Double Pumper scratch build

Here is the build thread I promised for my scratch built Double Pumper. I had ordered a 3" 2x24mm cluster motor mount from Mercury Engineering when I ordered my Hijacker, with the intent of building the Hijacker as a cluster instead of the single 29mm mount. I decided to build the Hijacker with the 29mm mount, though, and use the cluster mount in something else. I decided to build a scratch cluster rocket, and ordered a nose cone and 3" x 17" body tube from Mercury. I based the fins on the Quest Astra, and added tabs for through the wall mounting. I used two-part epoxy throughout the build, except for the external fin fillets. For those I used Titebond Molding & Trim Glue.

I assembled the cluster motor mount per the included instructions, but didn't epoxy the rear centering ring, which would be epoxied in later in the build. I did put the rear ring on the motor tubes while the epoxy set on the front ring, to be sure the tubes would be correctly aligned. I also added a small eye bolt to the top ring for the shock cord mount. I liberally slathered the nut and washer, and the area around them, with epoxy for strength, and so that the nut couldn't come loose.

I created a fin wrap guide at Payloadbay.com for the fin positions on the body tube, and cut out the slots. After cutting the 1/8" plywood fins with my bandsaw, and sanding the edges with my stationary belt sander, I epoxied them to the body tube with my homemade fin alignment guide. The thread on the guide can be seen here:

https://www.rocketryforum.com/showthread.php?t=9859&highlight=alignment+guide

I left the rear motor mount centering ring off, so I could put internal epoxy fillets on the fin tabs. When I epoxied the front centering ring in the body tube, I put the rear ring in place to make sure the motor mount would be aligned. After the epoxy set, I removed the rear ring, and applied an epoxy fillet to the front ring. After the fins had been epoxied on and set, I applied internal fillets to the tabs, and epoxied the tabs where they contacted the motor tubes.

Here you can see the motor tubes and fin tabs. You can also see that I cut the short tab too short, so I scabbed in a small piece of basswood. Probably not necessary, but I wanted the large fins to be strong.

You can also see that I forgot to attach the Kevlar to the eye bolt before I epoxied the motor mount into the body tube. Oops! Using a clip-on flashlight and some thin wire, I snaked the Kevlar through the eye bolt. I used a double length of 1/8" braided tubular Kevlar. I like this Kevlar because it's soft and thick, and hopefully will be less prone to zippering.

I usually take more photos than this, but didn't this time, for some reason. Somewhere along the line, I applied external fin fillets with Titebond Trim Glue, epoxied on a 3" long 1/4" launch lug (with the top of the launch lug even with the top of the fins), and epoxied the rear centering ring in place. I primered the entire rocket with white primer, then painted the nose cone red, and the places on the rocket where the red stripes would be. I masked for the stripes, re-primered it, and painted on the gold. Turned out very sharp, if I do say so myself!

I made a 24", 8 shroud line hexagonal parachute out of a 1.5 mil red garbage bag.

Its first flight was on two D12-5's, and was a great success. This turned out to be a sweet looking and flying rocket. Can't wait to see how it does on E9's or bigger!

https://www.youtube.com/watch?v=R_PQrzQznIc

I like it a lot. Very classic lines and the paint job, very nice.:clap:

Thanks for sharing with us.

Very nice!!!

Thanks for all the compliments, everybody!

I finally got the decal put on.

Man, that really looks nice. I dig the gold, it looks like it finished well. What brand of paint was that? I'm thinking gold and black may be on a future rocket of mine.

Congrats on the successful flight,
Chevis

Chevis said:

Man, that really looks nice. I dig the gold, it looks like it finished well. What brand of paint was that? I'm thinking gold and black may be on a future rocket of mine.

Congrats on the successful flight,
Chevis

Click to expand...

Thanks for the compliment! I believe the paint I used was Rustoleum. If you're going to use black, I highly recommend Rustoleum's 2X Painters Touch. Man, that black covers nice!

I got to fly the Double Pumper again yesterday, at the SARG launch. It was a drag race between my Double Pumper and Kit's Lupara (Double Pumper Jr.) Both rockets flew on pairs of D12-5's. It was a lot of fun!

twin F240's

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twin F30's

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