|Dec 17, 2008, 05:25 PM|
Paper or Cardboard Tubing Source
Because I occasionally see packaging with cardboard tubing, intuition tells be that there should be a source out there. Can somebody point me in the right direction?
Years ago, I built a thermal duration glider that had tubes in the wings for adding ballast centered on the CG.
These tubes were made of a light-weight cardboard (or heavy paper) and had a 1/2 inch inside diameter. I made 2 ounce lead-filled brass tubes to slide into the paper tubes.
It was a very flexible system, as I could fly with zero ballast, all the way up to several pounds. For ballast weights between zero and the max, I made wooden dowel spacers to fill unused space in the paper tubes.
Now, today, for a new project, I need to find a source for paper/cardboard tubing - not only for 1/2 inch ballast slugs, but for use as servo cable conduit in a large wing. A 3/8 inch I.D. would likely work for servo cable use.
Does anybody out there know of a paper tubing source?
|Dec 17, 2008, 07:19 PM|
Joined Sep 2003
Do a GOOGLE search on model rocket tubes. You will get a lot of hits on suppliers for tubes of differing lengths, diameters and wall thickness.
For servo cables, just handroll a tube from typing paper and tape the seam.
|Dec 17, 2008, 08:13 PM|
Use large diameter drinking straws, cut them lengthwise and shove the cables inside. You can then secure the straws gluing to the structure any convenient place.
Concerning changing the weight of the model, you will have better maneuverability if the added or removable weight is concentrated at the CG. It is easier to turn a mass on itself than distribute it in tubes in the wings and have to accelerate a mass far away when banking the aiplane.
|Dec 19, 2008, 12:07 AM|
Andrew0820: DUH! I should have thought of model rocket tubes long ago!! Today I found a package of cardboard tubes at one of my LHS's. They are the exact size I need.
Zor: Two excellent comments.
However, the servo connectors I have will not fit in any straws I am familiar with, so I will not likely use your straw suggestion for this purpose, but rather build my own tubing. I have a long 3/8" diameter nylon rod that I will coat with a suitable release agent, and wrap a strip of paper around in a sort of spiral fashion, spray with a thin coat of glue like 3M 77, and wrap once again but in the opposite direction.
Since I do not expect any need for strength, I will probably stop with two layers and remove the paper tube from the rod. If it turns out I need more layers, I can do that.
As for the ballast, the tubing mentioned above is an exact match for the several dozen cylindrical 2 oz brass-covered lead slugs that I already have.
As an engineer with several dynamics courses under my belt, I am familiar with the momentum (inertia) that occurs when rotating a mass, and would under other circumstances add ballast in the fuselage, minimizing this momentum - as you recommend.
However, in this specific case, adding ballast to the fuselage is not practical - which has lead me to the wing-based ballast configuration. Rest assured, I will keep ballast as close to the fuselage lengthwise centerline and CG as possible.
In the FWIW column, the particular plane I expect to use the ballast in is being built with two 132" wingspan wings: one with spoilers only, and the other with flaps, ailerons, a lower dihedral, and no spoilers.
The ballast option will be built into the aileron wing only, as the spoiler wing is expected to be flown in relatively calm air (read that "little or no wind")
Thanks to both of you for your replies.
|Dec 19, 2008, 12:51 AM|
For paper tubes for ballast, as Andrew0820 said, rocket body tubes. I ordered some a while back, but did not save the vendor. There are several options.
For the servo lead conduit tubes, rolled printer weight paper (20lb.) works fine. Roll it onto a wooden dowel (no need for more than 1-1/4 wrap) a bit smaller than the hole in the wing ribs that you will pass it through. Slide it in and hit a few ribs at the paper with CA. Done.
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