Air taxi

© Lilium GmbH

Aircraft of the future

Autonomous air taxis, panorama aircraft: Aviation is undergoing a transformation – and with it, the requirements of the materials used are also changing. For instance, windows and cockpit windshields will take on additional functions in the future.

While rising into the sky in your own aircraft was still a pioneering achievement a century ago, today it is a privilege of the super-rich. But in the future, autonomous air taxis could relieve the congested streets of large cities and transfer some private transport from the car to the sky. This is just one example of how aviation could change over the coming years.

Larger cabin windows

While it is likely to be a long time before air taxis are used on a mass level, airplane windows that give passengers a better view from the cabin are already a reality today. For example, airplane manufacturer Boeing has enlarged the windows of their current Dreamliner model by two thirds. “The trend is clearly towards larger cabin windows in commercial airplanes,” says Roland Mickal, Head of the Transportation market segment in the Acrylic Products division at Evonik. In its vision for 2050, aircraft manufacturer Airbus even believes that the top half of the airplane will be almost fully glazed.

The Future by Airbus - Concept plane cabin / source: YouTube / Airbus Aircraft

With these alterations to aircraft design, the requirements placed on the materials used in aviation are also changing. As one the world’s leading manufacturers of aviation materials, PLEXIGLAS® therefore started production of stretched polymethyl methacrylate (PMMA) sheets in lengths of up to 5.4 meters and widths of up to 3.7 meters this year. This acrylic glass marketed under the PLEXIGLAS® brand has an improved impact resistance and increased chemical stability compared to cast PMMA, making the material ideally suited to fulfill the strict requirements of the aviation industry. “The larger sheet format opens up completely new design possibilities for the size and shape of cockpit windshields and cabin windows,” explains Mickal.

Saving resources when flying

If the cabin windows of the future do grow in size, however, the weight of the materials used will be an even more decisive factor. “Lightweight materials have always been important in the aviation sector, as every gram that is saved helps reduce the kerosene consumption,” says Mickal. In the past, the front window in the cockpit was always made out of thick glass; today, however, some manufacturers use stretched acrylic glass sheets for this windshield, which are then laminated to form a block. The advantage is that acrylic glass is only half as heavy as mineral glass. Weight not only plays a key role in airplanes, but also in the large cockpit windshields of helicopters, where current examples provide pilots with a virtually panoramic view.

PLEXIGLAS® helicopter glazing provides a clear view in the H135. / source: YouTube / Airbus Helicopters

Safer windows

Alongside the weight aspect, safety considerations would make glass unsuitable for use in spherical helicopter cabins. In the event of an accident – such as when the aircraft hits a bird – glass would fragment into small pieces and endanger the pilots. PLEXIGLAS®, on the other hand, would break up into larger segments and thus reduce the risk of injury. “However, helicopters and small sports aircraft are becoming faster and faster. This also increases the force to which the windshield is subjected in the event of a collision with a bird, for example,” explains Mickal. “That’s why we are currently developing an innovative composite material that can absorb impacts better in addition to our stretched PLEXIGLAS®, which is already more robust than conventional windshields.”

The innovative solution, which has been patented, uses a transparent, formable “rubber layer” sandwiched between two PLEXIGLAS® sheets. In the event of an impact, it absorbs some of the force and prevents the inner sheet from also being damaged. “Several processors are already manufacturing these composite materials, but they laminate these two individually formed sheets together,” comments Mickal. “This is very complex and expensive. Our solution can be manufactured in a single process step and then immediately formed.”

In the future there will be an ever-greater emphasis on combining high-quality aircraft glazing with additional functions.

Roland Mickal
Head of the Transportation market segment in the Acrylic Products division at Evonik

Greater protection from skin cancer

Helicopters are now not only able to fly faster, but also higher. As a result, the inhabitants of the cockpit are also exposed to more solar radiation. “This means the cockpits heat up considerably and the pilots’ risk of skin cancer increases,” says Mickal. Aircraft glazing manufacturers therefore add substances that make the material impermeable to harmful radiation, where necessary. One of these solutions is PLEXIGLAS®, which, like PMMA in general, has UV protection inherent to the material and also considerably reduces infrared radiation. “The advantage of this is that the helicopter does not need to consume as much energy for air conditioning,” states Mickal. “On top of that, the high optical quality of our material is retained: PLEXIGLAS® is free from distortion, which means that it offers the pilots a clear view.”

Integrating functions

In the future, the passengers of air taxis could also enjoy the clear view from large panoramic windows – or, in contrast to their own cars, use the free time to watch a film on the display integrated in the panels. “The integration of functions such as this is definitely coming,” comments Mickal. Manufacturers are already experimenting with special films which are laminated on cabin windows. These would enable aircraft passengers to display information on what they are seeing through the window, such as the name of a city they are flying over. “In addition, cabin windows that dim at the touch of a button are already possible today,” explains Mickal. “As these applications show, in the future there will be an ever-greater emphasis on combining high-quality aircraft glazing with additional functions.”