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rec.models.rockets FAQ Part 06 - Model Rocket Construction and |
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Archive-name: model-rockets/construction
Rec-models-rockets-archive-name: rockets-faq/part06
Posting-Frequency: monthly
Last-modified: 1997 January 6
URL: http://dtm-corp.com/~sven/rockets/rmrfaq.toc.html
Rec.Models.Rockets Frequently Asked Questions: PART 06 OF 14
MODEL ROCKET CONSTRUCTION AND FINISHING
This section includes tips and suggestions on various topics having to do
with construction and finishing techniques. These have been posted to
r.m.r or mailed to the moderator by way of r.m.r request. Refer to the
High Power Construction section for additional tips, oriented towards high
power and advanced rocketry requirements. Even more construction tips can
be found in the Scale Modeling section.
[Note: This part of the FAQ is maintained by Robert C. Santore
(santore@ibm.net)
Any additions or corrections should be sent to that address]
-----------------------------------------------------
6.1 Cutting, Sealing, Attaching Fins
From: JCook@Epoch.COM (Jim Cook)
Skip using glue W/ balsa dust, dope, or any other junk for filling the
grain in balsa fins or nose cones. Use Elmer's "Fill 'n Finish" diluted
with water to a thick paint (like white glue is) and paint it on.
Non-toxic and a coat or two will do. Use Elmer's "Carpenter's Wood
Filler" thinned similarly to fill the spiral in body tube. Both come
in a white plastic tub with an orange lid. Note - the latter is
harder to sand, so don't make the mistake of using it on balsa as it
will require a lot of sanding.
From: cdt@pdp.sw.stratus.com (C. D. Tavares)
Fill your fins BEFORE attaching them. (Don't fill the root edge).
From: utidjian@remarque.berkeley.edu (David M.V. Utidjian)
[To hold fins in place and aligned while drying I bought an Estes
fin alignment kit]. At 15-16 bucks it seems a bit
expensive but is well worth the aggravation and time it saves. You
can even make your own if you are handy. I just set up my body tube
in the jig and then check the alignment of all of the fins to the body
tube. Then I use a thin bead of 5-min. epoxy. and in ten minutes I am
done. When I do the fillets I can do them all at once but don't have
to worry about the softening the glued on fins so they droop. You
still have to lay the model on its side though but only for 5 minutes.
From: kaplowro@hccompare.com (Bob Kaplow)
The Estes Fin Alignment Kit has now been discontinued for '96. You can
use the newer Rocket Builder's Marking Guide ($5-8) to do one fin at
a time. [Editor's note: This is a HIGHLY RECOMMENDED item to purchase.
It provides everything needed to mark BT-5 through BT-60 body tubes
for 2, 3, 4, 6, or 8 fins.]
-----------------------------------------------------
6.2 Body Tubes (Cutting, Joining, Filling)
From: cdt@pdp.sw.stratus.com (C. D. Tavares)
[On cutting Estes-style body tubes]
The simplest and best I ever used was Howard Kuhn's jig from the old CMR.
It's a simple piece of wood L-angle molding, with a notch for a razor
blade cut into one side (from the wing toward the elbow) at one end.
The only other parts are a wood block and a large black spring clip (the
kind you hold really thick reports together with). If you want, say, a
6" piece of tubing, you set the block 6" away from the razor notch and
clamp it there with the spring clip. Now lay the tube down the L-angle,
butting it up against the wood block. Insert the razor blade, press
lightly, and turn the tube. (Put a dead engine into it if the tube is
the right size to fit one.) Three to six turns, and you have an edge
that looks factory-cut.
----
( ) <- spring clip | <- razor (edge on,
/ \ | sharp edge down)
____________---------___________________________|_______
| /_| |__/| | |
| | |_______| || angle molding | |
| | wood block || |
|----------|____________|/-------------------------------j
/ lay tube here and spin it /
/________________________________________________________/
From: soc1070@vx.acs.umn.edu (Tim Harincar)
[On cutting Estes-style body tubes]
When I cut tubes, I always wrap the tube with about two
layers of drafting tape with the edge of the tape along
the cut line. This accomplishes two things: First the
thick tape edge providing a excellent knife guide. Second,
you can assure a straight cut. If the tape wrinkles when
you wrap the tube, you know it is not on straight; simply
remove the tape and try again until you know its down flat.
Drafting tape is better than regular masking tape because it
has almost the same thickness but is made to be removed.
This method is in addition to reinforcing the inside with
a stage coupler or spent motor. Also, always use a new
x-acto blade for the best cut.
From: Jim Bandy (NAR member not on net)
Use a piece of aluminum 'angle iron' for joining body tubes. Place one
tube in the angle, insert and glue the joiner, then insert and glue the
other tube. It give very straight joins. The angle can also be used
for marking fin lines on body tubes, etc.
-----------------------------------------------------
6.3 I'm fed up with tangled plastic parachutes with broken shroud lines. How
can I improve on the standard chutes, or make my own?
From: soc1070@vx.acs.umn.edu (Tim Harincar)
Making your own parachutes is pretty easy. Start with the desired
material (usually mylar or a light plastic). Make a cutting pattern out
of cardboard by first drawing a circle that will be the maximum size
of the chute (i.e. 16"). Take a compass [or] something that will give
you an accurate radius of the circle. Pick a point anywhere on the
circle and using the radius as a length draw an arc that crosses the
circle. At the point where the arc crosses, reposition the compass on
that point and draw another arc. Keep doing that all the way around
the circle - you will end up with six points including the starting
point on the circle. Connect these points with a straight edge and
Presto! a hexagon. Cut out the hex from the cardboard (I use artists
matte board...) and this is your cutting template. Lay the template on
the material and using an EXTREMELY SHARP XACTO KNIFE cut along the
outside of the template. Make shrouds from a heavy gauge thread -
cut three equal lengths twice as long as the diameter of the chute and
connect the ends to corner points adjacent to each other.
From: Roger.Wilfong@umich.edu
I usually build 12-24 line round chutes out of Estes material (just cut
around the outside of the red and white circle and attach at the red
/white boundaries) because they look more like real parachutes. I use
embroidery floss for shroud lines and separate the 6 strands (for 12
lines - use two lengths for a 24 line). This makes a strong chute.
With out crossing the lines over the top of the canopy, I've only had
one failure of a 12 line chute (an EL that tipped off dramatically -
i.e. cruise missile) and never had a 24 line fail. In the 10 years
I've been back in the hobby and using this technique, my shroud lines
have always come out the same length (within a couple of percent
tolerance).
From: hal@HQ.Ileaf.COM (Hal Wadleigh)
1. Use fisherman's snap swivels for your attachments. It lets you
store 'chutes separate from rockets and helps prevent fouling due
to spin at deployment.[Note...modelers have always reported mixed
results with snap swivels; they have been known to fail...Buzz]
2. Use nylon coat thread for shroud lines on homemade 'chutes (and
plastic bread wrappers are the best cheap 'chute material).
3. Pay special attention to the security of the attachment points.
Those standard stickers often look secure, but are actually not
attached. A small knot in the part of the shroud line under the
sticker serves as a good anchor point (with the rest of that part
looped around the knot, as per standard practice).
4. Very small 'chutes should be cross-form type. Cut about a 5" square,
then take out about 1.25" squares from each corner. Attach 4 lobes
of shroud across the flat ends and secure as above. Be careful to
use small stickers for the corner attachments. These make good
substitutes for streamers in .5" body tubes and can also be used as
drogues to help in the deployment of large 'chutes [A note from
cdt@sw.stratus.com (C. D. Tavares): Either round off the inside
corner of that 1.25" square or reinforce the angle with something.
Otherwise, it's a really handy place for the parachute to rip
during a fast deployment.]
From: smith@mrcnext.cso.uiuc.edu (Greg Smith)
Nylon coat thread is very good for small, lightweight competition
parachutes, but it's not real strong and does have a tendency to melt if
it encounters a bit too much ejection charge heat. For sport and
payload models with 12" - 24" plastic 'chutes, I use 15 lb. *braided*
nylon fishing line. It's thicker than the coat thread, similar in
diameter to the Estes cotton stuff, but tremendously stronger. In the
last fifteen years, of the plastic parachutes I have built using this
line (and always crossed over the top of the 'chute for reinforcement),
I have had *zero* shroud line or attachment failures. The braided line
has a hard, smooth surface that doesn't encourage tangling, and it
doesn't unravel where cut.
From: whitman@nssdca.gsfc.nasa.gov (Rusty Whitman)
I've tried about everything to keep shroud lines from pulling off of
plastic or mylar parachutes. Those little tape disks are just about
worthless. Tying knots and cyano'ing the ends helps but you still
have problems. I don't know why I never thought of this before but I
ran across a roll of duct tape in my closet and knew immediately that
was the answer. I cut out some little squares of duct tape and
attached some lines to a parachute and they won't pull free without
ripping the plastic. I don't know who invented duct tape but they
deserve some kind of statue, its got more uses than a paper clip.
From: kaplowro@hccompare.com (Bob Kaplow)
1. Make shroudlines from Kevlar thread. This won't burn through. Tie
a knot 1/2" from the end and fray the end. Attach that end to
parachute.
2. Use the much stronger kite snap swivels instead of fishing swivels -
make sure they lock, and don't just clip like a safety pin.
-----------------------------------------------------
6.4 Alternatives to Recovery Wadding
From jack@rml.com (Jack Hagerty):
Just go down to your local building supply store and get a bale of
cellulose wall insulation. This is just shredded newspaper treated in
the same fire suppressant [as Estes recovery wadding]. A $5 bag will give
you enough wadding to last years!
From MASSEY@TRAVIS.llnl.gov (Warren Massey):
I have found crepe paper to be a must more cost effective alternative.
It comes in either sheets or rolls (I prefer the sheets) in a variety of
colors and is every bit as flame retardant at a fraction of the price. I
can even get several flights off a single ball of wadding. It is somewhat
stiffer than the tissue but I've never found that to be a drawback.
Unattributed:
A piston ejection system works well on rockets of BT-60 size or greater.
Pistons eliminate the need for recovery wadding of any type. Plans
for a D powered rocket using piston ejection may be found on sunsite.unc.
edu in the file 'pub/archives/rec.models.rockets/PLANS/dust-devil.ps'.
The rocket was designed and drawn by pfeiffer@nmsu.edu (Joe Pfeiffer).
From: kaplowro@hccompare.com (Bob Kaplow)
Use a baffle system (I posted this to RMR a while back) to eliminate
the need for wadding. This also provides the benefit of a third centering
ring (see Pete Olivola article) as part of the baffle system. Stainless
steel mesh can be used to trap hot particles, but be careful that
ejection
caps don't plug it up.
-----------------------------------------------------
6.5 Are there any good tips when making my own nose cones?
From Chris Jennison
To keep nose cones from wobbling and coming out asymmetrical when using
an electric hand drill as a lathe...
Use a blank (dowel, broom stick or balsa block) 1/8 inch larger
(diameter) than the nose cone that you need. Drill a 1/4 in. diameter
hole
as close to dead center as you can and push in a 1/4 in dowel. Dowel
length should allow the nose cone end to seat against the face of the
drill chuck. Find dead center by running the drill clamped in a vise at
moderate speed & slowly move a soft pencil toward the end at what
appears to be the center of rotation. After a couple of tries you will
find the center because your misses will draw concentric circles like
a bullseye. Now remove the dowel from the drill, clamp the shoulder end
in the vise and rough shape the nose cone with a file or rasp using the
marked center as a guide. Final contouring and finishing is done in the
drill with progressively finer sand paper.
-----------------------------------------------------
6.6 Getting Paint to Stick to LOC and Aerotech Nose Cones
From: kwolfe@interramp.com (Ken Wolfe)
VERY VERY important......WASH THE PLASTIC FIRST!
I had this problem until I started to wash the plastic before even
assembling anything. This solved most of the problems I was having.
From: Roger.Wilfong@umich.edu (Roger Wilfong)
I have had success painting nose cones from both companies using Krylon
and Walmart paints. The technique I use is to wash the nose cone with
a Brillo pad followed by a thorough rinse. Fill the mold parting mark
with auto body putty and sand it smooth. I next use a coat of primer
(I've used Krylon's gray sandable, Walmart's gray and Black Baron - the
Black Baron was the best, but also the most expensive and took the
longest to cure). This is followed by a light sanding and another
coat of primer, followed by sanding. After the primer cures (a week, if
I'm in the mood to paint, a year if I'm not), paint it with some paint
that's compatible with the primer.
This technique works fine on the LOC nose cones, the only problem I've
had with the Aerotech nose cones is that the very tip tends to get
chipped off.
I have a LOC PNC-3.00 that has lawn darted into hard ground twice. The
original paint is scratched, but it shows no signs of flaking off.
From: smith@mrcnext.cso.uiuc.edu (Greg Smith)
I rough up the surface of plastic nose cones with 60 grit paper, then
use my basic epoxy painting regimen as I've described earlier. After
the first coat of primer, the surface is *really* fuzzy; the paint
reinforces and thickens all the little plastic strands that are raised
by the sandpaper, and the surface feels like rough concrete. But a
little sanding knocks off most of it, and after the third primer coat or
so, the surface is as smooth as anything else on the model.
The only time I've ever damaged the finish on one of these nose cones
happened when a model fell off the workbench and onto the concrete floor
in my basement, which chipped the tip of the cone a bit. Normal flying
(including one or two landings on concrete) hasn't affected them at all.
From: jsvrc@rc.rit.edu (J A Stephen Viggiano)
As I have said repeatedly, the most effective way to paint on these
plastics is to introduce carboxyl groups at their surfaces. This will
give the paints something onto which they can grab.
A carboxyl group, also known as a fatty acid group, consists of a
carbon atom, to which an atom of oxygen is doubly bonded, and also
a hydroxyl group is bonded. In order to convert the end of a polymer
chain into a carboxyl group, you need to provide oxygen and some
energy. The oxygen may, of course, come from the atmosphere.
In the packaging industry, when polypropylene and polyethylene must be
printed, they are given either a "corona discharge treatment," in which
the surface is passed beneath a high-potential device called a coratron,
or a "flame treatment," in which a gas flame is allowed to impinge
on the surface for an instant. For historic reasons, the second treatment
may be referred to as a "corona treatment," even though no corona
discharge is involved.
I've used the gas flame from my kitchen range with excellent results.
Don't overdo it, for obvious reasons. Only an instantaneous contact
with the flame is needed.
Since using this treatment, I have had virtually no problems with paint
flaking from my polypropylene nose cones.
From: M Preddy
I've had good luck with Rustoleum primer on LOC nose cones. Krylon
sticks to it fine.
From: kaplowro@hccompare.com (Bob Kaplow)
Consider covering nose cones with econo-kote.
-----------------------------------------------------
6.7 Is it possible to get a high gloss, durable finish on a model rocket?
From: p_hamilton@usa.pipeline.com (Paul Hamilton)
I put on a clear coat of dope or Krylon, sand with #600 wet-or-dry
sandpaper, and then buff with "Rotten Stone" or similar rubbing compound.
This is a fine abrasive that on mixes with water. I have used toothpaste
or silver polish as a substitute for rubbing compound when there has been
no hardware store around.
-----------------------------------------------------
6.8 Are there any good paints for silver details on scale models?
From: Orville ????
The Krylon silver paint looks very much like real silver, that's
because it's made of a clear coat plus real metal flakes.
The only problem is when you touch it the finish becomes dull.
The solution to this problem is:
Finish your surface as usually.
Spray a final coat of Krylon on and let dry 2 days, but don't
even think about touching it. After 2 days spray Krylon clear coat
over the silver with very light coats ,letting each coat dry 5 minutes
between sprayings. This will give you a very nice finish.
From: Peter "wondered if they had silver spray paint for the Tin Woodman's
axe in the Wizard of Oz" Alway (alway@pooh.physics.lsa.umich.edu)
I'm starting to get serious about silver paints, now that I am working
on 1930's rockets. I think it's worth getting a sense of several
metallic colors, all for different purposes. As near as I can tell,
most are either simply glossy (Testors Chrome, Dutch Boy silver) or
matte (Testors silver, and apparently Krylon.
As an experiment, I tried buffing some Testors siver on a nose cone
(it was still chucked up on the drill press wher I turned it) last
weekend. I found I needed to use dome #600 sandpaper to get a truly
smooth surface, then I just buffed it with ordinary paper. The result
was pretty convincing, but a darker shade than the original
paint. (unfortunately, on Goddard's rockets, the nose was usually
a lighter shade of Aluminum) I was impressed that the result looked
like real metal to me.
Testors has some buffable paints in their Metalizer line. I tried their
"Titanium" on a Glencoe 3-stage rocket ship (a von Braun design), but
when polished, I thought it looked more like hematite than actual
metal. I'm starting to believe that with silver paint, it's more
important that you represent the differences between silver shades
than get the siver just right. So for instance, on a Goddard
rocket, I would use the glossy Dutch Boy silver for the nose cone,
buffed silver paint for the nickel-steel propellant tanks, and
testors silver for the duralumin body. This should at least
suggest the differences between the materials that you can see
in the photos.
From: Bob Craddock (craddock1@aol.com)
After building and re-building about a half-dozen Saturn V's, I have a
couple of recommendations to make:
For the Service Module color, I suggest getting a bottle of Micro Metal
Foil Adhesive and some Reynold's Wrap. Spread the adhesive on the
**shiny** side of the foil. The silver on the SM was somewhat dull, and
just about ANY silver paint sucks badly! The foil will give you the
look
you need, and the adhesive is extremely easy to work with. The white
raditor details can be added by using shroud line or Evergreen styrene
strips. White glue works well with the shroud line, but I would
recommend
fast epoxy for the strips. Mask of the radiator areas so you can paint
them white when you paint the entire rocket.
-----------------------------------------------------
6.9 How can I prevent a rocket painted white from yellowing?
From: curcio@telerama.lm.com (LarryC)
Future floor polish (it isn't wax) doesn't yellow. I find it useful for
rockets but...
1) It must be used over some kind of paint or over acrylic gesso. If it
seeps into cardboard or wood, the material will become brittle;
2) It will cause dope and (even permanent) Magic Marker color to run.
This effect can be used to advantage, but it can also ruin a model if
it's unexpected. Future does not cause enamel paint to run, and may
certainly be used to cover decals. Don't know if the decal will yellow
beneath the coating.
3) A glossy finish is not always desirable, and Future yields only a
glossy finish. Art stores sell equivalent mixtures that come in gloss
or matte finishes. The are called "Acrylic Gloss Medium," and "Acrylic
Matte Medium," respectiely. They are thicker than Future, but they can
be thinned with water.
4) Acrylic colors, available in art stores, can be used on rockets, as
long as acrylic gesso is laid down first. The colors should be thinned
with water or Future. Acrylic paints are normally labeled to tell you
how opaque they are and how toxic they are. Both qualities vary from
color to color. Even though the tubes seem expensive, the opaque colors
have excellent covering power and they turn out to be very good buys.
5) From my own experience, commercial acrylic model paints are to be
avoided. They are over-thinned, and they yeild undesirable, cracked
finishes.
From: kaplow_r@eisner.decus.org (Bob Kaplow)
Try adding a small amount of BLUE to the white paint (a few drops per
bottle). The faint blue tint hides the yellowing, much like bluing in
the white laundry.
-----------------------------------------------------
6.10 Which is better, white or yellow glue? Epoxy? Cyano?
From: buzzman@netcom.com (Buzz McDermott)
Yellow wood glue, such as Elmers Carpenter's Glue or Titebond, is far
superior to regular Elmer's white glue for building wood and paper model
rockets. Built carefully, with proper fin fillets, yellow aliphatic resin
will hold together on rockets with up to G power. Yellow glue also dries
faster.
Three and five minute epoxy is often used for quick repairs. This quick
drying time does not allow the epoxy to soak into the wood and/or paper
very well, though. If epoxy is to be used, then use one with at least
a 15 minute, and preferably a 30 minute, listed 'drying' time. Thirty
minute epoxy will give a much stronger bond than yellow glue. However,
5 minute epoxy often yields a weaker bond than yellow glue.
Cyano is often used for quick building. It bonds strong, dries extremely
fast (especially when using an accelerator), and is relatively easy to
use. Regular cyano can also be used to bond plastic to wood or paper.
No matter which glue is used, the most important factor is to have a
properly prepared surface. Glassine coated Estes-stype body tubes should
be lightly sanded where the glue is to be applied. All bonding surfaces
should be clean and unpainted. You want whatever bonding agent is used to
be able to soak into the paper and/or wood.
From: kingrat@sisko.dnaco.net (kingrat)
I've been using CA to bond fins to the tube and then a fillet of
epoxy. If you go this route I recommend thin CA and a fin alignment
guide. Make sure the fins are aligned properly before you CA and check
again before applying the epoxy. Unlike white glue, if you mess up it's
REALLY hard to fix. It's also REALLY hard to pop the fin off too. :)
This works just fine with balsa or plywood fins from what I've seen. CA
is good for tacking the lugs in place too, however I would never use CA
on a vital part of the rocket (ie. motor mount) CA just isn't strong
enough because it turns brittle. Epoxy will flex somewhat without
breaking
and you can add microballoons to allow it to flex even more. In
short, use
CA to tack and epoxy to bond.
From: santore@ibm.net (Bob Santore)
There is an easy test to tell if the glue you are using is strong enough.
A glue joint only needs to be as strong or stronger than the material it
is gluing together. To test for glue strength you need to test the
strength of the glue joint relative to the strength of the material you
are bonding. This test is very easy and can be used for any type of
glue.
Glue some scrap pieces of whatever you are gluing together in a
configuration similar to how you intend to use it (i.e., don't test a
surface mounted fin if you intend to use a TTW fin). When cured,
pull the
two parts apart. Did the glue bond fail? If it did, don't use that
brand
of glue. If the pieces you glued didn't fail, then this glue is fine.
If your rocket falls apart anyway, then you need stronger rocket parts!
The only exception I can see to this very simple test would be near the
motor mount where heat can weaken the glue. You could always heat the
pieces before destructive testing to see if heat changes the
properties of
the glue joint.
-----------------------------------------------------
6.11 Improving on the Estes Shock Cord Mount
There are a number of ways to improve on the old paper-and-rubber-band
shock cord mount used by Estes for the past 35 or so years. The
following suggestions have been repeatedly made in r.m.r.
1. Replace the rubber band or short elastic in the kit with sewing elastic
at least twice the length of the model. This will help to avoid
tube zippering or ripped out shock cord mounts when you have a 'hard'
ejection.
2. Epoxy the shock cord mount to the inside of the body tube rather than
using white or yellow glue. Thirty minute epoxy works best for this.
Be sure and lightly sand the inside of the tube where the shock cord
mount is to be placed. Also be sure and 'cover' the entire mount with a
very thin layer of epoxy. This method works best for models with BT-60
or larger body tubes.
3. Use a 'Quest-style' kevlar-and-elastic shock cord mount. This type
of mount uses a length of 50 to 150 pound test Kevlar (such as Stren
Kevlar fishing line or Kevlar kite string). The Kevlar is tied and
glued to the motor mount (motor block, centering ring, or around the
motor tube). It is sized to end just shy of the front end of the
body tube when a length of elastic shock cord is tied onto the free
end of the Kevlar. This method eliminates any shock cord mount on the
inside surface of the body tube. Estes-style shock cord mounts have
been known to interfere with parachute deployment. You can used this
method on any sized rocket. Size the Kevlar appropriately.
4. You can also use a 'LOC-style' shock mount for body tubes in the
1.5" and up range. With this you take a short length of Kevlar line,
fold it in half, and make a !-2" loop in the closed end of the folded
line. You then epoxy the loop to the inside of the body tube in such
a manner as to have the end of the loop extend a little past the open
end of the body tube. A shock cord is tied to the loop. The advantage
of this technique is that is allows damaged shock cords to be easily
replaced. It tends to work better on body tubes greater than 1.5"
in diameter.
-----------------------------------------------------
6.12 I've built several BT-80 based models. How can I strengthen future
models to take larger motors, such as Aerotech 24mm or 29mm reloads?
Estes recommends using just D motors in their BT-80 based kits, such as
the Broadsword (Super Big Bertha) and Shadow (Optima). There are a number
of steps that posters to r.m.r have done to strengthen these rockets to
fly with larger motors. Remember in doing this that you are modifying and
using the rocket kit in a manner NOT recommended by the manufacturer.
From: Buzz McDermott (buzzman@netcom.com)
Here's a summary of what I've done to strengthen my Shadow and Broadsword
kits to fly on 24mm reloads and up to 24mm G42 motors. You will need
a LOC-style 2.56 inch tube coupler, 3/4 oz fiberglass, 15-30 minute
epoxy, and 20 minute 'coating' or 'finishing' epoxy:
1. If the kit comes with the 'plain' BT-50 type motor tube, replace
that with LOC-type, thick-walled 24mm motor tube. You will only
need about 6".
2. Reinforce each body tube section with 3/4 oz fiberglass. Apply it
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