Glue it to it

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

"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

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

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.

"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.

"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

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.

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

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

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