Jetex and Micro Jet Modeling
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Jetex is the trade name for those
little metal rocket motors made in England immediately
following WWII, and documented in various books
and magazines of the period on both sides of the
Atlantic. Aircraft models for these motors ranged
from simple sheet balsa gliders to detailed scale
subjects of full size jets rendered in stick and
tissue. Cars, boats, and rocket models were also
adapted to Jetex, with various degrees of success.
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was first marketed by Wilmot & Mansour
and later by Sebel (both in Great
Britain) from 1948 to 1972. The greatest years
of popularity were the early to mid 1950's
but the appeal of Jetex has traversed the
decades. The vintage hardware and memorabilia,
like so much else of the Baby Boom and Cold
War eras, is now actively collected and sought
after on web-based auction houses such as
eBay. |
The Arrow 100 was designed
and built by Ian Dowsett. A typical high
performance Jetex contest design from
the early 1950's
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The JETEX 100 was the
first motor marketed by Wilmot & Mansour.
It had three helical springs as part of
a safety valve. Larger motors of similar
design - the 200 and
the Spacemaster - were
also introduced around this time.
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Jetex has always represented one of the most
challenging forms of aeromodeling. One reason
is that the motors required a certain amount
of finicky persuasion to get them working.
Vintage Jetex publications that addressed
motor operation were typically concerned with
proper storage of the fuel pellets to guard
against moisture, careful arrangement of the
various internal parts for successful ignition,
and so on. |
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On top of these painstaking procedures for
operating the motor, the modeler also had
to posses better than average construction
skills. A sloppy assembly with warped surfaces
might manage some fair test glides, but any
minor instability would only get worse when
one managed to get the motor running. Models
had be small, light, and precisely built.
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when it all worked, the Jetex experience was
akin to magic. The motor sizzled to life and
the plane would start to tug at the modeler's
hand. A gentle hand launch got the plane tentatively
airborne, and flight speed steadily increased
over the course of the motor run. Depending
upon the particular motor size and fuel charges
loaded into it, acceleration lasted anywhere
from 12 to 18 seconds. Then, after the fuel
expired, the rocket plane became a glider
that gently descended to earth. |
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The Jetex Atom 35 was introduced
in 1953, and was the smallest motor of this
type produced. Note the single spring safety
clip that secured the end cap nozzle assembly
to the chamber. A larger variant of this motor
- the Jetex 50 - became the
most popular size, and was suitable for models
spanning 15" to 18". |
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The Jet Tube built by Al
Lidberg is prepped before a successful flight.
The model is powered by a Jetex PAALoader
150 motor and holds an AMA duration record. |
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The Jetex powered model airplane perfectly
complemented what was happening with full-scale
jet and rocket powered aviation at the time.
When one considers that the lowly propeller
is still the most common way to get a model
airplane moving, Jetex has to be thought of
as one of the most advanced power sources
ever made available to the consumer.
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 The
Jetex Scorpion, with its
dual spring safety cap, is shown here with
an augmenter tube. This accessory
tube provided a modest boost in thrust by
drawing cool air past the internally mounted
motor, into the tube's mouth, and out the
tail along with the hot gases. In actual practice,
any thrust gained by the augmenter tube was
usually offset by the increased weight of
the installation. An access hatch also had
to be built into the model to allow for servicing
of the motor and loading fuel pellets. A more
common approach dispensed entirely with mounting
the motor internally and, instead, had it
suspended from the underside of the plane,
partially hidden within a trough. A minor
concession to scale accuracy in favor of real-world
flying considerations. |
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As the Jet Age transitioned into the Space
Age, overall interest in Jetex diminished.
Pre-made black powder motors, like those
made by Estes, made vertical launching of
model rockets possible in a way that Jetex
never really could. This new type of building/flying
experience was easier for most people to
assimilate. Meanwhile, those who still wanted
to build flying jet models found it increasingly
easier to fashion them around piston-powered
ducted fans rather than adapt to the peculiar
requirements of Jetex.
By the mid 1970's Jetex was all but dead
in the consciousness of most modelers, and
especially in the model press. Only a dedicated
few kept the idea alive during this period.
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