Sunday, February 5, 2012

Formula 75 rocket kit has arrived

This kit will be my level 2 certification rocket. The Formula 75 is about 75mm x 48 inches with a 38mm motor mount. It is all fiberglass, including the highly impressive nosecone (more on that in a moment.) The kit arrived in a bag with the basic parts only: a nosecone with shoulder and bulkhead plate, pre-slotted airframe, motor mount tube, and two centering rings. No parachute is great, I already have too many. But it also lacks any Kevlar cord, motor retainer, rail guides, fin bevels, or most importantly any nosecone hardware such as an eye bolt. This is the price you pay to get a large fiberglass kit so cheaply, $95 shipped in this case.

I plan to get the additional hardware at giant leap, at a not insignificant cost (about $35) including 15 feet of 1/4th inch kevlar and a slimline. Even so, it would have cost more to go with the other kit I have been considering, a 4 inch dynawind kit from Giant Leap. And this kit is solid fiberglass, and comes with pigmented fiberglass. I have never loved painting rockets, largely because I live in an apartment and there isn't any great space for painting around here. With that convenience does come one condition: the fillets must be clean from the start with no hope for sanding as that may alter the smooth appearance of the airframe. Some amount of conditioning can be achieved with car wax and buffing with a rag.

The nosecone is particularly impressive. It is quite long, and made out of very sturdy fiberglass. The tip appears to be graphite composite. Aluminum tipped nosecones are also available, at a greater cost. The lack of eye bolt hardware in this kit is the only thing that surprised me. I do not think it would add much cost, and is not likely to be customized among most buyers. In any event, a trip to the hardware store should get 'er done well enough. I will go with a forged eye this time, despite never seeing the normal eye bolts fail. A recent thread over at the Rocketry Forum (not the first) has made me paranoid.

This will be my level 2 kit, but will only fly on small 38mm J motors from CTI such as the baby 648ns J285 with an 8 second delay. This motor is so close to an I, I think there is a very good chance of recovery on a day with low wind. That is important enough that I may put off a certification flight depending on the conditions of the launch day. Expected altitude is about 1,800 feet on a J, based on preliminary simulations. That is high, but not excessive for a rocket of this size. (The size affords greater visibility in the air and after recovery.) I specifically decided on a dark airframe color, which I find is better for tracking in the air. On the ground the "cherry" color - really some shade of burgundy, will not do so well. That is where the parachute and possibly a large streamer come in.

I want to built it strong as always, with an eye towards extreme, even excessive strength in some parts. The added weight will be welcome to keep apogee reasonable.

She wont fly dual-deploy, but will recover on a small skyangle that is normally reserved for the much lighter Loc Graduator and H45 kits that are only about half the weight. Extra weight will come with the use of epoxy internally, as well as foam in the fin can and perhaps the nosecone as well. I doubt that nosecone foam will add any significant strength, but I like it simply as additional weight and a way to remove the worry of air-pressure in this very large nosecone. In the fin can, I plan to drill a few holes in each fin root, and arrange to have the foam extrude through these if possible. A strong nosecone bolt, as well as a nice potting of epoxy in the nosecone shoulder and over the last centering ring should round out the rocket at 4 or even 5 lbs total. There will be further updates once construction starts. Stay tuned!

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