Inspired by Astron SPRINT

GlenP

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Link to the plans of the Estes Astron Sprint at JimZ

This is sort of a variation on the theme, instead of a 1" boat tail at the end, we just have a 1" tube for the nose cone shoulder and an entire body that is the boat tail, or a very long transition. This can be built pretty light and might not even need a streamer for recovery, but might require some nose weight for stability, do your own string test if you build it. I just printed this up and have not built it yet, so hopefully no major problems, but if I discover any issues I will try to update the pattern. I just was thinking about this rocket due to another thread, and thought, how could I make this differently (note I did not say "better") and for the heck of it thought why not make the body a transition, like some other contest models are made, and try to make it from cardstock to keep the weight down. Not sure if the cardstock fins will be lighter than balsa, depends on how many plies, I am going to try for as few as possible, just not sure if 3 will be strong enough, so I might taper the plies and have more at the root, but less at the tip, to mimic how you would sand the shape of the balsa fins.

Here is the pattern, feel free to post a picture of your build, if you happen to give it a try. I will post mine when I get started on it. Just wanted to go ahead and share the pattern with the rest of you paper modelers out there. The engine mount and nose cone come from Greg P's PDFs in the Project Paper thread, those are very useful. There is no thrust ring or centering ring in the template, I just kind of cut strips of paper by hand and wrap them to fit, not sure how many wraps will be needed for the top of the engine mount in the transition body tube.
 

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GlenP

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I usually start with the engine mount, but decided to do the main body tube and transition. Without a cone mandrel a long transition like this is a little tricky. I did not get the seam totally perfect, but looks close enough. The nose cone is like a couple of transitions joined together, so it is not that hard, just time consuming. Just kind of hard to color match a painted nose cone with a printed body, so I will stick with the cardstock nose for this one, even though that higher drag cone kind of defeats the purpose of the more efficient body. But I am not really going for performance, just style, and fun! with scissors, paper, and a glue stick!

A4CE44E6-1148-4702-B8AE-0697EE1214D4.jpeg BE22980D-579E-4F2C-B5F6-9BF048A00974.jpeg 1BBFD5EF-6B42-41CC-AD5C-6D33CC8F1564.jpeg
 

GlenP

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Basic engine mount, thrust ring wrapped from some scrap strips. I will make a centering ring in a similar manner. I will try to fit an engine hook on there, but will have to notch out the body tube for it.


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GlenP

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I have an idea for the fins, I was going to just freehand cut some smaller shapes to contour the fin, but will go ahead and draw these out and add them to the template, and will post that update later.

Basically the tip and outer edges will be only the two plies, which will overlay smaller fin shape plies that go to three at mid span and then five at the root over a portion of the chord. Not sure of the exact shape, so I may hand cut some test parts before I add these doubler shapes to the template. This will give a varying thickness cardstock fin, but still might end up heavier than a comparable balsa fin, not sure.

outline of the single doubler in red, and the double-doubler in blue, that will be sandwiched by the face of the fin sheet template outline in black. Blue outline will be a total of 5 ply, the red portion will be 3 ply, and the black portion is 2 ply.

Screen Shot 2020-08-18 at 6.16.10 PM.png

Alternately, I could make the fins hollow, or with thin cardstock ribs, just not sure how strong they would be, I may do a couple of different fin mockups to see what works.

EDIT - the Edit button seems to be gone from my first post, so I will post the updated PDF with the new fin sheet here. I haven't made these yet, but this is my plan. I hope it works out. I just use a glue stick to layer the doublers adding one ply at a time, and then run very light white glue around the edges when that has dried under a book for a couple of hours.
 

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GlenP

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installing the engine mount, I was planning to line up the retainer hook with the lug, but then decided to slot the body at the seam, which was a good idea, but then I realized that the bump extends up to the fin root. I will make the best of it, just might have to make an offset slot in the root of that fin to allow for the slight protuberance of the engine hook. I am getting down to the last of my Kevlar supply, even though it has been a while since my last build, about time to order some more. I will attach a similar length of elastic cord to the end of the Kevlar, which is wrapped around the engine hook.

2B9A8F74-C629-481C-A249-C6B3C8D10B62.jpeg A6B2D4B6-7628-4E48-86C4-445BB4E049E0.jpeg

Engine hook is from a wiper blade metal strip, it goes over the top of the thrust ring rather than the bottom. I slotted the body tube a little higher for the engine hook, right up to the TE of the fin, it still has a little bump over the hook, but I think I can get the fin on there okay. It started to split the seam open slightly, but the fin should cover it up.

I will get started on the fins next with my updated doubler templates. I always save the nose cone for last, those are just very tedious to cut out, maybe this one won't be so bad, but the 13mm cones have some pretty small transitions that require the tweezers to glue up.
 
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GlenP

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Jimmy Buffet could sing a song about this.

Made the internal 3-ply doublers and will sandwich them between the printed face sheets of the fins. I cut part of the template as a stencil to pencil in the outline of where to install the internal doubler on the back of the face sheets.

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GlenP

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Fins went together okay, they seem strong enough, but not sure how good a joint I can get at the body. I should have done TTW tabs on these. For the third originally blank fin, I pilfered the retro Astron and stencil SPRINT logo from the scans of the instructions on the JimZ plan site, those were not decals on any earlier versions.

Lugs with the Estes logo, on a stick! A BBQ skewer is just about the right dia for rolling lugs. And the bamboo grain helps to grab the paper, just be careful you don’t grip too tight or you can emboss the grain into ridges in the lug.

I am kind of dreading getting started on the nose cone... will save that for last.
 

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GlenP

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With a nose cone borrowed from an Alpha, actually looks pretty good.

I will add some fillets with clear drying Titebond quick&thick.

Bears a striking resemblance to the Sprint.

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GlenP

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And no decals! Thanks, I still have the matching yellow gold nose cone to build. And, yeah the finishing is easy, I just do a Krylon UV protective clear coat in semi gloss. But I do like the look of that Alpha nose on this rocket.
 
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GlenP

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E80E6502-C87D-4592-ACDD-E33EFB4FBE41.jpeg

This one wasn’t so bad at 24mm dia. The little 13mm are pretty tricky. The easy part is next, just feather cut the coupler glue tabs and glue them up. I start from the bottom up. Then when dry, I dab some white glue inside and spread it around with a skewer, just a light coating to add some strength. I may do that to the whole body tube also.

Printing the glue tabs the same color as the cone helps to hide any gaps in the glue seams, since you have the same background color in the gap instead of a brighter white paper in the gap.
 

GlenP

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For some reason the cone tip disc was not quite large enough, but I was able to glue it to the glue tabs folded over. I will add a glue fillet when it dries to reinforce it, but there is a gap there that should not be. That is the 24mm nose cone from Project Paper, maybe the nose disc should be a little larger.


Here are a couple of shots of the front and back with all the seams. I have the engine hook slotted into the body right up to the fin. I should have lined up the hook off the fin line. But it seems like it turned out okay and kind of hides the hook. This display stand had a notch in it, so the end of the hook is hidden. Both lugs are just flat on the body, I did not put the lower lug on a standoff or anything, the lug axis is not exactly parallel to the thrust line, but not much of an angle.

Will probably have to add some nose clay for balance and will swing test this. It is very light, it should be a pretty high flier even with the sharp corners on the nose. A short streamer is all this will need.

IMG_0596.jpg
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The Titebond Quick&Thick fillets have already shrunk a bit, so I will probably add another layer or two to the fin and lug fillets. It has been a while since I have done one of these cardstock builds, the full-length transition for the body was a little tricky. I like how the fins turned out, but should have planned to make them TTW. My top centering ring was maybe a little to large, so I had to force the engine mount into position, I should have made a better dry fit because these parts are so delicate. The main body is only 1-ply 110# cardstock, when I roll tubes, I usually make them 2-ply and they are plenty strong. With this one I wanted to keep the weight down. Right now empty, it is like only 0.3 oz, but will probably need nose clay.
 
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GlenP

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This would be a good candidate for a mini or micro downscale cardstock model.

You might be able to just print the template at like 75% 18/24 ratio, even though the engine mount ratio is 13/18 or closer to 72%, it would still probably work. For micro print at 6/18 or 33.33%. but I could also rescale the drawing and fit those patterns on one sheet of paper maybe. But for the micro, I would have to redraw an easier nose cone template, no way I could cut and build those smaller transitions at the tip any smaller than for a 13mm cone.
 
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GlenP

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The smallest transition I have made was dia1 1mm dia2 3mm L 4mm for the escape tower nozzles on my Zooch Saturn 1B ASTP model. Just large enough to cover the lead on the tip of a sharp pencil.

But this Sprint-style body tube is the longest transition I have made from BT-50 24mm to BT-20 18mm over 9.5 inches.

DSC_6427.jpg
 
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I did the vernier motor nozzles for the Thor Agena when I was a kid.
Formed bigger nozzles first then cut off the tips for the smaller ones.
Tiny, tiny nozzles.
Nozzelettes?
Nozzlecitos?
:D
 

GlenP

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Here is a 73.5% scaled version, should be suitable for 13mm power, I have not built this one, just scaled it down to one page, so if something is not the right size let me know.

Screen Shot 2020-08-19 at 2.51.39 PM.png
 

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GlenP

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I like how the fins turned out, them seem strong enough, but also have a nice tapered thickness. I had good enough weather to spray some glossy clear coat today. When it dries I will try to take another picture with my camera. For some reason my phone takes kind of fuzzy pictures, I think my case might have a smudge on the lens window, maybe.

Here's a side view where you can see the engine hook exposed right up to the TE of the fin, it really kind of blends in well there. The fin is mounted right on top of it just past the hook retainer ring which is hidden inside the body tube at that point and also serves as a centering ring between the engine mount and tapered body tube.

The clear coat really absorbs into the paper and deepens the colors. If I was smart I could have used the eye-dropper tool and copied the same yellow color from the decal to match, but I just picked a basic yellow/gold color from the palette. But I like how this looks almost like an insignia yellow after the clear coat. I should have color filled the shoulder of the nose cone, that little gap of white will show through unless the cone is on really tight.

DSC_8850 (1).jpg
 
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hcmbanjo

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Very nice work!
Those card stock nose cones are a bear - Yours looks great.
 

GlenP

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Many thanks! I realize the cardstock cones can be somewhat polarizing, like flame fins, you love em or you hate em. I like the challenge and simplicity of building a rocket from a sheet of paper, 2d printing instead of 3D printing. I just mostly use the patterns from @gpoehlein (Greg P) here or the @SpaceAXEplorer (Eric Truax) patterns (which seem to be hard to find on the internet now) for the nose cones.


I am a Recovering BAR, so here is what I use for the recovery stuff, I will cut a foot or so of some Mylar tape for the streamer. The elastic goes into the nose on a paper fold over patch. The Kevlar is tied to the top of the engine hook and under the top centering ring. I rolled another lug from some paper scrap and glued that to the Kevlar at the end of the body tube for zipper prevention. That’s about it. I will swing test this and add clay nose weight for a C engine, but I may never see it again on a C, this is much lighter than an Alpha, it might come close to max alt of a Wizard on a C, maybe. Depends on how much extra weight I add to maybe keep the max altitude down. But I may just stick to A or B engines.

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GlenP

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Well, after installing the streamer and putting this on the scale, no wadding, it weighs in at 1 oz, and according to the old Estes catalogs the original weight spec is 1oz. So much for building a lighter version of the kit as a cardstock rocket! If you primed and painted the kit, you might have a hard time building it to 1 oz, maybe. I think the 24mm nose cone pattern I used here is an inch or so longer than the kit cone, and I might have gone a little thick with the clear coat. But anyway I expect this thing could bust through 1500’ on a good day on a C.
 

GlenP

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I decided to print up the 13mm power version. So far seems to go together well enough. The nose cone and top of the body tube is 18mm. The boat tail terminates at 13mm. I think the fin design is about right for this size model, with the variable ply thickness. The 18mm power model could maybe have used some stronger fins with more plies, maybe. The story so far:

8E386821-33B0-4032-A69E-5A556D0CE523.jpeg

PS - I found a few more yards of Kevlar in another bin, I thought I was out, glad I found some.
 

banjonate

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Very nice work there!

I haven’t gotten the hang of paper nose cones yet; I recently built one with a simple conical one, but as far as any real shape is concerned, I just defer to balsa.

Great detail work as well.
 

GlenP

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Thanks! I have struggled with the nose cones in the past, having a good set of dowels the right dia helps, and tweezers for the topmost parts. But, sometimes I just feel like I should just order a bag of plastic and balsa cones to go along with these builds, they look so much better.

I just had to knock this mini version out, now to get back to the Cylon Raider model...
 

GlenP

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I found a BT-5 nose cone in my parts bin, white plastic so I won’t have to paint it, and I thought it would be cool to flip the transition and make an 18 mm power version of my downscale. I put about as much clay in the small nose as would fit, hopefully that is enough, will swing test it to see if it needs more.

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GlenP

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Many thanks! These are just small tweaks to the solid classic design by one of the greats. That boat tail, those fins, instantly recognizable. I really like how these cardstock fins simulate the airfoil and thickness taper with the contoured plies. They should be strong enough for LPR. My favorite is that sub-min-dia version that goes from an 18mm motor mount to a 13mm nose cone. I used the larger sized fins on that one. It just looks fast. Here is the PDF template for that last one. I changed up the "USA" type a little to look a little more like the original. Kind of like magic to make this much fun from a single sheet of paper and a nose cone...

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low-res screen shot, don't print this, print the attached PDF.
 

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GlenP

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One last glamour shot after a clear coat, satin (semigloss) it gives it a good sheen without too much.

2A510A8F-CAD2-4874-966C-ABA3F658ECD3.jpeg

I mask off the paint stick since I have had a few rockets get stuck when the new paint bonds with the old paint, this helps keep the paint from spilling into the motor mount and forming a bond with the paint stick.
 
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