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Why no plywood monocoque homebuilts?



 
 
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  #31  
Old October 28th 06, 08:01 PM posted to rec.aviation.homebuilt
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Posts: 32
Default Why no plywood monocoque homebuilts?

Orval Fairbairn wrote:
In article .com,
" wrote:

Morgans wrote:
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote

The hard part would be to come up with a reasonable replacement for the
spars
in the wings. To avoid the big expensive spruce planks, one might have to
consider an engineered product like Laminated Veneer Lumber (LVL)...

Have you ever used those? They are HEAVY, with a capital "H".


SNIP


--
Jim in NC


Jenny Craig strikes again :-)

I am still very intriqued by filament winding. Spars would probably be
most obvious use of this technology. Take a look at the pictures on
this page to get an idea why.

http://www.boatdesign.net/forums/sho...11160b889f2560
2fba&t=1774&page=2

Doesn't that kindof suggest the ability to make a whole spar, wing,
fueselage or control surface in one shot? I am presuming scaled
composites uses something similar but bigger. I've seen pictures of the
system NASA uses for booster casings, they stand about 20 ft. tall if
I remember correctly.

I will be checking the local yellow pages to see if there are any
mast-makers where I live. I'd like to take a closing look at a system
like this.


-Matt


Actually, filament winding would be a poor choice for spars, as the
filaments should run primarily parallel to the spar and be concentrated
at the top and bottom. You do need some in the webs, to handle shear
loads, but an "I" section is the most efficient. A tubular spar for a
wing is also a poor choice, as it concentrates a lot of its tensile
strength at its center, where it doesn't get much loading.


Couldn't that be controlled by adjusting the weave? Perhaps weave in
three angles instead of two, with the third being parallel to the
length axis? The form could be semi-rectangular as well, which would
give you your ability to concentrate fibers on the top and bottom.
Obviously you can't escape some wastage, but "perfect" is the enemy of
"good enough".

A mast is a different story, as it is expected to take similar bending
loads in all directions; a spar does not.


Are you quite familiar with filament winding? I've got a lot of
questions if you've got the time.

-Thanks
-Matt

  #32  
Old October 28th 06, 09:07 PM posted to rec.aviation.homebuilt
Orval Fairbairn
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Posts: 824
Default Why no plywood monocoque homebuilts?

In article .com,
" wrote:

Orval Fairbairn wrote:
In article .com,
" wrote:

Morgans wrote:
"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote

The hard part would be to come up with a reasonable replacement for
the
spars
in the wings. To avoid the big expensive spruce planks, one might
have to
consider an engineered product like Laminated Veneer Lumber (LVL)...

Have you ever used those? They are HEAVY, with a capital "H".

SNIP


--
Jim in NC

Jenny Craig strikes again :-)

I am still very intriqued by filament winding. Spars would probably be
most obvious use of this technology. Take a look at the pictures on
this page to get an idea why.

http://www.boatdesign.net/forums/sho...ec4011160b889f
2560
2fba&t=1774&page=2

Doesn't that kindof suggest the ability to make a whole spar, wing,
fueselage or control surface in one shot? I am presuming scaled
composites uses something similar but bigger. I've seen pictures of the
system NASA uses for booster casings, they stand about 20 ft. tall if
I remember correctly.

I will be checking the local yellow pages to see if there are any
mast-makers where I live. I'd like to take a closing look at a system
like this.


-Matt


Actually, filament winding would be a poor choice for spars, as the
filaments should run primarily parallel to the spar and be concentrated
at the top and bottom. You do need some in the webs, to handle shear
loads, but an "I" section is the most efficient. A tubular spar for a
wing is also a poor choice, as it concentrates a lot of its tensile
strength at its center, where it doesn't get much loading.


Couldn't that be controlled by adjusting the weave? Perhaps weave in
three angles instead of two, with the third being parallel to the
length axis? The form could be semi-rectangular as well, which would
give you your ability to concentrate fibers on the top and bottom.
Obviously you can't escape some wastage, but "perfect" is the enemy of
"good enough".


Filament winding wraps the material (carbon, Kevlar, glass, etc.) around
the item, whereas you want the filaments in the spar caps to run
longitudinally, because that is the direction of tensile and compressive
stresses. Filaments wrapped around the spar will carry shear stresses,
but are of little help in taking up bending loads, which comprise the
major stresses in a spar.


A mast is a different story, as it is expected to take similar bending
loads in all directions; a spar does not.


Are you quite familiar with filament winding? I've got a lot of
questions if you've got the time.



I haven't done any filament winding, but I am familiar with
filament-wound rocket motor cases.
  #33  
Old October 29th 06, 09:47 PM posted to rec.aviation.homebuilt
Capt. Geoffrey Thorpe
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Posts: 790
Default Why no plywood monocoque homebuilts?

"Morgans" wrote in message
...

"Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote

The hard part would be to come up with a reasonable replacement for the
spars in the wings. To avoid the big expensive spruce planks, one might
have to consider an engineered product like Laminated Veneer Lumber
(LVL)...


Have you ever used those? They are HEAVY, with a capital "H".

More fitting would be something like an engineered product such as "silent
floor" joists, which is best described as a wood "I" beam. A cheaper
wood, like fur could be used, because the wider flange top and bottom of
the "I" is the only part that is real wood, and there is not that much
volume of wood to incur very much weight penalty.

Holes can be put in the plywood web to help lighten it, with very minimal
strength loss.

Of course, this is a practice very similar to what is currently being used
in some homebuilt designs, today. g

A box spar is one of the best uses of strength to weight for spars, not
using a solid plank. The amount of real wood, top to bottom and spanwise
varies, so there is no extra wood where it is not needed, thus giving
maximum strength to weight. Also, you do not have to use expensive Sitka
Spruce, and if you do, you can cut up smaller (cheaper-no waste) pieces,
and splice them, and laminate them, to get all of the grain going in the
right direction.


I was thinking of a routed spar to save some of the weight, but you are
absolutely correct - a box spar would be the way to go in order to avoid the
big expensive spruce plank.


--
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.


  #34  
Old October 30th 06, 05:36 PM posted to rec.aviation.homebuilt
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Posts: 1,130
Default Why no plywood monocoque homebuilts?


Orval Fairbairn wrote:

Actually, filament winding would be a poor choice for spars, as the
filaments should run primarily parallel to the spar and be concentrated
at the top and bottom. You do need some in the webs, to handle shear
loads, but an "I" section is the most efficient. A tubular spar for a
wing is also a poor choice, as it concentrates a lot of its tensile
strength at its center, where it doesn't get much loading.

A mast is a different story, as it is expected to take similar bending
loads in all directions; a spar does not.


The spar in my Jodel is a one-piece box spar and is the only
spar in the wing. It takes the lifting and landing loads, the drag
loads, and the torsion loads. The washout is built into it. It's about
7" deep and 12" wide at the center. It has four lumber members, one in
each corner of the box, and the top two are larger than the bottom two,
since wood is stronger in tension than it is in compression. Plywood
diaphragms maintain the box shape and the whole thing is closed with
plywood skins with the outer plies at 45° angles to take advantage of
the maximum directional strength of the wood. The lumber members are
heaviest at the center and lightest at the tips. The dihedral is in the
outer panels, and the lumber members are spliced at those points.
Shrike had suggested building wooden airplanes with semi-skilled labor;
I don't think I'd want such a spar as this to be built by someone who
wasn't either thoroughly trained and apprenticed or who would be
eventually flying it. It's a most elegant piece of engineering and is
the most complex and time-consuming part of the whole airplane. One
foolish mistake in jigging or gluing could just about trash the whole
thing.

Dan

  #35  
Old October 31st 06, 12:10 AM posted to rec.aviation.homebuilt
Morgans[_2_]
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Posts: 3,924
Default Why no plywood monocoque homebuilts?


wrote

I don't think I'd want such a spar as this to be built by someone who
wasn't either thoroughly trained and apprenticed or who would be
eventually flying it. It's a most elegant piece of engineering and is
the most complex and time-consuming part of the whole airplane. One
foolish mistake in jigging or gluing could just about trash the whole
thing.


It is possible to use mass production techniques to this whole process.

Picture cutting enough individual parts for 50 spars, with each part being
reproduced in exact precision. By careful setup, (by one exacting craftsman)
you would produce parts at least as good as you could do, just making one.

Instead of jigging for one spar, a permanent steel jig could be set made that
would make the spar almost impossible to put together incorrectly.

Semi-skilled labor would be all that is needed to assemble the spar and glue it,
if they are taught and all of the parts fit right. I live in the furniture
belt, here in NC, and they do some pretty complicated assemblies; much more so
than a spar.

Granted, the spar being wrong is a lot more critical than some poorly assembled
furniture. Quality control would be important, but possible. It would be
advisable to test to destruction, a few at random, to verify correct assembly.
--
Jim in NC

  #36  
Old October 31st 06, 04:11 AM posted to rec.aviation.homebuilt
Roger (K8RI)
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Posts: 727
Default Why no plywood monocoque homebuilts?

On 30 Oct 2006 08:36:26 -0800, wrote:


Orval Fairbairn wrote:

Actually, filament winding would be a poor choice for spars, as the
filaments should run primarily parallel to the spar and be concentrated
at the top and bottom. You do need some in the webs, to handle shear
loads, but an "I" section is the most efficient. A tubular spar for a
wing is also a poor choice, as it concentrates a lot of its tensile
strength at its center, where it doesn't get much loading.

A mast is a different story, as it is expected to take similar bending
loads in all directions; a spar does not.


The spar in my Jodel is a one-piece box spar and is the only
spar in the wing. It takes the lifting and landing loads, the drag
loads, and the torsion loads. The washout is built into it. It's about


I have a section of the main spar out in the shop for Barracuda. It is
a box about 2 1/4 X 10 1/4 " at the inboard edge of the main gear
attach point. The sides appear to be about 3 /32" plywood (not the
big box kind) and the spar caps are three 2" X 3/4" internal, making
each cap 2" X 3". There are internal risers spaced along the length of
the spar. I don't have a rear spar and don't remember its dimensions.
That spar had thousands of hours on it.

I measured the Cuda spar, I'm going by memory on the G-III.

The main spar for the Glasair III is a monster. The web is a foam
core covered with BID on the 45 degree bias that is of a very heavy
weave. I don't know how many layers as it comes from the factory
bonded to the bottom wing skin. The caps are about 4 inches wide by
3/4 inch thick are basically a lot of parallel fibers running length
wise. It looks like a fiberglass I-beam. The rear spar caps are
molded into the trailing edges of the top and bottom skins and are
about 1/4" thick. The fibers are quite easy to see and are arranged
like those in the main spar caps. The web is 1/2" foam (forget the
weight) and several layers of BID on the 45 degree bias. They don't
even give you a template for the rear spar. Just a set of dimensions
and you sand to fit. The wash out is set into the wing fixture and
you just "twist to fit" at closing time.

The Cozy and I believe the LongEZ both use the same kind of spar.
Using the lay-up over foam type of construction they simply cut a slot
into the foam for the wing, pour in a bunch of epoxy and lay in a
fiberglass rope. They work the resin into the rope until it is
saturated. They keep doing this until the slot is filled with
saturated fiberglass rope. So you again end up with a very strong
spar that has the fibers laid out lengthwise (more or less)

Comparing the wing loading of the SR-22, the G-III is just shy of 30#
per sq ft. A power off descent to the runway in that is a real eye
opener. As I recall best glide produced a rate of descent in the
neighborhood of 2200 fpm. Rate of climb solo is close to 4,000 fpm. A
descent at best glide to the runway gives a roll out of only 700 to
800 feet with the round out being quite rapid and using little space
(If your nerves can handle it):-)) This procedure results in a
rather *firm* arrival. :-))

snip
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com
  #37  
Old October 31st 06, 01:27 PM posted to rec.aviation.homebuilt
Stealth Pilot
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Posts: 78
Default Why no plywood monocoque homebuilts?

On 26 Oct 2006 16:29:01 -0700, wrote:


wrote:
Suprisingly I keep coming back to wood as material for mass production
since the whole of the structure could be made of one material. There
are obvious logistic benefits there, and I think most wood techniques
could be practically achieved robotically.


Wood, especially good wood, is getting scarcer all the time.
Consistently good wood is hard to find. It's the reason ladder
manufacturers went to aluminum and/or fiberglass a long time ago. The
big Sitka Spruce and other types of trees that gave us good
aircraft-grade wood mostly went to build houses a long time ago when it
seemed we'd never run out of the stuff. What's left is protected in
parks.
Wood also needs more care in storage; it doesn't survive well
in moist conditions, especially warm, moist conditions, and the heat of
an intense sun can dry it out beyond the ideal 15% moisture content and
make if brash. Glues suffer in the heat. Wooden airplanes burn easily.
Gluing wood in the factory is a tedious affair, requiring a lot of
clamps, patience, and accuracy the first time. You can't CNC-punch
wooden sheets like you can aluminum.
The companies that used to build wooden airplanes gave it up
long ago. I think the Bellanca Viking was among the last airplane to
use significant wood in it (in the wing). Is the Falco still in
production? How much does it retail for?
Aluminum and composites start to look better all the time, huh?

Dan


good points dan but the market doesent care where or how the aircraft
is made.
the market wants a product that is fit for the purpose and durable and
cheap.
achieving all 3 is the engineering challenge.

aluminium has known engineering characteristics and has chemistry
available that can passivate the surface and make it durable.

composites have the benefit of being able to be shaped into exotic
aerodynamically slick shapes.

wood is lovely stuff to work with in the home workshop for private
amusement. has a number of permanent glues and can make lovely
aeroplanes. slow as hell and the materials are more variable than the
prior two. the aircraft require hangaring.

for commercial production aluminium and/or composite are the worlds
market leaders because they are the most economic engineering
solutions.
ymmv
Stealth Pilot
 




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