12,744' FTW!

[that's "For The Win" not "F*#k The World"]

Yesterday at Lucerne Dry Lake I flew EM-SEM-FITY on a Cesaroni L610-Classic motor to 12,744' and that's a new personal record!:

Here are some flame details (hot day, distant shot means serious convective optical warping):

That motor burns for 8 seconds and the flight was very cool with two exceptions:

• I've optimized this rocket for motors of full-M weight so the CG/CP relationship yields a static stability margin of ~1.6 fully loaded. Since the L610 motor is half that weight the static margin shoots up to ~2.1 making the rocket slightly overstable. This caused mild coning on the way up and I lost some altitude as a result.
• The drogue ejection charges popped exactly at apogee but the nose cone popped off as well thus dragging out the 7' main 'chute. This was supposed to be a dual-deploy flight so popping the main at over two miles can mean a big walk. And walk I did. I could see the parachute the whole time and found it about 1 mile out across the road. Luckily a fellow flyer named Steve kindly drove out to pick me up otherwise it would have been a long walk back.

Oh and I encountered a highly improbably coincidence yesterday. It took about 2 hours to prep the flight and before I carried it out to the pad I wanted to verify that my radio tracker was working. I turned on the receiver and got two out-of-sync signals. I walked around for a bit and located a flyer named Julian whose transmitter was running on the same frequency! There are roughly 50 transmitter frequencies available so how insane is this? I pulled the battery from my transmitter, Julian successfully recovered his rocket, and kindly pulled his battery shortly thereafter so I could reassemble and resume.

Now for some data... the initial fully loaded weight was 25.3 pounds and length is 94". Here are the flight summary and graph from the ARTS2 altimeter:

And the same for the Parrot 2 altimeter:

The average of the two barometric altitudes is 12,744'. I assumed a CD of 0.45 in RockSim and this predicted an altitude of 14,120' so this represents a large error. I attribute this both to the overstable coning I mentioned above as well as a guessed CD. If I iterate on CD in RockSim to match the average altitude I get 0.57. If I then re-run the M750 simulation with this CD I get 20,147' which is well below the San Diego club's 25,000' FAA waiver. More on this in my next blog entry.