What do the letters and numbers on a model rocket motor mean?
The NAR has developed a motors classification scheme which has been mandated by NFPA 1122 and most state regulations. This system specifies the motors total impulse class, average thrust, and ejection charge delay. This is printed on any motors certified by the NAR. the pieces are as follows, given the example: E15-10W The first letter indicates the power range, as specified in the table below. The number to the left of the dash is the average thrust of the motor, in newtons. The number to the right of the dash is the approximate ejection delay in seconds starting at the time of motor burnout. The final letter is an optional manufacturer designation for motor or fuel type. Note that letter designating total impulse of the motor specifies an impulse *range*, not an exact total impulse. For example, there are G motors that have anywhere from 90 to 160 NS of total impulse….an Aerotech G42 is rated at 90NS and a G40 is rated at 120NS. Motors with more than either 62.5 grams of total prop
