Helicopter Flight Dynamics Model Research Articles

An Approach to Developing Mathematical Software of On-Board Helicopter Flight Simulator Decision Support System

Abstract The work explores methods and develops aids to improve a pilot flight training level using Full Flight Simulators. It examines their didactic advantages over real helicopters by implementing on-board intelligent decision support systems (IDSS). These simulation programs monitor actions of learner, find the best ways to correct errors and generate appropriate instructions. The training is carried out by reference point methods while the helicopter flight dynamics model simulates a flight and helps an instructor in parallel. Sufficiently simple and accurate model of helicopter flight dynamics was selected and tested to assess the proposed methods and aids. Our analysis introduces a functional structure of IDSS as an adaptive control system with a reference model. We further conducted a study on developing models, methods and means of automatic analysis, forecasting, optimization and correction of actions. Combining single-criteria conditional and vector optimization methods, we found out optimal flight parameters. The research findings revealed that the chosen optimization method requires too many system resources for the optimal solution to be found in a short time. The study thereby comes up with applying ANNs to solve this problem.

Investigation on effects of time-frequency characteristics of ship airwake on helicopter flight characteristics

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is developed in this study. In the method, the ship airwake data is obtained by the high-accuracy DES model, and a strategy which can transmit CFD data to the flight dynamics model is established based on the "one-way" coupling idea. Then, the SFS2 ship model and UH-60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level. The time-averaged simulation results show that for the counterclockwise-rotor helicopter, although pilot could have more collective pitch margin under crosswind condition compared to the headwind condition, he might possess much less pedal margin due to the sidewash in the airflow. The unsteady results indicate that the unsteady loading level of the helicopter would increase significantly under the crosswind condition compared to the headwind condition due to the increase of turbulent density in the airwake. Furthermore, for the conventional helicopter, the disturbances on the forces and moments which along the rotor hub (i.e., thrust and yaw moment) are the critical factors that increasing the pilot workload during the landing procedure.

Adaptive neural network-based active disturbance rejection flight control of an unmanned helicopter

To enable the unmanned helicopter to fly autonomously in precise paths and reduce the influence of internal and external unknown disturbances of the unmanned helicopter, this paper proposes the adaptive radial basis function (RBF) neural network-based active disturbance rejection controller (ADRC). This controller is abbreviated as RBF-ADRC. Firstly, this paper introduces the flight dynamics model of the unmanned helicopter and the control features of the traditional ADRC. Subsequently, this paper uses modern control theory to establish a state observer and uses adaptive RBF neural network to estimate the unknown total disturbance. Finally, this paper constructs the unmanned helicopter's trajectory tracking control system based on the RBF-ADRC controller. The simulation results of the spiral ascent and the “8”-figure climb maneuver flight prove that the anti-disturbance, robustness and tracking accuracy of the RBF-ADRC are better than the traditional ADRC and proportion-integration-differentiation (PID) control methods.

Propeller design to improve flight dynamics features and performance for coaxial compound helicopters

The coaxial compound configuration has been proposed as a concept for future high-performance rotorcraft. The co-axial rotor system requires no anti-torque device, while the longitudinal thrust is provided by a propeller. A well-designed propeller can ensure both the performance and the cruise efficiency. The propeller design also influences the flight dynamics of such configuration. To design the propeller parameters of the coaxial compound helicopter, the propeller modelling and design method devised by Adkins and Liebeck is firstly introduced. A flight dynamics model of the coaxial compound helicopter is developed. Trim characteristics, power consumption results, and handling qualities features are calculated with variable propeller parameters at optimum (corresponding to the maximum flight range) and maximum speeds. The results indicate that the propeller parameters alter its efficiency and improve the performance characteristics of this helicopter. In addition, the propeller design also influences the flight dynamics characteristics and handling qualities of the coaxial compound helicopter, and consequently affect the power consumption indirectly. In this light, a design method for the propeller has been developed by formulating the design procedure into the nonlinearly constrained optimisation problem based on the flight dynamics characteristics. The method is demonstrated by evaluating propeller parameters to improve the performance in both optimum and high-speed range, which could also guarantee the handling qualities of the rotorcraft for related requirements.

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.

SIMSHOL: A Predictive Simulation Approach to Inform Helicopter–Ship Clearance Trials

This paper presents the development of a simulation framework, SIMSHOL, which has a predictive capability to inform and support real-world ship–helicopter operating limit trials for a range of helicopter–ship combinations. SIMSHOL is a desktop-based predictive simulation tool that presents an objectively optimized human pilot modeling technique within an integrated pilot–vehicle–environment that represents the helicopter–ship dynamic interface (HSDI). The overall scheme employs a multiloop pursuit “paper” pilot model, a linearized helicopter flight dynamics model with a new enhanced spatial turbulence model, together with an objective optimization loop. To simulate the ship-airwake turbulence effect, a new spatial airwake disturbance modeling technique has been developed, which, in real time, captures the spectral characteristics of the turbulence around the ship from a computational fluid dynamics-computed ship airwake. Time- and frequency-domain comparisons have been made between SIMSHOL and piloted simulation flight trial experiments. It was observed that the performance of the SIMSHOL tool in maintaining sufficient clearance between the aircraft and the ship’s landing deck and hangar, while rejecting airwake disturbances, is well within the desired task performance boundaries. These investigations have shown that the tool is capable of representing the dynamics of a pilot–vehicle–task system in the challenging HSDI environment. Moreover, an automatic error-minimization-based response optimization methodology has been developed and used, which uses the iterative gradient descent optimization algorithm to objectively tune the pilot–vehicle loop transfer functions to represent a pilot’s performance in the simulator. The results show that SIMSHOL is able to predict operational limits for a range of different helicopter–ship and environmental combinations.

Trim investigation for coaxial rigid rotor helicopters using an improved aerodynamic interference model

The coaxial rigid rotor helicopter has been proposed as a future high-performance rotorcraft concept. However, the aerodynamic interference of this helicopter is complicated because it couples with the unique flapping feature of the rigid rotor, which further alters the trim characteristics of coaxial rigid rotor helicopters. Thus, a multi-point vortex ring element (MVRE) model is developed to simulate the aerodynamic interference between rotors. The method for establishing this MVRE model is illustrated, and a wind tunnel experimental dataset is used to assess its precision hover and forward flight states. Next, a flight dynamics model of the coaxial rigid rotor helicopter is built based on the MVRE aerodynamic interference model and the flapping feature of the rigid rotor. The influence of the rotor wake on the fuselage and the horizontal and vertical tails can also be calculated using this model. The trim characteristics of this helicopter are evaluated with flight test data for speeds ranging from 0 m/s to 80 m/s, and the results confirm that this model can reflect the trim characteristics with satisfactory precision. In addition, the calculation process demonstrates that the MVRE model provides a much faster computing rate. Considering the aerodynamic interference and rigid rotor characteristics, the trim results of the coaxial rigid rotor helicopter present unique features: aerodynamic interference in the coaxial rotor system not only increases the collective pitch and the collective differential but also adds a negative gradient under the forward speed in the longitudinal cyclic pitch in the low-speed forward flight range. Moreover, the rotor wake effect on the other parts of the helicopter is distinct from the corresponding effects on conventional helicopters in terms of the trim characteristics.

Propeller control strategy for coaxial compound helicopters

The coaxial compound configuration has been proposed as a concept for future high-performance rotorcraft. The co-axial rotor system does not require an anti-torque device, and a propeller provides axial thrust. A well-designed control strategy for the propeller is necessary to improve the performance and the flight dynamics characteristics. A flight dynamics model of coaxial compound helicopter is developed to analyze these influences. The performance and the flight dynamics characteristics in different propeller strategies were first investigated. The results show that there is an improvement in the performance in high-speed flight when the propeller provides more propulsive forces. It also illustrates that a reasonable allocation of the rotor and the propeller in providing thrust can further reduce the power consumption in the mid speed range. In other words, the propeller control strategy can be an effective method to improve the cruise-efficiency. The flight dynamics analysis in this paper includes trim and handling qualities. The trim results prove that the propeller strategy can affect the collective pitch, longitudinal cyclic pitch, and the pitch attitude. If the control strategy is designed only to decrease the required power, it will result in a discontinuity in the trim characteristics. Handling qualities are investigated based on the ADS-33E-PRF requirement. The result demonstrates that the bandwidth and phase delay results and eigenvalue results in various speed at different propeller strategies are all satisfied. However, some propeller control strategies lead to severe inter-axis coupling in high-speed flight. Based on these results, this paper proposes the propeller control strategy for the coaxial compound helicopter. This strategy ensures good trim characteristics and handling qualities, which satisfy the related requirements, and improves the flight range or the performance in high-speed flight.

Towards real-time pilot-in-the-loop CFD simulations of helicopter/ship dynamic interface

This study presents the development of computationally efficient coupling of Navier–Stokes Computational Fluid Dynamics (CFD) with a helicopter flight dynamics model with the ultimate goal of real-time simulation of airwake effects in the helicopter/ship Dynamic Interface (DI). The flight dynamics model is free to move within a computational domain, where the main rotor forces are converted to source terms in the momentum equations of the CFD solution using an actuator disk model. Simultaneously, the CFD solver calculates induced velocities that are fed back to the simulation and affect the aerodynamic loads in the flight dynamics. The CFD solver models the inflow, ground effect and interactional aerodynamics in the flight dynamics simulation, and these calculations can be coupled with the solution of the external flow (e.g., ship airwake effects). The simulation framework for fully-coupled pilot-in-the-loop (PIL) flight dynamics/CFD is demonstrated for a simplified shedding wake. Initial tests were performed with 0.38 million structured grid cells running on 352 processors and showed near-real-time performance. Improvements to the coupling interface are described that allow the simulation run at near-real-time execution speeds on currently available computing platforms. Improvements in computing hardware are expected to allow real-time simulations.

Coupled Flight Dynamics and Computational Fluid Dynamics Simulations of Rotorcraft/Terrain Interactions

The objective of this study is the investigation of rotorcraft/terrain interactions using Navier–Stokes computational fluid dynamics coupled with a helicopter flight dynamics model. In the coupled simulations, the flight dynamics model is free to move within a computational domain, where the main rotor forces are translated into source terms in the momentum equations of the computational fluid dynamics solution. Simultaneously, the computational fluid dynamics calculates induced velocities that are fed back to the simulation and affect the aeroloads in the flight dynamics. The computational fluid dynamics solver models the inflow, ground effect, and interactional aerodynamics in the flight dynamics simulation. Free-flight simulations were performed with full rotorcraft flight dynamics regulated by a dynamic inversion controller. Simulation results are shown for a helicopter hovering in ground effect at different altitudes above the ground, over partial ground and sloped ground, and near a wall. A transition into forward-flight maneuver was performed, where a recirculation flow and ground vortex is shown. To verify the computational fluid dynamics predictions, predicted outwash flows were compared with recently published measurement data and showed reasonable correlation. Simulations of ground effect are shown to correlate well with recent experimental measurements of the power reduction of a rotor at constant thrust near a ground plane.

Identification method for helicopter flight dynamics modeling with rotor degrees of freedom

A comprehensive method based on system identification theory for helicopter flight dynamics modeling with rotor degrees of freedom is developed. A fully parameterized rotor flapping equation for identification purpose is derived without using any theoretical model, so the confidence of the identified model is increased, and then the 6 degrees of freedom rigid body model is extended to 9 degrees of freedom high-order model. Bode sensitivity function is derived to increase the accuracy of frequency spectra calculation which influences the accuracy of model parameter identification. Then a frequency domain identification algorithm is established. Acceleration technique is developed furthermore to increase calculation efficiency, and the total identification time is reduced by more than 50% using this technique. A comprehensive two-step method is established for helicopter high-order flight dynamics model identification which increases the numerical stability of model identification compared with single step algorithm. Application of the developed method to identify the flight dynamics model of BO 105 helicopter based on flight test data is implemented. A comparative study between the high-order model and rigid body model is performed at last. The results show that the developed method can be used for helicopter high-order flight dynamics model identification with high accuracy as well as efficiency, and the advantage of identified high-order model is very obvious compared with low-order model.

Set-Membership Identification Method for Helicopter Flight Dynamics Modeling

A new method based on the theory of set-membership estimation for time-domain identification of helicopter flight dynamics model has been developed. The parameters in most helicopter flight dynamics models are generally coupled, and it is difficult to obtain an explicit-function relationship between an identification model and the parameters to be identified. An indirect-identification algorithm should be established. The concept of generalized noise is introduced to solve the problems using the set-membership-identification method to construct a helicopter flight dynamics model. The identification of a six-degree-of-freedom linear flight dynamics model of the BO-105 helicopter in hover condition based on the new method is implemented. A comparative study of the new method with the maximum-likelihood method is also performed. The obtained results show that the new method increases the identification accuracy, efficiency, and robustness to noise by comparison with a conventional statistic-based identification method.

A coupled free-wake/panel method for rotor/fuselage/empennage aerodynamic interaction and helicopter trims

A coupled free-wake/panel method to predict the rotor downwash aerodynamic interaction and helicopter trims is presented. Free-wake method was developed to analyze aerodynamics interference of rotor wake, based on lifting-surface theory and vortex method, which relates the core radius, span station, and circulation of initial tip vortex with the blade-bound circulation distribution, and eliminates the empirical parameters during rotor free wake analysis. Helicopter fuselage with empennage was discretized into source panels. The vortex line mirror method was adopted to account for wake acceleration phenomenon that resulted from the close interaction between rotor wake and fuselage surface. The rotor wake geometry and downwash simulations were investigated including comparisons with the available measured data. Combined with the helicopter flight dynamics model and embedded in the trim procedure, the free-wake/panel coupled method was applied to calculate the rotor wake and its interference on other components of a full-scale UH-60A rotorcraft in level flight. Comparisons among predictions, referenced results, and experimental results are made for rotor wake geometries, blade-bound vortex, blade tip vortex, rotor downwash velocity, and control stick positions, and encouraging results were obtained. To validate the present method, this paper discusses the fundamental formulation, the numerical algorithms, and the simulation results.

A low cost flight simulator using virtual reality tools

A helicopter simulator is built using Head-Mount-Displays (HMD) and Data Gloves with trackers to test the viability of virtual reality tools in low-cost flight simulation. The simulator uses FlightGear as its simulation environment and an in-house developed UH-1H helicopter flight dynamics model. Running several clone simulations on different computers allowed stereo imaging on the HMD and instructor station applications. Data Gloves with trackers enabled interaction with the virtual cockpit.