Piloted Flight Simulation Research Articles

Evaluating the effect of frigate hangar shape modifications on helicopter recovery using piloted flight simulation

Turbulent ship airwakes can present a major challenge for a pilot landing a helicopter to the ship. A recent study has proposed modifications to the hangar of a simple ship, the SFS2, to improve the air flow over the deck. To assess the effect of the proposed hangar modification on the helicopter and pilot, the unsteady air flow over the modified ship has been computed using time-accurate CFD, and then integrated with a full-motion flight simulator for a pilot to conduct deck landings to the original and modified ship geometries in wind speeds from 30 kt to 50 kt. The effectiveness of the proposed modification was assessed through pilot workload ratings for the landing task, and by recording pilot control inputs and helicopter states. The study has shown that there are some benefits from the hangar modifications. In the headwind the helicopter was deemed to be at the safe limit at 50 kt when operating to the original SFS2, while the limit was not reached in the 50 kt wind for the modified ship. In an oblique wind, the safe wind speed limit was found to be 40 kt for the original ship and 50 kt for the modified version. Although the improvements are not substantial, they do represent a positive outcome.

Piloted Simulation-Based Assessment of Simplified Vehicle Operations for Urban Air Mobility

This work investigates the simplified vehicle operations paradigm, which seeks significant reductions in pilot workload and training requirements through the holistic design of flight control laws, control inceptors, and cockpit displays in the context of vertical takeoff and landing urban air mobility aircraft using piloted flight simulations. Two inceptor layouts, one similar to conventional fixed-wing aircraft and the other similar to conventional rotorcraft, differing in inceptor-to-command mappings, were incorporated into two research flight simulators. A lift-plus-cruise aircraft simulation model, a total energy control system–based fly-by-wire flight control architecture, and identical cockpit displays were used for both setups. Twenty-one participants, divided into three groups based on their prior piloting experience, were used to study pilot performance using representative handling qualities task elements. The piloted simulation data revealed that participants in each group were able to successfully perform the simulation tasks and allowed handling quality ratings to be calculated. They also highlighted instances of control coupling between inceptor axes in each setup for different tasks and the relative ease or difficulty of performing each task with the two inceptor designs.

A Turbulence Model for Flight Simulation and Handling Qualities Analysis Based on a Synthetic Eddy Method

A turbulence model based on a synthetic eddy method (SEM) has been adapted for flight simulation purposes and coupled with a FLIGHTLAB helicopter simulation model. The SEM is based on the generation of a random distribution of turbulence-generating eddies within a control volume surrounding the simulated aircraft. Eddies are displaced by the flow and regenerated at the inflow as they leave the simulation domain. The model allows adjustment of turbulence intensity and frequency spectra, allowing for a more realistic representation of broadband turbulence. Compared to other random turbulence models, preserving the location of the eddies in the control volume automatically ensures that turbulence across different aircraft locations is automatically correlated. Off-line and piloted flight simulation assessments have been conducted to test the viability of the SEM concept in flight simulation. Results show that the turbulence model generates upsets in all aircraft axes resulting in higher workload requirements for the pilot.

Atmospheric Disturbance Modelling for a Piloted Flight Simulation Study of Airplane Safety Envelope over Complex Terrain

A concept of a new energy management system synthesizing meteorological and orographic influences on airplane safety envelope was developed and implemented at the ZHAW Centre for Aviation. A corresponding flight simulation environment was built in a Research and Didactics Simulator (ReDSim) to test the first implementation of the cockpit display system. A series of pilot-in-the-loop flight simulations were carried out with a group of pilots. A general aviation airplane model Piper PA-28 was modified for the study. The environment model in the ReDSim was modified to include a new ad hoc subsystem simulating atmospheric disturbance. In order to generate highly resolved wind fields in the ReDsim, a well-established large-eddy simulation model, the Parallelized Large-Eddy Simulation (PALM) framework, was used in the concept study, focusing on a small mountainous region in Switzerland, not far from Samedan. For a more realistic representation of specific meteorological situations, PALM was driven with boundary conditions extracted from the COSMO-1 reanalysis of MeteoSwiss. The essential variables (wind components, temperature, and pressure) were extracted from the PALM output and fed into the subsystem after interpolation to obtain the values at any instant and any aircraft position. Within this subsystem, it is also possible to generate statistical atmospheric turbulence based on the widely used Dryden turbulence model. The paper compares two ways of generating atmospheric turbulence, by combining the numerical method with the statistical model and introduces the flight test procedure with an emphasis on turbulence realism; it then presents the experiment results including a statistical assessment achieved by collecting pilot feedback on turbulence characteristics and turbulence/task combination.

Handling Qualities in Rotorcraft Conceptual Design

This paper presents the development of a rotorcraft conceptual design tool able to incorporate handling qualities assessment at an early design stage. After a first conventional sizing, performed utilizing NASA’s NDARC software, a linearized model of the rotorcraft flight mechanics is built. The linear model is augmented by a simplified control system, designed according to structured H_{infty } techniques, to determine augmentation requirements, rather than design the actual flight control system. ADS-33 Bandwidth and Phase-Delay standards are exploited to objectively assess the handling qualities of the current design and to drive an iterative redesign process aimed at enhancing the handling qualities ratings. The rotorcraft parameters resulting from the augmented sizing are subsequently used to automatically generate a real-time capable multibody model, which can be used for the subjective evaluation of its handling qualities via piloted flight simulation. The tool capabilities are demonstrated by designing a conventional lightweight helicopter of the class of the Airbus Helicopters BO105.

Maneuvers During Automatic Formation Flight of Transport Aircraft for Fuel Savings

Formation flying techniques, demonstrated by migratory birds, have the potential to significantly save energy when two or more transport aircraft fly the same route at the same time. In fuel-saving formations, aircraft are flying straight trajectories for most of the time. For proof of concept, however, how vertical and lateral maneuvers can be flown has to be investigated. Those investigations require a flight simulator that is equipped with adequate flight mechanical models. Not much research exists on maneuvers of formation. The paper addresses the components that are needed to perform this research with real-time flight simulations. They are, first, a method to model wake vortices on curved trajectories; second, a formation flight control system, which comprises a method for the relative position determination, the design of control laws, and suitable cockpit displays; and third, techniques that allow vertical and lateral flight maneuvers. Two different strategies to position the following aircraft relative to the wake vortex during turns are described, and simulation results show their differences in terms of fuel savings and passenger comfort. Piloted flight simulator tests confirmed the usability of the proposed flight techniques for formation maneuvers, and the participating airline pilots indicated general consent to the concept.

Algorithms of Dynamic Piloted Flight Simulator Stand Based on a Centrifuge with a Controlled Cardan Suspension

The paper presents the structure of software for a control system of a dynamic simulation stand based on a centrifuge. The stand is intended for simulating manned flights with a broad range of overloads.

On Task Dependence of Helicopter Pilot Biodynamic Feedthrough and Neuromuscular Admittance: An Experimental and Numerical Study

In this article, the results of a piloted flight simulator campaign aimed at measuring biomechanical performance indicators of a helicopter pilot performing complex, realistic tasks are presented. The upper limbs' motion and the activation of the main muscle groups of the left arm were measured during ship-deck landings, performed flying several helicopter configurations with sea conditions of variable intensity. The analysis of the results shows an increase in the muscle activity relative to the increase in task difficulty, in agreement with subjective ratings (Bedford workload scale). The study provides useful indications to improve the corresponding biomechanical simulations, as well as to characterize pilot's performance during specific tasks.

Piloted Flight Simulation of Helicopter Recovery to the Queen Elizabeth Class Aircraft Carrier

This Paper describes how flight simulation has been used to investigate helicopter recovery operations to the deck of HMS Queen Elizabeth, the United Kingdom’s new aircraft carrier. A helicopter flight simulation environment has been developed in which the unsteady airflow over the ship has been created using full-scale computational fluid dynamics. A six-degree-of-freedom motion flight simulator has been used to conduct real-time piloted deck landings where a helicopter flight dynamics model representative of a Sikorsky SH-60B Seahawk helicopter was recovered to the designated rotorcraft landing spots toward the stern of the ship. A test pilot was instructed to land the helicopter and to give workload ratings for the difficulty of the task when flying in relative winds from Ahead, and 45 deg and 90 deg from starboard. The workload ratings, along with the corresponding pilot control activity and helicopter positional accuracy, are discussed in relation to the airflow to which the helicopter was subjected. The Paper demonstrates how flight simulation could be used to support flight trials and helicopter clearance activities but also notes that real-world trials data are needed to compare with the simulations before the techniques can be beneficially deployed.

Coupled Simulations of Atmospheric Turbulence-Modified Ship Airwakes and Helicopter Flight Dynamics

The influence of a neutral atmospheric boundary layer on a one-way coupled dynamic interface simulation is evaluated. The effort is performed within the context of time-accurate large-eddy simulations of Simple Frigate Shape 2, which is immersed into a turbulence-resolving atmospheric inflow that emulates the dynamics of a realistic atmospheric boundary layer. Several baseline cases are used to represent a traditional approach of modeling the incoming wind as a constant, uniform inflow. When comparing the atmospheric boundary layer-resolving to the baseline simulations, it is observed that the velocities in a ship airwake are considerably different when formed from an atmospheric boundary layer. The unsteady computational fluid dynamics solution is then saved as a database and used as external disturbances for flight dynamics analysis. Such an approach is common in piloted flight simulation. The pilot workload is evaluated using a helicopter approach scenario and multiple hover locations. Such cases are evaluated, and it is found that the large scales present in the atmospheric boundary layer notably disturb the helicopter. The disturbances result in increased controls input and aircraft movement. Frequency-domain analysis of the increased stick movement suggest that the atmospheric boundary layer impacts the 0.1–2 Hz stick controls, which comprise the frequency range known to affect pilot workload.

ATC simulation for flight training: The missing link

This paper presents the state of piloted flight simulation fidelity with a focus on the missing link needed to complete the flight simulation experience, namely the simulated ATC environment (SATCE). To date, there has been a great deal of effort invested in providing the highest level of flight realism possible. However, little investment has gone into systems which are used to improve communication skills with ATC while in a populated active airspace. It is important to note that the relatively few SATCEs is not due to the lack of technology, since such products have been available for about a decade. The primary reason for its absence is the inability and unwillingness for operators to justify the investment in such a training tool. In the meantime, the aviation industry has recognized that pilots need to have better communication skills while operating in various conditions. Consequently ICAO, with help from ARINC Industry Activities/FSEMC, has already taken steps to recommend the inclusion of SATCE characteristics in flight simulation devices. The aviation and research communities need to assist efforts by producing the necessary studies and metrics which can be used to evaluate and validate SATCEs used in the flight training.

Intelligent Flight Control Systems Evaluation for Loss-of-Control Recovery and Prevention

Recent developments in the field of loss-of-control recovery and prevention included improved pilot training, cockpit automation, and fault-tolerant control. The Flight Mechanics Action Group on Fault-Tolerant Control of the Group for Aeronautical Research and Technology in Europe demonstrated the advantages of fault-tolerant “intelligent,” flight control systems. The research enabled the improvement of the technology readiness level of these systems by evaluating one of them in realistic operational scenarios. The handling qualities results of a piloted flight simulator assessment with a damaged aircraft model showed that an online physical model identification approach contributed to improved pilot performance following potentially catastrophic structural and flight critical system failures. After the failures and subsequent control reconfiguration by the intelligent flight control system, airline and engineering test pilots experienced no difficulties in conducting a safe approach and landing.

Simulation of a Light Aircraft Encountering a Helicopter Wake

Different methods of modeling helicopter wakes are presented and compared with available wind-tunnel and flight-test data. A free-wake model was then used to generate the wake vortices of a helicopter hover-taxiing over an airport runway. A hybrid wake model, with a wake decay law, was also used to generate the far wake of a helicopter in level flight. The wake-induced velocity fields were integrated into an aircraft flight dynamics model, and piloted flight simulations were carried out to study a light aircraft encountering a helicopter wake during landing and level flight. It was found that, for the current landing wake-encounter scenario, the existing wake-encounter criteria and severity metrics for the determination of the hazardous distance might not be appropriate if the wake encounter occurs close to the ground. The landing simulation results suggest that, for a helicopter in low-speed hover-taxiing (less than 40 kt airspeed), the wake-encounter detectable horizontal distance is about three times the diameter of the rotor, which coincides with the current safety guidelines of the Civil Aviation Authority of the United Kingdom. The level-flight simulations revealed the effects of the vertical separation distance and of the wake decay on the encounter severity.

The Influence of Payload Mass and Inertia Properties on a Piloted Flight Simulator Hexapod Dynamic Performance

In order to improve the dynamic performance of a piloted flight simulator hexapod, a study was carried out to quantify the effects of payload mass and inertia properties on hexapod dynamic performance. Based on the Lagrange-Euler formulation, a dynamics model of hexapod parallel mechanism including the payload mass characteristics was built, and then analyzed with the real hexapod through experiments. According to a large amount of experiment datum, the influence of payload mass and inertia properties on a piloted flight simulator hexapod dynamic performance was obtained, and these results are significant for the high speed and high acceleration control of the hexapod mechanism.

Pilot Control Behavior Analysis Using Cutoff Frequency and Power Frequency for a Civil Transport Aircraft Encountering Turbulence Based on Flight Simulation

Atmospheric turbulence is one of the leading causes of serious personal injuries in nonfatal accidents of commercial aircraft and poses a significant hazard to aircraft in the terminal area. The pilot control behavior, workload and its difference from the normal flight situation also have essential impact on flight safety when the airplane encountered turbulence. In this paper, a unique frequency domain method, which used the cutoff frequency and the power frequency as the key metrics, was utilized to analyze the pilot control behavior in turbulence environment for a civil transport aircraft based on piloted flight simulation data. The results show that the cutoff frequency and power frequency consider both the frequency of pilot activity and the level of the activity at the same time, and could be a useful tool to analyze the pilot control behavior.

Effects of visual and motion cues in flight simulation of ship-borne helicopter operations

Good visual cues are necessary in the flight simulation of ship-borne helicopter operations. Operating in a degraded visual environment cues has a negative impact on pilot workload and task performance. However, the need for motion cues in piloted flight simulation is still a widely debated issue. This paper describes a preliminary piloted flight simulation study into the effects of visual and motion cues on the operation of ship-borne helicopters and pilot workload. Unsteady CFD airwakes have been computed and integrated into the FLIGHTLAB modelling and simulation environment with a simulated rotorcraft model, configured to be representative of an SH-60B helicopter. A series of ship-deck landing and hover manoeuvres have been conducted using the University of Liverpool’s HELIFLIGHT-R motion-base flight simulator representing different visual and motion cues, for a range of ship airwakes and sea states (ship deck motions). The usable cue environment (UCE), handling quality and pilot workload ratings were assessed using visual cue ratings, handling quality rating and the Bedford workload rating scale and Deck Interface Pilot Effort Scale. This paper presents the results from simulation trials with two test pilots examining the effect of the simulation cueing on task performance and workload. Visual cues were found to have a significant impact both on the UCE ratings and pilot workload ratings. In degraded visual environments, the pilot’s ability to make corrections in attitude and translational rates was reduced. Pilots experienced higher workload in terms of compensatory control inputs to complete the same mission task as compared to operations in a good visual environment. Analysis of the pilots’ workload ratings and control activity show that motion cueing can cause differences in pilot perceived workload. For the simulation of ship-borne operations, the impacts of motion cueing are dependent on other simulation conditions, which include visual environments, airwake, sea states and ship deck motion. The effect of motion cueing on pilot workload and control activity was found to be more significant when the visual cueing was degraded. The variations in pilot workload ratings and control activities under different motion and visual cues indicate that the Ship Helicopter Operating Limits can be affected by the simulation cueing fidelity.

Dynamic Soaring of Sailplanes over Open Fields

Dynamic soaring of a sailplane in the Earth’s atmospheric boundary layer was computationally investigated over a range of conditions to explore the feasibility of sustained unpowered flight over open fields by taking advantage of wind shear. A point-mass sailplane model was studied, as well as a full six-degree-of-freedom piloted sailplane model. For the point-mass model, parameter sweeps were performed around a baseline 3-m (9.58-ft) wingspan sailplane having a weight of 15 kg (33 lb) and an aspect ratio of 20. Results from the point-mass model show that, in certain high-wind conditions, dynamic-soaring energy-conserving orbits are possible for flight trajectories extending from the ground to (656 ft) aloft. A six-degree-of-freedom piloted flight simulator was used, and it produced similar results that showed dynamic soaring over open fields for large vertical extents (extreme climb). Together, these results support the conclusion that it is possible to perform dynamic soaring in high-wind conditions through the atmospheric boundary layer to high altitudes over open land with model-scale unpowered sailplanes having both high wing loadings and high lift-to-drag ratios.

Method of Trajectory Generation for Perspective Flight-Path Display in Estimated Wind Condition

A method to generate a three-dimensional trajectory for a perspective flight-path display to suppress tracking errors and excessive bank angles due to steady wind was devised. The proposed method transforms an original trajectory constructed from straight and arc segments into a clothoidlike trajectory, and then it replaces the arc segments with the results of a fast-time simulation that incorporates a steady wind, which may be acquired by onboard-sensed and/or uplinked information. The offline simulation demonstrates that the modified trajectory suppresses tracking error and excessive bank angles during path-tracking flight. The piloted-flight simulation also showed not only reductions of tracking errors and bank angles but also of subjective workload. The proposed method was integrated into the onboard system of an airborne sequencing and separation assistance experiment, and the function of the modification algorithm was demonstrated using actual wind information acquired by onboard sensors and ground measured and uplinked winds.

Ship-Helicopter Operating Limits Prediction Using Piloted Flight Simulation and Time-Accurate Airwakes

This paper gives an overview of the ship―helicopter dynamic interface simulation facility at the University of Liverpool, with an emphasis on recent improvements made through the inclusion of unsteady computational fluid dynamics (CFD) ship airwake data. A FLIGHTLAB model of an SH-60B Seahawk helicopter has been flown in a full motion base simulator to the deck of a Type 23 frigate and a Wave class auxiliary oiler, under the influence of unsteady airwakes derived from CFD. Pilot workload ratings have been obtained for the deck landing task, using both the Bedford workload rating scale and the deck interface pilot effort scale, from which fully simulated ship―helicopter operating limits have been derived. Analysis of pilot ratings, comments, and control inputs has also enabled both subjective and objective assessments of workloads at various wind-over-deck conditions, highlighting the dominant aerodynamic airwake features which contribute to the difficulty of the landing task. Having access to the underlying CFD data allows the aircraft handling qualities and pilot workload to be correlated with the aerodynamic characteristics of the airwake and identification of the geometric features of the ship that cause them.

Sliding mode methods for fault detection and fault tolerant control with application to aerospace systems

Sliding mode methods for fault detection and fault tolerant control with application to aerospace systemsSliding mode methods have been historically studied because of their strong robustness properties with regard to a certain class of uncertainty, achieved by employing nonlinear control/injection signals to force the system trajectories to attain in finite time a motion along a surface in the state-space. This paper will consider how these ideas can be exploited for fault detection (specifically fault signal estimation) and subsequently fault tolerant control. It will also describe applications of these ideas to aerospace systems, including piloted flight simulator results associated with the GARTEUR AG16 Action Group on Fault Tolerant Control. The results demonstrate a successful real-time implementation of the proposed fault tolerant control scheme on a motion flight simulator configured to represent the post-failure EL-AL aircraft.