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model rocket motor classification
Motors for rockets〔NAR website: http://www.nar.org/safety-information/model-rocket-safety-code/〕 and high powered rockets〔NAR website: http://www.nar.org/safety-information/high-power-rocket-safety-code/〕 (together, consumer rockets) are classified by total impulse (power) into a set of letter-designated ranges, from ¼A up to O as the largest. Class A is from 1.26 newton-seconds (4.448 N per Lb.) 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. The letter (M) would represent the total impulse of between 5,120.01 and 10,240.00 N·s of impulse. Motors G and below are in the realm of model rocketry. Motors which would otherwise be classified beyond O are in the realm of amateur rocketry (in this context, the term ''amateur'' refers to the rocketeer's independence from an established commercial or government organization). Professional organizations use the nomenclature of average thrust and burning time.
== Rocket Motor Codes ==
The designation for a specific motor looks like C6-3. In this example, the letter (C) represents the total impulse range of the motor, the number (6) before the dash represents the average thrust in newtons (4.448 N per Lb.), and the number (3) after the dash represents the delay in seconds from propelling charge 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.
An innovation called ILP was adopted by motor manufacturers starting in about 1982 to further clarify the motor code, for example 120G40-8FS, where the total impulse in Newton-seconds precedes the code so the burning time can be computed from the provided numbers (120/40=3.0 sec) , followed by a letter designation denoting the style of propellants (Firestarter™ brand, sparky style).〔USR website FS photograph: http://v-serv.com/usr/motors/images/CinerocFS5.jpg〕 Other styles include white smoke (W), black smoke (J), red flame (R), green flame (G) and others. Each manufacturer self designates these letter codes. The remainder of the numbers and letters represent the result of batch testing with data collection. The ILP method is important because you might have a G motor in your model rocket but a G can be anywhere from 81 N-s to 160 N-s and that is a sufficient difference to shred (mechanically destroy from combined forces of thrust and drag) some model rockets.
The largest model rocket motor is a 160 N-s G according to NAR, TRA, and the NFPA codes (1122, 1125, 1127) they drafted and invented. Although the largest FAA exempt motor is a 125g propellant 240 N-s (53.95 Lb-sec, 195 ISP) APCP propellant H motor, so they could conceivably change the codes to include that if they choose. A nearly perfect efficiency APCP motor with an ISP of 230 would have 283 N-s with the FAA exempt propellant mass of 125g. (0.276 Lb.). An efficient BP propellant motor with an ISP of 80 would have 110 N-s (24.9 Lb-sec) with the FAA exempt propellant mass of 125g. (0.276 Lb.)
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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