Editing Model rocket (section)

==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 typically only manufactured up to Class F. Each class's upper limit is double the upper limit of the previous class.
Model rockets only use motors that are class G and below.<ref>{{cite web |url=http://www.nar.org/modrocs.html |title=National Association of Rocketry |access-date=2013-09-25 |url-status=dead |archive-url=https://web.archive.org/web/20130928000247/http://www.nar.org/modrocs.html |archive-date=2013-09-28 }}</ref> Rockets using motors with a greater impulse are considered [[high power rockets]].

{| class="wikitable" style="text-align:center; float:right;"
|-
! align=right|&nbsp;Class
! Total Impulse<br> (Metric Standard)
|- style="text-align:right;"
| 1/4A || 0.313-0.625 N·s
|- style="text-align:right;"
| 1/2A || 0.626-1.25 N·s
|- style="text-align:right;"
| A || 1.26-2.50 N·s
|- style="text-align:right;"
| B || 2.51-5.0 N·s
|- style="text-align:right;"
| C || 5.01-10 N·s
|- style="text-align:right;"
| D || 10.01-20 N·s
|- style="text-align:right;"
| E || 20.01-40 N·s
|- style="text-align:right;"
| F || 40.01-80 N·s
|- style="text-align:right;"
| G || 80.01-160 N·s
|}

Figures from tests of Estes rocket motors are used in the following examples of rocket motor performance.<ref name=Apogee>{{Cite web|url=http://www.apogeerockets.com/estes_items.asp|title = Estes Motors : Apogee Rockets, Model Rocketry Excitement Starts Here}}</ref>

For miniature black powder rocket motors (13&nbsp;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&nbsp;mm diameter), there are three classes: A, B, and C. The A class 18&nbsp;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&nbsp;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&nbsp;mm diameter) rocket motors: C, D, and E. The C class 24&nbsp;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&nbsp;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&nbsp;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.  Estes has also released a line of 29mm black powder E and F motors.  The 29mm E produces 33.4 Newton-seconds of total impulse over a 2.1 second burn, and the F produces 49.6 Newton-seconds over a 3.45 second burn.

Several independent sources have published measurements showing that Estes model rocket engines often fail to meet their published thrust specifications.<ref name="TPT">Penn, Kim and William V. Slaton, Measuring Model Rocket Engine Thrust Curves, The Physics Teacher &ndash; December 2010 &ndash; Volume 48, Issue 9, pp. 591.</ref><ref name="Carter">[http://seit.unsw.adfa.edu.au/ojs/index.php/juer/article/download/108/69 An Investigation into the Combustion and Performance of Small Solid-Propellant Rocket Motors] M.G. Carter. University of New South Wales at the Australian Defence Force Academy. 2008.</ref><ref name = "Courtney">[https://arxiv.org/abs/0903.1555 Measuring thrust and predicting trajectory in model rocketry] M. Courtney and A. Courtney. Cornell University Library. 2009.</ref>