Sunday, October 31, 2010

UV Smooth Prime aging... fail.

For the second time I'm reminded that the yellow cross-linker included with the UV Smooth Prime product has a maximum shelf life of only a few months. On Friday I opened the little jar to find a rubbery solid therein. The white primer itself seemed fine so I rolled the dice and slathered it on Der Red Mix mark II anyway. Over the course of sanding for an hour today I noticed several spots where the dried primer was flaking out of the tube seams. I'd never seen this before with cross-linked primer so lesson learned: Use that $51 can of product quickly!!
They really should sell the cross-linker separately because of the aging difference of the two parts. In order to finish this rocket by Thursday I'll need to drive up to Aircraft Spruce in Corona tomorrow to buy another can. Hopefully they'll sell me a spare jar of yellow failure. Good... traffic... times.

Sunday, October 24, 2010

Improvement via iteration...

I hate crashing expensive, time-consuming rockets but there is one advantage: the same design turns out WAY better the second time. I wasn't very happy with the carbon fiber fin reinforcement on Der Red Mix last time because the fabric texture was pronounced, I had to pry the fins apart after they'd cured, and, of course, the carbon/kevlar hybrid was impossible to sand.
While 1/4" plywood is pretty rigid I still wanted to add some cloth reinforcement because the fins are high profile and I don't want them shredding or breaking off during flight or recovery impact. Last time I used a mix of carbon fiber cloth and remnants of carbon/kevlar cloth. I also used a material-efficient stack while laminating but it's that configuration that caused the fabric bumping and layer separation difficulty:
For this mark II build I decided that carbon fiber was overkill so I reverted to 6 oz fiberglass. I also added 3/8" ply layers between the fin layups to force a smoother surface and to completely segregate each stack for easy separation ('CF fabric' below should read 'Fiberglass cloth'):
This layup worked much better although the surface still isn't as smooth as I'd like so, again, priming/sanding is the best!! Here are some pix of the layup:
Oh and I completed the motor assembly/e-bay, cut all the slots and doors, epoxied the goodies together, and this baby is ready for fins:

Tuesday, October 12, 2010

Build progress update

Der Red Mix mark II suffers only from a lack of motivation. I am making progress and the build is far smoother the second time but, honestly, I should have been done by now. Here's the upper portion of the motor tube assembly with the e-bay door. I propped it upside-down in the airframe tube whilst it cured:
I'm also making marginal progress on the >2000MPH rocket. I completed the carbon fiber reinforcement of the coupler and grafted 12" of BlueTube 2.0 on the booster to fit the payload coupler and recovery system:

Yes I SHOULD have just used one continuous 48" length of 75mm BlueTube but I had committed the Slimline motor retainer to the 36" phenolic some time ago. I'm gonna wrap the whole thing with three layers of 6 oz carbon fiber so I think it'll be strong enough for an M3700 [shivers].

Plaster City... The DARK launch

No not a night launch... Last weekend it was thunderstorming in the east and the sky was supa dark so I bought an M795 reload for this year's M-moonburner-drag-race, tied KO in an I445 drag race, then high-tailed it outa there before my car got stuck in ex-lakebed sludge:
Then last weekend I was too lazy to get up and fly at Lucerne despite epic conditions. Again I'm a jenius.