Performance
The impulse (area under the thrust-time curve) of a model motor is used to determine its class. Motors are divided into classes from 1/4A to O and beyond. Black powder rocket motors are only commonly produced up to Class E. Each classes upper limit is double the upper limit of the previous classes. Low power rockets only use motors that are G and below. Rockets using motors with a greater impulse are considered high power rockets.
| Class | Total Impulse (Metric Standard) |
|---|---|
| 1/4A | 0.313-0.625 N·s |
| 1/2A | 0.626-1.25 N·s |
| A | 1.26-2.50 N·s |
| B | 2.51-5.0 N·s |
| C | 5.01-10 N·s |
| D | 10.01-20 N·s |
| E | 20.01-40 N·s |
| F | 40.01-80 N·s |
| G | 80.01-160 N·s |
Figures from tests of Estes rocket motors are used in the following examples of rocket motor performance.
For miniature black powder rocket motors (13 mm diameter), the maximum thrust is between 5 and 12 N, the total impulse is between .5 and 2.2 Ns, and the burn time is between .25 and 1 second. For Estes ‘regular size’ rocket motors (18 mm diameter), there are three classes: A, B, and C. The A class 18 mm motors have a maximum thrust between 9.5 and 9.75 N, a total impulse between 2.1 and 2.3 Ns, and a burn time between .5 and .75 seconds. The B class 18 mm motors have a maximum thrust between 12.15 and 12.75 N, a total impulse between 4.2 and 4.35 Ns, and a burn time between .85 and 1 second. The C class 18mm motors have a maximum thrust from 14 – 14.15 N, a total impulse between 8.8 and 9 Ns, and a burn time between 1.85 and 2 seconds.
There are also 3 classes included in Estes large (24 mm diameter) rocket motors: C, D, and E. The C class 24 mm motors have a maximum thrust between 21.6 and 21.75 N, a total impulse of between 8.8 and 9 Ns, and a burn time between .8 and .85 seconds. The D class 24 mm motors have a maximum thrust between 29.7 and 29.8 N, a total impulse between 16.7 and 16.85 Ns, and a burn time between 1.6 and 1.7 seconds. The E class 24 mm motors have a maximum thrust between 19.4 and 19.5 N, a total impulse between 28.45 and 28.6 Ns, and a burn time between 3 and 3.1 seconds.
Several independent sources have published measurements showing that Estes model rocket engines often fail to meet their published thrust specifications.
Read more about this topic: Model Rocket
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