City Research Online

Abstract

An investigation into the feasibility of using rotating circular cylinders as the primary means of generating lift for the class of very small (0.15 m maximum dimension, 50 g weight) unmanned aircraft known as Micro Air Vehicles (MAV) has been carried out. It is hoped that such a design would be able to exploit the large lift generating properties of the
rotating cylinder for the purposes of increasing the available payload weight. This would provide considerable benefits as, at present, the inability to support capable payloads significantly restricts the usefulness of MAV-sized craft.
A preliminary design study was performed to investigate possible configurations for the proposed design, resulting in the selection, for reasons of simplicity, of an arrangement having two rotating cylinders about a central fuselage. Initial assessments of the practical feasibility of such a design, as well as its likely performance (in terms of lift, drag, and power requirements) were then carried out. An examination of the consequences of the presence of the cylinders on the stability and control of such a vehicle was also performed. Existing understanding of the aerodynamic characteristics of a rotating cylinder in crossflow was extended through a series of wind tunnel tests examining all aspects of rotating cylinder flow, including force and moment coefficients, behaviour at non-zero yaw angles (−30� � � 10�), power requirements for spinning the cylinder, and wake phenomena. A particular focus was the use of endplates to improve aerodynamic performance. The tests were conducted with a cylinder of aspect ratio AR = 5 across a range of Reynolds numbers (1.6 × 104 � Re � 9.5 × 104, based on cylinder diameter) and velocity ratios (4) identified as being of interest by the preliminary design study. The results were generally found to be in very good agreement with existing published data, though power requirements for spinning the cylinder were much higher than anticipated, and revealed the influence of tip vortices to be of great significance. Wind tunnel experiments with a simple prototype aircraft, based on the outcome of the preliminary design study and isolated cylinder tests, examined the overall aerodynamic performance of this type of design for a single Reynolds number of Re = 1.8×104, across a velocity ratio range of 2.5, and at various angles of attack (−10� 25�) and yaw (−10� 30�). These tests also investigated the interaction between the cylinders and the other components of the aircraft to help determine the most favourable layout. The tests revealed the effect of propeller wash over the rotors, the influence of the cylinder wake on the tail, and the design of the tail, fin, and fuselage to be of considerable importance to the aerodynamic characteristics and performance of the vehicle. Overall, the study indicated that an aircraft of the proposed configuration and suitable capability was theoretically possible at the MAV scale of flight if an appropriate rotor geometry was chosen. However, the actual construction of a vehicle able to fully provide the desired performance within the constraints placed on platform size and weight was not currently possible using commonly available materials and components. Slightly larger designs (of dimension 0.4 m and weight 250 g) were more realisable, but still lacked in performance. Successful development of this type of design is thus dependent on technological advancement, particularly improvements in power and propulsion systems.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology Doctoral Theses School of Science & Technology > School of Science & Technology Doctoral Theses

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