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Author Topic: Glossary of rocket terms  (Read 5908 times)
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« Reply #14 on: June 29, 2009, 07:20:06 PM »

Ogive: A shape defined by the intersection of two circles. It is not the same as a parabola (q.v.). Both ogives and parabolas produce low drag sub-sonic nose shapes. They can be told apart since a parabola always has a rounded nose while an ogive comes to a point.

Olympic Torch: A rocket that power prangs (q.v.) with the motor still burning. Coined by Bob Kaplow after almost impaling former NAR President Mark Bundick with an RMS (q.v.) powered model that suffered a nozzle failure which dropped the thrust to zero even though the motor kept burning. See also "Roman Candle"

Optimum Mass: For any given motor and Drag Form Factor (q.v.) the liftoff mass for which a rocket will reach maximum altitude in dense atmosphere. At first this might seem to be just the lowest possible mass, but there is a two edged nature to mass covering both powered flight and coasting. Lower mass will give higher burnout velocity, but will dissipate its momentum to drag faster (think of a feather). Conversely, a heavier rocket will have more momentum at burnout to coast farther, but too much mass will hold down both burnout altitude and velocity. Hence, there is a "knee" on the liftoff mass vs. altitude graph.

For very low impulse motors (say "B" and below) this "knee" is right around the mass of the motor itself, so the rule of thumb is "the lighter the better." The higher impulses, though, have more leeway, and careful calculations should be made to determine the optimum mass for altitude attempts. In a multi-stage rocket with no staging delays, only the dead mass in the upper stage participates in coasting. Extra dead mass in lower stages cannot enhance coast distance, and so lower stages should be as light as possible. Strictly speaking, an undelayed staged rocket has no optimum liftoff mass, but the mass of the last stage may be optimized with respect to the(sub-optimal) lower stages. In dense atmosphere, the best single stage configuration is more efficient than the best multi stage configuration, provided all the propellant can be contained in one stage. Indeed, there are many instances when cluster rockets out perform staged rockets.

The opposite is true for rockets operating in the thin atmosphere of high altitudes. In that environment, staged rockets are more efficient (propellant-wise) than single-staged rockets, and lighter rockets always perform better. There is no optimum mass in a complete vacuum.
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« Reply #15 on: June 29, 2009, 07:21:49 PM »

Parabola: A shape produced by the formula y=x^2. Used to produce low drag nosecones. See also "Ogive"

PARC: Perth Advanced Rocketry Club INC

Payload: Anything carried aloft by the rocket that is not part of the rocket itself. Common payloads include altimeters, computers, cameras, and radio transmitters. The Safety Code specifically prohibits the launching of live payloads.

Phenolic: A heat-resistant plastic most familiar as the material from which plastic ashtrays are made. It is made by a reaction of phenol and formaldehyde. When mixed with carbon black, it is used to make casings for composite propellant rocket motors. It is also used to reinforce the cardboard in body tubes for competition rockets (e.g. "Blackshaft" tubing sold by Apogee). Phenolic body tubes are stiffer than ordinary tubes, but are also more brittle so that extra care must be taken to avoid damage during construction, transportation and recovery.

PMC: Plastic Model Conversion. The term used to describe a plastic, static model of some type (typically an aircraft, rocket or spaceship) that has been converted to fly as a model or high power rocket. This term is also used as an abbreviation for an NAR-sanctioned competition using converted models.

Prang: Term describing a failure mode whereby a rocket comes down aerodynamically stable, in other words, 'streamlines in'. This is almost always caused by some sort of recovery system failure, usually the result of a too-tight nose cone, too-tightly packed parachute or a too-loose motor that ejects out the back. Multistage models with upper stage ignition failures also result in a prang.

The results of a prang range from no damage at all (other than a few grass stains) on lightweight sport models to the total destruction of the rocket (usually a payloader with a VERY expensive payload on board :-(.

A Prang that occurs while the motor is still burning (e.g. a marginally unstable rocket that performs one large half loop) is called a 'Power Prang'.

Prototype: An initial, development design used to test out principles and concepts but never intended to be a finished or production design. In scale modeling, the original "real" rocket after which the model is patterned.
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« Reply #16 on: June 29, 2009, 07:24:04 PM »

RASP: The Rocket Altitude Simulation Program. Originally written by G. Harry Stine in BASIC in the late '70s (and included as an appendix in the later editions of the Handbook), it performs a simulation of rocket flight using small time interval approximations. The original was relatively primitive assuming constant Cd, vertical flight and other simplifications. There have been several rewrites into "C" and other languages to both broaden its appeal and increase its sophistication.

Red Baron: A boost glider which has tangled with the streamer or parachute of the booster pod. The entire model tends to nose dive into the ground, like a WWI airplane which has just been shot down.

Reef: A series of techniques used to gather the shroud lines of a parachute together to prevent it from fully opening. This is usually done on rockets that reach extreme altitudes or launched on windy days which need higher sink rates to help them land near the launcher. There is also a "traveling reef" technique of placing a soda straw or metal washer on the shroud lines and sliding it all the way up to the chute canopy during prep. At deployment, the parachute is prevented from opening until the chute is fully deployed and the rocket stabilized beneath it. The straw/washer then slides down the shrouds allowing the canopy to open gradually. This is used mostly on large rockets which might have very high speed or high altitude recovery deployment since it allows the rocket to slow and drop considerably before chute opening.

Re-Kitted: A (painfully) humorous term that refers to any situation where a rocket goes to pieces such as a prang (q.v.) or a CATO (q.v.). Thought to have originated at LDRS XIII. Typical usage: "That E-15 sure re-kitted my Black Brant!"

Reynolds Number (Rn): A dimensionless number used by fluid flow engineers to characterize the way a fluid (gas or liquid) will behave when passing over a solid surface. The number combines the fluid's density, viscosity and velocity with the length it's traveled along the surface. No matter what the fluid is or what size the surface, the flow conditions (laminar, turbulent, detached, etc.) should be the same at the same Rn. Discovered by Osborne Reynolds inthe 19th Century while studying the flow of water in pipes andchannels, it has proven most useful to aerodynamic engineers and naval architects in scaling up wind/water tunnel test results to full size.

Carl Dowd, a model aviator and NASA engineer, found it helpful to think of Rn as the "coarseness" of the air seen by a body. Move the body faster, and more particles will pass over it in a given unit of time, increasing Rn. Make the body larger, and there will be more particles over the body at any instant, increasing Rn.

R/G: Rocket glider. A glider which is boosted to altitude by a rocket. The entire model glides down together. No part of the model separates, as in a boost glider. Technically, an R/G is a particular form of B/G.

RMS TM: Reloadable Motor System. The trademarked name of the AeroTech/ISP reloadable motors. Often used (incorrectly) as a generic name for all reloadable technology.

Roman Candle: A failure of the motor restraint (thrust ring or engine hook)where the rocket stays on the pad while the motor flies out of the body (usually pushing the nose cone and recovery system ahead of it). Sometimes mistaken for a CATO (q.v.).

RSO: The Range Safety Officer, the individual responsible for ensuring that rockets presented for launch are properly constructed, prepped and balanced for stability.
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« Reply #17 on: June 29, 2009, 07:30:36 PM »

Safety Nazi: A person overly concerned with safety to the point of detracting from the enjoyment of the hobby. Someone who feels the Saftey Code doesn't go "far enough" in preventing injuries despite the hobby's outstanding safety record.

SARA: Sale Australian Rocketry Association a Victorian rocketry section of the ARA.

SB's: Stanbridges Hobbies located in Perth, Western Australia.

St. Louis Arch: The trajectory of a Prang (q.v) when viewed from a distance. Named for the famous monument whose shape it mimics. Popularized at NARAM 36 by Peter Alway who had driven through St. Louis on his way to Houston.

Scale Data: Drawings, photos, dimensions, and descriptions of a prototype (q.v.) rocket used in making a model of that rocket.

Scale Plan: Instructions, diagrams, and patterns for building a model of a prototype (q.v.) rocket. A scale plan specifies details of a model that may not have anything to do with the prototype,including materials, scale factor, internal construction, and compromises in accuracy necessary for safe flight or ease of construction. See also "Scale Data"

Sectional Density: A projectile's mass divided by the square of its diameter. Used as a measure of a round projectile's ability to coast. See also "Ballistic Coefficient"

Shred: A model which has lost one or more fins due to aero loads and/or acceleration. Also used to refer to a model which has completely come apart during takeoff. Can be used as either a verb or noun. See also "Strip"

Silver Streak TM: A black powder motor, made by Rocketflite, Inc., which produces a large plume of sparkling exhaust when ignited.

Single Base Propellant: A solid propellant based on a single monopropellant. In practice usually nitrocellulose in a mixture with stabilizers and plasticizers. Single base propellants are used as smokeless powders in ammunition. In rockets, such propellants have been largely replaced by composites. Single base propellants are not used in hobby rocketry. See also "Composite Propellant"

Solar Igniter TM: Estes Industries brand of Igniter. Made from two wire conductors with a piece of Nichrome wire connecting them at one end. The nichrome wire tip of the igniter is dipped in a pyrogenic compound which flares to ignite the rocket motor.

Spill Hole: An opening cut in the top of a parachute to increase the sink rate (thus decrease drift distance) and aid recovery on windy days.

Squib: A small explosive device used to detonate larger explosive charges. While the term is sometimes used to describe igniters used in hobby rocketry, especially HPR igniters such as electric matches (q.v.), true squibs are almost *never* used as igniters since their purpose is to set up a detonation pressure wave to set off pressure sensitive explosives (e.g. plastic explosive), while an igniter must start a (relatively) low speed flame front so that the motor burns, rather than explodes.



SRC: Spalding Rocket Club a South Australian ARA section.

String Test: A simple method for testing the stability of a model. A string approximately 10ft long is tied to the center of gravity of a fully prepped rocket which is then twirled overhead in a circle. If the nose points in the direction of the spin and the rocket does not wobble then it is very likely a stable design.

The string test is not very reliable IMHO since it introduces another component, namely radial acceleration, that is completely absent in normal flight. When you tie the string to the rocket at the CG, it's not really at the CG but attached to the outer surface of the body tube *above* the CG (which is actually inside along the center of the tube). In order for the rocket not to twirl, the projection of the string has to pass through the CG. This is fine as long as the rocket is moving in a linear fashion. But when you start swinging it, it's no longer moving linearly, but being constrained to a circle. This forces the rocket (if it's stable) to assume an angle of attack in order to keep pointing into the "relative wind". This angle means that the projection of the string no longer passes through the CG, but slightly behind it. You have to move the string slightly forward for the string to point through the CG while you swing it.

Strip, Stripped: Terms describing a parachute that has had one or more shroud lines pull free due to opening shock. Usual cause is recovery deployment at too high a speed, but can also be due to age (of the tape disks on a plastic chute) or poor construction. Can be used as a verb or noun. See also "Shred" and "Reef"

Suction Lock: The Mother of all Base Drag. See "Bernoulli Lock"

SWM: Spalding Welcome Mart supplier of rocketry motors in South Australia.
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« Reply #18 on: June 29, 2009, 07:37:51 PM »

Terminal Velocity: In the powered phase, the speed where the motor thrust equals the combined forces of gravity and aero drag. Theoretically, the rocket would continue ascending at a constant speed (i.e. no acceleration) with these forces in balance. This doesn't actually happen since motor thrust varies with time and aero drag with altitude. A second meaning is, when descending, where aero drag balances the weight of the descending model. If under a 'chute or other high drag recovery aid, this is quite slow. If in core sample (q.v.) mode this speed can be several hundred feet/sec. See also "Hyperterminal Velocity"

Thermalite: A material, originally used to detonate plastic explosive, which burns at a controlled rate and high temperature. Used with rocket motors as an ignition enhancement. It can be ignited by electric (nichrome) means, flash bulbs or the exhaust of a previously started motor. It comes in three burning speeds color coded as pink (slow), green (medium) and white (fast). For a rough order of magnitude, slow is around 1/2 in/sec and fast is 2 1/2 in/sec in free air, but this can be affected by temperature, humidity, pressure and whether or not the fuse is sheathed in a tube.

Tiger TailTM: An igniter sold by Quest Aerospace consisting of two very thin copper foil leads separated by and even thinner plastic insulator with the pyrogenic compound at the tip. Essentially a mini Copperhead (q.v.), its name comes from the orange and black striped tape strip provided to allow it to be used with ordinary alligator clip ignition systems.

Time Delay: See "Delay Train"

TRA: Tripoli Rocketry Association

Triple Base Propellant: A solid propellant based on three monopropellants and additives. In practice, the monopropellants are usually nitroglycerin, nitrocellulose, and nitroguanidine. In military rockets, such propellants have been largely replaced by composites. Triple base propellants are not used in hobby rocketry. See also "Composite Propellant"

Through The Wall (TTW): An HPR fin attachment technique which provides much greater strength than the typical surface mount used in model rocketry. To use TTW, slots are cut in the body tube where the fins mount and the fins are built with extended tabs on the root edge which fit through these slots. In one form of TTW, the tabs are short and just provide a surface to build up epoxy fillets on the inside as well as the outside. In a stronger version of TTW, the tabs reach all the way to the motor tube where they are glued forming a very rigid box structure (also known as TTW-GTMT for "Glued To the Motor Tube).
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« Reply #19 on: June 29, 2009, 07:39:02 PM »

Wadding: Any flame retardant material used to prevent the scorching of the recovery system do to the heat of the ejection charge. The material (usually a boron treated paper tissue) is placed in the body tube between the engine and the recovery system. See also "Ejection Baffle"

Waiver: The term used to describe the official permission given by the FAA allowing rockets with more than 113 grams of fuel or weighing more than 1 pound to be flown into FAA controlled airspace. See also "FAR 101"

Woosh Generator(w.g.): The humorous, genderless, politically correct way to refer to the propulsion device in a hobby rocket; thus avoiding the great motor/engine debate.
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« Reply #20 on: June 29, 2009, 07:39:27 PM »

YABAR: Yet Another Born Again Rocketeer.
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« Reply #21 on: June 29, 2009, 07:40:09 PM »

Zipper Motor Effect: A devastating side effect of mounting the shock cord to the motor mount (which is often done for strength or to anchor a piston ejection system). If strong and thin cord is used (e.g. Kevlar) and the recovery system opens at too high a speed and/or the piston comes all the way out of the body, then the line can "zip" open the body tube all the way down to the motor mount :-( A sufficiently strong top mounted shock cord can partially zip a body tube if opened at a high enough speed.
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Polecat Thumper on an M1297 yeah!!!!!


« Reply #22 on: June 29, 2009, 07:41:17 PM »

This list is still not complete please check back later. If you have any other suggestions send me a private message.

30/06/09 a few more terms added and typos corrected.
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