Replace fabric with glass

In article ,
Ernest Christley wrote:

Most of the fabric covered aiplanes I've seen didn't seem that hard.
That is, you could walk up to them and push the fabric in with your
hand. The way I understand the fabric process, it is basically a
composite structure. You have a nylon cloth with a paint "epoxy".

Could a much stronger and lighter covering be made by wetting out some
2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping
it around the airframe? The epoxy would be much lighter than paint, and
fiberglass cloth is MUCH stronger than nylon.

I've seen some places where builders used composites in place of fabric,
and it seemed that they all aimed for a multlayer, stiff panel, putting
the weight far above the original. I just don't understand why?



There have been some fibreglass/dope coverings around for at least 45
years. I remember a couple of Stearmans that the University of Illinois
had that were covered in glass/acetate dope. They looked like wrinkled
shirts whenever theweather was coll & humid. I understand that CAB dope
works bettere here. The shrinkage of the butyrate dope provides the
taughtness that the fabric needs.

Another disadvantage of this process is weight -- glass weighs more than
Dacron.

The glass process is also more susceptable to "ringworm" -- little
ring-shaped cracks in the finish.

As others have posted, fabric provides very little in the way of
structural loads -- all it really does is help to provide aerodynamic
shape.

Orval Fairbairn wrote:
In article ,
Ernest Christley wrote:


Most of the fabric covered aiplanes I've seen didn't seem that hard.
That is, you could walk up to them and push the fabric in with your
hand. The way I understand the fabric process, it is basically a
composite structure. You have a nylon cloth with a paint "epoxy".

Could a much stronger and lighter covering be made by wetting out some
2.5oz glass cloth on plastic, waiting till it's tacky and then wrapping
it around the airframe? The epoxy would be much lighter than paint, and
fiberglass cloth is MUCH stronger than nylon.

I've seen some places where builders used composites in place of fabric,
and it seemed that they all aimed for a multlayer, stiff panel, putting
the weight far above the original. I just don't understand why?




There have been some fibreglass/dope coverings around for at least 45
years. I remember a couple of Stearmans that the University of Illinois
had that were covered in glass/acetate dope. They looked like wrinkled
shirts whenever theweather was coll & humid. I understand that CAB dope
works bettere here. The shrinkage of the butyrate dope provides the
taughtness that the fabric needs.

Another disadvantage of this process is weight -- glass weighs more than
Dacron.

The glass process is also more susceptable to "ringworm" -- little
ring-shaped cracks in the finish.

As others have posted, fabric provides very little in the way of
structural loads -- all it really does is help to provide aerodynamic
shape.

There have been a lot of very informative responses in this thread, but
they don't seem to address the question I have; therefore, my
conclusion is that I didn't ask the question very clearly.

Razorback has been mentioned several times. Everyone seems to agree
that it's heavy, the glass will last forever...IF it is supported
properly, and that the dope which makes it taught needs some care.

Corky and several others make the point that the fabric doesn't need to
be strong, it's just there to catch the wind.

So let's take an example. I have an aileron that was designed for a
medium weight fabric (which is 4oz/sq yard?). A 2oz FG woven finish
fabric would still be much stronger by far, but it will be much thinner.
Being thinner, it won't need as much "filler" (whether that be epoxy,
dope, or paint).

The process would go like this. I cut a piece of fabric the dimension
of my aileron with an inch or so overlap. I wet out the glass on a
sheet of 6mil plastic, set the aileron on top of it and bring the
fabric/plastic up around the aileron sides...just wrap it over. The
fabric is bonded to the ribs and around all the edges. No shrinkage
necessary, since it will be the exact size. Once that cures, I repeat
the process for the other side. The FG will add no more to the
structrual integrity than the fabric did. It's bonded to the ribs, so
no more attachment work or possibility of fretting. It has the smooth
FG look, and even with an exterior coat of paint will be thinner and
hopefully lighter than the medium weight fabric. Concerning Corky's
excellent point about the aerodynamics, a suitably flexible epoxy will
allow the fabric to have just a slight amount of give just like a fabric
covering.

This seems like a way to make a stronger, lighter skin without as much
work. But on the other hand, I'm dreadfully afraid of falling out of
the sky. How could this technique be safely tested?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

On Fri, 09 Apr 2004 14:59:24 GMT, Ernest Christley
wrote:

So let's take an example. I have an aileron that was designed for a
medium weight fabric (which is 4oz/sq yard?). A 2oz FG woven finish
fabric would still be much stronger by far, but it will be much thinner.
Being thinner, it won't need as much "filler" (whether that be epoxy,
dope, or paint).

The process would go like this. I cut a piece of fabric the dimension
of my aileron with an inch or so overlap. I wet out the glass on a
sheet of 6mil plastic, set the aileron on top of it and bring the
fabric/plastic up around the aileron sides...just wrap it over. The
fabric is bonded to the ribs and around all the edges. No shrinkage
necessary, since it will be the exact size. Once that cures, I repeat
the process for the other side. The FG will add no more to the
structrual integrity than the fabric did. It's bonded to the ribs, so
no more attachment work or possibility of fretting. It has the smooth
FG look, and even with an exterior coat of paint will be thinner and
hopefully lighter than the medium weight fabric. Concerning Corky's
excellent point about the aerodynamics, a suitably flexible epoxy will
allow the fabric to have just a slight amount of give just like a fabric
covering.

This seems like a way to make a stronger, lighter skin without as much
work. But on the other hand, I'm dreadfully afraid of falling out of
the sky. How could this technique be safely tested?

Ernest, from what I've read and seen in the world of fabric covered
airplanes, it's really hard to substitute something for the fabric
itself and do any better in the weight saving department.

I've heard of people laying up fiberglass as a sheet and applying it
to fuselages, but the airplane ended up being heavier than when it was
covered with just fabric.

Fabric works fine by the way, it was used right through WWII on a
number of airplanes including bombers and fighters. The Corsair, one
of the most powerful fighters to fly originally had a portion of the
wing covered with fabric and even during the Korean War still flew off
carriers with a fabric covered rudder. The P-51 Mustang, one of the
fastest fighters of the war had a fabric covered rudder.

Are you trying to save money or weight, or both? When you wet out the
fiberglass fabric, it sometimes takes a lot of primer to fill the
weave, depending on the weight of the cloth. That could make for a
looonnnnggggg time of finishing to make it look good.

So what's the thought process you're going through? Why are you
interested in making the substitution? If you are looking for
additional strength, you don't really have to. Here's why: When a
friend of mine was covering his biplane, he thought it would be
interesting to test the fabric for strength, just for fun. He had a
metal stool with two loops on either side so he glued fabric across
the loops and taughtened it with the iron just like he did with the
wing. He then reached into his toolcabinet and pulled out a 16oz
ballpeen hammer. He made a half hearted swipe at the fabric and the
hammer bounced off without a mark. He swung harder and got bounced
off harder. So he stepped back and lunging forward, put every ounce
of his strength behind the swing. He hit the fabrice right in the
middle and was rebounded so hard he almost hurt himself. The fabric
was undamaged. Try that with an aluminum wing. ;-)

Corky Scott

Corky Scott wrote:

Are you trying to save money or weight, or both? When you wet out the
fiberglass fabric, it sometimes takes a lot of primer to fill the
weave, depending on the weight of the cloth. That could make for a
looonnnnggggg time of finishing to make it look good.


Doubt it would be any cheaper. Thought it could be a little lighter.

I guess a benefit would be a simplification in this project. I'm
already having to do a lot of fiberglass work with the wings and
turtleback. The fabric is a whole 'nuther skill set, tool set, and
chemical set. The fabric entails, gluing, shrinking, fabric-riveting
(which I understand is slightly different than metal riveting) then
filling the weave. While maybe all minor skills, they are all something
to be learned and all have their set of pitfalls. For instance, I've
been warned that when sanding the primer, the abrasive pad can easily
slice through the fabric at the edges of ribs or other hard supports.

I'm already doing the FG thing, so I'd get to amortize the learning
curve a little more. As I understand it, a 2oz fine-weave cloth doesn't
need much filling and if you wet it out on plastic, it won't need any.
It will come out as smooth as the plastic. The process would boil down
to wet out the glass between 2 sheets of plastic, pull of the top sheet
and wrap the rest around the part to be covered. Scuff sand and and
it's ready for paint.

I'm really not that concerned about strength, other than the FG is so
much stronger that you should be able to size it down accordingly.
Whichever type you choose, the resulting coverings weight will be
determined in large part by how thick the fabric was to begin with. It
seems that a thinner fabric wouldn't need as much filler to get 'full'.
And 2oz FG has got to be thinner than 4oz polyester. The comments
have been that the Razorback system is heavy, and I don't understand why
that should be. Why not use a thinner fabric since it has the strength
to spare?


--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

Ernest Christley wrote:

Corky Scott wrote:

Are you trying to save money or weight, or both? When you wet out the
fiberglass fabric, it sometimes takes a lot of primer to fill the
weave, depending on the weight of the cloth. That could make for a
looonnnnggggg time of finishing to make it look good.


Doubt it would be any cheaper. Thought it could be a little lighter.

I guess a benefit would be a simplification in this project. I'm
already having to do a lot of fiberglass work with the wings and
turtleback. The fabric is a whole 'nuther skill set, tool set, and
chemical set. The fabric entails, gluing, shrinking, fabric-riveting
(which I understand is slightly different than metal riveting) then
filling the weave. While maybe all minor skills, they are all something
to be learned and all have their set of pitfalls. For instance, I've
been warned that when sanding the primer, the abrasive pad can easily
slice through the fabric at the edges of ribs or other hard supports.

I'm already doing the FG thing, so I'd get to amortize the learning
curve a little more. As I understand it, a 2oz fine-weave cloth doesn't
need much filling and if you wet it out on plastic, it won't need any.
It will come out as smooth as the plastic. The process would boil down
to wet out the glass between 2 sheets of plastic, pull of the top sheet
and wrap the rest around the part to be covered. Scuff sand and and
it's ready for paint.

I'm really not that concerned about strength, other than the FG is so
much stronger that you should be able to size it down accordingly.
Whichever type you choose, the resulting coverings weight will be
determined in large part by how thick the fabric was to begin with. It
seems that a thinner fabric wouldn't need as much filler to get 'full'.
And 2oz FG has got to be thinner than 4oz polyester. The comments
have been that the Razorback system is heavy, and I don't understand why
that should be. Why not use a thinner fabric since it has the strength
to spare?

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber



Glass is a highly frangible material compared to polyester.
It is strong, yes, but brittle.

While tensile strength is a good thing, it is not the only thing
we need to consider.

My new plane is covered with 1.7 ounce dacron and Poly Fiber finish.
For a lightly loaded, low speed plane, this is quite adequite.

3.2 ounce fabric is twice as strong.
Why _not_ use it? (trick question!)

Because it's FOUR times heavier when finished?


Richard