A model rocket engine is used to power the flight of a model rocket in much the same way a real rocket motor powers the flight of space rockets and the space shuttle. The basic technology is the same, only at a smaller scale with much safer components, making model rocketry accessible to most everyone.
To unify the hobby, each model rocket engine is classified according to a Model Rocket Engine Classification standard, which indicates the amount of Impulse (e.g. the strength) of the engine. This classification is also used as part of the Model Rocket Engine Naming Convention which is used by almost every model rocket engine manufacturer when naming the rocket engines.
Most model rockets are powered by a single-use model rocket engine with a cardboard casing and molded nozzle. More powerful engines are constructed with a metal casing, and some of these are reloadable model rocket engines to save on the cost of a model rocket launch
Anatomy of a Model Rocket Engine
A model rocket engine is similar to a real rocket engine and consists of the motor casing, used to hold the engine together; the propellent which provides the thurst through the nozzle; a delay mechanism which is used to time the ignition of the ejection charge to deploy the recovery system.
- 1 : Nozzle
- 2 : Casing
- 3 : Propellant
- 4 : Delay Charge
- 5 : Ejection Charge
- 6 : End Cap
The propellant in most engines (A-class to a few E-class) is black powder. Black powder is difficult to use in large amounts safely, which limits the maximum size of a black powder engine to E-class. Model rocket engines of F-class and higher use a composite material for the propellant. Both composite and black powder engines can be found in D-class and E-class.
The motor casing is typically cardboard for smaller size engines since these are disposable single-use engines. Rocket engines that use composite material for the propellant use a metal of specialized plastic casing to handle the force of the propellant. Due to the higher cost of the metal casing, reloadable model rocket engines have been developed.
Reloadable Model Rocket Engines
A reloadable model rocket engine is a multi-use model rocket engine used for flying model rockets.
Most mid-power (D-class to G-class), and high-power (H-class through O-class), model rocket engines were originally custom made and difficult to produce. Technology and manufacturing improvements have made these engines more affordable to produce safely, but are still significantly more expensive than the cardboard cased lower power engines.
To make these engines more affordable, the reloadable model rocket engine was developed. The expensive metal rocket engine casing can be reused, saving much of the component cost. Since the reloads are assembled by the consumer, there is also savings from the labor cost of manufacturing a single-use engine.
Engine Classification and Naming
Classification
Engines for model rockets are classified based on the total impulse of the rocket engine. Classes A through G are for model rocketry, while classes H through O are for high power rocketry and require special certification and licensing.
| Classification | Impulse | Skill Levels | Typical Uses |
| 1/2A-class | .63-1.25 Newton-seconds | Skill Level 1 | kits, starter sets, launch sets |
| A-class | 1.26-2.50 Newton-seconds | Skill Level 1 | kits, starter sets, launch sets |
| B-class | 2.51-5.00 Newton-seconds | Skill Level 1 & 2 | kits, starter sets, launch sets |
| C-class | 5.01-10.00 Newton-seconds | Skill Level 1 & 2 & 3 | kits, starter sets |
| D-class | 10.01-20.00 Newton-seconds | Skill Level 2 & 3 | model rocket kits |
| E-class | 20.01-40.00 Newton-seconds | Skill Level 3 & 4 | model rocket kits |
| F-class | 40.01-80.00 Newton-seconds | Skill Level 4 | model rocket kits |
| G-class | 80.01-160.00 Newton-seconds | Skill Level 4 | model rocket kits |
Naming
For an example, a B6-4 model rocket engine would be:
- Class B (see the B-class engine definition, 2.51 to 5.00 Newton-Seconds of impulse)
- Provide 6 Newtons of thrust
- 3 second delay from burnout to the ejection charge
Please note that the last number can have a few variations:
- P means that the engine is plugged and there is no ejection charge.
- A value of 0 (zero) indicates this is a booster engine for a multi-stage model rocket.
External Resources
Testing and Certification
Model rocketry is a self-policed hobby, and model rocket engines are tested and certified by different organizations. Among them are
- National Association of Rocketry
- Tripoli Rocketry Association
- Canadian Association of Rocketry