Why no plywood monocoque homebuilts?

[[email protected]]

Howdy,

After reading a bit about the early Lockheed Vega, the Focker Albatross
DIII and the Dehavilland Mosquito I was a bit suprised that plywood
monocoque construction hasn't been used in any more modern airplanes.
(Or at least none that I can think of) What gives? Is it cheaper to use
glass than wood? Anyone here have any experience with this type of
construction and how it compares to truss style construction?

-Thanks!
-Matt

[Morgans[_2_]]

> wrote in message
oups.com...
> Howdy,
>
> After reading a bit about the early Lockheed Vega, the Focker Albatross
> DIII and the Dehavilland Mosquito I was a bit suprised that plywood
> monocoque construction hasn't been used in any more modern airplanes.
> (Or at least none that I can think of) What gives? Is it cheaper to use
> glass than wood? Anyone here have any experience with this type of
> construction and how it compares to truss style construction?

It is The Falco comes to mind. It is available as a kit here, and as a
production aircraft in Italy. (or it was available in Italy)
--
Jim in NC

[Ron Wanttaja]

On 20 Oct 2006 15:47:10 -0700, " >
wrote:

> Howdy,
>
> After reading a bit about the early Lockheed Vega, the Focker Albatross
> DIII and the Dehavilland Mosquito I was a bit suprised that plywood
> monocoque construction hasn't been used in any more modern airplanes.
> (Or at least none that I can think of) What gives? Is it cheaper to use
> glass than wood? Anyone here have any experience with this type of
> construction and how it compares to truss style construction?

Jim gave the Falco as an example of a monocoque wood aircraft, but keep in mind
that the three you mentioned are *molded* wood aircraft. Not really efficient,
for a homebuilt, unless you're planning on selling kits.

Ron Wanttaja

[[email protected]]

Ron Wanttaja wrote:
> On 20 Oct 2006 15:47:10 -0700, " >
> wrote:
>
> > Howdy,
> >
> > After reading a bit about the early Lockheed Vega, the Focker Albatross
> > DIII and the Dehavilland Mosquito I was a bit suprised that plywood
> > monocoque construction hasn't been used in any more modern airplanes.
> > (Or at least none that I can think of) What gives? Is it cheaper to use
> > glass than wood? Anyone here have any experience with this type of
> > construction and how it compares to truss style construction?
>
> Jim gave the Falco as an example of a monocoque wood aircraft, but keep in mind
> that the three you mentioned are *molded* wood aircraft. Not really efficient,
> for a homebuilt, unless you're planning on selling kits.
>
> Ron Wanttaja

It also depends on what you consider more modern, the last of the
all-wood european sailplanes were in the 70's but the performance had
reached impressive levels. The most common would have to be the Ka6cr
but the K6e was definitely the 15metre machine to have, far superior to
most other 15m gliders of the time. Wood gliders finished for the most
part with the SHK1, the 17m follow-on to the 15m Standard Austria. It
was a plain timber monocoque, but it made good use of glass for
finishing the wings and nose.
There's still a few gliders for homebuilding made with a monocoque
construction, but I think even a simple monocoque is probably just too
much work for a one-off.

Carlo Selman

[Roger (K8RI)]

On Fri, 20 Oct 2006 19:02:20 -0400, "Morgans"
> wrote:

>
> wrote in message
oups.com...
>> Howdy,
>>
>> After reading a bit about the early Lockheed Vega, the Focker Albatross
>> DIII and the Dehavilland Mosquito I was a bit suprised that plywood
>> monocoque construction hasn't been used in any more modern airplanes.
>> (Or at least none that I can think of) What gives? Is it cheaper to use
>> glass than wood? Anyone here have any experience with this type of
>> construction and how it compares to truss style construction?
>
>It is The Falco comes to mind. It is available as a kit here, and as a
>production aircraft in Italy. (or it was available in Italy)

How about the Barracuda?

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

[Morgans[_2_]]

"Roger (K8RI)" > wrote

> How about the Barracuda?

Does the Barracuda get its strength from its skin, or from a wooden framework
with plywood covering it? I don't know.
--
Jim in NC

[Ed Sullivan]

>How about the Barracuda?
>
>Roger Halstead (K8RI & ARRL life member)
>(N833R, S# CD-2 Worlds oldest Debonair)
>www.rogerhalstead.com

As I recall the Barracuda was just a plywood covered conventional
spruce frame.

[Ed Sullivan]

On Sat, 21 Oct 2006 13:58:52 -0400, "Morgans"
> wrote:

>
>"Roger (K8RI)" > wrote
>
>> How about the Barracuda?
>
>Does the Barracuda get its strength from its skin, or from a wooden framework
>with plywood covering it? I don't know.

Again as I recall the Barracuda has a
Warren Truss Fuselage, that is it has both verticle and diagonal
members. the strength is shared. On the other hand DeHavilland
aircraft frame had only verticle members therefore the skin prevented
the structure from skewing.

[Roger (K8RI)]

On Sat, 21 Oct 2006 20:56:12 GMT, Ed Sullivan >
wrote:

>On Sat, 21 Oct 2006 13:58:52 -0400, "Morgans"
> wrote:
>
>>
>>"Roger (K8RI)" > wrote
>>
>>> How about the Barracuda?
>>
>>Does the Barracuda get its strength from its skin, or from a wooden framework
>>with plywood covering it? I don't know.

I'm not sure how much strength the skin addes in the Cuda so I passed
this question on the the Barracuda users group. If my memory holds out
I'll bring their answer(s) back.

>
>Again as I recall the Barracuda has a
>Warren Truss Fuselage, that is it has both verticle and diagonal
>members. the strength is shared. On the other hand DeHavilland
>aircraft frame had only verticle members therefore the skin prevented
>the structure from skewing.
Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

[[email protected]]

It is called "complimentary structure". Most GA aircraft have a
structure consisting of a skin (alum or plywood) that carries most of
the load. However, the stringers and longerons have an important
function, that is, they provide out of plane stiffness to the skin,
thereby preventing it from buckling under load. Each element of the
structure has an axis about which it is weak, and it needs the other
elements to provide strength in that direction. They need each other
very much.

Bud

Morgans wrote:
> "Roger (K8RI)" > wrote
>
> > How about the Barracuda?
>
> Does the Barracuda get its strength from its skin, or from a wooden framework
> with plywood covering it? I don't know.
> --
> Jim in NC

[[email protected]]

wrote:
> It is called "complimentary structure". Most GA aircraft have a
> structure consisting of a skin (alum or plywood) that carries most of
> the load. However, the stringers and longerons have an important
> function, that is, they provide out of plane stiffness to the skin,
> thereby preventing it from buckling under load. Each element of the
> structure has an axis about which it is weak, and it needs the other
> elements to provide strength in that direction. They need each other
> very much.
>
> Bud

Semi-Monocoque is the term, not "complimentary." Your
average CessBeeMooPip is semi-monocoque in the aft fuselage. Most of
the rest has heavy structural members and the skin is used just to keep
things square.

Dan

[[email protected]]

wrote:
>
> Semi-Monocoque is the term, not "complimentary."

Whatever. My professor in graduate school (a Stanford Ph.D.) called it
complimentary, since the stringers and longerons compliment the skin in
that, as I said, they provide strength in a direction that the skin
does not have, which is out of plane stiffness. Since a true Mono
(meaning a single) coque (shell) structure has only a shell for
structure (an egg is a perfect example), any deviation from this is
often called semi-monocoque, even when the skin carries no load, which
is an incorrect way of describing such a structure.


> Your average CessBeeMooPip is semi-monocoque in the aft fuselage.

The fuselage skin from the firewall back is the primary structural
member everywhere except at the wing spar attachments, and the landing
gear on Cessnas.


> Most of the rest has heavy structural members and the skin is used just to keep
> things square.
>
> Dan

Well, I agree that many aircraft are much heavier than they need to be
because the designer couldn't or wouldn't do the calculations and
design that would eliminate excess weight (i.e. the Cirrus airframe,
even though it is supposedly made of modern high strength composite
structure, is actually about 300 lbs heavier than aluminum planes in
its class). Perhaps the longerons and stringers are heavy enough to
take the necessary loads, But the skin serves as the aerodynamic shell,
or Loft as it is called everywhere on the aircraft, and in places where
the skin is in tension, such as the bottom of the wings, the skin is
again a major structural member. In planes that have heavy wing skins,
such as private jets, the wing skin is again a major structural member.
Since the OP was inquiring about wooden aircraft, it is worth
noting that the reason wood still is a wonderful material even though
its tensile strength is much lower than metal (the strongest wood is
Hickory, which has a tensile strength of less than 2000 psi), is
because its weight versus volume is lower, resulting in a thicker
section for the same weight. This means that the thicker section has a
much better buckling load than metal for the same weight. Plywood skin
aircraft carry much more load in the skin (which is the best place to
carry it) due their superior buckling properties.
Aircraft skin, in a properly designed airframe, does much more
than just hold everything square.

Bud

[Orval Fairbairn]

In article . com>,
wrote:

> wrote:
> >
> > Semi-Monocoque is the term, not "complimentary."
>
> Whatever. My professor in graduate school (a Stanford Ph.D.) called it
> complimentary, since the stringers and longerons compliment the skin in
> that, as I said, they provide strength in a direction that the skin
> does not have, which is out of plane stiffness. Since a true Mono
> (meaning a single) coque (shell) structure has only a shell for
> structure (an egg is a perfect example), any deviation from this is
> often called semi-monocoque, even when the skin carries no load, which
> is an incorrect way of describing such a structure.

You mean "complementary," meaning "completes the function," not
"complimentary," as in "offerimg compliments."

[[email protected]]

Yes, you are correct. Thanks.

Bud

Orval Fairbairn wrote:
> In article . com>,
> wrote:
>
> > wrote:
> > >
> > > Semi-Monocoque is the term, not "complimentary."
> >
> > Whatever. My professor in graduate school (a Stanford Ph.D.) called it
> > complimentary, since the stringers and longerons compliment the skin in
> > that, as I said, they provide strength in a direction that the skin
> > does not have, which is out of plane stiffness. Since a true Mono
> > (meaning a single) coque (shell) structure has only a shell for
> > structure (an egg is a perfect example), any deviation from this is
> > often called semi-monocoque, even when the skin carries no load, which
> > is an incorrect way of describing such a structure.
>
> You mean "complementary," meaning "completes the function," not
> "complimentary," as in "offerimg compliments."

[[email protected]]

wrote:
> > Your average CessBeeMooPip is semi-monocoque in the aft fuselage.
>
> The fuselage skin from the firewall back is the primary structural
> member everywhere except at the wing spar attachments, and the landing
> gear on Cessnas.
>

The forward fuselage on the Cessna has heavy structural members.
There are hat-section channels to which the engine mount is attached,
and these run back to the doorposts, which are the primary lifting
members in the fuselage, since the wing's front spars, the spar
carrythrough and the strut attachments are all part of that big
bulkhead. The skin contributes much less in the way of tensile strength
in that area, and it's not a true semi-monocoque. There are sturdy ribs
under the floor and fuselage top, another bulkhead at the rear
doorpost/aft spar attach and carrythrough, and more frame members
behind that, especially around the windows, until we get to the aft
passenger compartment bulkhead. Past that point it's mostly skin. The
framework around the doorframes is fairly heavy to keep them square;
even at that, we find some distortion when we jack the R182 to swing
the gear. If those doors aren't set right, they end up taking flex
loads from the airframe and the hinges eventually break.

Dan

[Denny]

I refer the original poster to Low Power Laminar A/C Design by P.
Strojnik... A series of three books... Fascinating reading... The EAA
should have them at the book store...

But, to answer the question, the biggest impediment to the home builder
for making a monocoque fuselage in wood is the need for a plug to cold
mold or laminate the wood onto... If the fuse is symmetrical, a half
plug will work and join the two halves later... The favored material is
cement for making the plug, mostly for cost reasons I suspect - it
certainly would hamper portability...
The Mosquito was done this way, as was (I believe) much of the Spruce
Goose... Much of the Cirrus airplanes are plug molded as semi-monocoque
structures, but I don't think they use cement plugs :)

denny

[Morgans[_2_]]

"Denny" > wrote in message
oups.com...
>I refer the original poster to Low Power Laminar A/C Design by P.
> Strojnik... A series of three books... Fascinating reading... The EAA
> should have them at the book store...
>
So, I take it that the cold molding and/or laminating process is extensibly
covered in these books?

I might be interested in a read, if that is the case. I'm a carpenter/cabinet
maker, but I have to admit to being clueless about the cold molding process.
--
Jim in NC

[[email protected]]

Saying that something is the primary structural member doesn't mean it
is the only structural member. Aircraft structures typically have
several members sharing the load, hence the term "complementary
structure", as they complement each other in carrying the load. The
forward belly skin on my Cessna is .040 in thick, and 44 in wide. This
is approximately 1.75 sq. in. The forward side skins are .032 by 24 in
tall and has approximately .75 sq. in of area. The structural channels
you mention don't have anywhere near this much area, and are themselves
mounted to the forward skins. They are major structural members and
carry significant load, but the skin is still the primary load carrier.
The load paths and stress distribution of aluminum skin versus fabric
covered aircraft are very different. This is why fabric covered wings
require internal diagonal wire bracing, and aluminum skinned wings do
not. Fuselages behave in the same manner.

Bud

wrote:
> wrote:
> > > Your average CessBeeMooPip is semi-monocoque in the aft fuselage.
> >
> > The fuselage skin from the firewall back is the primary structural
> > member everywhere except at the wing spar attachments, and the landing
> > gear on Cessnas.
> >
>
> The forward fuselage on the Cessna has heavy structural members.
> There are hat-section channels to which the engine mount is attached,
> and these run back to the doorposts, which are the primary lifting
> members in the fuselage, since the wing's front spars, the spar
> carrythrough and the strut attachments are all part of that big
> bulkhead. The skin contributes much less in the way of tensile strength
> in that area, and it's not a true semi-monocoque. There are sturdy ribs
> under the floor and fuselage top, another bulkhead at the rear
> doorpost/aft spar attach and carrythrough, and more frame members
> behind that, especially around the windows, until we get to the aft
> passenger compartment bulkhead. Past that point it's mostly skin. The
> framework around the doorframes is fairly heavy to keep them square;
> even at that, we find some distortion when we jack the R182 to swing
> the gear. If those doors aren't set right, they end up taking flex
> loads from the airframe and the hinges eventually break.
>
> Dan

[Bob Kuykendall]

Earlier, Denny wrote:
> ...Much of the Cirrus airplanes are plug molded
> as semi-monocoque structures, but I don't think
> they use cement plugs...

I'm pretty sure that the Cirrus airplanes are female molded, which
seems to be the standard in modern composite aircraft construction. I
don't know of any modern male-molded composite aircraft. The only
composite male-molded production aircraft I can think of offhand is
Gerhard Waibel's ASW12 sailplane, and that was just for the fuselage.

Thanks, Bob K.
http://www.hpaircraft.com/hp-24

[[email protected]]

Denny wrote:
> I refer the original poster to Low Power Laminar A/C Design by P.
> Strojnik... A series of three books... Fascinating reading... The EAA
> should have them at the book store...

Thanks! I'll take a look.

>
> But, to answer the question, the biggest impediment to the home builder
> for making a monocoque fuselage in wood is the need for a plug to cold
> mold or laminate the wood onto... If the fuse is symmetrical, a half
> plug will work and join the two halves later... The favored material is
> cement for making the plug, mostly for cost reasons I suspect - it
> certainly would hamper portability...
> The Mosquito was done this way, as was (I believe) much of the Spruce
> Goose... Much of the Cirrus airplanes are plug molded as semi-monocoque
> structures, but I don't think they use cement plugs :)
>
> denny

I saw a concrete mold like that in a picture of lockheed factory taken
when the vega was being produced.

I've been very interested in sorting out what manufacturing techniques
would be most appropriate for mass production of light aircraft given
modern tooling.

Robotic welding is of high enough quality to handle steel tubing these
days. Obviously filiment wound composits present very high levels of
automation as well, but a much higher material cost. Aluminum obviously
has a reasonably high material cost, good workability, but the size and
flexibility of the sheets would concern me somewhat. I'd be inclined to
guess aluminum requires more skill in jigging than the alternatives.

I wonder whether filiment winding could be used with non-standard
materials. Could you filiment wind a fuselage with say... twine? Sounds
bizarre, but if it is encased in epoxy it might have a hope of
achieving a certain level of strength. If course most of the cost is
probably in the epoxy and not in the filiment.

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.

If you designed an aircraft to leverage modern production lines, what
would it be made of?

Thanks!
Matt

[Ernest Christley]

wrote:

> If you designed an aircraft to leverage modern production lines, what
> would it be made of?
>
> Thanks!
> Matt
>

Fairy dust 8*)
You have to consider the economics of the thing. Modern assembly lines
are set up and expected to produce hundreds of thousands/yr if not
millions/yr of a product. We're talking a yearly volume on the scale of
the entire US GA fleet. One airplane for every registered pilot. The
most you could hope with any airplane design is more on the order of
100s/yr. The type of tooling you speak of takes as much R&D as an
airplane design. All that cost has to be amortized somewhere in a
reasonable amount of time. You very quickly get to the point where you
can roll off airplanes that have never been touched by human hands, but
they're so expensive to pay for the tooling that no one can afford them.

And just having the work done by a machine doesn't get you home free.
Machines break. They are usually out of calibration, and they rarely
work as designed the first time. So now you're paying people to watch
the machines. Machines that makes airplanes that can't be sold any
faster than it took the people to make the machines.

SA gave a tour of the Cirrus factory a month or two back. I think they
have it right. Automate the simple things. Have humans do the
complicated things. Design the airplane with the lowest possible parts
count. I suspect that they will slowly add more automation as the
capitol budget allows.

[[email protected]]

Ernest Christley wrote:
> wrote:
>
> > If you designed an aircraft to leverage modern production lines, what
> > would it be made of?
> >
> > Thanks!
> > Matt
> >
>
> Fairy dust 8*)
> You have to consider the economics of the thing. Modern assembly lines
> are set up and expected to produce hundreds of thousands/yr if not
> millions/yr of a product. We're talking a yearly volume on the scale of
> the entire US GA fleet. One airplane for every registered pilot. The
> most you could hope with any airplane design is more on the order of
> 100s/yr. The type of tooling you speak of takes as much R&D as an
> airplane design. All that cost has to be amortized somewhere in a
> reasonable amount of time. You very quickly get to the point where you
> can roll off airplanes that have never been touched by human hands, but
> they're so expensive to pay for the tooling that no one can afford them.
>

I understand your argument, and it is absolutely valid. But humor me
for a moment, and lets assume that a market could be found. Call me an
optomotrist, but I think there might still be a market, even if the
pilots don't exist at the moment.

> And just having the work done by a machine doesn't get you home free.
> Machines break. They are usually out of calibration, and they rarely
> work as designed the first time. So now you're paying people to watch
> the machines. Machines that makes airplanes that can't be sold any
> faster than it took the people to make the machines.

Understood. But speculation is the inbred half stepbrother of
invention, (or something), and I might speculate that their is an
abundance of machines being discarded as modern factories go to third
and fourth generation robotics, and that much of it can be had for a
song.

>
> SA gave a tour of the Cirrus factory a month or two back. I think they
> have it right. Automate the simple things. Have humans do the
> complicated things. Design the airplane with the lowest possible parts
> count. I suspect that they will slowly add more automation as the
> capitol budget allows.
>

What parts did they automate?

-Thanks!
-Matt

[Ernest Christley]

wrote:

>> SA gave a tour of the Cirrus factory a month or two back. I think they
>> have it right. Automate the simple things. Have humans do the
>> complicated things. Design the airplane with the lowest possible parts
>> count. I suspect that they will slowly add more automation as the
>> capitol budget allows.
>>
>
> What parts did they automate?
>
> -Thanks!
> -Matt
>

Mixing the epoxy.

I'll grant your points about speculation (What else is a bull session
good for? 8*), and I will only counter that there are a lot of people
trying to do exactly as you say. 'T'aint easy.

[[email protected]]

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

[[email protected]]

wrote:
> Saying that something is the primary structural member doesn't mean it
> is the only structural member. Aircraft structures typically have
> several members sharing the load, hence the term "complementary
> structure", as they complement each other in carrying the load. The
> forward belly skin on my Cessna is .040 in thick, and 44 in wide. This
> is approximately 1.75 sq. in. The forward side skins are .032 by 24 in
> tall and has approximately .75 sq. in of area. The structural channels
> you mention don't have anywhere near this much area, and are themselves
> mounted to the forward skins. They are major structural members and
> carry significant load, but the skin is still the primary load carrier.



Very good points. Thank you.

Dan

[[email protected]]

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.

Understood. Which is why I was interested in plywood monocoque designs.
While domestic supplies of quality timber are depleted this is not so
everywhere. This is not a major factor IMHO because I forsee the
markets for new aircraft forming primarily overseas. So that would
resign a new aircraft company to building its factory in perhaps China
or one of the former Soviet states, or even Africa perhaps. (When you
weren't dodging bullets, graft, malaria, etc. etc.)

> 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.

Not punch, but drill/mill/saw/route/form certainly. I can imagine a
system for hot or cold pressing monocoque plywood skins that was
heavily automated. I can't invision an equivilant system for forming
and riveting aluminum because of the floppyness of it. (technical terms
abound :-) I'm thinking along the lines of a modern plywood
manufacturing plant adapted to make airplanes. I guess you could say my
approach would be to design an airplane around a factory instead of the
of the factory around the airplane.

> 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

Composites yes. Aluminum no. The reason really comes down to skilled
labor. I would prefer the assembly to be as idiot-proof as possible,
(predicting a probable shortage of skilled labor). While composites are
not idiot proof, I suspect composites would take to automated
manufacturing better. Specifically I've been VERY interested in
filament winding as a means of making both wings and fueselages. I
haven't seen this approached in any homebuilts either, though I do
understand that some hobbyists have built filament winding systems for
other things, like rocket motors for example.

Both the Falco and the Barracuda are beutious! From a hand-built
perspective their labor requirements are _huge_. But the variation of
techniques and materials is probably fairly low compared to other types
of construction. For a robot it is better to do one thing many times
than many things one time. So my hypothesis is that plywood aircraft
would benefit more from heavy automation than perhaps a Cessna or a
Maule would. The amount of data I have to support that position is
obviously lacking. But I would be interested in other opinions on the
matter.

-Matt

[Capt. Geoffrey Thorpe]

> wrote in message
oups.com...
>
> 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.
>

The airplanes mentioned in the original post were, I'm pretty sure, cold
molded - a very labor intensive process of laying individual strips of
veneer - each trimmed to shape - over a plug and either stapled of vacuum
bagged until the laminate cures.
But other methods exist to build wood stressed skin structures. e.g.
"Constant Camber" is a boat building method where full sheets of veneer are
placed in a somewhat generic female mold and vacuum bagged - the mold does
not have compound curves, but by changing the position of the layup, you get
different shaped panels that then can be assembled into whatever.

Another option is "tortured plywood" where thin plywood is forced into a
compound shape.

Amateur boat builders are also using a "stich and glue" technique to make
plywood hulls - I wonder how long before someone tries it for an airplane?

Or - consider a structure like a KR-2 - a plywood box with some sticks to
reinforce. Not a swoopy looking as a Mosquito bomber, but it works and it
doesn't require "premium" lumber

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)...


--
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.

[Morgans[_2_]]

"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.

This all gets a bit labor intensive, but semi-skilled labor can be taught to
make spars, with enough repetition for mass production to be cost effective.

I like the idea of wood mass produced airplanes, but I fear there are too many
advantages for other materials, and pre conceived notions against wood airplanes
to make them fly. (pun intended) <g>
--
Jim in NC

[[email protected]]

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/showthread.php?s=93d9524a4eec4011160b889f25602fba&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

[Orval Fairbairn]

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/showthread.php?s=93d9524a4eec4011160b889f2560
> 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.

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

[[email protected]]

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/showthread.php?s=93d9524a4eec4011160b889f2560
> > 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

[Orval Fairbairn]

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/showthread.php?s=93d9524a4eec4011160b889f
> > > 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.

[Capt. Geoffrey Thorpe]

"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.

[[email protected]]

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

[Morgans[_2_]]

> 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

[Roger (K8RI)]

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

[Stealth Pilot]

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