Active Cooling Approaches
There are other proposed methods for protecting vehicles from high temperature while flying at high speed or during reentry. Several active cooling concepts have been proposed where liquid is circulated through a hot area, then through a radiator to dissipate the heat. These concepts are quite complex and the risk is very high: failure of an active cooling system could result in loss of a hypersonic vehicle within a few seconds. None has been demonstrated in flight. Although work is continuing on active cooling concepts, their application will probably not be realized for many years.
As we look ahead to the future of aviation, it is easy to merely assess the current fleet of successful aircraft or spacecraft, and decide on what improvements we can provide, without considering the history and evolution that produced these vehicles. T he danger is that some of the past problems will reappear unless the design and test communities are aware of their history. This paper has attempted to summarize some of the problems that have been encountered, and resolved, during the technology explosion in aviation that has occurred over the last 60 years. The manner in which the problems were discovered, the methods used to determine causes, and the final resolution or correction that was implemented have been presented. Hopefully these brief summaries of historical events will stimulate further research by our younger engineers and historians into the various subjects covered, and to that end, the following works are particularly relevant.