Deck Landing Research Articles

Helicopter augmented control laws for ship deck landing: HACLAS ONERA/DLR Joint Team

Different types of control laws are implemented, tested and compared for maritime operations particularly ship deck landing maneuvers at the flight simulation facilities at both DLR (German Aerospace Center) and ONERA (The French Aerospace Lab). At DLR, “classical” cyclic and collective stick flight controls were used during the piloted simulator trials while active side-sticks were operated at ONERA. A joint maritime scenario for ship deck landing in the simulation environments of both institutes is presented. Test methodologies and assessment techniques to evaluate the ship deck landings are harmonized based on different criteria such as quantitative measures and handling qualities (HQ) ratings to analyze the developed control laws. Simulation results based on pilot studies for an EC135 in the DLR simulator and an EC225 at ONERA are presented.

An overall evaluation toolchain for assessing helicopter ship deck landings

AbstractA compact toolchain is implemented for the control system design for helicopter ship deck landings in a simulated environment which provides a cost-efficient and safe environment to test different scenarios. The evaluation of the ship deck landing manoeuvres is mostly performed for Ship Helicopter Operation Limits (SHOL) evaluation and performance of the helicopter. In most of the assessments, a subjective assessment is performed using different pilot rating scales which is not sufficient and the objective assessment of the simulation data for the mission success itself is seldom performed. The developed toolchain evaluates the successful operation of ship-based rotorcraft by considering both ship and helicopter dynamics, environmental conditions, and the pilot’s responses. The toolchain evaluates various touchdown conditions like helicopter position, velocity and attitude relative to the ship deck. It also displays additional evaluation parameters for the entire approach. A preliminary pilot study was performed in a simulator within a complete maritime scenario design. The maritime simulation environment includes a nonlinear helicopter flight model with a model-based flight control system, a ship dynamic model with the simulated turbulent air wake and realistic wave and water effects. For a subjective assessment of the ship deck landings, subjective pilot ratings using different rating scales were recorded during the pilot study. Simulation results show that the toolchain is convenient and well suited for assessing helicopter ship deck landing performance in a simulation environment as it provides a complete objective and subjective evaluation.

A Fuzzy-Based System for Autonomous Unmanned Aerial Vehicle Ship Deck Landing.

This paper introduces a fuzzy logic-based autonomous ship deck landing system for fixed-wing unmanned aerial vehicles (UAVs). The ship is assumed to maintain a constant course and speed. The aim of this fuzzy logic landing model is to simplify the task of landing UAVs on moving ships in challenging maritime conditions, relieving operators from this demanding task. The designed UAV ship deck landing model is based on a fuzzy logic system (FLS), which comprises three interconnected subsystems (speed, lateral motion, and altitude components). Each subsystem consists of three inputs and one output incorporating various fuzzy rules to account for external factors during ship deck landings. Specifically, the FLS receives five inputs: the range from the deck, the relative wind direction and speed, the airspeed, and the UAV's flight altitude. The FLS outputs provide data on the speed of the UAV relative to the ship's velocity, the bank angle (BA), and the angle of descent (AOD) of the UAV. The performance of the designed intelligent ship deck landing system was evaluated using the standard configuration of MATLAB Fuzzy Toolbox.

Evaluation of Helicopter Ship Deck Landing Control Laws in Piloted Simulations

This paper describes the implementation and the evaluation of newly designed helicopter ship deck landing control modes in a piloted simulation study. The ship deck landing modes are embedded in a model-following controller architecture. The employed control design is a complete model-following control system, which imposes the desired command model dynamics on the controlled helicopter. Different command types combined with various hold functions are implemented to make the task easier for the pilots. Three basic command modes and three advanced command modes, one without ship communication and two with ship communication, are implemented. A piloted simulation study was performed in a simulator to evaluate and compare the implemented control modes within a complete maritime scenario design. The evaluation of control modes is based on the success of helicopter ship deck landings which is assessed by a quantitative as well as a qualitative assessment. Simulation results demonstrate that the advanced command modes improved the task performance as well as reduced the pilot workload extensively in comparison to the basic command modes.

Autonomous ship deck landing of a quadrotor UAV using feed-forward image-based visual servoing

Autonomous takeoff and landing are crucial for unmanned aerial vehicles (UAVs) to perform various missions automatically. However, navigation sensors with low accuracy such as global positioning system (GPS) are limited in autonomous takeoff and landing for marine applications when ships are moving fast and oscillating by sea waves. In this study, an image-based visual servoing (IBVS) technique, which was originally used to land a UAV on a static target, is extended for a moving target. In particular, the ship velocity is estimated and used as a feed-forward term in the IBVS controller. To accurately estimate the velocity of the ship, velocity data from the GPS on the ship, image information obtained from the camera in the UAV, and dynamic model of the ship are combined using the Kalman filter framework. Besides, considering the under-actuated nature of the UAV and oscillation of the ship, a virtual plane concept, adaptive IBVS gain and feature shape compensation are introduced. Lastly, to apply the IBVS controller to the moving ship deck landing, a robust and safe autonomous landing procedure, starting from the approach to the touchdown phase, is also developed. The proposed autonomous landing system is validated via simulations and various real-world flight experiments simulating situations in which the ship is moving fast and oscillated by sea waves. In the flight experiments, the UAV lands successfully on the landing pad with the average touchdown error of 0.2m while the ship is oscillating at the Sea State 4 and is moving faster than 5m/s.

Ship Air-Wake Identification from Experimental Data for Automatic Deck Landing and Takeoff

Ship air-wake modeling is a critical task needed to support the design and validation of algorithms that can assist a helicopter’s pilot during shipboard launch and recovery operations. In fact, these operations are often carried out in challenging conditions and impose a significant workload on the pilot. In this framework, the paper presents an air-wake model applicable for flight mechanics analyses and real-time simulations. The definition of the model is based on system identification methodologies applied to wind-tunnel experimental data. The main innovation of the approach consists of the definition of a modular structure of the model that allows setting up a multistep identification strategy and exploiting the most suitable technique for the estimation of each set of the model’s parameters. The validation of the obtained model highlighted a good capability to reproduce the air-wake flowfield in several flow conditions. The model was applied to test trajectory generation and tracking algorithms for helicopter automatic takeoff and landing on a ship deck.

Autonomous deck landing of a vertical take-off and landing unmanned aerial vehicle based on the tau theory

The research on autonomous landing of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) is well established. However, the research on autonomous deck landing using visual methods is relatively not so mature and many of them require the support of ground infrastructures. In order to reduce such dependencies, a ship landing guidance strategy based on on-board vision is studied. Considering the characteristics of the ship landing issue, we propose a three-phase landing scheme and a decision-making method to ensure landing safety is also studied. For improving the traditional two-dimensional (2D) optical-flow method, a three-dimensional (3D) velocity vector estimation method using image spherical optical flow is studied. Furthermore, a guidance law based on the tau theory is employed by only using the visual information of the line of sight to the target. In this phase, a trajectory-tracking controller is applied to generate the velocity commands of the UAV. Finally, the whole algorithm is validated by simulation in different wave conditions developed with Unity3D. Compared with traditional trajectory planning methods, our method does not require complex optimization iterations and can meet both the real-time and accuracy requirements of deck landing. The average tracking error of our method maintains in 0.2 m. Moreover, the whole algorithm runs efficiently at around 30 fps on a Raspberry-Pi 3B+ microcomputer which meets the real-time requirements.

Helicopter Pilots Synchronize Their Altitude with Ship Heave to Minimize Energy When Landing on a Ship’s Deck

ABSTRACT Objective: This study aims at investigating helicopter pilots’ strategies to achieve ship deck landing. Background: Helicopter maritime operations are challenging, especially when it comes to landing on the moving decks of small ships, such as frigates, which can lead to dramatic accidents. Method: Expert pilots were requested to fly the full ship landing maneuver from approach to touchdown in an immersive simulator. Two sea states (3 and 4 on the Douglas Sea scale) and their resulting deck movements were used. Changes in helicopter altitude were correlated with deck heave movements throughout the maneuvers in order to scrutinize the helicopter-deck coupling. The energy at impact was measured. Results: The dynamics of helicopter-deck coupling evolved through two phases during the maneuver: Initially, no coupling then, coupling in phase between the helicopter vertical displacements and deck heave displacements. Moreover, the coupling reached higher values within the last 15 m to landing, corresponding to a hover phase and touchdown, and the correlation increased with sea level. This coupling might help in improving pilots’ safety since the greater the coupling at touchdown, the lesser the kinetic energy at impact. Conclusion: Coupling the helicopter vertical displacements with ship heave movements seems to be an efficient strategy to minimize energy at impact. Questions arise on both the rationale and the perceptual invariant behind such behavior and indicate the necessity of further investigation.

Maritime operation of an unmanned rotorcraft with tethered ship deck landing system

In security-critical situations in the maritime area, ship-based deployment of remotely piloted aircraft systems could enable automated acquisition of aerial images and other sensor data. If intervention is required, response times of federal institutions could be shortened significantly without endangering personnel. This paper gives an overview of research undertaken at DLR in cooperation with the German Federal Police for Maritime Tasks. For a safe ship deck landing of an unmanned rotorcraft a combination of precise navigation and tethered landing system has been developed and patented. Relative double-difference algorithms are used for precise navigation of the rotorcraft to a hover point over the ship deck. From there, an electromagnetic winch is lowered from the rotorcraft that connects to the ship deck. The resulting cable connection is used for aligning the rotorcraft during landing and securing it on the ship deck afterwards. First demonstrations on a real ship deck show the feasibility of the system.

Sinking Velocity Impact‐Analysis for the Carrier‐Based Aircraft Using the Response Surface Method‐Based Improved Kriging Algorithm

The deck landing sinking velocity of carrier‐based aircraft is affected by carrier attitude, sea condition, aircraft performance, etc. Its impact analysis is a complex nonlinear problem, and there even is some contradictory phenomenon that when the approach velocity increases, the sinking velocity decreases under certain circumstances. Aiming at exploring the impact of the various related deck landing parameters on sinking velocity for carrier‐based aircraft in the actual environment, response surface method‐based improved Kriging algorithm (IK‐RSM) is proposed based on genetic algorithm and Kriging model. Based on the deck landing measured data of the F/A‐18A aircraft in the actual operating environment, the impact degree of the 15 deck landing parameters on the sinking velocity is explored, respectively, by using the partial correlation analysis of multivariate statistical theory and the IK‐RSM. It can be found that the 4 parameters are strongly correlated with the sinking velocity; that is, the aircraft glide angle and deck pitch angle are highly correlated with the sinking velocity; next, the approach velocity and the engaging velocity are moderately correlated with the sinking velocity. The 4 parameters above could be used to establish the impact analysis model of the sinking velocity. The genetic algorithm is applied to the correction coefficients optimization of the IK‐RSM’s kernel functions, and the IK‐RSM of the F/A‐18A aircraft sinking velocity is formed. Compared with the Kriging model and the empirical formula, the sinking velocity prediction accuracy indexes of IK‐RSM are the best; for example, the determination coefficient is 0.981, the mean relative error is 1.813%, and the maximum relative error is 6.771%. Furthermore, based on the sinking velocity IK‐RSM and the sensitivity analysis method proposed, we have explained the reason for the contradictory phenomenon that when the approach velocity increases, the sinking velocity decreases at some samples. It could provide certain technical support for the flight attitude control related to the sinking velocity during the actual flight of carrier‐based aircraft.

Numerical investigation of the unsteady coupling airflow impact of a full-scale warship with a helicopter during shipboard landing

In this paper, a comprehensive computational modeling study of the unsteady aerodynamic environment around a warship with a helicopter is performed. An experimental validation exercise is also conducted, comparing computational fluid dynamics (CFD) results of the airwake calculated for a reduced-scale model of the isolated Landing Helicopter Assault (LHA) model with high-quality particle image velocimetry experimental data provided by the NASA AMES Research Center. Comparisons of the results generally obtain agreement, indicating that the CFD numerical method is able to resolve the large-scale turbulent airflow. Building on this, a numerical simulation of a real Robin helicopter, immersed in the unsteady airwakes of a full-scale Amphibious Assault Ship (AAS), is performed. The aerodynamic simulation of the influence on the coupled airflow of warship–helicopter is explored and compared with that of the solitary ship airflow field and the superposition airwakes, where the vortex patterns and pressure on the ship surface, as well as the velocity distribution, are circumvented. As a further step, dynamic landing analysis of the airflow field for a shipborne helicopter is implemented at an important location through the landing path for headwind. The aerodynamic characteristics of a helicopter during a flight deck landing are also explored for the unsteady ship airwakes impacting on rotor force during shipboard landings. In addition, different shipboard landing paths of the helicopter are comparatively investigated for obtaining an optimal landing path decision. The present study demonstrates an effective aerodynamic analysis and robust numerical approach, which creates a solid foundation supporting further alternative evaluations of ship airflow fields.

Numerical study of the rotational direction effect on aerodynamic loading characteristics of shipborne helicopter rotor

ABSTRACTNumerical simulations of ship/rotor-coupled flowfield have been performed to investigate the rotational direction effects on a shipborne single-rotor helicopter in different deck landing trajectories (i.e., lateral and longitudinal translation) based on Reynolds-averaged Navier-Stokes (RANS) solver. Both the momentum source model and moving overset mesh model are employed to simulate the effect of the rotor on the ship airwake for different levels of fidelity requirement. The aerodynamic loading characteristics in terms of time-averaged and root-mean-square (RMS) thrust and pitch and roll moments are compared for two helicopter rotors with opposite rotation directions in a starboard 30 degrees wind condition. The time-averaged results show that the mean thrust of a counterclockwise rotor is greater than that of a clockwise rotor, particularly in the lateral translation phase. This suggests that a helicopter with a counterclockwise rotor could provide more collective control margin under this condition. Furthermore, a more significant reduction in pitch moment is experienced by the counterclockwise rotor during the two landing trajectories, and thus the effect of the aircraft being pulled towards the hangar tends to be more severe on the helicopter with the counterclockwise rotor. RMS loading results indicate that the unsteady loading levels on the clockwise rotor are much higher than that of the counterclockwise rotor in all three axes for most of the lateral and longitudinal translation phases. As a result, the pilot is likely to experience a higher workload when operating a helicopter with a clockwise rotor in the case of a deck landing in this wind condition.

Robust linear output feedback controller for autonomous landing of a quadrotor on a ship deck

ABSTRACTShip deck landing control of a quadrotor requires certain robustness with respect to ship heave motion. Typical systems only provide relative height, therefore do not have relative heave rate information. In this paper, a linear output feedback control consisting of a full state feedback controller and a Luenberger observer is formulated. Invariant ellipsoid method is used to formulate an estimation of a bound on the response of a linear output feedback-controlled system subjected to external disturbances and measurement noise. The gains that result in a minimum bound are optimized using a gradient descent iterative approach proposed in this paper where the invariant ellipsoid condition is linearized into a tractable LMI condition. This approach is applied to a simulation of a quadrotor landing on a ship deck and results are compared with other gains. The gains selected using the proposed approach exhibits improved robustness to external disturbances and measurement noise.

TUNING FUZZY LOGIC MOTOR MODEL FOR PILOT CONTROL BEHAVIOUR DURING HELICOPTER FLIGHT MANOEUVRES

A helicopter pilot behavioural model was developed by the De-fence Research and Development Canada to conduct various flightmanoeuvres in a modelling and simulation environment that incorporates the Helicopter Deck Landing Simulator, the SimulatedOperators for Networks on the Integrated Performance ModellingEnvironment and the Language of Agents for Modelling Performance.

Quadrotor Autonomous Approaching and Landing on a Vessel Deck

Autonomous landing of a quadrotor UAV on a vessel deck is challenging due to the special sea environment. In this paper, we present an on-board monocular vision based solution that provides a quadrotor with the capability to autonomously track and land on a vessel deck platform with simulated high sea state conditions. The whole landing process includes two stages: approaching from a long range and landing after hovering above the landing platform. Only on-board sensors are used in both stages, without external information input. We use Parrot AR.Drone as the experimental quadrotor platform, and a self-designed vessel deck emulator is constructed to evaluate the effectiveness of the proposed vessel deck landing solution. Experimental results demonstrate the accuracy and robustness of the developed landing algorithms.

Selecting a Flight Path of an UAV to the Ship in Preparation of Deck Landing

Objectives: Automatic landing of an aircraft-type Unmanned Aerial Vehicle (UAV) on the ship is a complex research and engineering problem. In the general case, a set of problems must be solved subject to the initial position of the UAV and the ship, weather, visibility, reliable radio communication etc. in preparation for landing and capturing the initial point of a glide path for landing. These problems include the UAV flying to the ship location, searching for and identifying the ship, determining rolling parameters and estimating the position of landing markers on the ship deck. Method: Methods of UAV guidance to the ship search area have been compared. Conditions for the effective application of various methods of UAV guidance to the ship have been determined. Findings: It was demonstrated that insufficient attention is paid in available research to scenarios, when the ship may change its direction and a communication channel with the UAV is not stable due to the weather. The following tasks are discussed: • determining conditions of physical realizability of the successful ship search; • selecting a method to guide the UAV towards the ship, with view to ship maneuverability intensity and duration of transmission breaks to the UAV about current ship parameters according to the flight endurance minimization criteria; and • determining UAV flight endurance to the ship location subject to the duration of transmission breaks. Conditions of the successful ship search have been determined and the ratio of the initial search area and UAV flight endurance has been shown. Improvements: The results of the study can be used in the development of autopilots for autonomous UAVs based on the ships.

Autonomous ship deck landing of a quadrotor using invariant ellipsoid method

This paper proposes an invariant ellipsoid-based method for the controller design and gain synthesis of a low-cost quadrotor autonomous ship deck landing system subjected to wind disturbance and measurement noise. This method optimizes the quadrotor performance, hence achieving soft landing. A complete control architecture for the quadrotor is also presented. Simulations are performed using a realistic ship deck model in the presence of measurement noise and wind disturbance with a quadrotor.

Model Predictive Control for Helicopter Shipboard Operations in the Ship Airwakes

This study investigates the model predictive control design for helicopter shipboard operations in the presence of ship airwakes and rough seas. A control oriented helicopter model that captures the essential dynamics of a generic helicopter, including fuselage dynamics, blade flapping and lead-lagging, and main rotor inflow in the implicit nonlinear ordinary differential equations form, is used for model predictive control design and evaluation. The control equivalent turbulence inputs model and the computational fluid dynamics data of the airwake are incorporated into the nonlinear helicopter model to simulate the airwake’s effects on the helicopter. The feasibility of the model predictive control design is investigated using two case studies: automatic deck landing on a moving ship in sea state 5 with the control equivalent turbulence inputs airwake model, and lateral reposition toward the ship in different wind-over-deck conditions extracted from the computational fluid dynamics airwake data. To improve the overall model predictive control performance, an updating scheme for the internal model of the model predictive control is proposed for helicopter shipboard operations using linearization around operating points. Nonlinear simulations are also performed to explore the capabilities of the model predictive control in handling system constraints, flight deck tracking, and disturbance rejection.

Flight deck heat spreader

Deployment of modern aircrafts such as MV-22 Osprey or F35B Joint Strike Fighter has caused buckling of aircraft carrier ship flight decks due to excessive heat impact from aircraft engine exhaust plumes during landing. This work describes a development of Flight Deck Heat Spreader (FDHS) that is placed over a flight deck landing spot to protect it from hot exhaust plumes. The FDHS consists of aluminum panels with supporting pillars, aluminum wick sintered directly to panels and supporting pillars, water with corrosion inhibitor working fluid, and is sealed by welding together individual panels. The FDHS operates similar to a vapor chamber i.e. water vapor spreads the heat. The FDHS has 60% of the weight of solid aluminum of the same size, it is rigid with good strength and mechanical impact loading resistance, and it can be scaled to large areas of more than 50 m2. This paper focuses on thermal modeling of the FDHS, fabrication and tests of 450 cm2 and 3721 cm2 FDHS prototypes, and selection of working fluid corrosion inhibitor. FDHS was demonstrated to effectively shield the flight deck during high temperature thermal exposure and that the FDHS cools 8-times faster than similar weight aluminum alloy plate.

The virtual AirDyn: a simulation technique for evaluating the aerodynamic impact of ship superstructures on helicopter operations

AbstractThis paper describes a simulation technique that has been developed to quantify the unsteady forces and moments that are imposed onto a maritime helicopter by a ship’s airwake during a deck landing. An unsteady CFD-generated airwake, created using a CAD model of the ship, is integrated with a flight dynamics model of a helicopter. By holding the helicopter at a fixed position in the airwake it is possible to quantify the unsteady forces and moments imposed on the aircraft. The technique is therefore a software-based airwake dynamometer, and has been called the virtual AirDyn. As well as determining the mean loads, from consideration of the unsteady loads in the closed-loop pilot response frequency range of 0·2-2Hz it is also possible to quantify the magnitude of the unsteady disturbance in each axis. The loads are also indicators of the control activity the pilot would have to exert to maintain aircraft position and attitude. By placing the virtual AirDyn at different positions around the landing deck in different wind conditions, it is able to quantify the effect of the airwake on the mean and unsteady loads. The quantified loads can be explained by examining the CFD-generated flow field, and the geometric features on the ship’s superstructure that gave rise to them can be identified. The virtual AirDyn is therefore a tool that can be used to evaluate and inform ship design for maritime helicopter operations.