Plane windows are complex and they are completed with typical three layers; an outer, middle and inner pane. There is a small hole in the middle pane which helps the cabin pressure to communicate with the outer pane. This is because if the outer pane blows or cracks, the inner pane will be able to maintain this pressure temporarily. This will give the pilot enough time to drop down to a much lower altitude.
This tiny hole is designed in such a way that it regulates the amount of pressure that is exerted on the outer pane. This ensures that in the eventuality of glass cracking, the outer pane breaks first keeping the inner pane intact.
According to the Director of technology, Marlowe Moncur, GKN Aerospace, this hole is referred as a ‘breather hole’ or as a bleed valve. A patent filed by Daimlerchrysler Aerospace Airbus during 1997 described this as an ‘air conduit’ which maintains ‘external atmospheric pressure inside’ the panes.
Incidentally, plane flies in pressurized condition and this pressure is maintained by the engines which compress it with the help of a series of fans. To maintain pressure, this incoming air is confined within the cabin using a outflow valve. The function of this outflow valve is very similar to the way a tyre is inflated. As high pressure is compressed into the cabin, the sensors installed senses the pressure inside the cabin. The outflow valve releases the pressure at a suitable rate just to maintain the pressure.
As an example, when the plane is in static condition, this valve should be open. It slowly closes as the plane takes off. In the ground condition (at sea level) the air pressure both inside and outside should be around 14.7 pounds per square inch (PSI).
But, when a flight is at an altitude of say between 30,000ft (9,150 metres) and 40,000 feet (12,200 metres) the outside pressure will be around 4.3 PSI. Due to low density of the air the oxygen concentration will be low and that causes breathing problem. That’s why the plane is pressurized to makes it comfortable and safe for passengers.
Philip Spiers, head of Advanced Structural Testing Centre at the University of Sheffield Advanced Manufacturing Research Centre (AMRC) with Boeing explained that at high altitudes ‘there are not enough oxygen molecules to sustain life. Low pressure lowers the boiling points inside the body and at the edge of space, this can cause blood and tears to boil.’
Planes don’t fly very high but then, their flying altitude is generally higher than Mount Everest. The engines take air from the atmosphere and compress it at the front side to generate thrust. A portion of this compressed air is dehumidified and pumped into the cabin for maintaining pressure. .
‘Planes have a higher pressure inside than outside,’ Mr Spiers mentioned. ‘It’s like a bottle of Coca Cola – shaking a bottle makes it go stiff and hard but when you undo it, it becomes floppy again. This stretches the skin around the plane.’
As a technology lover you may like our daily important technology news series. It’s a playlist and you can retrieve the total day-wise videos. Please consider subscribing our YouTube channel:
Author: Technology and Beyond
