Model rocket motor classification
Encyclopedia
Motors for model rocket
s and high powered rocket
s are classified by total impulse into a set of letter-designated ranges, from A (the smallest, though ½A, ¼A, and ⅛A motors are also available), up to O as the largest. Class A is from 1.26 newton-second
s to 2.5 N·s, and each class is then double the total impulse of the preceding class, with Class B being 2.51 to 5.00 N·s.
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.
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.)
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 is FAA FAR Part 101. With the general Association bodies using TRA and NFPA 1127 safetycodes. In Canada the Canadian Association of Rocketry has a four-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, and have adopted NFPA safety codes for launch site requirements.
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.
In the late 1990s, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives
began demanding that individuals obtain a Low Explosives Users Permit (LEUP) to possess and use high-powered motors. On February 11, 2000, Tripoli Rocketry Association, Inc. and the National Association of Rocketry filed suit in the United States District Court for the District of Columbia claiming that the BATF applied "onerous and prohibitive civil regulations" against sport rocketry hobbyists due to the Bureau's improper designation of Ammonium Perchlorate Composite Propellant (APCP) as an explosive. APCP is used in most high-power rocket motors.
In 2009, the court ruled in favor of the hobby organizations and ordered the BATF to remove APCP from its list of regulated explosives.
Model rocket
A model rocket is a small rocket that is commonly advertised as being able to be launched by anybody, to, in general, low altitudes and recovered by a variety of means....
s and high powered rocket
High powered rocket
High-power rocketry is a hobby similar to model rocketry. The major difference is that higher impulse range motors are used. The National Fire Protection Association definition of a high-power rocket is one that has a total weight of more than 1500 grams and contains a motor or motors...
s are classified by total impulse into a set of letter-designated ranges, from A (the smallest, though ½A, ¼A, and ⅛A motors are also available), up to O as the largest. Class A is from 1.26 newton-second
Newton-second
The newton-second or newton second is the derived SI unit of impulse and momentum. It can also be expressed as the kilogram metre per second...
s to 2.5 N·s, and each class is then double the total impulse of the preceding class, with Class B being 2.51 to 5.00 N·s.
Model rocket motor codes
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 thrustThrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
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
Gas generator
A gas generator usually refers to a device, often similar to a solid rocket or a liquid rocket that burns to produce large volumes of relatively cool gas, instead of maximizing the temperature and specific impulse. The low temperature allows the gas to be put to use more easily in many...
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.
Motor impulse by Class
| Class | Total Impulse (Metric Standard) |
Total Impulse (Imperial Standard) |
|---|---|---|
| A | 1.26-2.50 N·s | 0.29-0.56 lbf·s |
| B | 2.51-5.0 N·s | 0.57-1.12 lbf·s |
| C | 5.01-10 N·s | 1.13-2.24 lbf·s |
| D | 10.01-20 N·s | 2.25-4.48 lbf·s |
| E | 20.01-40 N·s | 4.49-8.96 lbf·s |
| F | 40.01-80 N·s | 8.97-17.92 lbf·s |
| G | 80.01-160 N·s | 17.93-35.96 lbf·s |
| H | 160.01-320 N·s | 35.97-71.92 lbf·s |
| I | 320.01-640 N·s | 71.93-143.83 lbf·s |
| J | 640.01-1280 N·s | 143.84-287.65 lbf·s |
| K | 1,280.01-2,560 N·s | 287.66-575.3 lbf·s |
| L | 2,560.01-5,120 N·s | 575.31-1150.6 lbf·s |
| M | 5,120.01-10,240 N·s | 1150.61-2301.2 lbf·s |
| N | 10,240.01-20,480 N·s | 2301.21-4602.4 lbf·s |
| O | 20,480.01-40,960 N·s | 4602.41-9204.8 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
Amateur rocketry
Amateur rocketry, sometimes known as amateur experimental rocketry or experimental rocketry is a hobby in which participants experiment with fuels and make their own rocket motors, launching a wide variety of types and sizes of rockets...
. (In this context, the term amateur refers to the rocketeer's independence from an established commercial or government organization.)
Governmental regulation
In many countries, the sale, possession, and use of model rocket motors is subject to governmental rules and regulations. High-Power rockets in the United States, are only federally regulated in their flight guidelines by the FAA. However, the motor manufacturers and National Rocketry Organizations have established a self regulating industry through the outside help of National Fire Protection Association - NFPA. This self regulation of industry requires a user to become certified for use before a manufacturer will sell him a motor. In North America, the two recognized organizations that provide high-power certifications are Tripoli Rocketry AssociationTripoli Rocketry Association
The Tripoli Rocketry Association is one of the two major organizing bodies for high power rocketry in the United States. It was founded in 1964 in the Pittsburgh, PA region as a high school science club, integrating both rocketry and space science...
and the National Association of Rocketry
National Association of Rocketry
The National Association of Rocketry is the governing body for the sport/hobby of model rocketry in the United States. It was established in 1957 by Orville Carlisle and G. Harry Stine and is currently headed by Trip Barber. It is the oldest and largest model rocketry governing body in the...
, 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 is FAA FAR Part 101. With the general Association bodies using TRA and NFPA 1127 safetycodes. In Canada the Canadian Association of Rocketry has a four-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, and have adopted NFPA safety codes for launch site requirements.
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.
In the late 1990s, the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives
Bureau of Alcohol, Tobacco, Firearms and Explosives
The Bureau of Alcohol, Tobacco, Firearms and Explosives is a federal law enforcement organization within the United States Department of Justice...
began demanding that individuals obtain a Low Explosives Users Permit (LEUP) to possess and use high-powered motors. On February 11, 2000, Tripoli Rocketry Association, Inc. and the National Association of Rocketry filed suit in the United States District Court for the District of Columbia claiming that the BATF applied "onerous and prohibitive civil regulations" against sport rocketry hobbyists due to the Bureau's improper designation of Ammonium Perchlorate Composite Propellant (APCP) as an explosive. APCP is used in most high-power rocket motors.
In 2009, the court ruled in favor of the hobby organizations and ordered the BATF to remove APCP from its list of regulated explosives.