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Old 03-17-2019, 09:35 AM
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blackshire blackshire is offline
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Location: Fairbanks, Alaska
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Quote:
Originally Posted by Doug Sams
If you can mix in some fiberglass matting, that might enable making it lighter and also less brittle. I would mold it with the bottom open to facilitate inserting the matting. But some experimentation will be required to find a way to keep the wall reasonably thin.


Doug.
What is preferable to use depends on the part size, and the flight stresses it's expected to undergo. Kevlar veil (it's rather like panty hose--in fact, actual panty hose might be fine for some applications) or the equivalent glass or carbon fiber cloth, and a long-curing (an hour or more) epoxy, or polyurethane casting resin, should be fine for model rocket nose cones, transitions, and tailcones (and fins, which could use foam cores). One "wets" the mold cavity with the resin (after applying an appropriate mold release), then presses the cloth into it (a gel coat can also be applied if desired--as is often done with molded fiberglass boat hulls--to give the finished part a shiny surface). Toward the top of that size range (BT-70 or so and up), more layers of the Kevlar, glass, or carbon fiber could be built up in the mold, to provide additional strength. Also:

For LMR/mid-power rockets, using heavier glass, Kevlar, or carbon fiber cloth would ensure ample thickness and strength. Another option that could be implemented along with the heavier cloth--although it would be best done outdoors--would be to use polyester resin. It stinks abominably until it has cured, but it is very strong and also has a little flexibility, which is good for such large rocket parts (the pre-made fiberglass R/C model airplane and R/C model sailplane fuselages--and R/C powerboat and sailboat hulls and racing car bodies--are made of heavier glass cloth and polyester resin). If you have neighbors with whom you are feuding, making such rocket parts in the yard or on a balcony or deck (when the wind is blowing toward them) could serve two purposes at once... :-)
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