When it comes to glasses of the aircraft windshield, there are so many factors to be considered. The requirement of the glass material changes from light aircraft to high-speed aircraft. Also, the glass requirements are dependent on the wind force.
Some of the major factors that are considered while choosing an aircraft’s glass material are –
- Scratch resistivity
- Industrial standards
- Anti-static quality
- UV resistivity
- Noise reduction quality
- Anti-bacterial quality
- Heat Resistivity
Now, coming to the various glass materials used for aircraft windshields.
Shatterproof glass consists of 2 or more pieces of glass held together by a single-ply filler of transparent plastic. Vinyl plastic is the most commonly used transparent plastic. There are two different kinds of shatterproof glasses namely – Laminated plate glass and laminated sheet glass.
1. Laminated Plate Glass
Made of two pieces of class A polished plate glass, is procurable either curved or flat for the aircraft windshields. For the windshields, 3/16 and 1/4 are generally used. The property of being flat or curved relieves mounting strains which can crack the glass. Also, this property provides mechanical mounting allowing it to be procurable with an extended plastic edge which includes metal reinforcing strips. Screws can be mounted to the windshield frame with the extended edges. This arrangement results in a positive mounting with no strain in the glass.
In military aircraft windshields, bullet-resistant laminated plate glass is commonly used. It consists of a number of plate glasses with different thicknesses. This glass with the greatest light transmission (2 degrees) is the most expensive yet the most desirable for night flying. This glass resists penetration of a 0.30 calibre bullet hitting the glass with a velocity of 2700 feet per second and at an angle of 45 degrees.
2. Laminated Sheet Glass
Made from class B, has considerably more distortion than plate glass and is suggested to not to be used for aircraft windshields.
An exceptionally strong glass which is used for large aircraft windshields. This type of glass possess a compressive tensile strength of approx 36000 psi. This glass is manufactured only in 1/4 thickness or greater.
An ideal transparent plastic is expected to have properties like god strength, scratch resistivity, noninflammability and many more. Unfortunately, there is no such transparent plastic which can be perfect.
Some of the transparent materials available are –
A pyroxylin nitrocellulose plastic which is a solution of nitrocellulose in camphor. This nitrocellulose is less inflammable and non-explosive than guncotton nitrocellulose. This pyroxylin nitrocellulose is blended with alcohol and camphor, heated and pressed into solid blocks. These blocks are then sliced as per the desired thickness.
Pyralin is inflammable and was commonly used in commercial airplanes.
A cellulose acetate plastic which is manufactured using the same process as pyralin. Plastecele is flame resisting and is mostly used in military aircraft. It can be burned down slowly if a lighted match is held to it over a period of time. It is thermoplastic material which can be readily moulded by heat and pressure.
A copolymer resin of vinyl chloride and vinyl acetate, is a non-inflammable material. It is availble in general range of commercial sizes.
4. Plexiglas & Lucite
These are acrylic thermoplastics which are colorless and transparent. These are more scratch resistant than cellulose plastics. There are two types of acrylic plastics available namely standard and heat resistant.
Aircraft windshield is one of the most important part of an aircraft. These are the materials used for an aircraft windshield.