Model Rocketry and Siege Engine Glossary Letter S


Model Rocketry and Siege Engine Glossary Letter S

Glossary
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Safety Check Officer
At NAR and CAR organized launches, the person who examines rockets before they are assigned to launch pads. Reports to the RSO
Satellite
  • An attendant body that revolves about another body
  • A man-made object designed , or expected, to be launched as a satellite
SC
See Shock Cord
SCO
See Safety Check Officer
Scale
The practice of building model rockets which are replicas of existing rockets or other aircraft, which models are constructed to a size that is a particular percentage of the original aircraft’s size. Scale models are often built for competition, and their level of detail can be very exact
Scissors Wing
A variable geometry wing planform used on rocket gliders, where the wing unit rotates and aligns with the fuselage when not in glide mode
Scott Towel Special
A cheap rocket costing less than $1, made of a tube taken from paper towels, toilet paper or gift wrap, a hand rolled paper nose cone, and card fins or tube fins or other recycled material. The use of balsa for fins or any other conventional model parts immediately disqualifies the model as a Scott Towel Special
Screamer
A really, obnoxiously loud beeper
Screw Eye
A headless screw on which the shaft is extended and formed into a circular eye
Scrub
to cancel a launch attempt due to problems, technical or otherwise
SD
Streamer Duration; a common competitive event in NAR-sanctioned launches
Sealer
Paint-like substance to cover wood parts. Sealer seals the wood grain, preventing any penetration of moisture, allowing a smoother finish, and the use of less paint
Sears-Haack
A series of nose cones designed and used for maximum aerodynamic efficiency on very high-speed rockets. The most commonly encountered cone in this series is a Von Karmon cone
Seeker, Target
A receiving device on a missile that receives signals emitted from or reflected off the target that is used in guiding on the target
Servo
A small mechanical device, which upon receiving a signal from a radio or timer will perform an action such as the movement of a push rod
Shock Cord
A length of elastic or bungee which provides shock absorption for the rocket components at the point of flight where the deployment charge fires and the parachute opens
Shock Cord Mount
The attachment point for a shock cord
Shoulder
A slight sharp indentation at the base of a nose cone or top or base of a transition, allowing the part to be slid into a tube while allowing alignment of the rocket sections to be maintained
Shred
The condition in which a rocket’s airframe fails during launch. This is caused when the force applied by a rocket motor exceeds the tensile strength of the rocket airframe. The effect of a shred is similar to an explosion
Shroud, Parachute
Lines or strings which pull down on the edges of a parachute. The shrouds come together at their bottom ends to provide a point of attachment between the parachute and the rocket
Shroud, Transition
A piece of material, often card stock, used to smoothly allow the airframe to go from one diameter to another
Signal
Any wave or variation thereof with time serving to convey the desired intelligence in communication
Single-Stage Recovery
A process by which a rocket is recovered by means of a single parachute, streamer, or group of parachutes which deploy at one time. See Two-Stage Recovery
Sink Rate
The rate of vertical drop during the recovery phase of a flight, in feet or meters per second. Sink rate used to specify parachute or streamer size for a rocket
Skin
The thin outside surface of a hollow part or object
Skywriting
Slang term for the smoke trail left by an unstable rocket which does not fly straight
Snap Swivel
A small device, originally developed to connect fishing lures to leaders., which is attached to a model rocket’s parachute shrouds. This permits the parachute to be easily removed and replaced on the rocket, and permits the parachute to rotate in relation to its connection point, which reduces shroud tangling
Snuffer Tube
A small metal tube used to extinguish a wick such as in a dethermalizer
Sonic Barrier
The zone of high air density caused by the compression wave of an object traveling near the speed of sound
Solid Propellant
A rocket propellant consisting of a single solid substance, usually a powder made into a grain of a particular size and shape
Sonic
Velocity that is equal to the local speed of sound
Sonic Boom
Loud report caused by the passing of the compression front generated by an object as it exceeds the speed of sound
Sonic Speed
The speed of sound at the current conditions of air density. humidity and temperature
Sounding Rocket
A research rocket used to obtain data on the upper atmosphere
Spack
(Brit.) Slang for the sound of a model rocket hitting the ground from high altitude
Span
The long (side-to-side) dimension of a wing. See Chord
Spar
  • A long, thin, structural member of a airframe
  • Also, SPAR - Special Projects And Research, formerly a department of Bombardier/De Haviland Canada, now the maker of satellites and robotic arms for use in space
Specific Impulse, Fuel (Isp)
  • Thrust developed by burning one unit of mass of fuel in one second
  • the ratio of thrust to the fuel mass flow
Speed Of Balsa
That speed at which a rocket’s balsa fins shred or strip. The speed varies with thickness of balsa, thrust gradient, type of glue used and mostly quality of building technique
Speed of Sound
The velocity at which sound waves are transmitted through a medium. Speed of sound in the air varies as the square root of the absolute temperature. (See MACH NUMBER)
SPEV
Spare Parts Elimination Vehicle: a commercially-produced rocket kit which is designed and marketed by a manufacturer specifically to use up parts which have been warehoused after the cancellation of an earlier kit
Spill Hole
A hole in the center of the canopy of a hemispherical parachute, designed to reduce payload oscillations caused by the canopy spilling air unevenly from its edges
Spinerons
Tabs attached to the trailing edge of fins and set at an angle, intended to spin the rocket in order to stabilize it
Spin Stabilization
The use of spin along the long axis of a rocket to stabilize the flight, thus making the rocket act as a gyroscope
Spin Tabs
See Spinerons
Sport Model
A model rocket designed and built with no specific purpose in mind other than to fly it
Spot Landing
A competition event in which the goal is to land the model closest to a predetermined spot on the launch field
Sport Rocketry
Rocketry activities pursued as a pastime, diversion, or personal enjoyment. Term is often used as a contrast to "competition rocketry."
Squib
A small charge of black powder or other propellant, contained in a hollow tube and set off with an electrical igniter. The term is usually used in connection with an electronically-actuated deployment charge for a rocket’s recovery system. Not to be confused with a detonator which explodes
SSTO
Single Stage To Orbit
Static Firing
The firing of a rocket motor or rocket engine in a hold-down position to measure thrust and accomplish other tests
Stab - Stabilizer
Usually refers to the fin-like structures at the rear of a conventional boost glider
Stability
The tendency of a rocket to move in a straight line in the direction it is pointed at launch. See Passive Stability. See Active Stability. See Weather cocking.
Stall
The angle of maximum lift for an airfoil. Stalls are dangerous because lift dramatically decreases (often to near zero) at any angle past the stall point
Static Balance
A state in which a model’s center of gravity can be demonstrated to be in a proper relationship to the center of pressure by actually balancing the model on a narrow surface
Static Firing
The firing of a motor, mounted in such a way that the motor can not move. Used usually with instrumentation, to permit performance measurement
Static Margin
The diameter of the thickest part of a rocket’s airframe. The term is synonymous with "caliber" in determining the relationship between CP and CG
Statosphere
  • A stratum of the atmosphere lying immediately above the troposphere and, as treated by some meteorologists, immediately below the chernosphere
  • Also applied to a thicker stratum extending through the chemosphere
Stine’s Law
The guiding principle of Rocketry construction and flight: "If at first you don’t succeed, try following instructions."
Streamer
A device for slowing the descent of a rocket, sometimes used in place of a parachute in smaller rockets. The streamer consists of one or more long, narrow lengths of plastic, fabric or paper which are connected to the rocket in the same fashion as a parachute, and which deploy and flutter to slow and stabilize the falling rocket. Since streamers do not slow the descent as much as a parachute, they are normally only used on relatively small or very robustly-built model rockets. However, they are useful in windy conditions since they will not allow the descent to drift as much as a parachute will
String Test
See Swing Test
Strip
A condition in which a rocket’s fins, or a glider’s wings, are pulled off the airframe by excess thrust
Striptease
The "act" of having wings or fins stripped off an airframe.
Also, a pop-pod glider that separates from the booster pod prematurely
Stuffer Tube
A small-diameter tube - commonly an extension of the motor tube - which is used in large-diameter rocket airframes to duct deployment charge gases to the recovery system storage area. This reduces the internal area which must be pressurized by the deployment charge
Styrofoam
A very light material made of expanded polystyrene plastic. Though Styrofoam has little structural strength, is easily shaped into shapes, such as large nose cones and glider wings, that can be skin-reinforced by fiberglassing or lamination of thin wood veneers
SU
Single Use; a disposable motor which cannot be re-used
Subsonic
A velocity less than the local speed of sound, or than a Mach number of one.
Sustainer
A propulsion system which travels ' with and does not separate from a missile usually distinguished from an auxiliary motor, or booster
Superroc
Usually, a lengthened version of an existing model rocket design, used in altitude and duration competition. Scoring is based on altitude multiplied by airframe length. Super-Roc has different length limits for different motor classes. For example; A has a range of 75 to 150 cm, C has a range of 125-250cm. The rockets can be longer but the excess length is not counted into the length factor. In the altitude category the rocket may be recovered in more than one section
Supersonic
A speed greater than Mach 1 and less than Mach 5
Sustainer
In a multi-stage rocket, the last or top stage. In a parallel staged rocket, the longest-burning motor
Sweepback
The amount of angle that the leading edge of a wing has been shifted back from a line perpendicular to the airframe of a model
Swing Test
A stability test in which a string is attached to a model rocket at the center of gravity and then swung around the head. If the model is stable, it will head nose into the direction of travel. This test has a large margin of error, thus producing models often overly stable. It can not be used for large rockets, unless King Kong consents to twirl the string. Sometimes called a string test
Symmetrical Airfoil
An airfoil (wing) in which both the top and bottom surfaces are tapered

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