Using Balsa wood

[Lou Parker]

In many area's on my wood structure it calls for a filler. Usually
spruce, but for no other reason but to fill a gap. These are not
structural in the least, only to fill (i.e. on top of the spar a 1/4"
strip of wood to keep the plywood skin from saging in between the wing
ribs). Has anyone used Balsa wood to accomplish this to save on
weight. There seems to be alot of little areas like this in my plans.
Lou

[Rich S.]

"Lou Parker" > wrote in message
om...
> In many area's on my wood structure it calls for a filler. Usually
> spruce, but for no other reason but to fill a gap. These are not
> structural in the least, only to fill (i.e. on top of the spar a 1/4"
> strip of wood to keep the plywood skin from saging in between the wing
> ribs). Has anyone used Balsa wood to accomplish this to save on
> weight. There seems to be alot of little areas like this in my plans.

The only place I used balsa was on the fairing to shape the back of the nav
light housings on the wing tips. While every ounce counts, is there really
that much cubic volume where the difference between spruce and balsa would
add up to a significant amount (on the cheeseburger scale)?

Rich S.

[sean trost]

Hi Lou,
I am currently in the process of rebuilding a Jurca Mj-5 that has balsa
as a filler in many areas such as the firewall, some areas in the
fuselage and the wingtips and elevator tips are also balsa. The
condition of the balsa after 15 years is just abysmal. I would go with
polyeurathane foam or spruce.
all the best
Sean Trost


Lou Parker wrote:
> In many area's on my wood structure it calls for a filler. Usually
> spruce, but for no other reason but to fill a gap. These are not
> structural in the least, only to fill (i.e. on top of the spar a 1/4"
> strip of wood to keep the plywood skin from saging in between the wing
> ribs). Has anyone used Balsa wood to accomplish this to save on
> weight. There seems to be alot of little areas like this in my plans.
> Lou

[Vaughn]

"Lou Parker" > wrote in message
om...
> In many area's on my wood structure it calls for a filler. Usually
> spruce, but for no other reason but to fill a gap. These are not
> structural in the least, only to fill (i.e. on top of the spar a 1/4"
> strip of wood to keep the plywood skin from saging in between the wing
> ribs). Has anyone used Balsa wood to accomplish this to save on
> weight.

Some early fiberglass gliders use balsa as a filling in the wings and
mildew is an issue. I think that there is a procedure to chemically treat
the balsa inside the wing to kill it.

Vaughn

[Nolaminar]

Oldest fiberglass aircraft date from 1957. German made sailplanes and they used
balsa core and have had very few problems.
A fw of thsesl of these same older designs are still flying and have had
minimal problems if properly cared for and sealed properly...just as in any
wood aircraft.
GA

[Richard Riley]

On 6 Dec 2003 13:11:20 -0800, (Lou Parker) wrote:

:In many area's on my wood structure it calls for a filler. Usually
:spruce, but for no other reason but to fill a gap. These are not
:structural in the least, only to fill (i.e. on top of the spar a 1/4"
:strip of wood to keep the plywood skin from saging in between the wing
:ribs). Has anyone used Balsa wood to accomplish this to save on
:weight. There seems to be alot of little areas like this in my plans.
: Lou

On the prototype Berkut we used end-grain balsa as a core in a
fiberglass sandwitch structure. 3 years later one area, where water
pooled regularly inside the fuselage, had the balsa rot away. Other
areas were fine. We went to PVC foam, and later to SAN foam.

[frank]

Wouldn't the spruce fillers act as a lamination on the spar caps?

[Corrie]

That 1/4-thick strip may well carry flight loads from the skin to the
spar.

You might also read veeduber's "wood rant":
http://groups.google.com/groups?q=group:rec.aviation.homebuilt+author:veedu &rnum=18

(Lou Parker) wrote in message >...
> In many area's on my wood structure it calls for a filler. Usually
> spruce, but for no other reason but to fill a gap. These are not
> structural in the least, only to fill (i.e. on top of the spar a 1/4"
> strip of wood to keep the plywood skin from saging in between the wing
> ribs). Has anyone used Balsa wood to accomplish this to save on
> weight. There seems to be alot of little areas like this in my plans.
> Lou

[Martin Morgan]

frank wrote:
> Wouldn't the spruce fillers act as a lamination on the spar caps?

Yes but only where they are attached. Since "between the ribs" was
mentioned I'd say there was no benefit.

However, if the plywood skin is handling any loads eg. torque loads,
then the balsa may be a problem!!

Balsa is used in the Knight Twister (cantilever biplane). It has a
plywood torque box (probably a better term here), and uses the balsa to
fill in the leading edge and tips.

So yes, balsa (or foam) can be used in some places for lighter
structures. But I'd be wary of using it where it attaches two stronger
materials..

Regards

Martin Morgan

[Lou Parker]

Martin Morgan > wrote in message >...
> frank wrote:
> > Wouldn't the spruce fillers act as a lamination on the spar caps?
>
> Yes but only where they are attached. Since "between the ribs" was
> mentioned I'd say there was no benefit.
>
> However, if the plywood skin is handling any loads eg. torque loads,
> then the balsa may be a problem!!
>
> Balsa is used in the Knight Twister (cantilever biplane). It has a
> plywood torque box (probably a better term here), and uses the balsa to
> fill in the leading edge and tips.
>
> So yes, balsa (or foam) can be used in some places for lighter
> structures. But I'd be wary of using it where it attaches two stronger
> materials..
>
> Regards
>
Yes, part of it calls for in between the ribs on the spars for a
filler. That is the front and back of the main spar and across the
rear spar as a filler. Also on the trailing edge of the flaps,
ailerons, and elevator control, (lets see if I can explain this) where
the trailing edge meets the structural pieces. On top of these areas
plywood will be glued, and then Dacron. At the part where the trailing
edge meets the structural pieces, it calls for a 45 deg. filler to
help round out the plywood. Now, have I confused everyone, or just
a few?
Lou
> Martin Morgan

[Orval Fairbairn]

In article >,
(Lou Parker) wrote:

> Martin Morgan > wrote in message
> >...
> > frank wrote:
> > > Wouldn't the spruce fillers act as a lamination on the spar caps?
> >
> > Yes but only where they are attached. Since "between the ribs" was
> > mentioned I'd say there was no benefit.
> >
> > However, if the plywood skin is handling any loads eg. torque loads,
> > then the balsa may be a problem!!
> >
> > Balsa is used in the Knight Twister (cantilever biplane). It has a
> > plywood torque box (probably a better term here), and uses the balsa to
> > fill in the leading edge and tips.
> >
> > So yes, balsa (or foam) can be used in some places for lighter
> > structures. But I'd be wary of using it where it attaches two stronger
> > materials..
> >
> > Regards
> >
> Yes, part of it calls for in between the ribs on the spars for a
> filler. That is the front and back of the main spar and across the
> rear spar as a filler. Also on the trailing edge of the flaps,
> ailerons, and elevator control, (lets see if I can explain this) where
> the trailing edge meets the structural pieces. On top of these areas
> plywood will be glued, and then Dacron. At the part where the trailing
> edge meets the structural pieces, it calls for a 45 deg. filler to
> help round out the plywood. Now, have I confused everyone, or just
> a few?
> Lou
> > Martin Morgan

Years ago, I had a friend who built a Thorp T-18 with painted balsa tail
tips. It was tied down outside; one day he pulled a fin tip off for
maintenance and found it sopping wet! Be very wary of using balsa if it
gets exposed to moisture.