Saturday, January 19, 2013

Plaster Blaster 2012 launch report

PB2012 was a great launch for me featuring two days of amazing weather, no camping required as I've discovered El Centro hotels,  and I was very pleased with the fourth flight of my scratch-built Em-Sem-Fity minimum diameter 98mm rocket.
     Frank Hermes, Mark Clauson, and I entered this year's fourth and likely final M-Moonburner drag race.  The new BLM requirement that drag race flyers must ensure a recovery radius of 25% of the expected altitude from the nearest public features like roads and high-power wires was kind of a bummer.  This pushed our launch pads to the north edge of our 'bowl' and, earlier, we had set them up in patches of dirt distant from flammable brush.  After we'd prepped it was kind of Mark and Craig Clauson to drive all of us out to those launch pads where we set up quite quickly.
     I wasn't able to take any liftoff photos but can at least move the onboard video to this post (same as you might have seen earlier but why not watch it again? :)

     Frank really wanted to win again this year and I was with him the night before when he purchased plastic wrap and cellophane tape to seal up his 10g thermite bundle for ignition.  Jack Garibaldi offered the use of his super high current launcher and it did its job well. Frank's M750 of course pressured up instantly, followed by Mark's trusty M650 setup, and then my lagging ass standard igniter pressured up the M750 for third place.  All three rockets flew somewhat neatly apart from each other atop those fun long-burn M motors.  Note to self: I really want to start using more thermite in 2013.
     All three of used Beeline GPS units for tracking this time. Mark was having issues with his proprietary GPS setup so Frank loaned a spare Beeline to him.  I was using my brand new transmitter of the latest design and I was confident that it should work.  As always I threw in a Comm-Spec tracker as a reliable backup.  Strangely we all had intermittent issues with maintaining satellite lock on the ground. Likely causes might have included general satellite interference or possibly military jamming although that remains speculation on our part.
     After liftoff none of us received any GPS updates but my Comm-Spec receiver continuously produced a healthy blip.  Its signal conveniently increases in strength/volume at apogee because the transmitter moves outside the carbon fiber body tube.  So, even though I can no longer see the rocket, I have an audible indication of apogee separation.  Interestingly, and highly abnormally, my ~20,000' flight landed inside the bowl!!  I was really psyched on this and we could see the main pop at 800' as expected.  My elation quickly subsided, however, as my buddies Frank and Mark still lacked any trackable signal as I was gathering up my bundle.  We searched for some time but later learned that Frank's rocket had come in ballistic leaving little of salvageable value.  Mark was never able to find his rocket and it remains missing to this day.  Sorry fellas but it's happened to all of us.  :(
     Back to my new Beeline GPS... the downloaded .kml file produced a beautiful, firework-like burst of points all very near the ground:

WTF??  While no altitude data point in the file gets anywhere near 20k I can say that none of data rows seems askew as with my older unit (no negative latitudes for instance).  From this January's launch I'll foreshadow that the GPS unit is ignoring the 'convert meters to feet' flag in the programming software so the peak value in this data set would seem to be 178m or 583'.  I think this looks close to what I'm seeing in the plot above.  I'll attribute this data failure to GPS satellite or scrambling issues as the unit now appears to be working correctly so... YAY!!  Finally.
     As for altimeter data the Raven2 reports 19,465' AGL and the ARTS2 looks good at 19,561AGL (0.4% delta).  It appears that the ARTS2 motor performance data is whacked at 6964M1004 with a 6.98 second burn time.  From the onboard video the burn time is roughly 14.3 seconds so let's assume the ARTS2's motor performance estimate is null and void.  Here's the data for the numerically retentive:

Raven2: Graph, Tabular
ARTS2: Graph, Tabular, Motor Performance (WRONG), Coefficient of Drag (questionable)

Frank was understandably bummed at his loss and was talking of retiring from rocketry before leaving the launch.  Since then he says he's exited his slump and wants to build a nifty clustered/staged rocket using his Tilt-O-Meter2 at some point soon.  I'm glad he's back on the horse and hope that Mark's recovering from his loss as well.  I'm not sure what we'll do at this year's Plaster Blaster but I'd like to avoid the BLM constraint on launch distance so we'll see.
     We flew a mini drag race on Sunday limited to G motors.  I chose the CTI 110G250 and it was sorta fast.  Victory at last!!

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