Model Forum / General / Rockets / August 2008

August 10, 2008 - DART Rocket Launch

  The whole San Diego division of the Coppock family launched 4
rockets today.  The weather at the Fiesta Island launch site used by
the DART rocketry club was initially quite good at 8:00 AM with winds
increasing to marginally high by 11:00 AM when we left.  We had four
rockets previously loaded from the misadventure of the June Plaster
City Sunday launch that wasn't.  All that was needed were igniters.

  First up was a stretch version of the 24 mm DE series.  An E15-7W
powered its maiden voyage.  After some problems installing the
igniter, (I had a bad case of swelling in my hands and legs and could
do nothing right today.) this rocket took off from a long launch rail
in the high power area and quickly weather vaned Northward.   I
clearly saw an ejection, even an orange powder cloud.  Alas, there was
no orange streamer to go with it.  "It went beyond the roadway," a
helpful voice said.  While my wife, Gloria, guarded the car, my son,
Will, and I went Northward looking for it.

  We crossed the road, and met a bunch of resting bicyclists.  None
of them reported seeing our electric yellow rocket with black nose
cone and fins.  Will and I continued to the water's edge.  Will's
sharp young eyes saw it first.  Floating in the water about 40 feet
off shore was the carcass of the rocket.  We called, "Ahoy!" to some
of the watercraft riders, who seemed not to hear us.  The wind and the
watercraft wakes finally brought the waterlogged bent yellow tube
close enough to shore so my son Will could wade in after it.

 The ejection charge pushed the engine out the stern, but not the
streamer out the bow.  The waterlogged rocket was leaking what
remained of the 1 ounce of orange powder out its stern.  Trying to
keep the orange soup from polluting the entire island, I found the
nearest waste can.  With the waste can as my operating table, I
quickly performed an amputation of the waterlogged body tube, saving
what was useful, the 7X60 inch thin mill nylon streamer, the plastic
nose cone, and the shockcord, for later transplantation.

 This is the next to the last of the 4 rockets in the DE series.  One
remaining short rocket remains to drive tests of the clamshell
recovery deployment system.  My first design did a lot of good flying
and taught me a lot, too.  It was fun to see those large streamers
coming down from thousands of feet up.   My next 24 mm design series
will use a version of the fin design and construction I employed in my
Level 1 certification rocket.  That's lighter, stronger, and faster.
I'm also looking into better engine retainer designs; tape friction
mount just doesn't work.  There is also a lot more to be done with
streamer design.  Large 10 to 1 rectangles are hard to get out of 24
mm minimum diameter body tubes.  Different streamer shapes could get
the same drag with a lot less cloth, thus solving this deployment
problem.  This old man needs to take up sewing.

  My son and I returned to the flight line.  After cleaning the
orange stain off my body, I set up the next rocket, the SkyWriter.
This is a good kit from Estes.  We made ours better by replacing the
three-fold shockcord mount with a kevlar(tm) braid epoxy(tm) glued to
the inside of the tube coupler.  At the other end of that an elastic
cord, a swivel, and nylon cross fire parachute.  We did this all a
step at a time as we learned from flying our two SkyWriter kits, but
we replaced the entire Estes recovery system.  The combination works
very well.  After the great DE rocket catastrophe, we needed something
that worked.

 . . . And work the SkyWriter did.  It went the usual 1100 feet on a
C6-5.  Gee, it's nice to see this rocket fly!  Will recovered the old
veteran, and I reverently put the old gal away in the trunk of our
car.

  At about this point, someone gave away a 13mm rocket.  I was too
full of myself to get their name and thank them.  SHAME ON ME!

  Next I lined up another Estes kit, a Hi-Flier(tm).  The Hi-
Flier(tm) kit from Estes is unstable.  The design actually has fin
area forward of the center of lateral pressure, working against the
rocket's stability.  More powerful rocket engines are heavier and move
the center of mass aft more, making the rocket even more unstable.
This is a dangerous situation, an accident waiting to happen.  I don't
know how the same company can make both this piece of CRAP and the
SkyWriter(tm).  I solved Estes' stability problem by grafting in 4
more inches of body tube up front.  I also didn't like the tiny 12 by
1 inch plastic streamer Estes provided, so I made my own nylon 3X16
inch and attached Estes' little joke on the end of that.

  It all worked quite well.  A C6-7 took it an estimated 1400 feet
high.  It came down streamers flapping without the engine.  That was
another friction mount failure.  It could be that I am using the wrong
tape in my friction fits.  Or, the ejection wadding I'm using, home
insulation that members of the DART club call "rocket snot," coalesces
and dams up during high gee powered flight.  I found a compressed wad
of the stuff in both the DE and this rocket.

  The last rocket of the day was the Apogee Aspire(tm).  This old
bird flew on a D12-7 to test teamed streamers.  It roared off one of
the front low power 1/4-inch launch rods, weather vaned into the now
considerable North wind, and headed for the sky.  It was easy to see
the 7-inch wide orange nylon streamer with the 4-inch wide purple
mylar streamer on top of that.  The combination slowed this rocket's
descent quite well.  The rocket hung vertically below the two
streamers as the wind carried it back over the launch point and into
the flight line.  When I saw it heading for a lady sitting down behind
her SUV I yelled out a warning, "HEADS UP!"  The lady sat still as it
landed in a toolbox next to her.  I excused myself, and recovered my
rocket.  There were no broken fins, unusual for a flight on my
Aspire.   I made some modifications to the Aspire design; most were
improvements.   Fins mounted exactly on the rear rocket, not spaced up
a bit was one of my innovations that didn't pay off.  Although this
made the rocket even more over stable, it exposed the fins to damage
at landing.  That's the fun of model rocket design, there are many
variables to optimize for, and there are many times many tradeoffs.

  An examination showed that the larger nylon streamer tied up itself
in its harness.  Therefore, the rocket actually landed with one-and-a-
half streamers.  To get two streamers I need to look back to the
moment the ejection charge fires.  Apparently the larger streamer
nearer to the charge is pushed first, into the smaller streamer.  It
is then that things tangled up.  To use multiple streamers I need to
roll them together, like I did with the Hi-Flier, or to find something
to separate them if I put them in the body tube independently.  In
this case, next time I'll use a small cloth patch.

  It was a great launch!  What the heck, 3 out of 4 isn't bad.  Even
a 0 out of 4 would be a great launch.  After all, rocket failures lead
to better stories than rocket successes.  I spent more 'ink' here
telling the story of the failed launch than the three successes.
There just are not too many things a man can do where that is true.

-.-. --.-  Roger