I want to make several samples of materials for covering my plane,
(plywood, composite, ceconite, etc....)
And I would like to find the difference with some kind of scale or
pressure meter to find the breaking points. Has anyone done this?
Lou

Is this for structural or non-structural covering? Each of the listed
material have significant
differences in their properties, so the use really needs to be defined
first. The intended use
is going to help define what materials you can use and in what grades
or forms or thickness,
or orientations. For example, composites for structural applications
are going to be laid up
and reinforced one way, so that they take the designed loads without
failure, while those parts
that are things like fairings, hatches ect. are going to be done
another way.

A good example is my Fairchild. It uses ceoconite as a structural
cover in some places, but
others, it is used as a surface protector. Same material, but
completely different uses and
application methods.

Craig C.

Well,,,,,,,,,,, at this point I'll have to say half and half.
The plans call for plywood over the ribs of the wings, structural.
the other parts are to cover the fuselage but the strutural is taken
care of on the inside.
Lou

For the fuselage, I'd stick with either aircraft or marine grade ply
for glue strength between plies.
If it's all flat areas, then 90 deg. layups are going to be the least
expensive and should work fine. If there are curves
then you are probably going to be limited to using aircraft grade with
45 deg layups. Do the
prints give you any guidence on thicknesses to use for the various
areas? If so, then there are
tables out there that give the various strength data vs the number of
plies vs the ply materials. They
also give the testing method used to generate the data. For fabric,
the Maule tester is the accepted
method. Ply is done by tension and twist test if I remember correctly,
coupled with steam testing of
the bonding agent. Composite is done by tension, compression and
impact tests. Tension and
compression tests are reasonable easy to duplicate, impact can be done
too, but is most likely
going to be a bit more subjective without a decent lab setup.

When in doubt, talk with the designer is the best advice. Unless there
is a complete egineering
workup with the design, that's about the only way to know why the
particular material selections.

Food for thought...

Craig C.

"Lou" > wrote in message
oups.com...
> Well,,,,,,,,,,, at this point I'll have to say half and half.
> The plans call for plywood over the ribs of the wings, structural.
> the other parts are to cover the fuselage but the strutural is taken
> care of on the inside.
> Lou

I did it with different fiberglass years ago. I made lay ups with different
types and amounts of glass cloth. I cut my samples in 1" wide coupons and
took them to a testing company simply chosen from the phone book. Since I
didn't require any written reports with the test results, they did it
extremely cheap. I think the pulled 8 coupons for $20, in about 1985.
Roughly $40 today.

"Lou" > wrote in message
ups.com...
>I want to make several samples of materials for covering my plane,
> (plywood, composite, ceconite, etc....)
> And I would like to find the difference with some kind of scale or
> pressure meter to find the breaking points. Has anyone done this?
> Lou
>

See http://www.hpaircraft.com/hp-24/update_22_oct_07.htm for pictures of the
"Break-A-Tron"

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

That will break it, but will it measure?

On Oct 29, 4:09 pm, Lou > wrote:
> That will break it, but will it measure?

http://www.youtube.com/watch?v=ZyVD0FBLiFQ

On Sun, 28 Oct 2007 17:34:42 -0700, Lou > wrote:

>I want to make several samples of materials for covering my plane,
>(plywood, composite, ceconite, etc....)
>And I would like to find the difference with some kind of scale or
>pressure meter to find the breaking points. Has anyone done this?

The problem is, what question are you really asking?
In the labs we made coupons that tested tensile strength and
elongation in different planes such as pull yield, compression and
perpendicular to the surface. If it's shear then you have to define
over what length. If it's a pressure yield, over what area and how is
it distributed.

Many labs have the equipment to do the tests, but the problem is
defining what tests need to be done to display the pertinent results.
IOW, what strength and in what plane/axis, or what information do you
really need?

Roger (K8RI)
> Lou

On Mon, 29 Oct 2007 16:09:47 -0700, Lou > wrote:

>That will break it, but will it measure?
Even then does it give results that are appropriate?
It appears to give tensile strength in pull, but that is only
indirectly related to aircraft skin strength.

Roger (K8RI)

Well Roger, I was really just looking for a couple of simple
answers. Seeing how this is an experimental hobby, I thought
that I would compare the strengths of the plywood that the designer
put on the plans (old design) against some newer materials and idea's.
It may cost me a few bucks but I want to measure strength and breaking
points against each other.
Lou

In article om>,
Lou > wrote:

> Well Roger, I was really just looking for a couple of simple
> answers. Seeing how this is an experimental hobby, I thought
> that I would compare the strengths of the plywood that the designer
> put on the plans (old design) against some newer materials and idea's.
> It may cost me a few bucks but I want to measure strength and breaking
> points against each other.
> Lou

You should be able to find that information in the materials handbooks.

I would start with a Google search for "Forest Products Laboratory",
which is the central source of information on wood products. They test
materials and publish the results.

On Oct 31, 10:02 am, Orval Fairbairn >
wrote:

> You should be able to find that information in the materials handbooks.
>
> I would start with a Google search for "Forest Products Laboratory",
> which is the central source of information on wood products. They test
> materials and publish the results.

That's true as far as it goes. However, the design and development of
sport aircraft occasionally demands that one innovate beyond the
boundaries of what established laboratories and institutions have
deigned to test and approve.

Consider the practice of using cellulose fiber composite panels for
the reinforcement of truss junctions in chordwise wing members. First
developed in the 1930s, this practice was validated in a successful
glider design and is currently under evaluation for at least one light
sport aircraft.

However, it would never have seen the light of day of some poor guy
hadn't snipped a bunch of wing rib gussets out of cereal box cardboard
and tried them out. Necessity is the mother of invention. Theory often
follows practice.

Thanks, Bob K.

"Lou" > wrote in message
ps.com...
> That will break it, but will it measure?
>

What kind of measurement would you like to see?

>
> What kind of measurement would you like to see?


Well, I'm not sure how to put it. I want to see how other materials
and
combination of materials measure up to the original design. I probebly
will
stay with the original, but while I'm at this part, it would be, in my
opinion,
pointless not to venture down other paths while I can. The
measurements
don't even need to be a real measurement such as psi. As long as I can
have a comparible measurement. In other words, if it takes 50lb of
force
with a fish scale to break a certain peice of wood. I would compare
another
material with the same fish scale set up to have a comparable
measurement.
Lou

"Lou" > wrote in message
oups.com...
>
>>
>> What kind of measurement would you like to see?
>
>
> Well, I'm not sure how to put it. I want to see how other materials
> and
> combination of materials measure up to the original design. I probebly
> will
> stay with the original, but while I'm at this part, it would be, in my
> opinion,
> pointless not to venture down other paths while I can. The
> measurements
> don't even need to be a real measurement such as psi. As long as I can
> have a comparible measurement. In other words, if it takes 50lb of
> force
> with a fish scale to break a certain peice of wood. I would compare
> another
> material with the same fish scale set up to have a comparable
> measurement.
> Lou
>

The problem is that if you want to compare two materials for a particular
application - you need to match the way you measure the strength of the
materials with the kind of loading that will be applied when they are in the
stucture.

Example - heavy fabric and thin plywood may have similar tensile strength as
measured by your fish scale, but the fabric won't work for gussets and the
plywood will.

So, before you can decide what kind of test you should use to compare, you
have to determine how the material is loaded.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

Sounds reasonable to me. So, if I where comparing wing loads of
plywood
and fabric, how would you suggest I measure this against composite or
other materials? I'm open to suggestions.
Lou.

Lou wrote:
> Sounds reasonable to me. So, if I where comparing wing loads of
> plywood
> and fabric, how would you suggest I measure this against composite or
> other materials? I'm open to suggestions.
> Lou.
>
>

Maule fabric punch?

>> Sounds reasonable to me. So, if I where comparing wing loads of
>> plywood
>> and fabric, how would you suggest I measure this against composite or
>> other materials? I'm open to suggestions.
>> Lou.
>>
>>
>
> Maule fabric punch?

I don't think so.

The punch test tells you if your fabric is rotten, or not. The load it puts
on the fabric is a result of testing to know how much force the punch should
be able to apply, and not have the system of fabric and attachment fail, or
not.

If your punch test fails, you could develop a long rip , or a rip at a
stitch and/or glue by the rib, or in the middle of the fabric, and it could
let you fall out of the sky.

A point load like a punch is not the kind of load the (lets say) top fabric
will see. It will be an evenly distributed load, pulling up, with the glue
or stitching (on the ribs) resisting the upward lifting forces. The load at
the ribs would be a long attachment, or lots of small point loads from the
stitches, but still, the dope should be gluing the fabric to the ribs, also.

So, if there is two feet between the ribs, and the bay is 3 feet long, you
have 6 square feet of area. If you have a 20 pound per square foot wing
loading, you could have 120 pounds of force pulling at the attachments of
the ribs and spar caps. (front and rear spars) You want to know if the
fabric will fail or hold at those pressures.

You could make an airtight box with an open top, of 2' X 3', which would be
864 square inches area of the top. Glue and stitch the fabric on the top
flange (same sizes as the ribs or cap, and spar caps) of the box and put
120 pounds of force on the fabric, which would be 864 sq inches/120 lbs per
sq ft = 7.2 psi air pressure inside of the box. If it holds, you might not
fall out of the sky. <g>

You could then substitute the material you want to test for this application
(plywood, fiberglass, fiberglass/foam sandwich, aluminum foil <g>, or
whatever you want to test, and whatever holding method you want to use, and
test it.

That's my thinking in/out of the box, so to speak. Right, or wrong. I
don't know. It is how I would likely go about it. I'm not an aeronautical
engineer. I did stay at a Holiday Inn last night! ;-)
--
Jim in NC

Morgans wrote:
>>>Sounds reasonable to me. So, if I where comparing wing loads of
>>>plywood
>>>and fabric, how would you suggest I measure this against composite or
>>>other materials? I'm open to suggestions.
>>> Lou.
>>>
>>>
>>
>>Maule fabric punch?
>
>
> I don't think so.
>
> The punch test tells you if your fabric is rotten, or not. The load it puts
> on the fabric is a result of testing to know how much force the punch should
> be able to apply, and not have the system of fabric and attachment fail, or
> not.
>
> If your punch test fails, you could develop a long rip , or a rip at a
> stitch and/or glue by the rib, or in the middle of the fabric, and it could
> let you fall out of the sky.
>
> A point load like a punch is not the kind of load the (lets say) top fabric
> will see. It will be an evenly distributed load, pulling up, with the glue
> or stitching (on the ribs) resisting the upward lifting forces. The load at
> the ribs would be a long attachment, or lots of small point loads from the
> stitches, but still, the dope should be gluing the fabric to the ribs, also.
>
> So, if there is two feet between the ribs, and the bay is 3 feet long, you
> have 6 square feet of area. If you have a 20 pound per square foot wing
> loading, you could have 120 pounds of force pulling at the attachments of
> the ribs and spar caps. (front and rear spars) You want to know if the
> fabric will fail or hold at those pressures.
>
> You could make an airtight box with an open top, of 2' X 3', which would be
> 864 square inches area of the top. Glue and stitch the fabric on the top
> flange (same sizes as the ribs or cap, and spar caps) of the box and put
> 120 pounds of force on the fabric, which would be 864 sq inches/120 lbs per
> sq ft = 7.2 psi air pressure inside of the box. If it holds, you might not
> fall out of the sky. <g>
>
> You could then substitute the material you want to test for this application
> (plywood, fiberglass, fiberglass/foam sandwich, aluminum foil <g>, or
> whatever you want to test, and whatever holding method you want to use, and
> test it.
>
> That's my thinking in/out of the box, so to speak. Right, or wrong. I
> don't know. It is how I would likely go about it. I'm not an aeronautical
> engineer. I did stay at a Holiday Inn last night! ;-)

He was asking about test samples, not finished product.

For a replacement for fabric skin?

So f it punches good, it's ok, right?

My only question is how much weight is added replacing fabric.


Richard

Weight will be an issue. But that will also be part of the
comparisons.
Lou


>
> My only question is how much weight is added replacing fabric.
>
> Richard

"cavelamb himself" <> wrote

> He was asking about test samples, not finished product.
>
> For a replacement for fabric skin?
>
> So if it punches good, it's ok, right?
>
> My only question is how much weight is added replacing fabric.

My take was that he wanted to test alternative materials, like how strong
would fiberglass have to be for putting on a wing, instead of fabric. Or,
how strong would plywood have to be to replace fabric. Add to that many
different materials, and many different applications-all over the plane.

If that is not the jist of it, so sorry, I guess.

If I am right, then I don't see how you can get around testing the
alternative material in a "similar to the real application" type of test
like I described. Creativity would need to be applied to figure out other
tests for other areas.
--
Jim in NC

On Wed, 31 Oct 2007 10:28:53 -0700, Bob Kuykendall
> wrote:

>On Oct 31, 10:02 am, Orval Fairbairn >
>wrote:
>
>> You should be able to find that information in the materials handbooks.
>>
>> I would start with a Google search for "Forest Products Laboratory",
>> which is the central source of information on wood products. They test
>> materials and publish the results.
>
>That's true as far as it goes. However, the design and development of
>sport aircraft occasionally demands that one innovate beyond the
>boundaries of what established laboratories and institutions have
>deigned to test and approve.

Even fiberglass strength varies over quite a range depending on the
ratio of fiber to resin, fiber orienttion between layers, and type of
resin.

Plywood layups also vary some what.

Roger (K8RI)
>
>Consider the practice of using cellulose fiber composite panels for
>the reinforcement of truss junctions in chordwise wing members. First
>developed in the 1930s, this practice was validated in a successful
>glider design and is currently under evaluation for at least one light
>sport aircraft.
>
>However, it would never have seen the light of day of some poor guy
>hadn't snipped a bunch of wing rib gussets out of cereal box cardboard
>and tried them out. Necessity is the mother of invention. Theory often
>follows practice.
>
>Thanks, Bob K.

On Wed, 31 Oct 2007 05:19:17 -0700, Lou > wrote:

>Well Roger, I was really just looking for a couple of simple
>answers. Seeing how this is an experimental hobby, I thought
>that I would compare the strengths of the plywood that the designer
>put on the plans (old design) against some newer materials and idea's.
>It may cost me a few bucks but I want to measure strength and breaking
>points against each other.

Wellll... for an unscientific and relative comparison that might be
considered a bit crude but it is based on the way it's done in the
labs: We just have better equipment and measurement techniques. it
should even work with doped fabric.

You can get relative numbers this way to compare and these should work
with fiberglass, plywood, and even spruce scarf joints.

You would need to decided on the spacing between supports but take a
pair of pipes or even 2 X 4s and lay the sample over them. Place a
pipe or 2 X 4 over the sample and then start placing weight on the
pipe or 2 X 4. You can measure the deflection per pound of Kg and
that required for failure. This would also work in two axies on a
scarf joint. Of course with a two layer lay-up or thin plywood the
supports would need to be relatively close together. The important
thing is to use the same spacing and equipment for the different types
of material. You could probably come up with some methods a bit more
specific with a web search.

For pull I'd just take two pair of flat metal plates. create some
coupons or wood sections and clamp them in place on one end with a
pair of plates. On the other end use a pair of ViseGrips to clamp the
metal plates on the sample. Then hang a weight from the ViseGrips via
a scale.Keep adding weight. (be careful not to crush the sample when
using ViseGrips) You can measure stretch/elongation, creep, and
failure this way. It is crude, but should give a pretty good
comparison between materials.

For those not familiar with creep it is simply elongation or stretch
measured over time. This one can be surprising when using fiberglass
and resin at elevated temperatures like you'd get out in the sun on a
hot summer day. You can also find why it's not a good idea to clean
the wings with a solvent like acetone. <:-))

I saw a beautiful plane that had this done. The wings went from works
of art to having the outline of every rib visible.

Roger (K8RI)
> Lou
>

On Nov 2, 12:27 am, "Morgans" > wrote:
> "cavelamb himself" <> wrote
>
> > He was asking about test samples, not finished product.
>
> > For a replacement for fabric skin?
>
> > So if it punches good, it's ok, right?
>
> > My only question is how much weight is added replacing fabric.
>
> My take was that he wanted to test alternative materials, like how strong
> would fiberglass have to be for putting on a wing, instead of fabric. Or,
> how strong would plywood have to be to replace fabric. Add to that many
> different materials, and many different applications-all over the plane.
>
> If that is not the jist of it, so sorry, I guess.
>
> If I am right, then I don't see how you can get around testing the
> alternative material in a "similar to the real application" type of test
> like I described. Creativity would need to be applied to figure out other
> tests for other areas.
>

Me too. Do ragwings derive any of their strength from the skin?

If cloth is an option then the wing skins are so thin that they
will not carry a compressive load--they'll just buckle instead.

I also don't see how you could load cloth in shear, other than right
where it is glued, or when you're cutting it. Testing the strength of
the skin-to-underlying-structure bond is very important. But since
that wasn't the questiont, I'll continue on.

That leaves tension.

You can take strips of each material to be tested, rig up a clamp
for each end, and use that arrangement to hang a bucket. Fill
the bucket with weights until the sample fails. Weigh the bucket.
Keep you sore toes out of the way and wear eye protection.

That gives you a fair comparison of the ultimate tensile strengths
of the materials with the following caveats: Tensile strength of
a material is defined as the stress at rupture in pure tension.
Stress is force per unit area, you would need to calculate the
cross sectional areas of your samples and divide the force (weight)
at rupture by that number to arrive at the correct answer.

BUT, unless I am mistaken, OP is not interested in the intrinsic
properties of the materials so much as how much load a finished
wing skin would carry. So long as the samples are the same width
as each other and the same thicknesses as the proposed wing
skins what OP would want to compare is the actual force, not
the stress, at rupture.

Obviously you do not want to make the mistake of supposing this
comparison is all you need to know. A part may fail to perform it's
desired function due to deformation long before it actually breaks.
E.g. if you wing skins balloon out enough it may not matter if the
fabric
tears or not. A part may also deform so as to shift the load onto
another part, precipitating its failure whereas a weaker but stiffer
material might not.

I encourage OP to read up a bit on "Strength of Materials", perhaps
some introductory literature is available on the web. Commonly
used words like stiffness, strength, stress, force, and pressure
need to be carefully defined and used in their defined context in
order to understand and engage in a meaningful discussion of the
design issues.

--

FF