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Saturday, June 23, 2012 - Model Rockets

WHAT IS A MODEL ROCKET?

Constructed of lightweight materials and propelled skyward with commercially available model rocket motors, it is "rocket science in miniature".

 

 

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IS IT SAFE?

Very! The hobby has enjoyed decades of fun and launched hundreds of millions of Model Rockets without major incident.

The key to Model Rocketry's enviable safety record is due to three primary factors; the materials used in construction, the safety and reliability of commercially made engines and igniters, and the consistent implementation of the Model Rocket Safety Code.

If you follow the Model Rocket Safety Code, Model Rockets are as safe as any other hobby.

PARTS OF A MODEL ROCKET

A model rocket is constructed of lightweight materials; typically cardboard, paper, plastic and balsa wood.They may weigh anywhere from tens of grams to 1 ½ kilograms; although typical model rockets weigh in at well under 150 grams (5 ¼ oz).

A "typical" model rocket consists of; a body tube or airframe, nosecone, fins, a recovery system, recovery wadding, shock cord, launch lug, and a rocket engine or motor.

The nosecone and body tube provide a container for holding the recovery system, recovery wadding, rocket engine and payload (if one is present).

Fins add aerodynamic stability to the shape, and keep your rocket flying in the direction it is pointed.

A launch lug, is an external attachment on the rocket's body tube which allows the rocket to follow a guide rod or rail to keep it flying straight and directed during the first few fractions of a second of flight.

The "recovery system" is usually a parachute or streamer which retards the rockets fall back to earth. After all, one of the unique features of model rocketry over their larger "real" counterparts is the fact that a model rocket can be flown over and over again.

Recovery wadding is flameproof material which prevents the rocket engine's ejection charge from damaging the recovery system.

The shockcord, provides protection against the jolt of the recovery system deploying and provides a means of keeping all the rocket components together during recovery.

A model rocket engine is a commercially manufactured combustible propellant. These are the consumables of the hobby, once used they are discarded. While your model rocket may be flown over and over again, the burning of the propellant makes model rocket engines "one-shot" deals.


ENGINES & MOTORS

Model rocket engines (or motors, the terms are often used interchangeably), are commercially manufactured solid fuel propellant plugs which when ignited release large volumes of expanding gas which propels the model rocket skyward.

It is the classic example of Newton's Third Law of Motion; commonly paraphrased "for every action there is an equal and opposite reaction".

Model rocket engines come in different impulse classes. Impulse is just a measurement of the engines thrust over time. Think of the different impulse classes as a measurement of a rocket engine's power. While the technical measurement of a model rocket engine's impulse is measured in something called Newton-seconds, the common parlance is to refer to the alphabetic sizing convention used.

Model rocket engines are classified by a letter of the alphabet, starting with the letter A and ending with the letter G. Each step of the alphabet represents a doubling of an engine's total impulse. So a "C" engine is twice as powerful as a "B" engine, and four times more powerful than an "A" and ½ as powerful as a "D". Typically for "A" through "D" engines, the propellant fuel is black powder.

"E" through "G" engines (while technically still model rockets) are sometimes referred to as "mid-power". The propellant used for these engines is a composite material called Ammonium Perchlorate (AP). AP is the same material used in the solid fuel booster of the Space Shuttle, although it would take 8 million model rocket "G" engines to equal the power of a single Space Shuttle solid fuel booster.

There exist fractional sizes smaller than "A"; ½ A and ¼ A, for the smallest of model rockets. The scale also extends to engines larger than G. But this enters a realm called High Power Rocketry.

In a nutshell, bigger engines allow you to launch heavier models or take a given model to a greater altitude.

TYPES OF MODEL ROCKETS

We often think of a model rocket as mimicking, in miniature, the external appearance of a real rocket, and often they do.

In fact, one facet of the hobby is the building of scale versions of real rockets. From military missles, sounding rockets to space missions; there is no shortage of real rockets to model after.

Rockets need not be propelled skyward by a single rocket motor. Some rockets will "cluster" multiple engines to give even greater total thrust and impulse.

Some rockets will employ multiple stages. One or more booster stages launch the model and then after igniting an upper stage, fall away.

 

Some rockets are designed around lifting a payload skyward. Payloads may range from a simple plastic figurine which parachutes to earth, or raw eggs (where the goal is to return the payload safely and unbroken to the ground), to miniaturized electronics. Instrumentation such as altimeters and still and digital video are used to capture onboard data and imagery of the flight.

What goes up, must come down, and model rockets employ various means to return your model rocket safely to terra firma.

The smallest and lightest of rockets may employ nothing more than a "tumble" recovery where the rocket free falls to the ground after reaching maximum altitude.

Other rockets may slow their descent to earth through the use of a recovery system employing a streamer or parachute.

Others may deploy helicopter-style rotors and spin down, and others may glide to the ground like an aircraft.

Finally, some model rockets don't even look like the classic model rocket. In a category called "Odd-Rocs", aerodynamically stable shapes such as pyramids, cones, spools, flying saucers and yes even converted badminton birdies have been built into flyable model rockets.

In the hobby of rocketry, the sky IS the limit!

Fly High and Fly Safe with the Manitoba Rocketry Group!