Advances in understanding autogyro flight dynamics

A comprehensive flight dynamics study of the autogyro is presented in this paper. A state of the art generic simulation of the vehicle type was developed and validated against flight data. This validation is presented in the paper and it is shown that the model can be applied to the autogyro with some confidence within well defined limitations bounds. It is also shown that the general stability characteristics of the autogyro can be considered as a mix of helicopter and fixed wing aircraft modes of flight. Most significantly the autogyro has a lightly damped, high frequency phugoid mode. Further, it is demonstrated that the only significant configurational effect is related to the relative vertical position of the centre of gravity with respect to the propeller thrustline, a centre of gravity which lies above the thrustline being more desirable. Results from preliminary handling qualities trials applying the techniques of ADS33 to an autogyro are also presented. Results from flight trials to investigate the teetering motion of the rotor are described, and the influence of the research on air accident investigation is also discussed

Improving rotorcraft survivability to RPG attack using inverse methods

This paper presents the results of a preliminary investigation of optimal threat evasion strategies for improving the survivability of rotorcraft under attack by rocket propelled grenades (RPGs). The basis of this approach is the application of inverse simulation techniques pioneered for simulation of aggressive helicopter manoeuvres to the RPG engagement problem. In this research, improvements in survivability are achieved by computing effective evasive manoeuvres. The first step in this process uses the missile approach warning system camera (MAWS) on the aircraft to provide angular information of the threat. Estimates of the RPG trajectory and impact point are then estimated. For the current flight state an appropriate evasion response is selected then realised via inverse simulation of the platform dynamics. Results are presented for several representative engagements showing the efficacy of the approach

Development of an Autogyro Rotor Model with Rotorcraft's ‘Multiblade’ Simulation Approach

The University of Glasgow has involved in the research study of autogyro’s flight mechanics for more than 15 years. This paper is giving an overview of the mathematical model development of a light autogyro, emphasising on the rotor model that employs one of the existing helicopter modelling approaches developed at Glasgow, the ‘multiblade’ or the ‘rotor-disc’ modelling approach. The method is based on the analytical calculation approach of the rotor loads, in which the elemental load of the blade is analytically integrated over the whole span of the blade and forms an approximation of the rotor ‘disc’ loads as a whole. In this approach, the blade is considered as a simplified aerofoil with an average lift and drag coefficients, without capturing the aerodynamic details of each geometrical point of the blade. Validation of this model is done by comparing the trim simulation results against the existing trim flight test data acquired from the previous research of the same autogyro. There are good agreements between the simulation results and the flight test data for most of the flight parameters, not as precise as the other previously used ‘individual-blade’ model approach, but are acceptable due to the advantage this multiblade approach has as a trade-off between the fast computer processing time and the accuracy of predictions. This autogyro’s multiblade modelling approach is expected to be used in more autogyro applications where the advantages of this approach are required the most

Scottish contributions to rotary wing flight

This paper charts the history of rotorcraft development in Scotland. Beginning with the early efforts of Mumford to achieve rotor-borne flight, through the major technology advances of G and J Weir in the 30s and 40s up to present day activities. The paper shows that despite being a relatively small country, Scotland’s traditional expertise in engineering when applied to the development of rotorcraft,generated significant technological advances

Development of an aeroelastic stability boundary for a rotor in autorotation

<p>For the present study, a mathematical model AMRA was created to simulate the aeroelastic behaviour of a rotor during autorotation. Our model: Aeroelastic Model of a Rotor in Autorotation (AMRA) captures transverse bending and teeter, torsional twist and lag-wise motion of the rotor blade and hence it is used to investigate couplings between blade flapping, torsion and rotor speed. Lagrange’s method was used for the modelling of blade flapping and chord-wise bending. Torsional twist of the rotor blade was modelled with the aid of finite element method (FEM), and blade transverse bending could also be modelled in FEM. The model can switch between using a full FEM model for bending and torsion, or a FEM model for torsion and simple blade teeter, depending on the complexity that the user requires.</p> <p>The AMRA model was verified against experimental data obtained during a CAA sponsored flight test programme of the G-UNIV autogyro. Published results of modal analysis of helicopter rotor blades and other data published in open literature were used to validate the FEM model of the rotor blade. The first torsional natural frequency of the ’McCutcheon’ rotor blades was measured with the aid of high-speed camera and used for validation of the FEM model of blade torsional twist. As a further verification of the modelling method, Aérospatiale Puma helicopter rotor blade data were compared on a Southwell plot showing comparison between experimental results and AMRA estimation.</p> <p>The aeromechanical behaviour of the rotor during both axial flight and forward flight in autorotation was investigated. A significant part of the research was focused on investigation of the effect of different values of torsional and flexural stiffness, and the relative positions of blade shear centre/elastic axis and centre of mass of the blade on stability during the autorotation.</p> <p>The results obtained with the aid of the model demonstrate the interesting, and unique, characteristics of the autorotative regime - with instabilities possible in bending and torsion, but also in rotorspeed. Coupled rotor speed/flap/twist oscillations (flutter and divergence) occur if the torsional stiffness of the blade is lower than a critical value, or if the blade centre of mass is significantly aft of the blade twisting axis, as is the case in helicopter pitch-flap flutter. The instability shown here, however, is specific to the autogyro, or autorotating rotor, as it is coupled with rotorspeed, and so differs from both helicopter rotor flutter and fixed-wing flutter. The coupling with rotorspeed allows a combined flutter and divergence instability, where the rotor begins to flutter in rotorspeed, teeter angle and torsional twist and, once the rotorspeed had dropped below a critical value, then moves into divergence in flap and rotorspeed. It was found that the aeroelastic behaviour of a rotor in autorotation is significantly affected by the strong coupling of blade bending stiffness and teeter angle with rotorspeed, and the strong coupling between blade aeroelastic twist and rotor torque.</p&gt

Simulation study of helicopter ship landing procedures incoporating measured flow data

The aim of this article is to investigate the use of inverse simulation to help identify those regions of a ship's flight deck which provide the safest locations for landing a rotorcraft in various atmospheric conditions. This requires appropriate information on the wind loading conditions around a ship deck and superstructure, and for the current work, these data were obtained from wind tunnel tests of a ship model representative of a typical helicopter carrier/assault ship. A series of wind tunnel tests were carried out on the model in the University of Glasgow's 2.65 × 2.04 m wind tunnel and three-axis measurements of wind speed were made at various locations on the ship deck. Measurements were made at four locations on the flight deck at three different heights. The choice of these locations was made on the basis of preliminary flow visualization tests which highlighted the areas where the most severe wind effects were most likely to occur. In addition, for the case where the wind was from 30 to starboard, measurements were made at three further locations to assess the extent of the wake of the superstructure. The generated wind profiles can then be imposed on the inverse simulation, allowing study of the vehicle and pilot response during a typical landing manoeuvre in these conditions. The power of the inverse simulation for this application is demonstrated by a series of simulations performed using configurational data representing two aircraft types, a Westland Lynx and a transport helicopter flying an approach and landing manoeuvre with the worst atmospheric conditions applied. It is shown from the results that attempting to land in the area aft of the superstructure in a 30° crosswind might lead to problems for the transport configuration due to upgusts in this area. Attempting to perform the landing manoeuvre in an aggressive manner is also shown to lead to diminished control margin in higher winds

The Helinv Numerical Algorithm. Internal report no. 9408

This report gives a comprehensive description of the helicopter inverse simulation algorithm used in the latest generation of the package Helinv. As well as the description of the algorithm some results are presented, and a verification and validation of the algorithm is presented. Features unique to the results of inverse algorithms are also discussed along with the problems associated with the use of numerical differentiation, and finally an alternative scheme is outlined

Feedback methods for inverse simulation of dynamic models for engineering systems applications

Inverse simulation is a form of inverse modelling in which computer simulation methods are used to find the time histories of input variables that, for a given model, match a set of required output responses. Conventional inverse simulation methods for dynamic models are computationally intensive and can present difficulties for high-speed applications. This paper includes a review of established methods of inverse simulation,giving some emphasis to iterative techniques that were first developed for aeronautical applications. It goes on to discuss the application of a different approach which is based on feedback principles. This feedback method is suitable for a wide range of linear and nonlinear dynamic models and involves two distinct stages. The first stage involves design of a feedback loop around the given simulation model and, in the second stage, that closed-loop system is used for inversion of the model. Issues of robustness within closed-loop systems used in inverse simulation are not significant as there are no plant uncertainties or external disturbances. Thus the process is simpler than that required for the development of a control system of equivalent complexity. Engineering applications of this feedback approach to inverse simulation are described through case studies that put particular emphasis on nonlinear and multi-input multi-output models

The Use of Inverse Simulation for Conceptual Design

No abstract available