why isn't there composite tube fuselage design?

[Shin Gou]

I am just wondering...if composite materials are stronger and lighter
than steel, why composites tubes aren't glued together to form the
fuselage frame just like the traditional 4103 steel tubes being welded
together? Any reasons?

Shin Gou
Rans S-9
Warrenton, VA

[Rich S.]

"Shin Gou" > wrote in message
oups.com...
>I am just wondering...if composite materials are stronger and lighter
> than steel, why composites tubes aren't glued together to form the
> fuselage frame just like the traditional 4103 steel tubes being welded
> together? Any reasons?

They are. It's known as "wood". :-)

Rich S.

[......... :-\)\)]

see my recent post on the same subject .. a week back I guess.

"Shin Gou" > wrote in message
oups.com...
> I am just wondering...if composite materials are stronger and lighter
> than steel, why composites tubes aren't glued together to form the
> fuselage frame just like the traditional 4103 steel tubes being welded
> together? Any reasons?
>
> Shin Gou
> Rans S-9
> Warrenton, VA
>

[kalfreds0412]

I wonder how a direct comparison would fair. ie 1" OD .035" wall 4130 vs.
1" OD .035" carbon fiber? Has anyone ever seen a comparison like that?

Mike

"Shin Gou" > wrote in message
oups.com...
> I am just wondering...if composite materials are stronger and lighter
> than steel, why composites tubes aren't glued together to form the
> fuselage frame just like the traditional 4103 steel tubes being welded
> together? Any reasons?
>
> Shin Gou
> Rans S-9
> Warrenton, VA
>

[Shin Gou]

looked around on the Internet and found Zivko's Leo Loudenslager
"Shark" plane's fuselage was constructed from carbon fiber tubes
bonded to titanium clusters with mag-alloy side fairings. Empty weight
950 lbs with a Lycoming IO-540 engine.

More information and background story at
http://www.zivko.com/EDGE/news/leo.html
There's a video clip for download at the bottom of the page. See how
the control surfaces move!!! Also a close-up look at the carbon fiber
tube fuselage. Impressive. Can't wait for its flight.

[Shin Gou]

Now I think the conclusion of this carbon fiber tube fuselage
construction technique is: 1) it's lighter and at least as strong as
steel tube design. 2) it's more expensive than steel tube to build. 3)
it requires higher skills than steel tube welding to build. 4) this
method is not well proven in real flight (yet).

[Frank van der Hulst]

Shin Gou wrote:
> Now I think the conclusion of this carbon fiber tube fuselage
> construction technique is: 1) it's lighter and at least as strong as
> steel tube design. 2) it's more expensive than steel tube to build. 3)
> it requires higher skills than steel tube welding to build. 4) this
> method is not well proven in real flight (yet).

Not only that, you've got to ask yourself whether carbon fibre tube
fuselage construction would be better than what has become the standard
for composite construction -- monocoque, stressed-skin construction.

If you're using composites why limit yourself to 1" (or whatever)
diameter tubes and so on as per steel-tube-and-fabric? Why not build
large non-circular tubes, for example.

Frank

[LCT Paintball]

Round is very strong. The only way you could improve on a simple round tube
for strength would be to add material in the direction that you needed more
strength, and take away material where the strength wasn't needed.

--
"Don't be misled, bad company corrupts good character."
www.LCTPaintball.com
www.LCTProducts.com

[Evan Carew]

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Frank,

My response interspersed in your post:

Frank van der Hulst wrote:
> Shin Gou wrote:
>
>> Now I think the conclusion of this carbon fiber tube fuselage
>> construction technique is: 1) it's lighter and at least as strong as
>> steel tube design. 2) it's more expensive than steel tube to build. 3)
>> it requires higher skills than steel tube welding to build. 4) this
>> method is not well proven in real flight (yet).
>
>
> Not only that, you've got to ask yourself whether carbon fibre tube
> fuselage construction would be better than what has become the standard
> for composite construction -- monocoque, stressed-skin construction.
Well, a better way to phrase this question is what does composite
construction do best, & from my experience, the prepreg over stiff core
technique is much easier and doesn't require tubes or the large number
of ribs & bulkheads a monocoque design does. In fact, when pulled out of
the mold, you have a finished skin.
>
> If you're using composites why limit yourself to 1" (or whatever)
> diameter tubes and so on as per steel-tube-and-fabric? Why not build
> large non-circular tubes, for example.
>
> Frank

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[Morgans]

"Shin Gou" > wrote

> There's a video clip for download at the bottom of the page. See how
> the control surfaces move!!! Also a close-up look at the carbon fiber
> tube fuselage. Impressive. Can't wait for its flight.

Interesting that the elevator travel for nose up is very limited, compared
to nose down's extreme. Wonder why?
--
Jim in NC

[BobR]

Shin Gou wrote:
> I am just wondering...if composite materials are stronger and lighter
> than steel, why composites tubes aren't glued together to form the
> fuselage frame just like the traditional 4103 steel tubes being
welded
> together? Any reasons?
>
> Shin Gou
> Rans S-9
> Warrenton, VA

The better question would be why would you want to use carbon fiber to
build a tubular type framework? The real secret is to utilize the best
strengths of your material and design to that strength. There is no
technical limitation that would prevent using carbon fiber composite
tubes to create a tubular framework. The only limitation I can think
of is the joints for replacing the welded joints of the steel. That
could easily be solved by custom bondable carbon fiber joints. Clamps
could substitute for welded tabs and so on. One thing for certain, you
would never have to be concerned with rust.

One thing though, due to the very limited amount of composite vs steel
involved, you would not be saving a lot on weight.

[......... :-\)\)]

Bonding titanium to carbon tubes does not sound like a homebuilable
technique to me.

You are right the joints will always be the problem. However it is
interesting to study the way in which items such as bicycle frames and yacht
steering wheels are made in one piece from tubular sections in carbon ... I
won't say any more on this. You can find plenty of info on the web.

There are fouth major problems/issues that I can see.

First .... if you layup a tube from carbon you cannot put all of the fibres
along the tube axis. Some will need to wrap around. As carbon fibre is
highly orthotropic (i.e. different material properties in different
directions) then the impressive properties of the carbon fibre along the
fiber axis will not be attained in the completed tube. Don't get me wrong
the carbon will still be lighter and stiffer for a given weight but probably
not by as much as you would expect.

Second ... the properties of carbon composites are strongly dependant on
moisture and temperature conditions. For example the compressive strength of
Fibercotes E-765/T700 24K uni prepreg is 147 ksi at room temperature / dry
conditions. At elevated temperature and equilibrium humidity conditions in a
tropical environment the compressive strength drops to 88 ksi ! Not really
any better than steel. Compressive moduli and any other resin dominated
properties (such as shear) will exhibit similar behavior. Yout need to
design for these low strengths at the extreme environmental conditions in
any composite structure and thus at room temperature you will end up with
larger than required margins and hence more weight.

Third .. composites suffer from microcracking and other issues which will
limit the laminate strains to approx 4500 micro strain at ultimate load (a
rough number ... complicated issue not room to explain here). What this
means in plain english is that you can only use approximately 1/3 of the
potential strength of the material if you want a structure with long life.

Fourth ... composites have no ductility like metals and I would hate to be
sitting in a fuselage made of carbon tubes if it hit anything. The tubes
would fracture and splinter and the pilot would be in all sorts of trouble.
To control this behaviour you would need to add another tougher composite
material such as Kevlar to the laminate (common practise in fwd fuselages
for gliders to improve crashworthiness).







"BobR" > wrote in message
oups.com...
>
> Shin Gou wrote:
> > I am just wondering...if composite materials are stronger and lighter
> > than steel, why composites tubes aren't glued together to form the
> > fuselage frame just like the traditional 4103 steel tubes being
> welded
> > together? Any reasons?
> >
> > Shin Gou
> > Rans S-9
> > Warrenton, VA
>
> The better question would be why would you want to use carbon fiber to
> build a tubular type framework? The real secret is to utilize the best
> strengths of your material and design to that strength. There is no
> technical limitation that would prevent using carbon fiber composite
> tubes to create a tubular framework. The only limitation I can think
> of is the joints for replacing the welded joints of the steel. That
> could easily be solved by custom bondable carbon fiber joints. Clamps
> could substitute for welded tabs and so on. One thing for certain, you
> would never have to be concerned with rust.
>
> One thing though, due to the very limited amount of composite vs steel
> involved, you would not be saving a lot on weight.
>

[[email protected]]

LCT Paintball wrote:
> Round is very strong. The only way you could improve on a simple
round tube
> for strength would be to add material in the direction that you
needed more
> strength, and take away material where the strength wasn't needed.
>

Yep they're called box beams, or torsion beams for those
who like an extra sylable. Hollow beams are a very weight-
efficient approach to construction. In monocoque design
the entire fuselage and/or wing is designed as a box
beam.

--

FF

[BobR]

.......... :-)) wrote:
> Bonding titanium to carbon tubes does not sound like a homebuilable
> technique to me.
>

The joints would not need to be titanium but could be made from carbon
fiber as well. Bonding of carbon fiber to carbon fiber would present
few problems. The majority of tubular frames I have seen are designed
so that the stress on the frame remains in compression.

> You are right the joints will always be the problem. However it is
> interesting to study the way in which items such as bicycle frames
and yacht
> steering wheels are made in one piece from tubular sections in carbon
.... I
> won't say any more on this. You can find plenty of info on the web.
>

That would be the obvious method if you are constructing the frame from
raw materials instead of existing carbon fiber tubes.

> There are fouth major problems/issues that I can see.
>
> First .... if you layup a tube from carbon you cannot put all of the
fibres
> along the tube axis. Some will need to wrap around. As carbon fibre
is
> highly orthotropic (i.e. different material properties in different
> directions) then the impressive properties of the carbon fibre along
the
> fiber axis will not be attained in the completed tube. Don't get me
wrong
> the carbon will still be lighter and stiffer for a given weight but
probably
> not by as much as you would expect.
>

The solution to this was on display at Oshkosh about three years ago.
Ever see the Chineese finger lock? They were using the save weave
technique to form the carbon fiber tube, wetting out after forming to
desired size and curing. The result was the optimum strength in all
directions.

> Second ... the properties of carbon composites are strongly dependant
on
> moisture and temperature conditions. For example the compressive
strength of
> Fibercotes E-765/T700 24K uni prepreg is 147 ksi at room temperature
/ dry
> conditions. At elevated temperature and equilibrium humidity
conditions in a
> tropical environment the compressive strength drops to 88 ksi ! Not
really
> any better than steel. Compressive moduli and any other resin
dominated
> properties (such as shear) will exhibit similar behavior. Yout need
to
> design for these low strengths at the extreme environmental
conditions in
> any composite structure and thus at room temperature you will end up
with
> larger than required margins and hence more weight.
>

Those properties can be programmed to just about any desired result.
The accepted standard for most composite design is 2X vs 1.5X for steel
equilivent design. The issue will always be a design problem, and the
best would be to design to the best properties of the materials being
used.

> Third .. composites suffer from microcracking and other issues which
will
> limit the laminate strains to approx 4500 micro strain at ultimate
load (a
> rough number ... complicated issue not room to explain here). What
this
> means in plain english is that you can only use approximately 1/3 of
the
> potential strength of the material if you want a structure with long
life.
>

A property not unique to composites.

> Fourth ... composites have no ductility like metals and I would hate
to be
> sitting in a fuselage made of carbon tubes if it hit anything. The
tubes
> would fracture and splinter and the pilot would be in all sorts of
trouble.
> To control this behaviour you would need to add another tougher
composite
> material such as Kevlar to the laminate (common practise in fwd
fuselages
> for gliders to improve crashworthiness).
>
>

Composites have proven to be very crash worthy in practice but I agree,
that the carbon fiber tube frame would not provide the same protection
of a tube steel frame. It goes back to designing to the qualities and
strength of the material.