Van's Aircraft RV-8, Руководство по монтажу

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5.19 ACRYLIC CANOPY AND LEXAN WINDOW HINTS
DEFINITIONS
Plexiglas or Poly(methyl methacrylate) (PMMA) is a transparent thermoplastic often used as a light or shatter-resistant alternative to
glass. This material is specifically used for canopies and windows contained in RV Finish Kits. Beware of aftermarket canopies
made of material other than Plexiglas that promise easy installation because of resistance to cracking yet may not break in a roll
over accident and will be difficult to break by hand preventing egress from the aircraft. Lexan or polycarbonate resin thermoplastic is
the brand name for polycarbonate sheet and resin in a wide range of grades. This material with a fuel resistant coating is used
specifically for the RV-12 aft window. The Plexiglas canopy bubble and Lexan window are two of the most expensive and fragile
components in the kit. Mishandling, scratching, or cracking them are some of the most disappointing and gumption-robbing
experiences a homebuilder can have. Below are a few general Do's and Don'ts.
SAFETY
Most of us understand the importance of Shop Safety. Eye, ear, and respiratory protection are essential when fabricating Plexiglas
and Lexan. Die grinders will cut fingers without a second thought, turn at very high rpm, and can throw chips and dust at
un-dodgable velocities. Two hands are recommended to guide this tool. Drill bits can also break and become flying hazards. Eye
protection is a must. Remember to support your work well and use gloves when it makes sense.
HANDLING
The canopy is most vulnerable to cracking when moved or flexed before edges or holes have been deburred. Be especially
cautious when the canopy is in this state. Plexiglas and Lexan are dramatically less brittle when warm. Do not try to work on these
materials in a cold shop. Cutting or drilling the acrylic transparencies in temperatures under 60º F is asking for trouble. Heat the
shop to 75-80º -- it may be uncomfortable to you, but your canopy loves it. Many builders will put a small space heater under the
canopy when trimming, just as insurance. Take care not to overheat the canopy. Too hot is when any part of the canopy is hotter
than "warm to the touch". More than one builder has melted a canopy in an attempt to make sure it is "warm enough". Localized
heat is as bad as no heat and can deform the canopy. Be cautious when fitting your canopy over small protrusions and/or
transitions in canopy frame tubing diameters. You might elect to shim the tubing surfaces so that the acrylic is not pinched or
bridged over any given area.
CUTTING
CAUTION: DO NOT use a saw of any kind. You might get away with it once or twice, but eventually you will crack the
canopy
.
Cutting discs, supplied with the kit, do an excellent job when used in a high-speed die grinder. If a die grinder is not available, an
electric drill will work, but several passes will be necessary, going a little deeper each time to complete the cut. Practice on the
flanges of the canopy for both the cutting and drilling operations. Work slowly at first pass to begin cutting an initial slot and to gain
confidence with the procedure. Once the initial slot is made, continue cutting through the material. Once cut, the edges should be
smoothed and rounded with a scraper. For a scraper use an edge from a pair of quality scissors. Do not leave the edges rough.
Ensure that no edge has a sharp corner.
DRILLING
Special Plexiglas/Lexan drills are available from tool suppliers. Van's recommends two such tools; Diamond Dust drills and Unibits.
Clamping a piece of wood behind the acrylic material and drilling through into the wood can eliminate chipping on the backside of
drilled holes. Start drilling the warmed acrylic with slow speeds and light pressure. Increase speed and pressure as you progress.
As the drill bit starts to go through the canopy, reduce speed and pressure so that the drill bit penetrates the opposite surface
slowly. It is important to deburr both sides of the hole lightly with a machine countersink. No hole should have a sharp corner.
Practice drilling holes in scrap pieces until you are familiar and confident with the process. It is worth remembering that excessive
heat caused by machining and drilling may alter the acrylic's properties which may in turn allow even approved products to
negatively affect the material. For this reason it is important to cut slowly and avoid overheating the acrylic. To enlarge holes the
use of a step-drill (Unibit) or reamer is recommended.
CAUTION: DO NOT use a regular twist drill! A twist drill tends to fracture the acrylic due to its tip design. Using a regular
twist or plexi drill to enlarge a pre-drilled hole is not recommended and will practically guarantee a cracked canopy as a
result.
FIBERGLASS BONDING, CRACKS, ETC.
CAUTION: DO NOT use Polyester resin of any type, as it will cause crazing
.
Be certain to use ONLY epoxy resins. Do not use the more common polyester or vinyl ester resins since they are not compatible
with Plexiglas and cause crazing that will ruin the canopy. We have had excellent results with West Systems Epoxy products,
available from boat yards and mail order houses.
The three keys to getting a good bond between fiberglass and acrylic canopies and windows are proper surface prep, proper
surface prep, and proper surface prep. The bonding surface must be entirely de-glossed. Many builders think they have scuffed the
surface well, when it is not nearly enough. Fully scuff the surface using 60 - 80 grit sandpaper. Use an overhead light source to
inspect the surface carefully. Look between the scratches... there should be absolutely no sign of any shininess whatsoever. Just
to be sure, go over the entire area once more, this time using a circular motion. Clean the area with a lint free cloth and denatured
alcohol. To prevent contamination of the surface avoid touching it with your hands.
Cracks… Avoid jeopardizing or cracking the canopy at all costs. If the unthinkable happens and a crack appears it may sometimes
be repaired using a solvent adhesive such as Plasti-Fix or Weld-On 3. Stop-drilling the crack is typically required to keep it from
running.
CLEANING AND USE OF LIQUIDS
CAUTION: DO NOT use Loctite, aromatic solvents, acetone, benzene, ethyl acetate, carbon tetrachloride, lighter fluid,
lacquer thinners, gasoline, toluene, window sprays, concentrated alcohols, ketones, scouring compounds, ammonia, or
409 cleaner on or around acrylic or Lexan canopy materials.
The adhesive used on some brands of electrical tape may be incompatible with acrylic or Lexan. Test the tape on a scrap of
material before use. In all cases do not leave the tape on the canopy for extended periods of time (more than two days).
For general cleaning use Dawn dishwashing liquid or equivalent and water followed by a clear water rinse. To prevent water spots,
blow-dry with compressed air or wipe dry with soft cotton flannel. Plexus, Sprayaway #848 Industrial Plastic Cleaner, or All Clear
can also be used for day to day cleaning. Grease, oil, tape residue, etc. may best be removed with mineral spirits, refined kerosene,
white gasoline, naphtha, or isopropyl alcohol. Wash approved solvents off the canopy with Dawn dishwashing liquid and water. It is
best to avoid using products on your canopy that are not specifically formulated for acrylics such as Rain-X or Lemon Pledge.
SCRATCH REMOVAL
Small scratches can be buffed out with Meguiar's Mirror Glaze Plastic Cleaner #17. For deep scratch removal, use Scratch Off ,
Micro Mesh, or 3M Window Repair kits. Avoid removing scratches in critical areas where clear visibility is important, as the process
will usually result in some degree of optical distortion.
CANOPY PROTECTION AND VENTILATION
If the aircraft is tied down outdoors and subject to weather elements for any length of time, then the use of an aircraft canopy cover
is highly recommended. The cover will protect canopies and windows from abrasive dust, dirt, and sand kicked up by wind or prop
wash. Before purchasing, verify that the canopy cover is NOT waterproof as the trapped moisture and heat from the sun can be
deleterious. Acrylic subjected to this treatment over a period of time may turn slightly milky and eventually craze.
Keep your canopy ventilated or covered when your aircraft is parked in the hot sun. Cabin temperatures can easily reach 150-200
degrees F even on a mild day. The acrylic can generally take these temperature conditions multiple times without any apparent
adverse effect. It is the cumulative affect that will cause shortened service life of your canopy. The use of a Van's Aircraft Canopy
Cover will significantly reduce the internal temperatures inside your aircraft to just a few degrees above outside ambient
temperatures. Additionally it will also protect your expensive avionics from heat and your upholstery/seat belt harnesses from
harmful UV rays.
In winter conditions ensure that the cabin and canopy are warmed adequately prior to flight whenever possible. A heat lamp or
small, low output ceramic space heater can raise the cabin temperature to warm the acrylic, keeping it free from ice or snow. It will
also be less prone to cracking.
PAGE REVISION: DATE:
VAN'S AIRCRAFT, INC.
04/15/13 2
RV-ALL 05-17