Gemini Titan
Jzitani
need to know the length of the {main body tube} {stuffer tube} }engine tubes}
I saw the plans on JimZ's web site, and thought I'd do one. This the one that
uses BT-70 for the main body tube.If any one knows, please get in touch. Thanks
Joe Zitani
Graf Gulch
myself.
I could list all the tube sizes, but I think it would be better if I told you
where you could get a list of all the tube sizes Estes made (that is up to
1974). Its a must have for any "Cloner"
Here is the link for the body tube list:
http://www.ninfinger.org/~sven/rockets/custom_estes/custom_estes.html
Here are some links to sites that sell the hard to find body tube BT-70
KosRox
http://www.tela.com/~dtkostron/tubes.htm
Totally Tubular (e-mail site only)
mailto:jfac...@cac.net
Vaugn Brother Rocketry
http://www.vaughnbrothers.com
KosRox also sell the extra long launch lugs you will need.
Here is a site that has Adobe (pdf files) of the decals, fin and centering
patterns. (the fin sizes in the JimZ plans I think are too big and I don't
think they provide the centering ring patterns either.
http://www.geocities.com/CapeCanaveral/Hangar/9936/
Hope this helps you. If any of these links don't work write mr back and I will
take care of you.
"Keep on cloning"
Paul Graf
Tom
is the original balsa Gemini capsule nosecone that I bought at a hobby
shop 15 years ago.
Graf Gulch
else going to be improved? I'm always looking for good ideas. You know Balsa
Machining Service make a duplicate of the nose cone.
Peter Clay
>I'm building The Estes semi-scale Gemini Titan #GT-3 sp-21b from scratch. I
>need to know the length of the {main body tube}
I built one of those in 1967. I'm almost certain that the main BT-70 body tube
was 17" and the two motor tubes were 3.5" each; note that the motor tubes were
angled inward by the spacing of the holes in the centering rings. I don't
remember how the stuffer tube was arranged. I do remember trying to glue clear
butyrate sheets together with clear dope. One sheet was wrapped around the
bodytube and the fins were glued to it. The bond was not good. The fins were
not rigid. Surely there's a better way!
Peter W. Clay NAR 18619 SR L1
"Experience is a good teacher, but her fees are high."
Brett Buck
>
> I do remember trying to glue clear
> butyrate sheets together with clear dope. One sheet was wrapped around the
> bodytube and the fins were glued to it. The bond was not good. The fins were
> not rigid. Surely there's a better way!
Best way is to not use Butyrate Sheet!!! I shrinks a lot, and
forever. They recommended leaving on the rocket to keep it from
shrinking so small it wouldn't fit. All this did was collapse the base
fo the BT in and give it the infamous "starved horse" look around the
centering rings.
It you do use butyrate, repeated applications of SIG retarder (very
slow thinner) may give a better bond. R/C 56 might work, but I haven't
tried it.
I am using .050 Lexan sheet for both the fin ring and fins for my
Thor Agena A, held with 2/56 nylon screws. Still not entirely rigid, but
it's pretty tough.
Brett
Kurt Schachner
As for building the old Estes G-T model, I put one together about a year and a
half ago (a picture of it was on JimZ's site with the instructions but I'm not
sure it is there anymore). At that time I posted a build report which I'll
include at the end of this post.
Like someone has already mentioned you should go to my web site at:
http://www.geocities.com/CapeCanaveral/Hangar/9936/index.html
and dowload the fin, engine bell and centering ring patterns (and the decals for
the kit).
Good luck building the kit. It's a great looking model and easily one of my
favorites. Fly it on 2 B4-4 motors. The B6-4 is too fast off the pad and the
C6-5 puts it up too high for me.
Kurt
****************************
Well, I don't know if anyone really cares, but I did promise to post a build
report on the Estes twin-engine Gemini Titan. Despite all my mistakes in
construction (mostly due to late-night building sessions), it turned out pretty
nice after all. A picture of it is on JimZ's website, on the page with the
plans.
First off, my intent in construction was not to create a more "scale" model than
the Estes kit. I have seen posts that this kit, constructed as described, is not
very scale. My intent was to recreate a kit from my childhood To that end I am
happy with what I have.
A couple of general notes:
There was (and continues to be) confusion over the fin size, shape, and
geometry, with accompanying confusion over the height of the fin ring. I hear
from (I think Buzz) that he has an original kit with 2 7/16 inch root-length
fins. I have a set of plans from Bob Craddock that show a fin with a root length
of about 3 inches. The ones on Jim Z's site are longer.
I ended up using the 3" root-length fins that I had, mainly because I had
already cut them before I discovered the other sizes. Bottom line is that it was
stable in flight, probably would have been with the smaller fins too, and the
small length of ring and fins that extends below the bottom of the body tube was
absolutely no problem.
I built the fins out of 0.040" thick polycarbonate and the fin ring out of
0.020" PC. As I have posted here before I did end up having a machinist friend
make me a mandrel that I used to heat-treat the ring material into a nice,
stress-free ring. If you use polystyrene sheet instead of polycarbonate, perhaps
you wouldn't have to do that. However, a short piece of 2 1/4" diameter aluminum
rod is also the right diameter so you could use that. You will have to play
around with oven temperatures but on my home oven, I set it to between 300 and
325 degrees F. I used a solution of 10% polycarbonate in methylene chloride to
bond the ring together and the fins to the ring. There are commercial solvent
bonding agents available.
Going through the instructions, I have the following comments.
The engine mount is composed of two centering rings and a tube coupler. The
centering ring's holes (for the engine tubes) are off-center (one ring has the
holes slightly closer together than the other. I had a Xerox of two original
rings to go by which I redrew and are posted to my site.
Don't build the stuffer tube as shown in the instructions. I believe that is way
more complicated than is necessary, plus it makes it nearly impossible to get
the shroud on correctly. Build the stuffer tube out of a single piece of BT-50,
and leave 4" or so at the top of the BT-70 for the parachute. That makes a
stuffer tube about 8 1/2 to 9" long. You need to cut two RA-5070 rings for the
tube.
Then construct the capsule/shroud assembly like the Centuri (or Estes
re-release) Saturn 1B. Use an additional JT-70A and short piece of BT-60. This
way, the shroud (service module) and capsule are one unit and the whole thing
pops off at ejection. You get a couple of good benefits this way--a bigger
parachute tube (BT-70 instead of BT-60), simpler construction, and a much better
looking shroud. If you don't understand what I'm talking about, download the S1B
(or newer Estes SV) plans and it should be pretty clear. Trying to glue a shroud
onto the edge of a body tube is very difficult to do.
I also used CA to butt-join two shorter launch lugs together for the wiring
tunnels.
The engine bells on the pattern sheet were way off for me. Use the ones posted
to my site instead. It took me only about 20 tries to get it looking right :-)
I ended up attaching the fin unit with two 4-40 nylon screws, which screwed into
two nylon nuts I embedded in the two little balsa wood pieces at the bottom of
the rocket. This left two holes in the exterior of the tube, but it's not all
that noticeable and I like the idea of positive fin attachment.
Oh, and by the way, for the little engine combustion chambers just above the
bells, I cut a 7/16" piece of BT-50, and used two RA-2050 rings to make them.
Trying to cut down a tube coupler (and cut it straight) was impossible for me.
This looked very nice when done.
Now to finishing. I painted on the white and silver, and made black decals for
all the rest (except the capsule). You could paint on the roll patterns, but the
vents and UNITED STATES are difficult. For the capsule decals I called up
Revell-Monogram and got a set of decals for their Mercury capsule since they
were white. I also had the machinist cut my capsule windows with a 3/8" end
mill.
I used 3/64" wide white detailing tape to make the white stripes. The first
three were easy to put down, and the last one was difficult. Getting it to lay
down over the launch lugs is a problem.
Well that's about it. How dose it fly? Great! Especially on 2 B6-4s. The 2 A8-3
flight was kind of a cliff hanger, but nothing dangerous. I just liked the
higher boost on the Bs.
If