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Model Rockets & Model Rocket Parts

A model rocket is propelled by a motor which produces thrust, a delay for coasting and a ejection charge to activate the recovery system. The rocket motor is mounted in the body tube or in a motor mount inside the body tube.  At launch, model rockets are initially guided straight up by a launch rod which runs through one or more launch lugs attached to the side of body tube of the rocket.

The model rockets nose cone is shaped to reduce air drag at the front of the rocket and to seal the front of the body tube and the recovery system inside the rocket body tube. The model rockets fins give stability so that the flight is straight and forward. The larger the fins the farther the center of pressure is to the rear of the model rocket. The heavier the rocket motor the farther the center of gravity is to the rear. The center of gravity must be farther forward than the center of pressure for good flight stability.

The center of pressure is defined as the the center of all the drag forces in action on the model rocket. Drag is defined as induced and parasitic. Induced drag is the drag produced by surface not parallel to the direction flight. Parasitic drag is the drag force of the skin. The induced and parasitic drag can both be reduced by rounding the leading edges of the fins of the model rocket and choosing a good nose cone shape. Parasitic drag can also be reduced by filling all the rough surfaces on the fins and finishing with a good glossy coat of paint.

The center of gravity can be moved forward by adding weight as far forward as possible, such as inside or attached to the nose cone. It can also be moved forward by reducing weight at the rear of the fin section by using lighter fin material, reducing the weight of the motor mount or the motor and also by making the rockets body tube longer. Adding swept back fins will also move the center of pressure back and increase the stability of the rocket during flight.

For more information you can go to the web site at the NASA Glen Research Center.
Another good web site for information is at the National Association of Rocketry.

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Model Rockets & Model Rocket