A model rocket is a small rocket designed to reach low altitudes (e.g., for a model) and be recovered by a variety of means(parachute, streamer,etc.)
According to the United States National Association of Rocketry (NAR)'s Safety Code, model rockets are constructed out of lightweight and non metallic parts. The materials are typically paper, cardboard, balsa wood or plastic. 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. Despite its inherent association with extremely flammable substances and objects with a pointed tip traveling at high speeds, model rocketry historically has proven to be a very safe hobby and has been credited as a significant source of inspiration for children who have eventually become scientists and engineers.
History of model rocketry The first modern model rocket and modern model rocket motor, was designed in 1954 by Orville Carlisle, a licensed pyrotechnics expert, and his brother Robert, a model airplane enthusiast. They originally designed the motor 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 motors, often with tragic results. Some of these attempts were dramatized in the fact-based 1999 film October Sky. The Carlisles realized their motor 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 first American model rocket company was Model Missiles Incorporated (MMI), in Denver, Colorado, opened 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. Stine eventually 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 in 1960, and eventually, Estes dominated the market. Estes moved his company to Penrose, Colorado in 1961. Estes Industries was acquired by Damon Industries in 1970. It continues to operate in Penrose today.
Competitors like Centuri and Cox came and went in America during the 1960s, 1970s, and 1980s, but Estes continued to control the American 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- to medium-power rocketry hobby today. Estes produces and sells black powder rocket motors.
Since the advent of high-power rocketry, which began in the mid-1980s with the availability of G- through J-class motors (each letter designation has up to twice the energy of the one before), a number of companies have shared the market for larger and more powerful rockets. By the early 1990s, Aerotech Consumer Aerospace, LOC/Precision, and Public Missiles Limited (PML) had taken up leadership positions, while a host of engine manufacturers provided ever larger motors, and at much higher costs. Companies like Aerotech, Vulcan, and Kosdon were widely popular at launches during this time as high-power rockets routinely broke Mach 1 and reached heights over . In a span of about five years, the largest regularly made production motors available reached N, which had the equivalent power of over 1,000 D engines combined, and could lift rockets weighing with ease. Custom motor builders continue to operate on the periphery of the market today, often creating propellants that produce colored flame (red, blue, and green being common), black smoke and sparking combinations, as well as occasionally building enormous motors of P, Q, and even R class for special projects such as extreme-altitude attempts over .
High-power motor reliability was a significant issue in the late 1980s and early 1990s, with catastrophic engine failures occurring relatively frequently (est. 1 in 20) in motors of L class or higher. At costs exceeding $300 per motor, the need to find a cheaper and more reliable alternative was apparent. Reloadable motor designs (metal sleeves with screwed-on end caps and filled with cast propellant slugs) were introduced by Aerotech and became very popular over the span of a few years. These metal containers needed only to be cleaned and refilled with propellant and a few throw-away components after each launch. The cost of a "reload" was typically half of a comparable single use motor. While catastrophes at take-off (CATOs) still occur occasionally with reloadable motors (mostly due to poor assembly techniques by the user), the reliability of launches has risen significantly.
It is possible to change the thrust profile of solid-propellant motors by selecting different propellant designs. Since thrust is proportional to burning surface area, propellant slugs can be shaped to produce very high thrust for a second or two, or to have a lower thrust that continues for an extended time. Depending on the weight of the rocket and the maximum speed threshold of the airframe and fins, appropriate motor choices can be used to maximize performance and the chance of successful recovery.
Aerotech, Cesaroni, Rouse-Tech, Loki and others have standardized around a set of common reload sizes such that customers have great flexibility in their hardware and reload selections, while there continues to be an avid group of custom engine builders who create unique designs and occasionally offer them for sale.
Precautions and safety Model rocketry is a safe and widespread hobby. Individuals such as G. Harry Stine and Vernon Estes helped to ensure this by developing and publishing the NAR Model Rocket Safety CodesRadio Control Rocket Glider Safety Code High-Power Rocket Safety Code and by commercially producing safe, professionally designed and manufactured model rocket motors. The safety code is a list of guidelines and is only mandatory for National Association of Rocketry members.
A primary motivation for the development of the hobby in the 1950s and 1960s was to enable young people to make flying rocket models without having to construct the dangerous motor units or directly handle explosive propellants.
The NAR and the TRA successfully sued the US Bureau of Alcohol, Tobacco, Firearms and Explosives(BATFE) over the classification of Ammonium Perchlorate Composite Propellant (APCP), the most commonly used propellant in high-power rocket motors, as an explosive. The March 13, 2009 decision by DC District court judge Reggie Walton removed APCP from the list of regulated explosives, essentially eliminating BATFE regulation of hobby rocketry.
Model rocket motors
Most small model rocket motors are single-use engines, with cardboard bodies and lightweight molded clay nozzles, ranging in impulse class from fractional A to G. Model rockets generally use commercially manufactured black-powder motors. These motors are tested and certified by the National Association of Rocketry, the Tripoli Rocketry Association (TRA) or the Canadian Association of Rocketry (CAR). Black-powder motors come in impulse ranges from 1/8A to F.
The physically largest black-powder model rocket motors are typically F-class, as black powder is very brittle. If a large black-powder motor is the upper stage motor of a rocket that exceeds the maximum recommended takeoff weight, or is dropped or exposed to many heating/cooling cycles (e.g., in a closed vehicle exposed to high heat or a storage area with inconsistent temperature control), the propellant charge may develop hairline fractures. These fractures increase the surface area of the propellant, so that when the motor is ignited, the propellant burns much faster and produces greater than normal internal chamber pressure inside the engine. This pressure may exceed the strength of the paper case and cause the motor to burst. A bursting motor can cause damage to the model rocket ranging from a simple ruptured motor tube or body tube to the violent ejection (and occasionally ignition) of the recovery system.
Therefore, rocket motors with power ratings higher than D to F customarily use composite propellants made of ammonium perchlorate, aluminium powder, and a rubbery binder substance contained in a hard plastic case. This type of propellant is similar to that used in the solid rocket boosters of the Space Shuttle and is not as fragile as black powder, increasing motor reliability and resistance to fractures in the propellant. These motors range in impulse from size A to O. Composite motors produce more impulse per unit weight (specific impulse) than do black-powder motors.
Reloadable composite-propellant motors are also available. These are commercially produced motors requiring the user to assemble 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: firstly, because the main casing is reusable, reloads cost significantly less than single-use motors of the same impulse. Secondly, assembly of larger composite engines is labor-intensive and difficult to automate; off-loading this task on the consumer results in a cost savings. Reloadable motors are available from D through O class.
Motors are electrically ignited with an electric match consisting of a short length of pyrogen-coated nichrome, copper, or aluminum bridgewire pushed into the nozzle and held in place with flameproof wadding, a rubber band, a plastic plug or masking tape. On top of the propellant is a tracking delay charge, which produces smoke but in essence 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.
Model rocket motors mostly don't offer any sort of thrust vectoring, instead just relying on fins at the base to keep the vehicle aerodynamically stable. Some rockets do however have thrust vectoring control (TVC) by gimbaling the motor itself rather than the nozzle. This is done on some rockets built by many model rocket builders, such as Joe Barnard of BPS.space.
Performance The impulse (area under the thrust-time curve) of a model motor is used to determine its class. Motors are divided into classes from 1/4A to O and beyond. Black powder rocket motors are typically only manufactured up to Class F. Each class's upper limit is double the upper limit of the previous class. Model rockets only use motors that are class G and below. Rockets using motors with a greater impulse are considered high power rockets.
Class Total Impulse (Metric Standard) 1/4A 0.313-0.625 N·s 1/2A 0.626-1.25 N·s A 1.26-2.50 N·s B 2.51-5.0 N·s C 5.01-10 N·s D 10.01-20 N·s E 20.01-40 N·s F 40.01-80 N·s G 80.01-160 N·s
Figures from tests of Estes rocket motors are used in the following examples of rocket motor performance.