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THUNDERBIRD SAM CONSTRUCTION
SUSTAINER NOSE CONE
I was disappointed to discover that the LOC 3.9" nose cone I ordered was too blunt. Before I did any other construction, I reshaped the nose cone.
These pictures show, in sequence, the changes to the cone. I made a paper cone, filled it with resin, and centered it on the nose, the sanded and puttied, sanded and puttied. The nose cone pictured on the right shows the cone with filler putty prior to sanding. The modifications are undetectable on the finished product.
BOAT TAIL
I used the handy Rocket Team Vatsaas Transition Calculator to draw the poster board shroud to act as a skin for the boat tail.
Refer to the coupler illustration. To reinforce the shroud, a 12" x 3" tube is mounted around the 21" x 38mm motor tube. The poster board shroud was installed around this tube, flush with the 3" tube at the aft end. A centering ring supports the forward end. I filled this assembly with two-part foam. Had I been handy with Fiberglas at the time I built the sustainer, I would have also reinforced the shroud with Fiberglas before I attached the fins.
ASYMMETRICAL BOOSTER NOSE CONES
  I have to confess that this only became a design issue (in my mind) after my first flights and my brothers found a copious amount of data on the Internet. Rick must have spent a lot more time studying that library book years ago, because he was very keen on the design of the asymmetrical nose cones. I was less particular about it than he, and opted for a very simple 'preliminary' design (I cut the tube at a 45 angle and traced an oblong bulkhead). Rick maintained pressure on me to construct a more accurate booster cone, even learning how to design it on his CAD system.
Rick and Mark both made the trek to Arizona to participate in the G. Harry Stine Memorial Launch in October 2000. Rick was so thoroughly annoyed by the bulkhead solution that a couple of weeks later he sent me a construction template, also the product of his CAD expertise. At any rate, the modification was never made to the Basset, as I decided to retire the rocket in favor of a more accurate scale version of the Thunderbird SAM. Had Rick been less insistent, I doubt I would have ever built a second version of the Thunderbird missile.
 I used a copy machine to enlarge Rick's template to be 3.25" and formed a paper cone, which I then inverted and filled with casting resin. I then wrapped tape around the base of the resin casting and added a 1/4" base to the cone area. The paper was removed and the shape was then perfected using sandpaper and filler putty.
 From this plug I made a latex mold, and from the latex mold I made four castings from Durham's Rock Hard Water Putty. These were hollowed, shaped, sanded, and allowed to completely harden. Once cured, the cones are quite lightweight and, as advertised, rock hard. You see a picture of the resin plug, the latex mold, and the hollowed end of a finished nose cone to the left and a top view of everything fully assembled to the right. The Durham's Putty may not be the best ultimate solution, however - it tends to be somewhat brittle. I have since strengthened the tips of the cones by using the epoxy method shown at the top of this page.
UPDATE: As I predicted in the previous paragraph, I was unhappy with the nose cone castings. Several broke after the second flight, so I replaced them with fiberglass. I started with a paper cone, then added glass on the inside for reinforcement - a lot like the method documented [HERE!]
FINS
Of all the information gleaned from Adrian Hurt's web site, the photos of actual Thunderbird fins were the most valuable. These showed not only the fin profiles and details but also provided valuable data on booster mounting points and the rings that encircle the boosters at those mounting points.
(Steve Moore provided these photos of actual missiles to Adrian Hurt. Give credit where it is due…)
- Large fin on sustainer: from the training round at Coventry.
- Aft fin on sustainer: from the training round at Coventry. The spike on the leading edge is not present on the service round at the REME museum, so it is not include it on my model. I also see visions of shroud lines hopelessly tangled into that vicious protrusion as the sustainer plummets from the sky.
- Booster fin: from the service round at the REME museum (pictured below, left). Missing from this fin is the perpendicular tab (mounted on the outer edge) seen in many photographs (see top). This detail was added to the fins on my model (see below right).
 Click on the drawing for a larger image. BOOSTER COUPLERS
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The addition of the rings that encircle the boosters at both mounting points and the sustainer ring at the forward mounting point was also the key to creating stable and reliable couplers that will also decouple cleanly at high velocity. I used PVC to create the rings, a material far stronger than Kraft tubing. I bought four 2" PVC pipe couplers and one 4" PVC pipe coupler. From this I cut eight 1/2" slices off the 2" PVC pipe couplers and one 1/2" slice off the 4" PVC pipe coupler.
I opted not to permanently attach any of these rings until all the pieces were properly machined and fitted together. I estimate this saved me a lot of aggravation later on.
 Click on the drawing for a larger image. Booster Rings: From four of the 2" coupler pieces I then cut out a 1/4" section and joined it back together so it fit snugly around the booster tubes. A hose clamp works really well for this. From the other four I cut 1/2" section - this slot will fit to the sides of the booster fins, so I didn't have to join them back together.
Sustainer Ring: From the 4" coupler piece I then cut out a 3/4" section and joined it back together so it fit snugly around the sustainer tube. Using a 2" drum sander I formed smooth notches in the sustainer ring at 0, 45, 90, and 135. The forward booster rings should nestle right in these notches.
FORWARD COUPLERS
I drilled a hole in the center of each notch and used a Dremel tool to cut a slot to the forward edge of the ring. I used a countersink bit on the inner side of each slot to fit the head of a #6 machine screw.
(Nylon machine screws were used throughout the model because I figured that the would be secure enough in flight but would break away if a mishap occurred and could be replaced more easily than some of the other components. This proved to be a good decision!)
I then drilled a 1/16" hole in the center of each ring and tapped out the hole so I could thread in a #6-32 nylon machine screw. The screw was then fed into a slot in the sustainer ring and tightened to where it was snug but could still slide cleanly out of the slot. I was lucky that each of the rings moved easily in every slot. This relieved me from having to assign a ring to a specific position on the sustainer ring.
The booster rings were later attached to the aft edge of the forward booster section (nose cone, 4" section of 54mm Kraft tube, phenolic coupler). When fully assembled the forward booster ring covers the separation line on the booster so it looks very clean.
 Click on the drawing for a larger image. MID BOOSTER MALE AND FEMALE RIGID CONNECTORS
Using a 3/4" hole saw, I cut four plugs from the 2" PVC coupler and four from the 4" PVC coupler. I mounted a nylon post into each of the 2" PVC plugs. These formed a male connector, and 4" PVC plugs the female. I shaped the 4" PVC plugs with the 2" drum sander to form a notch similar to the notch in the forward sustainer ring.
These are mounted in a line between the forward and aft connection points. This connection point is to only static one and keeps the boosters from shifting forward or aft during flight.
AFT COUPLER
The aft couplers are similar to the prototype in concept, but the aft boat tail required the construction of a standoff coupling mechanism. I made four crescents out of PVC to nest the aft booster rings in a way similar to the notches in the forward sustainer ring. Each PVC crescent was carved with a screw slot opening aft, and countersunk screw holes. Aluminum tubing from the local hobby store was cut to size and threaded to take a #8-32 nylon machine screw. These were installed through the boat tail and the 3" reinforcing tube and epoxied to the motor tube. The PVC crescents were then attached to the aluminum tubes with #6-32 flathead nylon machine screws.
The forward section detaches upon the firing of the ejection charge, disconnecting the mounting screw from slot in the forward sustainer ring and deploying the recovery system. At the same instant, the ejection charge forces the aft section of the booster (containing the motor mount) backward about 1 1/2". This disconnects the mounting screw from slot in the aft booster standoff. When the aft coupler assembly is fully extended, a 1/4" 'blowhole' drilled in the coupler tube is exposed, which vents ejection gases and sends them jetting toward the main airframe. This, combined with the ejection of the nose section, separates the booster from the sustainer quite effectively.
Shown is the dry-fit of the model prior to epoxy. The only external components that are missing are the Booster Exhaust Nozzle shrouds, not attached because the centering rings are also not in place.
BOOSTER EXHAUST NOZZLE SHROUDS
The asymmetrical vectored nozzle shroud is one of the design features that I think makes this rocket completely cool, being a perfect compliment to the asymmetrical nose cones. I formed them out of poster board and reinforced them with 2 layers of 5.8 oz. Fiberglas. The photocopy of the template for the nozzle shroud is shown below.
Here is a photo of all four shrouds next to the plug I made for the nozzle mold along with a ruler for a sense of scale. (That makes my brother Rick happy.) One of the reasons I like this bird so much: I find a sense of symmetry in the way all the asymmetrical pieces fit together.
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