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All three rockets are made out of 20 oz. Dr. Pepper bottles. (that's
what the people at work drink, and they are kind enough to save them for
me). The first bottle is just a slightly blown end, basically hemispheric
with coroplast fins. This is the minimalist rocket if there ever was one.
The performance is VERY good, almost as good as the Y2K model. The second
rocket is my standard Y2K model. It uses a stock bottle with a shrink-formed
nose cone. This one also has coroplast fins. The third rocket is pretty much
the same except it uses foam core art board for fins (it's what I got for
free so I used it!) . The art board is lighter than the coroplast, but, I
don't see any visable difference in performance, and it is not as durable. I
prefer coroplast fins. Notice also, the foam pipe insulation used as a
bumper in the nose cone. It really helps! It is just stuck in between the
nosecone and bottle and minimizes (but not eliminate) damage to the
nosecone. But, perhaps more importantly, it help keep the fins from shearing
off on impact with the street.
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This is the sequence for shrink-forming nosecones. You take a stock
bottle and pressurize it to 40 psi. (with safety glasses, but don't worry
about ear plugs, they don't make that much noise when they burst. And you do
blow some holes in them while learning how much heat to use! It's no big
deal, about the same as exploding a balloon in your face. Safety glasses,
remember?) apply some heat with a hot air gun or B-B-Q or what ever until
the bottom starts to "guppy" . Then heat the sides until they start to bulge
a little. This is so when you cut the tapered neck off of the bottle , this
pre-form will slide onto your wooden shrink form. Not shown (sorry) is the
preform shrunk onto the wooden form. The form shown is just a fir 4X4 turned
down to the desired size and shape. Note the hole in the top. This is
drilled with a long 1/8" drill bit so you can use 100psi to blow the trimmed
nosecone off of the form! Don't even try to shrink form with out this
"ejection port" ! After using both mohogany and fir as forms, I can
definately recommend the mohogany. After shrinking down, the nosecone is
trimmed right on the form and then ejected. The finished nosecone is shown
on the extreme right hand side of the picture. Note the opaque look of the
plastic at the tip. With practice you can avoid this by not overheating.
It's a little tricky and I don't worry about it any more . I just mass
produce these 2 dozen at a time when I get enough bottles collected. Out of
2 doz. , maybe 4 will be transparent. But , they will all be good ,
flightworthy parts. Try it, it's really pretty fun, very satisfying. It's
a cross between glass blowing and , well , heat shrinking!
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This is a view of my fin jig. It is simply made up out of some old 1/8"
plywood paneling. I just cut up some rings and a platform and hot melt glued
it all together. You could do the same thing more easily with foam core art
board as you would'nt need a jig or band saw. One thing I would change on
the next one is to have longer "feet" so as to clear the last fin. In the
next pictures you will see what I mean
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In this view, you will see how the bottle fits into the two locating
rings. Notice the round indexing stop on the end of the jig. The bottle
seats up against this so as to repeatably locate the bottle in the jig,
everytime. The fin just rests on the platform. I used a platform design
because I can use many different fin shapes and they all work with this kind
of a jig! In use, one justs applies hotmelt glue to the fin, and just slides
it onto the bottle. After contact is made , just let go ! Don't touch it!
Just let it cool down and set up before disturbing the rocket. (This is the
hardest part ! :-) ). When it is cooled and set, just rotate the bottle to
the next position and repeat the process. Each and every fin is glued on
quickly , easily, and STRAIGHT EVERY SINGLE TIME! Every single rocket I
have ever made with this jig flies straight, every single time. I love it.
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This end view shows the location of the platform in relation to the
centerline of the bottle. If you look closely , this picture shows the 2
mistakes I made. 1: I located the fin platform exactly on the centerline of
the bottle. I SHOULD have off-set it 1/2 of the fin thickness, so the fin
centerline is in line with the bottle centerline. This makes no difference
in the flight of the rocket, so I lucked-out on this one. The second mistake
was to make the supports too short. If you look carefully, and check out the
fin span, you will see that after the 3rd fin is ready to be glued on, the
first one will be hitting the bench! Oh well, I just put the fin jig on a
4X4 when I'm using it. But, when you make one , incorporate the upgrades!
But, one little item that shows in this picture, if you look REALLY close,
are the three little index marks 120 degrees apart . I put the bottle in the
jig and take a felt pen and mark the three spots where the fins will go and
then there is no guessing while gluing!
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This is another view of the fin and bottle in the jig. Not shown
(sorry) is the bottle cap with a tire valve stem installed so as to be
able to pressurize the bottle to 40 psi WHILE attaching the fins with the
hot glue.
The basic gluing proceedure is as follows:
- pressurize bottle to 40 psi
- insert bottle into fin jig and mark locations at 120 degrees
apart with felt pen
- Remove bottle and take 180 to 220 grit sandpaper and scuff up
the areas where the fins will be attatched. Make sure there is
no skin oil or anything on the bottle BEFORE you do this! You
don't want to sand-in any contamination.
- Replace bottle into fin jig and line up the felt pen mark with the
platform
- Apply a bead of low temp crafts-type (the clear translucent type)
hotmelt glue to the end of the fin and immediately slide it onto
the bottle , using the platform as a guide. Once it has made
contact, leave it alone. See the above admonishment.
- When cool, rotate the rocket and repeat for the remaining fins,
allowing adequate cooling time at each joint.
- After adequate cooling, remove rocket from fin jig. Check to see if
there is still 40 psi in the rocket and then proceed to apply
a SMALL! fillet of adhesive on each fin. Do NOT, repeat, DO
NOT over heat the bottle or else it will weaken the bond line
strength through residule stress upon cooling. The reason for
the 40 psi is to keep the bottle from shrinking away from the
hot glue line.
- Slip on your nose cone. Taping it on is optional, but it looks
more "finished".
- Your rocket is ready for the launch pad!
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