In the paper by Messrs. Wood and Hammond it has been shown that titanium is likely to save weight compared with steel, where complexity together with the cost of manufacture make it necessary to have some material which is “structurally inert”. The presentation also showed that at high complexity factors, changing from aluminium to titanium would add weight. If the presentation could have included the effect of increasing the operating temperature it would have shown a narrowing gap until at temperatures above about 250 °C, aluminium is no longer viable.