Glue it to it

To All:

A few days ago I responded to Lou's question about the cold weather
performance of T-88...


http://groups.google.com/group/rec.a...40a97c3fdfa121

....where in closing I said, "Marvelous as epoxies are they don't even
come close to resorcinol when it comes to durability."

Boy, did I catch hell :-)

One feller politely provided me with a table of specifications for
various epoxies showing their shear strength, modulus of rupture and
modulus of elasticity. At least half of the figures were better than
the specs for Weldwood Resorcinol.

Another less polite message informed me I didn't know what I was
talking about. It seems this particular person had been using T-88
since it was introduced '...during the Second World War..' and
stated it was the best glue ever invented.

- - - - - - - - - - - - - - - - - - - - - - - - -

Allow me to repeat the obvious:

Bum Dope can get you killed.

At least half of the information on the internet is incorrect to some
degree.

Anyone offering an opinion should be willing to back it up, if not with
facts, at least with the basis for their opinion.

So here goes :-)

- - - - - - - - - - - - - - - - - - - - - - - - - -

'Epoxy' as a chemical term dates from the early 1900's with the
first patents applied for in Germany during the 1930's. During World
War II some epoxies were developed for various roles - - adhesives,
insulators, paints and so forth - - but commercial exploitation of
epoxies was not seen on any scale until the late 1940's with the
development of methods for making the stuff from natural gas.

With regard to T-88, as best I can recall it didn't arrive on the
scene until the early 1970's, not '...during the Second World War.'
I'll be more than happy to admit my error here if someone can offer
a better reference. (I'm old. I fart a lot and forget things.)

As I said in my response to Lou, epoxies are marvelous stuff as
adhesives but when it comes to their durability they don't do as well
as plain old-fashioned resorcinol. At least, not if we are talking
about gluing wood, and specifically so when the task is gluing birch
plywood to softwood stringers. Shear strength remains high but peel
strength declines with age. Fortunately, it's rare for a
birch-spruce joint in an aircraft structure to be subjected to a
delaminating load. Something else would have to fail first. (Hint:
Given enough time, simply allowing moisture to collect inside the
structure would be sufficient.)

This comes under the heading of Old News since the problem has been
around as long as epoxies themselves. But in the late 1960's there
were indications that certain chemical 'coupling agents' could
facilitate a CHEMICAL bond between an adhesive and whatever it was
applied to. This created an enormous amount of interest because it
hinted we might be able to GLUE metals together and end up with a joint
equal to welding, riveting, brazing and so on.

As you may have noticed, that hasn't happened. Yet. At least, not
with metals on an industry-wide scale. But it HAS happened with wood
and some plastics.

In 1995 a fellow named Charles B. Vick from the Forest Products
Laboratory presented a paper in Portland describing tests with a
coupling agent called HBR (hydroxymethylated resorcinol) as a means of
enhancing the adhesion of epoxy to wood. The results of the tests were
so promising that it lead to the academic equivalent of dancing in the
streets (which means more studies. :-)

The key point here is that the tests compared epoxies, enhanced or
otherwise, to plain old-fashioned resorcinol, which I believe justifies
my statement to Lou.

In the decade since Mr. Vick presented his paper on epoxy and HBR he
has completed a number of other studies, read with the keenest interest
by folks selling epoxy glues. And by guys like me who occasionally
trust their lives to an assemblage of glued joints. In responding to
Lou's message I felt I was doing what any other homebuilder would
have done had he gotten to the keyboard first. But if I erred in doing
so, please have the courtesy to state your correction publicly since
doing so privately makes it little more than a personal attack and
contributes nothing to the sum store of information.

- - - - - - - - - - - - - - - - - - - -

As I've mentioned in earlier articles ('Glue Wars,' etc.) ALL
modern adhesives are stronger than the softwoods normally used for
airplane construction. That means the question of strength drops out
of the equation when selecting what we're going to use to gluit toit.
While epoxies are the near-ideal adhesive for airplanes the gritty
reality is that it's more expensive than other equally useful glues.
Such considerations fly right over the head of someone who thinks a
thirty thousand dollar kit is 'inexpensive' and it's $25,000.00
engine 'affordable' but the hundred dollar difference between an
epoxy from Aircraft Spruce and a few pounds of Weldwood 'Plastic
Resin' from the local Borg is a CRITICAL factor to the tens of
millions of Americans who can simply no longer afford to be a part of
the General Aviation community.

-R.S.Hoover

wrote:

...where in closing I said, "Marvelous as epoxies are they don't even
come close to resorcinol when it comes to durability."

None of the Big Borg stores in my part of Northern California, nor the
local, well stocked and well run Ace stock resorcinol, and I was told
by the proprietor of a specialty woodworking store that it is not
stocked or distributed in California. I have had good luck mail
ordering it from various on-line hardware stores in Oregon, etc. But
when shipping is factored in, it's as expensive or more so than the
more readily available and still Adequate epoxy formulations like T-88.

How are you getting it down in Vista? Or have you decided that in spite
of it's advantages, it's not worth the hassle of getting it, and that
for most uses, moisture cure urethanes, epoxies, and plastic resin glue
are Good Enough?

flybynightkarmarepair wrote:


None of the Big Borg stores in my part of Northern California, nor the
local, well stocked and well run Ace stock resorcinol, and I was told
by the proprietor of a specialty woodworking store that it is not
stocked or distributed in California.
-----------------------------------------------------------------------------

Go to the DAP web-site and click on the 'Find Retailer' tab.

One of the Home Depot stores in Escondido ( 11 mile from the house )
carried it for a time and will apparently special-order it. DAP lists
the Home Depot store in Lemon Grove ( abt. 30 miles away ) as a
retailer.

Resorcinol apparently from China(!) is leaking across the border. The
powder is in a sealed foil/plastic/paper pouch, the liquid in
non-resealable tin can. Used primarily at small boat yards around
Sandy Eggo. (Same brownish-purple stuff; absolutely impervious to the
72hr boil-test.)

----------------------------------------------------------------------------------

How are you getting it down in Vista? Or have you decided that in spite
of it's advantages, it's not worth the hassle of getting it, and that
for most uses, moisture cure urethanes, epoxies, and plastic resin glue
are Good Enough?

-----------------------------------------------------------------------------------

I still prefer resorcinol for props. And as shown above, it is still
locally available. However, given our weather, Weldwood 'Plastic
Resin' does just fine for most everything else.

Despite the recent FAA warnings, if you'll check the provenance of the
failures that prompted the warning against urea-formaldehyde glue (ie,
Miles 'Messenger' and deHavilland 'Mosquito,' both in tropical
Australia) and compare that to the conditions under which Fly Baby's
(and others) enjoy here in the States, I think you'll see why I
continue to use it, at least until I hear of a documented case of
Weldwood 'Plastic Resin' failure. (Hint: If you want it to last,
don't leave your plywood-skinned bird parked out in the open, on the
equator, for four years.)

Which doesn't mean it is the only glue I use. I've posted several
comments and some test results regarding one-part urethane adhesives
and cyanoacrilates. I don't care much for the latter due to their
short working time (typically 30min ) but I've found urethanes to be
trustworthy when properly applied and sufficiently clamped. In that
regard, the FPL clamping and application instructions have proven to
give more reliable results than the instructions provided by most
urethane manufacturers. (ie, apply to both surfaces, limit open time
to 15min., clamp with up-to 150psi for 24hours and do not stress for
up to 72hrs) Indeed, I recently failed one of the hold-down bolts of
the vise I use to hold coupons for shearing tests whilst testing
urethane-glued coupons of Douglas Fir.

---------------------------------------------------------------------------

As a point of interest, I'm presently testing urethane for attaching
door-skins to hemlock stringers using pneumatically-driven brads and
staples. For a 'standard' I made up some test pieces using Sitka
spruce, resorcinol and nailing strips (ie, the 'traditional' method).

The tricky bit is determining the best type of fastener and the spacing
between them. Project is presently on hold due to cold weather (the
work is being done outside the shop).

I've taken advantage of the cold weather (it got close to freezing
Monday night) to test coupons of T-88. In theory, the chemical cure of
epoxy simply slows down, as opposed to urea-formaldehyde which must be
maintained above a certain temperature. Allowing the epoxied coupons
to remain clamped for up to seven days should result in an adequate
bond. The sledge hammer will tell me if that's correct :-) (2.25 sq.
in. of gluing surface should fail in shear at about 2365 psi for DF @
12% moisture content. )

--------------------------------------------------------------------------

When building a Box Store Bomber I feel the adhesive is even more
important than the wood. The tricky bit here is that while using
locally available wood has a dramatic effect on reducing the cost of
the airframe, the RELATIVE cost of the adhesive goes UP if you spec
something like T-88 or FPL-16A. This is what's behind my interest in
'Plastic Resin' and urethanes.

-R.S.Hoover

wrote:
[...]
I still prefer resorcinol for props. And as shown above, it is still
locally available. However, given our weather, Weldwood 'Plastic
Resin' does just fine for most everything else.

Despite the recent FAA warnings, if you'll check the provenance of the
failures that prompted the warning against urea-formaldehyde glue (ie,
Miles 'Messenger' and deHavilland 'Mosquito,' both in tropical
Australia) and compare that to the conditions under which Fly Baby's
(and others) enjoy here in the States, I think you'll see why I
continue to use it, at least until I hear of a documented case of
Weldwood 'Plastic Resin' failure. (Hint: If you want it to last,
don't leave your plywood-skinned bird parked out in the open, on the
equator, for four years.)
[...]
-R.S.Hoover

I've worked on three Fly Babies, two from the eighties and one from the
seventies. Their glue joints were sturdy, and one of them had had some
awful rough landings which broke the 4130 landing gear and ruined some
of the welded steel fuselage attach fittings. Best I could tell the
glue in all three was resorcinol. Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.

Somewhere in Ron Wanttaja's literature I read of a Fly Baby
cartwheeling and the wings did not collapse. Fuselage was damaged but
the pilot lived to tell the story.

On 7 Dec 2006 07:47:00 -0800, "jls" wrote:


wrote:
[...]
I still prefer resorcinol for props. And as shown above, it is still
locally available. However, given our weather, Weldwood 'Plastic
Resin' does just fine for most everything else.

Despite the recent FAA warnings, if you'll check the provenance of the
failures that prompted the warning against urea-formaldehyde glue (ie,
Miles 'Messenger' and deHavilland 'Mosquito,' both in tropical
Australia) and compare that to the conditions under which Fly Baby's
(and others) enjoy here in the States, I think you'll see why I
continue to use it, at least until I hear of a documented case of
Weldwood 'Plastic Resin' failure. (Hint: If you want it to last,
don't leave your plywood-skinned bird parked out in the open, on the
equator, for four years.)

I've worked on three Fly Babies, two from the eighties and one from the
seventies. Their glue joints were sturdy, and one of them had had some
awful rough landings which broke the 4130 landing gear and ruined some
of the welded steel fuselage attach fittings. Best I could tell the
glue in all three was resorcinol. Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.

Somewhere in Ron Wanttaja's literature I read of a Fly Baby
cartwheeling and the wings did not collapse. Fuselage was damaged but
the pilot lived to tell the story.

http://www.bowersflybaby.com/safety/horsten.html

Last report I had is that the pilot and his adult son were building another Fly
Baby....

Ron Wanttaja

jls wrote:
Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.
-----------------------------------------------------------------------------------------------------

Without meaning to lessen Pete's abilities as a designer, the praise
for the Fly Baby's strength should probably go to Tony Fokker or
Geoffery deHavilland. They were the first to break away from fuselage
structures using wire-braced hardwood longerons in favor of spruce
longerons and plywood shear-webs, which often weighed more.

The advantage here is rather subtle and was not appreciated until a
number of the 'plywood box' designs survived crashes that would have
reduced a wire & ash fuselage to flinders. The subtleties that had
escaped noticed (even today, in many cases :-) is that the continuous
bond between the load-bearing members allowed the loads to be
distributed in a fairly uniform manner, whereas the pinned and
wire-braced joints tended to concentrate the stress at those points.
With such high concentrations of stress the failure of a single wire or
fitting was enough to precipitate failure of the entire structure.

Once the early designers appreciated the advantage of the one over the
other they moved immediately to true monocoque structures of molded
plywood, welded steel tubing and so forth, but the structural integrity
of the 'box' structures combined with their simplicity of fabrication
makes the method ideal for homebuilders even today.

-R.S.Hoover

wrote

Once the early designers appreciated the advantage of the one over the
other they moved immediately to true monocoque structures of molded
plywood, welded steel tubing and so forth, but the structural integrity
of the 'box' structures combined with their simplicity of fabrication
makes the method ideal for homebuilders even today.

Correct me if I'm wrong, but isn't epoxy for homebuilders considered much more
"user friendly" than Resorcinol, because Resorcinol is very particular about
having uniform, tight fitting joints, and the correct clamping pressure?
--
Jim in NC

I once amazed myself by bouncing a Flybaby about 8 or so feet in the
air, which I thought wasn't possible with just tires for shock absorption
..

I've worked on three Fly Babies, two from the eighties and one from the
seventies. Their glue joints were sturdy, and one of them had had some
awful rough landings which broke the 4130 landing gear and ruined some
of the welded steel fuselage attach fittings. Best I could tell the
glue in all three was resorcinol. Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.

Somewhere in Ron Wanttaja's literature I read of a Fly Baby
cartwheeling and the wings did not collapse. Fuselage was damaged but
the pilot lived to tell the story.

On Thu, 07 Dec 2006 18:55:08 -0500, "J.Kahn" wrote:

I've worked on three Fly Babies, two from the eighties and one from the
seventies. Their glue joints were sturdy, and one of them had had some
awful rough landings which broke the 4130 landing gear and ruined some
of the welded steel fuselage attach fittings. Best I could tell the
glue in all three was resorcinol. Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.

Somewhere in Ron Wanttaja's literature I read of a Fly Baby
cartwheeling and the wings did not collapse. Fuselage was damaged but
the pilot lived to tell the story.

I once amazed myself by bouncing a Flybaby about 8 or so feet in the
air, which I thought wasn't possible with just tires for shock absorption

I pegged a 4-G g-meter on a landing once. No damage, and that was on a gear leg
that had been improperly repaired from a crash 15 years earlier.

Ron Wanttaja

"Ron Wanttaja" wrote in message
...
On Thu, 07 Dec 2006 18:55:08 -0500, "J.Kahn"
wrote:

I've worked on three Fly Babies, two from the eighties and one from the
seventies. Their glue joints were sturdy, and one of them had had some
awful rough landings which broke the 4130 landing gear and ruined some
of the welded steel fuselage attach fittings. Best I could tell the
glue in all three was resorcinol. Pete Bowers is an honored immortal
for designing such a great little wooden airplane that can flare 20
feet off the deck and still remain intact.

Somewhere in Ron Wanttaja's literature I read of a Fly Baby
cartwheeling and the wings did not collapse. Fuselage was damaged but
the pilot lived to tell the story.

I once amazed myself by bouncing a Flybaby about 8 or so feet in the
air, which I thought wasn't possible with just tires for shock absorption

I pegged a 4-G g-meter on a landing once. No damage, and that was on a
gear leg
that had been improperly repaired from a crash 15 years earlier.

Ron Wanttaja

I've seen 2G's on landing, but never more than that. Of course, the RV's
gear probably has more spring to it than the Flybaby's tires, so my 2 G
arrival may not have any more energy than your 4, but 4??? Ouch. That's a
nice way to chip a tooth or something.

KB