Model Forum / General / Rockets / June 2006

We had perfect rocket flying weather in Kansas last night (6/27), flat
calm and partly cloudy skies so we decided to give our new launch pad
and rocket a try.  Lately we've been using an Estes Porta Pad that came
with one of the ready to fly kits, but last weekend we bought a Mantis
Launch Pad to handle our new "D" powered Oracle.

When I built it, I opted for the camera down chute arrangement and used
a section of 50lb test Kevlar to substitute for the 12" braided line
suggested.  I also replaced the shock cord with longer 1/4" elastic
that had medium to soft stretch and attached it to the shock cord mount
provided at the plastic lower to upper tube coupler joint instead of
using folded paper.  I hoped the longer cord with softer stretch would
prevent spring-back and might provide some more stability during
descent.  Instead of the suggested plastic cement at the coupler, I
used a light coat of 10 minute epoxy after degreasing the plastic and
prepping everything.  The tube joint alignment was very good as
evidenced in the videos with hardly any rotation on ascent.

We brought along a laptop for downloading the videos, prepped
everything and launched it the first time on a D-12-3.  The flight was
excellent and landed just 20 yards from the pad.  We fly in a complex
of soccer fields, parking lots and baseball fields and our targeted
landing spot is the soccer fields with their softer turf which we
managed to make on all four flights.

The video was exciting to watch and our whole family enjoyed high
five's, ever since I was a kid I always wanted a Cineroc but never got
one :-(

After burning through a pack of D-12-3's, I opened up a pack of
D-12-5's.  This was the fourth flight and the video showed it to be
much higher.  We noticed when the motor popped to deploy the chute that
there was a much larger flash than normal, it was very visible from the
ground, and the shock cord failed.  The booster came down without
damage and the nosecone and chute combo arrived about a minute later.
Fortunately there wasn't any wind or we could have lost it to drift.

I checked the spent motor casing to make sure it wasn't a booster, and
it wasn't, so what explains the violent charge for chute deployment?
Since this was a new rocket we'd been careful to use extra squares of
wadding.  I'd searched for and read various opinions on here about
using elastic instead of rubber.  In retrospect I can see how the stock
shock cord mount mid-tube would be unprotected by wadding leading to
it's failure.

Opinions on retro-fitting a new shock cord and what to use?

Mike Doyle