OpenUCT :: Browsing by Author "Redelinghuys, Christiaan"

Browsing by Author "Redelinghuys, Christiaan"

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Open Access
Aerodynamic analysis and optimisation of a servo-controlled aileron
(2011) Day, Chris; Redelinghuys, Christiaan
The pressure for the airline industry to reduce its consumption of fuel is mounting. It has been conjectured that smart materials could be employed to control the aileron deflections via the tab, using with an electrically-actuated system instead of the bulky hydraulics currently used. In a collaboration between a leading aircraft manufacturer and four South African universities, potentially more efficient technologies for aircraft roll control, which would reduce the weight, are being investigated. This dissertation involves the aerodynamic analysis component of the collaboration project.
Open Access
The development, optimisation and testing of an unmanned parafoil launch system
(2010) Norton, William Alexander; Redelinghuys, Christiaan
Parafoils have been used in various aerospace, military and sport applications to return both personnel and payloads safely to the ground. Deflection of the trailing edge flaps by means of control lines allows for turn rates of up to 60° per second, which provides superior controllability when compared to conventional round parachutes. This steering ability has led to the development of autonomous control systems that are able to navigate a payload to land in close proximity to a designated landing site. In order to develop an autonomous navigation system a suitable dynamic model of the parafoil with suspended payload is required to determine the parameters and characteristics of the system in free flight. Flexible ram-air inflated parafoils display high sensitivity to atmospheric disturbances which complicates the comparison of measured flight-dynamic data to theoretical models in an open air free flight test. In order to improve the quality of results in studying the flight dynamics of an unmanned parafoil system in free flight, controlled conditions and a repeatable flight path are required to perform data analysis for various trim configurations. This leads to the requirement of a launching system that ensures consistent inflation of the canopy and repeatable launch velocities for various canopy and payload configurations.
Open Access
The effect of turboprop propulsion on the aerodynamic benefits of formation flight
(2017) McKenzie, Cameron Cedric; Redelinghuys, Christiaan
In order to determine the effect of turboprop propulsion on the aerodynamic benefits of formation flight, a 3D Vortex Filament Method (VFM) programme, which made use of a Burnham-Hallock viscous core model, was formulated and employed to model the progression and interaction of the wing and turboprop trailing wakes. Within this programme, an initial prescribed wake for the turboprop engines was discretised by shed helicoidal vortex filaments generated by the use of an amalgamation of the propeller theory of Goldstein and Theodorsen. The downwash velocity field of a B747 during cruise, obtained via the use of the VFM Burnham-Hallock (VFM B-H) model programme, was verified against both the simulation conducted by Ehret and Oertel, in which an integrated Biot-Savart law VFM was utilised, as well as against experimental results obtained by Burnham et al. in their ground-based measurements of the wake vortex characteristics of a B747 aircraft. The VFM B-H model produced peak upwash and downwash velocities which matched those obtained by Ehret and Oertel to within 95% accuracy. Furthermore, a distance of 47.48 m between the rolled up vortex centres was achieved utilising the programmed VFM B-H model, which differed from the Ehret and Oertel model by only 0.48 m. Qualitatively, the 3D VFM B-H plot displayed similar degrees of roll-up and descent when compared to their Biot-Savart VFM plot. As a result of this positive validation process, the programmed VFM B-H model was utilised to simulate turboprop aircraft wakes of a higher complexity. In order to compare the effects of the number of turboprop engines on the aerodynamic benefits of formation flight, the three-bladed single turboprop engine Lancair Propjet, the six-bladed twin turboprop engine ATR 72 and the four-bladed four engine Lockheed Martin P-3 Orion were selected for comparative simulations. As extended formation flight makes use of aircraft downstream separation distances of more than ten wingspans, a wake length of 330 m (which equates to 10.9 span lengths for the P-3 Orion, 12.4 span lengths for the ATR 72 and 36.3 span lengths for the Lancair Propjet) was selected. All aircraft were simulated via the use of the VFM B-H model programme for a range of flight states from cruise conditions to zero g wing loading with full propeller thrust, such as in vertical ascents. From said simulations a novel viscous core radius to simulation convergence relationship equation was developed. The induced velocity fields at 330 m downstream in the wake were then generated in order to investigate the effects of the inclusion of turboprop engines on the aerodynamic benefits of formation flight. From said downwash plots, it was found that the helicoidal vortices affected that region of the wake within an average value of 35% of the wingspan, measured from the fuselage symmetry plane, for all simulated aircraft. In aircraft design, wing mounted engines are placed in a more inboard position in order to reduce rudder strength requirements as well as to minimize the yawing moment due to asymmetric thrust in the event of an engine failure. These helicoidal vortices' areas of influence are a result of said aircraft design convention as well as the helicoidal vortex sheets having a much lower vortex strength and filament density than the wing wake. The regions of the wing wake dominated by upwash induced velocities are outboard of an average value of 40% of the wingspan, measured from the fuselage symmetry plane. It is this region in which the drag reduction, fuel saving benefits of extended formation flight are harnessed. Therefore, as a result of aircraft engine mounting convention and marginal outboard drift of the helicoidal vortices, the turboprops' helicoidal vortices have minimal to negligible effect on the 10% wing overlap outboard-most region that sees positive fuel savings of 10% to 16% for previous extended formation flight investigations.
Open Access
The effect of wing flexibility on ride comfort in formation flight
(2015) Biden, Kirsty Joy; Redelinghuys, Christiaan
The paper addresses the issue of passenger ride comfort during formation flight. The study focuses on the vibration attenuation that occurs due to the aeroelastic effect, more particularly, on the influences these effects have on the magnitude of the fuselage accelerations. No distinction is made between the fuselage and passenger accelerations in the present work. The objective of the present study was to develop a representative aircraft model incorporating an aerodynamic model, based on the classical Vortex Lattice Method (VLM) and structural and inertial models defined by stiffness and mass matrices. The VLM code was validated for both large aspect ratio wings with low frequencies in unsteady aerodynamic conditions, as well as swept wings in steady flow, using the Warren 12 wing planform as reference. The structural model was developed using both a discretization method, as well as a continuous integration method. The results of these two approaches were carefully compared with one another as discrepancies were encountered during the analysis. The BAH jet transport wing was utilised in this study as it is widely recognised as a standard calibration case. This model was successfully implemented within a MATLAB/Simulink simulation environment. This paper presents the theoretical development of both the structural and aerodynamic models, along with the results of various test simulations. The restrained fuselage model was validated by performing a modal analysis and comparing the results with the Nastran Aeroelastic User's Guide results for a BAH wing. When the fuselage was permitted to translate vertically, a Fast Fourier Transform (FFT) was used to highlight the dominant frequencies of the system's motion and the damping ratio determined by a least squares method used to best fit the peaks of the displacement. A simple flutter analysis was performed and the results compared with those documented in the Nastran Aeroelastic User's Guide. The trailing wake vortices shed by the lead aircraft in formation flight were considered to have a solid core using the Burnham-Hallock Model. The optimal positioning of the trailing aircraft in a two-aircraft formation was discussed and all subsequent simulations run with the trailing vortex core initially located at the wing tip and 0.1 of a wingspan above the wing. The Von Karman turbulence model was used to simulate random atmospheric turbulence and the trailing vortex pair was assumed to shift in an ideal fashion within the atmospheric turbulence, resulting in fluctuating aerodynamic disturbance loads acting on the trailing aircraft. The results indicated that while the effect of turbulence on the aircraft itself was noteworthy, the motion of the trailing vortex pair in the spanwise-direction due to the turbulence, dominated the trailing aircraft's response. This was because the turbulence in the y-direction effectively altered the spanwise separation of the aircraft, varying the downwash distribution over the wing. The motion of the turbulence in the z-direction merely affected the intensity of the aerodynamic loads caused by the trailing vortices. From these results, it was concluded that an aircraft flying in formation will experience greater accelerations in turbulent conditions than a solo aircraft, due to the movement of the trailing vortices. A comparison of the motion of the airplane in response to atmospheric turbulence was compared to that documented by Fung, who made use of the Dryden turbulence model. For reasons discussed the results did not correlate exactly; however, the trends of the two sets agreed well. The individual contributions to vibrations due to shifting trailing vortices and turbulence in solo flight were analysed separately and then combined. The findings indicated that a significant difference exists between the fuselage accelerations of an aircraft with a flexible wing as opposed to a rigid wing. The results showed that the variance of the accelerations for the flexible aircraft were approximately 25% of those for the rigid aircraft. It was also found that by flying in formation the variance of the fuselage accelerations increase by approximately 18% from those of a solo aircraft flying in turbulent conditions. The predicted acceleration responses of the trailing aircraft were used as an indication of the passenger comfort levels. Thus it was concluded that while flight in formation does adversely affect the passenger ride comfort, the vibration attenuation that occurs due to the flexibility of the aircrafts wing is so significant as to minimise the discomfort levels.
Open Access
The effects of atmospheric turbulence on fuel consumption in extended formation flight
(2014) Sanders, Drewan S; Redelinghuys, Christiaan
Extended formation flight (streamwise separations of between 10 to 40 spans), has been recently proposed as a method for reducing the induced drag of commercial aircraft. However, induced drag savings are not necessarily directly indicative of fuel savings. In a realistic environment, atmospheric turbulence will continuously perturb the formation’s aircraft and their wakes. As a result, each aircraft in the formation will experience fluctuations in aerodynamic loads. For an aircraft to maintain accurately its position within a formation, it must continually adjust its throttle setting. This dynamic throttling may result in inefficient engine operation, thereby detracting from the reductions in induced drag. In this work, a high-fidelity transient engine model, representative of a typical commercial high-bypass turbofan engine, has been incorporated within a simple twin-aircraft formation flight simulator. The aerodynamic interactions between aircraft were modelled using a horseshoe vortex method, specially adapted for extended formations. The aircraft were constrained to longitudinal motion, with altitude fixed. This created a two degree of freedom formation model that is analogous to wind tunnel experimentation. A simple proportional gain controller was used to manipulate the throttle settings, in an attempt to maintain the trail aircraft’s position relative to the leader, in a turbulent atmosphere. It was found that a fuel saving of approximately 25 may be achieved at a practical lateral separation of 1 span, corresponding to a stream-wise separation of 20 ± 0.3 spans, in moderate turbulence levels.
Open Access
The feasibility of a road vehicle mounted aerodynamic testing apparatus
(2011) Adams, Jordan; Redelinghuys, Christiaan
A ground vehicle mounted aerodynamic testing apparatus has been identified as a candidate concept for a low-cost alternative to traditional techniques. This dissertation explores the feasibility of a ground vehicle based system by identifying physical and practical issues facing such a system. The focus is on the two most important physical problems facing the concept. These are: the ride dynamics of a vehicle as it traverses a road, and the extent of the distortion of the airflow around a vehicle. Each of these problems is quantified using approximate methods in order to estimate their influence on the testing of the aircraft in order to determine if the concept is workable.
Open Access
Inferring parafoil glide slope by extending unsettled trajectories via simulation
(2014) Gomes, Roberto; Redelinghuys, Christiaan
A unique catapult has been developed at the University of Cape Town for launching parafoils from a hilltop or into a quarry. The initial objective to determine optimum glide slope of a parafoil using Design of Experiments via flight testing presented challenges. The flight tests and supporting simulations were carefully planned, and were to be conducted by making use of Design of Experiments to investigate the influence of factor effects on glide slope. The two factors to be investigated were the trim settings; plumb line length and trim angle. Each of these factors was to be tested at three discrete levels and it was decided that a 32 factorial will be used with the aid of Taguchi's methods. Due to serious flight test damages to the parafoil canopy, lines and payload, it was deemed necessary to revise the project objectives. The required repairs implied that testing could not continue within an acceptable period of time. The revised objective of this project was to ascertain if unsettled trajectory measurements could be extended by means of simulation to infer the steady glide slope. In order to conduct the simulations required, a rudimentary theoretical model of the unsteady parafoil motion was developed to investigate the influence of line length and trim angle on glide slope. The aerodynamic model focused only on the longitudinal motion of the parafoil-payload system, however the effects of wind and atmospheric turbulence were also investigated. The experimental flight tests in the quarry were unsuccessful due to flight test damages sustained and the focus of this investigation shifted to simulated results rather than experimental results. The simulated results suggest that increasing the plumb line length or the trim angle results in an increase in the settled glide angle of the system. On average, trim angle had a 2-3 times greater effect on glide angle than plumb line length. In addition, due to the lack of sufficient height in the quarry, simulations were run to extend the unsettled trajectory to a steady state in an attempt to estimate the glide angle. These simulations were capable of estimating a settled glide angle with reasonable accuracy in certain atmospheric conditions.
Open Access
Longitudinal stability and control analysis and parameter sensitivity investigation of fixed wing aircraft in ground proximity using various aerodynamic approaches
(2000) Pienaar, D van V; Redelinghuys, Christiaan
The investigation of the stability of longitudinal motion of fixed wing aircraft in ground proximity presented here focuses on rectangular wing and tail configurations similar to that of the Piper Cherokee PA-28-180. The majority of our results pertain to the height range down to one quarter of the wing span, and th main objectives of the investigation were the following: to reveal the physical nature and causes of the instability encountered in the close ground proximity; to assess the influence the design parameters such as the centre of the mass placement, tail length, tail height and wing aspect ration have on the stability of longitudinal motion; and to suggest a feedback control strategy that would alleviate the instability.
Open Access
A numerical investigation into the tactical advantages of supercruise for combat aircraft
(2000) Parbhoo, P; Redelinghuys, Christiaan
This dissertation describes a numerical investigation into the tactical advantages offered by upgrading a hypothetical aircraft with a newer engine model. The airframe is largely based on the Dassault Mirage III, and the engines are based on the SNECMA Atar 9k50 and M53. A brief overview of recent developments in combat aircraft design and engine performance is provided which illustrates the trend towards high thrust to weight ratio aircraft engines with lower fuel consumption.
Open Access
Passenger comfort during formation flight within atmospheric turbulence
(2012) Bizinos, Nicholas; Redelinghuys, Christiaan
Formation flight is currently being investigated as a means to reduce drag and improve fuel efficiency in commercial aviation. In light of this, the potential for passenger discomfort due to the formation flying through free air turbulence was considered in this study. In an attempt to approximately ascertain the increase in discomfort, a simple formation flight aerodynamic model for two aircraft in formation was developed. The wing trailing vortices were assumed to shift in an ideal fashion within atmospheric turbulence resulting in aerodynamic disturbance loads acting on the trailing aircraft. As the sensitivity of the human body to vibrations is frequency dependent, spectral representation of atmospheric turbulence was incorporated. Monte Carlo simulations were done for various levels of turbulence intensity.
Open Access
Wing trailing vortex paths in formation flight
(2014) Tipping-Woods, William P; Redelinghuys, Christiaan
Formation flight has been shown to reduce the induced drag for a formation of aircraft. The mechanism by which this is achieved is caused by the wake velocity field of the aircraft. This field is dominated by wing-tip trailing vortices. The paths of these vortices become too complex for rigid wake models downstream of the second aircraft in the formation. To tackle this problem, a combined vortex lattice and vortex filament numerical model was developed. For each simulation the vortex lattice model determined the lift distribution which was applied to the vortex filament model. The vortex filament model used the Burnaham-Hallock vortex profile with a core size of 5% of the wing span to eliminate numerical instabilities. Individual components of the model were verified successfully against literature and the overall approach was validated against wind tunnel data. The wind tunnel data was extracted from apparatus designed and build as part of this study. The apparatus consisted of two NACA 0012 rectangular planform wings mounted in various formation positions and a tuft grid placed downstream of the wings to visualise the vortex paths. Test were performed with both wings at 8◦ angle of attack. Span-wise wing-tip overlap distances were set at 38%, 10%, 0% and -10% of the span, where 0% implies wing-tip alignment and a positive value indicates a wing-tip overlap. Vertical separations were set at -3%, 0% and 3% of the span for each span-wise wing-tip overlap condition apart from 38% which was only tested at 0 vertical separation. The formation outboard vortex paths were predicted well within the 3% span accuracy of the tuft grid. The predictions of the paths of the formation inboard vortices, however were less accurate. The errors were attributed to a combination of bias errors in the experimental apparatus as well as the pseudo-viscous effects of the Burnham-Hallock vortex profile.

Browsing by Author "Redelinghuys, Christiaan"

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