Test 4

More KNER grains. Since we had 8 plausible grains from test 3 and want to burn 5 at a time, we decided to cast another 4 so we'd have enough for two motors plus a couple single-grain open air burn tests.

Formula is a simple mix of 65% KNO3 and 35% Erythritol. Both used in granular form directly from stock. A 275 gram batch for 4 2.25" 38mm grains.

Used our new casting bases, now with the mandrel holes drilled all the way through.

Process

Same as Test 3B.

Results

• Test 4, Grain 1, 61.50g net
• Test 4, Grain 2, 62.38g net
• Test 4, Grain 3, 60.18g net
• Test 4, Grain 4, excessive visible inclusions, set aside

Observations

Not surprisingly, results were essentially identical to test 3B.

Seems pretty clear that the post-casting process of having to cut off the "skin" at the top of the grain and impart a concave shape is losing .. means we'll never get uniform grain masses. REally need to figure out how to do this better.

The last grain was "poured" by spooning in material that seemed to be clumping a bit, and we probably didn't tap it down enough.