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