Hi,

A full 1/4" thick! Cool.

This brings up a question that some one in the group might be able to
answer. The question arises from some experiments I conducted while trying
to design an extraction tool for a true Lexan canopy.

A few years ago I did the initial test flights and then flew off the "first
40" hours on a friend's homebuilt for him. He spent the extra bucks for a
thick, true Lexan canopy with the gold UV barrier. The Lexan was chosen
over the less expensive Acrylics because we fly in an area where the
probability of bird strikes is higher and Lexan won't break easily. Because
of the geometry of the cowl-canopy-vertical stabilizer line, I was concerned
that it would be very difficult to open the canopy and get out of the thing
if it ever flipped over on its back.

I bought some 1' x 1" Lexan squares of the same thickness as the canopy and
fabricated a rigid frame that I could use as a test jig. I then tried a
number of different extraction "tools" to see which edge design would work
the best to break the Lexan. That stuff is tough! The blunt instruments
would not break it, but a very sharp axe edge could be used to eventually
"chew" through at a spot so that a thin pry-bar could be inserted. This
worked, but the initial creation of the hole for the pry-bar took so long
that a person could be a "crispy critter" before the process was complete.
I needed something with more energy concentrated.

Without going into the whole train of development, I ended up with a device
mounted on a 2' long by 1" diameter tube of 4130 steel. The "business end"
of the device used two of the 32 caliber "nail driver" blank shells to very
rapidly extend, from the end of the device, a captive sharp spike of case
hardened steel coated with carbide granules. The rear, full diameter,
section of the spike and "barrel" were machined like a course "jack screw"
so that the spike rotated as it extended. When the safety was removed and
the "trigger" was pulled with the end of the device held against the Lexan,
the spike would penetrate the Lexan. To me, the interesting part was that a
"smooth spike" coming out without rotation didn't work all of the time
because of recoil. The course, rotating spike actually friction melted its
way through the Lexan and then stuck in place. Once the spike had
penetrated through the Lexan, the 2' "level" portion of the could be used to
pry on the sheet to crack the sheet.

I can think of a modification that would also drive an impact head that
would shatter Acrylic canopys without the need for the spike. It would also
be possible to have a "T" device that provided multiple impact points along
a line.

Here is the question. I used the 32 cal blank shells because that was the
most direct way to get the gas pressure I needed in the chamber. I made one
version that used a modified 410 shot gun shell - but it required more bulk
than the 32 cal shell firing mechinism. And, I considered using the
internal volume of the "pry tube" as a pressure chamber for high pressure
Nitrogen, but the complexity of the filling fittings and the explosive
decompression valve was too much work. Also, it would mean flying with a
pipe bomb in the cockpit. I happened to be describing the device to a
friend over a $100 cup of coffee one day and a fellow in the next booth
overheard the conversation. He volunteered that the device violated FARs
because it could be considered as carrying an "explosive device" in a civil
aircraft.

At the time, I didn't want to "open Pandora's box" by contacting the FAA
about the issue. However, with the proliferation of low-wing homebuilt
aircraft designs that use bubble canopies, I wonder if it is a good time to
pursue further development as a safety device. I didn't apply for patents
because this sort of safety device should be in the public domain.

What think all?

J


"Russell Duffy" wrote in message
...
Greetings,

I've been looking for a canopy breaking tool, that would work on a 1/4"
thick canopy. I know the military has had a few of these over the years,
but I haven't been able to locate a used, or surplus tool. I'm betting
that
someone makes a tool for this, but I sure can't find one in any internet
search.

For the record, I've seen the life hammers, and such that are made for
tempered auto glass, but I don't think those would work. If anyone can
point me to a tool that's made for aircraft canopies, I'd certainly
appreciate it.

Cheers,
Rusty