Flying with an unfilled weave?

On 20 Dec 2003 15:47:22 -0800, (LakeCapt)
wrote:

Hello,

Has anyone seen any data/research showing the performance gains of
filling the fiberglass weave of a composite aircraft such as a KR-2?

For example, if a KR is built with a RAF-48 or NACA wing
(non-laminar), if layups were done over a smooth substrate (smooth
foam), and the weave of an "average" weave glass was left unfilled
(after peel-ply), how would speed be effected? Dacron-covered planes
of course get by with a bit of weave showing.

If the cruise speed of a given KR-2 was 120mph "filled," any idea on
how
much slower it would cruise if left bare but painted?

I'm not sure I follow all this and maybe I'm missing what you are
asking but...

With peel ply you can (using different materials) get a range from a
coarse surface that would make a good wing walk to just a dull, but
smooth finish ready for paint on par with something between 120 and
220 grit depending on the weave of the cloth. At a speed as slow as
120 mph I'd not expect to see much difference.

How is it bare, but painted? To me, if its painted, it's not bare.

Using the finer weave peel ply leaves a surface that takes paint and
leaves a very smooth finish.

Now that is not the same as block sanding which leaves a smooth *and
flat* surface.

Dacron, Rayon, and Nylon all make a good peel ply if the cloth is
heavy enough. I have 4 grades, or weaves. The coarsest takes a hefty
pull to get off the resin, while the fine comes off like tape, BUT the
fine really needs to be heavy enough that it doesn't fall apart when
removing it from the resin. ALL of them leave a finish that has none
of the fiberglass cloth weave showing.


The looks would probably suffer, but how about performance and safety?
All opinions and ideas are welcome.

Again, if we are talking about a plain paint job the looks should be a
glossy finish with no loss of performance of safety.
OTOH if you are comparing that finish to a surface that was block
sanded to be flat and smooth you will notice some speed difference.
There has been a Glasair III at Oshkosh for a few years that has had
the wings filled and block sanded to contour with in just a few
thousandths of an inch. (they claim) The surface has no visible
irregularities and looks like a mirror. As I recall they claim an
extra 5 knots or so and that is well over 230 knots. That is where
you fill and sand, fill and sand, fill and sand...

I'm not advocating eliminating sanding. Normally there are enough
irregularities a good block sanding is required. The same it true for
junctions of lay-ups as well as fairings. Probably a good many
hundred hours. BUT the fill and block sanding to give a super finish
that is flat and true takes hours and hours...some have reported up to
several thousand hours doing that kind of work. This is true of wings
made from shells like the Lancair or Glasair as well as wings made
from lay-ups over a base.

A rough surface on a non laminar flow wing does not necessarily
translate to a safety issue.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
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