Inspired by the recent discussion on carbon tubes, and those beautiful F1D
motor tubes that Tomasz Momot uses, I decided to try wrapping a few of my
own. For mold I tried similar technique (developed by Ossi Kilpeläinen in
the 70's) that I used in late 80's building P-30 body tubes and later wing
spars for F1B: a piece of PVC tubing is slided over a stiff mandrel, tube
is molded onto the tubing, and once the resin is cured, the mandrel is
removed and then the tubing is stretches so that it thins a bit and the
tubing pops off.
I recall that Tomasz told that he uses uni-directional carbon rowing for
his tubes, so this is what I tried first. I managed to get some parts of
the laminate off, but it was way to patchy and flimsy to be off any use.
Obviously it would be really hard to spread the rowing onto an even yet
thin layer. So I decided to try carbon fiber tissue next. Several years ago
I had bought some tissue that seems to be about 10g/m2 (similar thickness
is sold currently by several companies). The problem with tissue is that is
is quite stiff, but also somewhat fragile, so wrapping it around the
mandrel turned out to be difficult. After a few trials I ended up making a
narrow (12mm wide) strip, that I spiralled around the mandrel, with slight
overlap at the edge. This thing I managed to wrap, added some tape on top
to push the carbon onto the mandrel and let cure. The tubing was somewhat
fragile, so I could not get all off intact (it tore apart when I stretched
the mold tubing), but I got off a 20cm piece that is enough to evaluate.
Bending in hands the tubing does not seem any stiffer than comparable F1D
motor tube. But it is heavier, the 20cm (8in) piece weights 280 mg. And it
also seems quite fragile, so I doubt it would tolerate broken rubber any
better than balsa. So far, no cigar.
The 10g/m2 carbon paper might be useful material for making thinner tubes
(such as wing pylons or prop spars), but I fear that it would be really
hard to wrap around tight mandrels. At least at longer pieces; I have mode
some wing post sockets out of it though.
-Tapio-
- application/x-ygp-stripped attachment: stored
Received on Mon Sep 16 2013 - 23:51:48 CEST