Model Rocketry and Siege Engine Glossary Letter D


Model Rocketry and Siege Engine Glossary Letter D

Glossary
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Dart
An unpowered vehicle, with the same aerodynamic characteristics as a rocket. A dart is one method of propelling a payload package to a maximum altitude. The dart rides on top of a large booster, possessing a higher coefficient of drag. During powered flight the dart acquires all the momentum of the entire vehicle. As the booster begins to slow during the coasting phase, its greater drag causes it to fall away from the dart which continues to ascend to a higher altitude.
Davis Douche
Variant of the flash pan, where wicks are inserted into each motor and the wick ends are put into the pan of BP. See Flashpan, with Caution
Death Dive
See Power Prang
Decalage
The difference, in degrees, between the angles of attack of the wings and stabilizer of a aircraft. This difference builds in some inherent stability, allowing the aircraft to recover from dives and stalls
Deceleration
A reduction of velocity
Declination
In astronomy and celestial navigation, the angular distance of a celestial body from the celestial equator measured through 90 degrees and named north or south as the body is north or south of the celestial equator measured on an hour circle
Deflection
Bending or displacement from the neutral position due to loading from some outside force
Deflector
See blast deflector
Delay
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
DeltaV
Change in velocity
Delta Wing
Wing planform in the shape of a large triangle, used for supersonic flight conditions
Density
Ratio amount of a substance in a set volume
Deployment
The condition of releasing, or deploying, a parachute or other recovery device
Deployment Bag
A bag constructed of some fireproof material such as Nomex, in which a rocket’s parachute is packed. The bag serves to protect the parachute from hot deployment charge gasses, and assists in the orderly deployment of the parachute to prevent shroud tangling
Deployment Charge
The pyrotechnic charge which pressurizes the part of the rocket containing the recovery system, deploying the recovery device
Destructor
An explosive or other device for intentionally destroying a missile, an aircraft, or a compound thereof
Dethermalizer
A device designed to ruin the aerodynamic properties of a aircraft, enabling it to safely escape a thermal and return to the ground
Dhanook
To be tricked due to suffering a bad case of launch happiness
Diamond Airfoil
An airfoil on which the leading and trailing edges are tapered symmetrically to a point. This airfoil is used on missiles designed for supersonic flight. Sometimes called a Nike airfoil, since the classic example is the Nike family of missiles
Diffuser
A duct of varying cross section designed to convert a high-speed gas flow into low-speed flow at an increased pressure
Digital Computer
A computer that works on the principle of counting, as distinguished from measuring
Dihedral Angle
The angle at which a glider’s wing tips tilt upward from the horizontal plane, to impart roll and yaw control
Directional Stability
The ability of an aircraft to return to its original flight direction after being forced off course
Direct Staging
Air start of a sustainer motor caused by the burning propellant of the booster motor
Display Launcher
A launcher that is not functional and is used to show off a model
Dive
Motion of an aircraft in a head down or nose down attitude
Dope
A liquid lacquer based paint used to seal the grain of wood
Doppler Effect
Change in sound frequency caused by the source’s rapid movement towards or away from the observer
Doppler Effect
The apparent change in frequency of a sound or radio wave reaching an observer or a radio receiver, caused by a change in distance or range between the source and the observer or the receiver during the interval of reception
Dorcasitis
An uncontrollable competitor’s disease, the symptoms of which are to impulsively make last minute changes intended to improve a tested competition model’s performance, only to have the modification backfire or cause a disqualification
Douche Plate
Metal centering plate on the bottom of a cluster motor model to prevent damage caused by the BP flare-up using a flashpan or Davis Douche
Downdraft
The movement of a column of cooler air downwards, opposite to a thermal
DQ
Slang for disqualification
Drag
The component of the total air forces on a body, in excess of the forces owing to static pressure of the atmosphere, and parallel to the relative gas stream but opposing the direction of motion. It is composed of skin-friction, profile-, induced-, interference-, parasite-, and base-drag components
Drag Coefficient
See Coefficient of Drag
Drag Force
The resistive force (Fd) on a body moving through a fluid, such as air. It can be calculated using the formula: Fd = ½ * Cd * ρ * S * v2, where:
    Cd = the drag coefficient for the body
    ρ = the density of the fluid
    S = the cross-sectional area in the direction of motion
    v = the velocity of the body relative to the fluid
Drag Race
An event, usually informal, in which multiple rockets are launched simultaneously
Drag Recovery
Recovery method using the shape of the model to slow the model down enough for safe recovery
Drilling For Oil
See Core Sample
Drogue Parachute
Small, heavily reinforced parachute designed to slow the craft so safe release of the larger main chutes are possible
Drop Staging
See CHAD
DSE
Detectable Seismic Event; see Death Dive
DOT
US Department of Transportation: A federal agency responsible for laws concerning the roads, especially the interstate highway system. Transportation of motors and propellants is often regulated by DOT regulations
Dual Recovery
See Two-Stage Recovery
Ducted Propulsion
Generally refers to any propulsion system which passes the surrounding atmosphere through a channel or duct while accelerating the mass of air by a mechanical or thermal process
Dullcote®
A spray coating from Testor’s Corp. that protects the finish of a model while removing the sheen of the finish


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