Glue it to it

[[email protected]]

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.aviation.homebuilt/browse_thread/thread/0e40a97c3fdfa121

....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

[flybynightkarmarepair]

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?

[[email protected]]

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

[jls]

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.

[Ron Wanttaja]

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

[[email protected]]

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

[Morgans[_2_]]

> 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

[J.Kahn]

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.
>

[Ron Wanttaja]

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

[Kyle Boatright]

"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

[Ron Wanttaja]

On Thu, 7 Dec 2006 22:44:47 -0500, "Kyle Boatright" >
wrote:

>> 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.
>
>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.

My back hurt for a couple of days. I posted the story to RAH back then;
reproduced:

http://www.bowersflybaby.com/stories/humility.HTM

I've got a couple of photos of the G-meter, been meaning to dig 'em up, scan
them in, and add one to the web page....

Ron Wanttaja

[Morgans[_2_]]

"Ron Wanttaja" > wrote

> 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.

Thanks, Ron, for a partial confirmation of my concept.

See if you 'all can follow my reasoning, here.

A plane is commonly certified for -3 G's. That means all of the weight of the
plane is supported by the wing. Good engineering would place ultimate failure
at at least 1.5 times the 3 G's. That means the wing would hold 4.5 G's.

That means the wing was holding all of the weight of the plane. What would the
wing weigh, compared to the whole plane? Perhaps 1/4th of the weight?

If the wing were to fail from a landing, overflexing the wing, it would take a
landing of 4 times the 4.5 G's, or 18 G's.

Now, I give that it is unlikely to fail a wing from a hard landing, but people
do fail wings from crashes. (that is a landing, right? <g>) Wayne Hadley thinks
his crash was about 27 G's One has to think the gear absorbed at least 1/2 of
the force, right? So it follows that I would want my gear to stand up to at
least 10'G's before it folded flat, or ripped loose from the fuselage or wing.

So, if my gear were to stand up to drop test at 10 G's, and it had a 12" travel,
how high would the plane have to be dropped from, to achieve that force?
--
Jim in NC

[[email protected]]

Morgans wrote:
>
> 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?
> -------------------------------------------------------------------------------

Only among folks trying to sell you epoxy :-)

Epoxy is known to trigger an allergic reaction in some people, making
its 'user-friendliness' more hype than reality.

The same applies to the 'tight fitting joints.' The need is valid for
marquetry or cabinet-making but is fallacious when applied to aircraft
structures. The load-bearing capacity of the glued joint is a function
of its surface-area. In aircraft we use gussets and corner blocks to
achieve the required surface-area and such joints are typically
flat-to-flat, which are inherently 'tight-fitting.'

The point about clamping pressure is valid. Fortunately, most joints
in aircraft structures make it fairly easy to apply the required amount
of pressure. And when they don't, we have the option of using epoxy.

Much of the controversy over adhesives stems from the fact they are
materials as well as tools. Since all modern adhesives used in the
construction of wooden airplanes are stronger than the wood itself, the
factor of strength -- the 'materials' aspect -- drops out of the
equation. When that happens you will see that for the builder on a
budget the use of less expensive, locally available adhesives simply
reflects using the most appropriate tool for the job.

-R.S.Hoover

[jls]

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.
>
> -R.S.Hoover

Which reminds me. A little googling will bring up an Avions Mudry Cap
10B (also known as Apex), the left spar of which failed in Texas a few
years ago (c. 2001), killing the pilot. The problem was compression
fractures in the upper box spar cap and some other damage which could
not be (or was not) inspected and repaired, even after compliance with
several service bulletins requiring inspection and repair near the wing
attach fittings at the wing roots. According to the NTSB report, none
of the glue bonds failed; the failures were compression cracks in the
Sitka spruce and other woods in the main spar. Having read the reports
and seen the extensive photos of the failures, I think if I had a Cap
10, I would rebuild the wings or ground it.

[Capt. Geoffrey Thorpe]

"Morgans" > wrote in message
...
>
> > 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 see the primary shortcoming of Epoxy as the glass transition temperature.
There is a reason plastic airplanes are painted white, eh?

Anyone got data on just how hot it gets inside a wing in the Texas sun?

--
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.

[Kyle Boatright]

"jls" > wrote in message
oups.com...
>
> 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.
>>
>> -R.S.Hoover
>
> Which reminds me. A little googling will bring up an Avions Mudry Cap
> 10B (also known as Apex), the left spar of which failed in Texas a few
> years ago (c. 2001), killing the pilot. The problem was compression
> fractures in the upper box spar cap and some other damage which could
> not be (or was not) inspected and repaired, even after compliance with
> several service bulletins requiring inspection and repair near the wing
> attach fittings at the wing roots. According to the NTSB report, none
> of the glue bonds failed; the failures were compression cracks in the
> Sitka spruce and other woods in the main spar. Having read the reports
> and seen the extensive photos of the failures, I think if I had a Cap
> 10, I would rebuild the wings or ground it.

Compression failures are due to either an over-stress condition, poor
design, or poor materials. Compression failures have happened in every type
of aircraft structure (metal, wood, and/or glass).

Why would you ground your hypothetical CAP due to this one instance, which
was probably caused by an overstress at some point (assuming no pertinant
facts were omitted from this synopsis) ?

Beyond that, if you rebuilt the wings, how would you know that the next
person who flew it didn't overstress it on his/her first flight?

KB

[jls]

Kyle Boatright wrote:
> "jls" > wrote in message
> oups.com...
> >
> > 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.
> >>
> >> -R.S.Hoover
> >
> > Which reminds me. A little googling will bring up an Avions Mudry Cap
> > 10B (also known as Apex), the left spar of which failed in Texas a few
> > years ago (c. 2001), killing the pilot. The problem was compression
> > fractures in the upper box spar cap and some other damage which could
> > not be (or was not) inspected and repaired, even after compliance with
> > several service bulletins requiring inspection and repair near the wing
> > attach fittings at the wing roots. According to the NTSB report, none
> > of the glue bonds failed; the failures were compression cracks in the
> > Sitka spruce and other woods in the main spar. Having read the reports
> > and seen the extensive photos of the failures, I think if I had a Cap
> > 10, I would rebuild the wings or ground it.
>
> Compression failures are due to either an over-stress condition, poor
> design, or poor materials. Compression failures have happened in every type
> of aircraft structure (metal, wood, and/or glass).
>
> Why would you ground your hypothetical CAP due to this one instance, which
> was probably caused by an overstress at some point (assuming no pertinant
> facts were omitted from this synopsis) ?
>
> Beyond that, if you rebuilt the wings, how would you know that the next
> person who flew it didn't overstress it on his/her first flight?
>
> KB

Read the reports and you'll begin to see the problem. There's not that
big a Cap 10 fleet here in the USA but after the fatality, more bad
wings were found. Read the reports before you make your judgment. I
didn't make mine until I had seen them.

[J.Kahn]

I agree that metal structures can suffer compression related failures.
At my employer, a leading Regional Jet manufacturer, a situation came up
where landing gear legs were cracking due to localized stress during
hard landings, which were yielding a small zone of metal at the peak
stress point, within surrounding metal (300M steel) that did not quite
reach the compression yield point. As soon as the load was removed,
this set up a huge internal "force fight" between the yielded material
and unyielded material deep within the forging, leading to a cracked leg.

This requires the fitting to be capable of reaching a compression yield
limit before buckling, with just enough force applied to yield part of
the structure but not all of it. I think in the case of most metal wing
spars, the compression critical part of the structure will either
totally yield in compression or will buckle, leaving a bent wing.
Therefore, generally with metal wings after a wingtip strike, or
overstress in flight, the rule is if it ain't bent it's ok. With a wood
wing you have to somehow detect the compression failure within the wood
by inspection. This is the principal weakness of wood structures from a
practical operational standpoint.

John

Kyle Boatright wrote:
0, I would rebuild the wings or ground it.
>
> Compression failures are due to either an over-stress condition, poor
> design, or poor materials. Compression failures have happened in every type
> of aircraft structure (metal, wood, and/or glass).
>
> Why would you ground your hypothetical CAP due to this one instance, which
> was probably caused by an overstress at some point (assuming no pertinant
> facts were omitted from this synopsis) ?
>
> Beyond that, if you rebuilt the wings, how would you know that the next
> person who flew it didn't overstress it on his/her first flight?
>
> KB
>
>
>

[Roger[_4_]]

>
>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.
>

4Gs? That's just a good tight turn and you don't even need a G-Suit.

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

[Lou]

So, just to turn the corner a little, If a person was to consider
buying a project that is
wood glued with epoxy but, started over 20 years ago, should that
person consider the
project with 20 year old epoxy connections or should he run the other
way?
Lou

[Ed Sullivan]

On 14 Dec 2006 09:33:48 -0800, "Lou" > wrote:

>
>So, just to turn the corner a little, If a person was to consider
>buying a project that is
>wood glued with epoxy but, started over 20 years ago, should that
>person consider the
>project with 20 year old epoxy connections or should he run the other
>way?
> Lou

My Jungster II all wood construction is twenty years old this year. It
is stuck together with epoxy (T-88) and seems to be pretty sturdy yet.
It has been continuously hangered. It has been flown into the hot
south west and the damp middle west (Oshkosh) and lives in
California's central valley.

Ed Sullivan

[Bob Kuykendall]

Earlier, Lou wrote:
> So, just to turn the corner a little, If a person was to consider
> buying a project that is
> wood glued with epoxy but, started over 20 years ago, should that
> person consider the
> project with 20 year old epoxy connections or should he run the other
> way?

Plenty of 30-year-old composite sailplanes are glued together with
epoxy. Not only that, but about half of their structure (by weight)
_is_ epoxy. No sign of them spontaneously falling apart in the air.

So, I'd say that age itself isn't a factor. More important is how its
been stored or used, and the quality of the construction.

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

[[email protected]]

Lou wrote:
> should that
> person consider the
> project with 20 year old epoxy connections or should he run the other
> way?
--------------------------------------------------------------------------

Dear Lou,

The question of durability involved boiling sample coupons then trying
to peel them apart.

Based on musical instruments assembled with low-tech hide glue, when
properly sealed, the moisture content of the wood -- and the strength
of the joints -- can remain stable for a hundred years or more. By
comparison, when not subjected to an outside agency such as heat, mold
or moisture, the joints produced by virtually all modern-day adhesives
are relatively ageless.

When purchasing someone else's project a detailed inspection by more
than one pair of eyes is always the wiser course. We now have more than
seventy years of experience with epoxies as an aircraft glue. There is
no inherent fault in using epoxy versus some other adhesive. What
changes is the inspection criteria and that information is best
supplied by someone familiar with the particular adhesive used in the
project.

-R.S.Hoover