Saturday, April 18, 2009

Launch Report #29

I launched a few rockets today with Mandachan, but I didn't have much success. First time I've used a single-use composite motor, though.

First came the Deltie Thunder on a D15-4T reload. It took a while to ignite, but the two 1/2" wooden dowels I stuck into the ground braced it perfectly against the light wind, and the 6' of 1/4" steel rod stuck into the ground made a fine launch rod. However, even the 4-second delay, which I suspect was closer to 5 or 6 actually, was too long and it ejected about 25' up. The shock cord snapped and the nose cone came down nicely under the chute. However, the body took a (harmless) core sample and the glider snapped in half at the wing attachment point. I'll wood glue it back together and add reinforcement at the point with some thin plywood I have. The launch was pretty impressive, though. If I use it again on a reload, maybe an E11-3J, then I'll only use half the ejection charge.

Next came Mach My Day on the D21-7T. Unfortunately, It wasn't quite stable and it did spirals in the air about 75 feet up, then fell back and blew smoke. The ejection charge was stronger than even the Estes 'shotgun' charges and the streamer was torn off the shock cord intact. there's a small dent on the body tube. It's no longer useful as a Machbuster since it's not stable with a D21 inside, but I might use it for other stability testing, such as spin, longer rods, weighting, etc, or as an upper stage that uses only an A8, perhaps atop a huge booster with a D12.

Damn, burnt APCP smells bad. Even worse than burnt blackpowder.

Last came the Astron Invader on a C6-3. It did about 5 loops under power, slowly climbing to around 120 feet, then coasted up to around 300 feet before ejection. Even though the motor ejected, it never pulled out of its dive - no stab for incidence - and it came is pretty hard and fast. Amazingly, the only part of the 1/16" balsa airframe that broke was one vertical fin. a bit ow glue and it'll be good as new.

I'm up to 110 flights on 128 motors for 678 Ns total - 6% into the J range! That's 6.17 Ns (23% C) per flight and 5.3 Ns per motor - 6% into the C range!

It's a pain spending 10 minutes to hook up my unreliable ignition system and 5+ seconds to ignite composites, so I'm thinking of investing 40 bucks in a Pratt Go-Box controller and 8 bucks on a second 6V battery (one of my two is poor quality and doesn't generate much amperage - it has 2 smaller 3V cells rather than 4 1.5V cells. Cheaper but crappy.) or 30 on a 12V gel-cell or motorcycle battery.

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