Wednesday, January 12, 2011

Review: Margin of Error

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 Original Build
I didn't write this up for EMRR because, although it flew fine, the thick foam fins were too goofy for even ME! Now, I have forgotten much of the internal construction details.


I do remember the cone construction.  I used the top couple of inches of a Quaker Oats bin and another piece for the shoulder.  The latter piece was sectioned and re-joined.  The top section included the company logo, which is not only all over the body but is also visible through the clear Easter Egg tip.  The base of the cone is the bottom of an LOC 5.5" cone.  I lopped this off when building my Upscale Big Brute.  This was all glued together with polyurethane glue (except the cardboard-cardboard joints, which were attached with wood glue).


The Re-build
After removing the original fin section, the motor mount and lower coupler was intact.  The mount was nice and long and included a lower 3/32" ply centering ring. So, I slipped 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 new and old tubes, slotted the lower tube 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.