Cost to install a canopy?

I manufacture Transparencies for a living.
Mostly windshields for sports cars. There are so
many places to screw up that it can be a truly
humbling experience. What puzzles me is that
most folks give little atention to the canopy as
it ages. You can double the life of a canopy
by keeping it squeaky clean and polishing the
surfaces at least annually. Proper polishing
doesn't remove material from the plastic, it removes crap
from the plastic. Micromesh is NOT a polishing system
it is much too agressive, it is for repair work. Even
with normal care, the exterior (interior also) will eventually
degrade and start to produce chalk like deposits as the
monomers in the plastic sublimate. Once it gets to this
state, you basically are on life support. If you have
a canopy that is so old it just won't polish well,
Micromesh probably won't help as the sublimation is
in most cases deeper than the max grind depth of the system.
When you get to this place, toss the book aside, and get a bit creative.
The object of the game is now to stop sublimation and seal the canopy
surface with something you can see thru. Believe it or not, the
green can TURTLE WAX will make things a lot better. It
will fill the small scratches and surface pores and get you back
to a usable canopy surface. The downside is that it stops the canopys
ability to breathe and adjust to humidity changes which will cause
a higher internal hoop stress load to exist and make the canopy less
forgiving to bumps and racking. DON'T do this to a canopy with
life left in it, but when the choice is this or a replacement, I like doing
this first.
I've got some vintage race cars going on 5 or 6 years doing this. They
are one step from the grave as far as repairability, but they still work ok
enough to use. As far as day to day maintenance, a couple thoughts.
First, Plexiglass (PMMA) isn't really a solid. It is an incredibly viscous
liquid and is pourous. This means that the stuff it is made of can
"evaporate"
(sublimate) over time. It also means that stuff you put on it can "go into
suspension" inside the plastic. This is why I cringe so bad when I see
Lemon Pledge used on a canopy. Not only is the propellant, usually
isobutane, (a great solvent I might add) trapped inside the canopy by the
wax
so it can disolve the internal structure of the plastic, but the free
breathing of
the plastic and its ability to adjust its relative humidity are compromised.
Dust can do the same thing, it will plug the plastic pores and in most cases
it is acidic and will react adversely to the plastic. So what to do.
Keep a piece of dry flannel on the canopy when you aren't using it. Only
use good quality plastic cleaners designed for the plastic you have. Always
start a canopy cleaning with clear water to get the dust off the canopy
before you start smushing it into the plastic with your cleaning rag.
Only use soft cotton to clean the canopy, old diapers are the gold
standard. I hope this helps, and no, I'm not looking for canopy work....

Scott.

pbc76049 (removethis) wrote:
I manufacture Transparencies for a living...

Spectr Scott, I been trying to get ahold of you. Drop me an email when
you can.

Thanks, Bob K.

I've replaced a couple of Grob canopies, but it has been over 10 years
ago. Each went like this -

Tools -
Air powered die grinder with sanding disks and cutoff wheel
Screwdriver
Foil tape
Plastic drill and countersink
Small paint gun


Day one -
With the frame in place on the glider I used the grinder with sanding
disk and removed the gel where it contacts the frame. Cut off the
remaining canopy next to the frame with a cutoff wheel. (I once saw a
Grob mech beat one off with a hammer.) Chiseled and ground off all
plastic and the resin used to bond it to the frame. Grob uses small
screws to hold it place while the resin cures. Ground those off also.
(Approx 4 hours)

Day two-
The canopy comes oversize. Placed it on the still in place frame and
adjusted its position while overlapped and taped in place with clear
tape. Ran the cutoff wheel around and used the frame edge as a guide
removing all excess. Taped again in place. Drilled and countersinked
holes for small brass screws using a drill modified for plastic
(careful here or you'll break it). Removed canopy and put a bead of
resin on the frame. Pealed back the protective plastic around the
edge. Put it back on and lightly (real lightly) screwed it down.
(Approx 4 hours)

Day three-
Masked off at the level of the frame with metal foil tape. Hand
sanded the canopy edge to roughen and remove the resin squeeze-out.
Filled the gaps and screw heads with white Bondo and block sanded
level. Shot on gel coat with a touchup gun. After it cured, sanded
and polished the gel. Removed all the tape and protective plastic.
Cleaned and waxed it. Signed off the work in the log. (Approx 6
hours)

The moral(s) of the story is that it's not a huge task, break it and
you'll buy another, and these are hand built aircraft. The frame from
one probably won't fit another. Leave the frame in place while you
change the glass and it will fit like the original. Most of all, this
is how I did it. What you do is at your own risk. ;-)