R is for Rocket - The Basics of Model Rocketry
Welcome to the Best Hobby on Earth
What could be more awesome than trying to personally fulfill man's eternal dream to reach out and touch the stars? For as long as humans have roamed the Earth, we have strived to break through barriers and overcome the inherent limitations we were born with. What frail creatures are we! We can't fly, we can't swim underwater. We don't have great speed or strength. We are frail, vulnerable mammals, yet our superior intelligence has enabled us to surpass every other organism we know of and achieve awe-inspiring feats. Less than a century ago, we decided it was finally time to soar past the sky and into the great black beyond on a mission of peace, exploration and understanding.
Model rocketry encapsulates all of this by scaling down the grand mission of space exploration, to something that all of us can appreciate. A model rocket can reach several thousand feet into the sky, higher than the clouds and touch the edge of space. We model rocketeers start small but our efforts are continually rewarded as our experience and model building techniques improve. After exercising those techniques and acquiring the right certification levels, we can use more powerful motors, payloads, telemetry, video and guidance systems to reach even further. As a rocket becomes more and more sophisticated, it becomes an extension of our bodies and gives us new eyes to see what space is like without ever leaving the safety of the ground.
Stick around because this hobby is your past, present and future!
What is a model rocket?
A model rocket is a streamlined, non-metallic airframe, with control surfaces to provide stability, a motor to provide chemical propulsion and a recovery system to bring it safely back to Earth. Designs can vary wildly but the basic anatomy is the same. Rockets are deployed vertically or nearly vertically from the ground using a launch pad and electrical launch controller. They are aerodynamically stable and will fly to a peak altitude before deploying a recovery system, which slows the rocket's descent back to Earth. Typically, the model rocketeer engineers every part of the rocket except the motor. In some countries where model rocketry is prevalent, one can manufacture the motor as well but not always. As such there are several companies, such as Estes and Apogee, offering safe, reliable, pre-manufactured motors in a number of convenient sizes. Adhering to these very basic principles is why model rocketry as a sport and hobby has persisted for so long, with so much success and is accessible to so many ages. It's because, done correctly, it's fun, educational and SAFE.
Anatomy of a Model Rocket
All rockets consist of the same basic parts:
NOSE: This is the first component the air encounters as the rocket ascends. It has been called a "nose cone" for quite some time but the shape is rarely that of a true cone. Each type of nose has different benefits for a different aerodynamic regime and it is very important to make sure the nose design is sound because it will affect the airflow over the entire rocket. Noses are made by turning wood on a lathe and often hollowing it out as well but it's much more practical to buy blow molded plastic noses, which can be purchased cheaply, for the novice. Either way you can achieve tight dimensional control and good surface finish so it really depends what your design calls for. The nose is often detachable because it's often the thing to dislodge in order to deploy the recovery system
RECOVERY SYSTEM: This system usually (but not always) resides inside the rocket and is designed to slow the descent of the rocket after it reaches its highest altitude. The classic design is the parachute. It works well, especially for lower altitude flights but can cause the model to drift considerably. Shrinking the parachute mitigates that problem but causes it to fall faster. Sometimes a streamer (a very long piece of light fabric or plastic, which flaps in the wind) is more appropriate for high altitude flights. Another idea is to make the rocket itself break apart into a different shape and tumble or helicopter in the wind, slowing it down. Recovery systems stored inside the rocket are usually deployed by the "ejection charge" of the motor, which is the final phase in the burn, in which the motor deploys a puff of gas up into the rocket to push the recovery device and nose out.
BODY TUBE: This is comparable to the fuselage of a plane. It's the main structural element of the rocket and is often as simple as a cardboard tube. It may have multiple sections with transitions in between but it provides the rocket with a frame and is, needless to say, necessary. The length and diameter of the body tube are important for aerodynamics and the material should never be metallic because we are talking about a flying projectile here and it could become a lethal weapon if it goes off course and the recovery system does not deploy.
MOTOR MOUNT: Just like your car has an engine mount, a rocket needs a motor mount. Sometimes you can use the body as the mount but unless the rocket is intentionally designed that way, you will need something to center the motor within the body tube. Another benefit to having a mount is more accurate control over the position of the motor vertically within the body tube. Sometimes a mount is necessary because you need to create clearance around the motor in order to feed wires or other electronics up the rocket's length. In any case, it must have the strength to withstand the thrust produced by the motor against the inertia of the rest of the rocket.
MOTOR: This is the heart of the rocket. It's what makes it different from something that sits pretty in a display case at home. It is a durable casing, a carefully engineered nozzle to direct exhaust flow, a propellant grain, which can take on many cross-sectional shapes, an optional delay grain that produces no thrust and an optional ejection charge, which is fast-burning propellant that creates a small explosion intended to pressurize the body tube and deploy the recovery system and finally a weak end cap to hold the ejection charge. Some motors don't have the last 3 components because they are "booster" motors and need to ignite the next "stage" by sending fragments of burning propellant up the nozzle of the motor sitting on top of it.
Motors have many different designations, broken down by impulse (total energy), thrust (average force), delay (how long before the ejection charge fires), size and whether they are single use or re-loadable units. A rocket will fly optimally with a specific motor but will work with any motor you can fit into it so be very careful when choosing the motor for your rocket. You don't want the rocket to be underpowered because it will tend to veer off course due to lack of aerodynamic stability. You don't want it too strong either as it could literally gut the entire rocket while it sits on the launch pad, sending debris flying all over the place like a roman candle.
FINS: Even though all parts of a rocket are important, the fins are particularly important because they are the only control surfaces on the rocket and they WILL determine the rocket's flight path or trajectory. They are very sensitive to poor construction and installation so even if 1 is crooked or different in size by a couple of millimeters, it could send the rocket on a completely unanticipated path and turn it into a dog-seeking missile. Fins are sometimes injection molded, one-piece units that slide over the body tube but more often they are just sheets of balsa wood that you cut yourself, sand, paint and glue to the body tube with a butt joint or though slots for added strength. You must have a minimum of 3 fins for a rocket to fly properly but you can have as many as you want past 3. What you gain in stability is a trade-off with drag since more fins equals more drag and that will slow down your model.
This is the only book you'll ever need on rocketry.
Just because a rocket must contain all of the above does not mean it must be limited to those sub-systems. You can add all sorts of things to your rocket to make it stand out from the pack. A popular way to upgrade your more advanced rocket is to include electronics. You can put an altimeter in the nose or a camera so you can look back down at Earth from the rocket's point of view. There are many scientific payloads that make great upgrades.
Be aware that you should never ever put a living thing in a rocket. This is referred to as an LBP or a live biological payload. It's cruel and the only biological payload should be a human being so leave that to NASA ;)
Rocketry is Both a Simple Pleasure and a Complex Science
The great thing about model rocketry is you can make it as simple or as complicated as you want. You can use your Ph.D in engineering to design sounding rockets that reach miles into the sky or you can buy a $50 kit and fly a rocket with your kid 3 hours later in an open field. We've only touched the tip of the iceberg here by defining the scope of the hobby and telling you what rockets are all about. If you find yourself excited by the prospects of building and launching your very own creation up into the sky, stay tuned for more "R is for Rocket".