Shortcomings of Mica Insulation for Aviation Spark Plugs

THIS paper deals with the reasons for adopting mica as a spark-plug insulator, and its ultimate failure as demands on reliability and engine performance have increased.

The author points out in detail the mechanical make-up of an aviation spark plug, and the role the mica plays in the assembly, and its inability to function properly because of its characteristics.

It is suggested that the design features giving good account of themselves in the present type plug be retained if new insulating materials be proposed.

It is shown that the spark plug often is blamed for defects in the current-distributing system when the trouble may not be seated in the plug at all.