Time to build again - Estes Bull Pup 12D Upscale

After a bit of down time I decided it's time to start building some of the old kits I've got stockpiled in my basement.  After reading some reviews on RocketReviews.com I decided to hack an Estes Bull Pup 12D.

My kit is a boxed “Explorer Series”, EST 7000 on the box, labeled “Skill Level 2, with altitude of 245 meters (800 ft) on C6-5.  I paid $8.96 at WalMart.  My kit has the contents in a sealed plastic sleeve, with water slide decals and a 12” parachute that needs assembly.  The instructions are for an “Estes Explorer Series Bullpup 12D Flying Model Rocket Kit EST 1972”.  My box contains an Estes/Cox mini catalog with coupons that expired 12/31/98.  The current EST 7000 kit sells for $32.99 retail ($15.32 on Amazon as of 7/26/22).

I decided to upscale it from 18 mm engines (B's & C's) to fly on D/E engines per https://www.rocketreviews.com/estes-bull-pup-12d-frank-ross.html  I'll PROBABLY just fly it with B’s & C’s unless I'm launching at a REALLY large field, since OpenRocket predicts it will fly 1416’ on a D12-7 and 2116’ on an E12-8!  I'll build it to take D/E and use an 18 mm to 24 mm adapter (plus the D/E plug) to launch with B6-4 (351’ with 11 ft/sec deployment) or C6-5 (762’ with 19 ft/sec deployment).  OpenRocket predicts it will be over-stable with B's (2.4 cal) and C's (2.11 cal), stabile with D's (1.28 cal) and marginally stable with E’s (0.911 cal).

Other reviews suggest NOT to paint it white, since that makes it invisible, so I bought Rust-Oleum Orange paint (here's my attempt to simulate this in OpenRocket with black fins for contrast).

I used a 24 mm engine mount from an Estes D and E engine mount kit without an engine hook because of the boat tail effect on the nozzle.  The large green rings in the mount kit are almost the right size to fit into the 1.33 in. (34 mm) body tube, though I had to sand the inside and trim it a bit with my knife to get them to slide onto the engine mount.  Using a D12 engine and the D/E spacer I positioned a 24 mm engine plug at the end of the engine tube.  The engine will be held in place by friction fit using masking tape over the back end before launch.

The kit comes with a plastic part you have to cut to liberate the tail cone, so I used a hobby saw to separate.  I spent some time cutting the nozzle end so the 24 mm engine tube would fit through the boat tail by a combination of sanding the end, hacking off several millimeters with the saw and shaving it with an Exacto knife.  Once I was satisfied, I glued the 24 mm engine mount in place with wood glue and glued the boat tail with model cement.  I left it drying overnight.  Next to come is the fins.

July 30th update:

I attached the fins using my Estes fin guide after poking holes in the body and base of the fins with a safety pin (supposed to help the glue form a stronger connection).

The front delta-shaped "control" fins wouldn't fit in the fin alignment guide so I used the homemade slotted alignment guide on the right (above).

I let each control fin dry for ~30 minutes then moved on to the next.  I attached a slightly larger launch lug (3/16") instead off the one that came with the kit so I can use the larger launch rod to stabilize D engine launches.  Next will be to coat and sand the fins, paint with primer and sand before applying the final coat.

August 2nd update:

I decided for the sake of simplicity to forego the black fins and paint the rocket with just Rust-Oleum Orange paint:

I will probably add the decals but at least it's ready to launch and I've got one less kit on my build pile!

Decals added:

Final weight:

After the decals dried I applied a coating of clear paint then measured the final finished weight:  2 3/8 oz (2.375 oz, or 70 gm)

OpenRocket estimated 2.53 oz finished so my estimates for stability and altitude should be pretty accurate.  Ready to launch!