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Scratch-Built BT-60 Based Gemini Titan

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Michael Garretson

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A while back I was killing time waiting for a zoom call to start and was browsing through the eRockets website.

I happen to notice that Randy had a couple of BT-60 sized Gemini Capsule nosecones and got the idea to scratch-build a Gemini Titan – like the old Estes #1978 BT-60 based model.

I placed an order for the nosecone, and some other supplies, and couldn’t wait to get started.

I had a set of new BT-60 body-tubes on hand, and an old but damaged Estes Bail Out kit - which has the same/similar fin-can and locking-ring assembly as the #1978 Gemini Titan kit.

I figured that between the two, I had everything I needed to complete the project.

While I was waiting for the nosecone to arrive, kuririn sent me a copy of John Brohm’s Estes Body-Tube Guide (extremely helpful for sure), so I knew to cut one of the body-tubes to 12.5”.

Long story short, once the nosecone arrived, I pulled everything together and discovered that the Bail Out’s fin-can was horribly bent from being stored improperly. I even tried a “fix” suggested by linville86 to no avail.

Now what?

When I posted a message on the Forum about the fin-can issue, MALBAR 70 sent me a reply about other Estes kits that used the same assembly. However, in his reply he also mentioned that I might consider using clear fins to make the rocket have a more “scale look” to it.

Eureka.

When I ordered the nosecone, I had also ordered a set of clear plexi fins and a pre-slotted BT-60 body-tube I was going to use on another project.

Now I was ready to go.

I have never scratch-built a rocket before, so it was both harder, and took longer, than I thought. But in the end, it really turned out to be a blast.

Once I finished building it, I primed and painted the body-tube assembly and nosecone, applied a set of decals from Stickershock23.com, installed the fins, and glued on the launch-lug.

The plexi fins made it tail heavy, but a couple of metal washers under the nosecone’s eyehook, balance things out.

Over-all it’s heavy – about the same weight as the Estes RTF 200 Scale Saturn V – but I’m not looking for a highflyer – just a couple of flights with C6-3’s before it’s display time.

Thanks to kuririn, linville 86, and MALBAR 70 for your help and suggestions.

It may be my first, but it will certainly not be my last, scratch-built rocket.

Michael

Gemini Titan Pic.jpeg
Gemini Titan Pic.jpeg
 

mbeels

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Very nice! What glue did you use with the plexiglass fins?
 

Michael Garretson

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mbeels,

I used thick CA to glue the fins to a BT-55 body-tube that was part of the engine mount. I had to sand part of the "root" of each fin to make them flush with the outer body-tube, as well as to help give the CA something extra to "grab hold of."

I did get some "ghosting" from the CA on the fins, but covered it with thin bands of black paint to match the design of the outer body-tube decals.

Michael
 

NJRick

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WOW!! simply stunning! beautiful job!
 

linville86

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Really beautiful rocket. Sorry to here the my suggestion didn't work.
 

MALBAR 70

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Ok, I broke down and picked up one of the Gemini Titan nose cones from eRockets (there were only a few left) so I'll looks like I'll be scratching one together in the near future.

Michael, what pattern did you use for the fins? The shape complements the rocket well. Also, I was wondering what you used for the fin stock? It looks rather thick in the pictures, nice and sturdy, I like that. One last question, how did you get the edges of the fins to look like they were factory cut? Usually when I sand Plexi/Lexan it gets cloudy, your edges are a thing of beauty.
Now off to Stickershock for decals....

>Edit< I see you ordered the fins from eRockets, I didn't realize they carried them. Set ordered.
 
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Michael Garretson

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Ok, I broke down and picked up one of the Gemini Titan nose cones from eRockets (there were only a few left) so I'll looks like I'll be scratching one together in the near future.

Michael, what pattern did you use for the fins? The shape complements the rocket well. Also, I was wondering what you used for the fin stock? It looks rather thick in the pictures, nice and sturdy, I like that. One last question, how did you get the edges of the fins to look like they were factory cut? Usually when I sand Plexi/Lexan it gets cloudy, your edges are a thing of beauty.
Now off to Stickershock for decals....

>Edit< I see you ordered the fins from eRockets, I didn't realize they carried them. Set ordered.
MALBAR 70,

Pretty much everything I used for the build I got from eRockets: nosecone, body-tube, fins, shock-cords, and engine mount.

However, I had to modify the engine mount a little. It was their Semroc Engine Mount Kit #7 to BT-60 SEM-EM-7-60.

Here's what I did:

I used the engine tube, hook, thrust ring, and centering rings that came with the mount - I set aside the coupler tube for future use.

Once the thrust ring and hook were in place, I glued the bottom centering ring to the engine tube - leaving about 10mm of the back of the tube to extend out beyond the main body-tube when installed. I added a second centering that I had about 1/8" above that for extra strength - that's because when installed I wanted the bottom centering ring to be almost flush with the bottom of the outer body-tube - with just enough room to accept a fillet of glue.

Since the fin roots wouldn't reach the engine-tube, I cut a piece of BT-55 body tube that was sized to just go beyond the main body-tube's slotted openings when glued together.

I added top and bottom centering rings inside the BT-55 tube to center it correctly.

I then glued everything together - adding the top centering ring that came with the engine mount kit to the top of the BT-55 tube.

It was basically a tube within a tube type set up.

When installed, the fin roots were too long when they "hit" the BT-55 tube, so I had to sand each of them down to fit flush. No biggie.

I hope that I've explained it well enough to understand.

Michael
 

MALBAR 70

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Thank you so much! Yes,that makes perfect sense to me.
I'm going to have a couple of other obstacles to over come though. First, I have a bunch of BT60's but I'll have to slot them myself (no big deal). Second, I have a Sunward dual 18mm motor mount I'd like to use so the TTW fins are going to need to be modified a little (again, no big deal).
Thanks for taking the time to post the information for me, it'll help a lot.
 

Michael Garretson

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Thank you so much! Yes,that makes perfect sense to me.
I'm going to have a couple of other obstacles to over come though. First, I have a bunch of BT60's but I'll have to slot them myself (no big deal). Second, I have a Sunward dual 18mm motor mount I'd like to use so the TTW fins are going to need to be modified a little (again, no big deal).
Thanks for taking the time to post the information for me, it'll help a lot.
A duel motor setup would certainly address the weight issue caused by the plexi fins. Can’t wait to hear how it turns out. Good luck.

Michael
 

Joshua Smith

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Great work Michael. As a former Minuteman III ICBM operator, there's a special place in my heart for the former & current ICBMs. Hmmm, I bet a scratch build or kit bash would be easy for the LGM-118 Peacekeeper. Start with an Estes Doorknob perhaps. Tho the PK isn't exactly a challenging shape or anything. The interesting bit was the MIRV with 10-12 warheads. I guess 10 small parachutes would be funny but wouldn't exactly function well
 

Michael Garretson

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Great work Michael. As a former Minuteman III ICBM operator, there's a special place in my heart for the former & current ICBMs. Hmmm, I bet a scratch build or kit bash would be easy for the LGM-118 Peacekeeper. Start with an Estes Doorknob perhaps. Tho the PK isn't exactly a challenging shape or anything. The interesting bit was the MIRV with 10-12 warheads. I guess 10 small parachutes would be funny but wouldn't exactly function well
Thanks Joshua! Yep. Ten parachutes would be tough to handle.

Michael
 

MALBAR 70

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I'm almost done with mine, although it didn't come out nearly as nice as yours (I kinda botched the Stickershock decals).
I was curious where your CP/CG ended up and how much nose weight you used to balance it out?
I did end up using the dual 18mm mmt, but that will add a little more weight to the backside that'll have to be compensated for.
Thanks
 

Michael Garretson

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Sorry, I haven't visited this site in quite some time. Since I don't have Open Rocket, I didn't run any formal calculations on my build. I simply balanced it out by adding a couple of metal washers to the bottom of the nosecone. The balance point is just slightly above the leading edge of the fins. Since this was my first scratch build, I'm kind of new to the CP/CG stuff. Sorry I can't help you out to much.
 
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