Motor nomenclature

Motor nomenclature

Model rocket motors produced by companies like Estes Industries and Quest Aerospace are stamped with a code (such as A10-3T or B6-4) that indicates multiple things about the motor.
The Quest Micro Maxx engines are the smallest at a diameter of 6mm. The company Apogee Components made 10.5mm micro motors, but those were discontinual in 2001. Estes manufactures size "T" (Tiny) motors that are 13 mm in diameter by 45 mm long, while standard A, B and C motors are 18 mm in diameter by 70 mm long. Larger C, D, and E class black powder motors are also available; they are 24 mm in diameter and either 70 (C and D motors) or 95 mm long (E motors). Some motors, such as F and G single-use motors, are 29mm in diameter. High-power motors (most commonly reloadable) are available in 38mm, 54mm, 75mm, and 98mm diameters.

First letter

The letter at the beginning of the code indicates the motor's total impulse range (generally measured in newton-seconds). Each letter in successive alphabetical order has up to two times the impulse of the letter preceding it. This doesn't mean that a given "C" motor has two times the total impulse of a given "B" motor, only that C motors are in the 5.01-10.0 N-s range while "B" motors are in the 2.51-5.0 N-S range. The designations "1/4A" and "1/2A" are also used. For a more complete discussion of the letter codes, see Model rocket motor classification.
For instance, a B6-4 motor from Estes-Cox Corporation has a total impulse rating of 5.0 N-s. A C6-3 motor from Quest Aerospace has a total impulse of 8.5 N-s.

First number

The number that comes after the letter indicates the motor's average thrust, measured in newtons. A higher thrust will result in higher liftoff acceleration, and can be used to launch a heavier model. Within the same letter class, a higher average thrust also implies a shorter burn time (for example, a B6 motor will not burn as long as but have more initial thrust than a B4).Motors inside the same letter class that have different first numbers are most commonly for rockets with different weights.As an example a heavier rocket would require a engine with more initial thrust to get it off of the launch pad, where as a lighter rocket would need less initial thrust and would sustain a longer burn reaching higher altitudes.

Last number

The last number is the delay in seconds between the end of the thrust phase and ignition of the ejection charge. Black Powder Motors that end in a zero have no delay or ejection charge. Such motors are generally used as first-stage motors in multistage rockets as a lack of delay component and cap permit burning material to burst forward and ignite an upper-stage motor.
A "P" indicates that the motor is "plugged". In this case, there is no ejection charge, but a cap is in place. A plugged motor is used in rockets which do not need to deploy a standard recovery system such as small rockets which tumble or R/C glider rockets. Plugged motors are also used in huger rockets, where electronic altimeters or timers are used to trigger the deployment of the recovery system.
Composite motors most commonly have a letter or combination of letters after the delay length indicating which of the manufacturer's different propellant formulations is used in that particular motor.

Reloadable motors

Reloadable motors are specified in the same manner as model rocket single-use motors as described above. , they have an additional designation which specifies both the diameter and maximum total impulse of the motor casing in the form of diameter/impulse. A reload created for a 29mm diameter case with a maximum total impulse of 60 newton-seconds carries the designation 29/60 in addition to its impulse specification.

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