Jump to content

Model rocket

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Iomesus (talk | contribs) at 08:45, 9 March 2008 (→Motors). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

A model rocket launching

Model rocketry is a hobby similar to building model airplanes, where rocket-shaped models are flown vertically and recovered by a variety of means (see Recovery below).

Model Rocketry

Model rocketry usually involves commercially-manufactured black powder rocket motors. These motors are tested and certified by the National Association of Rocketry, the Tripoli Rocketry Association or the Canadian Association of Rocketry and come in standardized sizes (A's, B's, C's, etc.) --most often 10-, 13-, 18- and 24mm diameters in diameter..

Model rocketry

According to the National Association of Rocketry (NAR) safety code, model rockets are constructed of paper, wood, plastic and other lightweight materials. The code also provides guidelines for motor use, launch site selection, launch methods, launcher placement, recovery system design and deployment and more. Since the early 1960s, a copy of the Model Rocket Safety Code has been provided with most model rocket kits and motors. Model rocketry historically is a very safe hobby and is often credited as the most significant source of inspiration for children who eventually become scientists and engineers. See National Association of Rocketry (NAR).

History

While there were many small rockets produced over the years for research and experimentation, the modern model rocket, and more importantly, the model rocket engine, was designed in 1954 by Orville Carlisle, a licensed pyrotechnics expert, and his brother Robert, a model airplane enthusiast. They originally designed the engine and rocket for Robert to use in lectures on the principles of rocket powered flight. But then Orville read articles written in Popular Mechanics by G. Harry Stine about the safety problems associated with young people trying to make their own rocket engines. With the launch of Sputnik, many young people were trying to build their own rocket engines, often with tragic results. Some of these attempts were dramatized in the fact-based movie October Sky. The Carlisles realized their engine design could be marketed and provide a safe outlet for a new hobby. They sent samples to Mr. Stine in January, 1957. Stine, a range safety officer at White Sands Missile Range, built and flew the models, and then devised a safety handbook for the activity based on his experience at the range.

The National Association of Rocketry was founded in 1957 to help promote not only the hobby, but to promote the safety of the activities related to model rocketry.

Companies

The first model rocket company was Model Missiles Incorporated, in Denver, Colorado, by Stine and others. Stine had model rocket engines made by a local fireworks company recommended by Carlisle, but reliability and delivery problems forced Stine to approach others. Eventually Stine approached Vernon Estes, the son of a local fireworks maker. Estes founded Estes Industries in 1958 in Denver, Colorado, and developed a high speed automated machine for manufacturing solid model rocket motors for MMI. The machine, nicknamed "Mabel", made low cost motors with great reliability, and did so in quantities much greater than Stine needed. Stine's business faltered and this enabled Estes to market the motors separately. Subsequently, he began marketing model rocket kits, and eventually, Estes dominated the market. Estes moved his company to Penrose, Colorado in 1960, and it continues to operate there today.

Competitors like Centuri and Cox came and went during the 60's, 70's and 80's, but Estes continued to control the market, offering discounts to schools and clubs like Boy Scouts of America to help grow the hobby. In recent years, companies like Quest Aerospace have taken a small portion of the market, but Estes continues to be the main source of rockets, motors, and launch equipment for the low powered rocketry hobby today.

In the high powered arena, which began in the mid-80's with the availability of G through J class motors, a number of companies have shared the market. By the early 1990s, Aerotech, LOC/Precision, and Public Missiles had taken up leadership positions, while Aerotech and a host of engine manufacturers provided ever larger engines, at much higher costs. Companies like Aerotech, Vulcan, and Kosdon were widely popular at launches during this time as high powered rockets routinely broke Mach 1 and reached heights over 10,000 ft.

Engine reliability became a significant issue though, with "CATO"s, or catastrophic failures, occurring relatively frequently (est. 1 in 20) when motors of L class or higher were fired. At costs exceeding $300 per motor, the need to find an alternative was apparent. In the early 1990s, reloadable motors (metal sleeves with screwed on end caps and filled with cast propellant slugs) were introduced by Aerotech and became a popular way to reduce the price of launches. These engines dominate the market today. At this time (2006) single use motors above G class are quite rare, and many are collectibles. Aerotech, Dr. Rocket, Animal Motor Works, Rouse-Tech, Cessaroni, Ellis Mountain, and Loki Motorworks provide the majority of reloadable systems today.

Aerial photography

Cameras and video cameras can be launched on model rockets to take photographs in-flight. Model rockets equipped with the Astrocam or Snapshot film camera or the Oracle digital camera, or with homebuilt equivalents, can be used to take aerial photographs.

These aerial photographs can be taken in many ways and with many different types of cameras. Mechanised timers can be used to take photographs. Passive methods are also employed, such as strings that are pulled by flaps that respond to wind resistance. Microprocessor controllers can also be used. However, the rocket's speed and motion can lead to blurry photographs, and quickly changing lighting conditions as the rocket points from ground to sky can have an impact on video quality. Video frames can also be stitched together to create panoramas. As parachute systems tend to fail, model rocket cameras need to be protected from impact with the ground.

Instrumentation and experimentation

Model rockets with electronic altimeters can report and or record electronic data such as maximum speed, acceleration, and altitude.

Rocket modelers often experiment with rocket sizes, shapes, payloads, multistage rockets, and recovery methods. Some rocketeers build scale models of larger rockets, space launchers, or missiles.

High Power Rocketry

As with low power model rockets, high power rockets are also constructed from lightweight materials. Unlike model rockets, high power rockets often require stronger materials such as fiberglass, composite materials, and aluminum to withstand the higher stresses during flights which often exceed Mach 1 (~700 mph) and over 10,000 ft altitude.

High power rockets are propelled by larger motors ranging from class H to class O. Their motors are almost always reloadable rather than single-use in order to reduce cost. Recovery and/or multi-stage ignition may be initiated by small on-board computers, which use an altimeter or accelerometer for detecting when to ignite engines or deploy parachutes.

High powered model rockets can carry large payloads, including cameras and instrumentation such as GPS units.

The Bureau of Alcohol, Tobacco and Firearms (BATF) has classified Ammonium Perchlorate Composite Propellant (APCP), the most commonly used propellant in high power rocket motors as explosives. Therefore, at this time, to store and possess most high-power rocket motors in the US requires a permit from the BATF. The national rocketry organizations, Tripoli Rocketry Association and National Association of Rocketry (NAR), have sued the BATF to have APCP removed from the explosives lists. Among other things, Tripoli and NAR contend that APCP does not function by explosion and is therefore not subject to BATF regulation, and that the BATF added APCP to the explosives list without following the agency's own rules.

Many high power launches are held each year in wide open spaces throughout the United States, Canada, and Europe. At each of these events one can see many adult rocketeers realizing their dream of building bigger, more powerful, and higher flying versions of the model rockets they enjoyed as kid.

Recovery

Model and high-power rockets are designed to be safely recovered and flown repeatedly. The most common recovery methods are parachute and streamer. The parachute is usually blown out when the engine's recoil creates pressure and pops off the nose cone. The parachute is attached to the nose cone, making it pull the parachute out, and make a soft landing.

Tumble recovery

The simplest approach, and one only appropriate for small rockets or rockets with a large cross-sectional area, is to have the rocket tumble back to earth. Any rocket which will enter a stable, ballistic trajectory as it falls is not safe to use with tumble recovery.

Nose-blow recovery

Another very simple recovery technique, used in very early models in the 1950s and occasionally in modern examples, in nose-blow recovery the ejection charge of the motor ejects the nose cone of the rocket (usually attached by a shock cord made of rubber, Kevlar string or another type of cord) from the body tube, destroying the rocket's aerodynamic profile, causing highly-increased drag, and reducing the rocket's airspeed to a safe rate for landing. Nose-blow recovery is generally only suitable for very light rockets.

Parachute/Streamer

The approach used most often in small model rockets. It uses the ejection charge of the motor (see below) to deploy, or push out, the parachute or streamer. Air resistance slows the rocket's fall, ending (hopefully) in a smooth, controlled and gentle landing.

Glide recovery

In glide recovery, the ejection charge either deploys an airfoil (wing) or separates a glider from the motor. If properly trimmed, the rocket/glider will enter a spiral glide and return safely. In some cases, radio-controlled rocket gliders are flown back to the earth by a pilot in much the way as R/C model airplanes are flown.

Some rockets (typically long thin rockets) are the proper proportions to safely glide to Earth tail-first. These are termed 'backsliders'.

Helicopter recovery

The ejection charge, through one of several methods, deploys helicopter-style blades and the rocket auto-rotates back to earth. The helicopter recovery happens when the engines recoil creates pressure, making the nose cone pop out. There are rubber bands connected to the nosecone and 4 blades. The rubber bands pull the blades out, and let them copter down.

Motors

Anatomy of a basic model rocket engine. A typical engine is about 8cm long. 1. Nozzle; 2. Case; 3. Propellant; 4. Delay charge; 5. Ejection charge; 6. End cap

Most small model rocket motors are single-use engines, with cardboard bodies and lightweight molded ceramic nozzles, ranging in power class from 1/8-A to E. They contain a black powder propellant. These engines typically do not exceed the size of an E engine for black powder is very brittle. If one accidentally drops a "large" black powder motor on the ground or exposes it to many heating/cooling cycles (for example in a closed vehicle exposed to the weather), the propellant charge may become fractured in a hairline fashion. This increases the surface area of the propellant, and the internal chamber pressure of the engine exceeds the strength of the paper case, causing the motor to burst open. This can channel the blast pressure through the rocket's tubular body with effects ranging from a simple ruptured tube to the violent ejection (and occasionally ignition) of the recovery system.

Larger rocket motors are thus available, using composite propellants made of ammonium perchlorate, potassium nitrate, aluminum powder, and a rubbery binder substance contained in a hard plastic case. This type of fuel is similar to the solid fuel used in rocket boosters of the space shuttle. These motors range in impulse from the B to the O range. Composite motors produce more impulse per unit weight than do black powder motors. Also, the propellant is less fragile, resulting in few major failures.

Reloadable motors are also available. These are commercially-produced motors requiring the user to put propellant grains, o-rings and washers (to contain the expanding gases), delay grains and ejection charges into special non-shattering aluminum motor casings with screw-on or snap-in ends (closures). The advantage of a reloadable motor is the cost: because the main casing is reusable, reloads cost significantly less than single-use motors of the same impulse. Reloadable motors are available from D through O class.

Motors are electrically ignited with a short length of pyrogen-coated nichrome, copper, or aluminum wire pushed into the nozzle and held in place with flameproof wadding, rubber band, a plastic plug or masking tape. On top of the propellant is a tracking delay charge which produces smoke but essentially no thrust as the rocket slows down and arcs over. When the delay charge has burned through, it ignites an ejection charge, which is used to deploy the recovery system.

Motor Nomenclature

File:WikiModelRocketMotors.jpg
Rocket motors. From left, 13mm 1/2A10-0, 18mm C6-7, 24mm D12-5, 24mm E9-4, 29mm G40-10.

Model rocket motors produced by companies like Estes Industries and Quest Aerospace are stamped with a code (such as A10-3T or B6-4) that indicates several things about the motor.

Motors are commercially available in many sizes. The Quest Micro Maxx engines are the smallest at a diameter of 6mm. The company Apogee Components made 10.5mm micro motors, but those were discontinued in 2001. Estes then comes in with "T" (Tiny) motors that are 13 mm in diameter by 45 mm long, while standard A, B and C motors are 18 mm in diameter by 70 mm long. Larger C, D, and E class black powder motors are also available; they are 24 mm in diameter and either 70 (C and D motors) or 95 mm long (E motors). Some motors, such as F and G single-use motors, are 29mm in diameter. High-power motors (usually reloadable) are available in 38mm, 54mm, 75mm, and 98mm diameters.

The letter

The letter at the beginning of the code indicates the motor's total impulse range (commonly measured in newton-seconds). Each letter in successive alphabetical order has up to twice the power of the letter preceding it. This does not mean that a given "C" motor has twice the total impulse of a given "B" motor, only that C motors are in the 5.01-10.0 N-s range while "B" motors are in the 2.51-5.0 N-S range. The designations "1/4 A" and "1/2 A" are also used. For a more complete discussion of the letter codes, see Model rocket motor classification.

For instance, a B6-4 motor from Estes-Cox Corporation has a total impulse rating of 5.0 N-s. A C6-3 motor from Quest Aerospace has a total impulse of 8.5 N-s. [1]

The first number

The number that comes after the letter indicates the motor's average thrust, measured in newtons. A higher thrust will result in higher liftoff acceleration, and can be used to launch a heavier model. Within the same letter class, a higher average thrust also implies a shorter burn time (e.g., a B4 motor will burn longer than a B6).

The last number

The last number is the delay in seconds between the end of the thrust phase and ignition of the ejection charge. Black Powder Motors that end in a zero have no delay or ejection charge. Such motors are typically used as first-stage motors in multi-stage rockets as the lack of delay element and cap permit burning material to move forward and ignite an upper-stage motor.

A "P" indicates that the motor is "plugged". In this case, there is no ejection charge, but a cap is in place. A plugged motor can only be used in rockets which do not need to deploy a standard recovery system such as small rockets which tumble or R/C glider rockets.

Reloadable motors

Reloadable motor cases. From left: 24/40, 29/40-120, 29/60, 29/100, 29/180, 29/240

Reloadable motors are specified in the same manner as model rocket single-use motors as described above. However, they have an additional designation which specifies both the diameter and maximum total impulse of the motor casing in the form of diameter/impulse. A reload designed for a 29mm diameter case with a maximum total impulse of 60 newton-seconds carries the designation 29/60 in addition to its impulse specification.

Safety

Model rocketry is a safe and widespread hobby. Individuals such as G. Harry Stine and Vernon Estes helped ensure this by developing and publishing the National Association of Rocketry Model Rocket Safety Codes (Model Rocket Safety Code, Radio Control Rocket Glider Safety Code, High Power Rocket Safety Code), and by commercially producing safe, professionally-designed and manufactured model rocket motors.

One of the main motivations for the development of the hobby in the 1950s and 1960s was to provide young people the opportunity to construct flying rocket models without having to engage in dangerous construction of motor units and direct handling of explosive propellants.

Controversy in the United States

Both amateur and model rocketry have come under controversy in the United States following the terrorist attacks on New York and Washington D.C., as federal and state authorities allege that model rockets can be modified to act as weapons.

Authorities argue that all members of the hobby should have to be licensed and their purchases recorded and reported to federal agencies. Critics of such policies, particularly those involved in the hobby itself, argue that while building model rockets capable of high speeds and fairly impressive altitudes is a relatively simple feat, guidance systems are exceedingly difficult to design and expensive to implement. G. Harry Stine has stated in his Handbook of Model Rocketry that

"A model rocket literally disintegrates when it hits something because its airframe absorbs the energy of impact by destroying itself. This is the same principle used in modern automobiles where “crush zones” absorb the energy of a crash by deforming and collapsing. Model rockets have been deliberately launched directly into sheets of window glass; these experiments completely destroyed the models but didn’t even scratch the glass."

The National Association of Rocketry and Tripoli continue to pursue litigation against the BATFE in the matter.[citation needed]

References

  1. ^ National Association of Rocketry web site: http://nar.org/SandT/NARenglist.shtml

See also

Retrieved from "https://en.wikipedia.org/w/index.php?title=Model_rocket&oldid=196964520"