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How Does Autopilot Work on an Airplane?

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How does autopilot work on an airplane?

Joe Shelton:

David Micklewhyte’s answer is a good one. There are essentially a few types of features that different autopilots have. Some autopilots only have some of these features, while the more powerful autopilots do it all.

  • Heading Hold: There’s a small indicator that the pilot can set on the desired heading and the airplane will fly that heading. This feature doesn’t take the need for wind correction to desired routing into account; that’s left to the pilot.
  • Heading and Navigation: In addition to holding a heading, this version will take an electronic navigation input (e.g. GPS or VOR) and will follow (fly) that navigation reference. It’s sort of like an automated car in that it follows the navigator’s input and the pilot monitors.
  • Altitude Hold: Again, in addition to the above, a desired altitude can be set and the aircraft will fly at that altitude. Some autopilots have the capability for the pilot to select a desired altitude and a climb or descent rate and the aircraft will automatically climb or descend to that altitude and then hold the altitude.
  • Instrument Approaches: Autopilots with this capability will fly preprogrammed instrument approaches to the point where the pilot either takes control and lands or has the autopilot execute a missed approach.

The autopilot is a powerful computer that takes input from either the pilot or a navigation device and essentially does what it is told to do. GPS navigators, for example, can have a full flight plan entered from departure to destination, and the autopilot will follow the navigator’s guidance.

These are the majority of the controls on the autopilot installed in my airplane:

HDG Knob = Heading knob (Used to set the desired heading)

AP = Autopilot (Pressing this turns the autopilot on)

FD = Flight Director (A form of navigational display that the pilot uses)

HDG = Heading (Tells the autopilot to fly the heading set by the Heading Knob)

NAV = Tells the autopilot to follow the input from the selected navigator

APR = Tells the autopilot to fly the chosen approach

ALT = Tells the autopilot to manage the altitude, controlled by the following:

VS = Vertical Speed (Tells the autopilot to climb or descend at the chosen rate)

Nose UP / Nose DN = Sets the climb/descent rate in feet per minute

FLC = Flight Level Change (An easy manual way to set the autopilot)

ALT Knob = Used to enter the desired altitude

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

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Big Questions
What Does the Sergeant at Arms Do?
House Sergeant at Arms Paul Irving and Donald Trump arrive for a meeting with the House Republican conference.
House Sergeant at Arms Paul Irving and Donald Trump arrive for a meeting with the House Republican conference.
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In 1981, shortly after Howard Liebengood was elected the 27th Sergeant at Arms of the United States Senate, he realized he had no idea how to address incoming president-elect Ronald Reagan on a visit. “The thought struck me that I didn't know what to call the President-elect,'' Liebengood told The New York Times in November of that year. ''Do you call him 'President-elect,' 'Governor,' or what?” (He went with “Sir.”)

It would not be the first—or last—time someone wondered what, exactly, a Sergeant at Arms (SAA) should be doing. Both the House and the Senate have their own Sergeant at Arms, and their visibility is highest during the State of the Union address. For Donald Trump’s State of the Union on January 30, the 40th Senate SAA, Frank Larkin, will escort the senators to the House Chamber, while the 36th House of Representatives SAA, Paul Irving, will introduce the president (“Mister [or Madam] Speaker, the President of the United States!”). But the job's responsibilities extend far beyond being an emcee.

The Sergeants at Arms are also their respective houses’ chief law enforcement officers. Obliging law enforcement duties means supervising their respective wings of the Capitol and making sure security is tight. The SAA has the authority to find and retrieve errant senators and representatives, to arrest or detain anyone causing disruptions (even for crimes such as bribing representatives), and to control who accesses chambers.

In a sense, they act as the government’s bouncers.

Sergeant at Arms Frank Larkin escorts China's president Xi Jinping
Senat Sergeant at Arms Frank Larkin (L) escorts China's president Xi Jinping during a visit to Capitol Hill.
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This is not a ceremonial task. In 1988, Senate SAA Henry Giugni led a posse of Capitol police to find, arrest, and corral Republicans missing for a Senate vote. One of them, Republican Senator Bob Packwood of Oregon, had to be carried to the Senate floor to break the filibustering over a vote on senatorial campaign finance reform.

While manhandling wayward politicians sounds fun, it’s more likely the SAAs will be spending their time on administrative tasks. As protocol officer, visits to Congress by the president or other dignitaries have to be coordinated and escorts provided; as executive officer, they provide assistance to their houses of Congress, with the Senate SAA assisting Senate offices with computers, furniture, mail processing, and other logistical support. The two SAAs also alternate serving as chairman of the Capitol Police board.

Perhaps a better question than asking what they do is pondering how they have time to do it all.

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

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Big Questions
What Makes a Cat's Tail Puff Up When It's Scared?
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Cats wear their emotions on their tails, not their sleeves. They tap their fluffy rear appendages during relaxing naps, thrash them while tense, and hold them stiff and aloft when they’re feeling aggressive, among other behaviors. And in some scary situations (like, say, being surprised by a cucumber), a cat’s tail will actually expand, puffing up to nearly twice its volume as its owner hisses, arches its back, and flattens its ears. What does a super-sized tail signify, and how does it occur naturally without help from hairspray?

Cats with puffed tails are “basically trying to make themselves look as big as possible, and that’s because they detect a threat in the environment," Dr. Mikel Delgado, a certified cat behavior consultant who studied animal behavior and human-pet relationships as a PhD student at the University of California, Berkeley, tells Mental Floss. The “threat” in question can be as major as an approaching dog or as minor as an unexpected noise. Even if a cat isn't technically in any real danger, it's still biologically wired to spring to the offensive at a moment’s notice, as it's "not quite at the top of the food chain,” Delgado says. And a big tail is reflexive feline body language for “I’m big and scary, and you wouldn't want to mess with me,” she adds.

A cat’s tail puffs when muscles in its skin (where the hair base is) contract in response to hormone signals from the stress/fight or flight system, or sympathetic nervous system. Occasionally, the hairs on a cat’s back will also puff up along with the tail. That said, not all cats swell up when a startling situation strikes. “I’ve seen some cats that seem unflappable, and they never get poofed up,” Delgado says. “My cats get puffed up pretty easily.”

In addition to cats, other animals also experience piloerection, as this phenomenon is technically called. For example, “some birds puff up when they're encountering an enemy or a threat,” Delgado says. “I think it is a universal response among animals to try to get themselves out of a [potentially dangerous] situation. Really, the idea is that you don't have to fight because if you fight, you might lose an ear or you might get an injury that could be fatal. For most animals, they’re trying to figure out how to scare another animal off without actually going fisticuffs.” In other words, hiss softly, but carry a big tail.

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