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Jetex
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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.
Original Jetex motors
[edit]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.[2]
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]
Jetex imitators and successors
[edit]
Velojet
[edit]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]
Jet-X
[edit]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]
Rapier
[edit]In 1998, a new non-reusable motor, called Rapier, was introduced by a Czech inventor, Dr. Jan Zigmund. It had 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 was a single use motor with a cardboard case and a ceramic nozzle, visually closer to a model rocket motor than the original reloadable Jetex.[8]
Tendera
[edit]In early 2020, another range of non-reusable motors was introduced by a Polish inventor, Piotr Tendera. These are similar to the Rapiers, being one-time use motors having cardboard cases and ceramic nozzles.[9]
| 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 |
References
[edit]- ^ Brothwell, Ken (October 1985). "Whatever happened to JETEX?". Aeromodeller: 596–599.
- ^ a b Crawford, John Miller (21 May 2001). "The Path to Jetex – the Wilmot Mansour Story". Jetex.org. Retrieved 10 December 2022.
- ^ Meddings, Derek (1993). 21st Century Visions. Surrey, UK: Paper Tiger Books. p. 54. ISBN 978-1-85028-243-3.
- ^ Baddorf, Ron (February 1997). "The History and ABC of Jetex". Aviation Modeller International: 70, 71.
- ^ "Motor Mart". Aeromodeller. March 1953.
- ^ Freebrey, Peter (October 1986). "Back with a fizz!". Aeromodeller: 596–598.
- ^ Hunt, Bob (August 1995). "Editorial". Flying Models: 5, 6.
- ^ "Interview with Dr. Jan Zigmund". MinimaketyCZ. May 2007. Retrieved 10 April 2025.
- ^ Kidd, Terry. "Tendera developments". Jetex.org. Retrieved 10 April 2025.
External links
[edit]
Wikimedia Commons has media related to Jetex motors.
- Jetex.org This non-profit site is "the premier Web resource for information and advice about models powered by micro rocket motors, especially those exemplified by the Jetex series of engines".
Jetex
View on Grokipediafrom Grokipedia
Jetex is a historic brand of miniature solid-fuel rocket motors designed primarily for powering free-flight and control-line model aircraft, as well as model boats and cars. Developed and introduced in 1948 by the British company Wilmot, Mansour & Co., Ltd., these motors utilized compressed fuel pellets composed mainly of guanidine nitrate, ignited using a pyrogen wick typically by match or electric igniter to produce thrust for durations of 10 to 30 seconds depending on the model size.[1][2][3]
The origins of Jetex trace back to the pre-World War II era, when brothers Charles Mandeville ("Bill") Wilmot and John Wilmot, along with partner Joseph Naimé Mansour, established expertise in model aircraft manufacturing through their company International Model Aircraft Ltd. (IMA), which produced popular rubber-powered FROG kits. John Wilmot died in 1943, after which Bill Wilmot and Mansour left IMA in 1944 amid wartime disruptions and focused on rocket propulsion, drawing on earlier experiments with solid-fuel boosters dating to 1938.[1][4] Key innovations included lightweight molded cellulose acetate components and a patented fuel formulation developed by Alex Hutchison of Imperial Chemical Industries (ICI) in 1948, enabling safe, reusable motors that revolutionized hobbyist modeling by simulating jet aircraft flight without complex liquid fuels.[1][5]
Jetex motors debuted with the Jetex 100 and 200 models in June 1948, priced at 27s. 6d. and 37s. 6d. respectively, followed by the more powerful Jetex 350 later that year and the affordable Jetex 50 in May 1949, which sold for under 10s. and became the line's bestseller.[5][3] By 1951, Wilmot Mansour exported 60% of its production, generating £150,000 in U.S. sales alone, and offered kits like the Veron Air-O-Jet, Keilkraft Skyjet, and their own Tailored range featuring scale models of aircraft such as the Gloster Meteor and de Havilland Vampire.[5] The era's popularity sparked organized competitions, including the first International Jetex Contest at Fairlop Aerodrome in September 1949 and the S.M.A.E. Jetex Challenge Cup starting in 1951, highlighting achievements in duration flights and aerobatics until entries waned by 1956.[5]
Production peaked in the early 1950s with weekly kit output averaging 3,000 units, but declined due to rising competition from glow engines and safety concerns over fuel handling; Wilmot Mansour ceased manufacturing in the mid-1950s, after which production continued under licensee Sebel until the late 1970s, with the death of Bill Wilmot in 1981 contributing to the final end of original Jetex manufacturing.[5][6][7] Revivals occurred in the 1980s through Powermax's Jet-X brand, which reintroduced motors like the 50C and Z-series using rediscovered stock and new fuels, imported to the U.S. by DARE Products in 1995.[7] In the 2000s, the Czech-made Rapier motors emerged as a modern successor, offering one-shot L1, L2, and L-2HP variants with improved ignition reliability and thrust durations of 18-25 seconds, sustaining interest among contemporary modelers.[7]
For instance, the L3 variant delivered performance comparable to the classic Jetex 200, with an average thrust of 500 mN over 15-21 seconds and a total weight of 17 grams, making it suitable for mid-sized gliders and duration flights. These specifications prioritized consistent thrust profiles to support aerodynamic stability in reaction-powered models, echoing Jetex's emphasis on pendulum-like control without complex electronics. Distribution partnerships, such as with Klima Raketenmodellbau in Western Europe and The Vintage Model Company in the UK, facilitated access until the cessation of production. Efforts to import to the U.S. were explored but did not materialize amid the company's closure.[42][45]
Tendera's development spurred experimental applications beyond traditional aircraft, including hybrid designs like the TenderaCopter, which integrated dual long-duration motors for rotorcraft propulsion at 90 degrees to lifting blades. This adaptability highlighted the motors' role in advancing low-cost, solid-fuel reaction systems, potentially enabling innovations in model stability and fuel efficiency while maintaining compatibility with existing Jetex airframes. The suspension of operations in 2025 limited further advancements and availability.[42][46]
History
Development and Origins
The origins of Jetex trace back to the early 20th-century enthusiasm for model aircraft among three innovative British entrepreneurs: Charles Mandeville "Bill" Wilmot, his brother John Wilmot, and Joseph Naimé Mansour. In the 1910s, the Wilmot brothers launched The Aeroplane World magazine to promote aviation hobbies, laying the groundwork for their later ventures in model production. By 1931, the trio had established Wilmot, Mansour & Co., Ltd., partnering with Lines Brothers to form International Model Aircraft Ltd. (IMA), which revolutionized the industry with mass-produced, affordable flying models under the FROG brand. Their early innovations, such as lightweight papier-mâché fuselages developed by Mansour and aluminum structures experimented with by Bill Wilmot, addressed key challenges in durability and weight for rubber-powered aircraft.[8][9][2] The concept of Jetex emerged in 1938 amid growing interest in propulsion beyond rubber motors, with the Wilmots and Mansour envisioning rocket boosters to enhance model flight duration and speed. Prototypes were developed by 1940, featuring Bakelite casings and gas-generating compounds, and tested on various model sizes in collaboration with aviation experts like Group Captain C.H. Keith. World War II accelerated this work through involvement with the British War Ministry's Directorate of Miscellaneous Weapon Development (DMWD), led by Nevil Shute Norway, where the team contributed to rocket-assisted drones and target aircraft. John Wilmot's death in 1943 did not halt progress; instead, Bill Wilmot and Mansour refined smaller-scale motors for civilian use. In 1944, they departed IMA to focus exclusively on rocket technology at facilities in Bishop's Waltham, supported by Imperial Chemical Industries (ICI) for fuel development.[9][8][2] By 1947, operations had relocated to Totton near Southampton, where chemist Alex Hutchison finalized a safe, steady-burning fuel composition based on guanidine nitrate pellets, patented in 1948 as UK Patent 645,897 (filed March 1948, granted 1950) in collaboration with M. Wilson and ICI Ltd. Chief designer Bert Judge, a 1936 Wakefield Cup winner, oversaw the motor's engineering, ensuring reusability with consumable fuel wicks. The first Jetex motors, including the 100 and 200 variants, were demonstrated to the modeling press in early 1948 and commercially launched in June of that year by Wilmot, Mansour & Co., Ltd., marketed through Aeromodeller magazine as an accessible alternative to liquid-fuel jets. This marked the transition from wartime experimentation to a consumer product, emphasizing safety and simplicity for hobbyists.[8][3][9][2]Company Background and Production Timeline
Jetex originated from the pre-World War II model aircraft industry in England, where brothers Charles Mandeville (“Bill”) Wilmot and John Wilmot, along with model-maker Joseph Naimé Mansour, established Wilmot, Mansour & Co., Ltd. in 1931. This company partnered with Lines Brothers to form International Model Aircraft Ltd. (IMA), producing popular rubber-powered models like the FROG Interceptor, which reached production peaks of over 1,000 units per day by 1933. During the war, the firm contributed to aviation efforts, including target drones and gliders, while Mansour honed expertise in balsa wood fabrication. Post-war, the focus shifted to innovative propulsion, leading to the development of solid-fuel rocket motors in collaboration with chemist Alex Hutchison, who patented the proprietary fuel in 1948.[8] Production of Jetex motors began in 1948 under Wilmot, Mansour & Co., Ltd., based in Southampton, England. The first models, Jetex 100 and 200, were released in June 1948, priced at 27s. 6d. and 37s. 6d. respectively, followed by the Jetex 350 in late 1948 for the Christmas market. By May 1949, prices were reduced by over a third, and the smaller Jetex 50 was introduced at under 10s., significantly boosting sales and enabling exports that accounted for 60% of earnings by 1951. The company expanded its model kit lineup to 10 variants, including scale and duration designs, with weekly production reaching 3,000 kits. Innovative accessories, such as the Zyra Space Ship and SARO A/1 kits, were launched in the early 1950s, alongside annual International Jetex Contests starting in 1949.[5] In 1956, Wilmot Mansour sold its model production division to D. Sebel & Co., a toy manufacturer known for Mobo ride-on toys, allowing the former to focus on packaging expertise, including wartime-derived projects like atomic bomb equipment. Under Sebel, production continued from Erith, Kent, with new motors like the Jetex 50C introduced in 1956 and improved fuel in 1959. The “Tailored” series of kits debuted, and Sebel exhibited at the 1961 British Toy Fair. However, competition from diesel and glowplug engines, along with cheap imports, led to declining interest by the late 1960s. Sebel was acquired by Barclay Securities in 1970, and following Mansour's death in 1972, the Erith factory closed in 1972, ending official Jetex production as equipment was scrapped.[10]Design and Technology
Motor Mechanics and Operation
The Jetex motor operates as a miniature solid-fuel rocket engine, utilizing a compressed pellet of propellant primarily composed of guanidine nitrate (NH₂C(NH)NH·HNO₃), which serves as both fuel and oxidizer to enable combustion without external air supply. This self-contained design allows the motor to function in various orientations, producing thrust through the rapid expansion of hot gases generated by the pellet's decomposition. The core components include a lightweight aluminum or steel case that houses the propellant pellet, an insulator disc to separate the pellet from mounting elements, a jet wick (a combustible fuse) for ignition, and a nozzle at the rear for exhaust expulsion. Safety features, such as a spring-loaded clip and sealing washer on the end cap, prevent over-pressurization by releasing if internal pressure exceeds safe limits during combustion.[11] To prepare the motor for operation, a single or multiple propellant pellets—depending on the model—are loaded into the case, often with a balsa spacer for single-pellet configurations to ensure proper positioning. The jet wick is then inserted through the nozzle to contact the pellet's embedded ignition wick, which is coiled atop the propellant to promote even burning. Ignition occurs by lighting the exposed end of the jet wick with a match or fuse, initiating a low-temperature decomposition of the guanidine nitrate into nitrous oxide and nitrogen gases, followed by sustained combustion that releases carbon dioxide, water vapor, carbon monoxide, ammonia, and additional nitrogen. This process burns without ash residue, as all components convert to gases, and the controlled burn rate—slowed by the pellet's compaction—yields a steady thrust for 6 to 36 seconds, varying by model and pellet count. For example, the Jetex 50 produces approximately 0.5 ounces (14 grams) of average thrust over 15 seconds, delivering a total impulse of about 7.5 ounce-seconds.[12][13][11] During runtime, the combustion chamber heats rapidly, expelling gases through the nozzle at velocities on the order of 300 m/s, generating reactive thrust via Newton's third law.[14] Optional augmenter tubes, fitted over the nozzle, can enhance performance by entraining ambient air to increase exhaust mass flow and boost thrust by 20–30%, though precise alignment is critical to avoid inefficiency or vibration. Post-burn, the motor cools quickly, allowing reuse after cleaning the nozzle of any residue and inspecting for wear, with the entire cycle emphasizing safe handling to mitigate risks from the high-temperature operation.[11]Fuel System and Components
The fuel system of Jetex motors relies on solid propellant pellets, which are ignited to produce thrust through controlled combustion. These pellets are primarily composed of guanidine nitrate (NH₂C(NH)NHNO₃), an organic oxidizer that constitutes over 90% of the pellet weight, ensuring a clean burn with no ash residue.[15] The compound, with a molecular weight of 122.1 and a melting point of 215–216°C, generates gases such as carbon dioxide, water vapor, carbon monoxide, nitrogen, nitrous oxide, and ammonia upon ignition.[15] Early formulations, developed by Imperial Chemical Industries in Scotland, incorporated nitrated resorcinols as additives to enhance performance, marking the first commercial Jetex fuel introduced in 1948.[15] Later variants, such as V-Max fuel by American Telasco, maintained similar compositions while adapting to different motor sizes.[15] Key components of the fuel system include the propellant pellets, which vary in size and type (e.g., Jetex 50 pellets supplied in yellow Sebel tins containing 20 units) and are designed for low-temperature combustion to minimize model damage.[15][11] The jet wick, a combustible fuse, serves as the ignition source and is threaded through the motor's exhaust nozzle to contact the pellet surface.[11] Supporting elements comprise an insulator disc to separate the pellet from other parts, a balsa spacer for single-pellet configurations, a wire gauze disk to regulate burn rate, a flame shield to protect the end cap, and a cap sealing washer that acts as an over-pressure safety valve.[11] The main case, or thrust chamber in larger models, houses the fuel, while the end cap assembly and jet nozzle direct exhaust gases.[11] A spring safety clip secures the case during operation.[11] Fuel loading follows a standardized procedure to ensure safe ignition and thrust. Pellets are inserted into the main case, often with partial charges for controlled duration, and positioned using the spacer and insulator disc.[11] The jet wick is then placed in contact with the pellet and routed through the nozzle hole in the end cap, which is secured afterward.[11] Only commercially produced solid fuel for model rocket engines is recommended, with combustion initiated by lighting the exposed wick end.[11] Optional augmenter tubes can be added to the nozzle, drawing in cool air to boost thrust by 20–30% without altering the core fuel system.[11] This design emphasizes simplicity and safety, allowing reloadable use in model applications.[11]Original Motor Variants
Early Models (1948–1949)
The Jetex 100 and Jetex 200 were the inaugural models in the Jetex series, launched by Wilmot, Mansour & Company Ltd. in June 1948 following an initial demonstration to the modeling press earlier that year.[5] The Jetex 100, priced at 27s. 6d., was designed for small model aircraft such as gliders and lightweight powered designs, delivering an end thrust of up to 1.75 oz with a safety mechanism featuring three helical springs to release pressure if needed.[16] It utilized a drawn metal case and was equivalent in power to a 0.3 cc diesel engine, making it suitable for introductory free-flight applications where reliability and simplicity were prioritized over high duration.[16] The Jetex 200, at 37s. 6d., offered greater capacity with a thrust reaching 3 oz and durations exceeding 30 seconds, employing five coil springs and a multi-pellet fuel system that benefited from case preheating for improved subsequent burns.[17] This model supported duration flying in mid-sized aircraft, though it saw limited adoption due to fewer dedicated plans compared to later variants.[18] In late 1948, the Jetex 350 expanded the lineup for the Christmas market, priced at 50s. and targeted at higher-performance models with a thrust of up to 4 oz and a consistent 36-second burn time across three fuel charges.[5][19] Featuring five springs and minimal delay between charges, it equated to a 0.5 cc diesel in power and was marketed in the U.S. as the Spacemaster 600A, appealing to enthusiasts experimenting with control-line or speed-oriented designs.[19] Its robust construction, including a compression tool for the end cap, addressed early safety concerns in pulsejet operation, where exhaust heat and pressure buildup required careful management.[19] By May 1949, the Jetex 50 addressed demand for an entry-level option, retailing for under 10s. in a distinctive yellow box and quickly becoming the series' bestseller due to its compact size and affordability.[5] With a thrust of approximately 0.5 oz, it used 15 solid fuel pellets per pack separated by gauze discs, housed in a turned ribbed case that emphasized ease of assembly for beginners.[20] This model powered simple kits like the 40 m.p.h. Racecar and Mijet glider, marking Wilmot Mansour's first foray into ready-to-fly accessories and broadening Jetex's appeal beyond aviation purists.[5] Early iterations included an asbestos cap washer for heat insulation, setting a precedent for iterative improvements in fuel efficiency and wick ignition.[20]Later Developments and Accessories
In the early 1950s, Jetex expanded its motor lineup with improved designs addressing limitations in thrust, duration, and ease of use. The Jetmaster, introduced in 1952 as a successor to the original Jetex 100, featured a single spring mechanism and compatibility with the same fuel pellets, offering a 22-second burn duration that made it suitable for larger duration models.[18] Similarly, the Scorpion 600, launched in 1953, represented the largest Jetex motor at 6 oz average thrust over an 8-9 second duration, with innovative spring rollers for simplified pellet loading; it was the final major design from original manufacturer Wilmot Mansour.[18] The Jetex Atom 35, also debuting in 1953, was the smallest variant at 0.35 oz thrust but suffered from blow-back issues and short burn times due to its thin gauge construction, limiting its adoption among modelers.[18] By the mid-1950s, refinements to the popular Jetex 50 included the 50B and 50C models with extended alloy or steel cases for greater combustion space and dome-shaped end caps, enhancing performance and enabling augmenter tube use; the 50C, produced post-1956 by D. Sebel, prioritized durability despite corrosion risks.[18] The Jetex 150 PAA-Loader, released in 1956 by Sebel, accommodated up to three fuel pellets in its elongated body, boosting endurance for contest flying and inspiring specialized duration aircraft designs.[18] High-thrust options emerged with the 50R in 1955, delivering 5-6 oz thrust over 4 seconds using dual springs and specialized fuel, later rebranded as the 50HT for U.S. markets in 1963 by Telasco.[18] Accessories complemented these developments by enhancing thrust and versatility. Augmenter tubes, thin aluminum extensions with bell-mouthed inlets, were introduced for Jetex 50, Jetmaster, PAA-Loader 150, and Scorpion 600 models; performance tests in January 1954 by Aeromodeller magazine showed 20-30% thrust increases through cool air entrainment, while also cooling exhaust gases to protect model structures.[21] Kits varied by manufacturer, such as Sebel's two-part Jetex 50 version and Jetex's clip-together Jetmaster tube, requiring adequate airflow for optimal function.[22] The Dempster Turb-O-Prop, a 1955 accessory from the Dempster Company in Kansas City, Missouri, adapted Jetex 50 fuel to drive a 6-inch aluminum propeller at 4,000 RPM, generating 2 oz static thrust for 20-30 seconds and serving as a jet-powered alternative to rubber-band propulsion in small models.[21]Applications and Use
In Model Aircraft
Jetex engines were primarily designed and popularized as propulsion systems for free-flight and control-line model aircraft, enabling sustained powered flight through solid-fuel rocket pellets that provided short bursts of thrust. Developed in England in 1947 by Charles Wilmot and Joe Mansour, the first Jetex motors became commercially available in June 1948, quickly gaining traction among hobbyists for their simplicity and accessibility compared to earlier rubber-band or compressed-air systems.[23] In control-line applications, Jetex motors powered tethered scale models of jet aircraft, such as the F-86 Sabre, allowing for aerobatic maneuvers on circular flight paths.[24] Early adoption focused on lightweight balsa wood constructions, where the engines' compact size—typically 1-2 inches long—allowed integration into small-scale designs without excessive weight penalties.[11] In model aircraft applications, Jetex motors powered a diverse array of designs, including conventional tailplanes, canards, and flying wings, with recommendations for low aspect ratios (4:1 or less) and significant sweepback (40 degrees or more) to ensure stability during high-speed powered phases.[25] Scale models of jet fighters, such as the Gloster Meteor (using twin Jetex 100 engines) and Saab J29 (12.5-inch span, 18.5 grams), exemplified their use in realistic replicas, while duration models like the Zephyr emphasized glide efficiency post-burnout.[23][26] The Jetex 50, introduced in 1949, became particularly suited for beginner-friendly aircraft with wingspans of 250-400 mm and total weights up to 25 grams, delivering about 0.5-1 oz of thrust for 6-10 seconds.[11] Larger variants, like the Jetex 100 (1 oz thrust, 12-15 seconds duration) or Jetex 350 (up to 36 seconds with multiple pellets), supported more ambitious builds, including the X-15 research aircraft replica powered by a Jetex 150.[25] Performance tests in the 1950s, such as those conducted by Ron Warring for Aeromodeller magazine, highlighted thrust efficiencies improved by 20-30% with augmenter tubes, optimizing climb rates in nose-heavy trims positioned just forward of the center of gravity.[11] Jetex-powered models saw widespread competitive use in organized events. The Academy of Model Aeronautics (AMA) had introduced jet-propelled categories at the 1947 Nationals in Minneapolis (though initially non-scoring and using early rocket motors), with rules expanding to permit Jetex in free-flight scale events by 1955-1956, leading to a dedicated Jetex free-flight category and advisory committee by 1957-1958; these models competed in lightweight designs prioritizing high initial climb for maximum altitude.[27] The Pan American World Airways' PAA-Load events, running from the late 1940s to 1961, routinely featured Jetex aircraft, underscoring their reliability for duration flights—exemplified by a 12-inch span model with a Jetex Atom 35 reaching 300 feet and gliding three-quarters of a mile.[27][28] By the 1966 Nationals, jet events were streamlined into combined speed categories, reflecting Jetex's role in evolving model aviation toward faster, more dynamic propulsion.[27] Overall, since 1948, millions of Jetex-equipped model aircraft have been constructed worldwide, fostering a hobby that balanced scientific experimentation with recreational flight.[29]In Other Model Vehicles
Jetex engines found applications beyond model aircraft in other model vehicles, particularly cars and boats, capitalizing on their compact size and reliable thrust during the post-World War II era of fascination with jet propulsion. These uses emerged in the late 1940s and peaked through the 1950s and 1960s, as manufacturers like Wilmot Mansour & Co. expanded their product lines to include ready-to-run plastic kits and promotional tie-ins, appealing to hobbyists interested in high-speed ground and water effects. The engines' solid-fuel design allowed for straightforward reloading and ignition, making them suitable for tethered or free-running demonstrations, though their short burn times—typically 15-30 seconds—limited sustained operation.[30] In model cars, Jetex motors powered a variety of racing designs, often tethered to a central pylon to simulate circular tracks and prevent loss during runs. Early examples included the 1948 Jetex 40 MPH Racecar by Wilmot Mansour, a balsa wood kit propelled by a Jetex 100 or 200 motor, which achieved speeds up to 40 mph in tests and required simple assembly without soldering. By 1950, the plastic Jetex Jet Propelled Racing Car, also from Wilmot Mansour and using a Jetex 50 or 50C, became a popular ready-to-run option at around 20 mph, later upgraded for higher performance. Other notable models were the 1959 Monogram Firebolt, a 1:24 scale salt flats racer kit compatible with Jetex units for jet-like acceleration, and the 1965 Sebel Jetex Record-breaking Jet Car, a three-wheeled design powered by the Jetex 50C. Promotional variants, such as the 1960 BP Bluebirds car modeled after Donald Campbell's land speed record attempts and using the smaller Jetex Atom 35, were distributed at fuel stations to link toy play with real-world engineering feats. These cars highlighted Jetex's role in educational hobbies, demonstrating principles of thrust and aerodynamics on a tabletop scale.[30][31][32] Model boats, including hydroplanes and speedboats, benefited from Jetex's waterproof ignition and directional thrust, enabling pond or pool runs that mimicked full-scale powerboats. The 1951 Jetex Speedboat by Wilmot Mansour, a lightweight plastic hull powered by the Jetex 50B (later Atom 35), was marketed as unsinkable and capable of 20 mph bursts, with users igniting the motor via a fuse for short sprints. The Adamcraft Jet-Ho hydroplane kit, designed for the more powerful Jetex 200, used printwood construction and a plywood mount for stability during high-speed planing. In 1965, Sebel revived the concept with the Jetex Jet Hydroplane, featuring a metal exhaust shield for safety and updated packaging, while the BP Bluebirds boat variant echoed the car's promotional theme with Atom 35 propulsion. These aquatic applications were less common than aircraft uses but showcased Jetex's versatility, often requiring calm water to avoid capsizing from the engine's reactive force. Enthusiasts noted the thrill of visible exhaust plumes and rapid acceleration, though fuel pellet availability eventually curtailed widespread adoption by the 1970s.[30][31] Later Jetex variants with faster-burning fuel enabled limited use in model rockets, where early slow-thrust models had proven inadequate for vertical launch. By the mid-1960s, engines like the Jetex 50C powered simple boost-glide rockets, igniting multiple pellet surfaces for quicker acceleration, though this remained a niche extension compared to dedicated model rocketry systems.[32]Successors and Imitators
Velojet
The Velojet was a line of miniature solid-fuel rocket motors developed in New Zealand as a direct competitor to the Jetex engines, offering similar performance at a lower cost for powering model aircraft. Invented by Ivan Harrington, a former engineer with Mount Cook Airlines, the motors were designed to address the high price of imported Jetex units while providing comparable thrust for free-flight and control-line models. Production began in the mid-1950s under the Betta Model Aeroplane Supply Company in New Plymouth, with approximately 3,000 units manufactured during that decade. A small revival occurred in the 1980s, with limited batches produced in a makeshift workshop.[33][34] The Velojet lineup included the Velojet 50 and the larger Velojet 100, both machined from solid metal for durability and precision. Key design features emphasized safety and ease of use, such as a front pressure release disc backed by a pre-tensioned coil spring to vent excess pressure, and a screw-on end cap for refilling, though the cap was susceptible to corrosion from repeated exposure to fuel residues. Mounting was facilitated by an L-shaped bracket, allowing straightforward integration into model fuselages similar to Jetex setups. The motors were compatible with standard Jetex fuel pellets, typically including five pellets, a wick, and gauze in initial kits, though fuel and spares were often purchased separately. Priced at 13 shillings for the Velojet 50 and 22 shillings 6 pence for the Velojet 100 in New Zealand (with export prices slightly reduced), they were marketed as economical alternatives.[35][36][33] Contemporary reviews praised the Velojet's construction and power, describing it as a "very powerful, well-made job" suitable for enthusiast applications. However, its high-thrust profile resulted in a short burn duration of about 3 seconds, which could induce flutter or instability in lighter models, sometimes leading to crashes during testing. An "inhibited" fuel variant was noted for sputtering and underperformance. Despite these quirks, the Velojet contributed to the global spread of micro-rocket propulsion in hobby modeling, particularly in regions distant from major manufacturers like the UK's Wilmot-Hedge.[37][33][36]Jet-X
Jet-X motors were developed as a direct successor to the original Jetex line, aiming to revive the hobby of solid-fuel model jet propulsion in the late 20th century. Produced by the UK-based company Powermax, Jet-X utilized a similar reloadable metal engine design but incorporated updated fuel formulations to address issues with availability and performance of the discontinued Jetex products. The brand emerged from efforts to rediscover and repurpose existing Jetex components, marking a key attempt to sustain the technology after the original manufacturer's closure.[7] In 1985, Powermax founders Roy and Julie Lever discovered a significant stock of unused Sebel-era Jetex motors—specifically 50C and 50R/HT models—in the United States, which had been produced until 1972. This find prompted Powermax to manufacture compatible fuel pellets and igniter fuses, enabling the relaunch of the Jetex concept under the Jet-X name. By 1986, Jet-X motors and fuel kits were introduced to the UK market, initially pairing the salvaged Sebel engines with Powermax's guanidine nitrate-based fuel, which burned more consistently than earlier variants. The product line received positive coverage in modeling publications, such as a review in the October 1986 issue of Aeromodeller magazine, highlighting its potential to rekindle interest in free-flight and control-line model aircraft.[7] During the 1990s, Powermax expanded the Jet-X range with the "Z" series, featuring improved designs for better thrust and reliability. These included variants in sizes such as 35Z, 50Z, and 100Z, with the 50Z model adapting the nozzle diameter of older Jetex 50 engines to handle higher chamber pressures from the hotter ammonium nitrate fuel. The Z series motors were reloadable, requiring users to pack fuel pellets, gauzes, and wicks into the engine body, similar to Jetex operation but with enhanced safety features like blast diaphragms to prevent explosions. Jet-X fuel was formulated to be non-explosive under normal use, complying with hobby regulations, though it was cautioned against mixing with original Jetex components due to potential incompatibility. Production continued until approximately 2009, after which no new units were manufactured, though remaining stocks supported enthusiast communities.[38][9] In August 1995, Jet-X motors, fuel, and accessories were commercially imported into the United States by DARE Products, Inc., broadening access for American modelers and briefly boosting the hobby's popularity. This importation aligned with growing interest in vintage rocketry, allowing Jet-X to serve as a bridge between the classic Jetex era and modern RC applications. Despite these efforts, the brand faced challenges from regulatory restrictions on solid fuels and declining interest in non-electric propulsion, leading to its eventual phase-out.[7] A separate revival initiative emerged in 2017 under the Jet-X brand in the United States, focusing on a simplified single-use engine called the J-1 to bypass reloading complexities. Developed after years of research, the J-1 uses a paper tube filled with a smoke-producing mixture rather than traditional rocket fuel, delivering approximately 12 seconds of thrust without an ejection charge, and is classified as a non-fireworks novelty under U.S. Department of Transportation regulations. This modern iteration, distinct from Powermax's reloadable design, aimed to reintroduce the hobby to new generations but remained in pre-commercial crowdfunding stages as of 2019, requiring adult supervision for use.[39]Rapier
The Rapier series of model rocket motors represents a modern successor to the original Jetex engines, developed specifically for powering small balsa or paper model aircraft in recreational and sport flying. Introduced in the late 1990s and entering production around 2000, these single-use motors were created to address the market gap left by discontinued Jetex and similar systems, offering a simpler, safer alternative with extended burn times suitable for flights reaching 20-30 meters in height. Unlike the reloadable metal-cased Jetex motors, Rapiers employ disposable cardboard tubes, making them more akin to conventional model rocket engines while maintaining compatibility with classic Jetex designs.[40][41] Rapier motors were developed by Dr. Jan Zigmund, a Czech chemist specializing in explosives and propellants, who founded the Rapier Company on September 9, 1998, in Pardubice, Czech Republic. Zigmund's interest stemmed from his childhood modeling experiences and a 1997 visit to a hobby shop with his son, where he encountered the lack of available small jet motors following the cessation of production by firms like ZVS Dubnica nad Váhom. Drawing inspiration from earlier Synjet and Jetex designs, he focused on creating affordable, single-use units using perchlorate-based propellants with low combustion temperatures to enhance safety and reduce material costs. The first functional prototype was achieved by March 25, 1998, after overcoming challenges like a 1997 lab injury, with full production emphasizing granulation of propellant, clay nozzle molding, and high-pressure pressing at 100 MPa for reliability.[41][40] Key variants in the Rapier lineup include the L-1, providing 40-60 mN of thrust for lightweight models; the L-2, delivering 80-140 mN with a burn time of 18-25 seconds for balanced performance; and the higher-thrust L-2HP at 160-220 mN, which replaced the phased-out L-3 variant. Each motor features a 1.3 mm thick paper tube casing, a ceramic or clay nozzle for controlled exhaust, and an integrated fuse for ignition, prioritizing a favorable thrust-to-weight ratio through simple, lightweight construction. These specifications enable longer sustained flights compared to Jetex equivalents—for instance, the Rapier L-2 offers lower peak thrust than the Jetex 50 (125-140 mN) but extends duration, making it ideal for gliders and small jets without the need for reloading or complex maintenance. Production occurs in small batches, ensuring quality control, though availability has remained niche through specialized retailers.[40][41]Tendera
Tendera motors represented a revival of Jetex-style solid-fuel rocket propulsion for model aircraft in the 2010s, developed by Polish engineer Piotr Tendera following the discontinuation of earlier successors like Jet-X and Rapier. These motors utilized a sustained-thrust design with reloadable fuel pellets, enabling safe and reliable operation in free-flight and control-line models, much like their predecessors. Tendera's innovation lay in achieving European CE certification around 2019, which ensured compliance with safety standards and allowed over-the-counter sales in model shops across Europe, addressing regulatory hurdles that plagued prior Jetex imitators. However, production became commercially unviable by 2024, and the company suspended operations on March 1, 2025.[42][43][44] The Tendera lineup included several variants tailored to different model sizes and performance needs, with thrust levels ranging from low to high power. Key models featured:| Variant | Average Thrust (mN) | Burn Duration (seconds) |
|---|---|---|
| L1 | 100 | 11 |
| L2 | 170 | 17 |
| L2HP | 250 | 15 |
| L3 | 500 | 17 |
| L4 | 1000 | 19 |