Model rockets use a rocket motor for thrust, fins on the body for stability and a recovery system to bring the rocket back to the ground at safe speeds. A simple model may feature only a single stage, while more complex ones may have multiple stages, allowing them to reach higher altitudes.
Construction Rocket models look similar to their real world counterparts. They have a hollow body with stabilizing fins into which a motor fits. The body is topped off with a removable nose cone. Model rockets use non-metallic materials for construction, such as paper, wood or plastic. While most rocket motors are not reusable, the body of the rocket itself is often designed for multiple use.
Rocket motors Single-use rocket motors, or engines, often have cardboard bodies and clay nozzles, while reusable ones use aluminum casings with removable ends. Motors are commercially manufactured and come in different "impulse classes" ranging from A to O and beyond. However, engines that use black powder as a propellant usually stop at Class E. The upper limit of each class is double the upper limit of the class below it.
Motors are usually ignited remotely once the rocket is on the launchpad. As the propellant burns, it propels the model rocket into the air. Engines from a higher impulse class can propel rockets to higher altitudes. Alternatively, users can cluster two or more engines to generate more thrust.
Recovery systems Once a rocket reaches apogee, the highest point in its trajectory, an ejection charge blows the nose cone off and releases a parachute. The rocket then falls slowly back to the ground. While some ejection charges are timer-controlled, others use an altimeter to detect when a rocket is no longer climbing, triggering the charge automatically. Although parachutes are one of the most common recovery systems, others exist. Some examples include tumble, glide and helicopter recovery systems.