Amateur/Model Rocket Knowledge

Amateur Rocketry Basics

Model Rockets usually have a simple construction. They have a set of fins

A surface at the rear of a rocket that serves to stabilize it in flight. Fins are usually planar surfaces placed at right angles to the body tube.

source: rocketreviews.com
, a body tube

A cylindrical tube that makes up the body of the rocket. Typically made of cardboard, fiberglass or carbon fiber. See Airframe

source: rocketreviews.com

The airframe is a rocket’s main outer structure, usually the rocket’s body tube.

source: rocketreviews.com
), a nosecone

The pointed object at the front of a rocket. Cones are not always strictly cone-shaped. They are sometimes rounded but are most commonly ogive (a pointed arch). Nose cones are an important consideration in rocket design, since they provide two ways to move the center of gravity forward if needed; by using a longer cone, or by adding weight to the cone.

source: rocketreviews.com
, a parachute

A piece of plastic, cloth, nylon, or other material, shaped something like an umbrella when deployed, which slows the descent of a rocket.

source: rocketreviews.com
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

In rocketry, the highest point a rocket achieves before beginning its descent. (More literally, the point farthest on the flight path from Earth.)

source: rocketreviews.com
) where a small ejection charge expels the parachute so that the rocket can float back safely to earth.
Model rockets are typically constructed of cardboard, plastic, and electronics

Any of a number of electronic devices used in rocket flight, e.g. Altimeters, Timers, etc.

source: rocketreviews.com
used in High Power Rockets
  1. High Power Rocketry. High power rockets are defined as having: a single motor with more than 160 Newton-seconds total impulse or an installed impulse of 320 Newton-seconds and no more than 40,960 Newton-seconds, and an average thrust in excess of 80 Newtons. (H through N range);
  2. Depending on the context, may also refer to the title of the TRA’s journal.
source: rocketreviews.com
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

Ejection of the recovery device through the use of a solid sliding bulkhead inside the airframe. The use of a piston eliminates the need for wadding.

source: rocketreviews.com
can be used above the deployment charges

The pyrotechnic charge which pressurizes the part of the rocket containing the recovery system, deploying the recovery device.

source: rocketreviews.com
to aid deployment and protect the parachute from the heat of the black powder

Black powder is the original explosive said to have been invented in China. A mixture of carbon, (charcoal), sulfur and potassium nitrate (saltpeter).

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charge. Most Model Rockets, and some High Power Rockets, use timed

An electronic, mechanical, or pyrotechnic device that permits the rocket’s unpowered ascent between motor burnout and the deployment of the recovery device. Typically, the delay is a pyrotechnic grain which separates the propellant from the deployment charge and which burns at a known rate. The delay grain begins to burn either at the same time the propellant grain is ignited (composite motors), or at the end of propellant ignition (black powder motors). When the delay grain burns through, it ignites the deployment charge. Also, the period of time between propellant burnout and recovery system deployment.

source: rocketreviews.com
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

A device that measures altitude. Altimeters can be used simply to document a rocket’s apogee, but they are also commonly used to control electrical devices for airstarting motors or deploying recovery devices.

source: rocketreviews.com
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”.
Many High Power Rockets use dual deployment

A process by which a rocket is recovered by means of a streamer or drogue parachute which opens at apogee, followed by a main parachute which opens at lower altitude. See Single-Stage Recovery.

source: rocketreviews.com
where two parachutes are used in the rocket; a smaller drogue chute

Small, heavily reinforced parachute designed to slow the craft so safe release of the larger main chutes are possible.

source: rocketreviews.com
, 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 mid section, or payload bay

A portion of rocket airframe set aside for payloads. Also called payload bay.

source: rocketreviews.com
, 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

Reloadable Motor System (has also been called Reusable Motor System). A solid rocket motor which can be re-fueled and reused.

source: rocketreviews.com
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 by utilized for different “motor reloads”, most are brand specific.
Rocket Motors used in High Power rocketry most commonly consist of Ammonium Perchlorate

(NH4ClO4) The oxidizer used in most composite rocket motors. Other components are Aluminum powder (fuel) and polybutediene rubber (the binder holding it all together). This is the propellant mixture that the Shuttle SRB’s use. See Binder

source: rocketreviews.com
 Composite Propellant or APCP

Ammonium Perchlorate Composite propellant.

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. 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 rocketry, any pellet or cast section of propellant or other combustible material. The black powder propellant packed and shaped into a single-use model rocket motor is referred to generically as a grain. Also, the direction of the fibers in a piece of wood, such as balsa. See Wood Grain

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; 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

A rubber gasket used to contain gasses in solid rocket motors

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, nozzles

The part of the rocket motor that smoothly expels gas from the combustion chamber; typically made from phenolic (in SU or AT reloads), graphite (Kosdon-style reloads), or clay (Estes motors). Components of the nozzle include the entrance cone, throat, and expansion cone

source: rocketreviews.com
, 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.
Rocket motors are measured in total impulse

The total thrust produced by a rocket motor across its full burn time. Usually expressed in Newton-seconds.

source: rocketreviews.com
and are 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

Levels one through three: reference to the three levels of high power rocketry certification. Unless you are in Canada, Eh?

source: rocketreviews.com
by Tripoli

Tripoli Rocketry Association, Visit TRA

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and/or NAR

National Association of Rocketry, Visit NAR

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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

A device for keeping the rocket motor from being ejected by the force of the deployment charge.

source: rocketreviews.com
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”.
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

A piece of plastic or metal that mates with a Launch Rail; forms a ‘H’ shape when viewed from the side.

source: rocketreviews.com
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

Launch Control Officer. Person in charge of controlling the range and launching rockets.

source: rocketreviews.com
(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.