Electric-circuit burning-clear and damage phenomena on aircraft structures

IT is generally accepted that the correct performance of the electric system is vital to the effective use of an airplane. Electric-wiring faults, such as short circuits resulting from gunfire or other causes, may result in faulty control or fire hazard. Experience has shown that on the commonly used 28.5-volt d-c systems such short circuits are often self-clearing, and serious consequences do not result. However, this is not always the case, and it is possible that a significant number of airplanes have not returned from the combat area because of damage to the electrical system. Accordingly, it was felt advisable to investigate the conditions under which faults may be expected to clear and to determine the magnitude of current and length of time required to cause serious damage to the aircraft structure when a short circuit occurs. It should be recognized that, in practice, where circuit protection is used the fault duration and damage may be limited by this protective equipment which would remove the faulty circuit from the system. Such protection was not used in the tests as they were intended to show the effects of short circuit where system protection was not involved. Circuit protection is discussed in a companion paper.
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