Honest John 1B

This rocket is is a 4-inch sport-scale model of the Honest John 1B. The 1A, with the giant triangular fins, is more commonly modelled, but I prefer the look of the 1B.

This rocket was printed using PETG in an Army green color. The main feature was how I printed wraps to finish the body instead of painting. Not only did this avoid the mess of painting, but it made sure the body matched the color of the printed parts.

Watch directly on YouTube.

The Pictures

finished rocket

Tony "tfish" Alcocer was kind enough to fly this rocket (and the Nike-Smoke) to test out how 3D printed rockets survive L2 HPR flights.

Flight 1

Tony:
"The shapes of this rocket had me thinking about CG/CP too, but with the nose cone being big and bulky it might be over stable? Got it prepped and it seemed fine. First flight motor was a 38mm 4 grain Research motor similar too an AT I211.

"With the rocket prepped and ready to fly at 103 ounces this flight would be about 7:1 thrust to weight ratio… still no wind…out to the pad. The motor came to life and lifted the HoJo to 1244 feet where the 1+ gram charge did it's job to deploy the 60" flat sheet chute. The 1½ gram charge fired but was not needed. The rocket landed close at 19 ft/sec."

Flight 2

Tony:
"The second flight was prepped just like the first flight. The motor of choice for this flight was 54mm 3 grain Research motor, similar to the AT J415W. Still no wind, but at ignition the rocket left the pad at a 45 degree angle. It stayed on this course until it reached apogee. At 3015 feet, the deployment charge fired. I was surprised to see it all hold together. It had some pretty good speed to it when the parachute deployed.

"I hitched a ride with Ken Adams and the rocket was over a mile out. it landed at 24 ft/sec. It ended up with one of the fins corners being broke. This probably happend during the deployment process. It's fixable. Concidering the flight angle and speed during deployment I feel the rocket is pretty durable. The main question is why did it leave the pad at such and angle? CP/CG issue? just one of those things?"

fin broken side

fin broken aft

Learnings from this rocket:

The CF plate fin inserts seem to have created a week spot, so it's hard to know when reinforcement is necessary and probaly better not to add any until it's clearly needed.
The plate did indeed protect the aft end from heating due base drag and the fin can showed no obvious heat damage.
PETG printed parts are fine for I-J motors, which is great news.

The Design

My build uses mostly 3D printed parts, except that I still prefer standard phenolic body and motor mount tubes in most cases. However, using standard body tubes means filling spirals, priming, sanding, and painting. I didn't want to do that, so I came up with the idea of trying printed wraps, which turned out pretty well.

Of course, I couldn't print the wrap as a single part, so I split it into four pieces. There were longitudinal panel lines on the prototype, which I could take advantage of for the front/back split. However, there weren't panel lines that would camoflague the forward/aft split. In retrospect, I should have invented panel lines there to make it look more intentional.

My first attempt was a single filament layer using a 0.4mm nozzle. That worked, but was cruder than I like and so had some small holes at the corner of lettering. The final wraps were printed with the finest possible settings using a 0.2mm nozzle with 3 layers. The bottom layer was all the background color (green) and the white lettering and red squares were 2 layers thick. Using the minimum layer height, this made the wraps still flexible enough for a 4"e; tube and opaque.

4 wraps printed

In case anyone wants to do something similar, here are the printed parts:

Or one zip file of them all. Or you can download them from Thingiverse.

The CR and ebay were printed in PLA-CF, the body sections in PETG and the gasket in TPU. I always use gyroid infill with the CRs and fin can at 50% to maximize strength and the body parts at 15% to reduce weight.

The wrap is split into four pieces. the front and back along panel lines that exist in the prototype. The lettering is very slightly taller, enough to paint with color in the slicer, but not enough to print taller.