Editing Model rocket (section)

==Model rocket motors==
{| style="float:right;"
|[[Image:Model-rocket-engine.svg|thumb|left| Anatomy of a basic black-powder model rocket motor. A typical motor is about {{convert|7|cm|in|abbr=on}} long.<br>
1. Nozzle<br>
2. Case<br>
3. Propellant<br>
4. Delay charge<br>
5. Ejection charge<br>
6. End cap]]
|}

Most small model rocket motors are single-use engines, with cardboard bodies and lightweight molded clay nozzles, ranging in [[Model rocket motor classification|impulse class]] from fractional A to G. Model rockets generally use commercially manufactured [[Black powder rocket motor|black-powder motors]]. These motors are tested and certified by the [[National Association of Rocketry]], the [[Tripoli Rocketry Association]] (TRA) or the [[Canadian Association of Rocketry]] (CAR). Black-powder motors come in impulse ranges from 1/8A to F.
[[File:G64 rocket motor components.jpg|thumb|left|300px|alt=G64-10W Reload| The components of a motor made by Aerotech Consumer Aerospace for a 29/40-120 casing.<br> 
1. Motor Casing<br>
2. Aft Closure<br> 
3. Forward Closure<br>
4. Propellant Liner<br>
5. Propellant Grains (C-Slot Geometry)<br> 
6. Delay Insulator<br>
7. Delay Grain and Delay Spacer<br>
8. Black Powder Ejection Charge<br>
9. Delay O-Ring<br>
10 & 11. Forward and Aft O-Rings<br>
12. Forward Insulator<br>
13. Nozzle<br> 
14. Electric Igniter]]
The physically largest black-powder model rocket motors are typically F-class, as [[black powder]] is very brittle. If a large black-powder motor is the upper stage motor of a rocket that exceeds the maximum recommended takeoff weight, or is dropped or exposed to many heating/cooling cycles (e.g., in a closed vehicle exposed to high heat or a storage area with inconsistent temperature control), the propellant charge may develop hairline fractures. These fractures increase the surface area of the propellant, so that when the motor is ignited, the propellant burns much faster and produces greater than normal internal chamber pressure inside the engine. This pressure may exceed the strength of the paper case and cause the motor to burst. A bursting motor can cause damage to the model rocket ranging from a simple ruptured motor tube or body tube to the violent ejection (and occasionally ignition) of the recovery system.

Therefore, rocket motors with power ratings higher than D to F customarily use [[composite propellant]]s made of [[ammonium perchlorate]], [[aluminium]] powder, and a rubbery [[binder (material)|binder]] substance contained in a hard plastic case. This type of propellant is similar to that used in the solid rocket boosters of the [[Space Shuttle]] and is not as fragile as black powder, increasing motor reliability and resistance to fractures in the propellant. These motors 
range in [[Model rocket motor classification|impulse]] from size A to O. Composite motors produce more impulse per unit weight ([[specific impulse]]) than do black-powder motors.

Reloadable composite-propellant motors are also available. These are commercially produced motors requiring the user to assemble propellant grains, [[o-ring]]s and [[washer (mechanical)|washer]]s (to contain the expanding gases), [[delay charge|delay grains]] and [[ejection charge]]s into special non-shattering aluminum motor casings with screw-on or snap-in ends (closures). The advantage of a reloadable motor is the cost: firstly, because the main casing is reusable, reloads cost significantly less than single-use motors of the same impulse. Secondly, assembly of larger composite engines is labor-intensive and difficult to automate; off-loading this task on the consumer results in a cost savings. Reloadable motors are available from D through O class.

Motors are electrically ignited with an [[electric match]] consisting of a short length of [[pyrogen (pyrotechnics)|pyrogen]]-coated [[nichrome]], [[copper]], or [[aluminum]] [[bridgewire]] pushed into the [[nozzle]] and held in place with flameproof wadding, a rubber band, a plastic plug or masking tape. On top of the propellant is a tracking [[delay charge]], which [[smoke composition|produces smoke]] but in essence no [[thrust]], as the rocket slows down and arcs over. When the delay charge has burned through, it ignites an [[ejection charge]], which is used to deploy the recovery system.

Model rocket motors mostly don't offer any sort of [[thrust vectoring]], instead just relying on fins at the base to keep the vehicle aerodynamically stable. Some rockets do however have thrust vectoring control (TVC) by gimbaling the motor itself rather than the nozzle. This is done on some rockets built by many model rocket builders, the most notable of which is BPS.space.