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Title: Disc-wing aerodynamics
Author: Potts, Jonathan Roger
ISNI:       0000 0004 2734 5754
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2005
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Disc-wings are a class of un-powered, axi-symmetric flight vehicles that use spin to achieve acceptably stable flight characteristics. Examples of commonly encountered disc-wings include the Frisbee sports disc, the athletics discus and the clay pigeon. Historically, it appears that most disc-wing designs have been based on trial and error approaches. The main aim of the present work is to develop a theory of flight for spinstabilised disc-wings that can be used to inform the process of their design. This theory of flight is based both on theoretical analysis and experimental data. It is shown from a simple trim and stability analysis that a disc-wing with positive camber will trim at a positive angle of attack. However, for most axi-symmetric crosssectional shapes, the aerodynamic centre is ahead of the centre of the disc (which by definition is the disc centre of gravity). Hence, the static margin is negative and the disc is unstable in pitch. In practice, a disc-wing must be spun in order to fly successfully. The imparted angular momentum due to the spin means that, through precessional effects, the destabilising pitching moments tend to result in a rolling motion rather than a pitching motion. Thus, without spin, a disc-wing would tumble soon after release. With spin however, the discwing will not tumble, instead it tends to exhibit a relatively benign roll to the left or right, depending on the spin direction. The aerodynamic characteristics of various disc-wing geometries based around a Frisbee sports disc are investigated through a series of wind tunnel experiments on a spinning and non-spinning disc. It is shown that the basic lift and drag characteristics are consistent with those expected for a finite wing of the same aspect ratio. The pitching moment characteristic is key to understanding the resulting disc dynamics. A comparison of pitching moment curves is given, for a number of different cross-sectional profiles, some tested as part of the present work and some taken from data found in the literature. It is shown that the Frisbee cross-section is unique in that the pitching moment is zero at around 9° angle of attack, approximately coincident with the angle attack for best lift to drag ratio, and that the disc is approximately neutrally stable in this region. It is these characteristics that enable a typical Frisbee to fly successfully. Spin has almost negligible effect on aerodynamic forces and moments. Force and moment data is supported by surface pressure data, and by on and off surface flow visualisation. Surface pressure data shows that the aerodynamic centre of the Frisbee cross-section is shifted aft by the presence of an aft pressure peak that is not present on other cross-section shapes. The aft pressure peak is a function of both the upper surface geometry and the presence of the cavity on the under surface of the disc. Flow visualisation and pressure data are used to propose a model of disc-wing flow topology that is dependant on the angle of attack and includes leading edge separation and reattachment, recirculating cavity flow and a pair of trailing vortices. To understand further disc-wing flight dynamics and the effect of aerodynamic characteristics, a six-degree of freedom disc-wing simulation model was developed using Matlab. The simulation is validated against published Frisbee trajectory data obtained from free-flight experiments. Flight profiles are also discussed for a number of different launch conditions consistent with a range of typical Frisbee throws. The simulation is also used to demonstrate that with control moments from suitable control effectors, it is possible to generate a number of proscribed manoeuvres, including a spiral turn and a spiral roll.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available