The Jetex motor is a miniature solid-fuel rocket motor produced for use as a powerplant for flying model aircraft. Its production led to a number of imitators and, after its discontinuation, successors of similar type.
The Jetex motor is a miniature solid-fuel rocket motor produced for use as a powerplant for flying model aircraft. Its production led to a number of imitators and, after its discontinuation, successors of similar type.
Jetex was developed in 1947, by Wilmot, Mansour & Company Ltd of Southampton, which had started operations in a decommissioned hangar at RAF Beaulieu. [1] The first motor was demonstrated in early 1948 and was available to the public in June 1948, when Aeromodeller magazine featured Jetex power on its front cover. [2] The first motors were the Jetex 100 and 200, with the more powerful Jetex 350 following in November 1948. The most popular motor, the Jetex 50, was introduced in May 1949, along with kits for a model plane and model car using Jetex power. The subsequent popularity of Jetex led to the manufacture of numerous kits by third-party companies such as KeilKraft and Skyleada.
Jetex motors are powered by a solid pellet consisting mainly of guanidine nitrate, which burns to release an exhaust gas in large volume, leaving little solid residue. Thrust developed is modest and sustained, making it suitable for aerodynamically lifted flying models. The exhaust gas is not excessively hot, which confers a safety advantage.
Motors are loaded with one or more solid fuel pellets and a combustible 'wick' is led through the exhaust nozzle to ignite the fuel. Fuel and wick were manufactured by Imperial Chemical Industries (ICI). The engine casing of the early motors is made of an aluminium alloy. On introduction, fuel pellets and wick could be purchased separately, meaning that the system is reusable.
Jetex power made a big impact in the late 1940s and early 1950s, allowing new sorts of models, scale and duration, to be designed. During the 1960s, Jetex propellant pellets found another use by AP Films/Century 21, in their 'Supermarionation' TV series, when they were fitted to the undersides of miniature ground vehicles to emit jets of gas resembling dust trails. [3]
Jetex went through a change of ownership in the mid 1950s. Gradually its popularity waned. Ron Baddorf speculated that the development of radio control and the increasing reliability and power of diesel motors caused a lack of interest in "the little Jetex". [4]
The Velojet 50 and its larger sibling, the Velojet 100, were New Zealand designed and manufactured. They used standard Jetex fuel and had a safety pressure release at the front in the form of a disc against a pre-tensioned coil spring. [5]
In 1986, Powermax in the UK launched a range of newly formulated size 50 fuel and wick under the Jet-X brand. [6] In the latter half of the 1990s, the company introduced their own 'Z' series motors, corresponding to the original Jetex 35, 50 and 100. From August 1995 Jet-X motors, fuel and fuse were commercially imported into the US. Flying Models told its readers that "safe and viable rocket power for model airplanes is back". [7]
Around the new millennium, a new non-reusable motor, called Rapier, was introduced. It has similar weight, thrust and duration to Jetex, allowing many old plans for Jetex powered models to be built and flown with the new motors. The Rapier is a single use motor with a cardboard case and a ceramic nozzle, visually closer to a model rocket motor than the original reloadable Jetex.
In early 2020, another range of non-reusable motors was introduced, called Tendera. These are similar to the Rapiers, being one-time use motors having cardboard cases and ceramic nozzles.
| Jetex Type | Thrust ounces | Tendera/Rapier equivalent | Thrust mN | |
|---|---|---|---|---|
| Jetex | 35 | 0.35 | L1 | 97 |
| Jetex | 50 | 0.50 | L2 | 139 |
| Jetex | 200 | 2.0 | L3 | 556 |
A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
A rocket is a vehicle that uses jet propulsion to accelerate without using the surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely from propellant carried within the vehicle; therefore a rocket can fly in the vacuum of space. Rockets work more efficiently in a vacuum and incur a loss of thrust due to the opposing pressure of the atmosphere.
A ramjet is a form of airbreathing jet engine that requires forward motion of the engine to provide air for combustion. Ramjets work most efficiently at supersonic speeds around Mach 3 and can operate up to Mach 6.
A solid-propellant rocket or solid rocket is a rocket with a rocket engine that uses solid propellants (fuel/oxidizer). The earliest rockets were solid-fuel rockets powered by gunpowder; they were used in warfare by the Chinese, Indians, Mongols and Persians as early as the 13th century.
A hybrid-propellant rocket is a rocket with a rocket motor that uses rocket propellants in two different phases: one solid and the other either gas or liquid. The hybrid rocket concept can be traced back to the early 1930s.
The aerospike engine is a type of rocket engine that maintains its aerodynamic efficiency across a wide range of altitudes. It belongs to the class of altitude compensating nozzle engines. Aerospike engines were proposed for many single-stage-to-orbit (SSTO) designs. They were a contender for the Space Shuttle main engine. However, as of 2023 no such engine was in commercial production, although some large-scale aerospikes were in testing phases.
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A propellant is a mass that is expelled or expanded in such a way as to create a thrust or another motive force in accordance with Newton's third law of motion, and "propel" a vehicle, projectile, or fluid payload. In vehicles, the engine that expels the propellant is called a reaction engine. Although technically a propellant is the reaction mass used to create thrust, the term "propellant" is often used to describe a substance which contains both the reaction mass and the fuel that holds the energy used to accelerate the reaction mass. For example, the term "propellant" is often used in chemical rocket design to describe a combined fuel/propellant, although the propellants should not be confused with the fuel that is used by an engine to produce the energy that expels the propellant. Even though the byproducts of substances used as fuel are also often used as a reaction mass to create the thrust, such as with a chemical rocket engine, propellant and fuel are two distinct concepts.
A nozzle is a device designed to control the direction or characteristics of a fluid flow as it exits an enclosed chamber or pipe.
The Delta rocket family is a versatile range of American rocket-powered expendable launch systems that has provided space launch capability in the United States since 1960. Japan also launched license-built derivatives from 1975 to 1992. More than 300 Delta rockets have been launched with a 95% success rate. The series has been phased-out in favor of the Vulcan Centaur, with only the Delta IV Heavy rocket remaining in use as of June 2023.
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A rocket engine nozzle is a propelling nozzle used in a rocket engine to expand and accelerate combustion products to high supersonic velocities.
Ammonium perchlorate composite propellant (APCP) is a solid-propellant rocket fuel. It differs from many traditional solid rocket propellants such as black powder or zinc-sulfur, not only in chemical composition and overall performance but also by being cast into shape, as opposed to powder pressing as with black powder. This provides manufacturing regularity and repeatability, which are necessary requirements for use in the aerospace industry.
The air turborocket is a form of combined-cycle jet engine. The basic layout includes a gas generator, which produces high pressure gas, that drives a turbine/compressor assembly which compresses atmospheric air into a combustion chamber. This mixture is then combusted before leaving the device through a nozzle and creating thrust.
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Rocket propellant is the reaction mass of a rocket. This reaction mass is ejected at the highest achievable velocity from a rocket engine to produce thrust. The energy required can either come from the propellants themselves, as with a chemical rocket, or from an external source, as with ion engines.
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