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The Science Behind Why Airplane Wings Wobble in Turbulence

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Experiencing turbulence on a flight is worrying enough, so it certainly doesn’t help to look outside your window and see the plane’s wing bouncing up and down like it’s made of plastic. After observing such oscillation on a recent flight, one WIRED writer decided to dig deeper into the physics behind the phenomenon.  

By analyzing a video he shot using his iPhone, he was able to determine that the wing of the Boeing 737 he was aboard reached an oscillation amplitude of 10 centimeters (nearly 4 inches). The amount of time it took for the wing to move from one minimum position to the next was about 0.3 seconds. 

While all that wobbliness may seem like cause for panic, the flexibility of a plane’s wings is actually a sign of safety. The Federal Aviation Administration requires that all airplanes are able to withstand 150 percent of the maximum expected load for 4 seconds. According to CBS MoneyWatch, that means a plane’s wings can survive turbulence 50 percent stronger than the worst that’s ever been encountered before breaking. In order to absorb all that force, the wings are built like giant springs. If they were rigid and unyielding, it would take a lot less wind power for them to snap off—not something you want happening at 30,000 feet.

As for why the wings respond to turbulence by bouncing up and down, it’s simply a matter of physics. If an aircraft is flying at a constant speed and altitude, the net force pushing it up and down would amount to zero. If the plane moves into an area with higher air density (or experiences a similar atmospheric change), this results in more lift than there was before. This causes the plane to temporarily accelerate upward, and the wings to bend up farther. When the plane moves back to a place with lower air density the lift is reduced, causing the wings to bend back down. Sudden changes in lift force, which is what goes on during periods of turbulence, are what bring about the oscillation. 

So next time you see your plane’s wing wobbling during a bumpy flight, remember that it’s just a product of basic physics. And if that doesn’t do much to comfort you, maybe try shutting the window shade. 

[h/t: WIRED]

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Big Questions
When Flying, Why is Taking Off More Dangerous Than Landing?
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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.

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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.

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