Irving Family Web Pages: Rockets, Motors, and Clasifications

ockets and the laws associated with them are categorized according to liftoff weight and motor size. Rocket motors have letter designations based on their total impulse or power. An "A" motor produces a total impulse of 2.5 Newton seconds. (about 1/2 pound pressure for 1 second) Each subsequent letter designates a doubling of impulse, so a "B" motor produces 5 Newton seconds, a C motor produces 10, and so on. Below "A" there are the classifications "1/2 A" and "1/4 A".
Small model rockets must weigh less than one pound at liftoff and carry less than 113 grams of propellant. They are typically thin cardboard tubes with plastic or balsa fins and nose cones. The smallest ones climb only a couple hundred feet, and can be built by children from kits. Larger "small model rockets" may reach altitudes of a couple thousand feet or more and are a bit harder to build.
Small model rockets can be launched at community events in most metropolitan areas, and in any open field in some parts of the country. The motors typically use black powder for propellant. Motors up to size "D" contain less than 113 grams of propellant, and are therefore suitable for the "small model rocket" category. Most small motors are one-time-use cartridges.
Large model rockets weigh more than one pound at liftoff but less than 3.3 pounds. They must carry less than 125 grams of fuel. Large model rockets are usually made of cardboard like small model rockets, but the materials are stronger to be able to handle more powerful motors. The parachutes are typically nylon.
Large model rockets use motors in the range "E" through "G". The motors often use composite, solid rocket propellant instead of black powder. Composite fuel is more powerful by weight than black powder, and there are several types with different characteristics of impulse, sight, and sound.
High power rockets are those weighing more than 3.3 pounds or carrying more than 125 grams of fuel. They are made of strong composition materials and are often six or more feet tall. Some go miles high before coming down under brightly colored, nylon parachutes. They are very exciting to see and hear.
High power motors are "H" range and above. They traditionally employ composite, solid propellant, although hybrid fuels are now becoming common which use solid fuel with liquid nitrous oxide oxidizer. The upper end of high power rocketry is sometimes referred to as "ultra high power". These rockets are often more than 15 feet long and can weigh over a hundred pounds. They use motor sizes of "L" and above, and can only be launched at remote locations.
Regardless of size, all legal hobby rockets share a few things in common. They must all meet safety and construction standards; they must all have recovery systems to allow the rocket to descend safely to the ground; and they are all subject to a myriad of confusing and conflicting laws at the federal, state, and local levels.

Copyright © 1996 Donald J. Irving