What Do Pilots Use to Detect Turbulence?

iStock.com/Maravic
iStock.com/Maravic

by Joe Shelton

I think the concept of "turbulence" has gotten a bad reputation.

Just like the wind, turbulence isn't an on or off thing; it's a spectrum.

Step outside one day and a light breeze might be hard to feel, while the next day you might have trouble holding onto your hat because the wind is so strong. But most of the time it's somewhere in between those extremes.

Turbulence is exactly the same. Some days, some places, nothing. Some days it can rattle your teeth (or turn your stomach). But most of the time when turbulence exists, it is light or at worst case slightly annoying.

How do pilots detect turbulence?

Weather forecasts provide estimates when there might be turbulence. The thing to remember is the noun forecast: It's not a guarantee that it will be turbulent, nor is the lack of mention of turbulence in a forecast a guarantee that there won't be turbulence.

In addition, turbulence can be widespread as well as very localized.

I typically detect or expect serious or widespread turbulence as well as local turbulence in one of three of ways:

  • Cumulus clouds: If the clouds are tall and vertical and/or getting taller, then there is a good chance there is turbulence around. The taller the clouds and the faster they are growing, the worse the probable turbulence. Especially in the clouds. The worst example of that would be a thunderstorm. The turbulence within a thunderstorm can tear an aircraft apart.
  • Hot days: Also known as convection, warm and especially hot days mean that the hot air is rising and the reciprocal, cold air is descending. That's a recipe for turbulence. Depending upon the temperature and the aircraft's altitude the turbulence can be irritating or it can be very uncomfortable.
  • Wind: Wind can "tumble," especially downwind of mountains—often for many miles downwind—and it can even be turbulent over mountains, as winds are encouraged to rise following the upwind mountain side.

With very few exceptions, for the most part turbulence isn't dangerous. At least to aircraft. Pilots know how to manage turbulence, often simply by slowing the aircraft's airspeed and/or changing altitude.

However, clear-air turbulence (CAT)—severe turbulence that happens in what otherwise seems to be calm, clear air—can cause injuries to passengers who aren't wearing seat belts or, worse, are walking. And CAT is very difficult to detect until you experience it.

(By the way, clear-air turbulence got its name because although turbulence is often accompanied by clouds, this particular form isn't. Hence the name.)

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

Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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Are Any of the Scientific Instruments Left on the Moon By the Apollo Astronauts Still Functional?

Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Apollo 11 astronaut Neil Armstrong left the first footprint on the Moon on July 20, 1969.
Heritage Space/Heritage Images/Getty Images

C Stuart Hardwick:

The retroreflectors left as part of the Apollo Lunar Ranging Experiment are still fully functional, though their reflective efficiency has diminished over the years.

This deterioration is actually now delivering valuable data. The deterioration has multiple causes including micrometeorite impacts and dust deposition on the reflector surface, and chemical degradation of the mirror surface on the underside—among other things.

As technology has advanced, ground station sensitivity has been repeatedly upgraded faster than the reflectors have deteriorated. As a result, measurements have gotten better, not worse, and measurements of the degradation itself have, among other things, lent support to the idea that static electric charge gives the moon an ephemeral periodic near-surface pseudo-atmosphere of electrically levitating dust.

No other Apollo experiments on the moon remain functional. All the missions except the first included experiment packages powered by radiothermoelectric generators (RTGs), which operated until they were ordered to shut down on September 30, 1977. This was done to save money, but also because by then the RTGs could no longer power the transmitters or any instruments, and the control room used to maintain contact was needed for other purposes.

Because of fears that some problem might force Apollo 11 to abort back to orbit soon after landing, Apollo 11 deployed a simplified experiment package including a solar-powered seismometer which failed after 21 days.

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

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