design aspects


The homogenous nature of Advanced Composites allows a high degree of design freedom both in the shaping of almost any spherical structure and the ability to optimize its stiffness by adjusting its thickness and weave whereever needed.

Thus a particular structural section may have a graduated thickness over its area to precisely match with the flow of forces and loading conditions. This results in an efficient optimised structure (no useless material) with full factors of safety. Even when additional frames and bulkheads are added, the resulting structure acts as a single piece of material. With no areas of high stress there are no inherent problems with failure due to fatigue caused by vibration etc. In addition, because composites tend to absorb energy better than metals, vibrations and cyclic loading of engines, propellers and other machinery are better absorbed by the structure itself.

 

Modern 3D solid modelling CAD systems like IBM CATIA the leading software in the aircraft and space industry, are perfectly suited to support this design philoloshy that leads to a high design integrity providing maximum structural performance.

Aluminium is available only in standard sizes. Any single panel must have sufficient thickness to comply with the strength requirements of the most highly loaded part of that panel. Hence there will be excess material thickness greater than needed in the less loaded parts of the panel.

To combat the excess thickness of materials and to ensure the lightest possible structural weight, aluminium hovercraft structures can be designed with thinner materials but with lower factors of safety which would compromise resistance to damage etc. Any construction requires that joints are made and the material is distorted (bent) or welded to conform to the construction requirements.


Bending of material causes localised high stress areas. Welding material not only results in high stress areas but also reduces strength in the welded joint. When subject to vibration and cyclic loading of engines, propellers and other machinery, high stress areas can result in fatigue cracking and failures. Recent experience with aluminium Hovercraft structures confirm, that those drawbacks support the creation of cracks. The US Coast Guards therefore issued a warning on the use of aluminium in Hovercraft structures.

 

  copyright ABS 2014