraft control mechanisms, such as ailerons for roll, elevators for pitch, and rudders for yaw, have remained consistent.However, aircraft systems and cockpits have seen noteworthy progress.This change is illustrated in Figure 1.All these systems were designed with the goal of increasing flight safety.Concurrently, these advancements have heightened the demands on a pilot's instrumental situational awareness, one of three levels of situational awareness as defined Endsley [2].One of the major changes in recent decades has been the implementation of the glass cockpit.The glass cockpit has increased the amount of information a pilot can access and must process.It can be anticipated that aircraft control will evolve in tandem with rapid advancements in human-machine interaction observed in other disciplines such as car driving, human-computer interaction, or even military aircraft control.

Artificial haptic feedback in aircraft control
Recent research has highlighted a promising approach for pilot-aircraft interaction: the incorporation of artificial haptic feedback into aircraft controls.The authors designed and tested active pedals and a stick in response to the high demands on visual modality.The hardware, as shown in Figure 2, was designed to convey AoA and AoS to a pilot through haptic feedback [4].The test confirmed the readability of the haptic cues, including the vibrations in the pedals and the sliding element in the control stick in flight conditions.The sliding element, located on the left side of the figure, moves in the indicated direction inside or outside of the stick handle.A pilot can feel its position with his/her fingers.The most precise information is provided around the zero position, where the sliding element is close to a fixed reference element placed just above the sliding element.The pilot can feel the edge between the elements or just a smooth transition at the zero position of the sliding element.The pedals on the right side of the picture provide haptic feedback through vibrations.The greater the AoS, the higher the frequency of vibration intervals appears.In this paper, the potential usage and application in pilot-aircraft interaction are elaborated and discussed.

Human-centred design principles
A comprehensive introduction to human-centred design presented Billings [5].His key points are summarized in this paragraph which lay out principles and guidelines focused on human-centred automation in aircraft and the broader aviation system.A motivation for this work comes from aircraft accidents linked to the "Loss of Situational Awareness".This loss can be attributed to multiple factors including complexity, coupling, autonomy, and inadequate feedback.Complexity: Increasing complexity of automation systems makes the aircraft control more difficult for the pilot.Coupling: This refers to the often-obscured interactions between automation systems.Autonomy: This entails selfinitiated automated system actions, placing the pilot in occasionally challenging situations where they must decide if the observed behaviour is appropriate or not.Inadequate feedback: This situation arises when humans are left uninformed about the actions and decisions of the automation system.Given these challenges, the principles of human-centred design are posited as: • The pilot must be actively Involved and adequately Informed.
• The pilot must be able to monitor the assisting automation.
• The automated systems must be predictable.
• The automated systems must also monitor the pilot.• Every Intelligent system element must understand the Intent of other Intelligent system elements.
In addition to the principles of human-centred design, there is a demand for methods to assess pilotaircraft interaction.One of the most widely used methods for cognitive modelling is the Model Human Processor (MHP), developed by Card et al. [6].The MHP is designed to calculate the duration required to complete specific tasks.This model, which incorporates factors such as processor cycle times and memory decay durations, assists system designers to predict time efficiency of human operator interacting with the analysed system.

Research Objective
Given the topics discussed in the introduction section, following research questions have been posed.The answers to these questions should help identify possible ways to enhance cockpits and pilot-aircraft interaction in the segment of light aircraft.
• How can human-centred design principles be utilized to improve safety and efficiency in light aircraft control?• How can pilot-aircraft interaction be optimized to reduce workload and enhance situational awareness?• What types of information could be conveyed by haptic feedback to improve pilot-aircraft interaction?

Human centred design and haptics in light aircraft control: A review
The application of human-centred design principles is not new in the aircraft domain.This design evolved alongside the parallel implementation of automated systems in both large and military aircraft.Boy and Tessier [7] introduced a method called MESSAGE for cockpit analysis and assessment.This method utilizes a multi-task/multi-channel model to measure both workload and pilot performance.Over the last decade, another common research topic has been the single-pilot cockpit for airline operations.Graham et al. [8] presents a study that compares a two-pilot cockpit with a single pilot cockpit equipped with an onboard support system that automates some of the functions typically performed by a co-pilot.This study evaluates life-cycle cost, reliability, and processing times for flight procedures based on MHP.The topic of the single-pilot cockpit introduces the concept of fault-tolerant cockpit architecture, discussed in detail by Fayollas et al [9].A comprehensive study by Boy [10] profits the author's extensive experience in human-centred design.This paper introduces three conceptual models, providing a framework to understand and address operationalization issues in complex systems.The author highlights a shift from hardware to software in the design and development process, termed the "socio-technical inversion".While the mentioned publications represent only a fraction of the extensive research on the human-centred design of aircraft cockpits, they left limited room for improvement using general principles of human-centred design.Conversely, the domain of light aircraft remains less impacted by automation and is similarly less researched in terms of human-centred design.

Light aircraft cockpit
In the last few years, there has been a trend of replacing analogue instruments with digital ones, the socalled Glass cockpit.This study [11] dealt with the topic of implementing glass cockpits in light aircraft from the safety point of view.At the same time, it proved that the introduction of glass cockpits did not lead to the expected increase in safety compared to similar aircraft with traditional equipment.Advanced avionics have the potential to increase this safety by providing pilots with more operational information, but more effort is needed for pilots to take advantage of this potential.Currently, touch screens are also coming to the fore.In this respect, especially for light aircraft, it is also necessary to address overall ergonomics, human factors, and operational practicality, and thus not only replace the original display with the touch screen [12].Glass cockpits have the potential to enable a change in the distribution of information during individual flight phases.This issue was addressed in this paper [13], which investigated what information is most important for given phases of flight, where it should be located, how large it should be, and when and why it should be displayed.The analysis of eye movement on individual devices was dealt with in this work [14].Pilots participating in the experiment were to perform a standard circuit under visual flight rules.The study assigns to each phase of flight the attention the pilot pays to each instrument.

Previous Research Projects in Haptic feedback
In [1], a roadmap for the development of artificial airflow sensation via haptic feedback was introduced.This roadmap led to the formulation of a unique guidance method utilizing haptic feedback as described in [15].The efficacy of the haptic guidance method was notable, with root mean square error of just a few percentages of the front-back joystick range between the target and the actual joystick position.While the hardware was applied in flight test mediating AoA via haptic way, it has not yet been integrated into any pilot assistance systems, such as landing aids or stall warning systems.Concurrently, other research teams have turned their attention to the potential applications of haptic technology in the realm of aircraft control.D'Intino et al. [16] delved into the potential of a haptic support system in mastering a 2 degrees of freedom compensatory tracking task.This haptic assistance incorporated force feedback.To assess the efficacy of the haptic support system, a human-in-the-loop experiment was conducted with novices using a fixed-base simulator.The haptic aid proved advantageous during the tracking task's training phase for both axes when compared with manual control.These findings have paved the way for further exploration into the creation of sophisticated haptic support systems capable of adjusting to a user's proficiency, thus offering tailored feedback.Deldycke et al. [17] introduced a tool designed to aid in manual flare manoeuvre training.The study indicated only a marginal enhancement during the training's onset.Nevertheless, the haptic feedback led to a more uniform beginning of the flare.The researchers concluded that while the haptic aid offers potential in manual flare manoeuvre training, there is a need for additional research to augment its efficiency.It is crucial to acknowledge that the perception and response to haptic feedback are highly individualized.A paper by Arenella et al. [18] underscored this by emphasizing the tailoring of the Haptic system to individual pilots.They embarked on crafting an Adaptive Haptic Aid system that modulates the assistance level on the control apparatus based on the pilot's real-time performance relative to the anticipated outcome.Both simulations and hands-on trials with novice and veteran pilots demonstrated that the proposed Adaptive Haptic Aid system holds significant potential for the future design of haptic aids.Recent research undertakings are also geared towards enhancing haptic feedback in fly-by-wire controls.For instance, Van Baelen et al. [19] presented flight envelope protection through haptic feedback, incorporating both force and vibrations in the control stick.This system assists pilots in evading flight envelope speed and load factor threshold values, especially when there is a shift to an alternative control law.

2.2.1.
Results and experiences: While the hardware was designed to be user-friendly, flight testing revealed the appearance of a learning effect.To demonstrate this training effect in haptic guidance, twelve undergraduate and graduate volunteer students aged 19 to 26 (mean 21.67, SD 2.23) were recruited to participate in the experiment.The test comprised two tasks, each repeated twelve times by each participant.The first task involved guiding the joystick to 20 randomly generated front-back directional positions with random duration from 3 to 6 seconds, while the second task, as illustrated in Figure 3, required guidance to a continuously changing target position.Both tasks were performed without any visual feedback, and the entire test took approximately 3 minutes to complete.The results indicated that starting from the seventh session, participants were able to track the continuously changing target position of the joystick with an error rate of less than 5 percent of the joystick's range.The error rate in the first task, which involved guidance to randomly generated positions, was even lower.A more detailed experiment description with statistical evaluation will be published soon.

Figure 3
Results obtained in a haptic guidance task without visual assistance.On the left side, a sample task displays the target and actual joystick positions.On the right side, the graph illustrates the mean error between target and actual positions for all participants along sessions.

Roadmap for Future Development: "More Haptic Aircraft"
Sensory overload (especially in the case of vision) can be successfully addressed by representing information to maintain good situational awareness using other sensory modalities.Auditory modality is routinely used even in light aircraft to complement visual instruments (e.g., for stall warnings or audio variometers in gliders).Haptic feedback is also a part of light airplane control naturally -the stiffness of control changes appropriately to airspeed, or the vibrations to the control stick appear if the plane approaches stall speed.In complex planes with power-assisted controls, this natural interaction is still simulated with systems like stick-shaker.
Systems based on haptic interaction (providing artificial tactile and/or kinaesthetic stimuli) can successfully supplement vision as a primary sensory modality in aviation.The systems can potentially be used for the following tasks: • Notifications: Haptic systems notifies to attract his/her attention to something.The situation is later evaluated also by other means/sources of information.Examples are simple stick-shaker or auditory stall warning.• Feedback: Haptic system provides any system response using touch cues.Vibrations, force or any other touch sensation can by exploit to give the response to a user.• Guidance: Haptic system provides guidance towards particular position in X-dimensional space.It can be position of a control or position relative to aircraft frame of reference (e.g.waypoint position).Example of such a system is flight-director, that already has its haptic variant published by De Stigter [20].• Expressing complex information.Haptic systems can convey even complex spatial-temporal information.Typically, various kinds or tactile displays are used [21].However, the practical application of complex systems relying on actuators mounted pilot skin is questionable for light aircraft cockpit.
The following aspects define classical usability [22] and should be considered for designing future human-centred systems for light aircraft.
• Learnability: The designed system should require only a little training.In the best case, a particular design can achieve affordance (self-explanability) from the user's perspective.The pilot should rapidly achieve proficiency in the usage of the system.• Efficiency: The design is efficient in its primary task of conveying specific information to maintain situational awareness.• Retention over time: when a pilot returns to using the system after an extended period of time, it should be easy for the pilot to regain the associated proficiency quickly.
• Low error rate: The system design will cause as few errors (e.g., value misinterpretation) as possible.It will provide cues to allow pilots to detect possible errors.The new system mustn't interfere with existing ones.• Subjectively pleasing: The acceptance of a new system design also relies on subjective assessment of users -pilots.Properties like shape or materials should be carefully considered.
Apart from classical usability and consideration of human-centred design in aviation described in [5], the following aspects of a haptic system for light aircraft should be considered: • Portability of a new system and possibility of retrofitting into existing aircraft.In case of light aircraft, new systems should allow retrofitting into existing aircraft and integration with existing systems.Systems that are carried-in by the pilot can make the integration more complicated, on the contrary, they will allow better adaptivity.Potentially, individuals can accept more intrusive systems (e.g., devices relying on skin contact) if they are in their possession.• Adaptivity of data presentation.The amount, coding and scales of the represented information can be adapted e.g., accordingly to flight phase/aircraft configuration or personalized on basis of individual's requirements and preferences.However, the future system should preserve transparency of its function to avoid errors.

Haptic feedback applications to light aircraft control
The introduced hardware may have multiple functions in aircraft control.These functions can be divided into three levels.The first level serves a warning function (provides notification and feedback).Frontto-back vibrating movements of the sliding element can alert a pilot about approaching stall conditions.This function can supply the shaker warning system typical for large aircraft.Similarly, the second level can be likened to the function of a pusher system (provides feedback and guidance).If the pilot does not respond to warning vibrations, the sliding element can signal a command to push the stick with an accentuated movement in the front direction.The system does not actually push the stick but gives a clear haptic command indicating the necessary control action.The third level is comparable to a complex flight director system (provides feedback and guidance).The moving element retains the same guidance function as in the second level.However, this third level requires a system that knows or can estimate the target or optimal flight trajectory.
A similar application was published by De Stigter et al. [20], where a haptic director aided pilots in enhancing their performance in a trajectory-following task.The distinction with the hardware they used is that it controlled stick forces in the sidestick, moving the zero-force position in roll and pitch control, which subsequently led to task performance improvement.This third level necessitates an intelligent control system that offers guidance assistance to the pilot, for instance, during a flare manoeuvre.Another potential application might be supplying of haptic feedback in a fly-by-wire control system.

Discussion
Let's confront the proposed applications from the previous section with the research questions.Especially the first two levels supplying the function of the stick shaker and pusher were suggested aiming to improve the safety of flying in light aircraft.The real shaker and pusher used in large aircraft are not suitable for light aircraft due to the weight and costs of the systems.The efficiency of the aircraft could be linked to a possible extension of haptics to the third level.The haptic flight director could assist the pilot in flying more efficiently or even accelerate pilot training.
The second question concerns the reduction of workload and enhancement of situational awareness.This point might be found in the transfer of some information from the visual modality to a haptic one.The optimization of information flow in the cockpit could be analysed and optimized using MHP.The improvement of the pilot-aircraft interaction should have a positive impact on both the pilot's workload and situational awareness.
The last question aims to identify particular information that could improve pilot-aircraft interaction.In the first level stated in section 3.1, the information is connected to the AoA.It can be information proportional to the AoA value or its margin to the critical value.In higher levels, the information can be more complex.In this case, research must be conducted on the personalization of haptic feedback perception.Learnability, retention over time, and adaptivity should be measured and analysed to exploit the maximum benefit from the haptic system.

Conclusions
Human-machine interaction has been identified as an ongoing topic in general aviation.Recent avionics advancements in light aircraft provide pilots with richer and more detailed data than in the past.However, this also increases the demands on workload and situational awareness for the pilot.A general goal of this paper is to address the challenge of maintaining pilot situational awareness during the use of automation or under challenging or emergency conditions.
The authors have combined their expertise and results from haptic feedback systems with the general principles of human-centred design to devise a roadmap for the future design of light aircraft cockpits.The haptic feedback system, when connected to a control stick and pedals, can convey information about flow field characteristics to the pilot through tactile feedback.The presented roadmap offers both general guidelines and potential applications, drawing inspiration from large commercial aircraft systems.
The outcome of the paper highlights the necessity of integrating human-centred design principles into the design of future light aircraft cockpits.Increasing avionics complexity should be reflected in multimodal optimization of pilot-aircraft interaction.Several warning, feedback, and guidance cues could be transferred from the visual to tactile modality.However, this shift also introduces new challenges in the subjective perception of tactile cues, which should be a subject of future research.

Figure 1
Figure1Comparison of two aircraft cockpits a century apart.Left side is SPAD XIII from1918, the right side is Cessna 182 Skylane from 2010[3]

Figure 2
Figure 2 Hardware conveying AoA and AoS to a pilot through haptic feedback [4]