K-21 Gemini Titan Clone - Finally Completed!!!!! See current posts!
 

I purchased several parts from Semroc and a few from Apogee Components to build an Estes Gemini Titan K-21 clone. The problem I’m having is finding the tube lengths for part # JT-70A (stage coupler) or the JT-50B's. The most important length is for stage coupler. This length determines the cluster angle related to the main body tube. Does anyone one have the parts in an inbuilt K-21 kit to measure and let me know?

Thank You,

The info can be found on page 3 of the 1974 Custom Parts Catalog

(http://www.spacemodeling.org/JimZ/manuals/estp741.pdf)

The JT-50B is 1" long; the JT-70A is 1-1/4" long.

Hope this helps;

Excellent ! Thank You!

I am not sure I believe that the JT-50B is 1" long. Look at the weights, the B is about 1/3 the weight of the 1" long 50C. Can anyone confirm the correct length?

Edit...Roy, elsewhere, has stated that it is 7/16"

Hi all,

Help! I am not sure the measurement in the catalog is correct either. I put the engine section together and now the nozzles interfere. Seems there is something amiss. I have new parts on order from Semroc to try this again and dry fit it all. I think I could use the measurement from the main body tube across the gap between the engines tubes to figure the proper length of the JT-70A. If you all follow me with this logic it can be used to determine the length of the JT-70A. Anymore thoughts here would be greatly appreciated. Could I also get someone to measure the length of the Engine Shrouds from top to bottom? That would be another verification of proper scale I am using for them.
Thanks!

I believe the length specified for the JT-70A in the 1974 Parts Catalog to be correct. I have one, new in package, and the length is 1-1/4". Photo below.

OK. Thanks. If that is the case then I need to switch my focus to engine tube length and Engine shroud size as an issue.

Been over a year...
 

Been over a year, how much have you got done?(Just asking)

Got any pic's?

Gemini Titan Clone K-21 Update
 

Hi Guys,
I will post pictures soon. I am making some good head way on this challenging clone. I think maybe I am challenging myself more here since I have seen some awesome builds of this kit on the forum. I do have a few questions. Why did Estes not make this a dual recover for the capsule? My idea was to use a 6" or a 12" chute for the capsule and 24" for the booster. I was thinking about doing this for mine, but wanted some feedback. I also was wondering where the CG is on this model? If the engines are installed my concern was it would be too far aft. Do I need to consider some ballast for the nose?

The JT-50B is 1 inch long but cut down to 1/2 inch to create the two turbopumps. The capsule is attached to the booster simply to keep the two together. You would lose the capsule unless you put it on a streamer.

There is plenty of weight to counter aft balance when the fins are installed on the model prior to flight, and make sure that you checked the length of the JT-70 as that sets the angle on the motor tubes. It is also helpful to use the updated engine bells for the model to prevent the original templates from meeting each other in the middle. Also consider using 1/16th plastic rod to construct the thrust assembly on the motor tubes.

There is a trick to installing the main capsule shroud; on the model to create a small lip along the inside of the main tube which projects out the end of the tube a little less than a 1/16th. This eliminates a butt joint of the tube and shroud and provides something to key the two together.

About the only other suggestion I would make to add to the original kit is to use a set of paper wraps on the balsa capsule. Makes for an easier job finishing that part to a more scale appearance.