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I had a BT-70 nosecone from the BMS
sample pack, and some BT-70 tubes, so I cooked up this bad boy in Rocksim.
It's called the Apogee Dx in honor of the Astron Apogee. (It's not
a kit from Apogee Components.) It made its first flight at NARAM 44 (2002) in McGregor, Texas.
Two valuable lessons were learned that day. It crept off the pad
on a D12-0 booster. Rockets this heavy should use a cluster or a
composite motor in the booster section so that they leave the rod with
a little more speed.
The upper stage E motor's nozzle was closely inspected for excess clay,
but failed to light anyway. This was my first failure at gap
staging (and maybe my only one). Always clean out the nozzle (with a stick, a knife, a drill
bit, whatever) no matter how clean it looks. |
This beautiful rocket lawn darted big time.
Ouch. The airframe was totalled - there was no splicing it back
together.
The booster was OK. It had a normal wear-and-tear nick in one
fin which has been repaired (and painted red).
The nosecone was beat up pretty bad, but I sawed it off flat and then
glued some balsa blocks on, cut it to a rough outline and sanded it to shape.
It turned out pretty nice.
The sustainer fins, rings, and motor tube were all recycled into the
replacement.
At right is the re-built rocket before paint.
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Here's a good look at the repaired rocket on a single stage flight.
I prefer flying it in 2-stage configuration, as designed. Since
its only 2-stage flight showed it needed more booster, I decided to
build a new one which included a cluster of outboards. I had
success doing that with the Midget70, so I knew it was a good solution.
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The new booster is fairly straightforward. Three 18mm outboards surround a 24mm center motor.
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The design includes a somewhat inelegant step between the BT-70 airframe diameter forward and the BT-50 aft.
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The coupler runs the full length of the upper section (2.5").
A 1.5" length of BT-70 goes over that leaving 1" of coupler
exposed. The center motor tube extends about 1" into the coupler
where it is centered by two rings - one flush with the aft end of the
coupler, one 1" forward of that.
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Three vent holes in the
BT-50 motor tube duct the burn- through pressure into the annular space
around the motor tube. In turn, the gasses are vented aft out the
three holes shown two pictures up.
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Here's a closeup of one of the aft vent holes.
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Some Fill 'n Finish was applied to the forward ends of the outboard tubes to fair them into the BT-70.
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Two loops of piano wire allow easy attachment of a burn string to make sure the center motor has been ignited.
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At left is the aft end of the sustainer. The aft centering ring is well forward to allow for long staging couplers.
The foil lined motor tube is from Totally Tubular.
A motor hook was retrofitted to the motor tube.
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Here's a look at the full stack. Given all it has been through, it still looks pretty good.
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Here's a blurry liftoff
shot. All four booster motors lit, and in turn, the sustainer
did, too. It was a great flight.
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12-26-2008
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