Once the engine had been started and the temperature rose to the minimum operating level, the external air hose and connectors were removed and the resonant design of the tailpipe kept the pulse jet firing. Each cycle or pulse of the engine began with the shutters open; fuel was injected behind them and ignited, and the resulting expansion of gases forced the shutters closed. As the pressure in the engine dropped following combustion, the shutters reopened and the cycle was repeated, roughly 45 to 55 times per second. The electrical ignition system was needed only to start the engine - a V-1 carried no coils or magnetos to power the spark plug once launched.