Aft end of Little Joe booster, Wallops Island, Virginia.
Airframe Assembly
As mentioned back in the introduction to this project, the scale is dictated by the availability of a 4.546" tube sourced from Totally Tubular.
Our first step is to cut the airframe tube to the appropriate size. As the project progresses, I'm double checking many of the dimensions against multiple references, and I elected to make a minor change to the tube length based on a reinterpretation of the fin attachment fitting at the base of the rocket's airframe. A guide for marking the tube was made from a long piece of paper, wrapped around the tube and taped into place. This allows us to mark the appropriate length around the circumference of the tube, then the tube is cut after sliding the guide out of the way.
There is enough tube material to cut two separate body tubes. The remaining section of scrap tubing is cut down to produce a coupler section that will be used to construct the motor mount, using the section that was removed as a glue tab.
A lack of satisfaction with the way tube #1 was turning out finally prompted me to try an alternate approach to detailing the Little Joe airframe. In addition to rivet and panel line detail that was just a little bit too soft, matching up all of the various panels and getting them to stick to the underlying tube turned out to be a real bear of a task. So, I elected to try an approach that would eliminate the need to match panel lines by covering the tube with a single sheet of .020" styrene. An oversized sheet of plastic was backed with 3M permanent double-sided tape, then that sheet was wrapped around a spare tube and overlapped. After allowing the tape to set for a couple of days, the overlap was cut away, as shown above. The resulting seam was filled with medium CA, followed by a bit of accelerator applied with a microbrush. The seam was then immediately sanded with progressively finer grades of sanding sticks and film, resulting in an imperceptible seam.
With the tube seam taken care of, the excess plastic is removed from the ends of the tube, which had been sized to the appropriate length prior to the application of the styrene. Panel lines are then drawn into place onto the tube surface.
With the panel lines drawn accurately in place we can begin engraving panel line detail. Dymo label tape is used to guide the scribing tool and protect the surface of the tube. Once all of the panel lines are engraved we start marking the rivet locations, using a template created in Word. After taping the paper rivet template in place along a panel line, each rivet location is transferred to the tube surface by pressing a small awl through the paper into the tube surface.
Each individual rivet is then drilled out with a tiny (#71?) drill. Drilling out all of the rivets above station 471 took approximately eight hours, but the results were worth it (be sure to click on the left photo above to see the results up close). We'll next move on to the airframe aft of this point...
Rivets or Panel Lines? The mind reels...
Our next step is to map out the surface detail for the portion of the airframe aft of station 471, which can also be referred to as the "fin can." The drawing for this was done in Illustrator, and can be seen in PDF form above. Why the hell I chose to do this in Illustrator instead of Vectorworks is beyond me, and can probably be attributed to a bout of temporary madness associated with the drilling of thousand of little tiny rivets over the weekend. (I did finally come to my senses and prepare a drawing in Vectorworks, which is shown and linked above.)
Mapping out these details poses a bit of a conumdrum, as I'm not entirely convinced that the distinctive panel lines appeared on all of the Little Joe boosters. As validation of this, take a look at the aft airframe on this graphic prepared by Peter McQuillan. Not a panel line in sight, huh? Just a bunch of rivets. Thousands of the little boogers, in fact...
On the other hand, the panel lines do appear in all of the classic modeler's references for the Little Joe series, such as David Weeks' wonderful drawing set, Peter Alway's Rockets of the World, and even the drawings prepared specifically for modelers by North American Rockwell in the early 70's. Why do these features appear on so many of the widely accepted drawings? I propose that this is due to the fact that the two remaining Little Joe boosters, at Wallops Island and the Hampton Air Power Park, possess these panel lines, and probably served as a primary resource for these gifted researchers.
So, why the confusion? Given the thousands of hours spent musing over the Little Joe series over the years, I suppose that I've earned the right to have an opinion on the subject. I suggest that the Wallops and Hampton Little Joe examples are early versions constructed before the designers settled on the 74.5" capsule diameter, and were intended to loft an 80" diameter Type C capsule. This is supported by the presence of 24 bolt apertures around the circumference of the forward end of the booster; were these intended to attach to the Marman clamp that would hold the capsule to the booster? On all on the flown Little Joe boosters, the 24 bolt apertures are at the top of a transition section, not a part of the booster itself! Are the transition sections on the two "gate guard" Little Joe boosters just cosmetic components whipped up in a Wallops or Langley workshop years after the end of the Mercury program? It's a good guess that they were. Think about that for a moment: the two surviving Little Joe boosters might just be pretty lousy representations of the booster as they were actually flown!
As for the missing panel lines on the aft section of the flight rounds, I suggest that a decision was made after the two early LJ boosters were constructed to strengthen the fin can section by riveting on an extra layer of sheet metal, obscuring the panel lines. Hell, it's a good a guess as any, I suppose, but it makes sense.
That leads us back to the question of what to do for our model. The mantra of scale modeling is "build to your data," which is of no damn help if you have conflicting data. Although I've yet to make a final decision, I'll probably go with the panel lines, as the bulk of the classic references call for this approach. It will also take less time than drilling (literally) thousands of $%&#@ little rivets, and an argument could be made that it looks more interesting. Stay tuned...
A Decision Is Made...
The decision has been made to go with the panel lines for the fin can as opposed to the "scads o' rivets" approach. Going back to the "build to your data" truism, I've got to admit that more quality support for the panel lines exists than for the rivets. The two photos above show the Vectorworks drawing being positioned on the aft section of the airframe tube. After the panel lines are transferred from the drawing to the tube, the lines will be scribed into the surface.
We scribed the panel lines into the surface of the styrene using our trusty Dymo tape 'n scriber method, then set about about adding a bit of rivet detail to the sides of the panel lines using the rivet pattern we whipped up in Word as a template. The two right photos show the results from a couple of different angles. The next task is to cut the four serrations into the aft end of the tube, and then we'll line the interior of thetube with more styrene, along with more rivet detail.
I was pleased to receive an email from Josh Tschirhart in support of my decision to go with the "panel line" approach for the aft end of the tube. Josh pointed out a photo of Little Joe 1 that clearly shows the visible panel lines, and his affirmation of my decision was greatly appreciated as it came from a fellow modeler that I hold in high regard. Josh specializes in the early Saturn series, and I encourage all of you to visit his website. Perhaps we can persuade him to join us on a future US Team?
Chevron plates
With the rivet detail all in place, selected sections of the aft tube are carefully sliced away, resulting in the distinctive "notched" appearance that is one of the hallmarks of the Little Joe. Extra care was taken care to make sure that we were using sharp blades for this step, and completing the task consumed three #11 blades.
The first two Little Joe boosters had a unique feature known as "chevron plates," featured here on this very handy chart (created by Peter McQuillan) highlighting the differences between various rounds in the series. First, a strip of .015" styrene is glued into place on the interior section of the tube, with some of the material visible through the notches we just cut. The template for cutting the chevron pattern is a small section of the aft airframe drawing created earlier. Since the area to be cut is recessed a bit, taping it in place initially presented a bit of a challenge, so I simply punched a few holes in it for the tape to peek through. The final photo in this series shows the finished chevron plates.
This is the point in the project where even I have to admit that I may be going to extremes. When a modeler begins applying rivet detail to the inside of the airframe tube, there's a strong possibility that the cheese has slipped off of his cracker. Again, our trusty rivet templates make an encore appearance for the task.
After carefully measuring and drilling mounting holes, the fins are test fit onto the airframe. Note the addition of some hatch details just below the half-way position of the airframe tube; these represent the hatches where NACA/NASA technicians could insert and arm the igniters at the forward end of the four Recruit motors (click on the photo for the full-resolution version). Weight of the airframe at this point is 8 3/8 ounces, or 237 grams, so we're still well within our 2.2kg mass budget. Next we'll turn our attention to the engine mount, then work on aft compartment detailing, which promises to be the the most fun step in the project, as scale data is sketchy and we won't be able to obsess on dimensions.
The ability to remove the fins for shipment is a critical feature of this model, as we need to be able to break down our Little Joe to survive a trip to Kazakhstan via Moscow. Needless to say, not just any old piece of luggage will do. A Pelican 1650 case has been purchased to pack the components of the Little Joe model, my 1/26.5 scale Bumper WAC model for S5C competition, and all of my flight gear.
Back to part 1: Capsule assembly...
Back to part 2: Escape Tower assembly...
Back to part 3: Transition assembly...
Back to part 4: Boilerplate assembly...
Back to Part 5: Fin assembly...
On to part 7: Paint and Markings...
On to part 8: Motor Mount assembly...
