Model Rocketry Glossary of Terms
3FNC: Three Fins and a Nose Cone, the description of a generic rocket.
Advanced Rocket: see ‘High Power Rocket’
AGL: Above Ground Level. This is FAA-speak which, when talking about an altitude waiver, refers to the maximum altitude you can legally fly under that waiver. It is usually added to the MSL (Mean Sea Level) altitude of the launch site to give an altimeter reading that pilots must avoid. Example: if your launch site is at 1,500′ MSL and you have a 3,000′ AGL waiver, then pilots must stay above 4,500′ to be safe.
Air Start: Any motor that is started after first motion of the vehicle. Upper stage ignition of a multi stage rocket is a special case of air starting. Usually it is outboard boosters started after a central motor has lifted the vehicle, or visa versa. This can be done by a flashbulb/motion switch, timer, or simply a piece of fuse started by the exhaust of the pad start motor.
AmSpac/AmSpam: Deprecating but affectionate abbreviations for *American Spacemodeling* (q.v.)
American SpaceModeling: The journal of the National Association of Rocketry. Previously known as *The Model Rocketeer* (q.v.), it underwent yet another name change and became *Sport Rocketry* (q.v.) starting with the Sept/Oct 1993 issue.
Amateur Rocket or Experimental Rocket: The class of non-professional rocket beyond HPR. Amateur rockets use structural metal parts and very often the motor casing doubles as the airframe (as with professional rockets). These rockets can be very large and powerful, capable of placing payloads many miles up. Activities in this field (one can scarcely call it a hobby) include formulation and manufacture of propellants and thus can be EXTREMELY hazardous. This is the main reason that amateur rocketry is not to be attempted alone. Another is expense as these vehicles can run many hundreds or thousands of dollars and take months to build. The equipment necessary to safely pursue amateur rocketry (sandbagged bunkers, loading pits, standby fire truck, etc.) are quite beyond the resources of most individuals. Not all amateur rockets are so large. Many of the “beginner” vehicles would qualify as HPR or even model rockets in terms of liftoff weight and total impulse, but fail the NAR/Tripoli codes due to their metal airframes and user-compounded propellants. Note: There is a fine, but significant, difference between using a metal cased reloadable motor with pre-manufactured fuel slugs and packing a pipe with zinc/sulfur (a common amateur beginner fuel). Liquid fueled vehicles are becoming more popular among amateur groups. These can produce up to 1,000 lbs of thrust for up to a minute from a LOX/Kerosene engine which can propel the vehicle to altitudes of over 40 miles. Some hobby! Neither Tripoli nor the NAR sanction amateur rocket activities. See also:
Black Rock Society
Experimental Spacecraft Society
Pacific Rocket Society
Reaction Research Society
Rocket and Space Foundation
AP: Ammonium Perchlorate, the oxidizer used in 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.
Apogee: The highest point of a rocket’s flight path. (More literally, the point farthest on the flight path from Earth.)
AR: American Rocketeer – Centuri’s attempt to produce an MRN (q.v.) clone in the late ’60s. While the contents were fairly typical (product announcements, club news, rocket plans, reports on “real” aerospace events, etc.) it had a curiously over-produced look to it and ran very heavy on the advertising. Someone looking beneath the surface would notice that there was no reader input (e.g. rocket designs or “Idea Box” style tips); that all the rocket plans came from the Centuri design department and the “tips” were for problems that could be solved by items straight from the catalog! While each issue carried a Volume/Number identification, there was only one “Number” for each “Volume.” V1, N1 was in 1966 and continued for at least four years.
B/G: Boost Glider. A glider which is boosted to altitude by a rocket motor. The pod containing the expended motor may separate from the glider at ejection to be returned by streamer or parachute (this is typical but is not required). The more aerodynamically clean glider section is then free to glide more slowly.
Baffle: See ‘Ejection Baffle’
Ballistic Coefficient: A measure of a projectile’s ability to coast. It is defined as Cb = M/CdA where M is the projectile’s mass and CdA is the Drag Form Factor (q.v.). At any given velocity and air density, the deceleration of a rocket from drag is inversely proportional to this value. Intuitively, it is the principle behind why a tightly crumpled piece of paper can be thrown farther than a loosely crumpled one.
BAR: Born Again Rocketeer. An individual who has re-discovered the hobby/sport after an absence of several years. Contrast “BOR”
Base Drag: A component of aerodynamic drag caused by a partial vacuum in the rocket’s tail area. The vacuum is the hole created by your rocket’s passage through the air. Base drag changes during flight. While the motor is firing, the drag is minimal since the tremendous volume of gas generated by the motor fills thisvoid. The drag takes a sharp jump at burnout when this gas disappears (note: tracking smoke has very little effect on base drag due to its low density). Base drag can be reduced by the use of a boattail to transition the main body diameter down to the motor diameter which helps direct air into the evacuated area. When properly designed, a boattail can reduce base drag below zero (i.e. actually generate a small amount of forward thrust) by making use of the “pumpkin seed” effect.
Bernoulli Effect: A phenomenon first described by the 18th century Swiss scientist Daniel Bernoulli who studied the pressures in moving fluid streams. The effect states that moving air will have a lower pressure than the still air around it. This is the principle behind how airplane wings generate lift and why beach balls stay “balanced” on top of fans in those hardware store displays 🙂
The effect is significant in rocketry when using altimeters or any other kind of payload that senses the ambient pressure around the rocket. The air moving by the payload section could cause the payload to indicate a lower pressure than the ambient still air, thus giving a false altitude reading. The effectdrops to zero at apogee when your rocket stops moving, but thealtitude vs. time curve will be wrong.
Bernoulli Lock: A phenomenon similar to the “Krushnic Effect” (q.v.) where the rocket seems to be “glued” to the pad at liftoff. This afflicts larger, flat-bottomed rockets launched too close to pads with flat blast deflectors. The exhaust gasses escape at great speed through the small annular space between the rocket and the pad creating a venturi which generates a low pressure region at the base. This pressure deficit can be significant, and if it is greater than the thrust being generated by the motor, the rocket won’t go anywhere! This is quite possible as a 2″ dia.rocket has, potentially, over 45 lbs (200 N) of “suction” available to hold it back, while a 3″ rocket has over 100 lbs (460 N)! The old Centuri “Point” was an infamous Bernoulli locker when launched from an Estes Porta-Pad with its perfectly matching round blast deflector.
Black Powder: Basically, gunpowder. The ‘traditional’ model rocket motor fuel. Used by Estes and most other model rocket companies through F range. Rocketflite has black powder motors through the H range. See also “AP” and “Composite Motor”
Black Rock Society (BRS): An amateur rocketry organization founded by Tom Blazanin to cater to those who find HPR confining 🙂 It is a serious organization for those dedicated individuals who wish to explore rocketry in a semiprofessional vein. It is open to all forms of reactive propulsion: solid, liquid and hybrid. The mailing address is: Route 1, Box 100 Loving, TX 76460 Phone: 817-378-2590 FAX: 817-378-2593
Boattail: A transition section at the tail of the rocket which gradually narrows the body down to the motor diameter. Used to reduce base drag (q.v.).
Boosted Dart: A method of maximizing altitude for any given impulse motor. A sub-minimum diameter, unpowered “dart” section weighted for Optimum Mass (q.v.) is placed on top of the powered section. At burnout (maximum velocity) the dart is released and coasts higher than even a minimum diameter rocket could due to its smallcross sectional area. This technique is used in professional sounding rockets (e.g. Super Loki) as well as hobby rocketry.
Booster: On a multi stage rocket this refers to the sections (stages) which drop off in mid-flight. On single stage payload rockets,the term is used for the lower powered portion to distinguish it from the payload section. See also “Air Start”
BOR: Burned Out Rocketeer (facetious). Counterpoint to BAR (q.v.). Someone who has been going at the hobby too intensely, such as in preparation for a major contest.
Burn Out Velocity: The velocity the rocket is traveling when the motor runs out of fuel. Usually the highest speed achieved by the rocket. See also “Hyperterminal Velocity”
CA: Cyanoacrylate (‘super glue’). A very strong adhesive popular for use in competition and high power rockets, as well as ‘on the field’ repairs. The three most common forms of CA are often referred to as ‘hot’, ‘gap filling’ and ‘slow’. Hot CA is very thin and has strong wicking properties. It dries in only a few seconds. Gap filling CA is a little thicker and generally comes in 15 – 30 second bond times. Slow CA forms the strongest bond but its bond times are also much longer. Hot or gap filling CA is often used to tack parts into place prior to applying a stronger adhesive with a much longer bonding time (such as an epoxy).
Caliber: In rocketry, the diameter of the main body tube. Usually used when refering to some function of length, e.g. “The CP should be behind the CG by at least one caliber.” The term is borrowed from the small arms industry where it refers to the bore of a rifle or pistol barrel, e.g. a .38 caliber pistol has a barrel with a .38″ bore. Note that in large artillery, caliber refers to the *ratio* of barrel length to bore. For example, a 3 inch 40 caliber gun would have a barrel 120 inches long.
Capacitive Discharge: A type of launch controller which uses a large capacitor to store electrical energy from a battery. When commanded by thelaunch controller, the capacitor discharges a large current into the igniter. These controllers are often used with large cluster rockets to ensure all motors ignite simultaneously.
CATO: A motor failure, generally explosive, where all the propellant is burned in a much shorter time than planned. This can be a nozzle blow-out (loud, but basically harmless), an end-cap blow-out (where all of the pyrotechnic force blows FORWARD which usually does a pretty good job of removing any internal structure including the recovery system) or a casing rupture which has unpredictable, but usually devastating, effects. Another form of CATO is an ejection failure caused by either the delay train failing to burn or the ejection charge not firing, but the result is the same: the model prangs. A CATO does not necessarily burn all of the fuel in a rocket motor (especially true for composite fuels, which do not burn well when not under pressure). For this reason you should be especially careful when approaching a CATO.
Origin: Opinions on the meaning of the acronym range widely. Some say it’s not an acronym at all, but simply a contraction of ‘catastrophic’ and should be pronounced ‘Cat-o’ (which sounds better than ‘cata’ over PA systems :-). Others maintain that it is an acronym but disagree on the meaning, offering a broad spectrum of ‘CAtastrophic Take Off,’ ‘Catastrophically Aborted Take Off,’ ‘Catastrophe At Take Off’ and the self referential ‘CATO At Take Off.’ The acronym crowd pronounces it ‘Kay-Tow’, like the Green Hornet’s side kick. It has been pointed out, though, that all of the above are ‘post-hoc’ definitions since LCO’s were using the term over range PA systems long before any formal acronym was established.
Opinions on the origins say that it is either from the military rocket programs of WW II, the post war development era, or even a modroc-only term which originated with the MESS (Malfunctioning Engine Statistical Survey) performed by NAR’s Standards and Testing committee. There is also a claim that it started with the Boston Rocket Club and that the spelling has evolved over the years. It supposedly started out as ‘KATO’ which, of course, stood for KABOOM At Take Off!
CHAD: Acronym for CHeap And Dirty. Used to refer to a quick and inexpensive (but usually inelegant) way to solve a particular problem or produce some end result.
CHAD Staging: A simple technique used to make a multi-stage rocket out of a single stage vehicle. A booster motor is taped to the end of the standard, single stage motor in the rocket. The booster is totally external to the rocket. The booster is then ignited in the usual manner. This technique only works with black powder motors. It will only work with models that are VERY over-stable to begin with. When CHAD staging does work, however, it is the most efficient staging method because it minimizes increased drag and mass associated with an added stage. (See Optimum Mass)
Chuff: A form of unstable combustion marked by brief bursts of thrust separated by periods of no thrust. Typically, the bursts come faster and become longer as burning proceeds, until stable burning results. The sound of chuffing is similar to that of a steam locomotive starting up. It generally occurs in a composite motor that is ignited too low in the grain.Chuffing can be dangerous, since a short burst of thrust can launch the rocket off the launch rod, and a lull immediately following the burst can put the rocket on the ground. When stable burning ensues, such a rocket will be flying horizontally. See “Land Shark”
CG: Center of Gravity. The point about which a free body will rotate when disturbed by an outside force. For a model rocket, this is the point where the effects the masses of the individual components cancel out and the model will balance on a knife edge. As with a see-saw, a mass further from the CG will have a greater effect than the same mass closer in.
Clip Whip: A number of micro clips on short wires (usually three) all connected at their free end. Used to aid in the ignition of clusters (q.v) where each motor uses a separate ignitor.
Cluster: A rocket that fires more than one motor simultaneously. See also “Clip Whip” and “Davis Douche”
Composite Material: Hi-Tech materials, other than paper, wood or metal, used in the construction of rockets (see also “Phenolic”).
Composite Motor: The term used broadly to cover solid fuel rocket motors using propellants other than black powder. Composite motors require different igniters and igniter systems from black powder motors.
Composite Propellant: In Hobby Rocketry, any propellant other than black powder. In military parlance (where the term originated) the term is used to denote propellants that are mixtures of oxidizers and fuels and to distinguish them from Single, Double, and Triple base propellants (which are either monopropellants or mixtures of monopropellants). Note that by the military definition, black powder is itself a composite propellant because it consists of separate oxidizers (KNO3 and sulfur) and fuel (charcoal). Further note that by the hobby definition, single/double/triple base propellants are composites because they are not black powder. No ambiguity arises, however, since the military doesn’t use black powder (in rockets, anyway), and no hobby rocket motors use single, double or triple base propellants. See also “Single Base Propellants”, “Double Base Propellants” and “Triple Base Propellants”
Confirmation Certification: The process whereby a member of Tripoli or the NAR becomes certified as eligible to purchase high power (H and up) motors.
Contest Acronyms: The NAR uses a bewildering number of acronyms to describe its contests. As with most things of this nature, there is a logic to the naming which makes things much easier to understand once learned.
The basic structure of an event name is a prefix, the event acronym and a suffix. The prefix is always the motor code (currently 1/4A thru G) and the suffix is either an “A” for altitude events or “D” for duration events if such a distinction needs to be made (some events, such as parachute duration, have the suffix “built in” to its name, thus don’t use one). A futher appendage is the use of “MR” for “Multi-Round” events where you make several flights and pick the best ones.
Lastly, there is a set of scoring acronyms used in judging the events, but are not part of the event itself.Event Acronyms:
BG – Boost Glider
DEL- Dual Eggloft
DR – Drag Race
EL – Eggloft Single
FW – Flexwing BG
HD – Helicopter Duration
OSL – Open Spot Landing
PAY – Payload
PD – Parachute Duration
PMC – Plastic Model Conversion
PRA – Predicted Altitude
PRD – Predicted Duration
PSL – Parachute Spot Landing
R&D – Research & Development
RDA – Random Altitude
RDD – Random Duration
RC/RG – Radio Controlled Rocket Glider
RG – Rocket Glider
SC – Scale (often seen written out)
SCA – Scale Altitude (sometimes seen as Sc.Alt)
SD – Streamer Duration
SL – Spot Landing
SPSC – Sport Scale
SPSY – Space Systems
SR – Superroc
SSL – Streamer Spot Landing
STA – Set Altitude
STD – Set Duration
SUSC – Super Scale
Note that there is an ambiguity in the Eggloft event notation. “DELA” could mean the generic Dual Eggloft Altitude event or D Eggloft Altitude. For this reason, the prefixes are normally separated from the event acryonym by spaces.Flight Card/Results Acronyms:
BRK – Broken Egg or
EGG – Broken Egg
CATO – obvious, I hope
DQ – Disqualified flight
NC – Track Not Closed
NG – No Glide
NR – No Return
PRG – Prang
ROT – No Rotation
SHR – Shread
TL – Track Lost
Continuity Check: A group of electrical techniques for checking the firing circuit through the igniter to ensure that the circuit is functional. This usually involves some type of light or audio tone activated by a push-button. The techniques range from a simple current limiting light bulb or buzzer placed in series with nichrome igniters, to sophisticated bridge circuits for sensitive, low current flashbulbs and electric matches.
CopperheadTM: The trademark name for an igniter produced by AeroTech, Inc. It is a laminated assembly consisting of a two copper foil strips separated by an insulator, with a quantity of pyrogenic compound on one end. It normally requires a special clip for electrical connections, but some rocketeers have mastered the “Z-Fold” which allows use of normal alligator clips.
Core Sample: Synonyms describing a failure mode where the model comes down fast and hard (nose first) and ends up tail-high in the ground (this is where large, colorful fins come in handy :-). Often the nose cone has separated (taking the recovery device with it) and the body tube ends up containing a nice ‘core sample’ of mud/dirt when pulled out of the ground. Also known as:Auger In
CP: Center of (Aerodynamic) Pressure. The point on a rocket where stability-restoring forces due to airflow against the back part of the rocket (fins, etc.) exactly equal the disturbing forces against the part of the rocket ahead of that point.
The location of this point depends on the rocket’s orientation at the time of measurement. If it is at a very small angle to the “local wind” (line of flight), the fins’ restoring contribution will be large, while the nose’s disturbing contribution will be small, resulting in a CP that is way back. The CP in this case can be located using the Barrowman Equations. If the rocket is nearly sideways, the CP will be much more forward. The CP in this case can be located by balancing a cardboard silhouette of the rocket.
Since all free bodies can rotate only on their center of mass, stability is usually a simple matter of placing your CG ahead of your CP, which ensures that the restoring forces of airflow on the rear of the model will always overcome the disturbing forces on the front.
A good rule of thumb for sport models (both high and low power)is to design the rocket with the CP one or two body diameters behind the CG.
CPSC:Consumer Product Safety Commission. The government agency which has the task of deciding whether or not a given product is safe for ‘general consumer’ use.
Cruise Missile: A rocket which has failed in such a way that it ends up flying horizontally while still under power. A common example would be a multi-stage rocket which stages “dirty”(due to stability or structural problems) causing the upper stage to bend to near horizontal at ignition. Severe launch rod tip off or high winds have also been know to cause a cruise missile attitude.
Davis Douche: A method of igniting clustered motors by using a piece of fuse in each motor with all fuses dropping into a pie plate that has been dusted with black powder and taped to the bottom of the model. A single ignitor in the black powder “flashes the pan” igniting all the fuses at once. Developed in the early ’60s by Joel Davis and detailed in an early Model Rocketry Magazine [late 1968 or early 1969, before they went to color covers].
Delay Train/Delay Charge: Pyrotechnic material in the rocket motor which burns slowly between the propellant charge and the firing of the ejection charge. This allows the rocket to coast towards apogee and slow down to deploy the recovery system at low speed.
Double Base Propellant: A solid propellant consisting of two monopropellants (usually nitroglycerin and nitrocellulose) and various additives. Double base propellants are used as smokeless powders in ammunition. They are also used in smaller military rockets but have been largely replaced by composites in larger vehicles. Double base propellants are not used in hobby rocketry. See also “Composite Propellant”
DQ: Disqualified flight. See also “Midwest Qualified”
Drag Coefficient(Cd): A dimensionless number used in aerodynamics to describe the drag of a shape. This number is independent of the size of the object and is usually determined in a wind tunnel. It is part of the basic drag equation F=.5*rho*V^2*Cd*A where F is the drag force, rho is the air density, V is the air velocity and A is the cross sectional area. All of these, except Cd, are directly measurable in a wind tunnel so Cd can be thought of the “fudge factor” that accounts for all of the aerodynamic peculiarities of a shape. The Cd for most sport type hobby rockets is in the range of .4 to .5. See also “Reynolds Number.”
Drag Form Factor(CdA): The Drag Coefficient (q.v.) of an object multiplied by its cross sectional area. This is used to scale the drag value for a particular object from the dimensionless Cd. Theoretically, every object of a similar shape will have the same Cd regardless of its size, meaning that both a grain of rice and a Zeppelin would be the same. Multiplying by the area allows comparisons of the true drag between dissimilar objects. For example, the original Honda Civic had a horrible Cd, and makers of large luxury cars, with a little edge rounding, were easily able to beat it and proclaim “Lower drag than a Honda Civic!” in their ads. This is patently absurd as the Honda had such a tiny cross section, thus much lower *actual* drag. See also “Optimum Mass”
Drop Staging: See ‘CHAD Staging’
Effective Exhaust Velocity: See Impulse (Relative)
Ejection Baffle: A device used in some rockets to eliminate the need to use wadding to protect the recovery system. Usually composed of some type of metal wool or mesh to absorb the heat of the ejection gases before they reach the recovery compartment.
Ejection Charge: A small quantity of black powder used to generate gas pressure within the rocket to deploy the recovery system. This is activated when the delay train (q.v.) burns through. On rockets with electronic ejection timers, this may be a separate small container of black powder which is triggered by a signal from a timer or other control unit.
Electric Match: A type of igniter originally designed to set off fuse-type blasting caps (i.e. a match that can be set off from a great distance electrically). It requires a very low electrical current (~10 mA range) to activate.
Engine: A machine that converts energy into mechanical motion. Such a machine is distinguished from an electric, spring-driven or hydraulic motor by its consumption of a fuel (from *American Heritage Dictionary*).
Estes Dent: A semicircular deformation of the leading edge of the body tube cause by the nose cone snapping back and striking the body at ejection. The problem is intensified by short shock cords which don’t absorb as much energy before reversing and give the nose a closer target with better aim 🙂 So named due to that company’s policy of providing very short shock cords in their kits.
Experimental Rocket: See “Amateur Rocket”
Fillet: A reinforcement of the joint between the fin and the body tube of the rocket to improve the rocket’s aerodynamics and to strengthen the fin mount. See also “TTW”
FIREBALLS: An experimental rocketry/HPR launch hosted by AERO-PAC (q.v.) which has since been superseded by NXRL (q.v.). The emphasis was on VERY LARGE advanced rockets of “K” impulse or higher. The idea originated with Steve Buck and the first launch was sponsored by Bill Lewis of AERO-PAC. The name came from jokes surrounding the event (e.g. “It takes BALLS to launch a rocket that big”). Steve claims that it was never intended to mean “Big Ass Load Lifting Suckers” as implied in early advertisements. Against the wishes of its founder, “Fire” was placed in front of “BALLS” to placate those few who had a problem with the name.
Fireballs was traditionally held the Monday after LDRS (q.v.),but it was never formally a Tripoli launch. The 1992 FIREBALLS (where ‘Down Right Ignorant’ was launched) was sponsored by Tripoli for the purposes of insurance coverage, and after that they decided to “adopt” the event with a name change.
GSE: Ground Support Equipment. Anything you bring to the launch site which is necessary to fly your rocket, but doesn’t actually fly with it. Obvious examples are the launch pad, launch controller, a prep table, etc. Less obvious examples are payload support stuff like receivers and tape recorders if you’re flying a broadcasting type data collection payload.
Hang Fire/Misfire: Terms which refer to abnormal ignition. With hang fire, the motor usually ignites after a considerable delay. Misfires never ignite. Hang fires often appears as a misfire until the motor ignites some time later. This is the main reason the safety code advises not to approach a misfired rocket for one minute.
High Power Rocket(ry) (HPR): Hobby rockets that exceed the total weight, total propellant or single motor total impulse restrictions of model rocketsas defined in NFPA 1122 (q.v.) but otherwise conform to the same guidelines for contruction materials and pre-manufactuered, solid propellant motors. High power rockets have no total weight limits, but do have a single motor limit of no more than O power (40,960 NS total impulse) and have a limitation of 81,920 NS total impulse.
There is a draft NFPA document (NFPA 1127) under review which would formalize this definition.
HMR: The Handbook of Model Rocketry. The official NAR handbook for the hobby. Originally written by G. Harry Stine (NAR #002) in the mid ’60s (the first edition came out in 1965) and currently in it’s sixth edition. It has expanded it’s scope with the hobby by adding computer programs (not always the best sorted out) in the fourth edition and giving a nod towards the existence of HPR in the current (sixth) one.
Hobby Rocket: A general, collective term used to describe both model and HPR rockets to differentiate them from amateur/experimental rockets. The latter, while also non-professional, might better be called “Obsession Rockets” 🙂
HPR Lite: A term used to describe rockets using motors in the ‘E’, ‘F’, and ‘G’ power classes. Formerly called “Medium Power Rocket” (a term nobody used), it describes rockets which fall between the old NFPA 1122 weight limit of 1 lb (454 grams) and the current model rocket weight limit of 1500 grams. Rockets in the ‘E’ through ‘G’ class aren’t normally considered high power rockets but, to be successful, must be built using many of the same construction techniques as the larger rockets. Also, any rocket over 1 lb requires an FAA waiver to fly legally.
HPRM: High Power Rocketry Magazine – formerly *Tripolitan* (q.v.). An independent magazine dealing with all aspects of consumer rocketry, but with a definite emphasis on high power, advanced and experimental consumer rocketry. Published six times a year. A subscription is included with membership in Tripoli, but can be had separately. Also available on newsracks in larger hobby stores. Current editor: Bruce Kelley.
Hyperterminal Velocity: A situation where a rocket is traveling faster than terminal velocity (q.v.) for a given motor. This is possible, for example, with a staged model with grossly mismatched motor combinations such as an F-100 staged to a B6. At staging, the upper stage will already be beyond its terminal velocity for the “B” motor. In this case, the upper stage will actually *decelerate* during thrusting and approaches terminal velocity from above.
Igniter: An expendable device used to ignite a rocket motor.
Impulse(Relative): A measure of the efficiency of a rocket engine. Similar to Specific Impulse, it is defined as the Total Impulse (q.v.) divided by the mass of the propellants. A little dimensional juggling shows that this gives the same units as velocity (ft/sec or m/sec) hence is sometimes called “Effective Exhaust Velocity.” How quickly the reaction mass leaves the nozzle is a good measure of efficiency.
Impulse(Specific): A measure of the efficiency of a motor/propellant system. It is determined by taking the Total Impulse (q.v.) and dividing by the weight of propellants. This carries the potentially confusing units of “seconds” (as if it had something to do with the burn duration) but is due to weight and thrust both being force parameters hence canceling out (e.g. lb-sec/lb or N-sec/N). This is actually very handy since it makes the term independent of the units system (metric or English) since they both use “seconds” for time.
Impulse(Total): A measure of the total momentum imparted to the rocket by the motor. It is defined (for those who know calculus) as the integrated area under the thrust-time curve. For the rest of us, it can be thought of as the motor’s average thrust times the duration of the burn. Measured in N-sec or Lb-sec.
Kato: See “Cato”
Kicked: A term used to describe a motor which is ejected from the rocket while in flight. This often results in the failure of the recovery system. It is usually caused by not fitting the motor into the motor mount properly. See also “Prang”
Kitbash: Taking two (or more) kits and combining (“bashing”) them into a new design. Often used as a contest event (Team Kitbash, where teams compete, Kitbash Duration, Scale Kitbash, etc) where the idea is to be creative in a limited amount of time.
Origin: The term appears to have come from the model railroading hobby where kits for buildings and other diorama items have, for decades, been modified from their original intent to suit the needs of a particular layout.
Krushnic Effect: A very dramatic phenomenon where your rocket makes a tremendous amount of noise and smoke but doesn’t go anywhere! This happens when the motor is recessed into the body tube by more than one tube diameter. If so recessed, the cylindrical volume below the motor forms a secondary expansion chamber which allows the exhaust gasses to expand below atmospheric pressure before leaving the rocket. Surrounding air aspirated into the exhaust stream causes turbulence which negates much of the thrust, along with creating the characteristic roar. A multi-stage model that ejects its booster motor, but not the airframe, is a perfect example. Very damaging; it almost always destroys the lower body tube beyond use. Named for Richard Krushnic, the rocketeer who characterized the effect in the late ’60s. Not to be confused with “Suction Lock” (q.v.).
Land Shark/Worm Burner: A rocket which has failed in such a way that it ends up on the ground while still under power. Upper stages of unstable multi-stage rockets often end up like this, as do some (too) heavy HPR rockets with long-burning, low thrust motors.
Landis Loop: A ring used in a tower launcher to keep the back end of a egglofter centered during launch. Invented by Geoff Landis and named for him by Bob Kaplow.
LCO: Launch Control Officer: the individual responsible for safe operation of the launch range.
LDRS: The annual national high power sport launch sanctioned by Tripoli. LDRS stands for ‘Large Dangerous Rocket Ships,’ the derivation of which is best left to others. Note: LDRS has NEVER stood for ‘Lets Do Rocketry Safely’, despite what you hear from historical revisionists trying to mollify public officials 🙂
Lovelace Effect: A phenomenon where the nose cone is apparently “sucked” out of the body right at motor burnout. It is more prevalent on parabola, ogive and other low drag nose shapes. The theory (as yet unproven) is that since the nose cone has much less drag than the body, its momentum tends to carry it forward faster (or, more correctly, the body’s drag decelerates *it* more quickly) putting tension on the nose-body joint. The condition is exacerbated by any nose weights added for stability (which also raise the momentum of the nose) and/or a loose fit of the nose in the body.
Another possible contributing factor could be the denser air (trapped in the body tube from ground level) exerting pressure on the nose cone once the rocket reaches a higher altitude.
The term is named after an early ’70s movie actress who, ahh, um…well, go ask your dad 🙂
MagneliteTM;: An ignitor made by Rocketflite used mainly to start composite motors. A medium power device (2-3 amps at 12 volts), it requires significantly more than an electric match (q.v.), but not as much as a Copperhead (q.v.). It consists of a nichrome bridgewire dipped in a magnesium based pyrogen which burns *very* hot (~6000F), aiding in the ignition of stubborn composites, such as a “Blue Thunder”. They come both single and double dipped, depending on how much “oomph” you need. The head is quite large so they work best in 29mm and larger motors.
Medium Power Rocket: See “HPR Lite”
MIF: Missing In Flight. A rocket that disappears with no sign of the recovery system deployment, and no other obvious failure mode (e.g. Prang or CATO). Sometimes called “into orbit.”
Minimum Diameter: A rocket built with the smallest possible diameter body tube for the size of motor casing. Usually done to reduce drag in sport or competition models even though it can increase the difficulty of attaching fins and recovery systems. See also “Boosted Dart”
Model Rocket: An aero-vehicle that ascends into the air by means of a reaction motor, but without the use of aerodynamic lifting surfaces.
Modroc: Model Rocket. Also seen as ‘modrocer’, or similar spelling, to mean ‘model rocketry enthusiast’.
Monopropellant: See “Single Base Propellant”
Motor: Something that imparts or produces motion, such as a machine or engine. A device that converts any form of energy into mechanical energy (from *American Heritage Dictionary*).
MRN: The Model Rocket News – The oldest continuously published rocketry periodical. Started by Vern Estes and his small crew in 1960, it is still sent to all of Estes’s active mail order customers. Somewhat sophomoric in style, it contains a great deal of practical information, especially for beginners. It has survived a bewildering array of changes in format over the years, but is still published three or four times annually. Current editor: Mike Hellmund.
NAR: National Association of Rocketry. A national hobby organization promoting model and high power rocketry in the United States. The NAR promotes rocketry related sport flying, competitions, and education.
NARAM: National Association of Rocketry Annual Meet. The NAR national championships competition, held in August of each year.
NARCON: National Association of Rocketry Annual Convention. An annual event sanctioned by the NAR oriented towards non-competitive (i.e., sport) model and high power rocketry. It includes seminars, R&D presentations and lots of sport flying.
Newton & Newton-second: Metric units used to measure thrust and total impulse (q.v.)respectively. One pound = 4.448 newtons.
NSL: National Sport Launch. An annual, national sport fly sanctioned by the NAR. It is currently held in February of each year so that it is midway between NARAM national meets.
NFPA: National Fire Protection Association. A private for-profit organization responsible for crafting rules and regulations dealing with fire safety issues which are beyond the expertise of local agencies. The NFPA is NOT a government agency and has no enforcement power of its own. It gathers experts in various fields to write safety regulations for adoption by local fire agencies (at the discretion of the Fire Marshal). The current NAR Model Rocket Sporting Code was developed by the NAR and NFPA. Both the NAR and Tripoli are members of the NFPA. G. Harry Stine (‘the old rocketeer’) is currently the chairman of the pyrotechnics committee of the NFPA.
NFPA 1122: The current NFPA regulation defining Model Rocketry. This document defines a model rocket as having less than 1,500 grams total launch weight, containing less than 125 grams of fuel (no more than 62.5 grams in any one motor), and no more than 160NS total impulse in all motors (no individual motor having more than 80NS of total impulse).
NFPA 1127: The NFPA regulation defining High Power Rocketry. The draft provisions of 1127 (not yet ratified) defines HPR as follows:
High power rockets have no total weight limits, but do have a single motor limit of no more than O power (40,960 NS total impulse) and have a total limitation of 81,920 NS total impulse.
NXRL: The National Experimental Rocket Launch. An annual launch sponsored by Tripoli and hosted by AERO-PAC (q.v.) for the purposes of launching very large (K and above) HPR birds. An outgrowth of FIREBALLS (q.v.), Tripoli “adopted” the concept to provide insurance and continuity on an annual basis. The main difference between NXRL and other Tripoli launches (e.g. LDRS, Danville) are that no rockets *below* K power are permitted (which holds down the crowd) and that home made motors are allowed as long as they conform to the basic HPR safety code.
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 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.
Parabola: A shape produced by the formula y=x^2. Used to produce low drag nosecones. See also “Ogive”
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’.
Origin: If you insist on it being an acronym, the postwar military sounding rocket program had a quasi-official failure mode category “Parachute Recovery Apparatus No Good.” However, like CATO (q.v.), this is another “Post Hoc” definition. The term was in widespread use during WW II in aviation circles to describe aircraft crashes, especially experimental or military ones. Prior to use in the U.S., it was popular in Britain since at least the ’30s where the expression “Prang his Kite” was equivalent to our “Auger in” or “Buy the Farm.”
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.
Origin (in the modeling sense): The term comes from model railroading where hobbiests model sections of entire railroads including whole towns, mountains, lakes, etc. in addition to the engines, cars and tracks. See also “Scale Data” and “Scale Plan”
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.
RMSTM: Reloadable Motor System. The trademarked name of the AeroTech/ISP reloadable motors. Often used (incorrectly) as a generic name for all reloadable technology.
Rocket and Space Foundation: An organization in Holland that supports both model and amateur rocketry and amateur astronomy. It is currently trying to arrange a Get Away Special container for a space shuttle flight. The Secretary is Marcel Verhoef, Delft University of Technology, who can be reached at:Rocket and Space Foundation
P.O. Box 314
3350 AH Papendrecht
Internet: [email protected]
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.
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.
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 StreakTM: 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”
SNI: Slimy NAR Insider. A person who associates with (either professionally or casually) members of the NAR board of trustees, thus being privy to the “inner workings” of the organization. Said to have originated during “flame wars” on the CompuServe Sport Rocketry SIG.
SNP: Slimy NAR Politician. Coined by NAR President Mark “Bunny” Bundick, it refers to an SNI (q.v.) who actually manages to get elected to the NAR board.
Solar IgniterTM: 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.
Sport Rocketry: The journal of the National Association of Rocketry. Previously known as *American Spacemodeling* (q.v.). Published six times per year. Distributed as part of membership to all active NAR members but also available off the rack in larger hobby shops. It has no connection with the CompuServe discussion group of the same name. Current editor: Steve Weaver.
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.
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”
SuperRoc: An NAR competition based on high aspect ratio (i.e. large length-to-diameter) rockets. The length of the rocket is dependent on its motor size with the smallest (1/4A) having a minimum length of 25cm. The minimum length goes up 25cm for each motor class (e.g. 1/2A is 50cm, “A” is 75cm, etc.) so that a “G” SuperRoc must be at least 225cm long. Maximum length is twice the minimum and the scores are weighted in favor of longer rockets. In case your calculator needs recharging, this means that a “G” SuperRoc could be nearly 14 ft long!
Like many types of contests, SuperRoc has no real “point” other than to create a competition that is difficult to do. Some sanitized versions of SuperRocs have been put out as kits, such as the Estes “Mean Machine” (a D class SR) and the MRC “Big Ben” (a “B” or “C” class SR).
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”
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”
Tripoli (TRA): Tripoli Rocketry Association. A consumer rocketry organization founded to promote the interests of high power and advanced rocketry enthusiasts.
Tripolitan: *The Tripolitan…America’s High Power Rocketry Magazine* The bimonthly journal of the Tripoli Rocketry Association, published until July/August 1992. It became *HPR Magazine* (q.v.) with the Sept/Oct 1992 issue).
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).
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.
YABAR: Yet Another Born Again Rocketeer.
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.