Why no plywood monocoque homebuilts?

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.

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

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.

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

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

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

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.

"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

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... 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

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.

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