Jetex and Micro Jet Modeling
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A new product named Jet-X
(from the British based Powermax
concern) was introduced in the 1990's, but
it never really advanced the state of art
in any meaningful way. Jet-X merely replaced
some of the old Jetex shortcomings with new
and equally vexing ones. As with the classic
Jetex , Jet-X also required a reloading of
the motor in the field if another flight was
desired. |
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Other interesting developments over the past
few years have reinvigorated the idea of flying
rocket powered model airplanes. Web based
communication has enabled modelers to create
virtual communities and interact in more meaningful
ways - even across enormous distances. Today,
there are several Jetex websites offering
plans ready to download, and at least two
online discussion groups dedicated to the
subject
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The Hawker Hunter built by
Howard Metcalfe is based on a classic Jetex
50 scale plan from the 1950's, but reduced
in size to accomodate the newer single-use
Rapier L-2 motors. The model is finished with
tissue covering, a vacu-formed plastic canopy,
and a foil-lined trough for the underslung
motor mount. |
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But the largest catalyst for this renewed
interest has been the introduction of an entirely
new motor type - The Rapier.
Like the ubiquitous Estes model rocket motor,
the Rapier comes in the form of a thick cardboard
tube with a clay exhaust nozzle, and is available
in a variety of different sizes. It is fired
once and then discarded. But unlike a standard
model rocket motor a Rapier mimics the behavior
of a classic Jetex motor, with long steady
burn times and no nosecone-popping delay charge.
Rapiers began appearing in England in the
late 1990's and in the U.S. around the turn
of this century. Modelers soon latched onto
their potential and, once again, rocket-powered
model airplanes came back into vogue. Because
Rapiers are a single-use design, the turnaround
time to get a model into the air again is
considerably shortened compared to Jetex.
Modelers are now less hindered by motor maintenance,
and better able to focus on the considerable
task of flight-trimming their fast moving
planes.
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Rapier L-1 and L-2 motors
are current favorites among jet modelers.
Although match lit fuses are still employed,
practical electronic ignition has been developed
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most common Rapier sizes require that models
be built slightly smaller than those designed
for the once popular Jetex 50. Thanks to photocopiers
and computer scanning equipment, many old
Jetex designs were dusted off and quickly
adapted to what was becoming the new power
plant of choice: the Rapier L-2. Scale subjects
(particularly in England) were the first to
be resurrected and published. |
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For
the sake of light weight the majority of
rocket planes are still of traditional stick
and tissue construction (as with small rubber-powered
models), or sheet balsa with hardwood reinforcements
(like typical hand-launched gliders).But
the hobby continues to evolve, and extruded
foams, plastics, and composites have begun
to make their appearance on successful designs.
Likewise, extremely lightweight micro R/C
gear is now showing up at more affordable
prices, allowing some experimenters to make
radio-controlled rocket planes a reality.
The next direction in motor development
may be hybrid rocket technologies, which
mix nitrous oxide gas with safer inert solid
fuels.
It's difficult to conclude an introduction
to micro jet modeling, since the state of
the art is in continual flux. Suffice it
to say that the final chapter on this unique
form of model aviation - which started with
the pioneering Jetex motors of the late
1940's - has yet to be written.
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A sheet balsa rocket plane designed
and built by the author is really
little more than a child's hand tossed glider
toy - yet, it's capable of flying out of site
under the right conditions. The model is powered
by a Rapier L-1 motor and has a wingspan of
9 inches. Note the motor mounting tube, which
is made from Kraft paper tubing like that
commonly found in model rockets. The aft portion
of the motor is exposed to dissipate heat.
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Editor's
Note |
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article is intended only as a brief survey
of Jetex history and the current state of
the art in rocket powered model airplanes.
For more detailed information we recommend
visiting the author's website at www.jetex.org |
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