System software subsystems in an unmanned aircraft system share hardware resources due to space, weight, and power constraints. Such subsystems have different criticality, requirements, and failure rates, and can cause undesired interference when sharing the same hardware. A component with high failure rate can reduce the reliability of the system unless a fault containment mechanism is adopted.

This work proposes an asymmetric multiprocessor architecture to establish isolation at the hardware level for distributed implementation of safety-critical subsystems along with user defined payload subsystems on the same hardware with minimally reduced reliability of the system. To achieve that, subsystems are strategically segregated in separate processors, connected to an on-chip protective interconnect for inter-processor communications. A custom watchdog and reset mechanism are implemented to reset a specific processor without affecting the entire system if required. The architecture is demonstrated on a FPGA chip. In addition, an example of an optimised distribution is provided for a specific flight control system with five subsystems.

Predicting mental workload of pilots can provide cockpit designers with useful information to reduce the possibility of pilot error and cost of training, improve the safety and performance of systems, and increase operator satisfaction. We present a theoretical model of mental workload, using information theory, based on review investigations of how effectively task complexity, visual performance, and pilot experience predict mental workload. The validity of the model was confirmed based on data collected from pilot taxiing experiments. Experiments were performed on taxiing tasks in four different scenarios. Results showed that predicted values from the proposed mental workload model were highly correlated to actual mental workload ratings from the experiments. The findings indicate that the proposed mental workload model appears to be effective in the prediction of pilots’ mental workload over time.

Aeronautic Pitot probes (PPs) are extremely important for airspeed and altitude measurements in aviation. Failure of the instrument due to clogging caused by ice formation can lead to dangerous situations. In this work, a commercial aeronautic PP was characterised experimentally regarding its inner composition, material properties and its thermal performance in a climatic wind tunnel. Performance runs were taken out in order to analyse the thermal response of the PP under various operating conditions with a particular emphasis on the cooling process in the case of a heating element failure. Data for the thermal conductivity, diffusivity and specific heat for each material forming the PP were obtained. A numerical model to simulate the thermal behaviour of the PP was created using Comsol Multiphysics (CM). Experimental data were compared with their numerical counterparts for model validation purposes. After the model was validated, the operation of the PP in flight conditions was simulated. The failure of the conventional heating system was analysed to obtain the time until the PP reaches a tip temperature where ice formation can be expected. The tip temperature undercut the zero degrees Celsius mark 165 seconds after the heating element was switched off. The data collected in this work can be used to implement and validate mathematical models in order to predict the thermal performance of Pitot probes in flight conditions.

This paper deals with the actuation system design of a full-scale morphing aileron for regional aircraft. The aileron is allowed to smoothly change its geometrical configuration and perform the in-flight transition from a baseline shape to a set of optimal morphed ones pre-defined on the basis of aerodynamic requirements. The design of such innovative aileron is aimed not only at substituting the conventional aileron installed on a real aircraft but also to provide additional functionality. The aileron is free to rotate around its main hinge axis and it is also allowed to smoothly modify camber with two independent actuation systems. In such manner it can be used also during cruise with a symmetric deflection between the two half wings in order to reduce drag in off design condition. To accomplish variable aileron shape, a rigid-body mechanism was designed. The proposed aileron architecture is characterised by segmented adaptive ribs rigidly linked each other with spanwise reinforcements such as spars and stringers in a multi-box arrangement. Each rib is split into two movable plates connected by means of rotational hinges in a finger-like mechanism. The mechanism is driven by a load-bearing actuator by means of a kinematic chain opportunely tied based on the structural requirements in terms of shape to be matched and load to be withstood. The proposed device is an innovative arrangement of the quick-return mechanism composed of a beam leverage, commercial linear guides and a crank. The actuator shaft is directly inserted in the crank, which transmits the rotation to the linear guide that slide along a rail moving upward or downward the beam thus resulting in a camber variation. The entire aileron is moved by three leverages internally contained and distributed along the first two bays while the most external ribs are considered passive and their movement slaved. Two actuation layouts are analytically and numerically studied, the analytical theory is presented and validated by means of a multi-body simulation. Moreover, a linear static analysis was carried out under the hypothesis of glued contact between linear guides components simulating a jamming condition. This assumption has been formulated because it represents the most severe condition that envelop all the operative loads to which the actuation system is subjected. The analyses conducted are preliminarily aimed to verify that no failure occur under the imposed loads. In this first design loop, the vertical static force acting on the linear carriage exceeded allowable value and then a new configuration with double-sided linear guides was then investigated.

In this paper, we examine some of the physics behind Vertical Take-Off and Landing (VTOL) flying machines, and some of the emerging technologies that are driving the recent upsurge of new VTOL projects. The paper attempts to put these into context by examining some of the projects that have been publicised over the past couple of years, particularly those that transition from hovering into wing-borne flight. Although much progress has been made, there still needs to be significant breakthroughs in technologies, particularly battery technology, before the dream of fast, quiet and environmentally friendly inter-city VTOL aircraft can be realised.

This study focuses on the co-operative salvo attack problem of multiple missiles against a stationary target under jointly connected switching topologies subject to time-varying communication delays. By carefully exploring certain features of the typical pure proportional navigation guidance law, a two-stage distributed guidance scheme is proposed without any information on time-to-go in this study to realise the simultaneous attack of multiple missiles. In the first guidance stage, a co-operative guidance law is proposed using local neighbouring communications only to achieve consensus on range-to-go and heading error to provide favourable initial conditions for the latter phase, in which switching topologies and time-varying communication delays are taken into account when obtaining sufficient conditions of consensus in terms of linear matrix inequalities. Then, missiles disconnect from each other and are guided individually by the typical pure proportional navigation guidance law with the same navigation gain to realise salvo attack in the second guidance phase. Finally, numerical simulations are carried out to clearly validate the theoretical results.

The persistent coverage control problem is formulated based on cell discretisation of two-dimensional mission space and time-increasing cell ages. A new performance function is defined to represent the coverage level of the mission space, and time behaviour is evaluated by the probabilistic method based on the detection model of agents. For comparison, persistent coverage controllers are designed by a target-based approach and a reactive approach. Both controllers are designed in a distributed manner using Voronoi tessellation and Delaunay graph-based local information sharing. Numerical simulation is performed to analyse the evaluated mean age of cells and evaluated coverage level over time for the designed persistent coverage controllers. The differences between the evaluation model and simulation situation are discussed.

The combustion instability characteristics in a model dump combustor with an exhaust nozzle were experimentally investigated. The first objective was to understand the effects of operating conditions and geometric conditions on combustion instability. The second objective was to examine more generalised parameters that affect the onset of combustion instability. Three different premixed gases consisting of air and hydrocarbon fuels (C2H4, C2H6, C3H8) were burnt in the dump combustor at various inlet velocity, equivalence ratio and combustion chamber length. Dynamic pressure transducer and photomultiplier tube with a bandpass filter were used to measure pressure fluctuation and CH* chemiluminescence data. Peak frequencies and their maximum power spectral densities of pressure fluctuations at same equivalence ratios showed different trends for each fuel. However, the dynamic combustion characteristics of pressure fluctuations displayed consistent results under similar characteristics chemistry times regardless of the used hydrocarbon fuels. The results showed that characteristic chemistry time and characteristic convection time influenced combustion instabilities. It was found that the convective-acoustic combustion instability could be prevented by increasing the characteristic chemistry time and characteristic convection time.

To accurately predict the probabilities of impact damage to aircraft from runway debris, it is important to understand and quantify the aerodynamic forces that contribute to runway debris lofting. These lift and drag forces were therefore measured in experiments with various bodies spun over a range of angular velocities and Reynolds numbers. For a smooth sphere, the Magnus effect was observed for ratios of spin speed to flow speed between 0.3 and 0.4, but a negative Magnus force was observed at high Reynolds numbers as a transitional boundary layer region was approached. Similar relationships between lift and spin rate were found for both cube- and cylinder-shaped test objects, particularly with a ratio of spin speed to flow speed above 0.3, which suggested comparable separation patterns between rapidly spinning cubes and cylinders. A tumbling smooth ellipsoid had aerodynamic characteristics similar to that of a smooth sphere at a high spin rate. Surface roughness in the form of attached sandpaper increased the average lift on the cylinder by 24%, and approximately doubled the lift acting on the ellipsoid in both rolling and tumbling configurations.

One of the main challenges of future aircraft engines is to achieve low pollutant emissions while maintaining high combustion efficiencies and operability. The Flameless Combustion (FC) regime is pointed as one of the promising solutions due to its well-distributed reaction zones that yield low NOx emissions and oscillations. A dual-combustor configuration potentially facilitates the attainment of FC in the Inter-Turbine Burner (ITB). The development of such burner is dependent on knowledge regarding NOx formation and the parameters affecting it. It is known from the literature that the NOx formation mechanisms are different in FC. Therefore, in an attempt to clarify some of the mechanisms involved in NOx formation at relevant conditions, a chemical reactor network model developed to represent the ITB is explored. The role of prompt NOx was previously shown to be dominant at relatively low inlet temperatures and atmospheric pressure. In order to check these findings, five chemical reaction mechanisms were employed. All of them overpredicted NOx emissions and the overprediction is likely to be caused by the prompt NOx subset implemented in these mechanisms. Higher reactants temperatures and operational pressures were also investigated. Overall NOx emissions increased with temperature and the NOx peak moved to lower equivalence ratios. Operational pressure changed the emissions trend with global equivalence ratio. Leaner conditions had behaviour similar to that of conventional combustors (increase in NOx), while NOx dropped with further increase in equivalence ratio due to suppression of the prompt NOx production, as well as an increase in NO reburning. These trends highlight the differences between the emission behaviour of the ITB with those of a conventional combustion system.

An improved variational optimization approach is established to optimize and analyse the propulsion efficiency of the high-altitude contra-rotating propellers for high-altitude airships based on the Vortex Lattice Lifting Line Method. The optimum radial circulation distribution, chord and pitch distribution are optimized under the maximum lift-to-drag ratio of aerofoils. To consider the effects of the actual Reynolds number and the Mach number of each aerofoil section, aerodynamics such as lift coefficient, drag coefficient and lift-to-ratio are obtained by interpolating a CFD database, which is established by numerical simulations under different Reynolds number, Mach number and angles-of-attack. The improved method is verified by validation cases on a high-altitude CRP using the three-dimensional steady Reynolds-averaged Navier-Stokes solver and moving reference frames technique. The optimization results of thrust, torque and efficiency for both the individual front/rear propeller and CRP are shown to agree reasonably well with the CFD results. Using the improved approach, the influence of blade numbers, diameter, rotation speeds, axial distance and torque ratio on the optimum efficiency of CRPs is illustrated in detail by conducting parametric studies.

There is a growing interest in the use of alternative fuels in gas turbine engines to reduce emissions. Testing of alternative fuels is expensive when done on a large-scale gas turbine engine. In this study, a re-commissioned small gas turbine auxiliary power unit (APU) has been used to test various blends of Jet A-1, synthetic paraffinic kerosene (SPK) and diesel with as well as eight other novel fuels. A detailed analysis of performance, gaseous emissions and particulate emissions has been presented in this study. It is observed that aromatic content in general as well as the particular chemical composition of the aromatic compound plays a vital role in particulate emissions generation. SPK fuel shows substantially lower particulate emissions with respect to Jet A. However, not all the species of aromatics negatively impact particulate emissions. Gaseous emissions measured are comparable for all the fuels tested in this study.

A new aerofoil parameterisation method is put forward to represent an aerofoil by combining the leading edge modification class/shape function transformation (LEM CST) method and improved Hicks–Henne bump function’s method. The new class/shape function transformation (NEW CST) method has two additional basis functions comparing the original CST method. In order to confirm these two basis functions, the radial basis functions neural network (RBF) model is trained by some samples which are generated by the Latin hypercube design (LHD) method and Genetic Algorithm (GA) is proposed to achieve the basis functions of the NEW CST method. The NEW CST method has been evaluated in fitting precision of 1,545 aerofoils by comparison with the LEM CST method and the original CST method. And the improved ability of the NEW CST at the leading edge and trailing edge is verified by a series of complex aerofoil case studies within 1,545 aerofoils. The results indicate that the NEW CST method can represent the whole aerofoils and possesses the intuitive property as well as the original CST. Moreover, the number of control parameters (NCP) to parameterise aerofoils is the fewest among these three methods. Furthermore, when the NCP of the NEW CST and LEM CST is the same, the NEW CST method has the higher accuracy and smaller root mean square errors (RMSE) especially at the leading edge and trailing edge.

Generally, earth rotating and non-spherical perturbation of the earth in re-entry motion model are simplified using the standard trajectory guidance method. The re-entry motion is also simplified to horizontal motion and vertical motion and controlled, respectively. The simplification of re-entry motion model will lead to loss of motion accuracy and location accuracy. The direct decomposition will lead to the reduction of control accuracy because the horizontal motion and the vertical motion are coupled in re-entry. To improve the standard trajectory guidance method, the standard trajectory guidance method based on decoupling control variables and waypoint is proposed in this paper. The proposed guidance method will not simplify earth rotating and non-spherical perturbation of the earth in motion equation or decompose the re-entry motion to horizontal motion and vertical motion. Trajectory waypoint is adopted to reduce the change frequency of tracking states, because tracking states change frequently if the entire standard trajectory is tracked in real time.