Building the Delta 7 Mercury-Redstone 8 (part 2)

Next, the fins. Here’s a Rocksim file for an Estes Mercury-Redstone model rocket. If the dimensions therein are correct, it would appear the fins on that model are about 15% wider than scale. My hope was the CP estimated by Rocksim and OpenRocket, scaled to the body diameter, would be roughly correct if I used similarly widened fins. So I pulled the model PDF into GIMP and scaled it horizontally, but not vertically, by 115%, and printed the result to get the fins I used.

(By the way, here’s the CP and CG for the real thing as a function of time during flight. Notice what happens at about 88 seconds. Quoting the accompanying document, “The Mercury-Redstone was aerodynamically less stable than the standard Redstone. Because of the unique payload characteristics and … the elongated tanks, the Mercury-Redstone was expected to become unstable in the supersonic region approximately 88 seconds after lift-off. … To compensate for this instability to some degree, 687 pounds of ballast were added forward of the instrument compartment.” Okay then.)

I cut out the fins, folded them in half, and then glued one half to a piece of cardboard from a Pop Tarts box. Once that set I cut the cardboard to the same shape and glued down the other half to the opposite side.

Clearly I couldn’t use the whole fin shape: the part that would end up aft of the body tube on the inside would interfere with the motor, so needed to be cut off. Not yet, though. I figured I’d use these tabs to help with vertical alignment of the fins when gluing them on.

Then I cut them off. Launch lug went on too.


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