Thursday, November 24, 2011

PB2k11: Third annual M Moonburner drag race details

After posting two foreshadowing images below I'm finally getting around to documenting our nifty drag race three weeks ago.  I had trouble editing the Flip Slide video in Final Cut Pro 7.03 for some reason so I threw this together in Final Cut Pro X:

[I'm not really a huge fan of that software yet as it seems to be half way between iMovie and v7.03 in capability.]  Three of us flew the CTI 7521M840 and Mark Clauson chose the AT M650.  A HUGE thanks to Joyce Chan who skillfully photographed our drag race and was kind enough to share her source files with me.  Please head over to her site for larger versions or to buy prints of these or any of her other awesome shots:
L-to-R: Art/Tom Just, Frank Hermes, yours truly, Mark Clauson

Mark smoked us all with his minimum diameter L3 vessel on the M650!

I was second off the pad, then Art, then Frank.  I honestly thought we M840 flyers would have had an ignition advantage because there's a 29mm propellant grain with an embedded pyrodex pellet at the top of the core.  That plus the insane 459 pounds of initial thrust has me scratching my head.  Perhaps Mark was using a special igniter but, whatever the reason, he won the liftoff cleanly.
     I again used my Beeline GPS module to track the rocket as it was well out of site.  I threw in the beacon as backup and thought I'd need if as my Yaesu radio didn't receive any distance data until about 20 seconds before the rocket landed.  Not sure what's up with that but, in the end, the Beeline did the job and the Google Earth data was robust as shown in the post below.

As a fun aside we all kicked in $20 and employed a scoring equation including liftoff rank, peak altitude, and distance from the pad (highest score takes all):

Mark won with the highest overall score so congrats again!  While Frank didn't win this year he was the only participant to incur zero damage after a clean recovery.  Mark hit a power line on the way down and burned a 1/2" hole through the airframe and aft motor closure.  Art's 1/4" Kevlar shock cord snapped but he got all the parts back.  Mine suffered a hard impact that ruined my motor retainer ring and it took hours to free my motor casing.  I was able to salvage it however and will replace the ring with 10-32 screws through the retainer side wall.  Here my altimeter data if you're interested:

ARTS2 - tabular data
ARTS2 - graphical data
ARTS2 - motor performance estimate (7521M840->7045M989)
ARTS2 - CD plot
Raven - tabular data
Raven - graphical data

Thanks to all who participated and I look forward to another fun drag race at PB2k12.

Tuesday, November 15, 2011

I posted my Plaster Blaster 2011 shots from Sunday

And you'll find them here.  I also cleaned up my M840 drag race GPS data and plotted in Google Earth (looking east):
More info coming this week-ish so hang tight.

Sunday, November 13, 2011

Productive Sunday

I'm a week late on my Plaster Blaster 2011 entry but I'm still waiting for a few elements to come together.  I'll foreshadow a problem with an otherwise great M840 drag race flight last weekend: my Slimline motor retainer ring would not unscrew due to an impact with some harder soil.  Frank Hermes suggested that the retainer tube was probably out of round due to angled impact and I think he was right.  I started my Sunday trying to resolve that and get my motor casing out.

After 45 mins. of trying other methods I finally busted out my Dremel tool to grind a notch in the slot of the Slimline retainer ring.  I then used a chisel to wedge down into the threads and snapped the ring at that spot.  I was finally able to pop out the ring and extract my Pro75 6G casing. Although the retainer's threads are trashed I think I can drill into the sides of the retainer tube, tap them, and use tiny screws to retain future motors.  This is cool because I really didn't want to trash the booster despite a heavier-duty version being on deck:

Those who have flown moonburner reloads know that they rank among the more difficult cleanup jobs; especially when stuck in a booster and untouched for a week!  I was able to get the casing apart and the liner out without issue.  As expected some threaded parts and the casing interior were filthy despite liberal use of grease during assembly of the reload.  I emptied my tall-ish office trashcan, placed my casing into that, and poured hot, soapy water down into the casing.  I repeated the fill and then added a bit of white vinegar to the solution.  After soaking for a half-hour I flipped it over and started cleaning with a toothbrush taped to a dowel.  A few iterations later I then dried the casing and busted out the screwdriver to scrape and the brake cleaner to dissolve the crud.  This process took almost two hours in total today but my casing and parts are quite clean now.
    During the soak I started repairing other rockets.  My Madcow Squat suffered a minor zipper during the I445 drag race over a year ago. The short body tube is cardboard so I simply wrapped a swath of Gorilla Tape around the top of the tube.  It looks pretty cool and should survive another I445 flight.

    My '.38 Spatial' suffered a narrow Kevlar zipper in the payload section on its J350 flight.  I used a length of 38mm coupler, two layers of release film, a slice of 38mm body tube, and carbon-fiber-loaded-epoxy to patch that up.  I then wrapped the assembly in shrink tape and applied heat with a heat gun. This shrunk the film very tightly and I expect the gap to cure/fill quite nicely.

    On its last flight my Loc Bullet suffered a 1x2" zipper/chunk due to an excessively long J500 delay.  I used a technique similar to the above but this time I sandwiched a layer of carbon fiber fabric in the repaired area.  It's worth a try as I was about to trash this rocket and start again.

    I also scraped some unintended and ugly primer drips off of the 4' long payload section remnant of the otherwise lost Viciously Mean Machine.  It looks pretty cool now and I think I'll fly it with the Fity-Fo booster: