CERES :: Browsing by Author "Cooke, Alastair K."

Browsing by Author "Cooke, Alastair K."

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Open Access
Application of aerodynamic model structure determination to UAV data
(Royal Aeronautical Society, 2011-12-31T00:00:00Z) Carnduff, S. D.; Cooke, Alastair K.
This paper concerns aircraft system identification and, in particular, the process of aerodynamic model structure determination. Its application to experimental data from unmanned aerial vehicles (UAVs) is also described. The procedure can be particularly useful for determining an aerodynamic model for aircraft with unconventional airframe configurations, which some unmanned aircraft tend to have. Two model structure determination techniques are outlined. The first is the well-established stepwise regression method, while the second is an adaptation of an existing frequency response approach which instead utilises maximum likelihood estimation. Example applications of the methods are presented for two data sources. The first is a set of UAV flight test data and the second is data recorded from dynamic wind tunnel tests on a UAV configuration. For both examples, the model structures determined using stepwise regression and maximum likelihood analysis matched one another, suggesting that the maximum likelihood approach and the chosen thresholds for its statistical metrics were reliable for the data being analysed.
Open Access
CFD simulation of flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 - Part 1
(Elsevier, 2017-03-16) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, James E.; Cooke, Alastair K.
CFD modelling techniques are exploited to investigate the local velocity field around angle of attack and sideslip angle sensors fitted to the nose of a modified BAe Jetstream 3102 small airliner. Analysis of the flow angularity at the vane locations has allowed the vanes response to varying flight conditions to be predicted and errors in the readings to be quantified. Subsequently, a more accurate calibration of the system is applied to the current configuration on the Jetstream, and a better understanding of the position error with respect to the vane locations is obtained. The above aircraft was acquired by Cranfield University in 2003 with subsequent flow angle vane modifications taking place in 2005. The aircraft is currently in operation with the National Flying Laboratory Centre (NFLC) for research and demonstration purposes.
Open Access
CFD simulation of flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 - Part 2
(Elsevier, 2017-03-16) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, James E.; Cooke, Alastair K.
A previous study analysing the local flow around angle of attack and sideslip angle vanes on a BAe Jetstream 3102 turboprop is extended to study the additional effects of bank angle. A full matrix of CFD simulations is carried out to investigate how the introduction of a bank angle affects vane performance for a range of flight conditions. An updated calibration method to convert the raw vane readings into true values of angle of attack and sideslip, incorporating a correction factor as a function of the bank angle, is presented. The results are shown to be accurate for a wide range of flight configurations. Uncertainty analysis indicates that raw vanes reading errors should be below ±0.1°±0.1° to ensure that total calibration errors are restricted to less than 2%2% for angle of attack and 5%5% for sideslip angle.
Open Access
Control system development for autonomous soaring
(Cranfield University, 2010-01) Akhtar, Naseem; Cooke, Alastair K.; Whidborne, James F.
Thermal and dynamic soaring are two techniques commonly used by birds to extract energy from the atmosphere. This enables them to reduce, energy used during flight and increases their endurance. The thermal soaring technique involves extraction of energy from thermal updrafts and in dynamic soaring energy is extracted from wind shear. These techniques are investigated in this thesis using point mass and non-linear 6DoF models of an unmanned powered sailplane. The key challenges of autonomous thermal soaring are the ability to identify remote thermal activity using on-board sensors and to position correctly in a thermal. In dynamic soaring, a real-time fuel saving trajectory generation technique along with a trajectory following control system is needed. A hand held IR camera was used to assess the feasibility to observe hot spots associated with thermals. The thermal positioning capability was demonstrated in a 6DoF model using a positioning algorithm. The inverse Dynamics Virtual Domain (IDVD) technique was used to generate real-time trajectories for dynamic soaring applications using a point mass model of a powered unmanned sailplane and the fuel saving trajectories were validated using a high fidelity 6DoF model and a classical controller. An important outcome of the research is the fact that energy saved during dynamic soaring flight was also realized due to a sinusoidal manoeuvre using reduced thrust. In this manoeuvre the kinetic energy is converted into potential energy by gaining altitude and by reducing airspeed. Then initial values of altitude and speed are gained by loosing the altitude. In this process a horizontal distance is travelled by using reduced thrust.
Open Access
Detection of shaft-seal rubbing in large-scale power generation turbines with acoustic emissions. Case study.
(Professional Engineering Publishing, 2004-03-01T00:00:00Z) Mba, David; Cooke, Alastair K.; Roby, D; Hewitt, G
Rubbing between the central rotor and the surrounding stationary components of machinery such as large-scale turbine units can escalate into severe vibration, resulting in costly damage. Although conventional vibration analysis remains an important condition monitoring technique for diagnosing such rubbing phenomena, the non-destructive measurement of acoustic emission (AE) activity at the bearings on such plant is evolving into a viable complementary detection approach, especially adept at indicating the early stages of shaft-seal rubbing. This paper presents a case study on the application of high-frequency acoustic emissions as a means of detecting and verifying shaft-seal rubbing on a 217 MVA operational steam turbine unit. The generation of AE activity is attributed to the contact, deformation, adhesion and ploughing of surface asperities on the rubbing surfaces of the rotor and stator.
Open Access
Development of a pilot model suitable for the simulation of large aircraft
(Optimage Ltd. on behalf of the International Council of the Aeronautical Sciences, 2010-09) Lone, Mohammad M.; Cooke, Alastair K.
Effects of aeroservoelasticity on the manual control of large civil aircraft are investigated through a pilot modelling approach based on the modified optimal control model. A synopsis of modelling techniques is presented, followed by the description of the adopted technique. A simulation environment suitable for investigating pilot-vehicle dynamics in the longitudinal axis has been developed. The derivation of the pilot model was based on limiting the bandwidth. This approach showed that the pilot-vehicle system satisfied the crossover law between 3rad/s to 10rad/s for normal acceleration response. It was found that the pilot model and the low frequency tailplane bending mode introduced a resonant peak in the pilotvehicle frequency response that may be a cause for concern in high gain scenarios. Gust response simulations highlighted the contribution of fuselage bending mode on pilot perceived normal acceleration.
Open Access
Effect of wing flexibility on aircraft flight dynamics
(Cranfield University, 2012-02) Qiao, Yuqing; Cooke, Alastair K.
The purpose of this thesis is to give a preliminary investigation into the effect of wing deformation on flight dynamics. The candidate vehicle is FW-11 which is a flying wing configuration aircraft with high altitude and long endurance characteristics. The aeroelastic effect may be significant for this type of configuration. Two cases, the effect of flexible wing on lift distribution and on roll effectiveness during the cruise condition with different inertial parameters are investigated. For the first case, as the wing bending and twisting depend on the interaction between the wing structural deflections and the aerodynamic loads, the equilibrium condition should be calculated. In order to get that condition, mass, structure characteristics and aerodynamic characteristics are estimated first. Then load model and aerodynamic model are built. Next the interaction calculation program is applied and the equilibrium condition of the aircraft is calculated. After that, effect of wing flexibility on lift parameters is investigated. The influence of CG, location of lift and location of flexural axis are investigated. The other case is to calculate the transient roll rate response and estimate the rolling effectiveness of flexible aircraft, and compared with the rigid aircraft’s. A pure roll model is built and derivatives both for the rigid wing and the flexible wing are estimated. It has been found that flexible wing leads to the loss of control effectiveness, even cause reversal when reduces the structure natural frequency. The influence of inertia data for flexible roll is also investigated.
Open Access
Effects of nonlinear flight control system elements on aircraft
(Cranfield University, 2011-09) Lone, Mudassir M.; Cooke, Alastair K.
This report presents the experimental method and results from a series of desktop simulation tests designed to investigate manual control characteristics of young and relatively inexperienced civil pilots (24 years average age and 66 hours flight experience). Subjects were asked to perform tasks during which they had to establish longitudinal control through pitch attitude shown on a primary flight display. A linear aircraft model coupled with nonlinear flight control system was used to produce realistic vehicle dynamics. Increased encroachment into nonlinear command gearing was found to make aggressive subjects resort to high levels of crossover regression. The combined effects of rate-limiting and nonlinear command gearing was observed only for demanding tasks during which over-control was a typical feature. The classical precision and bimodal models were used for an in-depth study of pilot dynamics observed during compensatory tasks. Model parameters were found through the definition of a constrained nonlinear optimisation problem. A single feedforward equalisation element was used for tracking tasks. It was found that subjects developed similar low frequency feedforward equalisations, whilst large inter-subject variations exist for high frequency equalisations. The resulting models also provided some insight into the Neal-Smith and Bandwidth handling qualities criteria. Actuator rate-limiting could not be directly correlated to any of the pilot model parameters.
Open Access
Fault tolerant control of a quadrotor using L-1 adaptive control
(Emerald, 2016-01-01) Xu, Dan; Whidborne, James F.; Cooke, Alastair K.
Purpose – The growing use of small unmanned rotorcraft in civilian applications means that safe operation is increasingly important. The purpose of this paper is to investigate the fault tolerant properties to faults in the actuators of an L1 adaptive controller for a quadrotor vehicle. Design/methodology/approach – L1 adaptive control provides fast adaptation along with decoupling between adaptation and robustness. This makes the approach a suitable candidate for fault tolerant control of quadrotor and other multirotor vehicles. In the paper, the design of an L1 adaptive controller is presented. The controller is compared to a fixed-gain LQR controller. Findings – The L1 adaptive controller is shown to have improved performance when subject to actuator faults, and a higher range of actuator fault tolerance. Research limitations/implications – The control scheme is tested in simulation of a simple model that ignores aerodynamic and gyroscopic effects. Hence for further work, testing with a more complete model is recommended followed by implementation on an actual platform and flight test. The effect of sensor noise should also be considered along with investigation into the influence of wind disturbances and tolerance to sensor failures. Furthermore, quadrotors cannot tolerate total failure of a rotor without loss of control of one of the degrees of freedom, this aspect requires further investigation. Practical implications – Applying the L1 adaptive controller to a hexrotor or octorotor would increase the reliability of such vehicles without recourse to methods that require fault detection schemes and control reallocation as well as providing tolerance to a total loss of a rotor. Social implications – In order for quadrotors and other similar unmanned air vehicles to undertake many proposed roles, a high level of safety is required. Hence the controllers should be fault tolerant. Originality/value – Fault tolerance to partial actuator/effector faults is demonstrated using an L1 adaptive controller.
Open Access
Fibre optic sensing for measuring rotor blade structural dynamics.
(Cranfield University, 2019-04) Weber, Simone; Lone, Mudassir M.; Cooke, Alastair K.
Researchers and practitioners spend much e ort in developing theoretical methods to design and predict the performance of helicopter rotor blades. These blades have evolved to become complex structures designed to operate in extreme conditions and over the exceptionally broad flight envelopes of helicopters. As a result, these vehicles are subject to strict maintenance regimes that increase the overall operational costs. The need to reduce such costs and improve aircraft performance together with the emergence of novel fibre optic-based sensor technologies form the context of the research presented in this thesis. Opportunities for blade health and usage monitoring created by sensor technologies such as fibre Bragg gratings (FBG) for measuring strain and direct fibre optic shape sensing (DFOSS) present today's industry with a critical question: Does the designer follow contemporary technological trends and adopt a preventative approach where he/she invests in such instrumentation systems or is a reactive approach more appropriate where he/she awaits to have sufficient evidence of operational need? A survey was carried out as part of this research to understand this dichotomy faced by rotorcraft engineers and systems architects. Adhering to the safety orientated culture within the aerospace community, the aim of this research work is the numerical and experimental exploration of challenges associated with the deployment of fibre optic instrumentation systems for future health and usage monitoring. This was achieved through three objectives: (1) development of a computational framework allowing the simulation of rotor blade dynamics at an appropriate fidelity, (2) exploration of blade health monitoring capabilities using fibre optic instrumentation systems and, (3) laboratory-based structural testing. Health and usage monitoring capabilities were explored theoretically through a parametric damage study using the computational framework. The experimental testing highlighted the need for a sensor placement methodology for distributing FBG-based strain sensors over the blade (both in terms of spanwise and chordwise locations) for accurately recovering mode shapes. This was followed by investigating the accuracy of the novel DFOSS system by deploying it on a bearingless main rotor blade along with other commercially available instrumentation systems. Test results were used to (1) perform multi-step indirect finite element modelling to increase the accuracy of the developed structural model and, (2) to explore the suitability of FBG and DFOSS measurements for damage detection. The main finding of this work is that future rotor health and usage monitoring systems based on fibre optic sensing technologies require the development of a hybrid FBG and DFOSS instrumentation system. Although numerous areas of further work have been identified, it is hoped that the adoption of such an instrumentation system will not only help reduce operational costs but also provide much needed operational data on helicopter blade dynamics to validate methods and improve designs.
Open Access
Gust rejection properties of VTOL multirotor aircraft
(Elsevier, 2018-01-11) Whidborne, James F.; Cooke, Alastair K.
The effect of rotor aerodynamics on the stability and control of multi-rotor aircraft is explored by analysis of a conceptual planar birotor aircraft. In particular, the effect of rotor tilt on the stability and zero-location is investigated. Furthermore, it is shown that designing the vehicle with outwards rotor tilt potentially results in dramatic improvement in the gust rejection properties of the vehicle.
Open Access
Handling qualities of high aspect ratio wing aircraft.
(2018-07) Portapas, Vilius; Lone, Mudassir M.; Cooke, Alastair K.
To reduce the environmental impact of the aviation industry aircraft designers invest much effort to develop new and improve existing technologies to create new aircraft configurations. New high aspect ratio wings allow to improve aerodynamic efficiency while reducing aircraft weight through the use of new lightweight materials. However, their slenderness tends to introduce significant interaction between flight dynamics and aeroelastics. These interactions need to be identified in order to allow future pilots to anticipate behaviour of those aircraft. The literature review revealed a gap in the knowledge of flying and handling qualities (HQs) of large transport highly flexible wing aircraft. Hence, this thesis presents a comparison between rigid and flexible aircraft configurations carried out by the means of the pilot-in-the-loop simulations of flight test manoeuvres. Firstly, the analysis of the extended equations of motion, which consider the structural flexibility, revealed significant flexibility impact on the lateral/directional dynamics of the aircraft. Then, the equations were integrated into the Simulation Framework for Flexible Aircraft (SFFA) that was developed by integrating the aeroservoelastic model CA² LM with the engineering flight simulator EFS500. The simulation campaign was performed using the SFFA for the HARTEN aircraft model, which exhibited an unusually aft neutra point position. The results of the simulation campaign revealed minor differences in the longitudinal dynamics between the rigid and flexible aircraft. However, the lateral/directional dynamics showed significant differences, especially in the change of the Dutch roll shape from horizontal to vertical and the spiral mode from unstable to neutrally stable. It also highlighted the ‘wing rocking’ phenomenon and the ‘wing ratcheting’ significantly decreased roll performance. Finally, a new slalom task proved its applicability to efficiently assess HQs and revealed a degradation of HQs for the flexible aircraft configuration. The SFFA was also assessed and limiting hardware issues were indicated to support the comparison of aircraft HQs. For the future it is recommended to identify a set of dynamic parameters that would allow to highlight deficiencies of flexible aircraft and to improve the SFFA allowing pilots to fully concentrate on the task.
Open Access
Jetstream 31 national flying laboratory: Lift and drag measurement and modelling
(Elsevier, 2016-11-09) Lawson, Nicholas J.; Jacques, H.; Gautrey, James E.; Cooke, Alastair K.; Holt, Jennifer C.; Garry, Kevin P.
Lift and drag flight test data is presented from the National Flying Laboratory Centre, Jetstream 31 aircraft. The aircraft has been modified as a flying classroom for completing flight test training courses, for engineering degree accreditation. The straight and level flight test data is compared to data from 10% and 17% scale wind tunnel models, a Reynolds Averaged Navier Stokes steady-state computational fluid dynamics model and an empirical model. Estimated standard errors in the flight test data are ±2.4%±2.4% in lift coefficient, ±2.7%±2.7% in drag coefficient. The flight test data also shows the aircraft to have a maximum lift to drag ratio of 10.5 at Mach 0.32, a zero lift drag coefficient of 0.0376 and an induced drag correction factor of 0.0607. When comparing the characteristics from the other models, the best overall comparison with the flight test data, in terms of lift coefficient, was with the empirical model. For the drag comparisons, all the models under predicted levels of drag by up to 43% when compared to the flight test data, with the best overall match between the flight test data and the 10% scale wind tunnel model. These discrepancies were attributed to various factors including zero lift drag Reynolds number effects, omission of a propeller system and surface excrescences on the models, as well as surface finish differences.
Open Access
Machine vision and scientific imaging for autonomous air vehicles (UAV).
(Cranfield University, 2008-08) Jameson, Pierre-Daniel; Cooke, Alastair K.; Hobbs, Stephen E.
This thesis outlines the necessary requirements to determine an Unmanned Aerial Vehicles (UAV’s) pose relative to a lead aircraft or target, thus enabling a UAV to successfully follow a lead aircraft or target. The use of Machine Vision for Autonomous navigation has been investigated and two flight scenarios were chosen for analysis. Firstly, following a manoeuvring lead aircraft, and secondly, maintaining a steady heading behind a target/lead aircraft (as would be required for in-flight refuelling). In addition, the author has performed a literature review of current research in this field which is significantly dominated by eventual military requirements in order to improve UAV endurance. In addition, experimental work towards developing a passive vision based navigation system has been undertaken. It is hoped that after further research and development this will lead to an eventual flight trial using the flight dynamics department’s UAV’s. The experimental work has been performed using both equipment and software already available within the department and furthermore, it has enabled an analysis of the department’s currently available capabilities for passive visual navigation to be undertaken. Key points for further work have been outlined for the future advancement of the visual navigation project.
Open Access
Machine vison and scientific imaging for autonomous air vehicles (UAV)
(Cranfield University, 2008-09) Jameson, Pierre-Daniel; Cooke, Alastair K.; Hobbs, S. E.
This thesis outlines the necessary requirements to determine an Unmanned Aerial Vehicles (UAV’s) pose relative to a lead aircraft or target, thus enabling a UAV to successfully follow a lead aircraft or target. The use of Machine Vision for Autonomous navigation has been investigated and two flight scenarios were chosen for analysis. Firstly, following a manoeuvring lead aircraft, and secondly, maintaining a steady heading behind a target/lead aircraft (as would be required for in-flight refuelling). In addition, the author has performed a literature review of current research in this field which is significantly dominated by eventual military requirements in order to improve UAV endurance. In addition, experimental work towards developing a passive vision based navigation system has been undertaken. It is hoped that after further research and development this will lead to an eventual flight trial using the flight dynamics department’s UAV’s. The experimental work has been performed using both equipment and software already available within the department and furthermore, it has enabled an analysis of the department’s currently available capabilities for passive visual navigation to be undertaken. Key points for further work have been outlined for the future advancement of the visual navigation project.
Open Access
Model simulation suitable for an aircraft at high angle of attack
(Cranfield University, 2016-01) Mohmad Rouyan, Nurhana; Cooke, Alastair K.; Whidborne, James F.
Simulation of a dynamic system is known to be sensitive to various factors and one of them could be the precision of model parameters. While the sensitivity of flight dynamic simulation to small changes in aerodynamic coefficients is typically not studied, the simulation of aircraft required to operate in nonlinear flight regimes usually at high angles of attack can be very sensitive to such small differences. Determining the significance and impact of the differences in aerodynamic characteristics is critical for understanding the flight dynamics and designing suitable flight control laws. This thesis uses this concept to study the effect of the differences in aerodynamic data for different aerodynamic models provided for a same aircraft which is F-18 HARV combat aircraft. The aircraft was used as a prototype for the high angles of attack technology program. However modeling an aircraft at high angles of attack requires an extensive aerodynamic data which are usually di cult to access. All aerodynamic models were collected from open literature and implemented within a nonlinear six degree of freedom aircraft model. Inspection of aerodynamic data set for these models has shown mismatches for certain aerodynamic derivatives, especially at higher angles of attack where nonlinear dynamics are known to exist. Nonlinear simulations are used to analyse three different types of flight dynamic models that use look-up-tables, arc-tangent formulation and polynomial functions to represent aerodynamic data that are suitable for high angles of attack application. To achieve this, a nonlinear six degree of freedom Simulink model was developed to accommodate these aerodynamic models separately. The trim conditions were obtained for different combinations of angles of attack and airspeed and the models were linearized in each case. Properties of the resulting state matrices such as eigenvalues and eigenvectors were studied to determine the dynamic behaviour of the aircraft at various flight conditions.
Open Access
Modelling and simulation of flexible aircraft : handling qualities with active load control
(Cranfield University, 2011-03) Andrews, Stuart P.; Cooke, Alastair K.
The study of the motion of manoeuvring aircraft has traditionally considered the aircraft to be rigid. This simplifying assumption has been shown to give quite accurate results for the flight dynamics of many aircraft types. As modern transport aircraft have developed however, there has been a marked increase in the size and weight of these aircraft. This trend is likely to continue with the development of future blended-wing-body and supersonic transport aircraft. This increase in size and weight has brought about a unique set of aeroelastic and handling quality issues. The aerodynamic forces and moments acting on an aeroplane have traditionally been represented using the aerodynamic derivative approach. It has been shown that this quasisteady aerodynamic model inadequately predicts the aircraft’s stability characteristics, and that the inclusion of unsteady aerodynamics “greatly improves the fidelity” of aircraft models. This thesis thus presents a novel numerical simulation of an aeroelastic aeroplane for real-time analysis. The model is built around the standard six degree-of-freedom equations of motion for a rigid aeroplane using the mean-axes system, and includes unsteady aerodynamics and structural dynamics. This is suitable for pilot-in-the-loop simulation, handling qualities and flight loads analysis, and control law development. The dynamics of the structure are modelled as a set of normal modes, and the equations of motion are realised in state-space form. The unsteady aerodynamic forces acting on the aeroplane are described by an indicial state-space model, including unsteady tailplane downwash and compressibility effects. An implementation of the model is presented in the MATLAB/ Simulink environment. The interaction between the flight control system, the aeroelastic system and the rigidbody motion of the aeroplane can result in degraded handling qualities, excessive actuator control, and fatigue problems. The introduction of load alleviation systems for the management of loads due to manoeuvres and gusts is also likely to result in the handling qualities of the aeroplane being degraded. This thesis presents a number of studies into the impact of structural dynamics, unsteady aerodynamics, and load alleviation on the handling qualities of a flexible civil transport aeroplane. The handling qualities of the aeroplane are assessed against a number of different handling qualities criteria and flying specifications, including the Neal-Smith, Bandwidth, and CAP criterion. It is shown that aeroelastic effects alter the longitudinal and lateral-directional characteristics of the aeroplane, resulting in degraded handling qualities. Manoeuvre and gust load alleviation are similarly found to degrade handling qualities, while active mode control is shown to offer the possibility of improved handling qualities.
Open Access
Modelling framework for flight dynamics of flexible aircraft
(Vilnius Gediminas Technical University Press, 2016-12-20) Portapas, Vilius; Cooke, Alastair K.; Lone, Mudassir M.
The flight dynamics and handling qualities of any flexible aircraft can be analysed within the Cranfield Aircraft Accelerated Loads Model (CA2LM) framework. The modelling techniques and methods used to develop the framework are presented. The aerodynamic surfaces were modelled using the Modified Strip Theory (MST) and a state-space representation to model unsteady aerodynamics. With a modal approach, the structural flexibility and each mode’s influence on the structure deflections are analysed. To supplement the general overview of the framework equations of motion, models of atmosphere, gravity, fuselage and engines are introduced. The AX-1 general transport aircraft model is analysed as an example of the CA2LM framework capabilities. The results showed that, according to the Gibson Dropback criterion, the aircraft with no control system lacks the stability and its longitudinal handling qualities are unsatisfactory. Finally, the steps for future developments of the CA2LM framework are listed within conclusions.
Open Access
Neural network based dynamic model and gust identification system for the Jetstream G-NFLA
(Sage, 2016-05-18) Antonakis, Aristeidis; Lone, Mudassir M.; Cooke, Alastair K.
Artificial neural networks are an established technique for constructing non-linear models of multi-input-multi-output systems based on sets of observations. In terms of aerospace vehicle modelling, however, these are currently restricted to either unmanned applications or simulations, despite the fact that large amounts of flight data are typically recorded and kept for reasons of safety and maintenance. In this paper, a methodology for constructing practical models of aerospace vehicles based on available flight data recordings from the vehicles’ operational use is proposed and applied on the Jetstream G-NFLA aircraft. This includes a data analysis procedure to assess the suitability of the available flight databases and a neural network based approach for modelling. In this context, a database of recorded landings of the Jetstream G-NFLA, normally kept as part of a routine maintenance procedure, is used to form training datasets for two separate applications. A neural network based longitudinal dynamic model and gust identification system are constructed and tested against real flight data. Results indicate that in both cases, the resulting models’ predictions achieve a level of accuracy that allows them to be used as a basis for practical real-world applications.
Open Access
On scaling and system identification of flexible aircraft dynamics.
(Cranfield University, 2019-10) Yusuf, Sezsy Yuniorrita; Lone, Mudassir M.; Cooke, Alastair K.
The use of subscale models has been common practice in the industry and has helped engineers gain more confidence in their design processes. However, each subscale model is developed for a specifc test, and consequently, different types of models are needed for observing aerodynamic, structural and aeroelastic characteristics of a full-scale aircraft. Yet, traditional aircraft design methods face serious challenges when a novel aircraft de- sign emerges and a proof-of-concept is needed for investigating this multi-disciplinary problem. An example of such a problem is the development of aircraft configurations with high aspect ratio wings for which the disciplines of aeroelastic and flight mechanics are strongly interconnected. Moreover, if the prediction of dynamic behaviour is of interest, a method that utilises system identification for analysing experimental data is of importance. Therefore, this thesis aims to develop a methodology to investigate the complex flight dynamic behaviour of flexible aircraft by combining techniques for developing subscale models and methods with the field of system identification. This aim is achieved through three objectives: 1) assessment of system identification methods for subscale flexible aircraft, 2) theoretical development of subscale modelling in terms of scaling laws and aeroelastic simulation framework and, 3) wind tunnel testing of the subscale model. Aspects of System Identification have been explored through use-cases where experimental data for a rigid aircraft both in full-scale and subscale configuration is used. The results highlight the fact that in testing a subscale model, dynamics are more prone to exhibit non-linear behaviour when compared to the full-scale model. It followed by the application of system identification for a flexible aircraft based on a simulation framework. This study emphasised the need for non-linear identification methods, such as an output error method, to characterise a flexible aircraft system. The work continues with the exploration of scaling laws applied to a simple aerofoil that is free to pitch and plunge. These results build the foundation for the development of a subscale high aspect ratio wing for wind tunnel experiments. The work highlights the trade-o s and compromises faced during the development of a dynamically subscaled model and the practice of system identification. The main contribution lies in the development of a low-cost methodology in building a subscale model that allows the use of dynamically scaled models at the early design stages. This practice provides the designer with a means to de-risk novel aircraft concepts as early as possible and in doing so, reduce overall development costs.