ABOUT ROCKETS

Amateur/Model Rocket Knowledge

Amateur Rocketry Basics

Model Rockets usually have a simple construction. They have a set of fins, a body tube (airframe), a nosecone, a parachute for recovery, and a rocket motor to make it go. The motor burns and propels the rocket, the propellant in the motor burns out, the rocket coasts upwards and finally arcs over at the peak of its flight (apogee) where a small ejection charge expels the parachute so that the rocket can float back safely to earth.

Parts of a Model Rocket

  • Fins Flight Stability
    • The fins are airfoils that provide aerodynamic stability to the rocket.
  • Parachute Recovery System
    • A parachute provides slow descent and safe recovery of the rocket.
  • Nose Cone Forward Enclosure
    • A nose cone is the airframe’s forward closure providing aerodynamic ariflow around the rocket. A nose cone may also contain a payload.
  • Shock Cord Tether or Harness
    • The shock cord dissipates the energy of the ejection charge and ties all of the rocket’s components together.
  • Airframe aka: Body Tube
    • The airframe or body tube. Contains the payload or recovery system.
  • Motor Mount Engine Retainer
    • A motor mount or motor mount tube (MMT) accepts the rocket motor and provides its retention.
  • Launch Lug Initial Guidance
    • A launch lug provides initial guidance before the rocket’s velocity is sufficient for its fins to provide stability.
Model rockets are typically constructed of cardboard, plastic, and balsa wood and are fueled by commercially manufactured single-use rocket motors. Some of the electronics used in High Power Rockets are also employed in model rockets.
Some High Power Rockets operate as simply as Model Rockets, but others have added components to insure more accurate deployment of the parachute or parachutes. A piston can be used above the deployment charges to aid deployment and protect the parachute from the heat of the black powder charge. Most Model Rockets, and some High Power Rockets, use timed in the motor to ignite the ejection charge, deploying the parachute at apogee. Choosing the right delay is crucial and often difficult. Therefore, many High Power Rockets use an electronic altimeter to deploy the parachute instead of a motor ignited ejection charge. When the altimeter senses that the rocket is no longer climbing, it triggers an igniter which lights a small black powder charge blowing the nosecone off the rocket and deploying the parachute. Altimeters are also used to determine the altitude, speed and acceleration of a rockets flight. A second altimeter is often included to provide back up in the event the initial altimeter does not perform properly; this is referred to as “redundant deployment”.
  • Main Parachute
  • Nomex Blanket
  • Nose Cone
  • Payload ◊ AV-bay
  • Drogue Parachute
  • Booster ◊ Fin-can
Many High Power Rockets use dual deployment where two parachutes are used in the rocket; a smaller drogue chute, or a streamer, deploys at apogee and a larger main chute deploys later at a pre-designated, lower altitude. Several configurations are used for dual deployment rockets. However, most often the rocket is designed so the small parachute deploys from just above the motor section; the middle section, or payload bay, houses the altimeter; and the main parachute is deployed just behind the nosecone. The rocket falls fast on the small chute, bringing it closer to the ground, before a larger chute deploys slowing the rocket’s fall to insure a soft landing. This system increases the chances of a successful recovery by minimizing the distance a high flying rocket drifts “under chute”.
While some High Power Rockets fly on single use motors, most utilize reloadable motor systems or RMSs. RMSs are commonly constructed of machined aluminum, are referred to as “motor hardware” and vary by manufacturer. There are several different designs of motor hardware and while some hardware may be utilized for different “motor reloads”, most are brand specific.
Rocket Motors used in High Power rocketry most commonly consist of Ammonium Perchlorate Composite Propellant or APCP. The propellant in motor reloads is sold precast in cardboard or plastic tubes, ready to be loaded into motor hardware. These tubes of propellant are referred to as grains; in general, the size of a motor varies according to the diameter and number of grains. Some reloadable motors come as a kit that includes O-rings, nozzles, washers and other components; a clear set of instructions is included with all reloadable motors and should be followed explicitly. If assistance is needed in building a rocket motor at a launch, an experienced rocketeer can always be found. In fact, many clubs ask experienced rocketeers to wear special shirts or orange vests so they are easily identifiable to newer members in need of assistance.
  • ¼ inch launch rod
Rocket motors are classified by their total impulse and that total impulse is designated by letters of the alphabet. Each letter designates a range of total impulse and each motor size contains twice the total impulse of the previous letter. For example a B motor has a potential total impulse twice that of the total impulse of an A motor; a C motor has twice the potential total impulse of a B motor, etc. Rocket motors larger than G are considered High Power; use of them requires certification by Tripoli and/or NAR.
Motors are retained in rockets in several ways. Traditionally Model Rockets use masking tape to hold in the motors; High Power Rockets often have more elaborate retention systems as the replacement of lost reloadable motor systems is costly. Some rocketeers use commercially available motor retainers that rely on threaded caps, snap rings or brass inserts while others create their own “custom retention systems”.
  • 80/20inc 1010 launch rail
The old style of launch rods used as a launch guide to keep the rocket pointed straight up while being launched are giving way to launch rails. Instead of using sections of round tubing to fit the launch rod, rails require only small spool-looking buttons as guides that fit into a slot on the launch rail. It’s far more efficient and much steadier on the launch pad than using a rod. Both rods and rails are used at most launches.
Once the rocket is ready on the launch pad an electrical igniter (two wires with a head made of a easily ignited type-of propellant mixed with magnesium or titanium) is installed all the way up until the head of the igniter stops at the head of the motor.
The igniter wire is then hooked up to a solenoid switch that acts as the igniter’s link to a nearby high-current battery. The solenoid is wired to a launch control box where each pad can be independently selected and activated by the Launch Control Officer (LCO) at the range head.
Once energized, ignition in Model Rockets takes only a fraction of a second but High Power Rockets can take a full second or two to “come to pressure” before launching off the pad. As Ammonium Perchlorate Composite Propellant is a difficult material to ignite, some igniters burn out without igniting the rocket motor; rockets that fail to light are often greeted with a chorus of “No Joy” from the rocketeers and the spectators on the flight line.