Last fall, Chris LaPanse gave me his last G25 in the hope of helping to set a G world record before the motor contest cert expired. Well, I was too busy crashing and losing F10 rockets to make a rocket that would do Chris's G25 justice before the end of the year. But I finally had the right rocket and the right conditions on th 20th of July, Sunday morning. I wanted to fly something while the wind was low, before the high power waiver opened, and I had my Barack-it 29mm F record rocket that I had flown on G80s twice the day before. When I prepped the rocket, I noticed that only 1 of two screws went in cleanly to hold on the nosecone (the rocket uses the motor as a coupler, so the nosecone is supposed to stay put.) The nosecone seemed snug, so I decided to fly it with 1 screw. Looking back on it, I almost certainly had the nosecone rotated 180 degrees from where it should be. That also meant that the vent hole for the altimeter was totally covered and av-bay was sealed off except for a little leakage.

The boost looked perfect in almost dead calm conditions, with the rocket rising on a solid column of white smoke that looked almost perfectly vertical from the ground up to burnout at over 4000 feet. I got a good radio tracking signal at apogee, as designed, and it was in the air over 8 minutes. Then the tracking signal went dark, and I never picked it up again. Dave Rikkers found it "2 miles to the Northeast" and I don't know how I missed it. I swept the area with my receiver from the little chalk hummock on top of the hill about 2 miles to the NNE about 40-70 minutes after the launch. My recorded data shows that the tracker was on while the rocket was on the ground for the whole recorded duration, about 1/2 hour after launch. When I got the rocket back, I checked the battery voltages for the transmitter and Parrot, and they were both high enough that the transmitter and Parrot were turned off at some point before they ran out of juice. Maybe when Dave picked it up?

Anyway, here's some data from the flight:

The flight was quite high, at about 9350 feet. This is right about the Rocksim prediction for this motor. Staying subsonic really helps!

The anomaly that starts just after 15 seconds is odd. So is the fact that after the deployment the altitude reads way high, over 25,000 feet! Here is the longer-duration plot. Touchdown was at about 100 feet elevation above the pad, 530 seconds after liftoff:

I think that both pressure transients were caused by the av-bay moving relative to the nosecone. Here's a picture of the av-bay and the nosecone before it (unofficially) set the F record:

The red part is a 24mm cardboard coupler from Apogee. It slides into a 24mm airframe tube that's glued into the nosecone, so it acts like a piston if it moves.

Finally, one more mystery was why the fin can wasn't attached when the rocket was found. The short answer is that the charge I used was too big and it ripped the shock cord off of the motor where I had glued it on with 5 minute epoxy the night before. The data shows the forces involved:

250 Gs on a nosecone that's 66 grams is about 36 lbs. It ripped the nosecone off by pulling the single screw head through the hole in the CF-covered airframe tube. Where the acceleration is -100 Gs is where the shock cord went tight, and so the cord came off of the motor at about 16 lbs. I guess I had bad surface prep on that epoxy job.

Some more data for fun:

Lessons learned:

More G25s, please!
Don't make the deployment charge "just a little bigger, just to be sure" than the size used in ground tests.
If the rocket isn't going together correctly, stop and take it apart to find out why
If it was designed to be held together with 2 screws, one isn't good enough.
Try to figure out the tracking signal disappearance before the next flight