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Paper shroud as structual body tube? Astrocam Carrier plans

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Tramper Al

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Hi,

As a big fan of camera rocket models, I was pleased to recently discover plans for an Astrocam Carrier by Fred Williams, from Sport Rocketry, 1995.

http://oldrocketforum.com/attachment.php?attachmentid=44335

My question is about card stock paper shrouds. I know they were once much more commonly employed, but I think I have only built one rocket that called for a paper shroud, and that was the Camroc Carrier. In that case, however, the shroud is purely aerodynamic/aesthetic, as the balsa adapter for the payload section sits right into the body tube proper, so that the shroud is simply a second skin, if you will. You could certainly build it and fly without the shroud.

In the Astroccam Carrier plans, however, the paper card stock shroud seems to form the entirety of the connection between body tube below and payload above, and I wonder how can this be strong enough for the rigors of flight and recovery? For use with D engines, the modeler suggests plywood fins and heavy fillets, but I would have thought the weak point would be the paper shroud. Am I wrong? Should it be strengthened somehow? Or am I misreading the plans? Getting a perfectly straight alignment with a paper shroud may be another issue, I realize.

Thanks in advance . . .
 
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Tramper Al

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Thanks Chris, that makes sense. It led me to another Apogee article on the subject of making transitions.

https://www.apogeerockets.com/education/downloads/Newsletter349.pdf

Now, in both the figures in your article and all the details and figures in the other, it seems clear that the body tubes small/large actually are connected to one another directly by a coupler, and that the shroud simply provides an outer sheeting to the rocket. This makes sense to me, and I can see that the connection would be strong, with or without a covering shroud.

What puzzles me about the Astrocam Carrier plans (seen in figures C and D as well as the main full rocket figure) is that a long segment of the body is simply a hollow paper shroud, and the two body tubes are several inches short of coming into contact. The BT20 aft body tube seems to be sized (9") just long enough to reach into the bottom of the shroud, while the top of the shroud is glued to a 1/32" lip on the built BT56 coupler.

I think perhaps what I should do is simply use a much longer BT20 that comes all the way up to reach a BT20 balsa block ringed into the BT56 coupler. Or I could seek out a 56-20 balsa reducer. The shroud would then be the outside skin, and that's more or less how the Camroc Carrier goes together.

I am just wondering if I am misreading the design, or in fact (reinforced) paper couplers have been or are being used as actual structural components in place of body tubes.
 
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kjohnson

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For LPR this construction is just fine. You can adjust the weight(thickness) of the paper to accommodate for loads/ impulse.
An example that is commonly used in NAR competition are eggloft duration models where a small motor tube is attached to a paper cone that serves as the main airframe, with an egg capsule as the nose cone.

You do need to make sure the connection between the tubes and the transition is secure and straight. Using s slightly longer tube section with a centering ring that increases glue area in the inside of the transition can be helpful.

kj
 

Nytrunner

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There are always ways to reinforce it. I made a nosecone for my induction rocket by using 'shrouds' to form a cone and transition, then filling the tip with epoxy and smearing it on the walls. Survived a fall from 200 ft when it came off the shock cord. cereal box bulkheads/rings are also good for making it more solid.
 

samb

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Here is an example of what kjohnson was talking about:

IMG_0731.jpg

The Gassaway 2 minute egg design has been around since the '80s. While certainly not an everyday flier, mine has held up to high speed piston launches under D12 power quite well. 65# cardstock with thin CA coating the inner surface to add a little ejection charge debris protection. The motor tube extends about an inch and 1/2 or so into the shroud with a 5055 centering ring for support and extra glue surface. I had an 18mm model with a shroud/airframe made with Epson photo paper. ASP sells a kit of this design with a cool aluminized shroud. Tuff Enuff !


http://www.nar.org/wp-content/uploads/2014/05/TwoMinuteEgg-B-C-EL-Gassaway.pdf

http://www.asp-rocketry.com/ecommer...lofter-Kit.cfm?item_id=235&parent=9&navPanel=
 
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Tramper Al

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Thank you, so it is something that is done. I may have to build it the conventional way, though. OED confirms my impression that a shroud is something that covers up something else.
 

K'Tesh

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IINM, Apogee also has a video showing how they use cardstock shrouds for one of their lightweight competition rocket designs.

[EDIT] Yup... I was right.

[video=youtube;L6G34z5daHE]https://www.youtube.com/watch?v=L6G34z5daHE[/video]

BTW... Welcome Back Tramper! You've been gone for awhile.
 
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Tramper Al

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BTW... Welcome Back Tramper! You've been gone for awhile.
Thanks! Yes, in and out of the clouds. Back building this winter, and planning some big E-G launches mid-(frozen) lake in early 2017.
 

GlenP

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If you coat the inside of the shroud with White Glue-All it will add some strength. Doubling up the cardstock is also a good trick, I roll body tubes two-ply and they come out very strong. Another lighter option is to glue the white copy paper to the cardstock, print up the template on regular paper, then use a glue stick or thin layer of white glue all to attach that to the cardstock. Roll into the transition shape before the glue totally sets up. once dry it will be fairly strong, and you can coat the inside with another layer of white glue, or epoxy if you think you need the extra strength. do some experiments with it, paper and glue is cheap.
 
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