NEFAR Launch
5/13/06
With a new 5-grain 54mm motor casing from Loki, a new ARTS altimeter from Ozark,
and a whole bunch of straw candy from Publix,
the Sugar Rush is aiming for the mile marker in the sky!
But the REAL experiment:  I am placing a FULL soft drink can under the nozzle.  
Sometimes you gotta chuck the rules.

The Space Shuttle uses liquid for damping sound and making steam, so why not me!

The motor is loaded with 4 propellant grains of Pixy Stix propellant, total propellant mass is 762 grams.

But there is a fifth grain, an un-cored end-burner which is intended primarily to provide smoke after thrust ends.  It is also KN/sucrose with a little bit of Ti and red iron oxide to help it keep burning when the propellant grains are spent.  I assume that the first web-thickness of this grain will burn along with the propellant, adding 39 grams to the total propellant mass.

Ignitor is bridge wire wrapped with fuse paper, with a touch of black powder and Ti inside.  BP to make sure it fires, Ti for more sparkly heat.

Launch weightt:  9.75 lbs
Anticipated thrust:  960Ns
Burntime:  1.4 seconds
Altitude at apogee:  Different sims give different numbers, the lowest being 4800 feet, the highest 6000.  I'm guessing it will be somewhere in between.  
The Launch

Click Here for a movie of the launch and subsequent adventure
(13 meg .wmv file, 67 seconds of video)

Click Here for a short movie of the launch to apogee
(5 meg .wmv file, 26 seconds of video)

Launch was good.  A brief smoke (grains were damp) and off it went.  Smoke all the way to apogee and then some.  And then some more.  And more.  And.... where is the drogue?  Come on Drogue!    

No drogue.  
No sight of drogue.  No evidence of main.  Nobody I asked had seen anything pop.  Several fellow rocketeers offered consolation and/or false hope.  
I trudged off toward the crime scene, wondering if I should take yellow tape, shovel and bucket.  No, I'll go find it first, then come back for the heavy equipment.  Glad I had aimed it well away from humanity, sad that I might never find out what happened.  Without the 'chutes, it would have come down the way it went up, and hit the ground at 600+ feet per second.  All I could hope to find would be a spattering of pink around the smoking hole.  
So I trudged across the fields for awhile, but came back to the launch site to dump my big camera and tripod.  Also to quiz the natives on where they thought it might have landed.  Bernie Lalime, our Giant Leap distributor loaned me his binoculars, which helped the search immeasurably.  

Scanning the ground on the fourth field over, I spotted something suspiciously pink.  It was far pinker than anything a healthy cow might produce, and this one did not seem to be in great distress.  I walked over to see the fragments, covering one eye so the shock would not overwhelm me...
And there it was, whole and mostly well.  Pig-headed optimisim is again rewarded.  The main parachute was shredded and the nose cone cracked, but the altimeter was still beeping:  5526 feet.  It made the mile mark!

And the cows left me a little memento, a token of their esteem.  
The ARTS altimeter reported three different altitudes at apogee.  The beeping upon landing indicated 5526 feet.  The downloaded graph had two more, one from the barometric altimeter which read 5326 feet, another from interpretation of the accelerometer data, which read 5656 feet.  Good news is that all readings were over a mile, which was my target goal.  

Click Here for a larger version of the graph (126k)

The altimeter offered some other interesting bits:

Max G:  26.341
Max Acceleration:  847.38 ft/s/s
Max velocity:  684.33 ft/sec
Drogue Deployment:  19.990 seconds
Descent Rate under Drogue:  259 ft/s
Main Deployment:  37.140 seconds
Descent Rate under Main:  219 Ft/second.
Ok, so another piece of the puzzle.  Altimeter indicates drogue deployment at 19.990 seconds into the flight.  Looking closely at the video, that is the point where I lost sight of the rocket and began to zoom out.  So it is conceivable that the drogue might have deployed and not been seen.  But then there is no interruption on the acceleration curve during descent, so I must assume that the drogue did not deploy. The altitude curve is as smooth as honey down to about 300 feet, where there is an abrupt change.  That must be where the main parachute deployed.  Accelerometer indicates it was going 635 fps at that point, explaining the shredded parachute.   I am astonished that the airframe is not zippered, but it shows no such damage.  

The drogue 'chute was out when I recovered the rocket, so I'm guessing it was the shock of the main deployment that jerked it out.  

So Sherlock.  Why did this happen?  Right now e-match failure appears the strongest candidate.  Both of the ignitor heads were stripped off, so I have little evidence to go on.  But a guess would be that under an acceleration of 26gs, the drogue and its nylon cable mashed the e-match beyond its design limits.  Since these are made with Christmas-tree bulbs, the design would not have taken into account high pressure.  I will have to consider that on the next launch, and protect the e-match from this pressure.  Some degree of redundancy might be a good idea too, so I'll work toward that as well.  I wonder if this altimeter will fire TWO e-matches?  Might have to ground-test that idea a few times.

The only thing left unexplained by the e-match hypothesis is why the main fired just over 300 feet and not at 800?  Perhaps coming in hot confused the altimeter a bit, or maybe the ARTS has a "save the bacon" routine programmed into its little PIC chip.   Or perhaps it took a significant fraction of a second for the main to deploy, and at 635 fps, a rocket can cover some ground... air?  

Mission accomplished, in spite of my failure to find the blasted soft drink can.  By the time I got back to the launch site, cleanup was about done.  Darn.

But the Sugar Rush went a mile on Pixy Stix, I got data, and the rocket can fly again with a cheap and simple repair.   And I think I've figured out the problems, thus can implement solutions.

Life is good, and will remain so until further notice.

Jimmy Yawn
jyawn@sfcc.net
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