A numerical study was conducted to analyse the performance of different turbulence models and different turbulence intensities and turbulence length scales specified for the boundary condition of the inflow to the internal compression flow field of a typical supersonic inlet. The effect of the back-pressure ratio on the properties of the flow field was also investigated. Computational results obtained by the commercial software FLUENT, which is used to solve the full two-dimensional Reynolds-averaged Navier-Stokes equations, were validated through both graphical and quantitative comparisons with previously published experimental data. The two-equation models that were considered in this study are the RNG k-ε, realisable k-ε, standard k-ε, and SST k-ω turbulence models. The RNG k-ε model had the best performance among the four models and predicted good wall pressure distributions. The best agreement between the predicted results and experimental data was obtained when either the default values of the freestream turbulence intensity and length scale in the FLUENT solver were used, or the empirical formula was used to calculate the two parameters of the freestream turbulence properties. The shock wave pattern varied between the oblique mode and the fully developed normal mode with increasing back-pressure ratio, and the unstart phenomenon occurred when the back-pressure ratio was sufficiently high.

The numerical simulations for cycloidal propellers based on five aerofoils with different thickness are presented in this paper. The CFD simulation is based on sliding mesh and URANS. The results of CFD simulation indicates that all test cases share similar flow pattern. There are leading edge vortex and trailing-edge vortex due to blade dynamic stall. Interaction between the vortices shed from upstream blade and the downstream blade can be observed. There is variation of blade relative inflow velocity due to downwash in the cycloidal rotor cage. These factors result in large fluctuations of the aerodynamics forces on the blade. The comparison of the forces and flow pattern indicates that the thickness and leading edge radius of the aerofoil can significantly influent the flow pattern and hence the performance of the cycloidal propeller.

This paper provides an overview of techniques developed for the application of support vector regression in the domain of simulation and system identification of helicopter dynamics. A generic high fidelity FLIGHTLAB helicopter model is used to train and validate a number of pitch response SVR models. These models are then trained using flight data from a Sikorsky Seahawk helicopter. The SVR simulation results show significant promise in the ability to represent aspects of a helicopter’s dynamics at a high fidelity. To achieve this, it is important to provide the SVR kernel with knowledge of past inputs that encompass the delay characteristics of the helicopter dynamic system. In this case, the use of nonlinear auto regressive eXogenous input network architecture achieves this goal. Good performance was achieved using input data that encompassed between 300 to 500ms worth of historic response.

This paper describes a possibility-based multidisciplinary optimisation for electric-powered unmanned aerial vehicles (UAVs) design. An in-house integrated UAV (iUAV) analysis program that uses an electric-powered motor was developed and validated by a Predator A configuration for aerodynamics, weight, and performance parameters. An electric-powered propulsion system was proposed to replace a piston engine and fuel with an electric motor, power controllers, and battery from an eco-system point of view. Moreover, an in-house Possibility-Based Design Optimisation (iPBDO) solver was researched and developed to effectively handle uncertainty variables and parameters and to further shift constraints into a feasible design space. A sensitivity analysis was performed to reduce the dimensions of design variables and the computational load during the iPBDO process. Maximising the electric-powered UAV endurance while solving the iPBDO yields more conservative, but more reliable, optimal UAV configuration results than the traditional deterministic optimisation approach. A high fidelity analysis was used to demonstrate the effectiveness of the process by verifying the accuracy of the optimal electric-powered UAV configuration at two possibility index values and a baseline.

The landing approach for fixed-wing small unmanned air vehicles (SUAVs) in complex environments such as urban canyons, wooded areas, or any other obscured terrain is challenging due to the limited distance available for conventional glide slope descents. Alternative approach methods, such as deep stall and spin techniques, are beneficial for such environments but are less conventional and would benefit from further qualitative and quantitative understanding to improve their implementation. Flight tests of such techniques, with a representative remotely piloted vehicle, have been carried out for this purpose and the results are presented in this paper. Trajectories and flight data for a range of approach techniques are presented and conclusions are drawn as to the potential benefits and issues of using such techniques for SUAV landings. In particular, the stability of the vehicle on entry to a deep stall was noticeably improved through the use of symmetric inboard flaps (crow brakes). Spiral descent profiles investigated, including spin descents, produced faster descent rates and further reduced landing space requirements. However, sufficient control authority was maintainable in a spiral stall descent, whereas it was compromised in a full spin.

This paper presents the design, development and construction of a flight test stand for a quadrotor UAV. As opposed to alternate forms of UAV, the power plant in the case of the quadrotor serves a dual purpose of control and propulsion. Since control and propulsion are coupled, the power plant (BLDC motor coupled with propeller) was studied in detail using a black box structure. Extractions of motor parameters in previous studies used traditional BLDC motor equations and propeller theory however the accuracy achievable and confidence in the extracted parameters remained questionable. The developed data acquisition process served to satisfy this need by the construction of a test bench that allows for the extraction of the unknown parameters instilling confidence in the modelling process. The established relationships are then used as inputs into a developed six degree of freedom Euler based mathematical model. A mission profile was constructed with distinct phases of which the mathematical model was used to simulate. Each phase in the mission profile excited different modes of the quadrotor dynamics creating an ideal simulation environment in which changes can be implemented and studied.

An experimental, remotely-piloted aircraft has been designed and fabricated at University of Michigan that is aeroelastically representative of very flexible aircraft. Known as X-HALE, this Experimental High-Altitude Long-Endurance aircraft exhibits geometrically nonlinear behaviour and displays specific aeroelastic characteristics designed into the experiment. This paper presents the data from the initial flight tests of the lightly instrumented X-HALE Risk Reduction Vehicle that confirm the expected aeroelastic characteristics. This opens the way for future flight tests with a fully-instrumented platform which will provide data to support validation of coupled, nonlinear aeroelastic/flight dynamic codes.

Counter-rotating vortices form from the opposite edges of lifting surfaces, and gradually move laterally and dissipate as they travel downstream (as seen in a wing-fixed reference frame). Under ground effect conditions, the vortex from a lifting wing – such as that used in an aircraft application – moves laterally outboard from the wingtip as it progresses downstream; for a downforce wing in ground effect – such as that used in an automotive application – the vortex moves laterally inboard. An interesting case is the situation where the inboard moving vortices become in close proximity to each other. The objective of the present study was to investigate counter-rotating vortices produced from a low aspect ratio downforce wing operating in ground effect. The pair of vortices move towards each other and mutually induce an upwards directed motion which in turn reduces the inboard movement driven by the ground effect. Experimental data gained from three-dimensional Laser Doppler Anemometry in a moving ground wind-tunnel was used to validate a Large Eddy Simulation computational result.

This paper intends to develop a target trajectory estimation algorithm with application to the ballistic target estimation in the terminal phase. The proposed design is based on the application of a second-order extended state observer (ESO) technique using target information acquired from the seeker to estimate the trajectory of manoeuverable ballistic targets. Satisfactory results have been received while applying the design in estimation of either two-dimenional or three-dimentional target evasive acceleration via computer simulation.

The paper presents a new missile autopilot system design. The design is achieved through the pole-placement in quasi-continuous high-order sliding mode gains adjustment. Enhanced performance, strong robustness and smooth control are obtained through arbitrary increase of the number of non-oscillatory stable poles. The target application of this technique the two-channel pitch/yaw missile autopilot system is considered. Numerical simulations indicate that the arbitrary-order sliding modes based pole placement’s performance compares favourably against recently proposed high-order pole placement schemes.

The proposed arbitrary-order pole placement scheme presents a promising design tool for finite-time stabilisation and control of uncertain multivariable systems.

In an effort to increase the air-breathing endurance capability of current hypersonic research aircraft (i.e. X-43, 7 seconds; X-51, 5 minutes), the authors have explored the technical and operational solution space for a 30 minute cruise endurance demonstrator operating in the Mach 6 to Mach 8 speed regime. The focus of this activity has been on exploration of the available solution space through a unique screening process to assess the implication and interplay between the (a) mission, (b) baseline vehicle, and (c) operational scenarios. This study concludes that an air-launched, liquid hydrogen fuelled, 30 minute duration Mach 6 demonstrator (with 10 min Mach 8 capability) provides the largest feasible solution space of the trades examined (i.e. largest design margins, lowest technical risk) when compared to a kerosene-powered equivalent.

An investigation is presented to elucidate the performance of a staggered, spanwise cambered biplane. The spanwise camber yielded wings forming a ‘∧’ or ‘∨’ when viewed streamwise. The configuration is examined in terms of its aerodynamic and stability characteristics. The feasibility of negating the requirement for a conventional empennage is explored. Geometric variation encompassed front and back wing anhedral/dihedral angles yielding 49 combinations. Evaluation of the geometry was accomplished using both wind tunnel testing and numerical simulation. The results indicated that front wing dihedral in conjunction with aft wing anhedral was most beneficial, such that the benefit of wake spacing was maximised. Aerodynamic benefit was indicated compared to a conventional empennage geometry. The greatest disparity in behaviour of the fore and aft wing anhedral/dihedral distribution was in the high lift regime, where the nature of the stall varied. Simulations to establish the viability of the geometry in terms of controllability were also conducted and indicated that the configuration is viable.

This paper focuses on the three dimensional flight path planning for an unmanned aerial vehicle (UAV) on a low altitude terrain following\terrain avoidance mission. The UAV trajectory planning problem is to compute an optimal or near-optimal trajectory for a UAV to do its mission objectives in a surviving penetration through the hostile enemy environment, considering the shape of the earth and the kinematics constraints of the UAV. Using the three dimensional terrain information, three dimensional flight path from a starting point to an end point, minimising a cost function and regarding the kinematics constraints of the UAV is calculated. The geographic information of the earth shape and enemy locations is generated using digital terrain model (DTM) and geographic information system (GIS), and is displayed in a 3D environment. Using 3D-maps containing the geographic data accompanied by DTM, and GIS, the problem is modelled by deriving the motion equations of the UAV. Two heuristic algorithms are proposed for this problem: genetic and particle swarm algorithms. Genetic and particle swarm algorithms are general purposes algorithms, because they can solve a wide range of problems, so they have to be adjusted to solve the trajectory planning problem. To test and compare the paths obtained from these algorithms, a software program is built using GIS tools and the programming languages C# and MATLAB.

This paper presents the concept of custom-optimised departure profiles, as an advanced form of noise abatement departure procedures. This concept relies on fixed routes in combination with individually optimised vertical departure profiles. Although the use of fixed ground tracks results in some loss in environmental performance, the high degree of complexity associated with free routing is eliminated as well, leading to a concept that does not appear to be incompatible with today’s Air Traffic Control (ATC) principles. By using a primitive form of trajectory negotiation between airline and ATC, selected flights can be allowed to perform an optimised departure without interfering with non-participating traffic. Apart from the concept itself, this paper also describes the departure profile optimisation tool, which is based on a previously developed trajectory optimisation framework called NOISHHH. Finally, in a numerical example, a current standard ICAO-A procedure is compared with two optimised profiles for a Boeing 737 departure from Amsterdam Airport. Fuel burn, noise impact and the required flight time to a specified point are compared for the three departure profiles. It is shown that the custom-optimised departure profiles have the potential to both reduce fuel burn as well as noise exposure, relative to the ICAO-A procedure.

Military aircrafts are often subjected to severe flight maneuvers with high Angles-of -Attack (AOA) and Angles of Sideslip (AOSS). These flight attitudes induce non-uniform in flow conditions to their gas turbine engines which may include distortion of inlet total pressure and total temperature at the Aerodynamic Interface Plane (AIP). Operation of the downstream compression system with distorted inflow typically results in reduced aerodynamic performance, reduced stall margin, and increased blade stress levels. In the present study the steady state total pressure distortion induced to the Aerodynamic Interface Plane due to the aircraft’s flight attitude have been estimated in terms of distortion descriptors. The distorted conditions at the interface between the intake and the engine have been predicted by using Computational Fluid Dynamics (CFD), where 33 different aircraft flight attitudes have been tested. Based on the obtained results the effect of Angle-of-Attack (AOA) and Angle of Side Slip (AOSS) on the distortion descriptors have been studied. The results showed that the distortion effect becomes more pronounced whenever this specific airframe configuration is exposed to incoming flow with an AOSS. Among the tested cases, the greatest total pressure defect at the AIP in terms of difference from the average value and of circumferential extent was calculated for the flight attitudes of 0·35M flight with 0° AOA and 8° AOSS and 0·35M fight with 16° AOA and 16° AOSS.

This paper presents the optimum design of a PID controller for the Adaptive Torsion Wing (ATW) using the genetic algorithm (GA) optimiser. The ATW is a thin-wall, two-spar wingbox whose torsional stiffness can be adjusted by translating the spar webs in the chordwise direction inward and towards each. The reduction in torsional stiffness allows external aerodynamic loads to deform the wing and maintain its shape. The ATW is integrated within the wing of a representative UAV to replace conventional ailerons and provide roll control. The ATW is modelled as a two-dimensional equivalent aerofoil using bending and torsion shape functions to express the equations of motion in terms of the twist angle and plunge displacement at the wingtip. The full equations of motion for the ATW equivalent aerofoil were derived using Lagrangian mechanics. The aerodynamic lift and moment acting on the aerofoil were modelled using Theodorsen’s unsteady aerodynamic theory. The equations of motion are then linearised around an equilibrium position and the GA is employed to design a PID controller for the linearised system to minimise the actuation power require. Finally, the sizing and selection of a suitable actuator is performed.

A stratospheric airship flies at a working altitude of 20km when it takes off from the ground. During ascent and descent, the wind field and thermal environment are highly complex. The thermal environment affects altitude, whereas wind influences the horizontal position of the airship. At a low altitude, this horizontal position cannot be controlled by thrusts given the low thrust-to-weight ratio, especially under a large wind field. However, it may be controlled indirectly by the pitch angle during ascent and descent with a certain vertical velocity. This study therefore proposes ascending and descending schemes for a stratospheric airship based on the thermal model. In this model, altitude is determined by the net lift/weight, whereas the horizontal position is controlled by the thrust and pitch. The pitch angle is determined by ballonets and an elevator. To allocate pitch control between the ballonets and the elevator under different airspeeds, pseudo-inverse dynamics of varied weight are introduced. In horizontal position control, the method of chain allocation is then applied between a pitch angle and vectored thrust to control the position of a stratospheric airship during ascent/descent.

The design, construction, and validation of a new academic wind tunnel is described in detail. The wind tunnel is of a classical, blow-down type and generates a pressure-induced, turbulent separation bubble on a flat test surface by a combination of adverse and favorable pressure gradients. The Reynolds number, based on momentum thickness just upstream of separation, is Reθ ≃ 5,000 at a free-stream velocity of Uref = 25ms−1. The length of the separation bubble is estimated at 0°42 ± 0°02m by three different methods. Results of a numerical simulation demonstrate the absence of flow separation in the wind-tunnel contraction. This results in a turbulence level of about 0·05% in the test section. Oil-film visualisation experiments show that the flow near the wall is strongly three-dimensional in the recirculating region and that the topology of the limiting streamlines is consistent with experiments performed on configurations with fixed separation. Finally, spatial variations of the forward-flow fraction have been documented using a thermal-tuft probe and are shown to compare well with the results of the oil-film visualisation.

The use of active trailing edge flaps on rotors may lead to performance benefits as well as noise and vibration reduction. In this work, computational fluid dynamics, using the HMB2 solver, is used to assess the effect of the trailing edge flaps on the whole flight domain of a modern main rotor. Starting from a baseline blade design, multiple techniques are demonstrated. The flap is first assessed using 2D pitching aerofoil simulations, followed by dMdt simulations, that account for the simultaneous variations of pitch and Mach around the azimuth. It was shown that enhanced lift was obtained while inspection of the moment coefficient showed negative damping for the flap for a limited set of conditions. Due to the 2D formulation, dMdt computations are fast to perform and can be used to inform codes predicting the rotor performance. The flap was then assessed in hover, and only allowed for limited improvement in blade performance at high thrust. In forward flight, the flap was actuated at a frequency of 1 per revolution, and was found to have a strong effect on the loads on the retreating side. The effect on the moments was even stronger. The flight envelope of the blade was explored, and clean and flapped cases were compared. The most noticeable changes occur at high and medium thrust. The CFD method was found to be efficient and robust, without any substantial penalties in CPU time, due to the flap modelling, over the tested conditions.

This paper investigates a method for autonomous obstacle avoidance for fixed-wing unmanned aerial vehicles (UAVs), utilising potential fluid flow theory. The obstacle avoidance algorithm needs only compute the instantaneous local potential velocity vector, which is passed to the flight control laws as a direction command. The approach is reactive, and can readily accommodate real-time changes in obstacle information. UAV manoeuvring constraints on turning or pull-up radii, are accounted for by approximating obstacles by bounding rectangles, with wedges added to their front and back to shape the resulting fluid pathlines. It is shown that the resulting potential flow velocity field is completely determined by the obstacle field geometry, allowing one to determine a non-dimensional relationship between obstacle added wedge-length and the corresponding minimum pathline radius of curvature, which can then be readily scaled in on-board implementation. The efficacy of the proposed approach has been demonstrated numerically with an Aerosonde UAV model.