Starship Avalon: build thread

OK, I'm calling this the official start of build prep (debatably, that started with my balsa bending experiments, but whatever).

Because the first thing I'm actually going to do is fabricate the helical fins, the first bit of prep I need to do is create the template for them. This was an interesting little exercise. My template needs assist with three tasks:
1) cutting the balsa
2) positioning the balsa on the bending form
3) position the finished fins on the pylons for final assemply

Although it's not really the right tool for the job, I created the template with Paint.net. Here's a half-sized annotated version:



The footprints for the two pylons came first. Positions on the X-axis are easy: they come from OR. Positions on the Y-axis are slightly more interesting. The helical fins conform to a 5" cylindrical form, and the front and back are exactly 60 degrees apart. Therefore, the distance along the circumference of the cylinder is 1/6 the total, or 5*PI/6 = 2.62". And so that is the height on the Y axis of the front pylon on the flat paper.

Then, via all sorts of fiddling, I created a symmetrical tapered fin shape that covers the pylons, and looks about the way I want, as shown above. That will serve as a template for cutting the balsa.

I also put vertical rules left and right, to line up with the edges (or at least one edge) of the cylindrical form I'll use to bend the balsa. I'll wrap the paper onto the form, trace the fin outline onto the form, and then that will help me position the balsa correctly on the form.

Finally, after the pieces are finished, the pylon markings will help me mount the helical pieces onto the pylons in the correct position.

So everything is accounted for I think. We'll see!

I wonder if you can find a 5" PVC pipe section at one of the big box stores (or better, some construction site with plumbing work) to form that helical fin on? Just a thought, I don't even know if pipe is made in that size.

What I have is two 4" couplers that I shall connect back-to-back via a shorty piece of 4" pipe (I'll get that on Monday). The outside diameter of the couplers is just a hair over 5", so it works perfectly. The whole thing will end up about 7.5" long, which is perfect as I need about 6".


Once I have that assembled (in the picture the two are just stacked loosely) I'll start fabricating the helical pieces, which will take a while (I'll only do one at a time) but I'm in no hurry.

Based on my initial experiments I'm pretty confident about everything in this build other than the motor mount, which is kicking my ass at the moment. I'll figure something out eventually.

Hey, here's a look-see at my lil boiler plate rendition. This is built just to see if this kind of fin will stabilize a rocket. Maybe I can pop it up with a B motor this weekend. I'm not going to keep this though. I will re-purpose the nose section and airframe though. I really like the straked nose cone idea of yours.

Nifty.

You do not have a lot of fin area there, good luck with the flight.

Yeah, once I got it finished, the fin can looked a little small. Thing is, there's a lot of resistance down there and it might be enough to stabilize it. We'll see.

Nice avatar btw. How about a whole pic of that so I can see it....preeze?

Ha, was wondering if you'd comment on it.

It's just an OR render of course, but here you go:


The decals are as proposed by Mark Hayes; I still have a few more of his to add in but what's there now is a good start.

And yes, this avatar means that the build is now underway. I'll get the build thread going once I get a bit further into it.

[hmm, the forum uploader seems to have converted my PNG to a tiny JPG that looks like crap... that's never happened before. Anyway if I can figure out what's going on I'll replace that one with the original PNG]

[OK, replaced it with a better quality JPEG... strange goings on]

I like it just the way it is. Can't imagine what else you could want to do to it.

Put Der Red Max decals all over it?

neil_w said:

Put Der Red Max decals all over it?

Click to expand...

.......:kill:

So I finally got my 3" piece of 4" PVC, and could join the two couplers together. So I cut the fin out of my template, and taped it to the form, with both edges lined up, like so:

Then I Sharpied the outline of the fin and removed the paper. And here is the balsa-bending fixture, ready to go:

And here goes.

1) Take two pieces of balsa, cut to the same template. They're very rough for now because I will be sanding them to final shape after they have been laminated.

2) Apply Windex with Ammonia liberally to each piece. Supposedly the ammonia helps the balsa absorb water more readily or something like that; not sure but it seemed to work OK during my tests.

3) Soak in hot water (well, it started hot, ended up room temperature eventually) for about 2.5 hours. I used a water bottle for this, filled to the tippy-top; the rock on top kept the floaty wood submerged.

4) After soaking, the pieces were definitely more pliable. I applied a thin layer of Titebond II:

5) Then squeezed them together and clamped them to the form, aligning them to the Sharpie outline as closely as I could:


These new clamps really hold the edges down right against the form. I put a little piece of spare balsa (covered in scotch tape so it would stay slick and unglued) under each clamp so it wouldn't mash the balsa.

And now it sits until completely dry, probably two or three days. Doing one at a time, the three pieces should be finished by the end of next week.

This is definitely the oddest thing I've done in my short career as a BAR. I hope it all works out.

Well done!

A bit of advice for the future... For the thin balsa that you're using, and the relatively mild curvature you're asking for, the 2.5 hour hot, deep soaking really isn't required. In fact, just soaking the outside of the piece with normal luke-warm tap water is sufficient to get the balsa to want to bend toward the dry side. You certainly haven't done anything wrong, you just did more than you needed to. :wink:

TangoJuliet said:

Well done!

A bit of advice for the future... For the thin balsa that you're using, and the relatively mild curvature you're asking for, the 2.5 hour hot, deep soaking really isn't required. In fact, just soaking the outside of the piece with normal luke-warm tap water is sufficient to get the balsa to want to bend toward the dry side. You certainly haven't done anything wrong, you just did more than you needed to. :wink:

Click to expand...

Very possibly so. I don't really know how to judge what is "wet enough", so I figured best to error on the side of "too wet". Fortunately, the longer soaking doesn't take any actual effort (just sitting on my desk here as I work), so no biggie either way.

Now I must fight the urge for the next couple of days to take it out and look at it. Last experiment was fully dry over the weekend; guess I'll pull this one out on Friday and then put in the next one.

These pieces are gonna be funky.

Another tip/trick is to use ACE Bandage or Saran Wrap to wrap the balsa parts to the mold while it dries. No fear at all of leaving marks from clamps that way either.

In this case it takes a good bit of force to hold the piece all the way flush to the form; the wraps of tape I tried last time didn't quite handle the corners successfully. The clamps are strong enough for the job. I also like the fact that the majority of the piece is exposed to the air to dry; only the very tips are covered by the clamps.

Just looking at the piece now, it is possible that I'll still get a very slight bit of squishing at the very corners of the piece, but a bit of CWF ought to take care of it later, followed by (of course) papering.

Um... How is it that I missed this thread for all this time?

NICE!!!

One down, two to go:


Sanding and papering to come later. Pretty impressive looking part, and again rock hard and should be flutter free.

Interesting: the inside of the part, which was pressed against the PVC, came out extremely smooth. So did the edges on top that were under the clamp.

op:

Hope yer gettin' some exercise to burn off all that popcorn you've been consuming lately...

neil_w said:

One down, two to go:
View attachment 304544

Sanding and papering to come later. Pretty impressive looking part, and again rock hard and should be flutter free.

Interesting: the inside of the part, which was pressed against the PVC, came out extremely smooth. So did the edges on top that were under the clamp.

Click to expand...

The smothness is caused by the wood fibers not being able to "raise" as they dried. Woodworkers will lightly dampen a wood piece to "raise" the grain between final sandings before applying the finish that way the final sanding removes the wood fiber fuzz that would standout on a smooth finish.

Looks like a good technique and should be plenty strong now, even more so when you paper them. One thing to consider, is cutting the forms at slightly off axis and opposing angles to the balsa wood grain, such that you can still get a good bend. This will result in a even stronger plywood with variable grain directions in an X shape in the laminate.

GlenP said:

Looks like a good technique and should be plenty strong now, even more so when you paper them. One thing to consider, is cutting the forms at slightly off axis and opposing angles to the balsa wood grain, such that you can still get a good bend. This will result in a even stronger plywood with variable grain directions in an X shape in the laminate.

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Good idea in hindsight.

However I'm not concerned in this case because the finished part is *really strong*, almost shockingly so. Even the papering won't make much difference here strength-wise. The fact that I used a very hard piece of balsa no doubt is big contributing factor.

I'm really quite pleasantly surprised that this crazy thing has turned into a very workable design, and fabricating these pieces has been a lot of fun.

neil_w said:

Hope yer gettin' some exercise to burn off all that popcorn you've been consuming lately...

Click to expand...

There's no emoticon for spooning peanut butter. I really don't eat popcorn.

Gary Byrum said:

There's no emoticon for spooning peanut butter. I really don't eat popcorn.

Click to expand...

I wish they had one for "pigging out on leftover Halloween candy". That's the one I'd use.

TangoJuliet said:

Another tip/trick is to use ACE Bandage or Saran Wrap to wrap the balsa parts to the mold while it dries. No fear at all of leaving marks from clamps that way either.

Click to expand...

The bandage would likely be the faster option, as plastic wrap would probably slow down the drying process.

Helix #3 is on the form; by Monday I'll have all three. I decided that I'll officially upgrade this thread to "build thread" when I actually have all the parts in hand (I still need BTs, couplers, centering rings, motor mounts... all that stuff).

Anyway, in the meantime I decided to try papering my first helix, and though I vowed not to spend too much time in future build threads talking about papering (pretty much got that out of my system in the Biohazard build thread), doing these parts was a little bit different, so I'm gonna share.

The main trick is that I wanted to keep the paper clear from the areas where the helix was going to join the pylons; I wanted a solid wood-wood joint there with nothing in between. And so here's what I did.

First, my standard preparation: I sanded the part smooth, cleaning up the overall shape. All edges were rounded. As much balsa dust as possible was removed, first by wiping, then by brushing (dry paint brush), and finally by pulling it up with some blue painter's tape. Then the fun began.

First, I used my paper fin template to mark the joint locations on the fin:
->

Next, I made similar markings on my label paper. Then I drew a keep-out area around them: I want a bit of room for fillets, and also to allow for the potential imprecision of the build, since I can't guarantee that the joints will end up *exactly* where I draw them up.


Then I cut those areas out of the label paper, and applied it to the fin. I used the markings on the fin to ensure that the label paper was applied in the correct position, with the joint locations approximately centered in the holes.

I think in this case I might have made the keep-out areas larger than necessary. For the next two fins I'll make them a bit smaller.

The remainder of the papering proceeded as normal. Sand off the excess paper (always holding paper in my hand, never a sanding block!), apply glue (this time I used Titebond II) to all the edges, then sand to final smoothness:


The finished part looks and feels fantastic; I can't stop admiring it (pats self on back). It's hard to appreciate the shape and finish in a picture. Within a couple of weeks I should have all three completely finished (going away for a few days in the middle, so work will pause).

Geez! With all the football activity going on, I could hardly catch an empty field. Here's the latest poop on my boiler maker. Launched with an A8-3 and got about a 60-70' flight. This bugger is a spinner man. I could even hear it! I'm sure with your pylons being thinner, you should get more altitude. But I wasn't as concerned about all that as I was seeing if this fin can made for a stable flight. All in all, it was pretty much a textbook flight.

Sounds good! I'm not expecting max altitude with this one but it should go ok on a D.

The motor mount on mine is prepped for 24mm. I used a step down adapter for 18mm. I suppose if I had a big enough field, it could take a D. Prolly never get it back tho.