Pilot modelling for airframe loads analysis

The development of large lightweight airframes has resulted in what used to be high frequency structural dynamics entering the low frequency range associated with an aircraft’s rigid body dynamics. This has led to the potential of adverse interactions between the aeroelastic effects and flight control, especially unwanted when incidents involving failures or extreme atmospheric disturbances occur. Moreover, the pilot’s response in such circumstances may not be reproducible in simulators and unique to the incident. The research described in this thesis describes the development of a pilot model suitable for the investigation of the effects of aeroelasticity on manual control and the study of the resulting airframe loads. After a review of the state-ofthe- art in pilot modelling an experimental approach involving desktop based pilot-in-the-loop simulation was adopted together with an optimal control based control-theoretic pilot model. The experiments allowed the investigation of manual control with a nonlinear flight control system and the derivation of parameter bounds for single-input-single-output pilot models. It was found that pilots could introduce variations of around 15 dB at the resonant frequency of the open loop pilot-vehicle-system. Sensory models suitable for the simulation of spatial disorientation effects were developed together with biomechanical models necessary to capture biodynamic feedthrough effects. A detailed derivation and method for the application of the modified optimal control pilot model, used to generate pilot control action, has also been shown in the contexts of pilot-model-in-the-loop simulations of scenarios involving an aileron failure and a gust encounter. It was found that manual control action particularly exacerbated horizontal tailplane internal loads relative to the limit loads envelope. Although comparisons with digital flight data recordings of an actual gust encounter showed a satisfactory reproduction and highlighted the adverse affects of fuselage flexibility on manual control, it also pointed towards the need for more incident data to validate such simulations

Evaluating the Rationale for Folding Wing Tips Comparing the Exergy and Breguet Approaches

The design and development processes for future aircraft aims to address the environmental and efficiency challenges needed to facilitate the engineering of concepts that are far more integrated and require a multidisciplinary approach. This study investigates the benefit of incorporating span extension wing tips onto future aircraft configurations as a method of providing improved aerodynamic efficiency, whilst allowing the extension to fold on the ground to meet airport gate size constraints. Although the actuated wing tips are not studied in detail, the focus of this study is to compare two different methods of analysis that can be used to identify the benefit and limitations of adding such devices. The two methods considered are a quasi-steady implicit energy analysis based on the Breguet Range Equation and an explicit energy analysis based on the first and second laws of thermodynamics known as Exergy Analysis. It has been found that both methods provide agreeable results and have individual merits. The Breguet Range Equation can provide quick results in early design, whilst the Exergy Analysis has been found to be far more extensive and allows the complete dynamic behaviour of the aircraft to be assessed through a single metric. Hence, allowing comparison of losses from multiple subsystems

Identification of in-flight wingtip folding effects on the roll characteristics of a flexible aircraft

Wingtip folding is a means by which an aircraft’s wingspan can be extended, allowing designers to take advantage of the associated reduction in induced drag. This type of device can provide other benefits if used in flight, such as flight control and load alleviation. In this paper, the authors present a method to develop reduced order flight dynamic models for in-flight wingtip folding, which are suitable for implementation in real-time pilot-in-the-loop simulations. Aspects such as the impact of wingtip size and folding angle on aircraft roll dynamics are investigated along with failure scenarios using a time domain aeroservoelastic framework and an established system identification method. The process discussed in this paper helps remove the need for direct connection of complex physics based models to engineering flight simulators and the need for tedious programming of large look-up-tables in simulators. Instead, it has been shown that a generic polynomial model for roll aeroderivatives can be used in small roll perturbation conditions to simulate the roll characteristics of an aerodynamic derivative based large transport aircraft equipped with varying fold hinge lines and tip deflections. Moreover, the effects of wing flexibility are also considered

Development of a multi-directional manoeuvre for unified handling qualities investigation

A slalom and alignment tracking manoeuvre was developed for multi-directional handling qualities analysis of large transport aircraft in simulation environments. The manoeuvre is defined and scaled as a function of aircraft characteristics, flight conditions using a simple set of mathematical models. Throughout the manoeuvre, the trajectory and overall performances are monitored at a set of gross position and alignment control checkpoints methodically distributed and sized to buoy the task and allow handling qualities analysis based on Cooper Harper Ratings and quantitative data analysis. Initial tests have shown that the manoeuvre sizing method led to feasible manoeuvres at multiple points of the flight envelope of a large civil transport aircraft. The manoeuvre capability to highlight desirable and undesirable handling qualities was also highlighted based on the initial findings for a couple of commercial large transport aircraft, a high aspect ratio wing and in-flight folding wingtip aircraft concepts. The relevance and applicability of the manoeuvre for multi-directional studies are discussed and compared against a more conventional offset landing manoeuvre. Finally, the potential use of the manoeuvre for different aircraft type and test flight is also suggested based on augmented reality technology

In-flight wingtip folding: inspiration from the XB-70 Valkyrie

Wingip folding can be used to extend aircraft wingspan, allowing designers to take advantage of reduced induced drag whilst respecting ground operational limitations. Such devices can also be used in-flight for a variety of other benefits including load alleviation and flight control. The majority of in-flight folding research takes inspiration in past developments made on the XB-70 Valkyrie, which used the folding devices for stability and lift performance benefits. In this paper, the authors investigate the capabilities of the folding wingtip system and potential scaling to large civil aircraft. Manufacturing details are used to size the actuators whilst the aerodynamic loading acting on the wingtip hinges is found from flight test results. Dimensions and aerodynamic loading at cruise of a set of conventional civil aircraft wing are used to evaluate the scaling potential of the system for controlled in-flight folding. An estimate of the weight penalty due to the folding device is also given and compared to structural weight savings on the XB-70. The results presented herein help in the evaluation of conventional actuator limits for in-flight folding using arguably the most inspiring military example of wingtip folding so far

Flight Dynamic Modelling and Simulation of Large Flexible Aircraft

The drive for aircraft efficiency and minimum environmental impact is requiring the aerospace industry to generate technologically innovative and highly integrated aircraft concepts. This has changed the approach towards conceptual design and highlighted the need for modular low fidelity aircraft simulation models that not only capture conventional flight dynamics but also provide insight into aeroservoelasticity and flight loads. The key aspects that drive the need for modularity are discussed alongside integration aspects related to coupling aerodynamic models, flight dynamic equations of motion and structural dynamic models. The details of developing such a simulation framework are presented and the utility of such a tool is illustrated through two test cases. The first case focuses on aircraft response to a gust that has a spanwise varying profile. The second investigates aircraft dynamics during control surface failure scenarios. The Cranfield Accelerated Aeroplane Loads Model (CA2LM) forms the basis of the presented discussion

Neural network based dynamic model and gust identification system for the Jetstream G-NFLA

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

Regressor time-shifting to identify longitudinal stability and control derivatives of the Jetstream 3102

The Jetstream 31 G-NFLA aircraft is used as a national flying laboratory test vehicle for flight dynamics research and teaching purposes. It has been the subject of much theoretical and experimental modelling and therefore, the need for generating validation data through flight testing is critical. In this paper, the aircraft's short period pitch oscillation mode characteristics are identified using data from sixteen flight tests. An identification procedure based on the least squares method and reduced order state-space model is used and the need for pre-processing regressors due to the effects of sensor location and instrumentation delays is highlighted. It has been shown that time-shifting the regressors based on relative locations of the angle of attack vanes and the inertial measurement unit results in significant reductions in uncertainty bounds of the estimated aeroderivatives and also a model that provides a closer match to flight test data. The estimated models are validated using separate flight test data and the variations in aeroderivatives over a range of airspeeds and centre of gravity positions are also presented

Aeroelastic scaling for flexible high aspect ratio wings

This paper provides an overview of the work conducted as part of the Cranfield BEAmReduction and Dynamic Scaling (BeaRDS ) programme, which aims to develop a methodologyfor designing, manufacturing and testing of a dynamically scaled High Aspect Ratio (HAR)Wing inside Cranfield 8’x6’ wind tunnel. The aim of this paper is to develop a methodologythat adopts scaling laws to allow experimental testing of a conceptual flexible-wing planformas part of the design process. Based on the Buckinghamπtheorem, a set of scaling lawsare determined that enable the relationship between a full-scale and sub-scale model. Thedynamically sub-scaled model is manufactured as a combination of spar, skin, and addedmass representing the stiffness, aerodynamic profile, and aeroelastic behaviour respectively.The spar was manufactured as a cross-sectional shape using Aluminium material, while theskin was manufactured using PolyJet technology. Compromises due to the manufacturingprocess are outlined and lessons learned during the development of the sub-scaled model arehighlighted

Multi-objective optimal longitudinal flight control system design for large flexible transport aircraft

This paper presents a multi-objective evolutionary algorithm design of a longitudinal optimal controller for a large flexible transport aircraft. The algorithm uses a mixed optimization approach based on a combination of Linear Quadratic Regulator (LQR) control and a Multi-Objective Genetic Algorithm (MOGA) to search over a set of possible weighting function structures and parameter values in order to satisfy a number of conflicting design criteria. The proposed approach offers a number of potential optimal solutions lying on or near the Pareto optimal front of competing objectives. The approach is explained in this paper and some results are presented