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You can see the principles of rocketry when you launch a model rocket.
Model rocketry is a fun and rewarding hobby. Participants in the hobby construct their own rockets, then fire them off using factory-made rocket motors. After a successful recovery, the rocket is then reloaded with another motor and
launched again.
Model Rocket Flight
What exactly happens when a rocket lifts off? First, when electricity is applied to the
igniter it sparks, causing the motor to ignite. During the first few critical milliseconds, the rocket is guided by the launch rod. After the rocket leaves the launch rod, it has enough velocity for the
fins to stabilize it.
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The rocket is boosted by the motor
propellant.
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When the engine
propellant has exhausted, the delay charge burns. During this period, the rocket is
cruising with no propulsion to its peak level.
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Next, the motor's ejection charge activates, issuing a stream of hot gas into the rocket, ejecting the nose cone and deploying the recovery device, which is usually a steamer (a ribbon) or a parachute.
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Finally, the rocket coasts back to ground and can be reused.
Model Rocket Structure
The structure of a model rocket is simple. It includes the following basic parts:
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Nose Cone - Usually plastic, reduces drag
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Shock Cord - Attaches nose cone to body tube, takes the shock of recovery device ejection
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Recovery Device - Usually a parachute or streamer, slows rocket down during descent
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Wadding - Flameproof, tissue-like substance that prevents recovery device from being scorched by ejection charge
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Thrust Ring - Prevents motor from being forced into rocket
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Motor - Primary function is to propel the rocket
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Fins - Stablizes rocket during flight
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Body Tube - encases motor, wadding, and the recovery device
Rocket Motors
The technical name of a device that propels a rocket is a motor, not an engine. Model rocket motors include
propellant, a delay charge, and an ejection charge inside them.
Rocket motors are rated using the following format: B6-4. The first letter indicates the total impulse of the motor, which is in newton-seconds. Each subsequent letter in the alphabet indicates double the total inpulse. For example, an "A" rated motor will give 0.01 to 2.5 newton-seconds. A "B" rated motor will give 2.51 to 5.0 newton-seconds. And so on.
The first number indicates average thrust in newtons, which is the approximate amount of thrust coming out A rocket with a low average thrust will burn longer than a rocket of the same total impulse with a higher average thrust.
Therefore, a C4-3 will burn longer than a C10-3, but will give less thrust. As a general rule of thumb, heavier rockets should have motors with higher average thrusts, and lighter rockets should have motors with lower average thrusts.
The number after the dash equals the delay charge in seconds. After the rocket propellant has burned out, this number indicates the number of seconds until the ejection charge fires. Heavier rockets should have lower delay charges than lighter rockets.
How to Start
So you're interested in model rocketry. You're eager to have fun learning about the principles behind rockets. All you have to do is to go out to the store, buy a launch pad, a launch controller, model rocket motors, and a model rocket kit.
The total cost will be approximately $20-$40, depending on the quality and degree of complexity of the rocket. Have
fun while you soar and explore!
For more information, see the following links.
Source: The Handbook of Model
Rocketry by G. Harry Stine.
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