CLOSE
IStock
IStock

Why Are Airplane Windows Round?

IStock
IStock

While some passengers might be too terrified—or sedated—to notice, frequent travelers may sometimes wonder why the windows that line airplane rows are round. Windows in the home are rectangular; car partitions are angled, but mostly rectangular. Why don’t planes follow suit?

It’s actually not an aesthetic choice. Airplanes used to have square windows. And they wound up crashing because of them.

When commercial airlines graduated to faster and larger jets beginning in the 1950s, planes would sometimes essentially disintegrate midair. Two of them, both de Havilland Comets, fell apart within months of one another in 1954 and killed a total of 56 passengers. Investigators traced the flaw to the squared-off corners of windows, which collect the stress of a pressurized cabin and can be prone to fracture. During one test, the Royal Aircraft Establishment found that up to 70 percent of the airplane’s stress was concentrated on the window's sharp angles.

Circular windows, which are able to disperse that pressure more evenly, immediately became the new standard in passenger aviation. And for every one you see, there are actually three panes at work: one bears the burden of pressurization, another inner pane acts as a failsafe in case the outer pane fails—which is rare—and one “scratcher” pane faces the occupant, so that you can smudge and dirty it up to your heart’s content.

As for that little hole at the bottom: It’s there to make sure the working pane takes the brunt of the air pressure, maintaining the emergency pane for, well, emergencies.

Mystery solved.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

nextArticle.image_alt|e
iStock
arrow
Big Questions
When Flying, Why is Taking Off More Dangerous Than Landing?
iStock
iStock

Why is taking off more dangerous than landing?

Tom Farrier:

Landing is generally considered quite a bit more hazardous (and requires a bit more exacting handling), but both takeoffs and landings can have their challenges. Still, aircraft like to fly; sometimes it can be a little tricky to encourage them to stop doing so at the end of a flight, especially in the presence of unpredictable winds or slippery runways.

This is a graphic from my favorite go-to reference on commercial aircraft accidents, updated annually by Boeing but including all airliner accidents:

The shaded area under the aircraft silhouette shows the amount of time an aircraft spends in each “phase of flight.” At the top, there are two numbers worth looking at carefully. Final approach and landing is when 48 percent—essentially half—of all fatal accidents that have occurred from 1959 through 2016. By contrast, taking off and starting to climb is only about a quarter as hazardous (13 percent). These ratios used to be somewhat different; takeoffs used to see their share of accidents a lot more frequently than today.

The biggest challenge with taking off in the early days of jet airliners was the rate at which they could accelerate during their takeoff roll. Often, a lot of time was required between when the aircraft passed the speed at which the pilots were committed to taking off (V1) and when the jet actually could get into the air with a positive rate of climb. When an emergency would suddenly present itself in that window of vulnerability, sometimes there were no good options, and sometimes the pilots picked the wrong one.

One of the biggest ways pilots (and flight engineers in aircraft that use them) have to earn their paychecks is when something bad happens during a takeoff roll and they have to decide whether to continue the takeoff and deal with the problem in the air, or if the situation is critical enough that it’d be preferable to wrestle the fuel-laden beast on the ground and risk going off the end of the runway.

To try to address the need for added clarity in such situations, some of these early accidents led to recognition of the need for establishing a second speed benchmark (V2), which is the point at which the aircraft is going fast enough to make a successful takeoff with one engine out. Bear in mind that a lot of the biggest early jets had four engines, none of which was nearly as powerful as the current generation (some actually used water injection systems to boost their thrust during takeoff), and which suffered failures a lot more often.

“Rejected takeoffs” are pretty rare occurrences these days, and airport design has gotten better at minimizing the consequences of an aircraft running off the end of a runway if circumstances conspire to make things exciting for its inhabitants. For example, "engineered material arresting systems” are basically long slabs of pavement designed to collapse under the weight of an aircraft, grabbing hold of it and bringing it to a fairly enthusiastic stop.

This may not sound desirable, but some of the places EMAS has been installed (including Boston’s Logan and New York’s LaGuardia Airports) have seen more than their share of aircraft in trouble winding up in bodies of water during what are euphemistically (but accurately) referred to as “runway excursions.”

Such departures can happen either during takeoff or landing emergencies, and it’s nice to know that the chances of surviving both have been improved significantly with one ingenious invention.

This post originally appeared on Quora. Click here to view.

arrow
History
When Chuck Yeager Tweeted Details About His Historic, Sound Barrier-Breaking Flight

Seventy years ago today—on October 14, 1947—Charles Elwood Yeager became the first person to travel faster than the speed of sound. The Air Force pilot broke the sound barrier in an experimental X-1 rocket plane (nicknamed “Glamorous Glennis”) over a California dry lake at an altitude of 25,000 feet.

In 2015, the nonagenarian posted a few details on Twitter surrounding the anniversary of the achievement, giving amazing insight into the history-making flight.

For even more on the historic ride, check out the video below.

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios