Flying with an unfilled weave?

[LakeCapt]

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?

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

[Kevin Horton]

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

I'm not sure I would want to try this. The results would probably be
somewhere between like having frost on the wing and 40 grit sand paper.

Many people have gone off the end of the runway when trying the "I wonder
if it will fly with frost on the wing" experiment. 40 grit sandpaper is
used to simulate a thin layer of rough ice on the leading edge of the
wings as part of the icing approval flight testing on recent transport
category aircraft. I've flown these flight tests on two different types,
and there is a very large lift loss if the slats are retracted - something
like 40% loss in maximum lift IIRC.

So, I would spend the time to get a fairly smooth surface, at least up to
the point of maximum thickness of the wing. The aft part of the wing is
less critical, so you might get away with leaving the weave unfilled there.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Roger Halstead]

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
Return address modified due to dumb virus checkers

[LakeCapt]

Roger Halstead > wrote in message >...
> On 20 Dec 2003 15:47:22 -0800, (LakeCapt)
> wrote:

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

Sorry I wasn't so clear. You've generally touched on the major
points. The level of surface finish I am suggesting is as follows:

1) Construct a KR wing with an outside surface of one contiguous piece
of foam for the structure in front of the forward spar (the D
section), and a second single contiguous piece of foam between the
front and rear spars.

2) Cut this foam with hotwire from polystyrene similar to
A) Mike's KR wing (Ez-style):
http://www.fortunecity.com/marina/anchor/270/wing.html
or B) Mark's sanded-down urethane method:
http://home.hiwaay.net/~langford/owings.html

3) Sand the foam with a long straigt edge, as shown on Mark's page
(leaving out the joggle around the spar). This should leave a
*relatively* flat substrate/airfoil on which to glass.

4) Glass the wing wing a span-wise layer of glass top and bottom.
When layed-up from root to tip, this removes any possible glass
overlap joggle except on the leading edge.

5) Use peel-ply over the entire glass surface, leaving the fine
reciprocal weave of the Dacron exposed once the peel-ply is removed.
This is roughly the same roughness as your standard rag-and-tube
dacron covered plane (before dope).

6) Paint the wing with a primer like Smooth Prime. This should fill
just a little, and leave a good surface for a top coat.

7) Paint the wing with a final finish, which would provide minimal
filling ability but protect the surface.


So why all this hassle? The alternative is, of course, hundreds of
hours of sanding and filling micro to get that glass finish, which may
take as much time as building the rest of the structure on a plane
like a KR.

If one was happy with a 100mph cruise, this seems like a quick way to
produce a set of wings. The question is, again, is this safe from a
"draggy" surface standpoint on a NACA 4-digit airfoil.


Thanks for your input.

[Fred the Red Shirt]

(LakeCapt) wrote in message >...
> 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?
>
> The looks would probably suffer, but how about performance and safety?
> All opinions and ideas are welcome.

Along these lines I keep thinking about the dimples that are put on golf
balls ot reduce boudary layer seperation.

Are wings too broad for soemthing like that to be useful?

--

FF

[Nicholas Cafarelli]

I believe what you are seeking is a better way to achieve smooth
wingskins. I will propose two methods which have achieved varying
levels of success.

Method One:

Per the late aircraft designer/builder/pilot/writer Alex Strojnik,
outlined in his book, Low Power Laminar Aircraft Technologies, lay up
on a sheet of plexiglass, when the skin has partially cured peel it
off the plexiglass and place it over the wing smooth side up, stretch
another cloth - not fiberglass - over the wing weighting the
overhanging edges until the skin cures. He used about 40 lbs of
weight total on 4 foot sections. Strojnik claims this will work,
given practice, three out of four times. His idea of "working" was a
skin with virtually no defects, correct to "within 0.01 in." Your own
idea of acceptable might be much more reasonable. He also cautions
that at first it will work only half the time. Again when he says
"work" he means virtually perfect skins. He used this method to
produce d-cell leading edge skins continuous from upper spar to lower
spar. His d-cell was pointed toward the ceiling when he formed these
skins. He bonded them after forming them.

As another poster pointed out, it is the leading edges which is most
important.

Method Two:

Perform a normal layup directly on the wing, cover the wing with mylar
sheet, bag the wing, apply moderate vacuum until cured. This method
works very well on smaller sections and can work with larger sections
if they are accurately formed and sufficient care is taken. Among RC
modelers this method produces consistent mirror like finishes with
very little sanding.

The two most important factors to achieving a smooth surface are:

A smooth underlying surface.

A smooth surface contacting the outer surface of the layup while it
cures.

Any method that manages to create these two things will succeed. It
would be prudent to experiment with these ideas on smaller test
sections to hone your skill before doing a "real wing".

Fly right.

nc