High altitude flutter - Vne

I don't know if anybody has used tapered pultruded rods in a spar as
well but it may be a possibility given the complex rods and tube shape
being manufactured for other applications.

Rectangular profiles are made, the smaller the cross section of the
Pulltrusion the better you are able to match the bending moment. Naturally
it is more effort to built with smaller sections
but it provides for a near optimum spar.
Udo

On Jan 6, 8:30*pm, Udo Rumpf wrote:

Yes. Due to the alignment of the fibres and the higher tensile strength of
the resin, plus the high cure temperature.
Hand lay-up and vacuum bagging can only achieve a fraction of the
potential strength of the carbon fibre.
Unidirectional preprec have some of the same benefits but not to the same
extent as pultrusions.

To expound on what Udo writes:

Pultruded carbon fiber strips (or rods or ribbons or whatever profile)
are a neat way to make spar caps for wing spars because they have
great properties and don't require heroics in terms of fiber
alignment, lamination conditions, and climate control. Their
application to sailplane design was Pioneered (pun intended) by Jim
Marske who tested and developed a variety of ways to design and work
with them. Jim further did tests on a variety of hand-laminated
unidirectional carbon fiber test coupons and found that it is very
difficult, and sometimes impossible, to achieve handbook properties
without extreme control of fiber alignment and curing conditions.

Offhand, I think that pultruded strips offer max tensiles of around
300 ksi and (this is the important part) max compressive of around 275
ksi. That's around five times what you get in compression strength
from hand-laminated uni carbon. Their Young's modulus is somewhere
around 20 million.

The biggest arguement against pultrusions (and this might be the most
compelling thing for Greg), is that while they offer great strength,
their stiffness (as in Youngs modulus) has only a 10% to 15%
improvement over hand-laid uni. Since a lot of sailplane design
considerations are bound by stiffness more than by strength, the extra
strength of pultruded carbon doesn't have all that much effect on the
finished product.

I suspect that since Greg has good access to high-tech prepreg
materials, and more importantly to the expensive autoclaving equipment
and energy it takes to press and cook it, Pultrusions don't hold as
much advantage in his shop as they do in my more lowbrow and low-
dollar operation.

Thanks, and best regards to all

Bob K.
www.hpaircraft.com/hp-24

On Jan 7, 1:40*pm, Bob Kuykendall wrote:
On Jan 6, 8:30*pm, Udo Rumpf wrote:

Yes. Due to the alignment of the fibres and the higher tensile strength of
the resin, plus the high cure temperature.
Hand lay-up and vacuum bagging can only achieve a fraction of the
potential strength of the carbon fibre.
Unidirectional preprec have some of the same benefits but not to the same
extent as pultrusions.

To expound on what Udo writes:

Pultruded carbon fiber strips (or rods or ribbons or whatever profile)
are a neat way to make spar caps for wing spars because they have
great properties and don't require heroics in terms of fiber
alignment, lamination conditions, and climate control. Their
application to sailplane design was Pioneered (pun intended) by Jim
Marske who tested and developed a variety of ways to design and work
with them. Jim further did tests on a variety of hand-laminated
unidirectional carbon fiber test coupons and found that it is very
difficult, and sometimes impossible, to achieve handbook properties
without extreme control of fiber alignment and curing conditions.

Offhand, I think that pultruded strips offer max tensiles of around
300 ksi and (this is the important part) max compressive of around 275
ksi. That's around five times what you get in compression strength
from hand-laminated uni carbon. Their Young's modulus is somewhere
around 20 million.

The biggest arguement against pultrusions (and this might be the most
compelling thing for Greg), is that while they offer great strength,
their stiffness (as in Youngs modulus) has only a 10% to 15%
improvement over hand-laid uni. Since a lot of sailplane design
considerations are bound by stiffness more than by strength, the extra
strength of pultruded carbon doesn't have all that much effect on the
finished product.

I suspect that since Greg has good access to high-tech prepreg
materials, and more importantly to the expensive autoclaving equipment
and energy it takes to press and cook it, Pultrusions don't hold as
much advantage in his shop as they do in my more lowbrow and low-
dollar operation.

Thanks, and best regards to all

Bob K.www.hpaircraft.com/hp-24

Another consideration is transferring the shear loads
out of the caps at the root. With prepreg or wet-layup,
you can wrap the caps part way around the end of the
spar to help with this; not so with pultrusions. I don't
know how important this is...

Wet lay-ups in a glider factory environment are not
too hard (not at all trivial, but control of wetting and
fiber-straightness are understood). Perhaps not to
"handbook values" (nor designed to) ;-)

See ya, Dave "YO electric"

On Jan 7, 1:01*pm, DRN wrote:

Another consideration is transferring the shear loads
out of the caps at the root. With prepreg or wet-layup,
you can wrap the caps part way around the end of the
spar to help with this; not so with pultrusions. I don't
know how important this is...

The spars that Jim Marske has helped develop for the Genesis and LAK
ships, and the static tests that they survived, seem to demonstrate
that this is not a critical issue.

...control of wetting and fiber-straightness are understood...

1. O {Press Button}
2. ~~~ {Receive Ondulation}

Thanks, Bob K.

On Jan 7, 2:11*pm, Bob Kuykendall wrote:
On Jan 7, 1:01*pm, DRN wrote:

Another consideration is transferring the shear loads
out of the caps at the root. With prepreg or wet-layup,
you can wrap the caps part way around the end of the
spar to help with this; not so with pultrusions. I don't
know how important this is...

The spars that Jim Marske has helped develop for the Genesis and LAK
ships, and the static tests that they survived, seem to demonstrate
that this is not a critical issue.

...control of wetting and fiber-straightness are understood...

1. O * *{Press Button}
2. ~~~ *{Receive Ondulation}

Thanks, Bob K.


....
o
/|\
5. _/ \_ {walk on it} :-)


Darryl

The name is taken for a metal trainer made by a glider manufacturer in
Florida(?)

I never heard of a pulltrusion and can only guess what it means; I'm a
poltroon, my self.



At 05:46 07 January 2009, Darryl Ramm wrote:
On Jan 6, 9:16=A0pm, Greg Arnold wrote:
Udo Rumpf wrote:
Are pultrusions lighter than something made with vacuum =A0
bagged pre-pregs? =A0If so, why are they lighter?

Yes. Due to the alignment of the fibres and the higher tensile
strength=
of
the resin, plus the high cure temperature.
Hand lay-up and vacuum bagging can only achieve a fraction of the
potential strength of the carbon fibre.
Unidirectional preprec have some of the same benefits but not to the
sa=
me
extent as pultrusions.
Udo

Does a pultrusion work with a spar that is tapered as you get further
from the fuselage?

Yes, usually just like spar caps on conventional I beam spars also
allow tapered wings (was this a trick question?). See
http://continuo.com/marske/ARTICLES/...ods/carbon.htm

---

I'll suggest a marketing program to Greg Cole... let the first handful
of position holders rename the Duck Hawk. Peregrine (i.e. what a Duck
Hawk is) works for me. Ooops I'm not a position holder.

Darryl

On Jan 7, 2:30*pm, Nyal Williams wrote:
The name is taken for a metal trainer made by a glider manufacturer in
Florida(?)

I never heard of a pulltrusion and can only guess what it means; I'm a
poltroon, my self.


Opposite of an extrusion - which had already been named or it would
have been called a push-trusion I suppose.

Calling the opposite of an extrusion an intrusion didn't work either
so there you go...

9B

wrote:
On Jan 7, 2:30 pm, Nyal Williams wrote:
The name is taken for a metal trainer made by a glider manufacturer in
Florida(?)

I never heard of a pulltrusion and can only guess what it means; I'm a
poltroon, my self.


Opposite of an extrusion - which had already been named or it would
have been called a push-trusion I suppose.

Calling the opposite of an extrusion an intrusion didn't work either
so there you go...

9B
Maybe we can be more specific. A Pultrusion is where a solid is made in
a continuous process from a collection of fibres that are embedded in a
solid (usually resin - but also metals etc).
The process is to progressively pull a set of fibres off spools under
substantial tension through a shaped hole (former), while one of a
couple of processes apply the substrate (resin). This gives you a close
to perfectly aligned set of fibres in a very uniform substrate. Then the
result is usually heat cured in a die and cut to length...

Very uniform result - both dimensionally and in strength and also close
to theoretical strength limits, but typically quite "floppy"

On Jan 6, 9:16*pm, Greg Arnold wrote:

Does a pultrusion work with a spar that is tapered as you get further
from the fuselage?

[Warning: I am not an engineer. The following is not engineering
advice. Read and apply at your own risk. Via con Dios, Amigo!]

You have to make them work.

Designing economically with pultrusions is all about using
commercially-available profiles. You can order entire custom mondo
bars or strips or even angles or T-sections if you want, but the cost
per unit strength and stiffness is through the roof. Economically, it
makes better sense to select smaller strips or rods that have wide
application in consumer goods, and take a free ride on their economies
of scale.

Basically, you assble the spar as a box, I-beam, or C-section using
relatively conventional composite construction techniques, and use a
matrix (columns and rows) of pultruded elements in the spar caps to
collect the tensile and compressive loads. LAK has used 1/8" dia
pultruded rods in the past, as did the Genesis. I think LAK's recent
designs might tend towards the use of rectangular-section strips as do
mine.

You taper the spar in depth to match the wing depth by making the
shear web in the shape of one or more elongated trapezoids. You taper
the spar caps in cross-section to match the sectional moment of
inertia to the local bending moment by ending the pultruded elements
(or entire columns or rows of elements) at various spanwise stations.
So out by the tip there might be only an eighth or a tenth of what you
have at the side-of-body where the bending moment is at its maximum.

As Dave Nadler suggests, transferring loads between the upper and
lower spar caps in the spar stub, and transferring the moment from one
spar butt to the other through the main pins, is not trivial. However,
what I've seen of crashed and otherwise torn apart European racers
suggests that if you're methodical and consistent you can approach it
relatively casually and still have plenty of margin.

The tooling required to make spars using pultrusions can be as
substantial or as hokey as your workshop environment lets you get away
with. I've seen it done successfully with a pair of sharpie lines
drawn on a long level Formica tabletop. Using strips of wood on the
tabletop to guide the spar cap matrix alignment has also worked well.

Thanks, Bob K.