A New and Practical Approach for Mini-airship Design

A new mini-airship design approach was developed to allow size minimization and advanced streamline shaping. Conventional airships are usually categorized as the rigid, the semi-rigid, or the non-rigid. Minimization of their sizes and weights and streamline shaping of their hulls are usually conflicting design factors. Non-rigid airships are light in weight. However, it is difficult to implement advanced streamline shapes due to the non-uniform distribution of the pressure on the hull. Rigid airships employ internal gas cells to provide buoyant lift. Their rigid hulls allow advanced streamline shaping, but are usually large and bulky due to the heavy hull materials. Simi-rigid airships have the same disadvantages as the non-rigid ones. This project proposed a new design concept to combine the advantages of the rigid and non-rigid airships. The design employed a non-rigid hull made from a flexible envelope expanded by a carbon fiber skeleton frame and internal gas cells. Although the gas cells were not fully pressurized, their lifting force naturally provided a strong support to the hull. The skeleton frame and the gas cells therefore shared the responsibility of maintaining the hull shape. With this unique design, the hull envelope was not required to be air tight, and the gas cell material was not required to be extremely strong. Light weight materials thus could be used for the airship construction. The skeleton frame also allowed advanced streamline shaping of the hull. A mini-airship was constructed to demonstrate the concept.  An EXCEL workbook including more than 35 airship design equations was developed to perform iterative design.  Rigorous design procedures were followed to calculate the drag, weight, and other structural, mechanical, and electrical parameters. The streamline of Model 111 in NACA Report TN614 was selected as starting point of the design for its low drag at low Reynolds numbers. The mini-airship was 2.5m long with a maximum diameter of 1.0m and a volume of only 1.12 cubic meters. Two propellers driven by separate electrical motors provided differential thrust. A micro servo was used to adjust pitch moment. An onboard radio receiver enabled flight operation using a ground remote controller. Indoor flight test showed a lift capacity of more than 0.3 kg, an impressive number for such a small airship. The results showed that the approach is viable for mini-airship streamline shaping and size minimization. Future directions of this research include the development of a computer based remote control system for autonomous flight control.