Thursday, July 17, 2014

Tweaking the Mark 1

The more I thought about the Mark 1's design, the less happy I was about the fins. I like my rockets to be stable without needing weight up near the nose, and those 3 small fins kept coming to mind, kinda like that "Let it go" tune from Disney's Frozen (Disney is truly the evil Empire - stay away from their movies or you will have those medleys dancing though your head for days, morning until night). Even though OpenRocket said the rocket was stable - with the egg and altimeter - I kept having bad feelings about the margin. So I finally broke down and tweaked the design a bit by adding a fourth fin. This increased the stability to 2 calibers fully loaded, which brought some comfort to my tortured mind; I only wish getting that stupid song out of my brain was as easy.

While I was tweaking, I replaced the thick balsa coupler with a thin plywood bulkhead/cardboard tube coupler combo, thereby shedding some weight. The improved Mark 1 design shows 80 feet play room with just 2 D12 motors. If I watch the weight, I may be able to pull this off with just those motors rather than going for broke with the full 2xD12, 2xA10 cluster. That's good, because igniting 2 motors is easier than lighting 4. The big unknown here is how much weight the primer/paint will add.

The tweaked Mark 1 (click to enlarge). I is much happier!
I have started construction of both the Mark 1 and 2. Tubes and fins have been cut, motor mounts and shock cords installed. Tonight I shaped the Mark 1 fins - you can see them in the pic below along with the other parts (the Mark 2 fins are lying off to the left). I hope to have the assemblies completed and in finishing by the end of the weekend.

Mark 1 parts.
Off to watch "Catching Fire" now - maybe a little gratuitous violence can drive Elsa from my mind.

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