Discussion in 'Low Power Rocketry (LPR)' started by neil_w, Jan 2, 2018.
Thank you sir! Plenty more to go...
The lower part of the vertical stabilizer is straightforward. Skins go on:
And then the white area which will serve as the glue point for the nuclear ramjets is trimmed out:
Still gotta glue onto painted surface, oh well.
Horizontal stabilizer gets cuffs on first:
Then skins, and the upper tip of the vertical stabilizer is glued on. And so were are here:
The horizontal subassembly now is glued onto the vertical stabilizer. I stared at this for a while trying to figure out how I would hold it all in position for gluing. Eventually I put the vertical stabilizer, wrapped in a paper towel, gently into my bench vice. Then the top assembly was glued on fairly routinely.
I initially repaired a few lifted edges with tape, but learned that while the tape disappeared on the skins, it was ugly and visible on the painted fin edges:
I went back and sliced off the offending bit of tape, and glued the skin edges down with 3M 45. Much nicer:
Mind you: the 3M 45 is a pain in the neck. It seems almost impossible to work with it without at some point getting some on your fingers, and then putting nice sticky fingerprints on the rocket. I eventually decided to only use it when necessary, although it is definitely useful to have around. Later I found that a bit of CA under the edge of the skin could also seal it down.
Finally the entire assembly is glued onto the body tube and and here we are:
Medium CA fillets on all joints. That seems to work well.
When I plugged the nose cone into the BT just to preview how things were going, I noticed something:
The chameleon pattern on the nose cone (right side of image) is different from that of the rest of the model. It's noticeable but not tragic. I asked John about it and he was surprised, saying no one had ever mentioned it to him before.
The skin for this kit has been modified since I got mine, so I can't say if new purchasers will encounter this or not.
It's a bit annoying but there's nothing to be done about it, so nothing to do but soldier on.
The Ragnarok has a scoop on the underside that is *similar* to the one on the Cosmic Interceptor but not the same (also the Cosmic's scoop is on top). A piece of tubing is provided; originally I thought it was the same 2" PSII tubing but actually it's one size larger, so it'll slide over the body tube. I don't know its numeric designation. It's also somewhat thinner-walled than the body tube. Prospective scratch builders be aware.
Process for cutting the scoop is to apply the piece of skin, then use that as the cutting guide, much like the sausage cut at the aft of the BT.
As shown above, I drew an alignment line on the tube to ensure that the skin was applied straight. Here's the skin on the tube:
Knowing full well that the skin was going to want to lift, I taped the edges down, taking care to only tape of the white extra, and not on the blue skin itself. Time to cut!
The two end cuts were pure freehand. Because the tube was not too thick, it cut through in 3 or 4 passes with a fresh snap-off blade. For the long straight cuts on the side, I taped a piece of cardstock just to provide a bit of a guide to work from. Even though it didn't conform to the tube particularly well (or at all?) it definitely helped make straight cuts down the side.
Here's the cut-out piece.
Although these were some of the cleaner body tube cuts I've made (getting better, slowly), they still naturally needed cleanup. And so, CA was applied around the entire edge, then everything was sanded smooth, hit with black Sharpie, and then another layer of CA. Looking good:
Of course the edges started to lift:
I tacked them down with a bit of CA. They didn't need to be perfect, since they'd eventually be held down by the CA fillets after the model was assembled.
Two coats of Tamiya gloss black were applied to the inside, leaving a small border around the edge for gluing. I wasn't sure it really even needed the second coat; the Tamiya gets pretty good coverage with one, but why not.
Then I started to wonder: how the heck am I going to glue this thing on? TBII on the edges wouldn't be so great since they're CA-coated. And so what I did was this. I applied a heavy bead of TBII around the inside perimeter of the part:
I figured that when I laid it in place, the glue would flow down and make a decent bridge between the BT and the un-CAed parts of the scoop. So I turned it over and placed it down, and then realized that I had forgotten to come up with a plan to hold the scoop in place while drying. In the heat of the moment, all I could think was to tape it down:
The tape did not really hold it in place as tightly as I would like. To be fair, I don't think there is *anything* that could have done so, short of sitting there like an idiot holding it with my hands for 20 minutes while the big glob of Titebond set up. The good news is that the glue did seem to have pretty well secured the scoop to the BT; the less good news is that one of the sides of the scoop didn't quite sit down flush as it dried. In this picture you can see a bit of the TB through the gap:
I decided there wasn't much to be done here, so I just applied my nice CA fillets around all the edges, and as it turned out that pretty much hid the gap in the joint. I would say that when I was finished the scoop was really quite secure. Also, after the CA fillets were applied, the edges of the skin weren't going anywhere. Success!
Oh hey, look, the scoop skin has the same chameleon pattern as the nose cone...
Late to the party...... again. Interesting, very interesting. Thx for sharing.
Two ventral fins get mounted behind the scoop, overlapping it slightly.
First, the two cut-out slots get the goth eye makeup treatment to eliminate exposed white areas after the fins are attached:
Next the fins are skinned and attached. I mounted these aligned with the aft edge of the sausage-cut BT. They are glued to the exposed areas on the BT: the forward extensions the overlap the scoop was only glued by the now obligatory CA fillets around the entire root edges.
The light at the end of the tunnel is starting to shine through a bit.
The Cosmic comes with two 1" long 1/4" lugs. The Ragnarok instructions say to skin them and then apply them in the joint between the scoop and the wing.
Step 1: prepare for skinning. I Sharpied the ends to avoid any visible whiteness:
These lug pieces had a pretty glossy finish on them so I thought they'd be a good surface for the skins to grab onto. Then I went hunting for the skins and absolutely could not find them. I don't know if I somehow misplaced the pieces, or was misinterpreting which pieces were for the lugs, but I could not for the life of me find anything in the skin set that was intended for the lugs.
There was, however, some extra blue pieces leftover from some cuffs earlier in the build (save everything!!!). They weren't long enough to wrap all the way around, but that seemed OK because only a little more than 1/4 of the lug surface would be exposed. Also I would have wanted to have some exposed lug surface anyway for gluing. Sorry, no pictures of the skinned lugs (forgot).
Naturally, the edges started lifting up, so I glued them down and everything seemed good.
Next I laid them down in their intended destination to see how things looked. As you can see, only a small part of the lug surface is visible; the exposed white parts are nestled into the joint.
Then I realized that unlike the fin mounting points, there were no indicated cutouts for the lug glue joints. So I marked it myself and cut out a couple of rectangles, slightly shorter than the lugs and (hopefully) right underneath, on the wing, which seemed like a sturdier place to glue than the scoop.
Here are the cutouts:
Then I dolloped on a bit of 30 minute epoxy onto each glue pad...
And plopped on the lugs. Looked good. Then I applied CA fillets to the wing/lug joint and the scoop/lug joint. A few minutes later I checked on things and was greeted by this:
I was not in a good mood when I saw this, since I *thought* I had sufficiently glued the skins to the lugs. Apparently not. One of them held, but the pictured one, well, did that.
Not much I could do until the CA fillet was dry. At that point, I glued the skin back down with 3M 45, and when it seemed to be secure I applied another CA fillet. Thankfully it seems to have all held together.
Here's where we stand. Note the nose cone has already gotten a couple of coats of Future, so it has a glossier sheen to it. Eventually that should all even out when I Future the rest of the rocket.
It is pretty freakin' cool. But it is not quite done!
The "nuclear ramjets" are the final bit of exterior construction. These mount on either side of the vertical stabilizer.
The tubes are made from the yellow spacer tube that is used in building the motor mount (everything gets used!). I cut it into two 1.75" pieces, and then gave each one a coat of CA on the outside, so the surface would be slicker (after sanding) for the skin to adhere. An extra bit of strength is welcome also. A 1/4" wide strip is left bare, for eventual gluing to the rocket.
Here's the "jig" I used to hold the tube while I was applying the CA, and it made for a handy drying rack as well:
The cones in the jets can be done in one of two ways. First, and more "accurate", is with cardstock shrouds. However, although I've done a reasonable number of shrouds, the first one of these that I tried really kicked my ass. It's very long and skinny, and requires a very tight curve radius. My attempt was sufficiently awful that I discarded it to get it out of my sight before it even occurred to me to take a picture.
The alternate approach is to use a piece of wood to approximate the shape of the cone, and that's what I chose to do. Templates are provided, and.... I finally get to paper some balsa fins, woohoo! Here they are, papered and ready to go. The one in the back is inserted in the tube to show how it's gonna go.
Next up: priming, painting, blah blah blah. I did the fins, and then most of the tubes, leaving unpainted areas both for gluing the tubes to the stabilizer and also on the inside for gluing the cone/fin thing. I didn't completely paint the tubes because most of them would be covered by skin. I just painted the edges that would either be exposed, or would be attempting to hold the edge of the skin.
Here are the painted pieces freshly glued together, stuck to some tape to hold everything in position while drying:
The tubes were then skinned, again leaving a gap for gluing on the bottom. Of course the edges were lifting, but this time I was ready. While holding down half of each edge, I applied a bead of CA along the other half. When that dried, I held the glued half and then applied glue to the other half. The edges were secure, and the CA would be pretty much hidden in the joint. This picture shows the edges of the skins, and you can kind of see the CA.
Here are the finished assemblies:
I glued them to the stabilizer with 5 minute epoxy. Normally I use 30 minute, but hey I have a life to live here, and this isn't structural.
Here's a top view of the stabilizer showing the ramjets on each side:
And here's how it looks from the side:
Hey, guess what? Exterior construction is complete. I still have a few stubborn skin edges to glue down, but this is basically it. Recovery gear has not yet been installed, still thinking about options there. Also the whole thing needs a few coats of Future; that'll probably wait for better weather, gonna hang it from my shed ceiling and do it there.
Here's what it looks like.
Awesome! Lots of great tips on Accur8 skins too - thanks for taking us all along for your build.
Looks really good. Those tail feathers look a bit delicate, will they handle a landing?
It was fun. I really suspect that most Accur8 skin purchasers do not experience the edge lifting problems that I had, or else John would have changed the vinyl by now. Fortunately I was able to work through it all, despite a few bits here and there that are not as clean as I'd like.
I had the same thought, but only one way to find out. :wink:
I do not expect this to be a frequently flown model, but I do want to get it up in the air sometime this year when the conditions are favorable. An Aerotech E15/E20 should do nicely.
The inspiration plastic model kit was really ahead of it's time, considering the similarities to this recent proposed NASA Quiet supersonic low-boom flight test demonstrator design:
Ooh, that’s pretty...
Cool looking bird.
Wouldn’t want to be pilot trying to land the thing. Not much of a forward view!
-Unless it has forward mounted cameras in the nose.
Nuclear Ramjets....Now there's a terrible idea for accelerating the end of the world!
How's this build coming with the recovery and prep? Will it go flying with Avalon soon, or has something occupied your attentions?
I try not to think too hard about these fantasy models.
Great question. In fact, recovery has not been installed, either in this or my Trajector. I'm a bit stymied about what to do with them. I was gonna put some baffles in, but on this one at least it would be very tight to put in the baffle in front of the coupler and still have room for the recovery stuff. Also, the baffle would have been better installed before the two tubes were coupled together, although in theory I suppose there's no reason why I couldn't just swab the glue in with a dowel and shove the baffle down in there.
Maybe for this one I'll just put a laundry shelf in above the coupler, and for the Trajector I'll put in a proper baffle. Then I just need to keep track of which rocket has what in it.
This one also needs Future; I was waiting until it warmed up a bit so I could do it in out in the shed.
1) Avalon will fly at the first launch I go to this year, weather permitting. This one may or may not be ready at that point. It'll fly this year though, for sure.
2) I haven't the slightest idea what you're talking about.
Finally got a nice day to do some Future slobbering on the rocket. Normally I do it in my basement, but this one is just a bit too big to manage the way I normally do, so out to the shed I go.
Although I'd rather hang the rocket from its nose for this, I didn't have an easy way to do it, so I made a tail hanger out of... a hanger. Threaded through the end of a spent D motor.
And here it is, ready to go.
3 coats of Future later it is nicely shinified.
Now I just need to do something with the recovery gear already. I think I'm just going to fashion some sort of laundry shelf and butt it up against the coupler. This would leave a recovery compartment a bit over 9" long... does anyone think that'd be too small?
What's the weight difference before vs after the wax?
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