Sunday, February 22, 2009

First vacuum bagging project

Having watched Dave Triano's composite videos twice I've been ordering all the goodies necessary to create high-strength composite materials with optimal weight.  Several mistakes are likely but I embraced my enthusiasm and decided to invent on my very first vacuum bagging project today.  My idea was to build a fin profile by stacking progressively smaller fiberglass shapes on top of each other. This way I'm building some shape as I stratify rather than building a thick rectangular block, cutting it to shape, and grinding the airfoil. This method should (eventually with practice?) yield two fin halves that can be epoxied together to form a rigid, aerodynamic stabilizing structure.  Something along the lines of the following:

I designed both right and left halves in Adobe Illustrator, printed them all on 13x19" HP Professional Satin Photo Paper (300 gsm), cut them out, marked up the fiberglass cloth, and cut all the chunks using a razor blade.  Late in the game I'd also decided to apply a sixth layer of gorgeous carbon fiber/red Kevlar™ hybrid fabric.  There's a reason why Kevlar™ is used for modern bullet-proof vests... that shit is nearly impossible to cut with regular scissors!  I was able to cut the tiny swatch I needed for this first effort after several minutes but then ordered some Kevlar shears to make it easier next time.  Here's the vacuum bag setup:
Here's the layering
  • Well cleaned 1/8" mirror glass (12x12") from Home Depot.
  • Border of yellow vacuum bagging tape (but leave the liner on the top side until ready to apply the bagging film)
  • Apply Teflon release spray inside the tape border to facilitate removal of the cured part
  • Lay down a layer of West Systems resin  on the mirror/Teflon surface (this is just a test part and I plan to use high-temp Aeropoxy for the final design).
  • Lay down an oversized swatch of nylon peel-ply fabric (to facilitate bonding of the two fin halves later)
  • Lay down the shaped but oversized layer one of 5.8 oz fiberglass cloth (45˚ fiber orientation) and pat down with more resin
  • Lay down successively smaller layers 2-5 (alternating orientation between 0˚ and 45˚) with resin in between
  • Apply perforated bleeder film to allow resin to leave the structure for optimal weight.
  • Top that with breather fabric to absorb excess resin.
  • Punch a small hole in the upper right of a 12x12" chunk of vacuum bagging film (damn that plastic is tough!) and mount the vacuum plate into the sheet.
  • Progressively peel the yellow tape liner and adhere the film to form the bagging volume.
  • Turn on the vacuum and listen for hissing.  I only found one leak and pressing the film down into the tape sealed that up.  
  • Leave this setup to cure for two hours then turn the pump off.  You can see that resin has progressive sucked out of the strata, through the perforated film, and into the breather/absorber layer.  (See how awesome that red/black fabric will be as a fascia layer?!):
I'll pull this apart tomorrow morning and see how things cured.  In the mean time I've already learned a few things.
  1. That vacuum bleeder valve assembly might not be necessary.  I wasn't able to approach the 15 microns of mercury theoretically possible with the pump.  I'll probably hook the pump up directly next time.
  2. The vacuum pump constantly vaporizes oil!  I walked into my garage to see a cloud of fine mist dispersed throughout.  Duh. Next time I'll run this outside or with a fan blowing the effluent out the window.
  3. I'll probably use more resin in the center of the stack next time.  You can see that the breather layer is lean near the center.
  4. I'll need to cut the mirror to fit into the curing oven I just built (10" wide).  I should be able to fit two fin halves per mirror and cure/post-cure the Aeropoxy in the oven (1.5 and 3-4 hours, respectively).
I'll post an update tomorrow when I excavate the part.

Reinforcing couplers

You might recall my concern about the level 3 rocket folding under tremendous stress at the coupler interface between the booster and payload sections.  I was able to easily reach into the 7.5" space and apply 3-4 layers of fiberglass/resin to that region to prevent failure.  Now I'm building Giant Leap's Dynawind version of their Vertical Assault kit and I'd like it to survive any 54mm motor made. Overal the design seems very robust and the coupler doubles as the electronics bay with two all-thread bars running through it.  This seems strong but I wanted to reinforce the 3" coupler anyway and couldn't reach in easily.  I recalled that the Gates Brothers had used balloons to compress the reinforcement to the inside of their couplers for the Porthos design (scroll down to "avionics bays").  I'd forgotten their vertical orientation and water-filled balloons, however.  In any event I was able to do something similar with my air compressor, some resin spread inside the coupler, and two wraps of fiberglass unwound into the interior:
I also wrapped a section of polyethylene bag over the glass/resin before inflating the balloon.  I  failed to take a photo of the interior post-cure but suffice it to say that it's incredibly glossy and uniform!  I think this rocket will now survive a K1275 or 2675L730.

Saturday, February 7, 2009

TAP pursuit update

As I'd mentioned at the bottom of my L3 cert entry I continue to build experience pertinent to becoming a TAP member for San Diego's Tripoli club.  Dok and Kurt encouraged me to fly more M and larger motors, use a broader range of electronics, and fly hybrids.  Here are some direct and indirect updates:

1. I've flown a total of 2 M motors now (M1297 and M2030G) and I've planned an M1939 flight in my L3 rocket in March.
2. I purchased a G-Wiz LCX altimeter and I'll use that at the March launch as well.
3. I also purchased a radio transmitter to track small fast rockets up to several miles away on the ground and 50 miles in the air.  I plan to never lose another rocket.
4. I've started to research the purchase and use of hybrid motors but I'm having trouble locating a vendor.  Jack at What's Up Hobbies doesn't carry them so the search continues.

5. I also bought a set of incredibly powerful composite material tutorial videos from Dave Triano at Shadow Composites.  I knew most of basics video with the exception of his use of heat-shrink tape to optimize the matrix/reinforcement ratio to roughly 1:1.  The content on video 2, however, revolutionized my view of filling/priming, finishing.  The third disc covers vacuum bagging for irregularly shaped parts and I'm beginning to tool up for that process.  I highly recommend this set of 3 DVDs!
6. I used to paint very well using Krylon rattle cans.  This last year something has changed and I don't think it's my technique.  All of a sudden I get copious orange peeling and cracking defects while painting.  My theory is that the EPA has pressured paint companies into lowering VOCs and switching away from flurosurfactants.  I'm tired of sucking at this so, after reading this article featuring a gorgeous paint job, I purchased an HVLP paint gun, Martin-Senour car paint from Napa, and a 20 gallon air compressor.  I've only used their glossy, gray primer thus far but the results are blowing me away.
7. Finally I've decided to learn airbrushing to improve the appearance of my final paint jobs.  I bought an airbrush and started to learn flame painting.  I'm doing a bunch of practicing in Corel Painter and Illustrator using my Wacom tablet as well.

In a future entry I plan to post my rocketry résumé and provide updates as I add experience.

Cleanin' and buildin' for the '09 flying season

I have a two-car garage but only one car. As such I use this extra space to practice my rocket-nerdiness. I don't often get a cleaning urge, however, so things get dusty, dirty, and messy. I recently started cleaning out this critical garage space in preparation for the 2009 building/flying season and have two key updates:
The above are boxes of motor instructions and spent motor casings and nozzles. Since 2000 I've always saved them as a record of past flights.  I counted roughly 160 nozzles/casings in there so I was surprised how many flights that represents considering I only attend 4-6 launches per year.  I started in rocketry when I was about eight years old so, from that age to roughly 13 when I quit to pursue freestyle skateboarding, I probably had another 150 motors in the 1/4A through G range.  That's quite a bit of spent propellant considering I mostly fly the I-K total impulse range now.  Also during this cleaning session I had an unfortunate discovery:
I thought I'd taken care of my subterranean termite problem but... no.  I was cleaning off a low shelf containing a box with every single assignment I'd completed in chemical engineering school.  I lifted the box up and the bottom separated.  Upon further digging with a putty knife I found the bottom half of that stack riddled with termite mazes.  Oh and there were termites actively working in those canals as well.  I soaked the shelf with Raid and now I've got to contact the exterminator again.  Good f'in times!!