© Evonik Industries AG, Konzernarchiv Hanau

From open cockpit to panorama aircraft

Cockpit windshields and aircraft windows are becoming ever larger, giving both passengers and pilots the perfect view. PLEXIGLAS® is aiding this development in the aviation industry.

Shortly after the first airline was established over a hundred years ago, more and more passenger and airmail lines began to pop up. This marked the start of rapid development in commercial aviation. After all, aircraft have the key advantage of being able to cross bodies of water and mountains effortlessly – and are simply faster than other modes of transportation.

The rise of aviation

Ever since the early days of aviation, engineers have been working on reaching higher speeds and building larger planes. But their efforts soon reached their limits. In the beginning, pilots sat in open cabins, protected only by goggles and small, slightly curved windshields made of celluloid, an extremely flammable material. Later windshields were made of cellon, a material that would turn brown and opaque over time. Conventional window glass was not suitable for use in airplanes for safety reasons.

Historisches Bild von Frauen in der LUGLAS Produktion

Safety glass for aircraft

The first real leap forward in aircraft glass came with the invention of safety glass, which consisted of two glass panes joined by an elastic film layer. It offered protection and was transparent, but quickly turned yellow. The company Röhm & Haas, a predecessor of Evonik, invented a transparent and non-aging alternative named LUGLAS in the 1920s.

© Evonik Industries AG, Konzernarchiv Hanau

Curved canopies made of PLEXIGLAS®

However, LUGLAS was only suitable for flat shapes, and the frames holding the individual panes obscured the view. PLEXIGLAS®, a new material from Röhm & Haas at the time, made it possible to construct curved canopies. This provided the pilots with a clear view and reduced air resistance, which in turn increased speed. “As PLEXIGLAS® is lighter than silicate glass, as well as being more durable, easier to process and shape, and non-aging, our brand acrylic glass was an ideal material for aircraft construction,” explains Roland Mickal, Head of the Transportation market segment in the Acrylic Products division at Evonik. 

Larger planes, larger windows

Aircraft with curved canopies only offered room for four to five passengers and had a short range, which is why larger aircraft types were developed early on. They were not quite as fast, but could carry more passengers and, by the late 1930s, were even able to cover intercontinental distances.

Large viewing angle for pilots

In the late 1930s, larger commercial aircraft helped the transatlantic transport of both mail and passengers take off, with planes such as the Focke-Wulf Fw 200 Condor, which was built in 1937 and had room for up to 28 passengers. The cockpit windows of these early large commercial aircraft were made of panes that were joined together or only slightly curved. To give the pilots a better view, the windows became larger over the next few years – a period that was also influenced by the military necessities of World War II. The front part of the aircraft fuselage was often made transparent to give the pilots a large viewing angle.

To match the shape of the fuselage, the panes needed to be spherically arched, just like the sheet metal of the light metal cladding. “While it is relatively simple to shape sheet metal, shaping an acrylic glass panel is a technically sophisticated process, particularly when the optical quality cannot be impaired,” explains Mickal. “For an unrestricted view, the basic sheet needs to be free from optical defects.”

Multiple layers for greater stability

In recent years, manufacturers of aircraft glazing have experimented with combining different layers, such as those made from acrylic glass and Gorilla Glass, allowing for particularly robust yet thinner panes. The advantage is that a thinner material weighs less, and every gram saved in aircraft construction also saves kerosene. These panes are used in very fast helicopters, for example.

Greater stability

In the 1950s and 1960s, aircraft became faster and able to fly higher, which meant that aircraft window glazing needed to become more robust. The Röhm & Haas company continued its research and introduced Plexidur T 1951, a material related to acrylic glass, to the market. Although more expensive to manufacture, it had higher impact resistance and was more robust, thus making it suitable for aircraft glazing.

Stretched acrylic glass

Finally, stretched sheets of PLEXIGLAS®, or polymethyl methacrylate (PMMA), the correct chemical term for Evonik’s brand acrylic glass, were introduced in 1962. These are certified sheets of molded PLEXIGLAS® that are even more robust. “This material is still used today when the requirements are particularly high, for example for cockpit panes for helicopters,” explains Mickal.

How stretched PLEXIGLAS® is made.

Larger formats

Evonik is a leading manufacturer of the primary products needed for stretched sheets and, from 2018, will produce them itself on a new stretching and polishing line. The new plant will also enable larger formats to be produced than previously possible. “Manufacturers of aircraft windows can then produce more windows from a single plate,” explains Mickal. “Furthermore, the larger formats also open up new options for the design of cabin windows and cockpit windshields.” This is in line with the current trend in the aviation industry towards larger windows. In keeping with the trend, airplane manufacturer Boeing has already enlarged the windows of their current Dreamliner model by two-thirds. The field of view in the cockpits of gliders and helicopters is also increasing in size. “The more the pilot sees, the safer the flight,” emphasizes Mickal.

Panorama aircraft

Evolution in acrylics is our passion

This topic is a fine example of what “Evolution in acrylics is our passion” – the vision of Evonik’s Acrylic Products business unit – expresses, and what Evonik means by smart concepts in the chemical business. Here read why evolution is part of the DNA of PLEXIGLAS®, why passion is so important in new projects, and how Evonik’s expertise will advance the development of this material in the years to come.

Some aviation experts even predict that fully-glazed aircraft will circle in the sky in future, giving passengers and pilots an unimpaired view of their surroundings with huge panoramic windows. But what they see may not necessarily be reality. “It is certainly conceivable that the panes might be used as displays in the future,” says Mickal. They could be used to provide information on the flight path or tint the windows if necessary. “Known as function integration, this is an exciting field of development for us,” emphasizes Mickal. “At the moment, achieving these functions means applying layers on top of the material, but we are researching methods of integrating them into our PLEXIGLAS® directly.”

An example for the future of aviation: The Future by Airbus –  concept aircraft 2050 / (C) Youtube/Airbus Aircraft