I recently bought an Estes "Prowler" in a local hobby shop, after
looking at it and deciding that it would be an excellent candidate for
some modifications. Here's a brief summary about how to turn your
Prowler into a Growler. (What *were* they thinking...B4-2, B6-2, C5-3,
and C6-3? Nahhh...this seems more like a D15 through F39 type of rocket
First, some background and kit info...
The Estes Prowler is a new (1998) kit, originally designed for 18mm
motors. As kitted it was 40.5 inches long, with a listed weight of 4.2
oz. (120g), and comes with a 24" plastic parasheet (standard Estes
issue). This one uses through-the-wall, to-the-motormount fin mounting.
It comes with glow-in-the-dark stick-on decals, and warnings that these
are just for display purposes, and not to launch it at night due to the
danger of tripping over stuff and hurting yourself in the dark. (I
sometimes wish that our society hadn't become so litigious, and we could
just let Darwin do his job on those that would eventually be culled from
the breeding pool.)
The changes I decided to make were...
Since the kit was already using TTW fins, I figured it would be strong
enough to make good use of a 24mm motor mount. I also decided to modify
the motor mount to allow use of the Aerotech 24mm RMS system. The other
major change was to use the Anti-Zipper design from the recent Sport
Rocketry article. I also used the transition piece that came attached
to the nosecone as a boattail. This slightly changes the lines of the
rocket, giving it a "faster" look, and should help it achieve somewhat
Construction hints, tips, and gotchas...
I wound up using almost all of the kit parts that were supplied, with
the exception of the original motor mount tube, centering rings, and
black retaining ring. These can be used in other scratchbuilds, so
there was essentially no waste. (Actually, since I used the adapter
piece that came attached to the nosecone as a boattail for my modified
kit, I "wasted" one less part than Estes wanted me to.)
The first step in construction is the motor mount. I just used a piece
of 24mm Estes tube in place of the supplied motor tube. I also used a
large green thrust block from an old kit as a thrust ring. I used a
Dremel wheel to grind off a portion (about 1/2 of the original length)
of the front of the motor hook so that I could place a 24mm RMS casing
in the tube. I used double centering rings (2050 thin-stock rings,
glued together to make them double thickness...4 total used, 2 in front
and 2 at the rear). Measure carefully; you'll want the front and rear
edges of the fin tabs to *just* touch the centering rings, to give some
additional gluing surfaces and adding some more rigidity to the rear of
The motor mount was moved rearward about 1-1/2" so that the tube would
extend to be even with the rear of the boattail section. Some slight
"machining" was done on the plastic to allow the motor hook to work
within the boattail. (I just needed to "thin" the plastic; there's no
gap in the line of the boattail as viewed from the side...the motor hook
stays inside the diameter of the end of the boattail.) A small centering
ring was added inside the rear portion of the boattail to act as an
additional support and gluing surface for the motor mount.
System3 epoxy was used throughout the construction. Silica thickener
and phenolic microballoons were added as necessary for the various
functions (adhesive, fillet, etc).
The fins were made of the hardest balsa I have ever encountered. Since
I was using a larger motor tube, I had to remove some stock from the
mounting tab to get the fins to sit flush against the body tube. A
Dremel reinforced cutoff wheel was used, but it was really slow going,
and there was some scorching of the wood as it was being cut. As I
said, that was some *hard* balsa! Leading and trailing edges were
tapered with a sanding drum, and the tips were left squared off.
For the zipper-proof mods, only the front two body tube sections were
glued together. The rear tube section gained a 1/4" thick basswood
baffle plate glued into the coupler, with multiple 1/4" holes drilled
through it. A***eye was placed in the middle and epoxied in place.
One half of a "ChoreBoy" sc*** was pushed through the motor mount
tube to the area between the front of the motor mount tube and the
baffle plate. This can easily be removed for replacement when needed
from the tail end of the rocket.
All that's left now is the finishing steps; construction is done.
The fins and body spiral are going to be coated with thinned Elmer's
Fill-n-Finish, primed, and painted with Rust-Oleum Metallic paints. A
clearcoat over the paint and it should look *great*. Even with the
rearward-moved CG (larger motor mount, shifted back for the boattail,
and the baffle system) the kit should require no noseweight, since it's
a nice, long, overstable Estes design at its heart.
I'm looking forward to finishing this one and getting a decent-sized
motor into it. It's a clean design, and with the boattail and other
mods it should be interesting to fly.
NAR #70953 - Sr./Insured ~ SeaNAR - The Seattle Area NAR Section #568
NO Junk Email, please! Real email to: amphoto [at] wolfenet [dot] com.
<WARNING: Do not look into laser beam with remaining eye!>