Aircraft windshields, enclosures and windows.
Repairs are more manageable when they are repairs to plastic windshields, enclosures, and windows in non-pressurized aircraft. For pressurized aircraft, replace or repair plastic windows in accordance with the manufacturer’s recommendation. When acrylic aircraft windshields and side windows are damaged, they are usually replaced, unless the damage is minor and a repair would not be in the line of vision. Windshield repairs usually require a great deal of labour. Replacement parts are readily available, so replacement is normally more economical than repair. You can appreciate from this that ground support equipment design has long sought a solution for aircraft acrylic window refurbishment.
There are times when a windshield may be cracked and safety is not impaired. In that case, repairs can be made by stop-drilling the ends of the crack with a # 30 drill (1/8 inch) to prevent the concentration of stresses causing the crack to continue. Drill a series of number 40 holes a half-inch from the edge of the crack about a half-inch apart, and lace through these holes with brass safety wire and seal with clear silicone to waterproof. Diamond cutting head machines have also been developed to cut and remove crazing.
Temporary repairs too are possible. One way to make a temporary repair is to stop-drill the ends of the crack, and then drill number 27 holes every inch or so in the crack. Use AN515-6 screws and AN365-632 nuts with AN960-6 washers on both sides of the plastic. This will hold the crack together and prevent further breakage until the windshield can be properly repaired or replaced.
Ground support equipment design.
Permanent repairs using a special purpose diamond cutting head machine are now feasible. Aircraft windshields or side windows with small cracks that affect only the appearance rather than the airworthiness of a sheet, may be repaired by first stop-drilling the ends of the crack with a # 30 or a 1/8-inch drill. Then use a hypodermic syringe and needle to fill the crack with polymerizable cement such as PS-30 or Weld-On 40, and allow capillary action to fill the crack completely. Soak the end of a 1/8-inch acrylic rod in cement to form a cushion and insert it in the stop-drilled hole. Allow the repair to dry for about 30 minutes, and then trim the rod off flush with the sheet.
Polishing and Finishing can be achieved in the following manner. It is possible, within certain limitations, to remove scratches and repair marks from acrylic plastic. Sanding that might adversely affect the plastic’s optical properties and distort the pilot’s vision should be avoided.
If there are scratches or repair marks in an area that can be sanded, they may be removed by first sanding the area. Use 320- or 400-grit abrasive paper that is wrapped around a felt or rubber pad.
Use circular rubbing motions, light pressure, and a mild liquid soap solution as a lubricant. After the sanding is complete, rinse the surface thoroughly with running water. Then, using a 500-grit paper, continue to sand lightly. Keep moving to higher grit paper and sand and rinse until all of the sanding or repair marks have been removed. After using the forest abrasive paper, use rubbing compound and buff in a circular motion to remove all traces of the sanding.
Acrylic windshield refurbishment.
Acrylic windshield refurbishment can be nicely finished and aircraft windows may be cleaned by washing them with mild soap and running water. Rub the surface with your bare hands in a stream of water. Follow with the same procedure but with soap and water. After the soap and dirt have been flushed away, dry the surface with a soft, clean cloth or tissue and polish it with a windshield cleaner especially approved for use on aircraft transparent plastics. These cleaners may be purchased through aircraft supply houses.
A thin coating of wax will fill any minute scratches that may be present and will cause rain to form droplets that are easily blown away by the wind.
Acrylic windshield protection.
Acrylic windshields are often called “lifetime” windshields, to distinguish them from those made of the much shorter-lived acetate material. However, even acrylic aircraft windshields must be protected from the ravages of the elements.
When an aircraft is parked in direct sunlight, the windshield will absorb heat and will actually become hotter than either the inside of the aircraft or the outside air. The sun will cause the inside of a closed aircraft to become extremely hot, and this heat is also absorbed by the plastic windshield.
To protect against this damage, it is wise to keep the aircraft in a hangar. If this is not possible, some type of shade should be provided to keep the sun from coming in direct contact with the windshield. Some aircraft owners use a close-fitting, opaque, reflective cover over the windshield. In many cases, this has done more harm than good. This cover may absorb moisture from the air and give off harmful vapors, and if it touches the surface of the plastic it can cause crazing or minute cracks to form in the windshield. Another hazard in using such a cover is that sand can blow up under the cover and scratch the plastic.