Model rocket motor classification

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Motors for model rockets and high powered rockets are classified by total impulse into a set of letter-designated ranges, from A (the smallest, though 1/2, 1/4, and 1/8-A motors are also available), up to O as the largest. A is from 1.26 newton-seconds to 2.5 N·s, and each class is then double the total impulse of the preceding class, with B being 2.51 to 5.00 N·s.

The designation for a specific motor looks like C6-3. In this example, the letter (C) represents the total impulse of the motor, the number (6) before the dash represents the average thrust in newtons, and the number (3) after the dash represents the delay from motor burnout to the firing of the ejection charge (a gas generator composition, usually black powder, designed to deploy the recovery system). So a C6-3 motor would have between 5.01 and 10 N·s of impulse, produce 6 N average thrust, and fire an ejection charge 3 seconds after burnout.

  Class Total Impulse
(Metric Standard)		 Total Impulse
(Imperial Standard)
A 1.26-2.50 N·s 0.29-0.56 lbf·s
B 2.51-5.00 N·s 0.57-1.12 lbf·s
C 5.01-10.00 N·s 1.13-2.24 lbf·s
D 10.01-20.00 N·s 2.25-4.48 lbf·s
E 20.01-40.00 N·s 4.49-8.96 lbf·s
F 40.01-80.00 N·s 8.97-17.92 lbf·s
G 80.01-160.00 N·s 17.93-35.96 lbf·s
H 160.01-320.00 N·s 35.97-71.92 lbf·s
I 320.01-640.00 N·s 71.93-143.83 lbf·s
J 640.01-1280.00 N·s 143.84-287.65 lbf·s
K 1,280.01-2,560.00 N·s 287.66-575.30 lbf·s
L 2,560.01-5,120.00 N·s 575.31-1150.60 lbf·s
M 5,120.01-10,240.00 N·s 1150.61-2301.20 lbf·s
N 10,240.01-20,480.00 N·s 2301.21-4602.40 lbf·s
O 20,480.01-40,960.00 N·s 4602.41-9204.80 lbf·s

The letter-scale continues past class-O, beyond the domain of high-power rocketry. Motors and vehicles of such size and power are generally considered the domain of amateur rocketry. (In this context, the term amateur refers to the rocketeer's independence from an established commercial or government organization.)

In many countries, the sale, possession, and use of model rocket motors is subject to governmental rules and regulations. For example, in the United States, high-powered motors (above 160 newton seconds) are restricted to citizens who possess the requisite certification and permits. In North America, the two recognized organizations that provide high-power certifications are Tripoli Rocketry Association and the National Association of Rocketry, both of these organizations have three levels of certification which involves building progressively more complex and higher powered rockets and taking a test of safety rules and regulations. The U.S. government regulatory documents surrounding high-powered rocketry are FAA FAR Part 101 and NFPA 1127. In Canada the Canadian Association of Rocketry has a 4 step certification process, but all three organizations accept the other's certifications if a flyer shows up at a high-power launch and wishes to fly under their sanction. Some states restrict the maximum impulse to a G motor.

Level 1 certification qualifies you to purchase and use H and I engines, Level 2 certification J, K, and L engines and Level 3 certification M, N, and O engines. Note: Canada adds another step in between, and has a Level 4 which is the same as US Level 3.

Current BATF laws established since September 11, 2001, required that an individual must hold a Low explosive Users Permit (LEUP) to have a high-powered motor in their possession. The BATF does an intrusive background check and home inspection before issuing a LEUP. TRA and NAR have an ongoing joint law suit to remove this restriction. Until then, rocketeers must buy their HP motors from a vendor, who has a LEUP, at the launch site and fly them the same day. The new laws and court case have dampened the amount of young people joining the launches. Most 18 year olds cannot get their parents enthused about government background checks, a LEUP and intrusive home inspections.

Many, many high power rocketeers have read the book by G. Harry Stine, Handbook of Model Rocketry [4th Ed.], Follett Publishing. One of the prevailing attitudes or spirits in hobby rocketry is "pay it forward". Experienced fliers tend to spend much time and energy "repaying" the newcomer fliers with the help and education they themselves were provided by the oldtimers who mentored them. If a seasoned veternan helps you load a motor case or fan-fold your first parachute shock-cord, they most frequently say don't thank me, just pay it forward to the new guys in the future. This long-standing tradition in mid-power, high-power and amateur rocketry makes the sport enjoyable and provides a faster, higher, more in-depth learning curve for everyone.[citation needed]

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