# What are the factors behind increasing aircraft window sizes?

Modern airliners like the Airbus A380 and Boeing 787 have bigger windows than older designs, like the Boeing 737 and Airbus A320.

What factors have led to this change of window size, opposite to the trend of almost every other thing in the interior of the plane becoming smaller in size (like the seats).

• Look at that difference in hull size. – digitgopher Jul 14 '15 at 5:50
• It might have something to do with the frame dimensions. If it's farther from rib-to-rib within the body of the plane, there's room for a bigger window. I'd think that the A380 likely has a bigger frame size (front to back) than a 737. Here's a thread that has a lot of schematics, including frames, but, unfortunately, I don't seem to see actual frame dimensions. – FreeMan Jul 14 '15 at 13:04

In the early years of the jet age, which followed closely on the introduction of pressurized hulls, there was much fear of stresses specifically in the area of the window openings due to the loss of two DeHavilland Comets. Subsequent Comet hulls had different shaped, rounded, smaller windows and that trend continued in other pressurized, typically jet-powered, aircraft.

Only with modern CAD systems and new materials knowledge could windows be made larger again. The newest aircraft designs reflect that progress.

• up vote. Certainly engineering advancements is a key factor; but this particular accident in the very early days of high altitude pressurized flight was certainly a motivator for such engineering. – radarbob Jul 14 '15 at 13:10
• The Comets were lost in the mid-1950s; the A380 was designed in the early-2000s. You seem to be saying that very little progress was made during most of those ~45 years. – David Richerby Jul 15 '15 at 19:49
• @DavidRicherby: Quite the opposite. You don't need me to tell you that aeronautical engineers are conservative in dealing with safety issues on commercial aviation. The first fully computer-designed automobile, the LH-series Chryslers, were unveiled in 1992 or thereabouts. The fruits of those engineering efforts only came to commercial aviation in the models designed about or after that time period. As confidence built up in our ability to model the behaviours of metals and other materials under load, so did the size of the holes that we were confident to put in aeronautical structures grow. – dotancohen Jul 16 '15 at 6:37

I think engineering knowledge is an important factor, going from the time of the first 737 to the A380, there was a huge development in engineering techniques. Better material knowledge, more advanced modeling methods (such as Finite Elements) and better knowledge of structural optimization have improved the situation. Especially with windows, where a lot is happening due to stress concentrations, this improved knowledge makes a difference.

This means that bigger windows might still lead to an increase in weight, but there will be a less severe weight penalty than the same windows using B737 age techniques.

• It sounds strange to me that Finite Elements was not used in the design of the B737. Better materials knowledge, for sure, but FEM, I don't know. FEM got popular by 1950's at big corporations (like boeing), and Boeing 737 development had started in 1965. – Gürkan Çetin Jul 14 '15 at 19:40
• Do you have any sources for this? I can imagine that some form of FEM might have used, but with the computing power of those days, it couldn't be very detailed. And if you're correct, the argument still holds for the giant leap in progress that has been made because of better methods, more computing power etc. – ROIMaison Jul 15 '15 at 13:24
• It was a surprise to me, so before commenting, I googled for FEM history and B737 history. B737 is from Boeing's site, and the other one is from a university paper: home.iitk.ac.in/~mohite/History_of_FEM.pdf . On the other hand, You're correct that, the advances in computational methods (mainly of algorithms side) and computational powers have advanced the way aircraft design processes are conducted. – Gürkan Çetin Jul 15 '15 at 19:25

It is the use of composite materials in the aircraft body structure that has enabled larger windows.

Metals are a crystalline structure that over time tend to fracture along crystal structure defects. Some key areas (e.g. turbine blades in the engine) are actually created by growing a single crystal to obtain higher failure points. This is not possible over a structure the size of the aircraft frame.

When an aircraft is at altitude, it is like a pressurised balloon. its skin is under tension, and when it on the ground, that tension is removed. This is like constantly flexing a metal paper clip. The cross sectional area of the aircraft skin that carries this tension is reduced by windows - bigger windows put bigger strain on the airframe structure which tends to concentrate at corners. making corners rounded helps to spread this stress.

The composite materials used in new planes are fibrous in structure. This greatly reduces the risks from the repeated flexing, allowing larger windows (and as the rust risk is reduced, cabin air is allowed to be more moist with also aids in flight comfort of passengers)

Let me answer with a car analogy: In most cases, the next car model is larger than the one before. Similarly, the aircraft manufacturers make the windows a little bigger with every new model, just to have another argument why the new model is better than all the competition. This costs a little weight, but seems to be worth it for the airlines.

• Every next model is larger than the one before. This depends on the common trends of a particular period. Chevrolet Caprice, for example, is 18+ inches smaller than its predecessors. However, I agree that newer models are marketed as being better than the ones before, although there can be exceptions. – Farhan Jul 14 '15 at 15:10
• And the A319 is newer and smaller than the A320. The buyer is an airline, and they look first and foremost at the cost per passenger-mile. A bigger window isn't helping with that. – MSalters Jul 15 '15 at 11:43
• @MSalters: A derivative cannot have a different window size. And the car size increase within a model range doesn't mean the next compact model is larger than the sedan that came before it. Did you misunderstand me on purpose, or is my wording really so confusing? – Peter Kämpf Jul 15 '15 at 13:43
• @PeterKämpf I misunderstood in the same way so, yes, I think your wording is confusing. – David Richerby Jul 15 '15 at 19:50

One of the important things I'd like to add to the previous answers is that the old air-crafts used to have smaller windows to accommodate for the rate of cabin depressurization in case of an emergency. The old airplanes had much smaller windows to control the cabin depressurization rate in case of some emergency (some window actually breaking to cause hull breach). But with advancement in the design methods and manufacturing process and with the introduction of the newer materials for airplane manufacturing, it has become possible to increase the size of the windows without increasing the risk factor.

In addition to this, creating an ambient atmosphere for the passengers inside the airplane without increasing the cost of the flight has always been a priority. So, while decreasing the seat spacing to accommodate more passengers is being done to reduce flight cost, the increase in the size of the windows does not have determinal effect on the travel cost, and hence is favored to create a less claustrophobic atmosphere inside the plane.

As well as the advances in engineering, it is worth considering the comfort of the passengers. It is often thought that the more natural light in the cabin the better the experience for the passengers. More light increases the feeling of space, and can even reduce the fatigue experienced as a result of air travel. Whether or not there is much science in this I do not know.

Some Aircraft manufacturers use the window sizes as a big selling point. Gulfstream aircraft, for example, allow in more light than any comparable aircraft due to their oval shaped windows. In an attempt to compete Dassault are putting more windows on their newer Falcon 8x and Falcon 5x models.

Both companies have also introduced windows in the galleys in some models (Dassault famously with the 'sky light') as this is typically the darkest and narrowest part of the cabin. In the cabin configurations most typical in Europe, the galley is at the very front of the cabin and is the first thing you see when you enter the aircraft. I think it is safe to say that it is much nicer to walk into a bright, airy space than a dark, narrow corridor.

Gulfstream 650 window details:

Sixteen large Gulfstream panoramic windows, each 28 by 20.5 inches/71 by 52 centimeters, allow abundant sunlight into the cabin, even in the galley. Every window has been repositioned higher on the fuselage to maximize viewing comfort*

http://www.gulfstream.com/aircraft/gulfstream-g650

Falcon 5X window & 'skylight' details:

Increased natural light does more than improve the view. It elevates your mood and enlarges your perspective. The 28 large, expansive windows of the 5X provide unbeatable luminosity.

The Falcon 5X offers an unprecedented direct view of the sky overhead through its skylight ceiling window. This unique window on the sky transforms your perception of space while providing natural light from above.

http://www.dassaultfalcon.com/en/Aircraft/Models/5X/Pages/overview.aspx