Biohazard build thread

Time to get this build thread started. I debated whether to post it in the LPR or the Scratch Built forums: I think there's more participation in the LPR forum (it's just generally busier there), but I've decided give this one a shot here and see how it goes. I'm hoping I'll get this build finished this summer, but no guarantees; expect this build to move at a leisurely pace. I'll definitely have it done before winter, barring a zombie apocalypse. Much of this build is pretty standard but there should be a few interesting bits.

Anyway, after much mucking about with possible designs, I settled on this one:


ORK file is attached below. The paint scheme is probably close to final but not committed, meaning I haven't yet ordered anything from Stickershock. I like it overall but I'm not sure about the colors.

Onward!

[edit] And here's the kit's facecard!




View attachment biohazard_final.ork

Nice!

Staying tuned!

That'll be a work of art.

On aspect of this design that worried me was the required precision of the fin cuts, particularly the three that hold the ring, and the general curviness of all the fins would present some challenge as well. Furthermore, my recent attempts at hand cutting even simple fins accurately were not great, so at jqavins' urging I decided to go ahead and get the fins laser-cut. This would be my first time trying this.

Unfortunately, I'm not one of the lucky ones that has access to a cutter, or knows someone who does. So I had to find a cost-effective way to do it commercially. After querying a bunch of services, I decided to go with Laser Cutting By John, mostly because they had *by far* the smallest minimum, and were therefore the only one I found that could do this at manageable cost. It actually turned out that the minimum was still more than I needed for this rocket, so I bundled in a set of fins (and other goodies ) for a forthcoming build of my modified version of Gary Byrum's APRO Lander. Needing to get *that* design finalized before I could get any fins cut delayed the start of this build by several weeks.

Getting the files prepared for cutting turned out to be an non-trivial adventure. Most services wanted DXF files, and I didn't have a program that would generate them. I wanted something free, so I eventually settled on Inkscape, which presented a fairly steep learning curve for me but ultimately got the job done (mostly). The Mac version runs under X, which is pretty painful, but I muddled through.

I started by exporting the PDF fin templates from OpenRocket, and then importing that file into Inkscape. Inside Inkscape I then made the following adjustments:

1) cleaned up the curves (i.e., turned them into real smooth curves rather than the segmented approximations I used in OR)
2) split the ring-holder fins into two pieces
3) added TTW tabs to the rear fins (something else I probably wouldn't have done without the laser cutting)
4) laid out the fins on a sheet

For reasons that will probably never be clear, John had some problems with resulting DXF file, but I was eventually able to give him something he could work with after many (!) back-and-forths. I'm not even sure which file he ended up using to do the cutting, but this is a reasonable approximation of the final sheet layout:


Note that I made four pieces of each, to allow for screw-ups; that turned out to be a smart move. I fiddled with grain direction quite a bit; it's hard to know exactly how to do it when all the edges are curved. Ultimately I took my best guess, and everything will be papered anyway (there will be lots of papering in this build!) so they should end up plenty strong.

John was extremely patient with me and eventually shipped me some beautiful fins. I recommend his service highly, although I don't know if he would recommend me as a customer. Fins for two rockets were delivered to my door for $20, can't beat that. Here's the finished product:


You don't get to see what crazy stuff I got made for the APRO Lander until I get around to that build thread.

Epilogue: It turns out that a good deal of the problem I was having cutting my own fins was due to the ungraded 3/32" Revell balsa I bought at Michael's being outrageously dense and hard. I asked John for medium-weight balsa, around 10 lb/ft^3, and it is the perfect balance of light and stiff and easy to work with. If I can get my hands on some like-weighted balsa sheets in the future, I'll be ready to dive back into hand-cutting. But I'm still glad I got the parts for these two particular rockets laser-cut. Thanks jqavins for the motivation!

Really awesome design and really great executing on the fins! :clap:

If you're looking for balsa, check out the chain craft stores such as Michael's, Hobby Lobby and AC Moore...last I checked, they each had lots of sheets for you to choose from. I picked up some 3/32" x 4" x 36" from each of them recently and was happy to be able to choose on my own. Of note is that of those stores, one had Revell (can't remember which one), I think one had Midwest (which is a major balsa supplier and I would think much better at consistent quality), and Hobby Lobby had unbranded. YMMV.

WICKED PISSA DESIGN!!

KenECoyote said:

If you're looking for balsa, check out the chain craft stores such as Michael's, Hobby Lobby and AC Moore...last I checked, they each had lots of sheets for you to choose from. I picked up some 3/32" x 4" x 36" from each of them recently and was happy to be able to choose on my own. Of note is that of those stores, one had Revell (can't remember which one), I think one had Midwest (which is a major balsa supplier and I would think much better at consistent quality), and Hobby Lobby had unbranded. YMMV.

Click to expand...

Thus far I've purchased the rock-hard Revell balsa at Michael's, and some Midwest balsa... I think from Ace Hardware, and that turned out to be competition-like, despite not being labeled as such. I'm gonna end up being that guy with a scale, weighing each piece in the store. It does seem more of a chore to buy balsa stock than it ought to be.

I am *so* glad that the balsa John used was basically exactly what I was hoping for.

Scotty Dog said:

WICKED PISSA DESIGN!!

Click to expand...

Perplexing, your lineage is. But thanks anyway! :neener:

WOO HOO! I've been looking forward to seeing this one hit the bench!

Subscribed. op:

I'm in... op:

neil_w said:

You don't get to see what crazy stuff I got made for the APRO Lander until I get around to that build thread. :tongue:

Click to expand...

I hope you drew your own fin templates for this. Even though my Cad drawings are usually dead on, they were dead OFF on my build. There are just too many reasons why the design could have gone wrong, so I won't speculate. I had to cut and trim the fins until I got a good fit. Just be sure to get that big tranny right.

I'm really looking forward to seeing you pop this masterpiece together.

Gary Byrum said:

I hope you drew your own fin templates for this.

Click to expand...

And then some. You'll see, eventually (i.e. Later this summer).

Nice original design!!!
Excellent color scheme too!:clap:op:

TopRamen said:

Nice original design!!!
Excellent color scheme too!:clap:op:

Click to expand...

Thanks! Now let's see if I can get the durned thing built and finished. My shop time is appallingly limited right now.

I figure a build thread is the best motivation for me to keep pushing forward...

neil_w said:

Thanks! Now let's see if I can get the durned thing built and finished. My shop time is appallingly limited right now.

I figure a build thread is the best motivation for me to keep pushing forward...

Click to expand...

A build thread definitely helps, as you feel obligated to the work to satisfy all those that encourage you to build.
I kind of sputtered out on my TALOS, but KidRocket slipped in and took the reigns and built himself the finest looking TALOS model I've ever seen.
Now if he would only fly it,....
There were times when my SA-5 build thread was really reaching for the stars, but now I have every construction problem licked, and it is just a matter of putting the pieces together when I am able, in between all my other rocket projects and occasionally playing "Real Life".

You'll get it done and it will be awesome!
Take your time and enjoy it, and when it's time to fly, get a video, that we may all live vicariously through your efforts.:wink:
It looks like it will be pretty impressive, and my Mindsim is telling me there will be an audible whooshing sound when the thrust cuts out, so make sure to get a quality video.

I am going to bludgeon you all to death with tales of my papering.

Having first tried the technique on the Diamond Cutter, I liked it enough that I decided to try to keep using it and pushing it until it fails me. I use Avery Self-Stick Label Paper, originally suggested to me by KenECoyote and I really like it because it is incredibly easy to work with and you can get your papering done *fast*.

First up were the little canard fins. These are pretty small and of course I am also compelled to round the fin edges, just to make this more interesting.

After the fins are shaped, I apply the paper and sand the edges to remove excess, and finally apply thinned wood glue to the edges to seal them. I'll go over this in more detail in a a later post.

Here are my finished papered fins:


Two things to note:
1) The red circle shows the messed-up leading edge of one of the fins (it should be curved, not straight). That was the first one I did, and I was a little too vigorous when sanding that edge and inadvertently straightened it out. I was immediately glad I had gotten four of each fin made, because I was able to correct my technique and do better with the remaining three.

2) While sanding the paper off the root edges with a sanding block, I again got a bit over-enthusiastic and slightly beveled the edges of the root. It won't hurt me on these little guys, but I vowed to figure out a better technique for the remaining fins.

When finished I glued the three best fins to the transition (all my designs seem to have fins attached to transitions). Marking the transition was a bit of a pain; I used a printed paper transition with fin markings, and wrapped it around the balsa and marked. I still didn't get the canards quite as *perfectly* straight as I wanted but good enough. Some fillets with Titebond No Run-No Drip filled the bevels on the root edge and this subassembly was finished.... for the moment, at least.

Does papering with label paper add much strength, or are you doing it just to make a smooth surface? I have not used label paper, but I have papered with adhesive spray and wood glue. While the adhesive spray was easier to use, I think the wood glue strengthened the fin more, because it, in essence, made a very thin layer of plywood on surface of the fin.

BDB said:

Does papering with label paper add much strength, or are you doing it just to make a smooth surface?

Click to expand...

I do it for both reasons. Obviously, for these little canard fins, strength was not an issue. It will be for the other fins.

I have not used label paper, but I have papered with adhesive spray and wood glue. While the adhesive spray was easier to use, I think the wood glue strengthened the fin more, because it, in essence, made a very thin layer of plywood on surface of the fin.

Click to expand...

I don't doubt that wood glue would add *more* strength (in particular, surface hardness, which the paper itself doesn't really provide), but for my own purposes with LPR I sort of feel like at some point it's enough already. As long as the paper remains bonded to the balsa, it adds a tremendous amount of rigidity, regardless of the type of glue.

Long-term durability is the biggest risk, but the convenience of the label paper is so great that I'm willing to take my chances for now. Perfecting my edge-sealing technique is an ongoing focus of my efforts, because I feel like if the edges are all really well bonded to the wood, the rest of the label really shouldn't be able to budge.

Check back with me in 5 years.

We certainly can't have that transition being all bare and grainy like that. In my last build I did a couple of transitions with CWF and I was fairly happy with them (although not totally) until I got close to the end, when I noticed some pitting in the paint. It seemed like every time I touched these things I messed them up. For this build I decided to try something different, so I pulled out the label paper again (don't say I didn't warn you).

Theory: since I can easily print a transition template to match the dimensions of the transition, I can create an appropriately-shaped piece of label paper with which I can paper the whole transition.

Fact: well, almost.

First I headed over to the utterly wonderful transition template generator at delorie.com, entered my info, and printed. I like that one better than all the others because (a) it generates a PDF rather than an image, and (b) it includes 3- and 4-fin placement marks on it (that's actually what I used to mark the transition for the fins in the first place). I traced the template a couple of times onto my label paper (assuming I'd screw up and need extras; this time it turns out I didn't):

This would take three pieces of paper, one to fit between each pair of fins. I decided to get a little fancy and actually cut notches out for the fins, like so:

I was not worried about fitting perfectly against the fins; fillets would cover all the remaining exposed balsa anyway.

Once each piece was cut, I followed my new procedure or pulling off all (or most) of the remaining dust on the balsa with some blue tape, and then carefully applied the paper. To seal the edges, I filleted the fins, and applied thinned wood glue to the edge on the large end of the transition. The small end would eventually be glued to a BT-50 and I'll fillet that joint too to smooth it out, so no need to do any gluing at the moment.

The end result looks pretty good I'd say:

The only thing that came out less than perfect is the large end of the transition; it wasn't possible for me to get the edge of the paper perfectly smoothed out. We'll see how it looks after painting, but either way I'll live with it: the whole process was quick and painless and it looks *way* cleaner than when I used CWF.

I'll declare victory and hope the paper stays put.

I do not know how far into this build I'm gonna get before an imminent home remodeling project puts my whole workbench out of commission. Argh. :sigh:

This build is all about parts prep. Assembly will probably be quick once everything is ready. I suppose this is not the most interesting build thread. Oh well, you get what you pay for! :confused2:

Moving aft on the rocket, it was time for the two-piece ring holder fins (good lord that is a horrible name... I'll just call them "the middle fins"). These fins have two root edges, one to mount to the main airframe and one to glue to the ring. Those will be left square, all other edges were rounded. One day I hope to be cured of the need to round fins even on draggy low powered rockets.

I thought about whether I should assemble the two pieces and then round, or round them and then assemble. I decided on the latter, because I thought the separate pieces would be easier and safer to handle. This was a slight mistake, as the sanding took a little bit off the corner where the two pieces meet, creating a non-smooth joint:


(build four, use three)

I filled in the gap somewhat with Titebond NRND and it's not perfect but better. The picture actually shows the fins after I filled the gaps, but you can see a shadow there and get the idea.

Papering time!

I was not particularly looking forward to papering these fins, but I was interested to see if I could do better than on the canards. So for this time: no sanding block. All edges were removed by a small piece of 220 grit rubbed back and forth with my finger. I stopped and checked frequently to see when I had gone through the paper, so I wouldn't start taking off wood. My results were much better, I think.

I'm gonna show my process here, because I'm going to tweak it yet again later.

First: remove residual sanding dust on the fin surface with a soft paint brush, then finish with some blue tape.

Second: lay down the fin on a piece of label paper. I've never had an air bubble or any other problem with this part, one of the reasons I like the label paper.


Third: lay the second piece of paper on top, and stick it all together.


Fourth: sand off the edges with hand-applied 220 grit.

Fifth: apply thinned yellow glue to the edges, and sand smooth with 400 grit. Final result:


You'll notice that there is very little bevel showing on the root edges. My abandonment of the sanding block for this process made a significant improvement. Yay.

Looking great so far!

Don't rush it, just enjoy the build so we can enjoy it vicariously.

Subbed.

Shop time is very hard to come by right now, it is bumming me out.

Anyway: for the rear fins, I decided to go TTW, for two reasons:
1) they're fairly tall, extend past the rear of the rocket, and with the extra extension provided by the tubes on the ends, I thought it couldn't hurt to have a bit of extra strength. This is in contrast to the middle fins, which are pretty low, protected, and should gain a great deal of strength from the ring they'll all be attached to.
2) Laser-cut fins would afford me the opportunity to cut the tabs on the fins pretty precisely.


I had never slotted a tube before, but it didn't seem too hard. I marked the BT with a fin-marking guide and then marked a second line 3/32" away. Then cut using my trusty aluminum angle as a guide.

The results certainly *look* good:


However, the slots are a bit too wide, resulting in a sloppy fit. I'm not quite sure how that happened. Fortunately, I don't really believe this will be a problem because (a) despite my item #1 up above, strength is not really that big an issue here, and (b) I should be able to fill the gaps in some sort of reasonable fashion.

My general plan is to lean the fin against one side of the slot, and get a good glue bond there, and then fill the other side maybe just with a fillet (the Titebond NRND should have no trouble there). An alignment jig will make sure the whole thing is on straight.

Next time I will err on the small side and file the slots out as needed.

Regarding the wide fin slots, you could just add another layer of paper to the tab portion of the fin to get it snug, either on one side or both. Nice build thread and cool design!

You can also check to see if you still have the cut out pieces, match them up to each slot and then measure, cut, re-glue to one side to fill in.

I know because I've done this before.

KenECoyote said:

You can also check to see if you still have the cut out pieces, match them up to each slot and then measure, cut, re-glue to one side to fill in.

Click to expand...

Great idea! Of course I did not save them though.

Here's the largest gap, which was the first one I cut. It's quite substantial, but again it will get filled up some way or another when the time comes.


(That's light shining through the gap, with a fin held in place. Pic is out of focus unfortunately.)

neil_w said:

Here's the largest gap, which was the first one I cut. It's quite substantial, but again it will get filled up some way or another when the time comes.

Click to expand...

Don't feel too bad. My attempt at cutting those was on the first APRO Lander and they were worse than yours.

neil_w said:

Great idea! Of course I did not save them though.

Here's the largest gap, which was the first one I cut. It's quite substantial, but again it will get filled up some way or another when the time comes.
View attachment 292678

(That's light shining through the gap, with a fin held in place. Pic is out of focus unfortunately.)

Click to expand...

You can still fill it with some cut strips from the same size tubing and wood glue...I didn't say I found all of the cut strips from the time I learned this. :wink: