Lets talk about how planes fly
Date:
Fri, 02 Nov 2018 19:00:00 +0000
Description:
Flight isn't magic, it's physics. Josue Isai Ramos Figueroa / Unsplash How does an aircraft stay in the sky, and how do wings work? Fasten your seatbeltslet's explore. The post Lets talk about how planes fly appeared
first on Popular Science .
FULL STORY ======================================================================
Flight isn't magic, it's physics. Josue Isai Ramos Figueroa / Unsplash
How does an airplane stay in the air? Whether youve pondered the question while flying or not, it remains a fascinating, complex topic. Heres a quick look at the physics involved with an airplanes flight, as well as a glimpse
at a misconception surrounding the subject, too.
First, picture an aircrafta commercial airliner, such as a Boeing or Airbus transport jet cruising in steady flight through the sky. That flight involves a delicate balance of opposing forces. Wings produce lift, and lift counters the weight of the aircraft, says Holger Babinsky, a professor of aerodynamics at the University of Cambridge.
That lift [or upward] force has to be equal to, or greater than, the weight
of the airplanethats what keeps it in the air, says William Crossley, the
head of the School of Aeronautics and Astronautics at Purdue University.
Meanwhile, the aircrafts engines are giving it the thrust it needs to counter the drag it experiences from the friction of the air around it. As youre flying forward, you have to have enough thrust to at least equal the dragit can be higher than the drag if youre accelerating; it can be lower than the drag if youre slowing downbut in steady, level flight, the thrust equals
drag, Crossley notes.
[Related: How high do planes fly? ]
Understanding just how the airplanes wings produce the lift in the first
place is a bit more complicated. The media, in general, are always after a quick and simple explanation, Babinsky reflects. I think thats gotten us into hot water. One popular explanation, which is wrong, goes like this: Air
moving over the curved top of a wing has to travel a longer distance than air moving below it, and because of that, it speeds up to try to keep abreast of the air on the bottomas if two air particles, one going over the top of the wing and one going under, need to stay magically connected. NASA even has a webpage dedicated to this idea , labeling it as an incorrect airfoil theory.
So whats the correct way to think about it? Lend a hand
One very simple way to start thinking about the topic is to imagine that
youre riding in the passenger seat of a car. Stick your arm out sideways,
into the incoming wind, with your palm down, thumb forward, and hand
basically parallel to the ground. (If you do this in real life, please be careful.) Now, angle your hand upward a little at the front, so that the wind catches the underside of your hand; that process of tilting your hand upward approximates an important concept with wings called their angle of attack .
You can clearly feel the lift force, Babinsky says. In this straightforward scenario, the air is hitting the bottom of your hand, being deflected downward, and in a Newtonian sense (see law three ), your hand is being
pushed upward. Follow the curve
But a wing, of course, is not shaped like your hand, and there are additional factors to consider. Two key points to keep in mind with wings are that the front of a wingthe leading edgeis curved, and overall, they also take on a shape called an airfoil when you look at them in cross-section.
[Related: How pilots land their planes in powerful crosswinds ]
The curved leading edge of a wing is important because airflow tends to
follow a curved surface, Babinsky says. He says he likes to demonstrate this concept by pointing a hair dryer at the rounded edge of a bucket. The airflow will attach to the buckets curved surface and make a turn, potentially even snuffing out a candle on the other side thats blocked by the bucket. Heres a charming old video that appears to demonstrate the same idea. Once the flow attaches itself to the curved surface, it likes to stay attached[although] it will not stay attached forever, he notes.
With a wingand picture it angled up somewhat, like your hand out the window
of the carwhat happens is that the air encounters the rounded leading edge.
On the upper surface, the air will attach itself, and bend round, and
actually follow that incidence, that angle of attack, very nicely, he says. Keep things low-pressure
Ultimately, what happens is that the air moving over the top of the wing attaches to the curved surface and turns, or flows downward somewhat: a low-pressure area forms, and the air also travels faster. Meanwhile, the air is hitting the underside of the wing, like the wind hits your hand as it sticks out the car window, creating a high-pressure area. Voila: the wing has a low-pressure area above it, and higher pressure below. The difference between those two pressures gives us lift, Babinsky says.
This video depicts the general process well:
Babinsky notes that more work is being done by that lower pressure area above the wing than the higher pressure one below the wing. You can think of the wing as deflecting the air flow downwards on both the top and bottom. On the lower surface of the wing, the deflection of the flow is actually smaller
than the flow deflection on the upper surface, he notes. Most airfoils, a very, very crude rule of thumb would be that two-thirds of the lift is generated there [on the top surface], sometimes even more, Babinksy says. Can you bring it all together for me one last time?
Sure! Gloria Yamauchi, an aerospace engineer at NASAs Ames Research Center, puts it this way. So we have an airplane, flying through the air; the air approaches the wing; it is turned by the wing at the leading edge, she says. (By turned, she means that it changes direction, like the way a car plowing down the road forces the air to change its direction to go around it.) The velocity of the air changes as it goes over the wings surface, above and below.
The velocity over the top of the wing is, in general, greater than the velocity below the wing, she continues, and that means the pressure above the wing is lower than the pressure below the wing, and that difference in pressure generates an upward lifting force.
Is your head constantly spinning with outlandish, mind-burning questions? If youve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science . Ask Us Anything hits Apple , Anchor ,
Spotify , and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know youll want to stick around for.
This story has been updated. It was originally published in July, 2022.
The post Lets talk about how planes fly appeared first on Popular Science . Articles may contain affiliate links which enable us to share in the revenue of any purchases made.
======================================================================
Link to news story:
https://www.popsci.com/how-do-planes-fly/
--- Mystic BBS v1.12 A47 (Linux/64)
* Origin: tqwNet Science News (1337:1/100)