The general theory of the stability of equilibrium of discrete conservative systems is reviewed with an eye to implementation in finite element structural analysis. The approach features a natural parameter, such as the applied loading of a system, as the independent variable; all results are thus conveniently established without recourse to any of the artificial parameters advocated by some earlier authors. The criteria for identifying singular (critical) points, which include bifurcation points and limit points, and determining their stability are obtained in simple forms suitable for computation. Numerical results are given for an example problem characteristic of a loaded plate with multiple, stable and unstable, bifurcation points to demonstrate an application of the theory.

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.

In the context of future human spaceflight exploration missions, Rendezvous and Docking (RVD) activities are critical for the assembly and maintenance of cislunar structures. The scope of this research is to investigate the specifics of orbits of interest for RVD in the cislunar realm and to propose novel strategies to safely perform these kinds of operations. This paper focuses on far rendezvous approaches and passively safe drift trajectories in the Ephemeris model. The goal is to exhibit phasing orbit requirements to ensure a safe far approach. Ephemeris representations of Near Rectilinear Halo Orbits (NRHOs) were derived using multiple-shooting and adaptive receding-horizon targeting algorithms. Simulations showed significant drift and overlapping properties for phasing and target orbits of interest, motivating the search for safe natural drift trajectories and using impact prediction strategies.

Numerical investigation of the effect of pylon geometry within a pylon-cavity aided Supersonic Combustion Ramjet (SCRAMJET) combustor on mixing enhancement, flame-holding capability, fuel jet penetration and total pressure loss are conducted in the current study. RANS equations for compressed real gas are solved by coupled, implicit, second-order upwind solver. A two-equation SST model is used for turbulence modelling. Validation of the computational model is performed with the help of experimental data collected using surface pressure taps, Schlieren flow visualisation and particle image velocimetry (PIV). The study uses four distinct pylon geometry cases, which include the baseline geometry. Sonic injection of hydrogen fuel through a 1mm diameter hole at 2mm downstream of the pylon rear face along the axis of the test section floor is performed for every case. A crossflow of Mach number 2.2 at four bar absolute pressure and standard atmospheric temperature is maintained. A comparative study of mixing efficiency, total pressure loss, fuel jet penetration and fuel plume area fraction for the different cases evaluate the mixing performance. The simulations show that the Pylon 2 case gives a significant improvement in the performance parameters compared to the other geometries. It is observed that mixing efficiency and fuel jet penetration capability of the system are highly dependent on the streamwise vortex within the flameholder.

How much is known about high altitude clear air turbulence? Sufficient to show that aircraft may, with little or no warning, experience bumpiness which the pilot would describe as “ moderate ” or, on occasions, “ severe,” at altitudes up to at least 40,000 feet, thus including altitude bands where commercial jet aircraft will be flying during the next few years. The phenomenon, therefore, is of significance to airline operators and the requirement is for the aircraft commander to be supplied with sufficient information to enable him to avoid such turbulence, or to provide him with adequate warning so that crew and passengers can be properly prepared for it. This does not imply that there is evidence to suppose that clear air turbulence may be of such severity as to affect the safety of a flight. It is important, however, to take good care of the passengers and their comfort is an essential consideration.

The aim of this paper is to show how design improvements may lead to a reduction in direct operating cost, pence per passenger mile. In all the comparisons made it is assumed that equal standards of equipment, accommodation, powerplant efficiency, and so forth, apply and that equal skill and standards apply in manufacturing; differences therefore are due to design features. The paper is in two main sections:

(1) A Satellite's eye-view of the whole design problem of the cheap short-range transport aeroplane.

(2) A more detailed description of two specific examples which illustrate the conclusions drawn from the general survey.

The first part is historically fiction but technically fact; the second part (despite the temptation to interchange the above two nouns and adjectives) is, I claim, fact both historically and technically.

I have departed from the historical sequence of events for the first part because we have now realised that it is possible to present in a comprehensive general argument the rather confused mass of data, ideas, techniques, inspirations and false trails that, in the course of time, led us to an enthusiasm for the all-wing Aerobus.

The possibility of control of circulation around aircraft wings and gas turbine blades by ejection of air from the aerofoil into the main stream has drawn attention to the manifold problem. Discharge velocity distributions along the length of the wing or blade must be uniform, and it is important that the detailed nature of the flow in the supply manifolds should be understood. The distributions of velocity in manifolds supplying multicylinder internal combustion engines, in gas burners and in manifolds supplying canal locks are other allied problems.

Transverse sonic injection, usually in a staged manner, in a confined environment is a necessity in the design of an efficient combustion chamber. The design requires an analysis of the mixing of the injectant with incoming stream as efficient combustion depends upon good mixing. This kind of analysis needs numerical model/simulation to assess the mixing of the two streams. To determine the suitability of an existing software package for such a study, staged transverse sonic injection into a Mach 2 stream in a confined environment is taken as a test case. The experimental conditions of McDaniel et al are reproduced for this simulation. In this experiment, staged transverse injection of sonic jet behind the backward facing step in Mach 2 stream was carried out and profiles of various flow parameters were measured. The numerical simulation solves the 3D Navier-Stokes equations with a k – ε turbulence model using the PARallel Aerodynamic Simulator PARAS3D. Computed results show a good match for injectant penetration profile although the computations predict slightly higher penetration near the orifice location. Detailed comparison of flow parameter profiles between computed and experimental data reveal that in the zone away from the injection orifice, computations predict the flow field reasonable well. However, in the vicinity of the orifice, there are some differences between experimental data and computed results. These differences could be due to non-uniform inlet profile in the experiment and/or inadequacy of the turbulence model considered in the study.

This paper gives two improved tapered elements for vibration analysis derived using quintic polynomial displacement functions. The elements employ different nodal continuity conditions. Results are compared with those given by the basic cubic approximations and analytical solutions for various end conditions. The advantages of the new elements over the basic element are discussed.

For aircraft that employ distributed propeller propulsion systems, the distributed propeller slipstream increases the analysis complexity. The objective of this paper is to rapidly analyse the influence of propeller slipstream on a wing using a fast prediction approach to perform conceptual design studies. This fast approach is implemented through a panel/viscous vortex particle hybrid method taking into account the air viscosity effect. The parametric studies of propeller streamwise, spanwise, vertical installed position, propeller number and rotational direction are conducted for a rectangular wing platform in two different propeller-wing configurations. The results indicate that the propeller slipstream causes both the augmentations of the wing lift and drag in a traditional tractor propeller layout. For an over-the-wing propeller configuration, however, the obvious lift increase and drag decrease can be obtained. A rear propeller position relative to the wing chord leads to a beneficial increase in lift while a fore propeller location is able to decrease the wing drag. The maximum increment of the lift-to-drag ratio can be achieved by 17.6% when the propeller is located at 30% of the wing chord, which shows a considerable advantage in improving the wing aerodynamic efficiency.

The prime focus of this work is to estimate stability and control derivatives of an airship in a completely nonlinear environment. A complete six degrees of freedom airship model has its aerodynamic model as nonlinear functions of angle of attack. Estimating the parameters of aerodynamic model in a nonlinear environment is challenging as it demands an exhaustive dataset that could cover the entire regime of operation of airship. In this work, data generation is achieved by simulating the mathematical model of airship for different trim conditions obtained from continuation analysis. The mathematical model is simulated using predicted parameter values obtained using DATCOM methodology. A modular neural network is then trained using back-propagation and Adam optimisation algorithm for each of the aerodynamic coefficients separately. The estimated nonlinear airship parameters are found to be consistent with the DATCOM parameter values which were used for open-loop simulation. This validates the proposed methodology and could be extended to estimate airship parameters from real flight data.

Customer requirements and vision in aerospace dictate that the next generation of civil transport aircraft should have a strong emphasis on increased safety, reduced environmental impact and reduced cost without sacrificing performance. In this context, the School of Mechanical and Aerospace Engineering at the Queen’s University of Belfast and Bombardier have, in recent years, been conducting research into some of the key aerodynamic technologies for the next generation of aircraft engine nacelles. Investigations have been performed into anti-icing technology, efficient thrust reversal, engine fire zone safety, life cycle cost and integration of the foregoing with other considerations in engine and aircraft design. A unique correlation for heat transfer in an anti-icing system has been developed. The effect of normal vibration on heat transfer in such systems has been found to be negligible. It has been shown that carefully designed natural blockage thrust reversers without a cascade can reduce aircraft weight with only a small sacrifice in the reversed thrust. A good understanding of the pressure relief doors and techniques to improve the performance of such doors have been developed. Trade off studies between aerodynamics, manufacturing and assembly of engine nacelles have shown the potential for a significant reduction in life cycle cost.

Every structural member deforms under the forces acting upon it. In this paper the Maximum Principle, recently developed by Pontryagin is applied to the problem of determining that profile of a beam that deforms least under its own weight. The beam considered is a solid horizontal cantilever having constant density, modulus of elasticity and width. The height is taken as an independent variable subject to the restrictions that it lies between an upper and lower bound and is symmetrically distributed about the centre-line. The method is attractive in that it can readily be extended to take account of variable density, width and/or hollow members by extending the control vector u defined in the analysis.

Weight estimation methods are categorised in different classes based on their level of fidelity. The lower class methods are based on statistical data, while higher class methods use physics based calculations. Statistical weight estimation methods are usually utilised in early design stages when the knowledge of designers about the new aircraft is limited. Higher class methods are applied in later design steps when the design is mature enough. Lower class methods are sometimes preferred in later design stages, even though the designers have enough knowledge about the design to use higher class methods. In high level multidisciplinary design optimisation (MDO) fidelity is often sacrificed to obtain models with shorter computation times. There is always a compromise required to select the proper weight estimation method for an MDO project.

An investigation has been performed to study the effect of using different weight estimation methods, with low and medium levels of fidelity, on the results of a wing design using multidisciplinary design optimisation techniques. An MDO problem was formulated to design the wing planform of a typical turboprop and a turbofan passenger aircraft. The aircraft maximum take-off weight was selected as the objective function. A quasi-three-dimensional aerodynamic solver was developed to calculate the wing aerodynamic characteristics. Five various statistical methods and a quasi-analytical method are used to estimate the wing structural weight. These methods are compared to each other by analysing their accuracy and sensitivity to different design variables. The results of the optimisations showed that the optimum wing shape is affected by the method used to estimate the wing weight. Using different weight estimation methods also strongly affects the optimisation convergence history and computational time.

A composite guidance law is proposed for intercepting moving target while strictly satisfying the constraints on multiple No-Fly Zones (NFZs) distributed arbitrarily. The research has two major steps. In the first step, by considering only one NFZ, a guidance law is developed with three parts: Orientation Adjustment Scheme (OAS), Boundary-Constraint Handling Scheme (BCHS), and Proportional Navigation (PN). OAS determines the major flight direction by predicting the collision point of the missile and target. BCHS controls the missile to approach and then fly along the boundary of the NFZ smoothly so as to bypass the NFZ through a short path. PN is used to intercept the target in the endgame phase. In the second step, we use the multi-step decision process to set up a series of appropriate waypoints in order to avoid multiple NFZs. The superior performance of the proposed guidance law has been demonstrated by trajectory simulations.

The coaxial compound helicopter with lift-offset rotors has been proposed as a concept for future high-performance rotorcraft. This helicopter usually utilizes a variable-speed rotor system to improve the high-speed performance and the cruise efficiency. A flight dynamics model of this helicopter associated with rotor speed governor/engine model is used in this article to investigate the effect of the rotor speed change and to study the variable rotor speed strategy. Firstly, the power-required results at various rotor rotational speeds are calculated. This comparison indicates that choice of rotor speed can reduce the power consumption, and the rotor speed has to be reduced in high-speed flight due to the compressibility effects at the blade tip region. Furthermore, the rotor speed strategy in trim is obtained by optimizing the power required. It is demonstrated that the variable rotor speed successfully improves the performance across the flight range, but especially in the mid-speed range, where the rotor speed strategy can reduce the overall power consumption by around 15%. To investigate the impact of the rotor speed strategy on the flight dynamics properties, the trim characteristics, the bandwidth and phase delay, and eigenvalues are investigated. It is shown that the reduction of the rotor speed alters the flight dynamics characteristics as it affects the stability, damping, and control power provided by the coaxial rotor. However, the handling qualities requirements are still satisfied with different rotor speed strategies. Finally, a rotor speed strategy associated with the collective pitch is designed for maneuvering flight considering the normal load factor. Inverse simulation is used to investigate this strategy on maneuverability in the Push-up & Pull-over Mission-Task-Element (MTE). It is shown that the helicopter can achieve Level 1 ratings with this rotor speed strategy. In addition, the rotor speed strategy could further reduce the power consumption and pilot workload during the maneuver.

Vascular structures are contemplated for cooling the skins and leading surfaces of future high speed aircraft. This paper evaluates the proposal to cool with a flow architecture shaped as trees (dendritic) a parallelepipedic body that is heated uniformly. The coolant enters the body through one face and exits through the opposite face. The vasculature connects the two faces, and consists of trees that alternate with upside down trees. The fields for fluid flow and heat transfer are determined numerically in three dimensions. The effect of local pressure losses at bends, junctions and entrances is documented. Designs with tree-shaped architectures having up to four levels of bifurcation are evaluated for fluid flow and heat transfer performance, and are compared with the performance of a design with a single sheet of fluid sweeping the upper surface of the body. The fluid flow conductance of the tree designs increases when the number of bifurcation levels increases. The thermal performance of tree designs can be improved by endowing the tree design with more freedom such that the bifurcations generate asymmetric daughter channels. The tree designs outperform the fluid sheet design dramatically: the global thermal resistance of the tree designs is roughly one tenth of the global thermal resistance of the fluid sheet design.

The Unmanned Aerial Vehicles (UAVs) become more and more popular due to various potential application fields. This paper studies the distributed leader-follower formation flight control problem of multiple UAVs with uncertain parameters for both the leader and followers. This problem has not been addressed in the literature. Most of the existing literature considers the leader-follower formation control strategy with parametric uncertainty for the followers. However, they do not take the leader parametric uncertainty into account. Meanwhile, the distributed control strategy depends on less information interactions and is more likely to avoid information conflict. The dynamic model of the UAVs is established based on the aerodynamic parameters. The establishment of the topology structure between a collection of UAVs is based on the algebraic graph theory. To handle the parametric uncertainty of the UAVs dynamics, a multivariable model reference adaptive control (MRAC) method is addressed to design the control law, which enables follower UAVs to track the leader UAV. The stability of the formation flight control system is proved by the Lyapunov theory. Simulation results show that the proposed distributed adaptive leader-following formation flight control system has stronger robustness and adaptivity than the fixed control system, as well as the existing adaptive control system.

Flight testing is both vital for collecting data for aeronautic research and at the same time fascinating for its contributors. Taking a glider as a versatile test bed example, this paper presents a transnational measurement campaign within the framework of a collaborative project funded by the European Commission. This project Advanced In-Flight Measurement Techniques 2 (AIM²) is a follow-up of Advanced In-Flight Measurement Techniques (AIM) and dedicated to developing and enhancing promising optical metrology for various flight test applications up to an industrial level.

The Image Pattern Correlation Technique (IPCT) and infrared thermography (IRT) are two of these modern non-intrusive measurement methods that were further developed and applied to the glider test bed within the scope of AIM². Focusing on optical deformation measurements with IPCT the experimental setup, the flight testing and results are summarily discussed. Gliders are not commonly used flight test platforms, which is why this contribution concludes with some lessons learned in general and especially related to the presented application. The experience to be shared with the flight testing community addresses equipment preparation, data collection and processing as well as how to meet official requirements and perform test flight operations in a dense controlled airspace.

The flatness of a six-degree-of-freedom (6DoF) aircraft model with conventional control surfaces – aileron, flap, rudder and elevator, along with thrust vectoring ability is established in this work. Trajectory optimisation of an aircraft can be cast as an inverse problem where the solution for control inputs that yield desired trajectories for certain states is sought. The solution to the inverse problems for certain systems is made tractable when they exhibit differential flatness. Flatness-based trajectory optimisation has a significant advantage over an equivalent collocation-based method in terms of computational efficiency and viability for real-time implementation. An application for the flatness of 6DoF aircraft is shown in the trajectory optimisation for dynamic soaring, and its connection with an equivalent 3DoF flatness-based implementation is also brought out. The results are compared with that from a collocation-based approach.