My first cluster, a scratch build.

[kruland]

Hi all.

I recently finished the NARTREK Bronze challenge flights and now am moving to the Silver. One of them is a flight of a cluster model with 3 or more motors. I've never built a cluster model but decided to try scratch building one nonetheless. Please correct me and provide advice since I really don't know what I'm doing.

I decided to build a cluster of 4x13mm motors. Four BT-5's seem to fill a BT-56 pretty nicely. I used 1/4" slices of a spent T motor for the individual motor blocks and glued everything together.

I've cut a double layer of paperboard and glued it to the forward end of the motors. After this dries I'll cut out openings for each of the motor tubes to let the ejection gasses through.
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SC2 REPLAY

 

[Blades]

Looks like a good start to me. Clusters sure are fun.
Make sure you get some of Quests Q2G2 ignitors, they make the ignition process so much more reliable.

 

[kruland]

I have always liked the looks and flight performance of the tapered body tube. I went to payload bay and printed up a transition from bt-60 to bt-56 over 10 inches. After cutting out and steaming the long transition, I glued it with white glue.

For the aft, I wrapped cardstock around the end of a bt-56 about three times so the tapered tube would have two places to hold on to. After a test insert in the tapered tube, I cut it so it was flush with the transition.

For the fore end, I cut a piece of bt-60 1" wide to hold the nose cone.

I glued the 4x13mm motor tubes into the bt-56. Then tied a piece of kevlar around it. I didn't want the kevlar to go between the built up section and the paper tube because it would inevitably cause a bulge. So I poked a hole in the bt-56 and passed it through.

I then glued the sections of bt into the paper tube.

I'm thinking I'll soak the rolled paper tube in CA to harden it, but will take other advice.

Now I need to craft some fins. I'm thinking double-ellipse out of 1/64" ply.

 

[kruland]

I decided to douse the paper tube in CA and it really made it more rigid. Unfortunately, the printing on the inside showed through. It isn't going to win any beauty contests but I hope it does well in Cluster Altitude.

For fins, I picked 1/32" ply. I cut them into a nice double ellipse and sanded in the airfoil.

I cut slits through the paper transition so the fins would bond against the inner tube and the transition. Just like TTW fins on those big MPR/HPR birds. I attached the fins with a double glue joint using yellow glue.