Scratch Margin of Error Original Design / Scratch Built

Scratch - Margin of Error {Scratch}

Contributed by Dick Stafford

Manufacturer: Scratch
(by Dick Stafford - 6/22/05)

Background
I really love the 5" Quaker Oats bins (and I like the contents too - tastes good, helps your cholesterol, and even is relatively low carb). My previous rocket was made out of three bins (four if you count the one I cut up for couplers) and used a clear plastic Easter egg for the nose cone. I made the fins out of 1 1/8" (or thereabouts) styrofoam. Odd I know, but that's why they call them odd-rocs. It flew fine, but I wasn't that happy with the fins, and was thinking about adding a bunch of 24mm mounts to eat some of the $3.50/pk D12-0s I have been buying. So the solution was simple - rip off the lower bin and fins, clean up the rings and coupler, and rebuild.

The Re-build
The lower coupler was nice and long and included a lower 3/32" ply centering ring. So, I sliped a new bin on part way, leaving enough spacing at the bottom for a bunch of 24mm mounts. I decided on eight mounts with gaps to clear the 29mm motor retainers. I plugged the gap between the tube, slotted it for three fins, and cut some nice big fins from light, cheap Luan plywood. I made the 24mm motor unit removable, which should help in prepping the motors with quickmatch. Here are some pics:

Flight Report
I flew The Margin of Error on 11/14/2004 at MDRA's ESL-78. It flew on a G80-7 and eight D12-Ps lit using quickmatch. Well, actually only three of the D12s lit. The boost was slow and several seconds late due to the reduced thrust. Nevertheless, it was a good flight. Upon inspection, the quickmatch was pulled out of the unlit motors, but had burned at the pad.

The second flight was on 12/12/2004 at ESL-79 with a G79-6 and eight D12-Ps. I took more care in taping the fuses to the D12s and positioned them using a dowel inserted into the main motor's core. The dowel was of course removed before flight. This time, all eight motors lit. Ejection was just past apogee and recovery was A-OK.

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