1.6 What do the letters and numbers on a model rocket motor mean?
Description
This article is from the Model Rockets FAQ, by Wolfram von Kiparski with numerous contributions by others.
1.6 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 propellant or have more
than 160NS of total impulse are considered High Power motors. You must
be certified to purchase and fly these motors. Soon, it may also become
necessary to have a license to store high power motors.
Andrew Mossberg (aem@hypertek.com) recently posted this chart to
rmr, which includes approximate propellant weights for maximum impulse
motors for each class:
P
O
W Low High Low High 200 ISP Propellant
E Limit Limit Limit Limit Weight
R (NtSec) (NtSec) (lbsSec) (lbsSec) (grams) (lbs)
= ======= ======== ========= ========= ======== =======
A 1.26 2.5 0.28 0.56 1.3 0.0028
B 2.51 5.0 0.56 1.12 2.5 0.0056
C 5.01 10.0 1.13 2.25 5 0.0112
D 10.01 20.0 2.25 4.5 10 0.02
E 20.01 40.0 4.5 9 20 0.04
F 40.01 80.0 9 18 41 0.09
G 80.01 160.0 18 36 82 0.18
H 160.01 320.0 36 72 163 0.36
I 320.01 640.0 72 144 326 0.72
J 640.01 1,280.0 144 288 652 1.44
K 1280.01 2,560.0 288 575 1,305 2.88
L 2560.01 5,120.0 575 1,151 2,609 5.75
M 5120.01 10,240.0 1,151 2,301 5,219 11.5
N 10240.01 20,480.0 2,301 4,602 10,438 23.0
O 20480.01 40,960.0 4,602 9,204 20,875 46.0
P 40960.01 81,920.0 9,204 18,409 41,751 92.0
Currently, consumer rocketry stops at rockets with a total of no more
than 81,920NS of total impulse. Anything larger than that is by
definition an amateur rocket.
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