Submission Summaries

AeSSA Annual Conference 2017

Summary of submissions


Dylan Williams

Structural design of a Filament Wound Oxidiser Tank for use on the Phoenix1B Mk II Hybrid Rocket

This presentation focuses on the design of a filament-wound composite pressure vessel to form the oxidiser tank on the Phoenix 1B Mk-II 35km hybrid rocket, which is to contain nitrous oxide at nominal pressure of 65 bar. The tank will replace the aluminium oxidiser tank currently used on Phoenix-series rockets. The composite tank must be lightweight in comparison to its aluminium predecessor and must integrate effectively with the rocket structure. The tank must meet specific design criteria, including weight, volume and pressure targets. Furthermore, it must be cost-effective and manufacturable in South Africa.


Livison Mashoko

A Review of the Aerospace Industry Support Initiative (AISI)

The Aerospace Industry Support Initiative (AISI) supports the local aerospace industry through focussed initiatives primarily for supplier development and technology advancement. A review of the AISI support over 10 years was carried out in order to understand the impact achieved over those years and help formulate future AISI programmes. Over R 100 million has been invested in the Aerospace industry through the initiative. The figure below shows the number of organisations supported under the initiative in the last five years. The decrease in number of organisations supported is a result of a drive to support bigger projects as opposed to many small projects in order to improve the impact from the projects.

After the review, it was determined that AISI needs to concentrate on technology based supplier development. As a result 75% of the budget is now directed towards supplier development. In addition, Technology Roadmapping workshops were identified as a suitable tool to develop project scope for technology enhancement projects going forward. However, the strategic focus remains on SMMEs with the objective of ensuring industry transformation, and the broadening of the economic base participating in the industry.


Bennie Broughton

Semi-Realtime Assessment of Flight Dynamics Data Quality

Modern flight test instrumentation systems provide the ability for flight test personnel to monitor a large number of parameters in real-time on the ground during a flight test. The data may be sent to the ground station at sufficiently high frequencies to conduct relatively sophisticated analysis in real-time or, as discussed in this paper, in semi-realtime. The latter term in this paper refers to immediate analysis of a dataset upon completion of a given test manoeuvre. The type of analysis may range from a simple time domain qualitative review of a set of parameters, to a relatively detailed analysis of the spectral content of dynamic data, to a higher level system identification class of analysis or even real-time parallel simulation to compare simulation models with the response of the actual flight vehicle.

The utilisation of modern commercial telemetry software, such as VuSoft from JDA Systems, has significantly improved the ease with which flight test information can be monitored during flight. Besides providing multiple solutions for viewing real-time data, most modern software also provide additional capability such as running/real-time Fast Fourier Transforms (FFT) on selected parameters for the most recent time history of selectable length. However, occasionally it becomes necessary to perform a more sophisticated analysis to determine whether data collected from a given manoeuvre was satisfactory or not, and what needs to be changed to improve the result. For this purpose we have developed a process where we record the parameters for a given manoeuvre directly from the telemetry software, then transfer those parameters to Matlab, perform the analysis using in-house developed software, provide the necessary plots and information to the specialists in the test room who in turn provide feedback and an immediate decision on the outcome to the test conductor. This whole process is usually completed within seconds after completion of the manoeuvre. The approach has significantly improved the efficiency with which all tests related to flight dynamics and performance are conducted by IADS and virtually eliminated the need for repeat flights due to data of insufficient quality.


Duran Martin

Injector design for a LOX/RP-1 liquid propellant rocket engine

This project addresses the design of an injector for a liquid rocket engine. The engine is intended for use on a small satellite launch vehicle able to deliver a payload of 50 kg to a sun-synchronous orbit from a South African launch site. The research considers the question of the most efficient method of supplying liquid oxygen (LOX) and kerosene (RP-1) to the thrust chamber of the SAFFIRE engine in the requisite amounts and for the given chamber pressure.


Timothy Velthuysen

Closed Loop Throttle Control for a Nitrous Oxide/Paraffin Wax Hybrid Rocket Motor

The throttling of a hybrid rocket motor enables greater control over a flight vehicle’s trajectory and helps mitigate the decay in thrust that naturally occurs in pressure-fed systems. Thrust control can lead to better apogee performance and more tolerable loading on sensitive payloads, but the implementation of throttling is complex as it relies on the formulation of a control scheme whose inputs may include motor combustion parameters, propellant mass flow rates and vehicle flight dynamics. The work focuses on the development of a combustion model for a laboratory-scale motor, and design and implementation of a suitable control regime.


RA Maharaj

Additive Manufacturing to produce waveguides

This project is aimed at revolutionising the way high frequency bespoke waveguide systems are manufactured. It is an AISI and NewSpace Systems co-funded project aimed at establishing a feasible process to alternatively manufacture low-cost waveguide systems to be used in space applications. A waveguide is a structure employed to confine electromagnetic waves to propagate in one or two dimensions only, between its endpoints. They are usually used in satellites for such purposes as connecting microwave transmitters and receivers to their antennas to ensure minimal or no losses while propagating. Traditionally waveguide systems are manufactured in sections via CNC machining, which add to the overall mass of the systems, and are limited in the shapes that can be produced. With the increasing need in industry to go further into the millimetre microwave spectrum (which implies smaller and more bespoke designs), the current fabrication of complex waveguide systems presents a challenging problem. For this reason, it’s vital to develop alternative enabling manufacturing technologies to reduce the cost of production to make it accessible to developing nations.

This research explores the possibility of using Selective Laser Melting (SLM) metallic 3D printing to produce millimetre-wave waveguide prototypes. The SLM is used to melt the powder bed to build up the waveguide layer by layer. The waveguides will be monolithically printed but require post-processing to reduce the inherent surface roughness of the prints to make them functional (the wave propagates at the surface of the metal, and any roughness causes signal losses). The parts will be printed using the commercial SLM printer (EOS M280) at the Central University of Technology, and it will be printed in titanium metal alloy (Ti6Al4V). Titanium, with its light weight and high strength to mass ratio, has become a more commonly used material in aerospace applications. The focus is on producing a feasible process to print and post-process (via a combination of processes) light-weight and functional titanium waveguides. The project is split into two phases. The first phase is to print prototypes, across X-band and Ku-band and various structures, to test the various post-processing techniques and the ability of the 3D printer itself. Thereafter, the next phase will be focused on printing more complex waveguide structures to optimise the post-processing method.

The prototypes will undergo first round qualifications and will be compared against traditionally manufactured waveguides. The test techniques will use physical measurements to assess the quality and accuracy of the finished surfaces, but the ultimate test is that of the RF performance of the prototypes, through two-port S-parameter measurements using a vector network analyzer.


Nico Calitz

Development of a Stellar Gyroscope Solution for Accurate Attitude Propagation on Small Satellites

One of the biggest challenges in the field of satellite attitude determination and control is the problem of maintaining a high-quality attitude estimate throughout orbit, particularly during eclipse. Where sun and magnetic field vectors can be used to find attitude estimates during the sunlit part of orbit, attitude estimation in eclipse is more challenging. In the absence of a sun vector measurement, attitude estimates are often obtained by propagating rate information from the rate gyroscopes (typically MEMS – micro-electromechanical systems – based for small satellites). Because of the inherent bias (offset) of such solutions, estimates are inevitably impaired by angular drift. This drift is cumulative, resulting in a loss of attitude knowledge after a sufficient amount of time.

NewSpace Systems (co-funded by AISI) propose a promising, innovative solution to the problem of drift in traditional gyroscopes in form of a stellar gyroscope, a relative attitude sensor that can be used to reset angular drift during eclipse. More specifically, the proposed solution is an optical sensor subsystem that can be used to propagate a spacecraft’s attitude from a known initial condition based on the displacement of a series of stars between successive image frames. Attitude propagation via such methods is also without drift, assuming that sufficient stars are common across frames. As the camera pans the sky, after sufficient time all stars may leave the image frame, in which case some error would accumulate as rotation estimates are stacked. However, this happens over a significantly longer period of time compared to a traditional MEMS rate integrator. Image-based rotation estimates from a stellar gyro can complement a set of MEMS gyroscopes as a means of drift compensation. Such an integrated solution would be particularly beneficial when trying to maintain a high-accuracy estimate at low angular rates, where MEMS gyroscope drift is most severe.

Simulations show clear performance and reliability advantages of using the proposed stellar gyro solution in combination with traditional MEMS gyroscopes. NewSpace Systems has also been able to manufacture a prototype solution to demonstrate functionality using images of the night sky. Initial results have been promising, suggesting estimation accuracies comparable to existing optical subsystem solutions.


B.J.G. de la Bat

Theoretical simulation, manufacture and experimental evaluation of a free piston Stirling engine for deep space application

Free piston Stirling engine (FPSE) electric generators are a type of Stirling engine in which the displacer and piston are not linked via a kinematic mechanism, such as a crankshaft in conventional Stirling engines. The displacer and piston run mechanically free of one another in a shared natural frequency, driven only by an internal oscillatory pressure variation that results because of thermal expansion and compression of a helium working fluid. The removal of the crankshaft eliminates crank stresses and rotary wear, which greatly enhances the lifetime of the engine. The entire engine is hermetically sealed and requires no servicing during its lifetime, this being but some of the advantages of FPSEs over kinematic Stirling engines. When coupled with a radioisotope heat source, the FPSE becomes a suitable candidate for electricity generation in deep space application (Jakubowski, 1980).

This paper presents the theoretical simulation, manufacture and experimental evaluation of a 100 We FPSE prototype. The theoretical model was developed by discretising the working fluid into a network of one-dimensional control volumes. The principle conservation of mass, momentum and energy were applied to each control volume and in doing so a system of finite difference equations was generated. A FORTRAN computer program was developed to solve the governing equations over finite volume elements, by using a fully-explicit method to solve the temporal gradients. The geometrical layout of the prototype was based on the works done by Microgen Engine Corporation (Microgen, 2016), but with the addition of a linear motor that attaches to the displacer shaft. The linear electric generator was based on the 12.5 kWe Space Power Research Engine that was developed by Mechanical Technology Incorporated during the late 1980’s (Dhar, 1999). In-lab testing was performed under various heat inputs, charge pressures and electrical loading conditions, and served to validate the theoretical model. The paper concludes by discussing key design and manufacturing improvements that have been identified from the study.


Nino Wunderlin

Design of an Ablatively Cooled Combustion Chamber for the SAFFIRE Engine

The SAFFIRE engine is the first iteration of a low cost liquid propellant rocket engine capable of delivering a payload of 50 kg to a 500 km sun synchronous low earth orbit. This paper describes the design process for the ablatively cooled composite combustion chamber used in the SAFFIRE engine.


Coenraad Swanepoel

Experimental Validation of a Mixed-Flow Compressor and Cross-over Diffuser

This project sets out to experimentally validate the Mixed-Flow Compressor and Cross-Over Diffuser designed by (Diener, 2016) and (Kock, 2016) respectively. The results from the experiments will be used to compile a performance map of the compressor and cross-over diffuser. The compressor was designed with a tip clearance of 0.2 mm. This is not necessarily achievable and therefor the effect of tip clearance on the performance of the compressor is studied numerically and validated experimentally. Experiments are executed in the Gas Dynamics Laboratory of the University of Stellenbosch.

The numerical performance of the compressor as well as the effect of the tip clearance on the compressor and diffuser is validated. Preliminary numerical results indicate that an increase in tip clearance does indeed affect the performance of the compressor and diffuser negatively as displayed in Figure 1 below. By increasing the tip clearance from 0.2 mm to 0.4 mm the efficiency of the compressor decreases with a value of 4.75%. The efficiency decreases by a further 9.46% from the design efficiency when increasing the tip clearance to 0.6 mm. The increase in tip clearance also affects the operating margin of the compressor negatively. Numerical results obtained from (Diener, 2016) also indicate that rotational speeds from 70 000 – 90 000 rpm should be avoided to reduce the risk of the flapping mode occurring on the main blade of the compressor.


Kai Mitchell Broughton

PV-3 Firebolt: A New Hybrid Rocket Motor for UKZN’s 35 km Apogee Phoenix-1B Mk II Vehicle

The Phoenix-1B (P1B) Mk II is the third hybrid rocket demonstrator developed by the University of KwaZulu-Natal’s (UKZN) Aerospace Systems Research Group (ASReG). This paper describes the design of the vehicle’s hybrid rocket motor, designated the PV-3 ‘Firebolt’. The performance objective of the motor is to propel the rocket to an apogee of 35 km, so as to double the target apogee of the vehicle’s Mk I predecessor. Improvements on the previous motor include the use of energetic metal additives in the fuel grain and a reduced inert vehicle mass.


Chris Dreyer

Knowledge Mapping: increased mentorship efficiency with contextualized information

Knowledge transfer and mentorship are a core functions in a very technical environment. The South African Aerospace industry is no exception. The information age is marked by easy access to vast amounts of information through the internet and theoretically anyone, when given enough time and resources could download much of it. However, inexperienced engineers often have difficulty knowing where to start searching (i.e. which keywords to type into a search engine) and many experience difficulty to quickly filter large amounts of information or place it into proper context.

The knowledge map created at Denel Dynamics Mechanical Engineering aims to solve some of these challenges. In its simplest terms the Knowledge Map is a Mind Map which started as a tool to categorize information resources (material properties databases, technical manuals, standards, tutorials etc.) for daily use in design and development work, with specific focus on aircraft store vibration and fatigue. However, this Knowledge Map evolved as a mentorship tool to refer mentees to relevant (and reliable) information resources that can be referenced quickly. Subsequently the map became a tool to contextualize information and is also used as a starting point for further mentorship discussions, internet searches and mentee self-study.

A simple Mind Map was created in MS Visio using various connections of discipline specific topics. The MS Visio file was then exported as an .html file and shared on the departmental local network, giving those with access to it a quick path to contextualized information. Current users of the Knowledge Map include interns, young engineers, experienced engineers and Mentors. It has so far helped to increase a culture of knowledge sharing and significant positive feedback has been received by its users. Currently there are efforts to expand the Knowledge Map to additional interdisciplinary topics (including Electronics & System Engineering), as well as making it more collaborative by getting more specialists to add resources and place more information into context.


Col. (Dr.) Alan Nelson

Positive youth development in the aerospace domain

Positive youth development refers to international efforts of other youth, adults, communities, government agencies, NGO’s and schools, to provide opportunities for the Youth to enhance their interests, skills and abilities, through scientific literature, practitioners and youth programs, designed to optimize developmental processes. Since the birth of our new Democracy, and more specifically in the Aerospace domain, youth development programs have been focused on Recreational participation in Aviation “games” and outdoor activities, while the Country, and industry, are crying out for skilled Engineers, Technologist, Technicians and Artisans, in support of much needed technical skills throughout the spectrum of Aerospace Mustering’s. The South African Air Force’s Air Force Base Ysterplaat, has established and is operating, a Youth Development Program, to prepare Grade 10,11 and 12 Learners, for a potential career in the Defence and Aerospace Industry. This paper will present a case for Positive Youth Development in the Aerospace Domain, with the intent of prospecting the youth of today for utilization in the future.


Prof Josua P Meyer

The constructual size of heat exchangers in aerospace

The architecture of heat exchangers is a classical subject that has been studied extensively in the past. Except that the free stream velocities may be orders of magnitude different, the fundamental approach and equations do not distinguish between the design of heat exchangers used in stationary applications used in power plants (fossil fuel, nuclear, solar, etc.), industrial applications (manufacturing, transport, processes, etc.), air-conditioning and refrigeration, and aerospace.

In this paper, we address the fundamental question by making use of the Constructal Law to determine what the optimum size of a heat exchanger should be in aerospace applications, in addition to what architectural features it should have. When the Constructal Law is used together with the Second Law of Thermodynamics, the answer to the size question follows from the trade-off between (1) the useful power lost because of heat transfer and fluid flow, and (2) the power destroyed during transportation. Changes in heat exchanger size induce changes of opposite sign in the power requirements (1) and (2). This fundamental trade off regarding size is illustrated by considering one side of a heat exchanger (one flow passage) in laminar flow and in fully rough turbulent flow, several duct cross sectional shapes, and arrays of channels in parallel. The size trade-off is present in heat exchanger applications across the board, from vehicles to stationary power plants. It shows for the first time that the approach to be used in the design of aerospace heat exchangers is different and that the optimum size of a heat exchanger in aerospace is different from the size of heat exchangers in stationary application.


Steven E. Katzeff

An investigation into prying models in tension clips

Summary of Paper

Contact between deformable bodies is complex. In structures, contact has always been treated as an 'uncertain' science, and load paths are designed to steer clear of modelling it. It is, however, inevitable that the load path of structure, especially secondary structure like simple 'bracketry', requires contact to react load. Any mechanically fastened load path requiring contact to react moments will result in the 'prying effect'; which effectively increases the axial tension force in the fastener. Figure 1provides a simple overview of typical T and L type tension clip configurations. Models of the prying phenomena found in the literature can essentially be split into two types; simple analytical and semi-empirical. Simple analytical models, for example the assumed 2/3rd triangular prying distribution, offer simple design formulae, but employ equally simplistic assumptions regarding the moment distribution and prying force in the clip and fastener respectively. The advantage of these simple analytical models is that they yield easy-to-implement design formulae, and seem to be justified by some Finite Element modelling or tested data-albeit for thicker (>16mm) clips. They do not however address many important variables governing the complexity of prying; ignoring the correct moment distribution, preload, bolt bending & deformation and most significantly, they can lead to non-conservative results-as is demonstrated in the paper. More complex, semi-empirical approaches to prying offer some advantage over the simplistic analytical models. These models, which consider preload and plasticity, are generally based on simplifying assumptions that yield good approximations to tested data. A comparison of these two types of modelling philosophies is presented in this paper, addressing both their advantages and disadvantages.

A method is then proposed that assumes the clip to rest on an infinitely stiff, tensionless Winkler foundation.


Busisiwe Nkonki

The impact of long-term investment on the successful commercialisation of aerospace technologies

The commercialisation of aerospace technologies has always presented significant risks and uncertainty, therefore limiting the chances of small aerospace companies to attract investors. Thus this research investigates how long-term investments influence the successful commercialisation of aerospace technologies in the long run. The results should outline the link of a clear commercialisation strategy showing the guidelines for investment to the commercialisation of aerospace technologies and to breach the gap between development R&D and commercialisation. The Mitsubishi Regional Jet (MRJ) and the Eclipse 500/Eclipse 550 were used as case studies to further assess the impact of investment cash flow on the success of aerospace projects. The aerospace industry is a volatile industry that has many uncertainties, related to cash flow of the production cycle of aircrafts, which makes investors reluctant to invest in such projects. The case studies provided insight on the dependence of the success these projects on vigorous investments throughout the production and distribution cycle of the aircrafts. Although there were many financial failures due to lack of funds and production failures due to the emphasis on safety for aircraft, the success of these projects depended on more and more cash flow from investors. Thus there is a correlation between long-term investments to the successful commercialisation of aerospace technologies. The findings further show the influence of a clear commercialisation strategy that illustrates the risks and mitigation strategies associated with investing in aerospace technologies. A commercialisation strategy acts as a guideline to commercialise technologies and should contain investment strategies that clearly indicate the risks and mitigating strategies associated with investing in the aerospace industry. Therefore investors should understand the implications and the risks associated with investing in aerospace technologies, it should also be clear that return on investments (ROI) and revenues of this sector might take years as the costs encompassed are high even after production.


Johan A Heyns

An update on the development of the high-speed aerodynamic (HiSA) solver

The work presented here considers the use of the OpenFOAM finite volume library to model high-speed, compressible flow. The project was initiated in 2013 following the requirement for a stable and efficient high-speed, external aerodynamics solver to support the national test facilities, to assist the aerospace and defence industry with the aerodynamic characterisation of airframes as well as the need for high fidelity flutter predictions.

Although density-based solvers provide an effective solution to resolve the sharp discontinuities of propagating shock waves associated with transonic and supersonic flows, a fully coupled approximation of the governing equations are essential to ensure an efficient solution. In addition to higher resolution shock capturing schemes used to describe the inviscid flux terms, the approximation of gradients in high aspect ratio cells describing the viscous boundary layer of high Reynolds number flows needed to be resolved.   

To establish confidence in using OpenFOAM to model compressible, high-speed flow over representative airframes, an extensive set of verification and validation cases were completed. Initial verification cases (eg. shock tube and forward facing step) considered comparisons with analytical solutions while validation cases compared the numerical results with experimental measurements as well as published results of commercial CFD codes. 


Dwain Dunn

Unsteady Analysis of A Generic Non-Axisymmetric Hub Endwall Contour As Applied To A Rotating Turbine At On And Off-Design Conditions

Numerous researchers have investigated various techniques to reduce loss in gas turbine engines. One such technique that has shown promise is endwall secondary flow control using non-axisymmetric endwall contouring. Previous steady state investigations have shown that the generic endwall contour designed for a cascade reduced the loss in a rotating turbine test rig. The current investigation was to determine if there were unsteady effects introduced by the contour at design and off design conditions. An experimental and numerical study was performed to investigate the rotor flow field for any unsteady changes to the rotor exit flow field. The investigation was performed at an increased loading condition, design and a decreased loading condition to determine how changes in operating condition altered the flow field. The experimental results showed that the velocity magnitude of the hub endwall secondary flow vortex system for the contoured rotor was reduced. The peak difference in oscillation of the flow was also reduced. The effect of the endwall contour reduced the over and under turning of the endwall secondary flow vortex system as well. The magnitude of the FFT at the blade passing frequency was reduced below midspan.


Simeon Pienaar

The use of optical measurement techniques to observe helicopter blade anomalies during operation

Helicopters are notorious for high levels of structural vibration.  The primary sources of high magnitude, and low to medium frequency vibration are the large main rotor and tail rotor of the helicopter. These vibrations are characterized by mass and aerodynamic imbalances during operation, which are inherent to any rotor wing aircraft. Helicopters also experience vibrations of higher order from the drive train and turbine engines. The focus of this paper is on the medium frequency vibrations caused by the tail rotor.

Stereo-photogrammetry and 3D point tracking (3DPT) are optical measurement techniques that have experienced major advances in recent years. These techniques do not only offer non-intrusive measurements but also full field measurements of multiple points on the structure simultaneously.Introducing these measurement techniques to the helicopter rotor health monitoring field has the potential to open new opportunities in the measurement and observation of the dynamics of helicopter rotor blades during operation.


Irshaad Mahomed

Transonic Flow-field for a Decelerating Axisymmetric Cylinder

This study is a fundamental investigation to demonstrate the effect of significant deceleration on the transonic flow field around a blunt cylindrical projectile through a numerical approach implemented in ANSYS Fluent. The projectile geometry and order of acceleration magnitude is based on a study by Jiang et. al who investigated the near blast flow-field of a supersonic projectile emerging from a barrel into ambient air; using an Euler solver. This study considers the region of flight once the projectile has travelled away from the barrels outlet. Two projectile shapes is considered (25x25mm and 50x25mm cylinders) and two deceleration magnitudes (10 000 m/s2 and 5000 m/s2). The projectiles are decelerated from steady state Mach 1.2 to 0.8, at zero-incidence. The bow shock and wake recovery compression waves is shown to propagate forward relative to the body where the compression waves overtake the body and appear ahead of the nose. Strong coupling exists in the flow field between the near wake and outer region of the separation bubble for an aspect ratio of 1, influencing the shock dynamics during deceleration. The effect of deceleration in the lower transonic Mach regime was more pronounced at 5000 m/s2 than at 10 000 m/s2.

Simulation of shot peening process on turbine blades

This paper proposed a numerical method to simulate and optimise shot peening process on turbine blades. At first, a 3D model of shot peening process was created through a time-saving method combing discrete elements and finite elements. Through this model, the residual stresses, material hardening and plastic strains were then determined. These simulation results were employed to build an approximation model for shot peening process to reduce time cost further in optimisation process. Lastly, the controlling parameters of shot peening process were optimised by employment of genetic algorithm and optimum combinations of the parameter were obtained.


L Nel

Wind Tunnel Testing Considerations in the Modelling of Expansion Fan/Shock Wave Interactions

When aerodynamic bodies are in close proximity during supersonic flight (such as in the cases of store carriage and release, engine inlets, and formation flying) shock waves and expansion fans interact and alter the flow field around the aircraft, thus warranting further study of an expansion fan/shock wave interaction.  Wind tunnel testing allows experimental investigation of an expansion fan/shock wave interaction under controlled conditions.  This paper outlines the considerations involved in supersonic wind tunnel testing – design of a model of sufficient strength to withstand the aerodynamic loading and small enough to prevent tunnel blockage and subsequent prevention of tunnel startup, appropriate setup of a Schlieren system to visualize the interaction while reducing optical aberrations, and interpretation of the results accounting for flow features arising from the model finite leading edges and three-dimensional flow phenomena.


Aarti Panday

Optimal Control Design for Non-Minimum Phase Receiver Aircraft during Aerial Refuelling

Autonomous aerial refuelling (AAR) of an unmanned aerial vehicle (UAV) relies on control system design to maintain a fixed orientation relative to the tanker aircraft, whilst subject to varying mass, inertia and wind effects. Linear analysis of the receiver aircraft during AAR revealed that the system was non-minimum phase. Optimal Control techniques were applied to the AAR problem to obtain desired closed loop behaviour. The designed full state-feedback Linear Quadratic Regulator (LQR) controller met design specifications. A Linear Quadratic Gaussian (LQG) compensator was formed which included the regulator and a Kalman Filter estimator. While the compensator was stable in the closed-loop, there was a loss in robustness properties. Loop Transfer Recovery (LTR) was used to recover the full state-feedback properties for the non-minimum phase system. Properties at the plant output were partially recovered. Three of the four channels were recovered fully. An increased bandwidth gave faster response dynamics as needed in aerial refuelling, however, this was achieved with greater overshoot in the transient response.


Nana Arthur

Microstructure and material properties of optomec lens fabricated ti6al4v alloy components for aerospace construction

Cylindrical components of dimensions 15 mm in diameter and 11 mm in height were laser printed by additive manufacturing. Process parameters used in layer by layer build-ups, viz. laser power, scanning speed and powder flow rate, were varied in order to determine their influence on the physical properties, and resulting microstructure of Ti6Al4V Extra-Low Interstitials (ELI) build-ups. The components were manufactured using the Optomec LENS™ system and evaluation was conducted for the qualification of additively manufactured aerospace components. As a continuation from previous investigations, results of this paper will analyze the influence of developed microstructures on mechanical properties such as hardness (HV) and tensile strength of components. Test coupons for evaluation were produced employing optimized laser process parameters. Specimens consisted of laser printed cylindrical components and tensile specimens were produced and machined according to specifications contained in applicable test standards. Mechanical properties of “as-built” samples are discussed in this paper.


Monnamme Tlotleng

LENS manufactured TNB turbine blade characterised of a lamellar microstructure containing β remnants and γ precipitates

Metal materials with good creep and fracture toughness properties are required in the manufacturing of turbomachinery parts. The 4th generation alloys such as Ni-based super alloys, which have improved high temperature creep properties and possess a homogenous microstructure post manufacturing, are necessary for the production of aerospace parts. These alloys are somewhat lighter and able to withstand operational temperatures above 700°C without deformation. Currently, Inconel 713/8 is used in the manufacturing of air foil blades of compressors. Properties like high strength, good stiffness, creep resistance and light-weight are the perfect candidates for aerospace applications. These properties are synonymous to gamma titanium aluminides (γ-TiAl) alloys which have half the density compared to Ni-based super alloys and can perform at temperatures above 1000°C. γ-TiAls are well ordered intermetallic materials that exhibit attractive elevated-temperature properties due to their long-range ordered super-lattice structure that is able to reduce dislocation movement at high temperatures. γ-TiAl lack room to moderate temperature ductility hence they are difficult to cast into finished products. While cast and hot isostatic pressed γ-TiAl show improved homogenised microstructure, it seems electron beam melting achieves even more superior microstructure and thermomechanical properties required for finishing γ-TiAl in the manufacturing of miniature gas turbine blades. In this study, laser additively manufactured γ-TiAl gas turbine blade was 3D printed using the 850-R Optomec LENS machine. During printing the As-built sample showed stress-induced thermal cracking. The sample had a finer and near lamella β microstructure before heat treatment. Heat treatment was performed at 1400°C with a holding time of 4 hours in a Carbolite tube furnace under Ar controlled environment and furnace cooled to room. Heat treated sample showed a fully lamellar and elongation microstructure with precipitates of γ and remnants of β phase.



S Hoosain

Development of contour scanning parameters to improve surface finishing of additive manufactured parts

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques have been developed to accomplish this via melting or solid-state joining. The surface topology of AM produced parts is typically worse than that of other manufacturing technologies, such as machining and casting, due to the layer-wise manufacturing process. The objective of this work was to develop a process parameter set for application to the contours which define the edge of every consolidated part and ultimately also the properties of the external and internal surfaces of any part that is produced by the SLM (Selective Laser Melting) method. Contours follow the edges of the part, melting along free surfaces of the part geometry. Contour scans are done in SLM to improve the surface finish of components. Experiments were set up on the custom built selective laser melting platform within the LENS enclosure. The laser used was an IPG YLS 5000 ytterbium 5kW fibre laser. Wavelength 1076 nm. Delivery fibre core diameter of 50 μm. The scanner used was an Intelliweld 30 FC V system. Materials used were Ti6Al4V, gas atomized with particle size 20-60μm. Surface roughness measurements were done using a commercially available calibrated Talysurf mechanical probe and micro X ray tomography. There is a marked improvement in surface finish compared to the standard sample without contour scanning. The contour-hatch overlap showed a significant effect on surface finish however there is a trade-off between surface finish and porosity


Schoombie J

A comparison of ANSYS Fluent and STAR-CCM+ simulations for a tangent ogive slender body with a structured mesh at incompressible flow conditions


Computational fluid dynamics (CFD) is a valuable tool in analysing external aerodynamics. This paper compares two commercial CFD codes, ANSYS Fluent version 15.0 and STAR-CCM+ version 11.06. A tangent ogive slender body with very low aspect ratio wings was simulated in ANSYS Fluent in 2013 and the structured mesh was imported into STAR-CCM+. Simulations were carried out in STAR-CCM+ and the results were compared to the Fluent data. Some differences were observed between the Fluent and STAR-CCM+ axial force coefficients at high angles of attack. In general the STAR-CCM+ results correlated well with the Fluent data for the normal force and pitching moment coefficients as well as centre-of-pressure and vortex locations.


Naidoo K

A Facility for the Investigation of Dynamic Shock Wave Reflection Phenomena


The phenomena of regular and Mach reflection of shock waves generated by a stationary wedge in a steady supersonic free stream have been investigated extensively since the early work by Ernst Mach in 1878. The theory of steady state shock wave reflection and the transition between regular and Mach reflection is well established and documented. In the last decade, numerical flow simulations of a rapidly rotating wedge showed, for the first time, that it is possible to observe regular and Mach reflection outside the theoretical bounds governed by steady state considerations. This paper documents the development of the first experimental facility used to verify these dynamic effects. The facility includes a novel rig that generates the dynamic phenomena of interest with rapid wedge rotation in a supersonic wind tunnel. The rig includes an actuator that achieves accelerations in the order of 1000m.s2. The duration of the event of interest is of the order of 10.0 msec and wedge rotation rates up to approximately 11000 deg/s were achieved at approximately Mach 3.0. High-speed imaging up to 1000 frames per second was employed for adequate temporal and spatial resolution of the dynamic flow field.


Duncan Stanton

The Gecko Imager – Around the World in 90 Minutes


The Gecko imager was realised from a technology development focussed on putting the building blocks in place for a hyperspectral nanosatellite imager. Through the funding provided by AISI, the initial building blocks of the optics, sensory chain and mass storage was realised up to Critical Design Review level. The effort by Space Advisory Company in taking the design and development further to realise the Gecko Imager was accelerated by an opportunity undertaken by SCS-Space to form part of the QB50 constellation mission. In a very compressed period of time of 6 months, a payload and satellite had to be designed, developed, assembled, integrated and tested. The 2U nSight-1 satellite would result in less than 1U of volume available for the imager payload, and the effort to rapidly redesign and integrate a payload into such a volume was undertaken. The final result was a camera system, able to deliver 30m resolution images at 60km swaths, from space.

The camera has been successfully operating for 125 days in space, having taken numerous images of landmarks across the globe. In addition, the camera system is able to test and evaluate radiation mitigation techniques for an algorithm developed by Nelson Mandela Metropolitan University.


Sean van Staden

Effects of Laser Shock Peening on Aeronautical Aluminium Alloy 7075

Laser Shock Peening (LSP) is a surface enhancement technique that induces a beneficial residual stress field in metals to improve their fatigue performance. Internationally, LSP is being used in a number of aeronautical applications. It is controlled by various parameters, e.g. power intensity, coverage and spot size; to develop an aeronautical industry-ready laser system a database of the effect of these parameters on the residual stress profile, microhardness, microstructure, and surface morphology must be obtained for relevant alloys.

This work is now being conducted on high strength-to-weight ratio aluminium alloy 7075-T651. LSP was performed at the CSIR National Laser Centre and the residual stresses were measured using different complementary techniques at various locations worldwide. Other metallographic properties are being investigated using appropriate equipment at Wits University. The results show that LSP is inducing high magnitude compressive residual stresses to a substantial depth