Sport Rocketry

tion that fits into a 1.5" diameter phenolic airframe tube. Four more pounds of lead shot mixed into an epoxy slurry serve as the nosecone's conical transition section. In addition to epoxy at the lead-phenolic surface, the lead nose tip was cast with an embedded steel eyebolt that provided a secondary attachment point, via a nylon strap, down to plywood bulkheads at the base of the nose section. Like the transitions, the conical base flare is made of expanding polyurethane foam, and is further supported by a set of four triangular G10 fiberglass fins. Carbon fiber and fiberglass sleeves run the entire length of the rocket (excluding an upper portion of the nosecone), including air- frame sections, transitions, and the base flare. Three sections of cable guide that run along the missile body are modeled with thin-walled brass tubing. The upper two are sealed top and bottom with epoxy putty, but the lower cable guide is left open and runs all the way through the base flare. This was done to allow for using a launch rod in the event that the tube-launched ap- proach did not prove feasible. 40 JANUARY/FEBRUARY 2020 SPORT ROCKETRY Figure 5. Minuteman launch prep. Photo credit: David Wilkins. Launch System Ideally, the model Minuteman II would fly out of a miniature silo buried in the launch field. Despite the obvious appeal of that approach, it seemed a bridge too far. Images of early Minuteman test launches at Cape Canaveral demonstrate the next best thing, namely, an above-ground silo tube affixed to a launch tower. My surro- gate launch tower was a 6'3" tall stack of milk crates that were bolted together and used to support a 12" diameter concrete form tube. A two-piece foam sabot cen- ters the rocket in the tube during launch, and then breaks away after the rocket makes its exit. The inter- nal surface of the sabot is shaped to fit over and be lifted by the base flare. It was con- structed by wrap- ping the com- pleted rocket in greased plastic, placing it inside a short section of launch tube, and then pouring ex- panding foam in around it. Once the foam had set, the sabot was cut lengthwise into two clamshell pieces, removed, and then shaped, sanded, and paint- ed. Launch setup begins by anchor- ing the tower with four steel cable guides that extend outward and connect to tent stakes in the ground. The rocket rests on a milk-crate pedestal that protrudes out from the base of the tower, beneath which is an angled steel blast deflector. Once the rocket is in place, the launch tube is lowered over it while the sabot is held in place about the base of the rocket. The launch tube is then fastened via zip ties to the tower. Cutouts in the milk crate on which the rocket rests provide access for motor preparation. Fig- ure 5 shows the launch preparations. Minuteman II First Flight An AeroTech K550W motor was se- lected in part for the its realistic-looking and plentiful white smoke. The predicted apogee was about 3,000 feet, which was about as high as I cared to go with this single deployment experimental rocket. A standard 10-second ejection delay was just right for driving the piston ejection system at the optimal time. Following set- up, the requisite period of anxious waiting ensued, during which there was time to men- tally run through, count, and recount all the things that could go cata- strophically wrong, including standard failure modes as well as those more specific to this par- ticular rocket. The sabot could bind in the tube and de- stroy the launch apparatus. Or, de- layed, asymmetric, or otherwise un- clean sabot separa- tion could perturb the early flight, sending the rocket off on a non-vertical trajectory. Or, the flight path might decay into the cart- wheels that would prove the stability calculations inad- equate. Fortunate- ly, none of those things happened. The Launch Con- trol Officer finally announced "OK, going to pad 8, what do we have? We have...that tube-launched thing..." and a spectacular launch followed a few moments later. The Minuteman II flew straight, loud, and striking. The flight had just one problem. Short- ly after motor burnout, which occurred at about 1,100 feet, the nosecone separated prematurely from the body. The body con- tinued up to a height of about 2,000 feet (flying remarkably straight, given the lack HHHHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHHHHH H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H ESTES, QUEST, CUSTOM • Rockets • Engines • Bulk Packs • Accessories • Parts PERFERRED CUSTOMER SPECIAL DISCOUNTS NAR & Tripli Members Only Telephone or Fax Orders (include your member number) Send for your free catalog or visit us at: Belleville Wholesale Hobby Inc. 1944 Llewellyn Road Belleville, IL 62223-7904 www.bellevillehobby.com www.estesrocketswholesale.com www.questrocketswholesale.com Call Toll Free: 1-866-250-5949 or 1-618-398-3972

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