They´re usually taken for granted, as critical to aircraft operation as they are – the glass (which is actually not glass, as we´ll see later) that separates the comfortable interior of an aircraft cockpit from the dangerous low pressure and -50⁰ Celsius (-58⁰ Fahrenheit) outside.
Just like that of a land vehicle, the windshield helps pilots see what is in front of them. This may seem like stating the obvious, but it´s especially important is the case of aircraft, since an airplane cannot fly at 10,000-12,00o metres without pressurising the interior (it would simply be unfeasible); and of course that interior needs a front transparent surface.
One-fifth as long as the airplane fuselage, it has various other functions in addition to visibility and insulation. Similar to that of a car, this ultra-resistant barrier protects against potential external elements such as high winds, rain, snow, hail – and in the case of thunderstorms, electric shock. Then of course there is the rare case of bird strikes, though when this infrequently occur, it´s usually at a very low altitude – during landing and takeoff – and inflicts minimal damage to the aircraft (for the bird on the other hand, it´s of course often fatal).
What an Aircraft Windshield Is Made Of
First off, windshields have not one but several layers. Most commonly these are a composite of reinforced glass, acrylic plastic and polycarbonate, joined together using intermediate layers of a polymeric adhesive material.
This layered structure provides, on the one hand, resistance to all conceivable external impacts and conditions. Yet despite its exceptional strength, at the same time it´s also constructed to be as light as possible – which of course is critical in terms of efficiency of fuel usage and other factors. And of course this like the rest of the fuselage undergoes extremely demanding safety testing before and after installation.
Its thickness is between 2.5 and three centimetres (about an inch to just under 1¼ inches), compared to just a half centimetre (just ⅕ of an inch) for an automobile – that´s between five and six times thicker. And it’s pretty much the same for short- and long-haul models, with insignificant differences.
And by the way, if you’re wondering how scratches are removed from windshields, it’s through polishing during routine maintenance work after each flight. Obviously this polishing reduces the thickness of the outer layer, which is why the thickness of a windshield is constantly measured with special devices to verify that it remains within optimal standards for its use. When this minimum is finally reached, it’s time to remove the windshield, and an aircraft will throughout its life have five different windshields mounted.
And by the way, the thickness of a windshield installed on a short-haul aircraft does not vary with respect to one mounted on a long-haul aircraft. Afterwards, the manufacturer may vary the thickness by a few thousandths with respect to another, but these are insignificant differences.
Why the Shape Also Matters
Aeronautical design is constantly evolving, and engineers are always working to improve the aerodynamic profiles of aircraft. But by now a level of technological evolution in commercial aviation has been reached that leaves room for only subtle changes.
Currently we can see mainly two types of windshields: curved and flat panels forming a curve. In the Airbus A320 and A320Neo, the metal in the central windshield is slightly curved so that it perfectly supports the six layers of material with which it is made. This shape, aerodynamically very solvent, allows optimal visibility for the pilots.