Sanding composites

Tim Ward wrote:


Well, on sailplanes, anyway, you sand to make sure the airfoil is the
right
shape, (shrinkage can occur over the spars after some time out of the
molds), and to make sure that any waves in the contour are less than
..004
inches.


That's another reason to try scraping. Scrapers can be filed to a
particular curve for just that sort of work.

--

FF

wrote in message
oups.com...

Tim Ward wrote:


Well, on sailplanes, anyway, you sand to make sure the airfoil is the
right
shape, (shrinkage can occur over the spars after some time out of the
molds), and to make sure that any waves in the contour are less than
.004
inches.


That's another reason to try scraping. Scrapers can be filed to a
particular curve for just that sort of work.

--

FF

The curvature changes continuously chordwise, and most sailplane wings have
taper, so the curvature will change with the spanwise station as well. So
it's difficult for me to see how you could cut a single curve that would
match.
Now, for a constant chord wing, that might make an interesting production
technique:
Build your wing, then build up an extra layer of filler, then "extrude" the
whole wing panel through a CNC cut scraper, getting exact, smooth
coordinates on the way.

Tim Ward

Tim Ward wrote:
wrote in message
oups.com...

Tim Ward wrote:


Well, on sailplanes, anyway, you sand to make sure the airfoil is
the
right
shape, (shrinkage can occur over the spars after some time out of
the
molds), and to make sure that any waves in the contour are less
than
.004
inches.


That's another reason to try scraping. Scrapers can be filed to a
particular curve for just that sort of work.


The curvature changes continuously chordwise, and most sailplane
wings have
taper, so the curvature will change with the spanwise station as
well. So
it's difficult for me to see how you could cut a single curve that
would
match.

You can do that by skewing the scraper and adjusting the angle of
atttack between the scraper and the wing.

How do you vary the curvature when shaping with sandpaper?

Now, for a constant chord wing, that might make an interesting
production
technique:
Build your wing, then build up an extra layer of filler, then
"extrude" the
whole wing panel through a CNC cut scraper, getting exact, smooth
coordinates on the way.


Yes, that would be easier though I still don't see how it would be
done with sandpaper, and think it would be especially difficult
with sandblasting!

It is also the case that not all homebuilt aircraft wings are
fabricated
to the same exacting tolerances as state-of-the art sailplanes, right?
--

FF