You don't need to be a rocket scientist to launch a model rocket into the air. If you want to understand the mechanics of the engine, though, it might not be a bad idea to do some science research. A model rocket engine is a scientific device that produces thrust in the same way a big rocket would. The solid propellant burns, producing gases, and these gases are expelled through a nozzle. When these gases exit at supersonic velocities, they produce thrust in the opposite direction (Newton's Second Law of Motion). This law states that acceleration is produced when a force acts on a mass. The greater the mass of the object being accelerated, the greater the amount of force needed to accelerate the object.
Thrust isn't the only important thing an engine provides. If the high-powered rocket engine simply produces thrust then ejects the parachute, the parachute would be ripped to shreds due to the two or three hundred miles per hour the rocket was traveling. Instead, the rocket engine has a special slow-burning delay material, which produces dense smoke and causes the rocket to coast. Once coasting is finished, the ejection charge is initiated, and this ejects a large volume of gas, which rushes into the forward part of the rocket and pushes out the parachute.
Here is an illustrated step-by-step process of how the engine works.
1. An igniter is inserted into the engine and held with a wire plug. Clips from the launch controller are attached onto the wire. When electricity begins to flow, the wire heats up, causing the tip to burst into flames.
2. The black-powder propellant quickly burns and creates thrust.
3. After the propellant is consumed, the delay composition starts burning, not producing thrust. This is where the rocket coasts. A trail of black smoke helps you to see the rocket.
4. At the end of coasting, the ejection charge ignites. The fast burning ejection over-pressurizes the case and bursts through a clay cap. This also pushes off the nose cone and ejects the parachute. The engine cannot be reused.
These types of engines are single-use engines, but they are effective enough to reach heights of almost 3,000 feet. There are several types of engines, but your model rocket kit will tell you which ones are compatible with the rocket you're using. Also, many rockets require that you use a lower-powered engine on the initial flight. These have less thrust and let see if you manufactured the rocket correctly without exposing it to the harsher forces of a more powerful rocket. Once your rocket is ready, let it launch into the air. And if anyone asks you how the engine works, you can impress them with your rocket-science answer.