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If you are starting into model rocketry, you may have been confused by the letters and numbers that are printed on the motor or on the motor package.  You may have asked yourself "Which motor should I use?" or "What do the numbers mean?".  Well, this is what I want explain.  The picture below shows typical motors used in sport rocketry.

Let's look into one in more detail.  For example, the B6-4 motor:

B  - The letter indicates the total impulse or total power produced by the engine. Each succeeding letter has twice the power of the previous letter.

Letters for motors range from  'A' to 'O' and indicates the range for the total impulse of the motor, not an exact value.  For instance; a 'B' motor would have a total impulse between 2.51 Newton/ seconds and 5.00 Newton/ seconds. The ranges for each letter are listed below:
As you can see, when the power doubles with each letter, it doesn't take long to reach very powerful motors.  A 'G' motor averages 64 times the power of an 'A' motor.  Motors ranging from 'H' to 'O' require special certification from either NAR or Tripoli to purchase and fly.


Code Newton/Seconds Code Newton/Seconds

½ A

0.656 to 1.25

H 160.01 to 320.00
1.26 to 2.40 I 320.01 to 640.00
B 2.51 to 5.00 J 640.01 to 1280.00
C 5.01 to 10.00 K 1280.01 to 2560.00
D 10.01 to 20.00 L 2560.00 to 5120.00
E 20.01 to 40.00 M 5120.01 to 10240.00
F 40.01 to 80.00 N 10240.01 to 20480.00
G 80.01 to 160.00 O 20480.01 to 40960.00

6 - The first number shows the engine's average thrust in Newton's or the average push exerted by the engine. (4.45 Newton's = 1 lb.) Average thrust = Newton-seconds divided by thrust duration.

Refer to the graph showing the thrust curve for the B6-4 motor:

As you can see, the initial thrust is higher than the listed average thrust.  This is typical of rocket motors.  To find out about the thrust curve for a particular motor, contact the manufacturer or search for the motor at http://www.thrustcurve.org.  All rocket motor manufacturers publish thrust curves for their motors.  The total thrust online casino will fall inside the range of the letter classification of the motor.  From the graph above, ?????? ????????? ???????? the average impulse is 6 Newtons and the burn out occurs at about 0.8 seconds.  The total impulse would be 4.8 Newton/ seconds, which falls inside the range of 2.51 to 5.00 Newton/ seconds.  This same calculation can be derived from most manufacturers' thrust curves.

4 - The second number of seconds between the end of thrusting and the ejection charge.

This number is placed on the motor for the rocket flyer to use to determine the delay desired for deployment of the recovery system (streamer, parachute, etc.).  This usually depends on the weight of the rocket.  A lighter rocket may want a longer delay because the rocket will coast higher before slowing to a safe ejection speed, while a heavier rocket will slow faster and need a shorter delay.  Some motors, known as boosters, have a '0' for the delay time indicating that they have no delay.  These motors are used for the lower stages of multiple stage rockets.  This is desirable because you want a lower stage to immediately ignite the next stage when it burns out.  Be careful not to use a booster motor in a single stage rocket since the recovery system will deploy immediately when the motor burns out.

The motor code provides information for the rocket flyer to use to determine how best to fly his/her rocket in the safest possible mano