Sunday, May 4, 2008

Great success!! I liiiiiiike!

I've had a bad streak of luck in the last few months:
  • In February I made a mistake setting the timer on a two-stage project (how sweet is the dude in that picture!) and crashed my AltACC 2A altimeter.  That little device served me perfectly for five years and now it's gone.  To make things worse they're now out of production!  Grrrr.  I did some homework on a replacement and decided to buy the Ozark Aerospace ARTS2 altimeter.  It's bigger than the AltACC and lacks a convenient built-in 9V battery mount but it's FAR more capable.
  • At the Lucerne launch last month I launched a new, sturdy little rocket on the new Aerotech Mojave Green 350I245, it flew and landed perfectly, then was dragged along the lake bed by the parachute for several minutes and was really beaten up.  It's functionally intact and I was able to repaint it but... stupid wind.
  • At that same launch I flew my Public Missiles Sudden Rush (those dudes rock too!) on the new ARTS2 altimeter but I was rushing to make the last flight of the day.  As a result the up part of the flight was beautiful but we lost site of it and nobody saw it after that.  I drove around the lake bed as best I could but, shocker, the IS300 doesn't deal with ruts very well.  I never found the rocket [crash site] and that was a $550 mistake.  Learning's expensive in this hobby.
Well that streak is done.  Ever tenacious, and convinced that I'd made some sort of mistake on that last failure, I bought yet another ARTS2.  The Plaster City launch was yesterday, 5/3/08, and I had three totally successful flights of three attempts.  Yay! One of those flights used this second ARTS2 in my V2 scale missile.  After reading the altimeter manual several times I figured out my mistake on that last failed attempt... there's a jumper that needs to be enabled when you're using only one 9V battery.  The default configuration disables this jumper as they recommend you use one battery to run the altimeter and another to fire the electric match(es)/ejection charge(s).  I never noticed this, used a single battery, so power was never sent to either of the two e-matches; hence the pile of expensive rubble in the Mojave Desert.
I'm very pleased that I figured this out before my level 3 attempt!  Despite the ambiguous and somewhat confusing documentation/ configuration the ARTS2 is impressive.  It has a feature I just discovered that allows one to analyze the performance of the motor(s) flown.  All you need to enter is the liftoff weight (rocket + motor), the propellant weight, temperature and pressure at the launch site and the program twirls those up with the flight data to give a damned accurate estimate of total impulse and average thrust.  In this case I flew the new Aerotech 1762K805 Mojave Green motor and the program calculated it to be a K820.  Now that's close!

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