Finally, the Ejection charge is ignited. It activates the recovery system. Model Rocket Engines have three characteristics, which are stated on each engine in the form of a three digit identification code. The letter indicates the total impulse range of the engine. Total impulse is the total amount of power the engine produces, which basically indicates how much propellant it contains.
Total impulse is measure in Newton seconds.
One Newton second is the amount of total impulse by one Newton of thrust for a duration of one second. All Estes engine have the maximum total impulse power permitted for a given size. The first number states the average thrust that the engine delivers during the thrust phase. The actual thrust varies, and is shown on the time thrust curve. The second number show the time delay.