Motors

Hobby rockets are powered by commercially made rocket motors. Rocket motors work by expelling mass at high speed through a converging nozzle. This creates a force pushing the motor in the opposite direction, as described by Newton's Third Law. This force is the thrust a motor generates.

Most hobby motors contain a solid fuel, such as black powder, or Ammonium Perchlorate Composite Propellant (APCP). Other, less common motors use a combination of liquid and solid fuels, which are called hybrid motors. They work in much the same way, burning the fuel to create gases which flow out a nozzle.

Motor Classification
Motors are classified according to the total impulse they produce. A baseline A motor produces a total of 1.25-2.5 Newton-Seconds (N-s) of impulse. A through D motors are considered model rocket motors; E’s, F’s, and most G’s are considered mid-power rocketry motors; and a few G’s on up are considered high power rocketry motors. Each letter classification is twice as powerful as the last; for example, a D motor is twice as powerful as a C motor and eight times as powerful as an A motor.

Additionally, a motor is given a number designation that describes its average thrust in Newtons, then a hyphen and a number that indicates the time delay before the ejection charge fires. An example is an Estes B6-4 motor, which has a total impulse of between 2.51 and 5.0 N-s, has an average thrust of 6 N, and has a delay charge of 4 seconds from burnout to ejection. Some motors are plugged and use a P designation in place of the delay time. Other motors, called booster motors, have no ejection charge and use a 0 in place of the delay time. Booster motors are used in the lower stages of multi-stage rockets.