Little Joe 1A being prepared for flight at Wallops Island, VA, fall 1959
Building the Escape Tower
The toughest component to fashion on any Mercury-themed model is probably the escape tower. Fortunately, I've constructed several of these beasties in the past and have managed to get pretty proficient at the task. The aft closure is where I've elected to start. Using a technique first developed for my 2003 Beach Abort model, the tiny bolts on the closure were replicated by "lacing" a strip of .030" styrene rod through a series of 45 holes. Once all of the bolt heads were in place, they were all cut and sanded to the appropriate height. Next, the three tower attach points and bolt details were added. The finished master, just over an inch in diameter, contains 59 individual pieces.
Construction begins with the preparation of a pair of simple jigs to help keep everything aligned properly. The jig above (shown atop a Chopper, fast becoming one of my favorite tools) is used to hold the V-shaped parts at the base of each tower upright while the glue dries. The entire tower lattice structure is made from carefully fitted little fiddly bits of styrene tubing and rod, glued together with Ambroid ProWeld adhesive. The choice of adhesive is important: ProWeld is far more aggressive than other hobby glues, and serves to literally "weld" the tower lattice components together.
Here the three tower lattice uprights have been fitted into the tower assembly jig, which is fashioned from (predictably) more styrene hoo-hah, along with some scrap modroc airframe sections. A rejected aft closure part has been pressed into service as the top alignment part for the jig.
Time for another sanity check, as a completed lattice is placed atop the capsule along with the antenna section assembly for a fit verification. You'll note a pair of additional tower lattice assemblies in the background of this photo; as noted earlier, multiple Little Joe and Beach Abort versions are being constructed.
Construction of the tower lattice raises an interesting philosophical conundrum, or at least as close to one as we scale modelers tend to get. What is preferable: an accurate model, or a realistic one? If appropriately-sized tubing diameters are used to construct the lattice, the completed assembly has a heavy look to it, as if oversized tubing was used. It's accurate, but it's just not "right," at least not to most informed folks. By using slightly undersized tubing diameters, the tower takes on the gossamer-light look appropriate to a Mercury model. It's not entirely accurate, but it is far more realistic...
So, what to do? Depends on the audience. For the flying FAI model, there is a (slight) possibility that the diameter of the tower components may be measured, so I'll go with the accurate (but less realistic) "heavy" part. For the IPMS-bound Beach Abort model, I'll go with the more realistic-looking (but less accurate!) "light" tower. Oy, vey...
Tower Motor
The next component to be fashioned is the tower motor tube. The prototype motor casing is 15" in diameter, or about .86" at our scale of 1/17.44. Scrounging about failed to produce a ready-made commercial tube of the proper size, so we'll need to make our own. More scrounging (I'm the guy who roams the aisles of Home Depot with a micrometer, measuring everything in sight) unearthed a PVC tube that was slightly undersized; in other words, a perfect mandrel to lay up a fiberglass tube, as the additional thickness of glass and resin will yield a tube of the appropriate diameter. We begin by spraying a few layers of Crown wax-based mold release on the tube, then cut a piece of 3/4" ounce glass cloth to about 8" x 12". The glass is placed on a sheet of wax paper, then a bit of West 105/206 slow-cure epoxy is drizzled over the cloth.
Another layer of wax paper is placed over the glass cloth and epoxy, then a plastic card is used as a squeegee to saturate the cloth with epoxy and remove excess resin. After peeling the top layer of wax paper back, the saturated glass cloth is carefully wrapped around the PVC tube mandrel, taking time to work out any air bubbles or other hickeys that pop up. Rolling the cloth onto the mandrel will result in a tube made from several layers of glass, which is ideal for strength. The picture on the right above shows the mandrel with the transparent glass/resin layup in place.
Tip: hang on to old hotel key cards and expired credit cards, as they are ideal squeegees for epoxy/glass layup work.
The escape motor tube part needed for the finished model is only 3.15" in length, so we'll be able to cut a couple parts from the finished tube. Because of the particular slow-cure epoxy resin chosen, it will be several days before we're ready to remove the finished tube from the mandrel.
Once the layup has had plenty of time to cure (several days, ideally) it should be ready to come off of the PVC mandrel. First, a light sanding with 320-grit sanding film takes care of any rogue glass threads. There's no need to put the final finish on the tube yet, so we won't knock ourselves out with the sanding chore. A large pot of water is brought to boil on the stove, and as much of the layup as possible is dunked into the water, with a ladle used to get hot water to the upper parts of the tube that won't fit into the pot. This will cause the wax release layer to melt, and with a bit of persuading the tube will slide right off the mandrel. The tube sections are light, strong, and EXACTLY the right diameter!
Escape Motor Nozzles
The escape tower motor nozzle master was fashioned by turning a chunk of Delrin rod stock on a lathe, then making a mold from the master. Despite many years of looking I have never been able to locate a reference that specifies the correct length of the Mercury motor nozzle, and the only reliable dimension for the part seems to be the exit diameter of 16". Working from a number of photographs and David Weeks' Mercury drawings set (highly recommended, by the way), I settled on a nozzle length of x".
The parts are created by rolling a small amount of resin around the inner surface of the mold until the goo begins to set up. It takes a bit of practice, but the results are finely molded nozzle parts with a very thin wall. A bit of work cutting the part to the correct length with the razor saw and polishing the cut with a sanding stick completes the job.
Completion of the Beach Abort version of the model is covered on a separate page.
Tower Motor
After cutting the glass escape motor tube to the correct length, a pair of BT-50 engine blocks are peeled to the correct size to fit into the fore and aft ends of the tube. This wil provide a bit of critical surface area for gluing other components to the tube. Next, a scrap of .030" styrene sheet is CA'd to the forward end of the tube, then trimmed and sanded to the appropriate circular shape. I use sanding sticks in a variety of grits, available from the Squadron Shop.
The final version of the cast aft closure and tower jettison motors have been chosen from several candidates, and are in the midst of a bit of final sanding and part clean-up. A few extra nozzles have been cast, looking for that elusive thin wall.
Additional study of various references has led me to decide that the antenna canister on the LJ-1A round did not feature any corrugation details, so a new canister has been rolled out of .015" styrene sheet, again using Robert Blaske's indispensible Shroud Calculator.
Aft closure detail
One of the areas for improvement uncovered during construction of the Beach Abort Test verison of the model was the need for more detail on the lower surface of the escape tower aft closure. This part of the Mercury escape tower has a gentle convex shape that the motor nozzles and tower jettison motor attach to, and I agonized for months over just the right way to go about the task. I briefly considered slicing a section of a ping pong ball, but couldn't conceive of a way to accurately mark and cut the ball. Of course, it might have helped if I had actually gone to the store and bought a ping pong ball to experiment with, but that's a story for another time.
I ended up slicing a racquetball in half to use as a mold for a resin part, and it worked far better than expected, needing only a bit of finish sanding to complete. I simply glued the part to the underside of the resin aft closure created earlier, and the completed closure assembly was ready to attach to the tower lattice.
Back to part 1: Capsule assembly...
On to part 3: Transition Shroud assembly...
On to part 4: Boilerplate assembly...
On to part 6: Airframe assembly...
On to part 7: Paint and Markings...
On to part 8: Motor Mount assembly...