| Most small model rocket motors are | | | | motor has twice the total impulse of a |
| single-use engines, with cardboard | | | | given "B" motor, only that C motors are |
| bodies and lightweight molded ceramic | | | | in the 5.01-10.0 N-s range while "B" |
| nozzles, ranging in power class from 1 | | | | motors are in the 2.51-5.0 N-S range. |
| 8-A to E. They contain a black powder | | | | The designations "1/4 A" and "1/2 A" are |
| propellant. These engines do not exceed | | | | also used. For a more complete |
| the size of an E engine for black powder | | | | discussion of the letter codes, see |
| is very brittle. The bigger the motor, | | | | Model rocket motor classification. |
| the worse the problem becomes. If one | | | | For instance, a B6-4 motor from Estes |
| accidentaly drops a large black powder | | | | Corporation has a total impulse rating |
| motor on the ground, it may get a | | | | of 5.0 N-s. A C6-3 motor from Quest |
| hairline crack in it. That means that | | | | Industries has a total impulse of 8.5 |
| when it is launched, the motor will | | | | N-s. |
| burst open, and cause the model to crash | | | | The first number |
| and break, possibly causing a fire. | | | | The number that comes after the letter |
| Larger rocket motors are thus available, | | | | indicates the motor's average thrust, |
| using composite propellants made of | | | | measured in newtons. A higher thrust |
| ammonium perchlorate, potassium nitrate, | | | | will result in higher liftoff |
| aluminum powder, and a rubbery binder | | | | acceleration, and can be used to launch |
| substance contained in a hard plastic | | | | a heavier model. Within the same letter |
| case. This type of fuel is similar to | | | | class, a higher average thrust also |
| the solid fuel used in rocket boosters | | | | implies a shorter burn time (e.g., a B4 |
| of the space shuttle. These motors range | | | | motor will burn longer than a B6). |
| in impulse from the B to the O range. | | | | The Last Number |
| Composite motors produce more impulse | | | | The last number is the delay in seconds |
| per unit weight than do black powder | | | | between the end of the thrust phase and |
| motors. Also, the propellant is less | | | | ignition of the ejection charge. Black |
| fragile, resulting in few major | | | | Powder Motors that end in a zero have no |
| failures. | | | | delay or ejection charge. Such motors |
| Reloadable motors are also available. | | | | are typically used as first-stage motors |
| These are commercially-produced motors | | | | in multi-stage rockets as the lack of |
| requiring the user to put propellant | | | | delay element and cap permit burning |
| grains, o-rings and washers (to contain | | | | material to move forward and ignite an |
| the expanding gases), delay grains and | | | | upper-stage motor. |
| ejection charges into special | | | | A "P" indicates that the motor is |
| non-shattering aluminum motor casings | | | | "plugged". In this case, there is no |
| with screw-on or snap-in ends | | | | ejection charge, but a cap is in place. |
| (closures). The advantage of a | | | | A plugged motor can only be used in |
| reloadable motor is the cost: because | | | | rockets which do not need to deploy a |
| the main casing is reusable, reloads | | | | standard recovery system such as small |
| cost significantly less than single-use | | | | rockets which tumble or R/C glider |
| motors of the same impulse. Reloadable | | | | rockets. |
| motors are available from D through O | | | | Reloadable motors |
| class. | | | | Reloadable motors are specified in the |
| Motors are electrically ignited with a | | | | same manner as model rocket single-use |
| short length of pyrogen-coated nichrome, | | | | motors as described above. However, they |
| copper, or aluminum wire pushed into the | | | | have an additional designation which |
| nozzle and held in place with flameproof | | | | specifies both the diameter and maximum |
| wadding, rubber band, a plastic plug or | | | | total impulse of the motor casing in the |
| masking tape. On top of the propellant | | | | form of diameter/impulse. A reload |
| is a tracking delay charge which | | | | designed for a 29mm diameter case with a |
| produces smoke but essentially no thrust | | | | maximum total impulse of 60 |
| as the rocket slows down and arcs over. | | | | newton-seconds carries the designation |
| When the delay charge has burned | | | | 29/60 in addition to its impulse |
| through, it ignites an ejection charge, | | | | specification. |
| which is used to deploy the recovery | | | | Safety |
| system. | | | | Model rocketry is a safe and widespread |
| Meaning of numbers | | | | hobby. Individuals such as G. Harry |
| Model rocket motors produced by | | | | Stine and Vernon Estes helped ensure |
| companies like Estes Industries and | | | | this by developing and publishing the |
| Quest Aerospace are stamped with a code | | | | National Association of Rocketry Model |
| (such as A10-3T or B6-4) that tells | | | | Rocket Safety Codes (Model Rocket Safety |
| several things about of motor. | | | | Code, Radio Control Rocket Glider Safety |
| Motors are commercially available in | | | | Code, High Power Rocket Safety Code), |
| many sizes. The Quest Micro Maxx engines | | | | and by commercially producing safe, |
| are the smallest at a diameter of 6mm. | | | | professionally-designed and manufactured |
| The company Apogee made 10.5mm micro | | | | model rocket motors. |
| motors, but those were discontinued in | | | | Controversy in the United States |
| 2001. Estes then comes in with "T" | | | | Both amateur and model rocketry have |
| (Tiny) motors that are 13 mm in diameter | | | | come under controversy in the United |
| by 45 mm long, while standard A, B and C | | | | States following the terrorist attacks |
| motors are 18 mm in diameter by 70 mm | | | | on New York and Washington D.C., as |
| long. Larger C, D, and E class black | | | | federal and state authorities allege |
| powder motors are also available; they | | | | that model rockets can be modified to |
| are 24 mm in diameter and either 70 (C | | | | act as weapons. |
| and D motors) or 95 mm long (E motors). | | | | Authorities argue that all members of |
| Some motors, such as F and G single-use | | | | the hobby should have to be licensed and |
| motors are 29mm in diameter. High-power | | | | their purchases recorded and reported to |
| motors (usually reloadable) are | | | | federal agencies. Critics of such |
| available in 38mm, 54mm, 75mm, and 98mm | | | | policies, particularly those involved in |
| diameters. | | | | the hobby itself, argue that while |
| The letter | | | | building model rockets capable of going |
| The letter at the beginning of the code | | | | great distances is a relatively simple |
| indicates the motor's total impulse | | | | feat, guidance systems are exceedingly |
| range (commonly measured in | | | | difficult to design and expensive to |
| newton-seconds). Each letter in | | | | implement. |
| successive alphabetical order has up to | | | | The NAR and Tripoli continue to pursue |
| twice the power of the letter preceding | | | | litigation against the BATFE in the |
| it. This does not mean that a given "C" | | | | matter. |