Baffle 2.0 - Testing Results
Today I was able to run 8 tests with Baffle 2.0. These tests took place in 86 degree weather (F) with 51% relative humidity. The baffle was tested in the Apprentice + Alpha III hybrid rocket utilizing an extra long MMT as seen in the previous pics. I also tested my quasi-reusable denim wadding. Here are the test results:
Test 1: Used a C5-3 engine - perfect test
Test 2: Used a C5-3 engine - perfect test
Test 3: Used a C6-5 engine - perfect test
Test 4: Used a C6-7 engine - perfect test
Test 5: Used a C6-3 engine - perfect test
Test 6: Used a C6-3 engine - perfect test
Test 7: Used a C6-3 engine - Good test; nose cone ejected, but parachute didn't fully eject. The parachute was halfway sticking out the end of the main body tube. It got warm and had zero to very very slight charring. The parachute was not damaged in any way that would inhibit its ability to operate properly. The clay cap at the top of the engine was fully gone.
Test 8: Used a C5-3 engine - perfect test
Here are the pictures:
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That is regular, untreated blue jeans denim in a 3" x 3" square. Up top/on the left is the inside of the wadding that touched the parachute and on the right is the part that was exposed to the exhaust gases coming from the baffle (in all 8 tests). I didn't do this test b/c I'm trying to save money on disposable wadding. Rather, I like the idea of nothing being ejected from my rocket during the ejection process.
Here's the top of the baffle, with the top picture showing Baffle 2.0 after the first launch, then the 4th launch, then the 8th launch (at the bottom):
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Here's the bottom of the baffle (that's closest to the ejection charge), with the top picture showing Baffle 2.0 after the first launch, then the 4th launch, then the 8th launch (at the bottom). That "blister" you see on the inside of the baffle? That's the JB Weld pulling away from the engine casing wall...interesting. I'm curious as to whether wood or white glue will avoid that problem. At the the very least, they're cheaper than JB Weld and dry much faster...
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And here's the outside othe baffle. A bit of charring on the outside edge closest to the bottom (that's closest to the ejection charge), but overall, looks good! Definitely no soft or weak spots as was the case with Baffle 1.0 after eight A8-3 tests.
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Discussion/Conclusion
Using the spent engine casing and JB Weld helped alot. Using a longer baffle helped, too. As expected, there aren't very many bright line conclusions to draw from these tests. Rather, any adjustments have resulted in a sliding scale of changes. For example, will Baffle 1.0 still work with C engines, despite being 17mm shorter and made from less robust materials? Sure, but it won't last as long as Baffle 2.0. But then again, it's a little bit lighter and easier to make. Pick your poison...
Also, I think using wood or white glue on the inside might be a better option than JB Weld. As long as it perform 90% as well as JB Weld, it's a worthy substitute as they dry much faster, are easier to work with and are less expensive.
I think Baffle 2.0 in an extended MMT (a la stuffer tube) and retainer ring is a great set up. It's clean, neat, more consistent and lasts longer. But it's heavier and requires a BT-50 or larger rocket. Based on how Baffle 2.0 looked after the 8th test, I wouldn't be surprised if it could easily last 20 launches, even when using C engines.
Addendum: I think my next removable baffle built will have some sort of "lip" at the bottom thrust ring to "mate" with the top of the engine. I'll see if this can reduce the charring on the bottom of the baffle (and the small amount of black/soot build-up on the inside of the MMT. I'm thinking this lip will be small...maybe 2-3 mm? Can't be too long to interfere with the clay cap of engines with bigger delays, like the C6-5 and C6-7. This lip can help deal with variations in model rocket engine length. Check out this picture as a demonstration:
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That's about 1mm or so of play where the baffle and rocket engine and slide forward and backward within the MMT (I added those red marks to make it easier to see). I'm guessing a combination of me not fully screwing on the retainer and some play between the engine casings caused the "ejection bleed through" between the baffle and engine which the lip should help deal with. I could also add some spacer to the inside of the retainer ring, too...