They are always brittle.Indranil wrote:It is not about heat tolerance etc. composites are brittle under some stress conditions. So you can’t use them in airframe parts which experience those stress conditions. It is unlikely that you will see the percentage of composites to go up much further in LCA. It is already one of the highest in spite of being such a small plane. You will instead see weight savings by decreasing the number of parts.nam wrote:
Of course, I understand, like areas around the engine, where heat is an issue.
Having said that, hunger to find a way of doing it better is what drives innovation. Like the composite created by NAL, which can handle upto 200C and used on the engine bay.
No harm in trying!
Certainly you need metals when design requirement is driven by toughness rather than resilience and/or delayed failure or early indication of failure is a must rather than an abrupt failure as how Composites fail. Composites don't save significant weights everywhere and every time (at least as of today). A well designed an manufactured metallic aircraft structure can easily compete with Composite one in certain situations considering all operational factors in design, MFG, cost and MRO. But Composites have other unassailable advantages such as in stealth or relative ease of significant reduction in part count. The design philosophy itself is not matured enough to use composites to their full potential as of today, let alone the manufacturing and inspection/repair capabilities. For example, the key advantage of composites is inherent ability of having tailor-made anisotropy in material properties or in layman term to put material only where its needed. But as of now, the design philosophy forces the designers to create quasi-isotropic composite materials by trying to balance the layup pattern. That erodes a considerable weight advantage that composites should have had over an isotropic material like Metal. Its easier to save weight in predominantly uniaxial or planer loading conditions. Composites do not really offer significant weight advantage in complex multi-axial loading situations as of now. Metals still offer cheaper and more convenient option in some such situations due to more matured design and manufacturing technology it has.
Additive Manufacturing is adding a new dimension to metals' capabilities parallel. So we are not going to see metals surrendering completely to the composites.
Also "Composites save weight" is same kind of saying as "Canards are bad for stealth" or "canards are draggy". These are engineering statements which always have context and not a Physics statements like "Speed of light is constant". Engineering statements should be taken with pinch of salt.
