Metal vs Wood or T2 vs VP (Part II)

On Mar 29, 12:54*pm, Bob Hoover wrote:
On Mar 29, 9:17*am, Copperhead wrote:

Oddly enough I've had more fun researching and experimenting with
plans and parts building then I'd ever have thought possible and have
spent very little money so far. Mostly this has been due to the fact I
already have most of my woodworking power tools as well as a lot of
metal cutting and bending tools.

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Dear Joe,

Normally, when you have the option of building from either aluminum or
wood, you would opt for metal but there are a few cases where wood may
prove to be the better choice. *In the mid-1930's Virginias Clark, the
fellow who gave us the Clark-Y airfoil, patented a process of making
plywood called 'Duramold' that was superior to aluminum in several
ways, but especially with regard to compound curves. *Howard Hughes
acquired the rights to the process (I believe through Fairchild
Camera) and used it to produce the HK-1 'Hercules' *-- *which we
generally know as 'the Spruce Goose,' even though it is mostly birch.
The 'K' part of 'HK' referred to Henry J. Kaiser, who was supposed to
assemble the giant flying boat, Hughes to fabricate the parts.

One reason we've never heard much about Dura-mold is because of
fiberglas.... and a small Swiss company that came up with epoxy.
Combine the two and even a back-yard craftsman has the ability to
produce complex parts stronger than steel but weighing as much as two-
thirds less.

-Bob

PS -- I've got a hunch that threads such as this often turn into
something useful.

Bob,

I’d read about the composite construction techniques of the ill named
“Spruce Goose”, but never made a correlation with respect current
fiberglass composite aircraft. Merely at a guess, it would appear that
one would need to make they’re own “duramold” ply (glass) wood while
constructing an airframe.

I certainly agree that such a practice would eliminate the need for
applying fiberglass to foam for panels or coverings. Current vacuum
bagging practices used on KR’s with hand made mold would most
certainly work. Now I’m going to have to do some research and
experimentation to see what epoxy and wood veneer bond together best.

For this, I believe the local boat builder’s and marine plywood supply
distributors are going to be a good information source. I think your
right about the weight savings coupled with enhanced strength of such
a project. It also looks like it would eliminate a lot of glass cloth
as well as grinding and sanding. Very interesting and informational,
thanks.

Regards

Joe S.

On Mar 29, 11:45*am, Copperhead wrote:

I’d read about the composite construction techniques of the ill named
“Spruce Goose”, but never made a correlation with respect current
fiberglass composite aircraft. Merely at a guess, it would appear that
one would need to make they’re own “duramold” ply (glass) wood while
constructing an airframe.
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Dura-mold used a 'resin' similar to Plastic Resin Resorcinol in
APPEARANCE (or so I'm told; second-hand information coming at you
here). That is, there was a powder and a liquid which had to be mixed
according to a critical ratio. The wood was then impregnated with the
resin using a lay-up process similar to doing a boat hull. cabin tops
or what-have-you... with one critical exception. It was a CLOSED mold
-- you had to get the lid on the thing -- and the cure was done using
HEAT. In this case, steam or hot water.

The molds could be concrete & hot water -- and most of them were --
but some parts used ALUMINUM molds and electrical or steam heat.

Hughes ponied up an incredible amount of cash to resolve a lot of
unforseen problems relating to serial production, producing panels of
larger size, attaching panels together ...ever heard of FPL-16a
(HUGHES GLUE) ? Once all the bugs were out of the production process
you start popping HK-1's out of ship yards on both coasts at a
guesstimated rate of thirty PER DAY. And of those eight humongous
engines, it took only FOUR to FLY the thing... but all EIGHT were
needed for a fully-laden take-off

The deal with fiberglas & epoxy was that it weighed less and was
stronger than Dura-mold, plus you could formulate it for room-
temperature curing. All of that development work -- and all of that
MONEY -- had been overtaken by events.

(So what was the big flap between Hughes and the government? Hughes
had a piece of paper signed by 'the government' that said they would
pay ALL COSTS incidental to production of the HK-1, which the Hughes
lawyers read to mean all those bucks spent in development work. The
Government disagreed, saying they meant the cost of setting up
production facilities, NOT costs associated with basic research. Plus
there were more than a few Congressmen who kept pointing out that the
thing had not actually FLOWN... that it might be nothing more than a
bogus scheme to screw the American tax payer, yada yada yada...

Hughes won, by the way. But it was often said that he spent more on
legal fees than he recovered.)

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I certainly agree that such a practice would eliminate the need for
applying fiberglass to foam for panels or coverings.

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I'm not sure why it is, but a lot of people seem to think that mold-
less composite work was something new; that Kenny had come up with a
better mouse trap. In fact, that method of fabrication has been in
use for literally THOUSANDS of years. Although I wasn't around back
then (despite what you may have heard...) they have found numerous
examples of PLYWOOD in Egyptian tombs and the re-curve bow used by
Genghis Khan's mounted troops was of mold-less composite structure.
Closer to home, when tasked with producing 1200 sets of Roman-era
armor for the movie 'Ben Hur,' the set designers cranked them out
using paper mache. But of more practical use, it was fairly common
for fishermen to re-enforce spars and booms using canvas & varnish.

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Current vacuum
bagging practices used on KR’s with hand made mold would most
certainly work. Now I’m going to have to do some research and
experimentation to see what epoxy and wood veneer bond together best.

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Homebuilders could turn out some damn good airplanes on the cheap if
we can come up with a mini-production line for vacuum bagging leading-
edge sections for a couple of standard airfoils, such as 4412, 4415 or
the M6, in lengths of about 48 inches. Properly done, the section
gets peel-ply'd on the interior and the edges get stepped. It locks
you into a rectangular plan-form but you can come up with a good D-
cell, allowing you to produce a really good wing.

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For this, I believe the local boat builder’s and marine plywood supply
distributors are going to be a good information source. I think your
right about the weight savings coupled with enhanced strength of such
a project. It also looks like it would eliminate a lot of glass cloth
as well as grinding and sanding.

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The information everybody wants is out there but it's fragmented.
Unfortunately the only body that claims to speak for the lowest level
of aviation in America -- logically the organization that should
concern itself with such matters -- has not.

-Bob

On Mar 29, 7:04*pm, Bob Hoover wrote:

Homebuilders could turn out some damn good airplanes on the cheap if
we can come up with a mini-production line for vacuum bagging leading-
edge sections for a couple of standard airfoils, such as 4412, 4415 or
the M6, in lengths of about 48 inches. *Properly done, the section
gets peel-ply'd on the interior and the edges get stepped. *It locks
you into a rectangular plan-form but you can come up with a good D-
cell, allowing you to produce a really good wing.

I've had similar thoughts and have done some small experiments with
the TPG process. Haven't yet found the right core material. High
density PVC foam looks promising in place of Taylors paper. I have
some to play with but started projects must be completed first.

As for being "locked" into a rectangular plan-form, I'm not so sure.
There seems to be enough flexibility in the formed leading edges to
squish them down a bit after cure. The leading edge radius stays
larger then a full scaling down but that might work out to be an
advantage when it comes to tip stall?

While I'm thinking about it - vacuum sources. Mine is a water bed
drain tool. Works great and cost little. Set it up on the lid of a
Rubbermaid type tub of water with a small recirculating pump and you
have an inexpensive and reliable source of vacuum. When your finished
everything stores in the tub for the next use. Just remember to put a
check valve on the outlet or you risk sucking in water if the power or
pumps prime gets interrupted. A good source of check valves ... power
brake hose from about any salvage auto. For vacuum control a fish
tank air valve works well enough.
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Leon McAtee