Sunday, January 30, 2011


Today I finished primary assembly of the Extreme DarkStar (right) and there's the final Nike Smoke my parents bought for me (left). [Update: While I was authoring this entry I figured out they'd shipped the wrong DarkStar fins to me. Awesome now that's it's friggin' built! The Nike Smoke is fine, however. Details below...]
I still need to foam the fin slots, fillet the fins, drill vent holes and static port, attach the rail guides, and layout the electronics board but it'll fly next weekend on a CTI Pro75 6162M1675 Pink. Based on KO's previous flights this rocket seems to get about 3 feet per Newton-second of total impulse. As such I would estimate about 17,000-18,000' from that motor. I'll also fly it dual deploy but plan to run both a Beeline GPS transmitter and my workhorse tracker beacon to assure recovery. Here are some build details from previous weeks:
On the above motor assembly I elected to use the SlimLine 75mm motor mount so no screws are required (unlike the AeroPac which is a very tight fit). I also left off the Kevlar strap as I prefer to link the recovery system to a drop-forged screw eye in the motor's forward closure. That longitudinal masking tape serves as a shim for the centering rings as the tube is tapered and they would have been loose during the cure otherwise.
For some reason Wildman provided WAY too much tab depth on those fins but my new carbide-coated bandsaw blade cut through the 3/8" high stack like butta. That blade was spendy at over $100 but there really is no other way to cut fiberglass on a bandsaw with any reasonable blade life.
I went retro and simply taped each fin pair on with manual alignment. This was a bit difficult because the slots were about 50% too wide for those fins. I chose to datum to the left side of each slot and they all look perfectly aligned to my eye. I'm now wondering if Wildman had intended to ship 3/16" thick fins with this kit? Hmmmm. Low and behold they WERE supposed to ship 3/16" fins as indicated in the kit specs. That's strange because the fin tabs matched the slot length correctly so I assumed they'd just messed up on the fin template. Maybe mine won't fly on any 75mm motor made then... Dammit.
Above is another view of the simple yet effective fin attachment.
Above is the electronics bay. Today I JB Welded those aluminum tubes to the sled so, apart layout out the board positions and switches it's all set to go. Wow I'm really bummed about that fin thing now. This was too much money and work to be uncertain of fin strength at this point.

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