Wednesday, July 29, 2009

My blog is like watching primer dry

Finishing is becoming easier and more rewarding so I continue to muddle through but this remains my least favorite phase. I wanted to share the final approach to booster section greatness with some pics, info, and time stats:

Since I used only gravity on the fin reinforcement (no vacuum or shrink tape) I did my best to squeegee out the excess resin to optimize weight/strength. The resultant texture was very pronounced and 10^6 coats of primer never would have filled it. Instead I used the miraculous SuperFil to fill and obscure that fabric texture as well as ramping the motor retainer lip down.
Mixing/application time: 45 minutes
Curing time: overnight

Here I've just applied the two heavy coats of UV Smooth Prime:
Mixing/application time: 60 minutes
Drying time: overnight

This is my new favorite trick from Dave Triano... spray a light guide coat of matte black paint, let dry, and start sanding. This pre-coat takes no time to apply and dry and it's easily the best way to ensure your final sanded area is completely uniform. It also shows gaps that require subsequent SuperFil. Buy those ShadowAero videos right now!!
Sanding time: 90 minutes (even with 60 and 80 grit sandpaper dammit!)
The very smooth, uniform sanded result:

I applied yet another ramping layer of SuperFil to transition/smooth out that motor retainer lip. I also found some areas with pits too deep for primer and filled those too.
Mixing/application time: 20 minutes
Curing time: overnight

Here are the final two heavy layers of UV Smooth Prime
Mixing/application time: 40 minutes
Drying time: overnight

I'll be sanding that off tomorrow and vibrating my hand nerves so they'll be numb for hours afterward. Seriously... can I hire someone to sand for me? Anyone? It'll pay better than minimum wage.
I should also note that, if you're using car primer and paint, there's literally no need to use finer than about 80 grit sandpaper. In fact it's obvious that the resultant grooves improve paint adhesion and Napa's single-stage paint film is still astonishingly glossy. I'll probably apply a couple of layers of clear coat as well once the vinyl lettering is on.

Monday, July 27, 2009

The mask of... V2

Best masking job I've ever done...

I should note that I found a masking mistake as a result of shooting this photo. It's fixed now and all we need is black car paint.
Bonus: for the ULTRA observant you might have noticed that my masking job is mirrored from the yellow/black paint guide image in the previous post. This was indeed intentional as I wanted to paint over a small tube defect near the top and mirroring was the only way to achieve this.
Bonus #2: I realized I made yet ANOTHER mistake on the nose cone!! The wrong two regions are masked so I'll switch those. In retrospect I suck at masking.

Saturday, July 25, 2009

First successful car paint sesh

Last weekend I'd posted pix of the priming session. Well that primer was ready to sand in 2 hrs so I did. I then enthusiastically proceeded to apply paint and here are the results:
I'm very pleased with the outcome this time although there's still room for improvement:
  • I left the primed V2 (white rocket) booster outside drying for awhile. I should have then cleaned off the dust before applying the white paint and that would have eliminated the repellencies you can still see up close.
  • Also the metallic purple Vertical Assault still shows some pinholes in the fiberglassed surface. This paint is thick and coalesces/covers well but not for pinholes. As such I'm paying extra attention to the EM-SEM-FITY exterior finish with filler and primer prior to car primer and paint.
  • Finally I erred on the side of less paint overall to reduce the chances of ugly drips forming. As a result there's a low amplitude, low frequency ripple on the surface of the purple Vertical Assault. This isn't a big deal and I'll probably be a bit more aggressive in wetting out the paint evenly on my next attempt.
I've also decided to paint the little V2 authentically:
...although mine will be white where the yellow is. In searching for this paint scheme I also came across a logo that was used in the WWII days called "Frau Im Mond" which I think translates to "woman in the moon":
I really like this logo 'cause I'm a perv so I'm either going to render the moon, stars, and rocket in 3D and superimpose a picture of a real girl or ask my friend to try to paint that logo. Either way I'll print it out on adhesive white film and spray clear coat over the whole rocket as the final step. Should be cool.

Friday, July 24, 2009 rocks!

The consensus was that the all caps version of the logo won. I contacted and Mark quickly replied with a mock-up and a quote. I had mentioned the font in my quote inquiry and Mark cleverly downloaded the font, fed it into his CAD cutter software, and exported a JPEG preview for me. I paid via PayPal and the vinyl lettering arrived two days later:
The price was a bargain and I can't recommend Mark's services highly enough! Cheers to another custom build soon so I can design and order a new logo.

Sunday, July 19, 2009

Big automotive primer session

After two previously failed car paint attempts the stars finally aligned today. I had queued up six parts that had been sanded and ready to spray prime with Martin Senour Crossfire primer. I carefully sprayed each part with their cleaner, wiped each down, and allowed all to dry. I then sprayed their plastic adhesion promoter on one PE nose cone and a fin can to ensure a good bond. Here's my spray setup on my upper deck outside having just finished all six parts:
It turns out that I WAY overestimated the amount of primer I'd need so I ended up wasting about half. Good thing it's only $40/quart... dumb ass. :( Here are four of the parts are drying:
I probably shouldn't be allowing these isocyanate-cured parts to dry near my kitchen but ya can't live forever. Also I can't praise my respirator sufficiently! I can't even smell a hint of acetone while I'm wearing that thing.

This just in...

The entire phenolic/plywood/carbon fiber/Kevlar/motor retainer booster section weighs only 4 pounds!! [G's jaw drops] Now it's into the curing oven for a one hour of post-cure on the fin layups:

Saturday, July 18, 2009

Progress galore

Alright so I masked off the fins and applied the black high-temp epoxy fillets:
I had a scare while preparing the epoxy. It's approaching its shelf life of 6 months and the curative is yellowing. According to Dave Triano the resin:curative ratio is critical so he provides the former in a white cup and the latter in a syringe. I began to squeeze the syringe into the cup but the plunger stuck then slipped and splashed a bunch out onto my work space. I'm grateful that it splashed back and not into my eyes! Always wear goggles, kiddies. Since the system was aging I guessed the failure mechanism would be unintended polymerization so I chose to roll the dice and assume the ratio would work. This expensive 500F Tg resin appears to have cured correctly as the Kevlar pulp-augmented fillets seem incredibly strong.
I then cut a piece of Kevlar/carbon fiber hybrid fabric to just fit inside the perimeter of each fin and bridge the body tube. I also cut a slighly larger piece of 6 oz carbon fiber cloth to extend just beyond the first piece. I mixed up a 50g batch of Aeropoxy and added a bit of colloidal silica to prevent it from running down the fins as it cured. I also added 3 wt. % white epoxy-compatible pigment as a visibility aid. Here's the third pair of fabric layers laid up and curing:
Once I finish the fourth fin pair surface I'll post-cure in my oven to maximize strength and temperature resistance. Then begins the fun process of filling, priming, sanding, priming, and painting. Wish me luck.

Sunday, July 12, 2009

Ist eine Rakaten fantastisch!

Sorry I was channeling BrĂ¼no for a moment there... So I pieced the beast together and it's looking just as I'd hoped it would:
The metal-tipped, filament-wound carbon fiber nose cone doesn't quite fit yet and, since it's the single most expensive part, I plan to finish that fitting last. I love the high aspect ratio and carbon fiber reinforcement allows me that luxury for an M-powered rocket. I also wanted to share a macro-ish shot of how thin the CF wall is on the exterior of the phenolic:
Three wraps of carbon fiber is only ~2/3 the thickness of the original phenolic wall! Very thin. Very strong.

EM-SEM-FITY fin attach

For months now I'd planned to reinforce the 1/4" fins with at least one fascia layer of carbon fiber/epoxy prior to attaching them to the booster. I mentally devised several layup scenarios ranging from vacuum bagging individual fins through stacking all four, stratified, and curing simultaneously under a 10 lb weight. In the end I decided the risk was too high for pre-reinforcement and reverted to what I know -- bonding plywood fins to the tube then post-reinforcing. This results in a less optimal resin:reinforcement ratio but oh well... this thing is already extremely lightweight!! I started by laying out the fin positioning guides in Illustrator:
I then printed this on a 13x19" sheet of HP Advanced Photo Paper using my HP B9180 printer. I cut the two guide patterns out using a sharp X-Acto knife and set the freed inner areas aside leaving inset guide patterns in the larger sheet. I laid these guides on a piece of 3/16" foam core, traced them, and again cut the inner pattern leaving these two 12x12" fin alignment guides:

I then test fit the four pre-sanded fins with these two guides on the booster tube:
All parts fit perfectly so I then marked a single, silver line for the first datum fin. The purpose of this first fin is to prevent unintended rotation of the two guides relative to each other for the three remaining fins. I applied JB Weld Kwik to three points on this first fin and ensured it was perfecly aligned along the silver guideline:

JB Weld Kwik sets in 4 mins but I let this first attachment cure for 45 mins before doing the same for the other three fins (one at a time with ~10 mins in between). The final fin is curing now and I'll pull the guides off and cheer. Next comes the ultra-high-temp black epoxy as key fin attachment and fillet material.

Sunday, July 5, 2009

M750 = Em-Sem-Fity or EM-SEM-FITY!?

I've decided to channel my rap alter-ego and name the as-yet-to-be-named-vessel-under-construction "Em-Sem-Fity" or "M750" as 50 Cent would utter it. Which logo do you prefer: mixed or all caps?:

You can vote via comment below. And please do.

Friday, July 3, 2009

Success on the most expensive part yet

I'm, like, sorta happy... or something! I test peeled some of the film this morning and the part had obviously cured. When I cut the Mylar™ film free it popped right off exposing a virtually perfect surface! There are still some surface voids in the resin but far fewer than when I first cured the part in the oven on previous failures. The blue peel ply is still intact here and the motor retainer is at bottom:

I decided to peel the blue fabric off before post-curing the part in my convection oven. Once you get it started it peels easily and leaves a very rough surface for bonding high-strength, high-temperature fins:

Now it's into the oven for an hour...

M750 build progress

Can ya tell it's a holiday weekend and I'm fired up?! Happy early Independence Day by the way, my vast readership.
Last week I used JB Weld to bond the 98mm Slimline motor retainer to the end of the 48" long booster section and this worked well. I should also note that it took me roughly 20 minutes to grind off the lip several months ago using a griding wheel. This is some seriously hardened aluminum!
Last night I got a second wind at about 8:30PM and, over the course of three hours I:
  • Pre-cut all materials: 48x37.5" piece of carbon fiber cloth, 48x16" piece of waxed/buffed 14 mil Mylar™ film, and 17x13" piece of release fabric for the exterior of the fin section.
  • Correctly mixed up a 180g batch of Aeropoxy
  • Laid up three wraps of 6 oz carbon fiber on the exterior of the booster section forward of the motor retainer.
  • Applied the blue, coated 17" release fabric directly north of the motor retainer lip. When removed this fabric leaves a perfectly rough surface for subsequent bonding of the fins.
  • Wrapped the Mylar™ film around the part and applied many individual pieces of gaffer's tape to hold it in place. I employed a great deal of tension on each piece so this should be a smooth surface.
  • Spiral-wrapped the exterior with 2.5" wide heat shrink tape and secured the ends with gaffer's tape.
  • Placed this final part into my curing oven for only 15 minutes. I was trying to get the tape to shrink a bit and to kick off the epoxy's polymerization. I then moved this part back into my garage to finish its cure cycle overnight.
I checked the part this morning and it looks good through the films but no resin has squeezed out:

As such I'm guessing the aesthetics will rock on this part but the resin:reinforcement ratio will be much higher than desired. This will add weight but I can say that this sustainer section still feels comparatively light to me. I'll post pictures later today and then pop the excavated part in the curing oven for an hour to post-cure it.
Finally I also filled the surface-challenged payload section with SuperFil filler. That is some great stuff. I'll rough up the surface with some coarse grit sandpaper then apply two coats of UV Smooth Prime at some point this weekend:

Continuing composite saga

OK so I've worked in chemical engineering-related R&D for almost 15 years now. As such I can attest to the fact that, when you're pushing the limits of your personal or collective knowledge, things can fail.
My most recent rocket science failure stemmed from a) the hasty use of b) a handy resin ratio spreadsheet I cooked up for some odd materials. For those of you who have used two part systems like epoxy you'll know that most employ simple ratios like 4 parts resin to 1 part hardener or the even more common 1:1 ratio.
Well Dave Triano teaches that "UV Smooth Prime" is the best possible filler and primer for rocketry use and I agree. I calculated its "resin":hardner ratio to be ~79:1. Gee that's easy. Similarly Dave recommends Aeropoxy as the resin system of choice for rocketry composite material lay-ups. It's ratio is exactly 100:27. So, as I prefer to tailor each material batch size to fit the job, I assembled a table to get those odd ratios right:

This table has proven invaluable to me this year. However when you're rushed and throw together a batch of Aeropoxy to test a new part design and refer to the first block of columns, UV Smooth Prime, you're ratio will be WAY off!! And how the hell did I not notice the ridiculous imbalance of otherwise familiar Aeropoxy components?!
The result of this error was that my vacuum-cured, carbon fiber-faced fin never cured and all the gelled monomer selectively sucked into the breather/bleeder fabric. Sadly I'd also used the excess resin to bond the reinforced coupler into my M750 rocket's payload section. All this did was wet both parts with monomer. Good thing this only affected about 7 previous hours of work on the constituent parts!! :(
Yesterday I stopped moping, manned up, scrapped the fin, and cleaned the payload/coupler up with acetone. I got the latter clean enough that I was able to properly bond the other ends of each part and all is well again. Lesson learned: think before you pour!!