|Predecessors||Estes Industries, Estes-Cox Corp.|
|Founded||Penrose, Colorado, U.S. (1958 )|
Estes Industries (AKA Estes-Cox Corporation) is a company based in Penrose, Colorado, USA that designs and builds model rocket and model aircraft engines and kits. They were the best known model rocket company during the "golden age of rocketry" in the 1970s and early 1980s, competing primarily with Centuri Engineering and a host of smaller firms like Canaroc and Flight Systems, Inc. In the 1990s the hobby had almost disappeared, and Estes bought Centuri, folding their product lines together. Throughout the 1990s Estes owned North Coast Rocketry (NCR), which served as their mid-power and high-power rocketry division, although Estes discontinued the NCR line in 2000. Today, in addition to producing model rocket engines, Estes offers model rocket kits for various skill levels of modelers, as well as remote control airplanes. Several independent sources have published measurements showing that Estes model rocket engines often fail to meet their published thrust specifications.
Estes Industries was founded by Vernon Estes in 1958, after he created "Mabel". "Mabel" was a machine designed to inexpensively manufacture model rocket engines for Model Missiles Incorporated. At some point, Vernon Estes sold Estes Industries. Then, on August 30, 2002, Barry Tunick, who had been the Chief Executive Officer since 1991, acquired Estes-Cox Corporation from the private equity fund, TCW Capital, for the sum of $15 million. On January 15, 2010, Estes-Cox was acquired by Hobbico, Inc.
Estes produced a wide variety of rocket model kits, normally using paperboard tubing for the fuselage and balsa wood for fins and nose cones. Early models tended to be relatively simple in design terms, differing in terms of size, number of stages and recovery method. One particularly well-known design from this era was the Camroc, a small camera that replaced the nose cone of larger models that was designed to take a single image on a small disk of film when the motor had burned out and the rocket was facing downward. The Cineroc used a small movie camera that could be launched from larger rockets, taking a series of frames as the rocket ascended.
Later model kits from the late 1970s and early 1980s tended to be more for show than performance, including a series of scale or sport-scale designs and "exotics". Centuri was also well known for these sorts of designs, and the two companies often copied design elements from the other's latest models. The downturn in the hobby in the later 1980s led to consolidation of the two companies. During the 1990s the model line was dramatically reduced, and the ones that were left were typically very simple "three fins and a nose cone" designs that were partially or entirely completed.
Estes rocket engine color-coding
Estes engines are color-coded for recommended use. GREEN engines are for use in single-stage models; PURPLE engines for the top stages of multistage rockets and very light single-stage rockets; RED engines for all booster and intermediate states of multi-stage models. BLUE are “plugged” and are used for rocket-powered racers, aerobrake recovery rockets, and radio controlled gliders; they contain no delay or ejection charge. BLACK has been used in the past for static test engines, which were also plugged to prevent blow-through.
It can be dangerous to use upper-stage engines in normal single-stage rockets. The large delay in ejection can be problematic. The rocket may already be halfway through its descent when the nose comes off and the rocket may not slow down enough before it hits the ground.
Estes number coding
|Type||Total Impulse (Newton seconds)|
Each rocket engine has a code printed upon the outer jacket. This code is defined by the National Association of Rocketry (NAR). An example of one such code is A8-3.
The capital letter (e.g., A) indicates total impulse produced by the engine. Each succeeding letter represents a power range with maximum total impulse twice the impulse of the previous letter. (Example: A single C engine can produce anywhere from 5.01 to 10 newton-seconds of impulse, a G engine 80.1 to 160 newton-seconds.) Anything over a G engine is considered high power model rocketry.
The first number (e.g., 8) specifies that engine's average thrust in newtons or the average push exerted by the engine. Thus a B6-0 and a C6-0 will both produce the same average thrust of 6 newtons, but the C6-0, having twice the total impulse, will fire for twice as long. The rocket engines produce maximum thrust shortly after ignition and thrust declines to a steady-state which is maintained for up to 2.5 seconds prior to burnout.
The final number (e.g., 3) indicates the delay between the thrust and the ejection charge, in seconds. Engines with a delay of zero are typically used as booster engines in multi-stage rockets and there is no ejection charge. In this case, the burning propellent ruptures through the top and hot bits of propellent enter the nozzle of the upper stage engine, thus igniting that engine and forcing the booster assembly away, hopefully to tumble safely to earth.
Estes engine construction
The solid propellant is ignited by a coated wire inserted through the nozzle and in contact with the propellant. An electric current heats the wire and ignites the solid propellant. An engine can also be ignited by the hot gases from the propellant of a booster engine.
Estes model rockets are popular and used by a large number of hobbyists and educators. However, measurements reported by a group at the University of Central Arkansas found that Estes rocket motor models A3-4T, A8-3, B4-4, B6-4, C6-5, and D12-3 have a measured impulses from 15.4% to 22.8% below the claimed impulse. A study at the Australian Defense Force Academy found Estes D11-P motor to have an impulse 11.4% below Estes specifications and the C6-0 motor to be 4.45% below Estes' specifications. A third study found the A10-PT motor to have a total impulse 20% below Estes' claims.
- Penn, Kim and William V. Slaton, Measuring Model Rocket Engine Thrust Curves, The Physics Teacher -- December 2010 -- Volume 48, Issue 9, pp. 591.
- An Investigation into the Combustion and Performance of Small Solid-Propellant Rocket Motors M.G. Carter. University of New South Wales at the Australian Defense Force Academy. 2008.
- Measuring thrust and predicting trajectory in model rocketry M. Courtney and A. Courtney. Cornell University Library. 2009.
- "Hobbico acquires model rocket maker Estes-Cox" Champaign-Urbana News Gazette - January 2010
- "Estes Engine Chart".
- "Estes Model Rocket Engines, Engine Time/Thrust Curves".
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